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Key message Correlations between morphological traits of cabbage rosette leaves and heads were found. Genome-wide association studies of these traits identified 50 robust quantitative trait loci in multiple years. Half of these loci affect both organs. Abstract Cabbage (Brassica oleracea var. capitata) is an economically important vegetable crop cultivated worldwide. Cabbage plants go through four vegetative stages: seedling, rosette, folding and heading. Rosette leaves are the largest leaves of cabbage plants and provide most of the energy needed to produce the leafy head. To understand the relationship and the genetic basis of leaf development and leafy head formation, 308 cabbage accessions were scored for rosette leaf and head traits in three-year field trials. Significant correlations were found between morphological traits of rosette leaves and heads, namely leaf area with the head area, height and width, and leaf width with the head area and head height, when heads were harvested at a fixed number of days after sowing. Fifty robust quantitative trait loci (QTLs) for rosette leaf and head traits distributed over all nine chromosomes were identified with genome-wide association studies. All these 50 loci were identified in multiple years and generally affect multiple traits. Twenty-five of the QTL were associated with both rosette leaf and leafy head traits. We discuss thirteen candidate genes identified in these QTL that are expressed in heading leaves, with an annotation related to auxin and other phytohormones, leaf development, and leaf polarity that likely play a role in leafy head development or rosette leaf expansion.

Korla fragrant pear (Pyrus sinkiangensis Yü) depends on cross-pollination by honeybees (Apis mellifera) but may suffer from low honeybee visitation. We assessed whether honeybee abundance and visitation frequency are enhanced by using synthetic Nasonov gland pheromone (NGP), which is naturally produced by worker bees to stimulate the aggregation of bees to food resources or nesting sites. The response of honeybees to synthetic NGP was firstly assessed using Y-tube olfactometer tests in the laboratory, and subsequently in the field, by placing NGP lures on Korla fragrant pear trees in orchards with and without beehives. Honeybee abundance was assessed using coloured pan traps while honeybee visits were assessed by visual observations on pear flowers. Y-tube olfactometer tests showed a significant preference of honeybees for NGP. In pear orchards with beehives, honeybee abundance was 2.5-fold higher on trees with NGP lures than on trees without NGP, and 2.2-fold higher in orchards in which all trees contained NGP lures than in orchards without NGP lures. Such positive effects were not observed in orchards without beehives. Flower visitation by honeybees was significantly higher in trees with NGP lures than without NGP lures, irrespective of the presence (5.7-fold higher) or absence of beehives (27.6-fold higher). In mixed pear-apricot orchards, honeybee abundance was higher in pear trees with NGP lures than without lures. Our results show that NGP lures attract honeybees to flowering pear trees in monoculture pear and mixed pear-apricot orchards, and that this effect is greatest in orchards with beehives.

In vitro-propagated potato plantlets are commonly used in potato seed tuber production. Four experiments were carried out to identify how the duration of the last in vitro phase (‘age’) before planting of in vitro-produced plantlets affects the early growth and development ex vitro, assessed 10–14 days after planting. Experiments included varying ranges in age of the in vitro plantlets at planting (10–40, 15–45, 14–28 and 14–56 days old at the moment of planting in the respective experiments) and different cultivars. Because in vitro plantlet size increases with age, the first experiment studied interactions between age and planting method. Planting ‘deep’ (the upper four visible leaves above the ground) seemed more robust than planting ‘shallow’ (all nodes/leaves above ground except the lowest two), and in later experiments, only deep planting was applied. Across experiments, plants grown from younger in vitro plantlets had smaller leaf areas 10–14 days after planting than those from older in vitro plantlets. The increase in leaf area levelled off with increasing age of the in vitro plantlets used, especially when plantlets were older than c. 28 days. Larger leaf areas 10–14 days after planting were related to the older in vitro plantlets having higher absolute growth rates after planting and a larger above-ground leaf area at planting, even though four leaves were kept above ground in all treatments. Below ground, plants from older in vitro plantlets had more stem nodes, initiated stolons earlier after planting and initiated more stolons per plant. Tuber initiation rarely occurred within 14 days after planting, but was observed in some plants from 42- and especially 56-day-old in vitro plantlets of the very early cultivar Gloria and a single plant from 56-day-old in vitro plantlets of the mid-early cultivar Bintje. The data show that planting older in vitro plantlets can enhance early leaf area growth. Plants from older in vitro plantlets also more readily initiate stolons below ground and may be more advanced in the tuber formation process, especially when from early cultivars.

The study was conducted to determine the dormancy and physiological age characteristics of diverse potato genotypes as influenced by growing altitudes and seasons for future breeding strategies and optimal patterns of use. Dormancy and sprouting characteristics have an impact on tuber production, storability and seed quality for planting and ware for consumption and the market. This study presents the results of dormancy and physiological age measurements conducted on 47 potato genotypes grown at three altitudes with three replications at each location and in two contrasting growing seasons. The seed tubers were evaluated at low altitude under darkness on moist sand storage conditions to assess their dormancy release, number of sprouts, sprout weight, sprout length and percentage tuber weight loss. Results showed significant (p

Lucerne (Medicago sativa L.) is a widely grown perennial legume worldwide which can provide high biomass and protein yields, biological N fixation, deep soil water extraction and a range of ecosystems services relevant to current and future agricultural systems. The potential to expand lucerne beyond its current cultivated areas in New Zealand, and its potential productivity across the country's contrasting climate zones, are currently unknown. To gain such insights, we estimated land suitability and spatial distribution of lucerne above-ground biomass across New Zealand lands considering contrasting growth conditions (rain-fed or irrigated for different soils types) and two simulation methods of different complexity (process- and GIS-based approaches). This aimed to assess yield-estimate spatial patterns and sensitivity to model selection for a wide range of combinations of water supply (i.e. irrigation and soil water storage) across New Zealand climate zones. For example, highly suitable areas for lucerne cultivation, were estimated in ∼21 thousand km2 when considering the exclusion of steep slopes, poor soil drainage and excess annual rainfall. The two crop-yield models were applied in response to 30 years of daily historical (1971–2000) weather data downscaled at 5 km resolution on suitable areas. Simulated average lucerne yields ranged from ∼4.5–28 t dry matter/ha per year. Simulations showed a distinct spatial pattern of yield decline from north to south, mainly in response to decreasing temperatures. Temporally, water limited yields were up to 4-fold more variable than under irrigation, depending on the degree of drought stress across different years. Results also unveiled systematic spatial patterns of model uncertainty quantified as yield sensitivity to model selection. For instance, simulated yields were most sensitive to model selection (6–31% of total variability, Ti) within high abiotic-stress environments (e.g. low temperature and limited water supply). Overall, soil type selection accounted for most of yield variability (58–78% Ti), being particularly important in warmer environments with variable seasonal rainfall regimes (e.g. northern regions). As expected, water supply (i.e. rain-fed or irrigated systems) was relatively more impactful on yield (8–20% Ti) for limited rainfall areas, where crops are most drought prone (e.g. east coast and central southern regions). Long-term regional scale comparisons of annual lucerne yield, between 30-year simulated distributions and point-based observations from the AgYields database, helped identify hotspots of yield overestimation. Such insights are useful to guide future research on high yield gap areas (e.g. southern colder and drier locations) and highlight key areas for model improvement (e.g. representation of multiple biotic stresses). Overall, our results provide a first gridded-model assessment of lucerne suitability and yield at national scale and quantify the share of variability explained by key climatic, management and methodological components in spatial analysis studies. These insights can inform future modelling efforts and support agricultural planning that considers the expansion of lucerne and other perennial legumes.

CONTEXTMillions of people living in the Eastern Gangetic Plains (EGP) of India engage in agriculture to support their livelihoods yet are income poor, and food and climate insecure. To address these challenges, policymakers and development programs invest in irrigation-led agricultural intensification. However, the evidence for agricultural intensification to lift farmers’ incomes above the poverty line remains largely anecdotal. OBJECTIVEThe main objective of this study is to use a large household survey (n=15,572; rice: 8,244, wheat: 7,328; 2017/18) to assess the link between agricultural intensification and personal daily incomes from farming (FPDI) in the rice-wheat systems of the EGP – the dominant cropping system of the region.METHODSWe use the Intensification Benefit Index (IBI), a measure that relates farm size and household size to FPDI, to assess how daily incomes from rice-wheat production change with irrigation-led intensification across the EGP.RESULTS AND CONCLUSIONSRelative to the international poverty line of 1.90 Purchasing Power Parity (PPP)$ day-1 and accounting for variations in HH size in the analysis, we found that small farm sizes limit the potential for agricultural intensification from irrigation to transform the poverty status of households in the bottom three quartiles of the IBI. The estimated median FPDI of households with intensified systems in the bottom three quartiles is only 0.51 PPP$ day-1 (a 0.15 PPP$ gain). The median FPDI increases to 2.10 PPP$ day-1 for households in the upper quartile of the IBI distribution (a 0.30 PPP$ gain). Irrigation-led agricultural intensification of rice-wheat systems in the EGP may provide substantial benefits for resilience to climatic change and food security but achieving meaningful poverty reduction will require complementary investments.SIGNIFICANCETransforming the poverty status of most smallholder farmers in the EGP requires diversified portfolios of rural on- and off-farm income-generating opportunities. While bolstering food- and climate security, agronomic intervention programs should consider smallholders’ limited monetary incentives to invest in intensification. Irrigation-led agricultural intensification programs and policies should explicitly account for the heterogeneity in household resources, irrigation levels, and degree of dependence on agricultural income.

In Ecuador, farmers poorly adopt practices to manage potato seed degeneration. This could be related to the deficient understanding of the farmers’ capacity to experience seed degeneration and respond to it. We contribute to this understanding by answering: How do farmers experience seed degeneration?; What practices do farmers implement when their seed is degenerated?; and Is experiencing degeneration the pivotal factor determining how farmers replace their seed regardless their income? We analysed data collected in Ecuador through farmers’ focus group discussions, farmers’ surveys and interviews, and the Ecuadorian employment status survey. We found that approximately half of the farmers experienced degeneration. Farmers experienced it through low yields, change in seed appearance, crop weakening, and seed physiological problems. When farmers experienced degeneration, they replaced their seed, sought for technical advice, applied more agricultural inputs, or grew other crops. Income was an important trigger for farmers to change their seed replacement practices.

CONTEXT: Wheat-maize (W-M) double cropping is the dominant land use system in the North China Plain (NCP). This system has high grain output but suffers from high fertilizer input and nitrogen (N) surplus. Meanwhile, the market demands more protein and oil crops, such as soybean or peanut. OBJECTIVE: Here, we assess whether incorporation of legumes into W-M via intercropping with maize can contribute to lower annual N input while maintaining high annual outputs and diversifying products with high yield stability. METHODS: We compared yield, yield stability, and profitability of six rotation systems: W-M30 (at the maize inter-plant distance of 30 cm), the density-increased W-M20, wheat-soybean (W-S), wheat-peanut (W-P), and wheat with an intercrop of maize (at the inter-plant distance of 20 cm) and soybean (W-MS) or peanut (W-MP). Four annual N input levels were compared: N0 (no N input), N1 (reduced N input), N2 (target practice), and N3 (current high input). RESULTS AND CONCLUSIONS: Results over four years showed that replacing maize by maize/legume intercrops had a similar wheat yield as that of W-M while the N input was intermediate between W-M and W-legume rotations. Total actual/equivalent grain yields and gross margins of W-MS or W-MP were consistently intermediate between W-M and W-legume rotations. Intercropping enhanced the yield and temporal yield stability of maize per plant, with benefits for both yield stability of the intercropping system of maize season and the annual rotation system. Averaged over six rotation systems, increasing N supply increased the annual total actual/equivalent grain yield, gross margin and yield stability to a plateau starting at N1 or N2, without a further significant increase at N3. Specifically, the response of total equivalent yield or gross margin of each annual system to increasing N supply could be fitted by the linear-plateau model. Compared to the response curve of W-M, W-MS and W-S reached the plateau with a lower N input and higher yield and profit, while W-MP and W-P reached the plateau with lower N input but decreased the yield and profit. Compared to W-M with 240–360 kg N/ha/year, W-MS used 210–320 kg N/ha/year saving 11.1–12.5% fertilizer N, while maintaining or improving production by 9.1–13.0%, and improving profitability by 12.1–15.6% and temporal yield stability by 12.8–50.6%. SIGNIFICANCE: W-MS diversifies products with lower N input and higher outputs, profitability, and temporal yield stability than conventional W-M, thus is highly recommended towards productive and sustainable agriculture in the NCP.

Managing outbreaks of alien plant pests is key to preserving biodiversity and safeguarding crop production. Zoning strategies are applied by plant health authorities to tailor measures to the risk of spread in relation to distance from the outbreak epicentre and the biology of the pest. Here we synthesize information on outbreak management to evaluate the diversity and consistency of such approaches. We collected information on the zoning strategies of 121 outbreaks of 25 plant pests in the European Union (EU). According to the organism’s presence and the measures applied, five zones were distinguished: an infested zone (83% of cases), a buffer zone (76%), a clear-cutting zone (28%), an eradication zone (1%) and a containment zone (1%). Infested zones and buffer zones were adjacent non-overlapping zones, while the clear-cutting zone, eradication zone or containment zone was within either the infested zone or buffer zone. A combination of infested and buffer zones was used in 51% of recorded cases. Measures differed within different zones. Destruction of infested plants in the infested zone was done in 78% of the cases, while surveillance was always applied in the buffer zone. Regulation of an organism at EU level led to a convergence of zoning strategies applied by different member states. Regulations often prescribed the greatest widths used before regulations were issued. Further analyses are needed to explore the efficacy of different strategies including the costs of each strategy. Such analyses should combine insight from practice with bio-economic modelling.

To identify if and how the age of in vitro potato plantlets at planting affects the later tuber formation, an extensive pot experiment was performed under controlled conditions. In vitro-derived plantlets of different ages (14, 28, 42 and 56 days old at planting) and cultivars varying in maturity type (Gloria, very early; Bintje, mid-early; Elkana, late) were grown after planting for 10 weeks at photo/thermoperiods of 16 h (standard conditions) or 12 h (short-day conditions). Plants raised from older in vitro plantlets produced higher total dry weights, harvest index and tuber dry and fresh weights than plants from younger in vitro plantlets when grown under standard conditions after planting. By contrast, total and tuber dry weights were not affected by plantlet age when grown under short-day conditions. The number of tubers per plant increased with increase in in vitro plantlet age in the later cultivars and in the oldest age classes of the very early cultivar when plants were grown under standard conditions. Short-day conditions resulted in fewer, but larger tubers than standard conditions. Results support the ideas that (1) plants from older in vitro plantlets and earlier maturing cultivars are more advanced in the tuber formation process; however, this may benefit tuber yield only when plants are grown under conditions that are not strongly inducing tuberization, and (2) higher tuber numbers can be achieved by more below-ground nodes—as in older in vitro plantlets—and/or by later or less strong tuber induction—as in less inducing conditions (16-h vs. 12-h), later cultivars or younger in vitro plantlets.

Context or problem: The reallocation of dry matter (DM) and nitrogen (N) from vegetative tissues to the grains are critical for both yield quantity and protein content of cereal crops. However, it is unclear to which extent the dynamics in DM and N reallocation depend on N availability, and how individual leaves within the maize canopy respond to different N availabilities in terms of these processes. Objective or research question: This study aimed to quantify DM and N accumulation, partitioning, and reallocation from vegetative to reproductive parts in maize in relation to soil N availability. Methods: A long-term N fertilizer trial was conducted in Jilin province, Northeast China, growing maize at three N fertilizer levels (low N availability, N0; intermediate N availability, N1; and high N availability, N2). The accumulation, partitioning, and reallocation of DM and N were quantified at the whole-plant, organs, and single-leaf scales in 2015 and 2016. Results: Although both post-silking DM accumulation and post-silking N uptake increased in response to higher N availability, 8.3–38.8% of grain N still needed to be reallocated from vegetative organs with a larger fraction coming from leaves (10.5 – 36.5%) than from stems (4.4 – 11.6%). This dependency of grain N on N reallocation from vegetative parts increased at lower soil N availability. Furthermore, the vertical patterns of reallocated leaf DM and reallocated leaf N changed with N availabilities. While in general leaves in the middle part of the canopy tended to reallocate more DM and N to the grains than leaves from the upper or lower canopy parts, these most-contributing leaves were higher in the canopy at low than at high N availability. Conclusions and implications: Grain N relies on reallocation more than does grain DM. At lower N availability, more grain DM and grain N need to be reallocated from vegetative organs. Furthermore, the leaf ranks from which most DM and N were reallocated, gradually increased from the bottom to upper ranks as N availability decreased. Together, our results on the dynamics of N and DM uptake and reallocation during the reproductive phase are important for plant and crop models that require these processes for accurate predictions of maize performance.

Improving the quality of seed potatoes that smallholder farmers plant continues to represent one of the most important challenges of the potato sector in most developing countries to counter the long-lasting poor yields. This study aimed to better understand the way farmers choose seed potato by exploring the attributes they look for and the benefits they expect from them. We used means-end chains analysis in combination with Kelly’s repertory grid as an elicitation technique and disaggregated data for male and female partners. In total, farmers named 38 attributes they look for when selecting seeds. Farmers associate “good” seeds to those that are well-sprouted, have many eyes, are of a variety they know, are medium in size, are certified, and are undamaged. Most preferred attributes lead to a higher yield and consequently higher income which is the most predominant avenue for farmers to achieve their desired values in life. Female farmers mentioned fewer attributes and also pursued fewer values than their male counterparts. Users and non-users of certified seed were shown to use the same attributes to select their potato seeds. Non-users of certified seed thus seem to be aware of the benefits of certified seed even though they are not using it. The results from this study indicate that increasing the availability of certified seed is not necessarily a straightforward way of improving the quality of seed potato planted by Kenyan smallholder farmers.

Cocoa is an important commodity crop and source of income for millions of small-holder farmers. Nonetheless, questions on cocoa tree functioning, best management practices and climate change responses remain. Modelling is a powerful tool to address these questions, complementing experimental work that is expensive and time consuming due to the long productive cycle of the cocoa system. However, compared to other crops, cocoa modelling has not received as much attention. OBJECTIVE: We reviewed existing cocoa models and identified the main gaps in the literature and possible strategies to advance models of cocoa production. METHODS: We first classified relevant research questions in cocoa production along three main axes (fundamental-applied, spatial organization, prediction horizon) and aligned modelling approaches along these. We then reviewed six published cocoa models using these axes as framework. This comparison revealed several modelling gaps for which we provide an overview of data availability for future model development. RESULTS: (i) Several plant processes (i.e., water stress responses, respiration, climate change responses, nutrient effects and phenology) are either missing from existing cocoa models or are simulated based on general plant physiological knowledge rather than cocoa-specific knowledge. (ii) The only currently existing 3D model of cocoa architecture has very limited scope and does not include physiological processes. (iii) There are no model-based decision support tools available for supporting the main management practices such as irrigation, fertilization and pruning. (iv) Data for model calibration and validation are often scarce. CONCLUSIONS: We conclude that data availability for model design, calibration and validation is currently the main bottleneck for further development of cocoa models. Extensive cooperation within the cocoa research community and a large network of long-term experiments under different climatic and management conditions are required to close the identified modelling gaps.

CONTEXT: To avoid excessive chemical-fertilizer application and improve agricultural productivity in rice, a fertilizer recommendation system called Nutrient Expert® (NE) was designed. However, the ability of NE to balance yield, profitability and environmental sustainability in rice production needs to be further evaluated, as it is still difficult for farmers to assess the proper nitrogen (N) application rate. OBJECTIVE: The objective of this study was to demonstrate the advantages of the NE system in balancing yield, profitability and N loss in rice production, and recommend proper N application rates for different cropping seasons of rice. METHODS: This study describes results from field experiments conducted in five main rice cropping provinces from 2017 to 2020 in China, to investigate any advantages of NE compared with local farmers' practice (FP), and to determine the proper N application rates for different cropping seasons of rice. RESULTS AND CONCLUSIONS: Compared with FP, NE had 12.1% lower N-fertilizer application, but increased rice grain yield by 4.3% and net profit by 7.4%, and decreased yield-scaled N loss by 20.7%. We showed how yield, profitability and N loss were affected by N balance (i.e., N applied to the field minus N removed from the field by the harvested crop biomass), and quantified relationships between N balance and N application rate, and between N output and input. Based on relationships between N balance and N application rate, we recommend N application rates in a range from 122 to 214 kg ha−1, depending on cropping seasons of rice. We demonstrated that NE can simultaneously improve yield, profitability and environmental sustainability. SIGNIFICANCE: Our study provided quantitative support for NE-based recommendations on the N application rate for smallholders farming in different rice cropping systems, and these recommendations can serve as a reference for avoiding excessive N application rate in paddy fields in other regions with similar eco-environment.

Combinability of species in intercrops depends on the production conditions and there is limited information on the potential of intercropping under conventional (i.e., non-organic) management in Western Europe. Here we determined productivity of four crop species (maize, Zea mays L.; wheat, Triticum aestivum L.; faba bean, Vicia faba L.; pea, Pisum sativum L.) in six different bi-specific mixture compositions. Species were spring-sown and fertilized in their strips according to common practice for monocrops. Strips were 1.5 m wide enabling strong interspecific interactions. Intercrops with maize, a species sown and harvested later than the other three species, had land equivalent ratio (LER) values that were in four out of six cases significantly greater than one, from 1.14 ± 0.04 to 1.22 ± 0.05 in 2018, and from 0.98 ± 0.06 to 1.15 ± 0.01 in 2019. Simultaneous intercrops comprising two of the other three species had LER values that tended to be lower than one, even though many LERs were not significantly different from one: from 0.94 ± 0.02 to 0.95 ± 0.04 in 2018, and from 0.80 ± 0.08 to 0.93 ± 0.04 in 2019. The yield gain (net intercropping effect; NE) in relay intercrops with maize ranged from 1.33 ± 0.59 to 2.01 ± 0.54 Mg ha−1 in 2018, and from 0.29 ± 0.41 to 1.04 ± 0.14 Mg ha−1 in 2019. The NE of simultaneous intercrops ranged from −0.43 ± 0.13 to −0.27 ± 0.22 Mg ha−1 in 2018, and from −1.17 ± 0.49 to −0.36 ± 0.22 Mg ha−1 in 2019. Results indicate that temporal complementarity between species drove the LER (or NE) in these experiments. On the other hand, values of the LER (or NE) were similar in species combinations with or without legumes, suggesting no major role for complementarity for nitrogen capture under the conditions of the study. Faba bean was the most competitive species and reached high partial LER and NE values in intercrops at the expense of the companion species. Competition from faba bean reduced the grain yield of wheat and pea more than it increased faba bean grain yield, resulting in negative net effects. Results suggest that relay strip intercropping can improve land use efficiency and total grain yield in conventional farming in Western Europe if species have temporal complementarity.

Preceding crop and nitrogen (N) fertilization affect N cycling and productivity of subsequent wheat in double cropping. However, the effects of preceding crop and N fertilization on relationships between yield and “mineral nutriome” or nutritional quality (amount and bioavailability) in wheat grains have not been well characterized, particularly not in the case of multiple mineral nutrient elements and when considering cumulative effects of fertilization strategies in long-term field experiments. Here we present effects of preceding crop (monocultures of maize, peanut or soybean, and intercropping of maize with peanut or soybean) at 4 levels of annual fertilizer N input (0–440 kg/ha) on yield traits, major mineral nutrients and their relationships in wheat grains in a 4-years continuous double-cropping field experiment in the North China Plain. Nitrogen fertilizer increased wheat grain yields, mass concentrations of N and copper (Cu), and micronutrient (mainly zinc: Zn and iron: Fe) bioavailability, while no N supply was associated with low grain yield, N and Cu concentrations and micronutrient bioavailability, high mass concentrations of Zn, manganese, phosphorus (P), calcium, magnesium and phytate-P, and a high ratio of phytate-P/P. Moderately lowering N input from the in-season 240 to 200 kg/ha (but not 120 kg/ha) would not harm grain yield and most nutritional traits. Compared to significant effects of N application level on almost all grain yield and nutritional traits, and soil properties, preceding crops had less impact and only grain yields and Zn concentrations were significantly affected. Grain yields, N and Zn concentrations varied dramatically from an average of 2.7 to 7.6 t/ha, 16.5–19.3 g/kg and 15.1–19.8 mg/kg with different N application levels, respectively; while varied relatively little from 5.9 to 6.6 t/ha, 17.8–18.3 g/kg and 16.1–18.1 mg/kg under different preceding crops, respectively. Compared to the conventional wheat-maize rotation, a legume pre-crop monoculture but not maize/legume intercropping increased grain yields by 5.0–11.9% on average, but reduced grain Zn concentrations from 17.5–17.8 to 16.1 mg/kg significantly. The legume effect was most significant at zero or low N supply. The relationship between grain yields and Zn concentrations was adequately described by a concave-up parabola (R2 = 0.3001, P < 0.0001, n = 288), suggesting appropriate N fertilization and rotation can achieve high-yield while ameliorating the dilution of grain Zn density. Therefore, our findings provide new insight in relationships among agronomic practices, wheat grain yield and grain nutritional quality (particularly for Zn).

Abstract Field trials to evaluate the performance of new varieties are an essential component of potato breeding. Besides the genetic differences, environmental factors can lead to variation in a trial. In variety trials, the observed differences amongst varieties should reflect genetic differences, without a large impact of the random or systematic variation in the field. One way to reduce within-field variation is to adjust the plot size and its shape in a trial. Two years of field trials in which individual plants in 90-plant plots of both diploid hybrid and tetraploid varieties were measured provided data to derive relationships between LSD% and plot size and shape. We provide a method to estimate the equations to calculate the expected variation when using different plot dimensions in a relatively homogeneous trial field for tuber yield, tuber volume, tuber count, tuber shape and the standard deviations of tuber volume and shape. Compared with the yield traits, the variation for tuber shape was relatively small. The effect of plot shape was minor. With these equations, breeders can determine what plot dimensions are needed to reach the desired precision for each trait.

To contribute to the development of a novel cropping system for potato grown from greenhouse-derived seedlings from hybrid true potato seeds, planting density trials were carried out under normal Dutch agronomic conditions. For two consecutive years, 5-week-old seedlings of two experimental genotypes were transplanted into farmers’ potato production fields at two contrasting locations: a flat-bed system on sandy soil and a traditional ridge system on clay soil. Planting densities were 6.25, 12.5, 25, 50, 100 and 200 plants/m2 in the flat-bed system, and 3.125, 4.688, 6.25, 12.5, 25 and 50 plants/m2 in the ridge system. In general, increasing planting density of hybrid seedlings per area decreased tuber fresh weight per plant and reduced the number of tubers per plant. On a per hectare basis, an increased planting density resulted in increased total tuber yield and number of tubers up to very high densities, but finally both parameters levelled off. Highest total tuber yields harvested were 107 and 45 Mg/ha for the flat-bed and ridge system, respectively. On flat-beds, the optimal planting density for total yield was 50 plants/m2. On ridges, planting density interacted with year and genotype, resulting in an optimum planting density of 25 plants/m2 to reach the maximum total yield. Obtained yields in the commercial size classes Baby Baker (20 2. The current study showed that transplanted hybrid seedlings are feasible alternatives for seed-tuber-grown systems for certain potato outlets.

Viruses pose a major challenge to sweetpotato production in Tanzania. Use of cleaned-up, virus-tested seed vines distributed through a formal seed system is among the proposed strategies to address this challenge. However, virus-tested seed vines can get infected once in the field and it is not known how they will perform following several seasons of on farm propagation. We assessed the performance of virus-tested seed vines and farmer-sourced seed vines of a susceptible variety, Ejumula, and a relatively tolerant variety, Kabode, over five seasons to understand the trend in root yields, vine yields and virus incidences. The experiments were done in high and low virus pressure areas. The most prevalent viruses were sweet potato chlorotic stunt virus (SPCSV) followed by sweet potato feathery mottle virus (SPFMV) and sweet potato leaf curl virus (SPLCV), respectively. Both farmer-sourced and cleaned-up, virus-tested seed of cv. Ejumula were rapidly infected with SPCSV. The incidence of this virus on Ejumula's farmer-sourced material at the high-virus-pressure area reached 100% by the second season. The incidences for all three viruses remained stable for cv. Kabode across the five seasons. Plants generated from cleaned-up, virus-tested seed had lower incidences for all viruses compared to those from farmer-sourced planting material. Virus-tested seed produced significantly higher root yields for cv. Ejumula in the high-virus-pressure site, with a gradual drop across the seasons. The findings show that regular replenishment of clean, virus-tested seed is more economical in high-virus-pressure areas and for more susceptible varieties like cv. Ejumula. They also indicate that farmers may be reluctant to invest in cleaned-up, virus-tested seed in cases where they have virus-tolerant varieties such as cv. Kabode due to lack of obvious virus effect on yields.

Maize-legume intercropping is common in sub-Saharan Africa. Effects of legumes on the companion maize crop are determined principally by choice of legume species and relative introduction time. Performance of intercrops is optimized when legumes' planting is timed such that their peak growth phase occurs after maize harvest, with legumes utilizing the residual soil moisture. OBJECTIVE: We sought to understand the role of inter-specific competition for water in maize-pigeonpea and maize-lablab intercrops. METHODS: We analysed experimentally determined shoot biomass of sole and intercropped maize, lablab, long and medium- duration pigeonpea. Experiments were conducted in northern Tanzania for two consecutive seasons. The second season was drier (236 mm) than the first (551 mm). We constructed a parameter-sparse growth model, calibrated based on sole crops data. The model calculates growth rate as radiation interception × radiation-use efficiency. When simulated actual soil moisture content fell below a species-specific critical level, the ratio between actual and potential transpiration for that species decreased, and crop growth rate was reduced proportional to this reduction. RESULTS AND CONCLUSIONS: There was good agreement between simulated and observed shoot biomass of maize and the legumes. With rooting depth of 60 cm, maize was simulated to be sensitive to annual precipitation, resulting in 3.5 t ha−1 (34%) reduction in shoot dry matter production in the second season. By contrast, the legumes, with a rooting depth of 200 cm did not experience water shortage in either of the two seasons, resulting in nearly identical shoot dry matter production in both seasons. Explorative simulations assuming the legumes to have shallower rooting depth confirmed the importance of this trait for avoidance of water stress, with simulated reductions in dry matter production of 23–34% for the legumes when rooting depth was reduced from 200 to 60 cm. Maize in the intercrop was modestly influenced by the legumes due to light competition. In the low precipitation season, additional competition for water occurred and water shortage for maize was aggravated. Maize influenced the legumes only through competition for light, as a tap root allowed the legumes to utilize water stored in deeper soil layers. During the co-growth period, competition for light exerted by maize on the legumes was strong, but they partly compensated for this in the period after maize harvest. SIGNIFICANCE: Our results emphasize the important role of the deep legume tap root for the success of maize-legume intercrops under rain-fed conditions.

A novel cropping system for potato was tested for two consecutive years under normal Dutch agronomic conditions. Seedlings from two experimental genotypes of hybrid true potato seeds were produced in a greenhouse nursery and transplanted into the field 5 weeks after sowing to assess tuber yield levels and to study effects of hilling on tuber yield and number, tuber size distribution and tuber greening. Field experiments had a split-plot design with hilling treatments as the main plots and genotypes as the sub-plots. Final harvest was at 122 and 132 days after transplanting in 2017 and 2018, respectively. Hybrid seedlings were transplanted into small initial ridges and irrigated straight after planting. Three hilling treatments were applied between transplanting and 100% canopy cover. Treatment ‘zero hilling’ did not receive any additional hilling after transplanting. Treatments ‘double hilling’ and ‘triple hilling’ received two and three additional hilling treatments, respectively. Total tuber yields at final harvest in both years were not affected by the hilling treatments. Yields for the respective genotypes were 26 and 30 Mg/ha in 2017 and 25 and 32 Mg/ha in 2018. Total tuber numbers were only affected by hilling treatments in 2017, where under hilled conditions, plants produced more tubers compared with plants under zero hilling. Plants under zero hilling yielded more tubers in size class > 40 mm compared with triple hilling in 2017. In 2018, no significant effects of hilling on tuber numbers were found, but the trend was similar to that in 2017.

Plant breeding for increased crop water use efficiency or drought stress resistance requires methods to quickly assess the transpiration rate (E) and stomatal conductance (gs) of a large number of individual plants. Several methods to measure E and gs exist, each of which has its own drawbacks and shortcomings. To add to this toolbox, we developed a method that uses whole-plant thermal imaging in a controlled environment, where aerial humidity is changed rapidly to induce changes in E that are reflected in changes in leaf temperature. This approach is based on a simplified energy balance equation, without the need for a reference material or complicated calculations. To test this concept, we built a double-sided, perforated, open-top plexiglass chamber that was supplied with air at a high flow rate (35 L min− 1) and whose relative humidity (RH) could be switched rapidly. Measurements included air and leaf temperature as well as RH. Using several well-watered and drought stressed genotypes of Arabidopsis thaliana that were exposed to multiple cycles in RH (30 to 50% and back), we showed that leaf temperature as measured in our system correlated well with E and gs measured in a commercial gas exchange system. Our results demonstrate that, at least within a given species, the differences in leaf temperature under several RH can be used as a proxy for E and gs. Given that this method is fairly quick, noninvasive and remote, we envision that it could be upscaled for work within rapid plant phenotyping systems.

The recent invention of hybrid breeding technology for potato has led to an increased interest in hybrid potato R&D. Hybrid true potato seeds (TPS) are used to produce planting materials such as transplants and seedling tubers, but can also be used for direct seeding of seed or ware crops. Transplants and seedling tubers can be used to produce seed tubers or ware tubers. The rise in R&D in hybrid breeding creates the need for phenological scales of growth and development of plants produced by the various planting material types of hybrid-TPS. The BBCH (Biologische Bundesanstalt, Bundessortenamt and CHemical Industry) scale is one of the phenological scales developed for the description of the growth and development stages of plants. In 1993, a BBCH scale with descriptions for potato plants was released. The original BBCH scale gave standardised descriptions for TPS- and tuber-grown plants. Differences in the morphology of plants originating from the different planting materials in terms of types of branches and differences in below-ground growth and development were not included. Moreover, for reproductive growth stages, crucial for hybrid breeding, the original scale is incomplete as it does not carefully take the complex sympodial branching into account. Methods of describing growth of tubers and berries are complex and impossible to use when final tuber mass or berry size is unknown. The current paper augments the original BBCH scale, while retaining its structure and logic. It provides alternative and comprehensive descriptions of growth stages suitable for potato plants grown from different types of planting materials, and for all end uses of these plants. The proposed scale is detailed enough for research and breeding but still general enough for agricultural use.

Rice yield reduction due to water limitation depends on its severity and duration and on the phenological stage of its occurrence. We exposed three contrasting rice genotypes, IR64, UPLRi7 and Apo (adapted to lowland, upland and aerobic conditions, respectively), to three water regimes (puddle, 100% and 60% field capacity) in pots during the vegetative (GSI), flowering (GSII) and grain filling (GSIII) stages. Stress at all the three stages significantly reduced yield especially in lowland genotype IR64. Effect of water limitation was more severe at GSII than at the other two stages. Stress at GSI stage reduced both source activity (leaf area and photosynthetic rate) and sink capacity (tiller number or panicle number per pot). When stress was imposed at GSII, spikelet fertility was most affected in all the three genotypes. In both GSII and GSIII, although leaf area was constant in all the three water regimes, estimated relative whole-plant photosynthesis was strongly associated with yield reduction. Reduced photosynthesis due to stress at any given stage was found to have direct impact on yield. Compared to the other genotypes, Apo had deeper roots and maintained a better water relation, thus, higher carbon gain and spikelet viability, and ultimately, higher biomass and productivity under water-limited conditions. Therefore, screening for these stage-dependent adaptive mechanisms is crucial in breeding for sustained rice production under water limitation.

Bans on the use of synthetic herbicides require innovative management approaches to maintain the attractiveness and usability of turfgrass swards. Such measures should include the use of locally adapted cultivars that germinate and establish quickly, resulting in the densest possible stands. Additionally, a number of turfgrasses have been reported to produce allelopathic substances that inhibit common turfgrass weeds. Mowing heights should be set to achieve maximum weed suppression while still providing acceptable quality for desired use. Sustainable turfgrass management programs have led to a reduction in fertilizer inputs; however, without the availability of herbicides, fertilization regimes need to be re-examined. The literature suggests that broadleaf weeds are reduced but never fully controlled when more N is applied; therefore, finding a balance between what is needed and what is environmentally safe and sustainable is critical. Organic herbicides include plant pathogens from the fungus Phoma and strains of the bacterium Pseudomonas fluorescens. Both can be used to control several weeds common to turfgrasses. Acetic acid has also been shown to have herbicidal activity; however, it has limited residual activity, and its efficacy remains questionable on mature weeds. Thermal weed control can be used to sterilize a seedbank or spot treat existing weeds. Future turfgrass breeding programs could focus on understanding and enhancing the allelopathic potential of turfgrasses to outcompete weeds more effectively. Furthermore, more research should be directed at assessing the competitiveness of certain turfgrasses against weeds within the limitations of producing turfgrass areas of acceptable aesthetics and playing quality.

The technology of hybrid breeding in diploid potatoes creates opportunities to design novel and improved cultivation systems based on hybrid true potato seeds. A promising cultivation pathway to produce seed or ware tubers is by transplanting greenhouse-raised seedlings into the field. This study explored the effects of transplanting date and seedling age on tuber yield, using greenhouse-raised seedlings. Field trials with experimental hybrid genotypes were conducted in three consecutive years. In 2017 and 2018, 4- and 6-week-old seedlings were transplanted at four dates: March, April, May and June. In 2019, transplanting dates included April, May and June and seedling age was 5 weeks. In 2018, the March planting experienced severe frost during the initial field period resulting in crop failure. In 2017 and 2019, plants could withstand shorter and less severe frost events. Seedling age did not significantly affect tuber parameters. Transplanting in June resulted in lower marketable yield (> 28 mm) compared with earlier transplanting dates when crops were harvested in September. At full crop senescence, no differences in marketable yield were observed. The optimal transplanting window, taking into account weather-related risks, is approximately between early April and end May. For some genotypes, crop cycle length was observed to be a more important yield-determining factor than transplanting date.

Intercropping maize and soybean is renowned for improving crop production and resource use efficiencies. Interspecific competition and complementarity with respect to root plasticity is essential knowledge for understanding the mechanisms of overyielding and optimizing intercropping species selection. We conducted a three-year field experiment (2017–2019) to quantify land and water productivities in relation to above- and below-ground interspecific interactions, root growth and distribution under different nitrogen rates in maize/soybean intercropping. The land productivity in terms of land equivalent ratio (LER) in maize/soybean intercropping was 1.10 across all years and N rates. The yield increase in intercropped maize was mainly gained from an 45% increase in kernel numbers, while the yield loss of intercropped soybean was caused mainly by an 35% decrease in the pod numbers compared to sole cropping. The system level water use efficiency, defined as water equivalent ratio (WER) was also 1.10. Compared with sole stands, intercropped maize consumed more water during the vegetative stage, but intercropped soybean took up more during the reproductive stage. That indicated a temporal complementarity of water use in the intercrop, which benefited maize kernel formation and partially offset the negative shading effect of soybean grain filling. Soybean showed a marked increase in root length density (RLD). Compared to the produced aboveground biomass (DM) in the intercrop, the intercropped soybean invested more assimilates into root than shoot, as defined as root plasticity, the RLD/DM ratio of soybean in the intercrop was 76% more than sole system. However, the intercrop did not change root plasticity of maize. The overlap of maize and soybean roots, i.e. interspecific interaction interface, occurred mainly within the position between two border rows and at first soybean row. Under interspecific competition, soybean in the intercropping created both temporal and spatial differentiation for water uptake, which might be a key reason for enhancing intercropping land and water productivities. Our results contribute to understanding the mechanism of interspecific interaction for maximizing land and water productivities in rain-fed intercropping.

Potato production in low-income countries is threatened by seed degeneration, i.e., the accumulation of seed-borne diseases and pests in potato seed tubers when these are vegetatively propagated over consecutive cycles, leading to a reduction in seed quality and yielding ability. Agroecological settings and seed recycling (on-farm propagation over consecutive cycles) determine the process of seed degeneration. However, it is poorly understood how these factors affect this process. Therefore, to reduce this knowledge gap, we analysed two datasets collected in Ecuador, one from a multi-annual field experiment and one from a farmers’ seed study. The experiment, carried out from 2013 to 2016, aimed to assess seed degeneration at agroecological settings present in three different altitudes. The farmers’ seed study, in which 260 farmers were surveyed in 2018, aimed to understand potato seed degeneration in farmers’ fields under diverse agroecological settings. Our results of the multi-annual field experiment showed that agroecological settings have a heterogeneous influence on the presence of seed-borne diseases and pests. We also found that both the agroecological settings at the three altitudes and the number of on-farm propagation cycles affected the rates at which seed-borne diseases and pests on the seeds increased and yield decreased. However, the farmers’ seed study challenged these results by indicating that this was not clear on farms. Combining these results, this article shows that agroecological settings and seed recycling only partially explain the process of seed degeneration. This suggests that more research about seed degeneration needs to also take place under farmers’ conditions to fully understand the complex of potato performance factors. We expect that such research will support the design of improved seed interventions, while simultaneously it may generate discussion about when potato seed degeneration plays an important role in productivity.

CONTEXT: Studies in the Andes have demonstrated that seed degeneration of potato occurred in experimental conditions, but was negligible in farmers' conditions. There are two hypotheses for this difference: (1) farmers cultivate resistant varieties, or (2) they use on-farm practices that can manage seed degeneration. Farmers may replace some of the seed saved from their fields with outside seed, but it is an open question what level of benefit farmers experience from partial replacement. OBJECTIVES: The objective of this study was to investigate the role of the cultivated varieties, the on-farm seed management practices, and seed replacement in potato seed degeneration. Moreover, this study evaluated the potential effect of partial replacement of the farmers' seed lot each season with healthy seed, compared to less frequent nearly full replacement, in simulations. METHODS: We surveyed farmers in the Cotopaxi province, Ecuador, in 2008, 2010, and 2018, and performed a study on the incidence of pathogens and pests in farmers' seed lots in 2018. We also evaluated the potential effects of the timing of replacement of farmers' seed lots by healthy seed to manage degeneration, applying the seedHealth model. RESULTS AND CONCLUSIONS: We found that farmers experience no or only slow degeneration in their varieties. Analysing yield data reported by farmers to detect degeneration, we did not detect yield declines. The type of variety and year of data collection explained the variation in yield. These results seem to confirm the hypothesis that varieties cultivated in the Andes are resistant to the impact of seed degeneration on yield, and that seed degeneration depends on the agroecological conditions present within a cropping season or year. Because we did not find an impact on yield, we hypothesized that on-farm practices affect seed-borne pathogens and pests causing seed degeneration. We identified multiple on-farm practices playing a role in the process of seed degeneration: they either slowed down or accelerated this process depending on the seed-borne pathogen and pest causing seed degeneration. Our scenario analyses using the seedHealth model showed how replacing farmers' seed lots by healthy seed could usefully reduce seed degeneration compared to using the same amount of seed to periodically replace nearly all seed in a season. Our results showed that on-farm practices are also critical drivers in the process of seed degeneration. SIGNIFICANCE: This study demonstrated the importance of considering on-farm seed management practices (i.e., use of cultivated varieties) to strengthen seed systems interventions aiming to manage potato seed degeneration. Additionally, this study showed the potential of partially replacing farmers' seed with healthy seed as an alternative when complete seed replacement is not an option.

Potato is the second most important food crop after maize in Kenya. However, most farmers produce potatoes under sub-optimal management, resulting in low yields, despite the introduction of improved varieties. Potato production practices were documented and compared to contribute towards improved potato management and productivity in Kenya. The study was guided by the hypothesis that potato farming and management practices influence potato performance and can depend on the production environment. Focus group discussions and household surveys were conducted in three major potato growing areas in Kaptama, Saboti and Lelan in Bungoma, Trans Nzoia and Elgeyo Marakwet counties in Kenya. Farming was the main occupation of 58.2% of the respondents. Respondents across the study sites indicated that they grew potatoes with their main focus as a cash (83.6%) and food (16.4%) crop. Most respondents had planted potatoes during both the last long (96.4%) and short (92.4%) rainy seasons. The four most important constraints limiting optimal potato production according to respondents were lack of quality seed, diseases (specifically late blight and bacterial wilt), poor marketing and lack of adequate technical knowledge on potato management. Low yields realized by farmers were mainly influenced by poor farmer practices in the use of seed, fertilizers, pesticides and crop rotation. This was compounded by farmers’ perceptions on input quantities applied, frequencies and farmers’ access to agricultural extension information on potatoes, which heavily relied on family members and neighbouring farmers. Provision of quality seeds and training of farmers with the support of demonstrations on fertilizer and pesticide and appropriate crop rotation practices are recommended for improved potato production and yields. Use of irrigation where possible should be enhanced through government and development partners’ support to ensure sustainable potato production and supply. Also, the use of viable extension information channel(s) could enhance potato production for household food security, livelihoods and national goals.

Context: Global cocoa production is largely concentrated in West Africa where over 70% of cocoa is produced. Here, cocoa farming is largely a rain-fed, low-input system with low average yields, which are expected to decline with climate change. With increasing demand, there is a need to evaluate opportunities to increase production whilst avoiding deforestation and expansion to croplands. Thus, it is important to know how much additional cocoa can be produced on existing farmland, and what factors determine this potential for increased yield.Objective: The objective was to quantify the cocoa yield gap in Ghana and identify the factors that can contribute to narrowing the gap.Methods: We calculated the cocoa yield gap as the difference between potential yield (i. water-limited potential(Yw) quantified using a crop model, ii. attainable yield in high-input systems(YE), iii. attainable yield in low-input systems(YF)) and actual farmer yield. Both absolute and relative yield gaps were calculated. We then related each yield gap (absolute & relative) as a function of environment and management variables using mixed-effects models.Results and conclusions: There were considerable yield gaps on all cocoa farms. Maximum water-limited yield gaps (YGW) were very large with a mean absolute gap of 4577 kg/ha representing 86% of Yw. Attainable yield gap in high-input (YGE) was lower with mean absolute gap of 1930 kg/ha representing 73% of YE. The yield gap in low-input (YGF) was even lower with mean absolute gap of 469 kg/ha representing 42% of YF. Mixed-effects models showed that, absolute YGW were larger at sites with higher precipitation in the minor wet and minimum temperature in the minor dry season explaining 22% of the variability in YGW. These same factors and cocoa planting density explained 28% of variability in absolute YGE. Regardless of climate, absolute YGF and relative YGW, YGE and YGF were reduced by increasing cocoa planting density and application of fungicide against black pod. The models explained 25% of the variability in absolute YGF, and 33%, 33% and 25% in relative YGW, YGE and YGF respectively.In conclusion, climate determined absolute YGW in Ghana whilst absolute YGE were determined by both climate and management. In contrast, absolute YGF and relative YGW, YGE and YGF can be reduced by agronomic management practices.Significance: Our study is one of the first to quantify cocoa yield gaps in West Africa and shows that these can be closed by improved agronomic practices.

Increasing fresh water scarcity is a major constraint for rice (Oryza sativa) productivity under future climatic conditions. It is important to understand why rice cannot perform like other dryland cereals, when grown under drier soil conditions. The responses of plant growth, plant water status, leaf and stem anatomical attributes to soil water deficit were examined at two developmental stages of three rice and two wheat (Triticum aestivum) cultivars grown under three water regimes in a pot experiment. Yield and yield components were determined at plant maturity. The stress sensitivity of plant growth was slightly more prominent at vegetative than at flowering stages. Water deficit limited root growth but had little impact on above-ground growth in rice plants. The xylem system of the leaves was more developed in rice than in wheat, but the opposite was true for the root xylem system. Compared with stem xylem attributes, leaf xylem attributes played a larger role in modulating leaf water potential under water deficit. In addition, the variation in yield response to water deficit between various types of rice, and between rice and wheat was closely associated with the response of leaf water potential to water deficit. To grow rice in drier conditions, its xylem system should be balanced by increasing root growth and modifying leaf anatomy.

The Nutrient Expert system (NE) has been proposed to improve yield and nitrogen (N) use efficiency (NUE) in the double rice cropping systems in China. However, the advantage of the NE system has yet to be quantified experimentally. A four-year field experiment was conducted in a double rice cropping system in China, to evaluate the ability of NE in improving yield and NUE. The experimental treatments consisted of NE based fertilization, current farmers’ practices (FP) and soil test based fertilizer recommendation (ST), and a series of nitrogen (N) rate treatments. The NUE decreased with increasing N application, while the yield did not increase significantly beyond N application rates of about 140 kg ha−1 (corresponding to the amount proposed by NE) in both early and late rice. NE increased grain yield (by 10.3% and 6.3%) and N uptake (by 5.7% and 4.0%) compared with FP and ST, respectively. NE significantly increased NUE compared with FP, and decreased the N surplus in comparison to FP and ST. The N dilution curve was Nc = 34.50 W−0.55 for early rice and Nc = 37.71 W−0.59 for late rice (where Nc is the N concentration in g kg−1, and W is the dry matter accumulation in t ha−1). The relationship between relative yield and the nitrogen nutrition index derived from the dilution curves confirmed that NE offered an optimum N application rate (approximately 140 kg ha−1) for both early and late rice. Carbon (C) and N translocation from vegetative organs to grains was enhanced with increasing N rate, while NE significantly increased C and N translocation compared with FP. Overall, the NE system ensured a high rice yield, increased N uptake and NUE. Therefore, the NE, as a user-friendly tool, is a sustainable fertilizer recommendation approach suitable for double rice cropping system, especially when soil testing is not available or timely for smallholders.

Rising temperatures and more frequent droughts caused by global climate change reduce yields and increase climate risk, especially in rain-fed agriculture. Together with scarce land and water resources, this poses a serious threat to food security. Field experiments have shown that relay intercropping systems under irrigated conditions can improve productivity. However, little is known whether these improvements could also be obtained with simultaneous intercropping in rain-fed agriculture under water-limited conditions. To investigate this question, we analyzed a maize/soybean simultaneous intercropping system, using a modeling approach. A light interception model for strip intercrops was implemented into the APSIM classic model for simulating crop growth and yield in strip-intercropped maize and soybean and then calibrated and validated using field experiments conducted from 2017 to 2019 at 4 sites in Northeast China. We then ran a simulation using climatic data (1961–2020) from these sites. Model validation showed good agreements between observations and simulations. The results obtained from our simulation over the period from 1961 to 2020 showed that intercropping was predicted to increase total yields by 41.3% and subsequently enhanced total economic revenue by 23.8% compared to sole systems. It also reduced yield gap of maize by 33%, soybean by 56%, and the system by 45%. Attainable land equivalent ratio (LER) under rain-fed conditions was 1.27 over 60 years across the 4 sites, with a relative yield gain of maize of 0.35 and a relative yield loss of soybean of 0.08. Attainable LER was higher than potential LER. Yields and LER were significantly higher between 1991 and 2020, indicating a potential increase in land productivity with intercropping under a warming climate. Our results thus suggest that simultaneous intercropping offers great opportunities for yield enhancement in rain-fed agriculture under global climate change.

Low productivity of rice in Uganda is attributed to sub-optimal production practices related to soil nutrient, crop and weed management. Application of improved management practices could enhance productivity. Returning 1 year after a joint experimentation in which different components of recommended agronomic practices (RAP) for rice were tested, we assessed change in management practices and grain yield of participating farmers (participated in joint experimentation) and non-participating farmers (did not participate) with plots in the same irrigation scheme. Participating farmers belonging to the lower-yielding farmers under farmers' practice (FP) during joint experimentation improved their management practices, compared with the middle- and top-yielding farmers. Sixty-one, 24 and 7% of lower-, middle- and top-yielding farmers, respectively, weeded earlier after experimentation compared with weeding time under FP during joint experimentation. Seventy-nine percent of lower-yielding farmers used fertiliser after experimentation compared with 18% during experimentation, with a higher N rate increase than middle- and top-yielding farmers. Overall, participating farmers transplanted and weeded earlier, and applied slightly higher N rates compared with non-participating farmers. Top-yielding farmers had significantly (p = 0.03) higher grain yield, followed by middle- and lower-yielding farmers. However, lower-yielding farmers made significantly (p < 0.001) higher yield gain than middle- and top-yielding farmers. A paired t-test showed that average yield gain was 1,358 (1,027–1,689), 473 (252–695) and −91.7 (−397–213) kg ha−1, respectively, for lower-, middle- and top-yielding farmers. Participating farmers had higher grain yield (4,125 kg ha−1) than non-participating farmers (3,893 kg ha−1). Three farm types were identified that differed in application of RAP, however, with small differences in household characteristics. The farm type with higher fertiliser use in nursery and field, line transplanting, timely weeding and higher N rate had the highest grain yield. We conclude that joint experimentation had a larger effect on raising yield of lower-yielding farmers, bringing farmers closer in their management and outputs. Lack of differences among farm households could indicate that wealth is not crucial in innovation adoption in this production system.

CONTEXT: Sustainable cropping systems need to balance productivity and profitability with resource and environmental conservation. Within a population of cropping system observations, there might be positive deviants that outperform others in terms of sustainability, which could serve as “model systems” for future development. Wheat-maize double cropping is the dominant system in the North China Plain, which is facing multiple economic, societal, and environmental sustainability challenges. Identifying exemplary positive deviants out of a multitude of wheat-maize observations might provide solutions to enhance overall sustainability. OBJECTIVES: We aimed to 1) identify exemplary wheat-maize systems that reached optimal performance across seven sustainability indicators, 2) determine which factors regarding management practices and farming contexts resulted in the sustainability gaps between exemplary and other systems, and 3) propose a sustainable wheat-maize prototype. METHODS: Based on a farmer survey dataset (n = 344), we developed a cropping system-level positive deviance approach, including multi-criteria assessment, positive deviant identification (Pareto ranking) and positive deviant clustering, to identify exemplary wheat-maize systems. We then compared exemplary and other systems to quantify the sustainability gaps and identify the key variables explaining sustainability gaps. RESULTS AND CONCLUSIONS: Sixteen percent of wheat-maize cases were Pareto-optimal and were classified as positive deviants. These were sorted into seven clusters representing contrasting sustainability patterns. Among these clusters, one comprised exemplary systems due to the best compromise over the indicator set. Compared to remaining wheat-maize cases, exemplary systems, on average, resulted in 49% and 17% higher gross margin and dietary energy output, respectively, and 33–51% lower labor use, groundwater depletion, N loss, net greenhouse gas emission, and pesticide use. Key practices conferring exemplary system performance included higher maize seeding density, lower fertilizer N input in wheat, partial substitution of inorganic fertilizer with manure, a smaller number of irrigation events, and a lower frequency of pesticide and herbicide application. No significant difference in farming context was found between exemplary and other systems. SIGNIFICANCE: Since the practices of exemplary systems were already locally adopted and proven, we expect that farmers in the region can increase the sustainability of their wheat-maize production by adjusting their management to resemble the exemplary systems. The positive deviance approach thus provides a pragmatic bottom-up approach to identify practices that can improve the sustainability of cropping systems, and can be used for other cropping systems elsewhere.

International audience Intercropping has been advocated as an environmentally benign method to suppress weeds in agriculture. However, it is not evident from the literature what size of weed suppressive effect is achieved on average by intercropping, and how species choice and crop management affect this effect. We conducted a global metaanalysis of published data to quantify the effect of intercropping on weed biomass in annual arable intercrops grown for their final product. We searched the literature to identify all papers reporting usable experimental data and extracted 339 data records from 39 publications containing data from 76 independent experiments. Two metrics of weed suppression were defined to assess the weed suppressive effect of intercropping: the ratio of observed weed biomass in an intercrop to weed biomass in the less weed suppressive sole crop (Rweak), and the ratio of weed biomass in the intercrop to weed biomass in the more weed suppressive sole crop (Rstrong). On average, weed biomass in the intercrop was substantially and significantly (58%) lower (Rweak = 0.42) than in the less suppressive sole crop. No significant difference was found between weed biomass in the intercrop and weed biomass in the more weed suppressive sole crop, even though weed biomass tended to be slightly larger in the intercrop than in the more weed suppressive sole crop (Rstrong = 1.08). Findings were consistent across different groups of species combinations, such as maize/legume and small-grain cereal/legume intercrops. Intercrops with an additive design had stronger weed suppression than intercrops with a replacement design. In the latter, a mixed arrangement gave stronger weed suppression than a row design, while spatial arrangement did not affect weed suppressive ability in additive designs. No significant effects on weed biomass were found of simultaneous vs. relay intercropping, and of nitrogen fertilizer input. The Rweak decreased significantly with the land equivalent ratio in additive intercrops but not in replacement intercrops, while Rstrong was unrelated to LER in both designs. The results confirm that intercropping is generally a useful approach for suppressing weeds in annual crop cultivation. Further work is needed to disentangle the contributions of species density, species traits and mixing ratio to weed suppression in intercropping.

Rural households across the world are increasingly turning to off-farm sources of income to complement or replace farm income. A better understanding of these livelihood adaptations, their consequences, and the processes behind them will facilitate more effective rural development policies and projects. The objective of this research was to examine how off-farm income influences rural livelihoods, elucidate factors that determine different livelihood strategies, as well as understand how these livelihood strategies are associated with different approaches to farm management. Using data from 588 Rural Household Multi-Indicator Surveys (RHoMIS) in three rural Andean regions in Bolivia, Ecuador, and Peru, we identified a typology of farming household livelihood strategies, and assessed the differences among these household types with regard to household and farm level characteristics, and farm management. We found that among the household types that incorporated off-farm income into their livelihood strategies, there were significant differences in approaches to farm management. Specifically, we observed an increased use of industrialized farming techniques among one household type, a deintensification, or a stepping-out of farming activities in another household type, and a tendency toward livestock specialization in the other household type. Moreover, our findings revealed that household level characteristics (age and education level of head(s) of household, and household composition) played an important role in mediating which type of livelihood strategy the households employed. For example, “stepping-out” households generally had younger and more educated household heads. Location-specific factors such as access to markets, irrigation, and off-farm employment opportunities were also likely to be highly influential in terms of which pathways farming households adopted as their livelihood strategy. We conclude that rural development programmes and projects must be driven by the rural communities themselves taking into account this heterogeneity in household characteristics and livelihoods and engaging in the already advanced conversations around different approaches to farming and the conservation of common natural resources.

The original version of the article was unfortunately published online without approval of that latest version by the authors of the article. Corrections for the too early published version are listed below (locations are indicated by Heading, paragraph, sentence): Introduction, 3rd paragraph, 1st sentence: incorrect hyphenation of “gen-otype”, should be changed to “geno-type” Table 1: the descriptive header cell, “Date of:” should cover both "Planting" and "Harvest" a headline below Field Locations, Experimental Design and Cultural Practices, 2nd paragraph, 4th sentence: Inconsistent use of Figure vs Fig.: “(Figure S3)” should be changed to “(Fig. S3)” Fig. 1: In the caption “(T-Σ, T-base = 0°Cd)” should be changed to “(T-Σ in °Cd, T-base = 0 °C)” Observations, Measurements and Calculations, 2nd paragraph, last two lines: in the previous version these last two lines were shifted to previous page. Also in the final version these two lines should be shifter to the previous page Fig. 2: The white lines between the figure caption and the main text is too large, 30% more compared to previous version. These white lines should be reduced.

peer-reviewed Potato is highly productive crop and can provide a cheap and nutritionally-rich staple food. Its potential as a cash generator and source of food is much under-utilized in many emerging economies. In this paper we study the impact of an intervention that introduced improved potato technologies in Chencha, Ethiopia on the livelihoods of smallholder farmers. We collected information through in-depth interviews in order to explore possible pathways of impact on farmers’ livelihoods; and used this information as the basis for designing a household survey. The results show changes in agronomic practices and consumption; these changes were most pronounced among wealthy farmers who participated in the intervention. Farmers used the additional income from potato in different ways: wealthier farmers improved their houses and increased their livestock, whereas poor farmers mainly invested in furniture, cooking utensils, tools and in developing small businesses like selling and buying cereals, milk and weaving products in the local markets. Some wealthy farmers, who did not participate in the project, also derived some indirect benefits from the intervention. This underscores: i) interventions that promote uniform farming technologies in themselves are not always sufficient to improve the livelihoods of poor farmers, and ii) the need to broaden the scope of interventions so as to take into account the resources available to farmers in different wealth categories, and the diversity of strategies that they employ for improving their livelihoods. Our approach allows to understand and describe the different developmental effects of a single technological intervention on the different aspects of farmers’ livelihoods.

Wheat yields in Ethiopia need to increase considerably to reduce import dependency and keep up with the expected increase in population and dietary changes. Despite the yield progress observed in recent years, wheat yield gaps remain large. Here, we decompose wheat yield gaps in Ethiopia into efficiency, resource, and technology yield gaps and relate those yield gaps to broader farm(ing) systems aspects. To do so, stochastic frontier analysis was applied to a nationally representative panel dataset covering the Meher seasons of 2009 and 2013 and crop modelling was used to simulate the water-limited yield (Yw) in the same years. Farming systems analysis was conducted to describe crop area shares and the availability of land, labour, and capital in contrasting administrative zones. Wheat yield in farmers’ fields averaged 1.9 t ha− 1 corresponding to ca. 20% of Yw. Most of the yield gap was attributed to the technology yield gap (> 50% of Yw) but narrowing efficiency (ca. 10% of Yw) and resource yield gaps (ca. 15% of Yw) with current technologies can nearly double actual yields and contribute to achieve wheat self-sufficiency in Ethiopia. There were small differences in the relative contribution of the intermediate yield gaps to the overall yield gap across agro-ecological zones, administrative zones, and farming systems. At farm level, oxen ownership was positively associated with the wheat cultivated area in zones with relatively large cultivated areas per household (West Arsi and North Showa) while no relationship was found between oxen ownership and the amount of inputs used per hectare of wheat in the zones studied. This is the first thorough yield gap decomposition for wheat in Ethiopia and our results suggest government policies aiming to increase wheat production should prioritise accessibility and affordability of inputs and dissemination of technologies that allow for precise use of these inputs.

Planting cover crops after harvest of the main crop has become a key practice in temperate agriculture to reduce N leaching and increase soil organic matter. However, the growth of cover crops can be affected by adverse weather. Growing mixtures is thought to increase yield and reduce variation in productivity, but quantitative information on this subject is limited. Moreover, uncertainty remains on the optimal choice of species and mixture composition for cover cropping to obtain high cover crop yields and resilient performance under different conditions. Here we tested a broad selection of pure stands and mixtures of cover crop species in two years (2017–2018) at four sites: three sites in the Netherlands (Wageningen, Neer and Scheemda) and one site in Germany (Grundhof). All pure stands and mixtures were grown for a period of 11–13 weeks between August and November in each year. Aboveground biomass and N yield were determined. Yields in different treatments (unique pure stands or mixture compositions) in each site-year were regressed on the mean yields in each site-year to assess differences in responsiveness between treatments. Mixed effects models were used to estimate and compare yield variability in pure stands and mixtures at three levels: 1) between site-years, 2) between treatments and 3) between plots. This analysis was performed for biomass and N yield. Across all pure stands and mixtures tested, average biomass was greater in mixtures than in pure stands, but average biomass was similar when this comparison was made between the five highest yielding pure stands and the five highest yielding mixtures across all site-years. Thus, the lower mean productivity in pure stands was mostly due to some low yielding species. The five best mixtures had 9% higher N yield than the five best pure stands. The response of treatment yields to mean site-year yield was similar for mixtures and pure stands. Variation in cover crop yield over site-years was large in both pure stands and mixtures. On the other hand, mixing species significantly reduced the variability in biomass between treatments and between plots. However, when pure stands with low productivity were excluded, this difference in yield variability disappeared. This implies that the risk of choosing a sub-optimal cover crop is lower when a species mixture is used instead of a pure stand, unless the highest yielding species are known in advance. The results indicate that the positive effects of diversity on productivity and yield variability in cover cropping are restricted to reducing variability within the field and do not provide insurance against adverse conditions related to variability in growing conditions amongst sites and years.

Intercropping cereals and legumes can increase agricultural productivity and reduce inputs of nitrogen fertilizer but there is a need for further literature synthesis on the size of intercropping advantages and the factors affecting these advantages. Here we present a global meta-analysis of 36 studies, 66 experiments and 260 treatments addressing the land productivity of maize (Zea mays L.) and peanut (Arachis hypogaea L.) intercropping. Data were extracted from the literature and analyzed with mixed effects models to assess the land equivalent ratio (LER) and the factors affecting LER. The worldwide average LER of maize/peanut intercropping was 1.31 ± 0.03. The LER did not vary with continent, intercrop planting pattern and temporal niche differentiation, but sowing maize earlier than peanut (relative sowing time: RSTm

Rice is a staple food and cash crop for smallholder farmers in sub-Saharan Africa; however, yields are very low, with indications that both macro and micro-nutrients may limit rice productivity in East Africa next to the need for good agronomic practices. Diagnostic on-farm experiments were conducted in Uganda and Tanzania between 2015 and 2017 to assess the contribution of macro, secondary and micro-nutrients on lowland rice yield and identify options by which smallholder farmers can increase productivity. All treatments included good agronomic practices combined with: zero fertilisation as a control, NPK fertilisation with and without secondary and micro-nutrients (B, Mn, Zn, Cu, Mg, S), and/or treatments where B, Mn and Zn were omitted one at a time from the NPK + secondary and micro-nutrient treatment. NPK fertilisation significantly (p < 0.05) increased grain yield under irrigated condition by ca. 32 and 29 % during 2015 and 2016, and 24 and 100 % during 2016 and 2017 in Tanzania and Uganda, respectively; however, inconsistent effects were observed under rainfed condition. Observed higher yields corresponded mainly to higher panicle number with an additive effect of grains per panicle indicating major effects were at earlier growth stages supporting higher sink size development. Adding secondary and micro-nutrients to NPK enhanced yield significantly (p < 0.05) under irrigated condition in Tanzania 2015 and 2016 by 7 and 11 %, respectively, while varying results were obtained under rainfed condition. In Uganda, no significant (p> 0.22) effects of secondary and micro-nutrients were observed in both years and growing conditions. This study indicates that the first step to improving lowland rice productivity is proper water management, under otherwise also good crop management in terms of timely transplanting and weeding, and further yield gains can be realised with NPK fertilisation. Secondary and micro-nutrients were effective only when NPK were applied and on the fluvisols of Tanzania, and were not co-limiting yield on the plintosols of Uganda.

Regulatory restrictions on herbicide use for managing turfgrass weeds has prompted the search for alternative control strategies. Fescue (Festuca) species were identified for their potential to interfere with growth of annual and perennial weeds. In a study conducted in 2018 and 2019, six fescue cultivars were tested from five different species for interference with the growth of three common turfgrass weeds: white clover (Trifolium repens L., WC), daisy (Bellis perennis L.) and yarrow (Achillea millefolium L.). Fine (Festuca L. spp.) and tall fescues (Schedonorus arundinaceus (Schreb.) Dumort.) were sown and grown in a field trial for 14 days before overseeding with different weeds. vigor and visual quality of grasses, weed cover, and vegetation cover was recorded regularly for 84 days. Differences in mean temperatures and precipitation between the two years of the study resulted in differences in growth of grasses and weeds, as well as in the extent of weed interference of fescue cultivars. Cultivars Musica (F. rubra L. ssp. commutata Gaudin) and Barpearl (F. rubra L. ssp. littoralis) were least affected by weed growth during both years, but there was overlap with other cultivars for the measured parameters. Melyane (tall fescue) was deemed unsuitable for natural weed suppression because growth and vigor declined after first mowing, ultimately leading to unacceptable visual quality. Turfgrass visual scores were moderately negatively correlated to weed cover in both years. Future research should focus on F. rubra L. ssp. rubra Gaudin and F. rubra L. ssp. littoralis subspecies and identify the mechanisms used to interfere with weed growth.

Yield gap (Yg) analysis is useful to map the scope for sustainable intensification of agriculture, but explaining and quantifying the underlying causes of yield gaps remains a considerable challenge. The objective of this study was to decompose maize yield gaps under different nitrogen (N) application rates and soil quality conditions across irrigated and rainfed cropping systems in China. A comprehensive database consisting of 5228 on-farm trials located in three major maize production regions of China was used for this purpose. The on-farm trials contained detailed information for four different treatments: fertilizer omission (control), optimal N rate (optimal N), 50% of optimal N rate (low N) and 150% of optimal N rate (high N). These were combined with biophysical and yield potential data from the Global Yield Gap Atlas (http://yieldgap.org). An analytical framework integrating stochastic frontier analysis and principles of production ecology was applied to decompose the overall maize yield gap into components of efficiency (and respective management and soil quality effects, Yg-M and Yg-S), resource (Yg-R), and technology Yg (Yg-T). The potential yield (Yp) of irrigated maize averaged 14.5 Mg/ha in Northeast China (NE) and 11.9 Mg/ha for North China Plain (NCP), and the water-limited potential yield (Yw) of rainfed maize averaged 12.0 Mg/ha in NE and 10.5 Mg/ha in Southwest China (SW), respectively. Maize yield gaps were highly variable across N treatments and cropping systems and ranged between 27–56% of Yp or Yw. Larger absolute yield gaps were observed in irrigated cropping systems in NE (4.8–8.1 Mg/ha) than in NCP (3.8–6.1 Mg/ha) and in rainfed cropping systems in NE (3.6–6.7 Mg/ha) and SW (2.8–5.9 Mg/ha). The components of the yield gap differed in size across cropping systems and N treatments. Yg-T was fairly small and consistent across N treatments ranging between 7.0% and 12.0% of Yp for irrigated maize and only ca. 2.0% of Yw for rainfed maize in NE. Yg-R was strongly associated with the N treatment explaining between 16.0–26.0% of Yp (or Yw) for control and low N treatments and being close to negligible for the optimal and high N treatments. Yg-M due to inefficient crop management accounted for 6.0–14.0% of Yp (or Yw) across cropping systems and N treatments, which is equivalent to 0.7–1.8 Mg/ha. The Yg-S explained the largest proportion of the total yield gap, especially in trials with low and medium soil quality levels, accounting for 11.0–24.0% of Yp or Yw (1.3–3.1 Mg/ha). The Yg-S was linked to partly manageable soil properties, such as low soil organic matter contents and low available P and/or K. This study is one of the first to incorporate the effects of soil quality in yield gap analysis and provides a basis to target management practices that can improve soil quality and N use efficiency while narrowing maize yield gaps in China.

Cereal-legume intercropping can increase yields, reduce fertilizer input and improve soil quality compared with pure culture. Designing intercropping systems requires the integration of plant species trait selection with choice of crop configuration and management. Crop growth models can facilitate the understanding and prediction of the interactions between plant traits, crop configuration and management. However, currently no existing crop growth model has been calibrated and tested for cereal-legume intercrops throughout Europea. We calibrated the Agricultural Production Systems sIMulator (APSIM) for pure cultures of wheat and faba bean using data from Dutch field trials, and determined the phenological parameters to simulate pure cultures and intercrops from seven field experiments across Europe. APSIM successfully reproduced aboveground dry matters and, for wheat only, grain yields in pure cultures. In intercrops, APSIM systematically overestimated the aboveground dry matter and grain yield of faba bean and underestimated those of wheat. APSIM was reasonably capable of simulating plant heights in pure cultures, but respectively overestimated and underestimated the height of faba bean and wheat in intercrops. In order to simulate wheat-faba bean intercrops better, APSIM should be improved regarding the calculation of biomass partitioning to grains in faba bean and of height growth in both species., HNCB, MW, AJK, EA, ÁMV, LPK, ACN, CS, ST, and GV received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 727284, project DIVERSify: Designing InnoVative plant teams for Ecosystem Resilience and agricultural Sustainability, https://www.plant-teams.eu/. WvdW received funding from the European Union Horizon 2020 Research and Innovation Programme under grant agreement no. 727217, project ReMIX: Redesigning European cropping systems based on species MIXtures, https://www.remix-intercrops.eu.

CONTEXT Cocoa (Theobroma cacao L.) is one of the world's most important agricultural commodity crops with the largest share of global production concentrated in West Africa. Current on-farm yields in this region are low and are expected to decrease in response to climate change, through warming and shifts in rainfall. Interventions intended to improve yields and climate adaptation require an understanding of the main drivers of yields across farms. OBJECTIVE In this regard, we quantified the extent to which environmental (i.e., climate and soil) conditions drive cocoa yields and how this differs for farms achieving on average low- and high mean production levels based on an unprecedented dataset of 3827 cocoa farms spanning the environmental gradients of Ghana. We further quantified the relative importance of management practices based on a subset of 134 farms for which management information was available. METHODS We modelled on-farm annual cocoa yield as a function of environmental variables for the large dataset and cocoa yield per tree as a function of environmental and management variables for the subset farms using mixed-effects models. Differences in effects on yield between farms with low and high mean production levels were evaluated using quantile mixed-effects models. RESULTS AND CONCLUSIONS There was considerable variability in yields across farms, ranging from ~100 to >1000 kg ha−1 (mean = 554 kg ha−1). Mixed-effects models showed that the fixed effects (i.e., environmental variables) only explained 7% of the variability in yields whilst fixed and random effects together explained 80%, suggesting that farm-to-farm variation played a large role. Explained variation in cocoa yields per tree of 134 farms in the subset increased from 10% to 25% when including management variables in addition to environmental variables. In both models, climate-related factors had a larger effect on yields than edaphic factors, with radiation of the main dry season and that of the previous year having the strongest effects on on-farm- and tree yields, respectively. The quantile regression analyses showed that productivity in high-yielding farms (90th percentile) was more strongly driven by environmental factors than in low-yielding farms (10th percentile). In conclusion, agronomic management is the dominant determinant of on-farm cocoa yields in Ghana, more so than environmental conditions. Furthermore, high-yielding cocoa farms are more sensitive to environmental conditions than low-yielding ones. SIGNIFICANCE Our findings suggests that good agricultural practices need to be in place before investing in additional climate adaptation practices.

Different fertilisers were field tested to investigate whether they (1) suppress the obligate parasitic weed Striga asiatica and the facultative parasitic weed Rhamphicarpa fistulosa, and (2) favour rainfed rice yields under parasitic weed infestation. Four years of experiments were conducted in southwest Tanzania, in a S. asiatica-infested rainfed upland and a R. fistulosa-infested rainfed lowland field. Treatments included sole mineral (NPK or Di-Ammonium Phosphate —DAP— plus urea), organic (cattle manure or rice husk), combinations of mineral and organic fertilisers and a no-fertiliser control. Fertilisers moderately suppressed the obligate parasite S. asiatica, but no correlations between infestation level and soil fertility status were observed. In the lowland field, fertilisers promoted the facultative R. fistulosa, in particular the ones that included organic components. Plant-available phosphorus, exchangeable potassium and soil organic matter content correlated with R. fistulosa infestation levels. Positive fertiliser effects on yields were found in both parasitic weed infested fields, except in years with high S. asiatica infestation levels. Rice husks alone and rice husks or manure combined with DAP and urea increased yields and soil fertility most. We conclude that fertilisation differentially affects the obligate and facultative parasitic weeds of rice systems; obligate parasites may be slightly suppressed, but facultative parasites may even be stimulated. Meanwhile, consistent rice yield increases under parasitic weed infested conditions cannot be obtained with fertiliser application when parasitic weed infestation levels are too high.

Eggplant shoot and fruit borer, Leucinodes orbonalis, is a major pest in eggplant production in South and South-East Asia. Farmers frequently spray insecticides to control it. Integrated pest management (IPM) based on mass trapping or pheromone trapping and sanitation (removal of infested shoots and fruits) has been suggested but poorly adopted. This study tested, together with farmers, combinations of IPM components that fit their farming practices, increase income, and preserve natural enemy populations. A 2-year participatory study was negotiated with these farmers, comparing (i) an untreated control, (ii) farmers’ conventional weekly spraying, with pheromone trapping either (iii) alone, or combined with (iv) trap-based biorational spraying, or (v) bi-weekly conventional insecticide spraying. Farmers rejected testing sanitation as too labor-intensive. In both years, pheromone trapping alone or combined with biorational spraying reduced fruit infestation, increased yield and income, and preserved natural enemies, showing technical efficacy at costs comparable with farmers’ practice. Replacing biorational spraying by conventional insecticides did not provide any control beyond pheromone trapping alone but reduced natural enemies. In contrast, farmers’ practice neither reduced infestation nor increased yield but reduced populations of natural enemies. Aphid and jassid populations were reduced only by biorational and conventional spraying. As farmers were reluctant to use only pheromone trapping, the addition of biorational spraying might be suitable. Discussion with farmers allowed us to understand how practical applicability of the tested IPM depends on farmers’ knowledge levels on insect biology, farmers’ desire to still use some spraying, and labor constraints to sanitation. Although technically and economically viable, the tested IPM may prove difficult to scale out, as farmers had difficulty understanding the lifecycle of Leucinodes orbonalis and the pheromone trapping mechanisms. This study is the first to disentangle the technical efficacy of pheromone-trapping-based IPM from its practical applicability for the targeted smallholder eggplant growers.