Search

Understanding the long-term responses of crop yield and soil organic carbon to fertilization is necessary to sustain food supply in a context of global change. The time-course of winter wheat yield and soil organic carbon were established in a 31-year long experiment with four fertilization regimes: unfertilized control; fertilized with mineral nitrogen and phosphorus, NP; fertilized with mineral N, P and K, NPK; and fertilized with manure and mineral NPK, MNPK. Over the time series, mean temperature increased at 0.054 ℃ year−1 (i.e. 1.67 degrees over the course of the experiment) and annual precipitation increased at 8.9 mm year−1. Yield did not show trends in unfertilized controls, increased at 210 kg ha−1 year−1 in the first 20 years and decreased slightly afterwards in the NP and NPK treatments, and increased at 310 kg ha−1 in the MNPK treatment until 2006, and leveled off afterwards. Soil organic carbon increased linearly with rates from 0.05 g kg−1 year−1 in unfertilized controls to 0.24 g kg−1 year−1 in MNPK. In fertilized crops, yield correlated nonlinearly with annual precipitation, and linearly with average temperature during the growing season. Across fertilizer treatments, yield correlated nonlinearly with soil organic carbon and the thresholds of soil organic carbon for peak yield increased with water supply. It is concluded that the combination of organic and inorganic fertilizers contributed to yield and soil organic carbon against the background of a warmer and wetter climate. • Application of mineral fertilizer alone cannot sustain high wheat yield over time. • Applying both organic and inorganic fertilizers maintained high wheat yield. • There was a quadratic-linear relationship between wheat yield and SOC content. • Organic manure input could be beneficial to mitigate climate change. [ABSTRACT FROM AUTHOR]

Technologies, from molecular genetics to precision agriculture, are outpacing theory, which is becoming a bottleneck for crop improvement. Here, we outline theoretical insights on the wheat phenotype from the perspective of three evolutionary and ecologically important relations—mother–offspring, plant–insect and plant–plant. The correlation between yield and grain number has been misinterpreted as cause-and-effect; an evolutionary perspective shows a striking similarity between crop and fishes. Both respond to environmental variation through offspring number; seed and egg size are conserved. The offspring of annual plants and semelparous fishes, lacking parental care, are subject to mother–offspring conflict and stabilizing selection. Labile reserve carbohydrates do not fit the current model of wheat yield; they can stabilize grain size, but involve trade-offs with root growth and grain number, and are at best neutral for yield. Shifting the focus from the carbon balance to an ecological role, we suggest that labile carbohydrates may disrupt aphid osmoregulation, and thus contribute to wheat agronomic adaptation. The tight association between high yield and low competitive ability justifies the view of crop yield as a population attribute whereby the behaviour of the plant becomes subordinated within that of the population, with implications for genotyping, phenotyping and plant breeding. [ABSTRACT FROM AUTHOR]

The evolution in the definition of crop yield—from the ratio of seed harvested to seed sown to the contemporary measure of mass of seed per unit land area―has favoured less competitive phenotypes. Here we use binary mixtures of cultivars spanning five decades of selection for yield and agronomic adaptation to ask three questions. First, what is the degree of symmetry in the response of yield to neighbour; this is, if an older, more competitive cultivar increases yield by 10% with a less competitive neighbour in comparison to pure stands, would the newer, less competitive cultivar reduce yield by 10% when grown with older neighbour. Lack of symmetry would indicate factors other than competitive ability underly yield improvement. Second, what are the yield components underlying competitive interactions. Third, to what extent are the responses to neighbour mediated by radiation, water and nitrogen. A focus on yield components and resources can help the interpretation of shifts in the crop phenotype in response to selection for yield. The rate of genetic gain in yield over five decades was 24 kg ha−1 year−1 or 0.61% year−1. A strongly symmetrical yield response to neighbour indicates that yield improvement closely associates with a reduction in competitive ability. Response to neighbour was larger for grain number and biomass than for grain weight and allocation of biomass to grain. Under our experimental conditions, competition for radiation was dominant compared to competition of water and nitrogen. High‐yielding phenotypes had lower competitive ability for radiation but compensated with higher radiation use efficiency, a measure of canopy photosynthetic efficiency. Genetic and agronomic manipulation of the crop phenotype to reduce competitive ability could further improve wheat yield to meet the challenge of global food security. [ABSTRACT FROM AUTHOR]

Wheat, rice, and maize collectively provide the bulk of energy and protein to the human diet worldwide. Over the last seven decades, China increased 5.8-fold the aggregated production of the three cereals, but further gains are required to meet the predicted demand of 776 Mt. by 2030. Here, we report the rate of genetic gain in yield of 0.65% year-1 for wheat between 1937 and 2012, 0.69% year-1 for rice between 1934 and 2011, and 0.77% year-1 for maize between 1950 and 2014 in China. National farm yield in the same periods increased 1.38% year-1 for wheat, 1.15% year-1 for rice and 1.32% year-1 for maize. Hence, genetic improvement (G) accounted for 47%-60% of the increase in farm yield, with improved management (M) and G × M interaction accounting for the balance. The absolute rate of genetic gain (kg ha-1 year-1) was proportional to environmental potential. Genetic gain in nitrogen utilization efficiency (yield per unit nitrogen uptake) was significant for all three crops and was achieved at the expense in grain N concentration that decreased at 0.19% year-1 in rice and 0.47% year-1 in maize. To guarantee future food security and environmental sustainability, breeding and agronomic efforts need to increase the rate of gain in yield and revert the declining trends in grain protein by improving nitrogen uptake and nitrogen harvest index. [ABSTRACT FROM AUTHOR]

Highlights • Root pruning improved wheat grain yield, HI and WUE by 6–11%. • Root pruning in spring performed better than that in winter. • Root pruning was more effective at high seeding rate in low-yielding conditions. • Root pruning improved apparent translocation of water soluble carbohydrates. Abstract Improved management practices are necessary to increase grain yield and water-use efficiency of rainfed winter wheat in semiarid environments. Yield and its components, evapotranspiration, and accumulation and apparent remobilisation of stem water soluble carbohydrates (WSC) were measured to understand the effects of root pruning and its interactions with seeding rate, water and nitrogen supply. Two factorial studies under straw mulching with continuous wheat were established in the Loess Plateau of China. Study 1 was repeated over four seasons and included six treatments from the combination of three root treatments, i.e. root pruning in winter before dormancy (RPw), root pruning at the re-green stage in spring (RPs) and untreated control (CK), and two seeding rates. Study 2 was repeated over three seasons and included twelve treatments from the combination of two root treatments (RPs and CK), two nitrogen rates and three pre-sowing soil water levels. Yield ranged from 2571 to 7722 kg ha−1, harvest index from 0.28 to 0.56, and water-use efficiency from 5 to 20 kg ha−1 mm−1. Root pruning improved grain yield, harvest index and water-use efficiency by 6–11% across environmental conditions. Grain yield increased more (i) by pruning roots in spring than in winter, (ii) in high plant density than in low plant density crops, and (iii) in low-yielding conditions. It is concluded that spring root pruning is a viable option to improve wheat yield and water use efficiency under straw mulching in semiarid environment. [ABSTRACT FROM AUTHOR]

Insufficient nitrogen applications may contribute to yield gaps in low rainfall environments of Western Australia (WA). This study tested a nitrogen nutrition index (NNI) for wheat tailored for low rainfall regions, which is based on rainfall-scaled dilution curves. We analyzed yield, shoot biomass, and nitrogen concentration from 32 field trials in WA. An empirical rainfall threshold of 400mm (summerþgrowing season rainfall) returned two parallel dilution curves accounting for the reduction of critical N in drier and lower yielding conditions. Scatterplots of relative yield and rainfall-adjusted NNI returned a robust boundary function that may lead to greater adoption by growers. The NNI defined in this research study can be applied and further tested by growers in WA, but may also apply to other low rainfall environments, to close nitrogen related yield gaps. [ABSTRACT FROM AUTHOR]

On historical timescales, enhanced availability of water and nitrogen has been a major driver of improved crop yield worldwide. The interaction between water and nitrogen has received attention, but theories and conceptual tools lag behind our fast-increasing capacity to monitor crop nitrogen and water status using remote sensing. Theory, mostly developed in ecology, predicts that plant growth is maximized when all resources are equally limiting. Therefore, for a given level of stress, growth is maximized under colimitation of resources. The concept of colimitation is less developed in agriculture, where the notion of sequentially, single limiting factors has been dominating since von Liebig law of minimum. During the last two decades, the concept of colimitation of resources has been used to explain yield gaps in wheat, barley, and canola in Mediterranean-type environments of Australia and Europe, and in maize in the Pampas of Argentina. These studies conform to theory: high yield is usually associated with high water and N colimitation. In view of the increasing capacity to measure crop water and N status of crops using remote sensing, we reviewed N-water colimitation as this concept provides a robust framework to integrate otherwise dispersed measurements. First, we revise the concept of colimitation in terms of timescale, level of organization, and thropic level; an agronomic definition of colimitation is advanced. Second, we outline the methods to quantify colimitation between two resources in a generalized crop model, and between water and nitrogen in particular. Third, we summarize studies providing experimental and modeling evidence of colimitation. A notion of crop yield at the biophysical "boundaries" of nitrogen and water use efficiency is presented within the colimitation context. Finally, we propose future directions to develop tools to quantify water-nitrogen colimitation using remote sensing. [ABSTRACT FROM AUTHOR]

Here, we show a unique crop response to intraspecific interference, whereby neighboring sunflower plants in a row avoid each other by growing toward a more favorable light environment and collectively increase production per unit land area. In high-density stands, a given plant inclined toward one side of the interrow space, and the immediate neighbors inclined in the opposite direction. This process started early as an incipient inclination of pioneer plants, and the arrangement propagated gradually as a "wave" of alternate inclination that persisted until maturity. Measurements and experimental manipulation of light spectral composition indicate that these responses are mediated by changes in the red/far-red ratio of the light, which is perceived by phytochrome. Cellular automata simulations reproduced the patterns of stem inclination in field experiments, supporting the proposition of self-organization of stand structure. Under high crop population densities (10 and 14 plants per m²), as yet unachievable in commercial farms with current hybrids due to lodging and diseases, self-organized crops yielded between 19 and 47% more oil than crops forced to remain erect. [ABSTRACT FROM AUTHOR]

Rainfed crops rely on two sources of water: stored soil water at sowing and seasonal rain. In strongly seasonal winter-rainfall environments, stored soil water at sowing is minor, and uncertain seasonal rainfall is a source of risk. In south-eastern Australia, under-fertilisation is a common outcome of nitrogen risk management with implications for wheat yield and mining of soil organic matter. Here we explore the use of carbon isotope composition (δ 13C) to capture the effects of crop water status on grain yield in a context of nitrogen top dressing. In the sampled environments, crops receive at least 50% of seasonal rainfall by stem elongation, and at least 70% of seasonal rainfall by flowering. In a sample of 1518 plots, yield varied from 0.07 to 9.96 t ha-1 and correlated with δ 13C measured with isotope ratio mass spectrometer (IRMS) at flowering (r = −0.76, p < 0.0001); this is consistent with the rainfall pattern and the physiology of the crop featuring a critical period for yield from 300 °Cd before to 100 °Cd after anthesis. In a sample of 135 plots, yield varied from 1.2 to 8.4 t ha-1 and correlated with δ 13C measured with IRMS at stem elongation (r = −0.56, p < 0.0001). Yield response to nitrogen, defined as the difference between yield in fertilised crops (50–200 kg N ha-1) and unfertilised controls, correlated with δ 13C measured with IRMS at stem elongation, except for late-sown crops. Mid-infrared spectroscopy (MIR) returned estimates of δ 13C that agreed with δ 13C measured with IRMS (calibration: R2 = 0.82, RMSE = 0.53‰, n = 833; validation: R2 = 0.70, RMSE = 0.75‰, n = 364). We conclude that a MIR based, high-throughput, affordable measurement of δ 13C could be scaled to guide nitrogen management of wheat in winter-rainfall environments. • In a sample of 1518 plots, yield varied from 0.07 to 9.96 tha-1 and correlated with δ 13C at flowering. • Yield response to nitrogen correlated with δ 13C at stem elongation, except for late-sown crops. • Mid-infrared spectroscopy is a cost-effective, high-throughput approach to estimate δ 13C for agronomic applications. [ABSTRACT FROM AUTHOR]

Abstract: Yield components are relatively easy to measure and their interpretation is intuitive. However, strong environmental influences, genetic and physiological controls, and evolutionary constraints collectively lead to lack of independence among yield components that restrict their value in breeding and agronomic applications. Here, we first sketch a framework of plant responses to environmental factors to highlight the modulation of yield components by resources and their interplay with non-resource factors including developmental cues (e.g. maternal effects), extreme events (e.g. frost), predicting factors (e.g. photoperiod) and synchronising and integrating information (e.g. spectral composition of light). We suggest that, to the extent that non-resource cues allow plants to predict future availability of resources, simple resource-based models may be sufficient to capture the macroscopic responses of yield components to the environment. Next, we expand the original concept of hierarchy of plasticities between grain size (a relatively stable trait) and grain number (a plastic trait) to test the hypothesis of a broader hierarchy in the plasticities of yield components. Using published data for wheat, rice, barley and triticale, we verified that heritabilities capture the established hierarchy between plasticity of grain size and number. Median heritabilities of 0.31 for tiller number, 0.58 for inflorescence number, 0.59 for grains per inflorescence, and 0.79 for grain size supported the hierarchy of plasticities: tiller number > inflorescence number ≈ grains per inflorescence > seed size. The heritability of grain yield was consistently higher than the heritability for tillering, consistently lower than the heritability for grain size, and suggestively close to the heritability of inflorescence number and grains per inflorescence, the components of grain number per unit ground area. We conclude that understanding the environmental regulation of yield components in cereals would benefit from a dual focus on yield-related traits per se and their plasticity. [Copyright &y& Elsevier]

We used a water-centred framework (yield = transpiration × transpiration efficiency × harvest index) to investigate the effect of soil salinity on growth and yield of wheat and barley. Our working hypothesis is that salinity reduces transpiration proportionally more than transpiration efficiency. We established a glasshouse experiment with the factorial combination of four varieties (wheat: Janz, Krichauff; barley: Mundah, Keel) and three soil treatments: a control with no NaCl added, and NaCl added to achieve soil EC 0.75 dS m and 1.5 dS m. Pot-grown plants were watered to weight to determine transpiration and shoot dry matter was determined using a non-destructive image analysis system. Consistent with our hypothesis, salinity reduced transpiration (30-60%) proportionally more than transpiration efficiency (0-35%); transpiration accounted for 90% of the variation in shoot growth across varieties and treatments. Against this pattern, there were time- and variety-dependent responses. The rate of leaf appearance and the transpiration efficiency of Janz, Krichauff and Keel showed a two-stage response to salinity. In stage 1, salt-stressed plants maintained rate of leaf appearance and transpiration efficiency close to or slightly below those of the controls. After a clear break point where the slope changed, stage 2 was characterised by a substantial reduction in both traits. Stage 2 was not evident in salt-stressed Mundah, which maintained a relatively high rate of leaf appearance and transpiration efficiency. Across species, harvest index increased from 0.40 in controls to 0.47 at 0.75 dS m. Harvest index of plants grown at 1.5 dS m was unaffected in wheat, and was reduced in barley. We propose that an understanding of the effect of salinity on crop development, growth and yield requires integration of low-level traits in a framework of resource capture, resource-use efficiency and plant allocation. Osmotic stress tolerance, Na exclusion, and tissue tolerance to accumulated Na would improve yield of salt-stressed crops to the extent that these traits contribute to the maintenance of water uptake and harvest index. [ABSTRACT FROM AUTHOR]

• We develop a novel method to non-destructively measure crop growth rate in lentil. • Lentil yield correlated non-linearly with crop growth rate. • Lentil yield correlated with biomass and crop growth rate in stressful conditions. • Lentil yield decoupled with biomass and crop growth in higher yielding conditions. • The association of lentil yield and harvest index was significant for all yields. Growth and yield can be decoupled in lentil whereby excessive vegetative growth leads to self-shading, reduced pod and seed set, low harvest index and higher risk of disease and lodging. We evaluated the degree of coupling between growth and yield in 20 lentil lines grown in eight environments varying in water and photothermal conditions returning a 10-fold yield range, from 21 to 221 g m−2. Calibration curves between shoot biomass and canopy cover measured with NDVI and green canopy cover measured with Canopeo app were improved with canopy height as a multiplication factor returning a 3-D trait. Calibration curves were used to phenotype shoot biomass and calculate crop growth rate. For the pooled data, yield correlated non-linearly with crop growth rate, with an x-intercept of 0.09 g m−2 [oCd]-1, suggesting a minimum plant size for reproduction, and an inflection point at 0.43 g m−2 [oCd]-1. Yield correlated with biomass and crop growth rate in the more stressful conditions (yield ≤ 107 g m−2) and was decoupled in higher yielding conditions (yield ≥ 170 g m−2). Yield associated with harvest index at all yield levels, but more strongly in high-yielding conditions. Biomass and harvest index correlated in environments with yield ≤ 107 g m−2, and decoupled under more favourable conditions (yield ≥ 170 g m−2). Yield associated with phenology under stress but not in favourable conditions. For the combination of lines and environments in this study, broad sense heritability was 0.96 for flowering time, 0.93 for harvest index, 0.89 for yield, 0.87 for crop growth rate and 0.39 for biomass. Selection for harvest index would improve yield across environments whereas selection for growth rate could further improve yield under stress. Agronomic practices to improve the coupling of yield and growth under favourable conditions need to be explored; for example, using precision seeding to reduce rectangularity of crop arrangement and favour penetration of radiation into the canopy and pod set. [ABSTRACT FROM AUTHOR]

Availability of nitrogen and water are major constraints for crop yield, and their interactions are manyfold. Yield gap analysis in rainfed systems commonly uses water-limited yield potential (Y w ) as a benchmark; benchmarking against nitrogen-limited yield potential (Y N ) is less common. The aim of this study was to benchmark wheat yield against Y N in winter-rainfall regions of Australia. We established experiments, and sampled both farmers’ fields and National Variety Trials spanning wide ranges of soils, management practices, and water supply (seasonal rainfall + irrigation) from 153 to 759 mm in South Australia, and from 178 to 428 mm in Western Australia. We measured yield, quantified crop nitrogen nutrition index (NNI) at stem elongation, anthesis or both, derived boundary functions relating Y N and NNI, calculated yield gaps as the difference between Y N and actual yield, and explored the associations between yield gaps and environmental, crop and agronomic factors. In South Australia, NNI at anthesis ranged from 0.45 to 1.45 and yield from 0.9 to 8.9 t ha −1 ; in Western Australia NNI at stem elongation ranged from 0.27 to 1.16 and yield from 1.0 to 7.1 t ha −1 . Bi-linear boundary functions were fitted with a linear Y N – NNI phase up to a NNIx threshold (0.95 ± 0.134 in South Australia, 0.87 ± 0.145 in Western Australia), and a plateau reflecting yield potential (7.8 ± 0.38 t ha −1 in South Australia, 6.5 ± 0.52 t ha −1 in Western Australia). Similar bi-linear boundaries, with congruent NNIx (≈0.9), were found for grain number and shoot biomass at maturity. In South Australia, water supply explained 54% of the yield gap, which declined linearly from about 6 t ha −1 to zero with increasing water availability. Further, the yield gap correlated negatively with carbon isotope discrimination at anthesis, a direct measure of crop water status. In Western Australia, the direct association between yield gap and rainfall was weak, but there was an indirect agronomic link, where low seeding rate in low rainfall environments contributed to low biomass at stem elongation, which in turn explained a large part of the yield gap. In two out of five National Variety Trials, where the aim is comparing the yield of current and emerging varieties, crops were nitrogen deficient. This is a potential source of bias as some varieties were above and others below the NNIx threshold of nitrogen sufficiency. Supply of nitrogen in varietal comparisons needs attention. The approach advanced in this paper can be applied to benchmark yield against crop nitrogen status and identify causes of yield gaps, and for in-season quantification of crop nitrogen status to assist fertiliser decisions directly, or indirectly as a reference for spectral indices. [ABSTRACT FROM AUTHOR]

Donald’s ideotype and empirical evidence in cereal and oilseed crops indicate high yield is associated with less competitive plants. In this study we grew 20 chickpea lines in six environments to investigate the association between yield and intra-specific competitive ability and its genetic underpinnings using Fst genome scan based on whole genome resequencing data. We measured yield and its components and calculated response to competition (RC) as the ratio between the trait in outer rows (relaxed competition) and the trait in inner rows (higher competition). Crop yield correlated negatively with RC for yield, biomass, harvest index, seed number, and pod number. Fst genome scan revealed 14 genomic regions under selection for response to competition of yield, seed number or biomass, and 6 genomic regions under selection for yield in inner or outer canopy rows. Candidate genes in these regions include members of the nitrate-transporter 1 family, patatin and hormone-related genes. The top genomic regions found to be under selection for yield in inner rows and outer rows did not coincide. This genetic architecture provides a mechanistic basis for the observation that phenotypes that are adequate for relaxed competition often perform poorly in dense stands. [ABSTRACT FROM AUTHOR]