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Highlights • Genetic gains of Australian wheat were associated with higher water-nitrogen co-limitation. • Higher water-nitrogen co-limitation associated with a higher nitrogen uptake per unit of evapotranspiration. • Nitrogen traits are critical for drought adaptation. Abstract The interactions between nitrogen (N) and water are manifold, and the concept of co-limitation provides a quantitative framework for integration. This paper tested the hypothesis that selection for yield increased water-N co-limitation in wheat adapted to winter rainfall environments of Australia. To test this hypothesis, we measured evapotranspiration, N uptake and yield in a historic collection of varieties released between 1958 and 2007 (exp. 1) and between 1969 and 2015 (exp. 2). Crops were grown under 5 (exp. 1) or 4 (exp. 2) environmental conditions resulting from the combination of sites, seasons, and supply of N and water. Genetic gain of yield, i.e. the slope of the regression between yield and year of release was 14–24 kg ha−1 y−1 or 0.36–0.52% y−1. This yield gain was associated with a linear increase in water-N co-limitation, in turn associated with an increase in N uptake per mm of evapotranspiration at a rate of 0.0019 kg N mm−1 y−1. Our findings highlight the critical role of nitrogen for the adaptation of wheat to low rainfall environments, and the scope for further yield improvement based on traits that integrate resources. [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]

Highlights • Yield correlated with five senescence traits from NDVI-time curves. • No correlation for yield between environments in 5 out of 6 comparisons (broad sense heritability = 0.39). • All senescence traits correlated negatively with concentration of water soluble carbohydrates at anthesis. • Water soluble carbohydrates correlated between environments in 6 out of 6 comparisons (broad sense heritability = 0.89). • Selection for low concentration of WSC could improve yield by improving both grain number per m2 and leaf area duration. Abstract High throughput phenotyping of canopy senescence based on Normalized Difference Vegetation Index (NDVI) could be useful in plant breeding. The aim of this paper was to assess the association between grain yield and canopy senescence quantified with NDVI in oat lines selected for grain yield and milling quality. Sixteen lines were grown in four winter-rainfall environments where logistic curves between NDVI and thermal time from anthesis (GS60) were fitted to return five traits: maximum NDVI, NDVImax ; minimum NDVI, NDVImin ; thermal time to 50% senescence, x50; rate of senescence, rate; and the area under the NDVI curve, area. Across sources of variation, residuals of yield after removing the effect of phenology correlated with area (r = 0.69), NDVImax (r = 0.67), x50 (r = 0.57), NDVImin (r = 0.51) and rate (r = −0.30), all significant at P < 0.05. All five senescence traits correlated negatively with concentration of water soluble carbohydrates at anthesis, particularly area (r = −0.75, P < 0.0001). There was no correlation for yield between environments in 5 out of 6 comparisons (broad sense heritability = 0.39) and water soluble carbohydrates correlated between environments in 6 out of 6 comparisons (broad sense heritability = 0.89). Correlations between environments were irregular for senescence traits. Selection for low concentration of water soluble carbohydrates could increase oat grain yield by improving both grain number per m2 and leaf area duration. [ABSTRACT FROM AUTHOR]

Highlights • Grain quality associated with environmental conditions between GS31 and 200 °Cd after flowering. • In stressful environments, trade-offs between yield and quality were important. • Water soluble carbohydrates were the crux of these trade-offs. • Breeding targets "specialist" phenotypes for grain and fodder but traits meeting market standards spread across types. • "Generalist" phenotypes can accommodate multiple agronomic uses but specialists are required where trade-offs are involved. Abstract The profitability of oat crops depends on quality attributes in relation to milling and hay marketing standards. The aims of this paper were to (i) quantify grain and hay quality traits in varieties and advanced grain, hay and grazing oat lines, and (ii) analyse the effect of line, environment and their interaction from the viewpoint of phenotypic plasticity. The experiment included 29 lines grown in the winter-rainfall region of South Australia. Grain traits included hectolitre weight, screenings, groat percentage, brightness and concentration of oil and protein. Hay traits, measured at GS71, included digestibility, crude protein, water soluble carbohydrates, acid detergent fibre, and neutral detergent fibre. High temperature, high vapour pressure deficit, and water deficit in the developmental window from GS31 to 200 °Cd after GS60 reduced hectolitre weight and groat percentage, and increased screenings. For hay, the proportion of water soluble carbohydrates declined, the proportion of both acid detergent fibre and neutral detergent fibre increased, and digestibility decreased with higher minimum temperature in a window from approx. −500 to +500 °Cd centred at anthesis. For both grain and hay, current lines returned high yield and high quality in favourable environments, where further improvement could focus on yield and maintenance of quality. In stressful environments, trade-offs between yield and quality were important; water soluble carbohydrates were the crux of these trade-offs. For grain, high concentration of water soluble carbohydrates favoured high hectolitre weight, low screenings and high groat percentage, at the expense of yield. For hay, high concentration of water soluble carbohydrates associated with higher digestibility and lower fibre, at the expense of yield. Nitrogen adds a layer of complexity to these relations, which were partially captured by leaf greenness measured with SPAD. Greener leaves associated with lower concentration of water soluble carbohydrates, hence capturing the established negative correlation between nitrogen and water soluble carbohydrates. Greener leaves associated positively with yield and protein concentration in grain and hay, lower digestibility and higher neutral (and acid) detergent fibre. Whereas the breeding program targets "specialist" phenotypes for grain and fodder, quality traits meeting market standards were spread across types. "Generalist" phenotypes can accommodate multiple agronomic uses but specialists are required where trade-offs are involved. [ABSTRACT FROM AUTHOR]

Senescence is a key physiological process that can regulate crop grain yield. Patterns of leaf senescence and its association with grain yield for a short maturity maize hybrid were investigated in a factorial combination of two tillage treatments (conventional and no-till), three amounts of stubble (0, 3 and 5 t ha −1 ) and three N rates (0, 80 and 120 kg N ha −1 ) over three seasons in 2015 long rains, 2015/2016 short rains and 2016 long rains. Leaf senescence from flowering to harvest was assessed at (a) the whole-plant scale by the visual scoring of dry leaves and (b) the canopy-layer scale by measuring leaf greenness with a SPAD 502 chlorophyll meter. A bilinear model was used to quantify the patterns of senescence at the whole-plant scale. A logistic function was fitted to estimate the traits of senescence at three canopy layers (top, mid, bottom), including minimum and maximum SPAD, onset of senescence (EC90), time to loss of 50% maximum SPAD (EC50) and the rate of senescence in each layer. Nitrogen rate effect on patterns and traits of senescence were large and its interactions with stubble were more frequent than interactions between other treatments. Tillage and stubble amount had marginal effects. EC50 was delayed in the unfertilized controls compared with fertilized crops and was negatively correlated with grain yield. Rate of senescence was faster in fertilised crops compared with unfertilized controls at both whole-plant and canopy-layer scales. Grain yield, grain number and nitrogen remobilization efficiency were associated with faster rates of senescence in the top and mid leaves but with slower rates of senescence in the bottom layer leaves. We advance a sink-driven leaf senescence ideotype for high yield and efficient use of nitrogen for short maturity maize. [ABSTRACT FROM AUTHOR]

Controversy around the benefits of NT and stubble retention, and weaknesses in the underpinning science arise from a limited understanding of the mechanisms that operate in these systems. Two experiments were conducted at the Kenya Agricultural and Livestock Research Organization research station in Embu (0.515°S and 37.273°E) over three seasons during the 2015 long rains, 2015/2016 short rains and 2016 long rains to explore the mechanisms that regulate crop growth, nitrogen uptake and yield in maize ( Zea mays L.). In the first experiment, crops were grown in a factorial combination of conventional tillage (CT) and no-till (NT), three amounts of stubble (0, 3 and 5 t ha −1 ) and three N rates (0, 80 and 120 kg N ha −1 ). The second experiment investigated the interaction between tillage (CT, NT) and timing of N supply (80 kg N ha −1 ) that was supplied at sowing, six- (V6) and 12-leaf stage, with 5 t ha −1 of stubble. Grain yield ranged from 2.3 to 5.3 t ha −1 , with small effects from tillage and stubble retention. Nitrogen had the largest impact on grain yield and influenced crop response to tillage and stubble by modifying crop growth rate (CGR) and nitrogen nutrition index (NNI). However, the effects of N timing on crop growth, yield and traits associated with N use efficiency were independent of tillage system. High CGR between V6 and flowering was associated with high NNI, which led to increased grain number. The value of stubble in water storage at sowing, and crop growth and yield was greater in a dry season (<300 mm rainfall) compared with wet seasons (>600 mm). Irrespective of tillage system, moderate amounts of stubble, higher N rates and better matching of N supply to the critical window for yield determination could improve maize yields in sub-humid tropical environments. [ABSTRACT FROM AUTHOR]

We measured yield and its components, phenology, leaf greenness, and concentration of water soluble carbohydrates and concentration of nitrogen in shoots of 29 oat varieties to determine (i) the phenotypic plasticity of these traits as a means to capture genotype-by-environment interactions, (ii) the role of these traits and their plasticity in adaptation to drought, and (iii) putative trade-offs between drought adaptation and yield potential. Varieties spaned grain, hay and grazing types, and ranged from 1301 to 1927 °Cd from sowing to anthesis. Yield was measured in nine environments while other traits were measured in 4–7 out of the 9 environments. Averaged across varieties, yield varied from 0.3 to 4.2 t ha −1 . The main environmental drivers of yield were water supply:demand from 500 °Cd before to 500 °Cd after anthesis, and minimum temperature in the same period. Phenotypic plasticity of yield, quantified as variance ratio, ranged from 0.60 to 1.22 for grain types and from 0.28 to 1.06 for their grazing and hay counterparts; high yield plasticity was associated with an asymmetric response to growing conditions: yield increased 3.3 ± 0.28 t ha −1 per unit increase in plasticity under favourable conditions, and 0.6 ± 0.16 t ha −1 per unit increase in plasticity under stress. For our combination of varieties and environments, genotypes were better discriminated in favourable environments, where selection for high plasticity would improve both yield potential and drought adaptation. After accounting for plasticity, yield residuals revealed consistent phenological thresholds (943 °Cd for GS31, 1470 °Cd for GS60) for adaptation to both favourable and stressful conditions. Yield correlated with leaf greenness (SPAD), particularly during grain fill. As expected from theory, yield was closely related to grains per m 2 and weakly related to grain weight. Grains per m 2 were negatively related to concentration of water soluble carbohydrates in shoots, which were in turn negatively correlated with shoot nitrogen concentration. Under favourable conditions, some varieties maintained a high concentration (>20%) of water soluble carbohydrates at harvest. Selection against this trait could improve yield potential, but residual labile carbohydrates can also be exploited in dual grain-feed varieties, and can provide flexibility for hay growers when logistics preclude cutting at the common water ripe (GS71) target. [ABSTRACT FROM AUTHOR]

Cropped area under no-till (NT) is increasing worldwide, but the extent to which breeding for yield is selecting for adaptation to NT is unclear. In addition, the consequences of selection for yield and that of tillage system on senescence patterns are not known. This study compared yield and senescence patterns of fourteen Australian wheat varieties released between 1958 and 2011, under no-till with stubble retention, and under conventional tillage (CT) without stubble. Grain yield increased at a rate of 21 kg ha −1 year −1 irrespective of tillage system, which implied that selection for yield did not improve wheat adaptation to no-till. Selection for yield changed the pattern of canopy senescence, whereby modern varieties had lower peak normalised difference vegetative index (NDVI), higher NDVI at maturity, a faster rate of senescence, and greener leaves, compared with older counterparts. [ABSTRACT FROM AUTHOR]

Late-season nitrogen (N) application has been proposed to boost grain yield and grain protein concentration (GPC) in cereals; however, its effects on bread and durum wheat have been inconsistent in field experiments. We performed a meta-analysis to (i) assess the effect of N applications to wheat after flag leaf visible (GS 37) on grain yield and GPC; and to assess the variation in these responses with (ii) N fertiliser management, (iii) environmental factors, and (iv) physiological traits. We searched ' Agronomy Journal ', ' Crop Science ', ' European Journal of Agronomy ', and ' Field Crops Research ' for articles published between 1980 and 2021 that allowed for a direct comparison of wheat yield and GPC between N application after GS 37 to an otherwise equally managed crop that received basal N fertilisation. We also collected other traits such as stover biomass and N uptake at plant maturity, and dough rheological properties, when available. The search resulted in 38 articles that, in addition to one unpublished trial from our group, evaluated 542 pairwise comparisons in 127 environments. Across studies, grain yield ranged from 1.15 to 10.63 Mg ha−1 and showed a negative relation with GPC, which ranged from 65 to 189 g kg−1. Late-season N fertilisation was consistently neutral for grain yield (I2, proportion of the overall variance due to variation in real effects rather than chance, 26.2 %) and increased GPC with a pooled estimate of 3.96 %. The response of GPC was heterogeneous (I2 = 84 %), suggesting the need for exploration of potential moderators of the response. Meta-regression suggested that increasing the proportion of late N relative to the total available N positively associated to increases in GPC, and the residuals of this analysis suggested that later applications increased GPC response, with no effect of N fertiliser source or placement. Environments with low temperature, high photothermal quotient, and long duration of the critical period associated with greater GPC response to late-season N applications. The relative response of GPC to late fertilisation correlated with the relative response of both stover N uptake and nitrogen concentration in stover at maturity, but not with stover biomass at maturity. Alveogram index and dough extensibility increased when late-season N increased GPC. Enhancing GPC through late N applications should consider associations between management, environmental, and physiological factors. Future research should focus on forecasting GPC response to late N, based on GPC response drivers identified in the current research. • Meta-analysis highlighted physiological drivers of wheat response to late N • Grain yield was unaffected by late N across a broad range of environments • Late N increased protein by 3.96% and its effects were heterogeneous • Protein increased linearly with the proportion of late N and with later applications • Higher protein response to late N associated to favourable growing conditions [ABSTRACT FROM AUTHOR]

Robust associations between yield and crop growth rate in a species-specific critical developmental window have been demonstrated in many crops. In this study we focus on genotype-driven variation in crop growth rate and its association with chickpea yield under drought. We measured crop growth rate using Normalised Difference Vegetative Index (NDVI) in 20 diverse chickpea lines, after calibration of NDVI against biomass accounting for morphological differences between Kabuli and Desi types. Crops were grown in eight environments resulting from the combination of seasons, sowing dates and water supply, returning a yield range from 152 to 366 g m −2 . For both sources of variation – environment and genotype – yield correlated with crop growth rate in the window 300 °Cd before flowering to 200 °Cd after flowering. In the range of crop growth rate from 0.07 to 0.91 g m −2 °Cd −1 , the relationship was linear with zero intercept, as with other indeterminate grain legumes. Genotype-driven associations between yield and crop growth rate were stronger under water stress than under favourable conditions. Despite this general trend, lines were identified with high crop growth rate in both favourable and stress conditions. We demonstrate that calibrated NDVI is a rapid, inexpensive screening tool to capture a physiologically meaningful link between yield and crop growth rate in chickpea. [ABSTRACT FROM AUTHOR]

Natural selection does not lead to optimal solutions due to trade-offs and environmental variation, genetic and developmental constraints, and historical contingency. In this paper we propose that constraints like these also often apply to the improvement of both crop varieties and management practices, creating a dual biological and agronomic barrier for the optimisation of crops. We discuss constraints on optimisation of 1) crop ancestors, by natural selection, 2) crop traits, by artificial selection and biotechnology, and 3) crop management. We outline how trade-offs and environmental variation make single-factor optimisation (e.g. “optimum leaf angle” or “optimal fertiliser rate”) impossible. Definitions of “optimal” that recognise trade-offs and variability can help, but we argue there are major constraints on even those forms of optimality. Optimality theory may be useful to formulate null hypotheses, however, as divergence between actual traits and theoretical optima can highlight constraints that are biologically interesting and agronomically relevant. Understanding the nature and size of these constraints can help us map more likely pathways for future improvements in agriculture. [ABSTRACT FROM AUTHOR]

Drought affects the growth of legumes directly, and indirectly, by reducing total nitrogen fixation. Here, we compiled published data to compare the sensitivity to water deficit on plant growth and total nitrogen fixation traits, i.e., the number of nodules per plant, average nodule mass, and nitrogen fixation per unit nodule mass. Hierarchies of phenotypic plasticity have been established for seeds and organelles, whereby variation in number associates with conserved size. By analogy, our first hypothesis is that there is a hierarchy of plasticities between nitrogen fixation traits. Our second hypothesis is that determinate nodules are more sensitive to water deficit than their indeterminate counterparts, because the latter can reactivate meristems when water becomes available. In our sample, onset of stress treatment averaged 28 d after sowing; median duration of stress was 12 d; and intensity of stress (ratio of shoot biomass between stressed and control) averaged 0.65. These drought conditions (i) reduced total nitrogen fixation and average nodule mass more severely than plant shoot mass, (ii) elicited a hierarchy of plasticities whereby number of nodules per plant varied substantially, and average nodule mass and nitrogen fixation per unit nodule mass were relatively conserved, and (iii) affected more severely Milletioids (determinate, ureide exporting nodules) than their IRLC counterparts (indeterminate, amide exporting nodules). • Total N fixation was partitioned as nodule number, average nodule mass, and nitrogen fixation per unit nodule mass. • Early-season drought reduced nodule number more than average nodule mass and N fixation per unit nodule mass. • Drought effect were more severe in Milletioid (determinate, ureide) than in IRLC (indeterminate, amide) nodules. [ABSTRACT FROM AUTHOR]

Against the backdrop of climate change, genotypes with improved adaptation to elevated temperature are required; reliable screening methods are therefore important. Sowing date experiments are a practical and inexpensive approach for comparison of large collections of lines. Late-sown crops usually experience hotter conditions and phenotypes thus partially capture this environmental influence. Two sets of confounded factors, however, limit the value of sowing date trials. First, daily mean temperature correlates with both minimum and maximum temperature, photoperiod, radiation and vapour pressure deficit, and it may also correlate with rainfall. Second, temperature alters the genotype-dependent phenology of crops, effectively shifting the timing and duration of critical periods against the background of temperature and other environmental variables. Here we advance a crop-level framework to unscramble the confounded effects of sowing date experiments; it is based on four physiological concepts: (1) annual crops accommodate environmental variation through seed number rather than seed size; (2) seed number is most responsive to the environment in species-specific critical windows; (3) non-stressful thermal effects affecting seed set through development and canopy size can be integrated in a photothermal quotient relating intercepted photosynthetically active radiation (PAR) and mean temperature during the critical window; (4) stressful temperature reduces yield by disrupting reproduction. The framework was tested in a factorial experiment combining four chickpea varieties with putatively contrasting adaptation to thermal stress and five environments resulting from the combination of seasons and sowing dates. Yield ranged from 13 to 577 g m −2 . Shifts in phenology led to contrasting photothermal conditions in the critical window between flowering and 400 °C d after flowering that were specific for each variety–environment combination. The photothermal quotient ranged from 2.72 to 6.85 MJ m −2 °C −1 ; it explained 50% of the variation in yield and maximum temperature explained 32% of the remaining variation. Thus, half of the variation in yield was associated with developmental, non-stressful thermal effect and (at most) 16% of the variation was attributable to thermal stress. The photothermal quotient corrected by vapour pressure deficit accounted for by 75% of the variation in yield and provided further insight on photosynthesis-mediated responses to temperature. Crop adaptation to non-stressful, developmental thermal effects and stressful temperatures disrupting reproduction involve different physiological processes and requires partially different agronomic and breeding solutions. Our analytical approach partially separates these effects, adds value to sowing date trials, and is likely to return more robust rankings of varieties. [ABSTRACT FROM AUTHOR]

Chickpea seed yield is highly variable as a result of biotic, mostly fungal, and abiotic stresses including extreme temperatures and water stress. The effect of stress on yield depends on its intensity, timing and duration, hence the importance of knowing the critical window of yield formation and stress vulnerability. This window has not been determined in chickpea. To fill this gap, we compared the effect of sequential 14-d shading periods on the yield and yield components of two chickpea varieties, PBA Boundary and PBA Slasher, in three environments where unshaded controls yielded between 2880 and 3130 kg ha −1 . Unlike other species which do not respond to stress early in the season, shading reduced yield from emergence until the beginning of the critical period, 300 °Cd before flowering (base temperature = 0 °C). The critical period was found to be at least 800 °Cd long centred 100 °Cd after flowering. Seed number accounted for most of the variation in yield, which was unrelated to seed size. Pod number accounted for most of the variation in seed number prior to the critical period, while pod number and seeds per pod contributed to seed number within the critical period. After 400 °Cd post flowering, seeds per pod was the main variable affecting seed number. This information can be used in breeding and agronomy to improve stress adaptation. [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]

Owing to the high contents of oil and protein, soybean [Glycine max L. (Merr.)] seeds are energy-rich. Genetic improvement of soybean yield is linked to the dilution in seed protein; changes in low-energy compounds such as carbohydrates have received less attention. We tested the hypothesis that selection for yield in soybean has shifted seed composition in favor of low-energy compounds. We characterized the dynamics of three seed fractions (protein, oil, and residual) during seed filling in seven commercial soybean varieties released between 1980 and 2013 in a two-year field experiment. Genetic gain in yield was linked with reduced seed energy cost: seed protein concentration decreased by 0.06% yr−1, oil remained stable, and the residual fraction increased by 0.09% yr−1. Seed accumulation of the residual fraction revealed a shorter lag phase and a longer effective filling period for the modern relative to the older soybean varieties. Seed energetic requirement significantly decreased − 0.06% yr−1. Resource availability per seed during the seed-filling period was not limiting across all tested varieties. Further research is warranted on the biochemical nature of the residual fraction, and on the implications of seed composition for future breeding, soybean meal and end uses. [ABSTRACT FROM AUTHOR]

The nitrogen economy of the crop is a critical driver of biomass and grain production, and its importance is reflected in a large, worldwide research effort to link nitrogen, growth and yield. Particular research questions require measurement of specific traits, hence the need to quantify multiple, often complementary traits including crop nitrogen uptake, nitrogen use efficiency and its components, nitrogen concentration in the crop and its parts, down to relevant enzymes (e.g. nitrate reductase) and other products of gene expression. Nitrogen uptake, however, is co-regulated by both soil nitrogen availability and crop biomass accumulation; hence, crop nitrogen uptake or shoot nitrogen concentration reflect univocally crop nitrogen status only if comparisons are made at similar biomass. Although the allometric relationships between biomass and nitrogen uptake have been established for over two decades, many studies still report results in terms of nominal treatments, e.g. high vs low nitrogen, which are uninformative; curves relating yield and fertiliser rate, which are of local interest but provide little insight on the underlying processes and have low generic value; and nitrogen-related traits that are incomplete or inadequate to quantify crop nutrition status. Often, the allometric relationships between nitrogen and biomass are overlooked. In this opinion paper, we summarise the already well established concepts of dilution curves and nitrogen nutrition index, outline the standard partitioning of nitrogen use efficiency, and highlight the confounded effects in nitrogen use efficiency when the allometric relationship between nitrogen uptake and biomass is ignored. A sample of recent papers is used to survey the most common approaches to characterise nitrogen related traits. We illustrate the application of dilution curves and nitrogen nutrition index in the assessment and interpretation of crop responses to agronomic practices and comparisons of wheat cultivars and maize hybrids. [ABSTRACT FROM AUTHOR]

Highlights: [•] Review of phosphorus, potassium and sulphur effect on symbiotic N2 fixation. [•] Nodule mass and number are more responsive to nutrient deficit than shoot biomass. [•] N2 fixation is more responsive to P and K deficit than shoot and nodule mass. [•] The ratios N/K, N/P and N/S in shoots increased under nutrient deficiency. [•] Patterns of growth, N2 fixation and nutrient concentration were similar for P, K and S deficiency. [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]

Abstract: In a worldwide context of agricultural intensification, cropping systems in Mediterranean-type environments have been reducing the frequency of long-fallow in a shift to continuous cropping. The focus of this paper is the short summer fallow between successive winter grain crops in environments of South Australia with winter-dominant rainfall. Our aims were to (i) estimate wheat yield response to summer rainfall, (ii) explain yield responses in terms of capture and efficiency in the use of radiation and water, (iii) explore the incidence of the amount and disposition of stubble on storage of summer rainfall, and (iv) assess the interaction between summer rainfall and nitrogen supply. We used trickle irrigation to manipulate summer water supply in two factorial experiments combining water and stubble treatments, and three factorials combining water and nitrogen supply. Addition of 50–100mm of water increased soil water content at sowing between 8 and 46mm compared to controls that only received the background summer rainfall (10–74mm). Yield gain from additional water input in summer declined from 1.1tha−1 to zero when the yield of controls increased from 2.0 to 7.8tha−1. Where yield response was related to a single resource, water or nitrogen, capture of radiation and water were major drivers of growth and yield response. Where yield response was related to the interaction between water and nitrogen, both capture and efficiency in the use of resources were important. Amount (0–5tha−1) and disposition of stubble (standing or flat) did not affect the amount or distribution of water in soils, and had no effect on grain yield. High nitrogen rate was critical to capture the benefits of additional summer water and reciprocally high water supply was required to capture the benefits of nitrogen fertilisation; this highlights the resource co-limitation for wheat production in these environments. In a water×nitrogen factorial, crops with either low nitrogen or no additional summer water supply had radiation use efficiency ∼1.6gMJ−1, biomass per unit evapotranspiration ∼33kgha−1 mm−1 and yield per unit evapotranspiration ∼15kgha−1 which increased to 1.9gMJ−1, 40kgha−1 mm−1 and 18kgha−1 mm−1 in crops with both additional water and high nitrogen. Across experiments and treatments, grain number accounted for 88% of the variation in yield. Grain number was proportional to crop growth rate between stem elongation and anthesis; crops with high nitrogen produced 116±5.0 grains per unit crop growth rate and their low nitrogen counterparts 99±4.6. Building evidence from Mediterranean environments worldwide highlights the importance of grain number as the main source of variation in yield and therefore the critical period between stem elongation and anthesis where both water and nitrogen supply are critical. [Copyright &y& Elsevier]

Abstract: We measured the effects of increased daytime temperature during 2- (2007/08) or 3-week periods (2008/09) on the yield and yield components of irrigated Shiraz vines in the Barossa Valley of Australia. A simple and inexpensive open system was used to elevate temperature during a single phenological window, either bracketing budburst (E-L stage 4), shortly after flowering (E-L stage 23), bracketing pea size (E-L stage 31), around veraison (E-L stage 35) or shortly before harvest (E-L stage 38). Two important features of the heating systems were tracking of diurnal temperature dynamics, and maintaining relative humidity, hence avoiding the interaction between temperature and vapour pressure deficit. Minimum temperature was unchanged. Compared to controls, maximum ambient temperature was increased between 1.8 and 4.1°C in treated plots but canopy temperature of treated vines only increased by 0.9–1.1°C. Elevation of bunch temperature was 2.3–3.2°C. Increasing temperature around budburst transiently accelerated development in comparison to controls; no phenological changes were detected for other timings of treatment. Yield averaged 4.3kgvine−1 in 2007–08 and 6.1kgvine−1 in 2008–09. In both seasons and for all timings of treatment, increasing temperature did not affect yield or its components; lack of yield response did not result, therefore, from compensatory mechanisms, e.g. heavier berries compensating for fewer fruit. The dynamics of berry growth and total soluble solids were largely unaffected by temperature. Under our experimental conditions, the capacity of irrigated Shiraz canopies to partially buffer a 2–4°C increase in maximum ambient temperature may have been important for the maintenance of yield, and berry growth and sugar accumulation. [Copyright &y& Elsevier]

Abstract: Whereas the concept that availability of resources drives seed production is sound in principle, it is incomplete as there are many solutions to the allocation of resources that derive from the trade-off between number and size. This paper examines evolutionary aspects of this trade-off in annual grain crops. The analysis is centred on the working hypotheses that, for a given species and environment, allocation of resources to reproduction involves (H1) high plasticity in seed number, which allows for variable resource availability, and (H2) a relatively narrow range of seed size that results from evolutionary and agronomic selection. Comparisons between crops and fish are used to highlight common evolutionary elements in taxa where parents provide little or no care to their offspring, with the consequence that both number and early survival of offspring, hence fitness of parents, are partially related to embryo size and reserves. The plasticity of seed number in relation to availability of resources is analysed against the established relationship between offspring number and parent growth rate during critical stages. The notion that seed size is under stabilising selection is analysed against three conditions: (1) mean seed size is conservative for a given species and environment, (2) seed size affects fitness, and (3) seed size is heritable. Databases from published papers were compiled to analyse the relative variability of seed size and number, and the heritability of seed size. Evidence for and against the link between seed size and parental fitness is revised using the Smith–Fretwell model as framework (Am. Nat., 108, 499–506). The proposal of high plasticity of seed number and narrow variability of seed size resulting from stabilising natural selection is generally consistent with evolutionary and genetic considerations. Agronomic selection may have reinforced natural selection leading to relatively narrow seed size in species such as wheat and soybean, where cultivated types retained high plasticity for seed number. In contrast, selection for one or few inflorescences in crops like sunflower and maize may have morphologically reduced seed number plasticity and increased variability of seed size and its responsiveness to resource availability in relation to their wild ancestors. [Copyright &y& Elsevier]

Abstract: A data base including grain yield, nitrogen uptake (N u) and phosphorus uptake (P u) was compiled to investigate the N:P stoichiometry of cereal (n =759), grain legume (n =413) and oilseed species (n =421). Actual ratios and slopes of functions relating nitrogen uptake and phosphorus uptake were used to characterise N:P stoichiometry. The focus is on variability in N:P ratios of field crops, and N:P stoichiometry of crops achieving maximum yield. N:P ratios varied between ∼20, the maximum for legumes and oilseed crops, and ∼1.5, the minimum for cereals. By definition, N:P ratios are a direct function of N uptake and an inverse function of P uptake. The expected association between N:P ratio and N uptake was not evident except for grain legumes whereas the expected relationship between N:P and P uptake was verified for all three crop types. This highlights the role of P uptake as the main source of variability in N:P stoichiometry. The relationship between N uptake (N u) and P uptake (P u) for crops achieving maximum yield in each experiment was markedly non-linear. Functions of the form N u = N max P u/( + P u) described the way in which N:P stoichiometry scaled with grain yield. Maximum uptake of nitrogen (N max) was similar for all three crop types (≈240kgNha−1), but it was achieved via different avenues, i.e. high yield and low grain protein concentration for cereals compared to lower yield and higher grain protein concentration in oilseed and legume crops. Phosphorus uptake at half N max () ranged from 27kgPha−1 for oilseeds to 14kgPha−1 for legumes. The N:P ratio at was 4.5 for oilseed crops, 5.6 for cereals and 8.7 for legumes. For cereals and oilseeds, over 40% of crops attaining maximum yield had N:P ratios in a relatively narrow range between 4 and 6. Variation in grain protein concentration was a major source of instability in N:P ratios of legumes. Being at the base of agro-ecological food webs, the N:P stoichiometry of crops has implications for both decomposers and consumers, and stoichiometric concepts might be of interest in fertiliser management and modelling. Variability in N:P stoichiometry related to plant storage products, however, restricts its application. [Copyright &y& Elsevier]

• Modern maize hybrids sown at low densities tiller in non-restrictive environments. • Light quality and plant growth rate at early stages govern tiller emission. • Tiller fertility would be determined by shoot growth rate around flowering. • Reproductive plasticity is needed to stabilize yields in ultra-low density settings. • The impact of tillering on crop water and nitrogen economies is hypothesized. Selection for maize (Zea mays L.) grain yield in high-yielding environments at high population densities has favored a compact phenotype tolerant to crowding stress, bearing a single, well-grained ear. However, by contributing to vegetative and reproductive plasticity (i.e., multiple shoots and ears per plant, respectively), tillering may be adaptive in environments with low and variable availability of resources, chiefly water and nutrients, where crops are sown at low plant population density. In this work we present a robust, new conceptual framework for vegetative and reproductive plasticity in maize with direct agronomic applications, combining original data from new experiments and data reviewed from the literature. First, we describe production systems where tillering in maize would be relevant in terms of grain yield. Next, we discuss possible masked effects of genetic selection at high plant densities on tillering and present novel experimental results showing genotypic variation of tillering in modern maize hybrids and genotype x environment x management effects (plant density x location x sowing date) on tillering expression. We follow with a two-part framework to analyze tillering and prolificacy. In the first part (from axillary buds to tillers), we integrate the early effects of the light environment (through photomorphogenesis) and carbon balance on tillering emission, and discuss the environmental factors (temperature, photoperiod, radiation, water, nitrogen) that modulate tiller emission and tiller growth. In the second part (from tillers to kernels), we summarize the functional relationships governing kernel set on the ears of main shoot (apical and sub-apical ears) and tillers, focusing on the growth rate of shoot cohorts, rather than the whole plant. We then provide examples of the diverse patterns of contribution of multiple shoots to crop grain yield for maize husbandry in low-yielding environments. Finally, we address the effect of tillering on resource capture and use efficiency of maize crops by discussing its relationship with biomass and grain yield and provide supportive experimental data. We conclude with identification of knowledge gaps leading to testable hypotheses. [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]

• Yield gaps for temperature-limited yield potential Y T varied with location, time of sowing, cultivar and nitrogen. • Y T related negatively to mean temperature in the critical period returning a slope of -0.53 t ha−1 °C−1. • Elevated temperature reduced the duration of the critical period and was the largest driver of reduced grain number and yield. • Yield-temperature relationships crossed over in the response to nitrogen fertilisation. Elevated temperature, water deficit, low nitrogen availability and their interactions, constrain wheat yield in Mediterranean-type environments. Our working hypothesis is that, owing to the non-linearity of yield response to water and nitrogen and the non-linearity of biological processes in response to temperature, the outcome of the interactions between temperature, nitrogen and water is range-dependent. To generate a broad range of conditions in testing this hypothesis, we established two experiments. Experiment 1 combined factorially four sowing times, six cultivars and four nitrogen rates in four locations-seasons. Experiment 2 combined factorially two cultivars, two nitrogen rates, and two thermal regimes to further untangle interactions. Thermal regimes were unheated controls, and crops heated with passive open-top heating chambers increasing temperature by 0.5 °C during grain set or grain filling. Across the 384 combinations of treatments in Experiment 1, yield ranged between 0.12 t ha-1 and 5.96 t ha-1. The duration of the critical period (300 °C d before anthesis to 100 °C d after anthesis) decreased with mean temperature at an average rate of 5 d °C-1 and accounted for 75% of the variation in yield. We used quantile regression to calculate a temperature-limited yield potential Y T and derived a linear function between Y T and mean temperature in the critical period, returning a slope of -0.53 t ha-1 °C-1. Yield gap, i.e., the difference between Y T and actual yield, was larger in nitrogen and water-deficient crops. Yield-temperature relationships crossed over in response to nitrogen fertilisation. Fertilised crops (100−200 kg N ha-1) outyielded their unfertilised counterparts when mean temperature during the critical period was below 13 °C, and unfertilised controls were superior above this threshold. Locally calibrated thresholds can be used as a rule-of-thumb adding a further dimension to the management of combined stresses and risk of wheat in Mediterranean-type environments. In Experiment 2, yield responded to the interaction between temperature and nitrogen, whereby elevated temperature during grain set reduced yield by 17% in unfertilised crops with no effect on crops with 100 kg N ha-1. Elevated temperature during grain fill reduced yield by 14% with no effect of nitrogen or nitrogen x temperature interaction on grain yield. [ABSTRACT FROM AUTHOR]

• Harvest index is inconsistent across literature to describe genetic gain in reproductive allocation at maturity. • Allometric analysis was used to characterize genetic gain in reproductive allocation in R5 in seven soybean varieties. • Allometric analysis at the end of the seed set revealed an increase in relative allocation into pods. • Allocation to seed must have increased, but HI did not capture this necessary change in allocation. Seed yield is commonly expressed as the product of shoot biomass and harvest index (HI) at physiological maturity. However, HI is a size-dependent ratio unsuitable to describe shifts in reproductive partitioning in historical soybean [ Glycine max (L.) Merr.] studies where selection has enhanced shoot biomass. The aim of this work was to analyze allocation of biomass to reproductive organs in the onset of seed filling (R5) using allometric analysis in a set of historical soybean varieties. Seven varieties released between 1980 and 2013 were evaluated in field trials in Rossville (Kansas, United States) under two N fertilizer rates (0 and 670 kg N ha−1) in 2016 and 2017. Seed yield increased at a rate of 0.74 % yr−1 (p < 0.001); while the shoot biomass increased at a rate of 0.41 % yr−1 (p < 0.001), suggesting an increase in allocation to reproduction. However, the rate of increase in HI at maturity was not different from zero highlighting the inadequacy of this trait. Allometric exponents (slopes of the log-log relationships) relating pod and shoot biomass, pod and leaf, and pod and stem plant fractions increased linearly with the year of release (p < 0.05). Allometric analyses thus revealed genetic gains in reproductive allocation not detected by HI at maturity. The latter outcome highlights the contribution of improved reproductive partitioning to soybean yield gains, and the need for allometric analyses to account for size-dependence in allocation of shoot biomass. [ABSTRACT FROM AUTHOR]

• We explored N and S co-limitation and stoichiometry in maize. • Yield gap increased with the degree of N and S deficiencies. • N and S use efficiency decreased with the degree of S and N deficiency, respectively. • N-S co-limitation was negatively related to yield gap and positively related to their nutrient use efficiencies. • A N:S ratio ∼9.6 in shoot at maturity and ∼11.2 in grain maximized N-S co-limitation. Nitrogen (N) and sulfur (S) deficiencies, individually and in combination, produce gaps between actual and potential yields in maize (Zea mays L.). Our objectives were to evaluate the effect of N and S status and their interaction on yield gap, and nutrient use efficiency (yield per unit of nutrient supply) using frameworks of co-limitation and stoichiometry. Factorial trials were established combining two N (unfertilized, N-fertilized) and two S (unfertilized, S-fertilized) treatments in five site-years. Yield ranged from 6.7 to 15.4 Mg ha−1. In a scale from 0 (no stress) to 1 (maximum stress), N stress varied from 0 to 0.67, and S stress from 0 to 0.66. Yield gap varied from 0 to 10 Mg ha−1, diminished as both N and S stresses reduced, and with higher N-S co-limitation. Both N and S use efficiencies increased with reductions in nutrient stresses and with increases in some of the N-S co-limitation indices. Co-limitation between N and S was maximized with N:S ratio ∼9.6 in shoot biomass and ∼11.2 in grain, indicating the balanced nutrient ratio in each plant organ at maturity. Both co-limitation and stoichiometry frameworks captured the interacting N and S effects on yield and nutrient use efficiency. [ABSTRACT FROM AUTHOR]

• Selection for yield favours low competitive ability. • Hypothesis: the yield-nitrogen curve mirrors the competition-nitrogen curve. • Hypothesis held in early sown crops where switch in resource competition occurs from N to radiation and water when increasing N availability. • In late-sown crops fast development outweighed competition as driver of yield. • Genetic and agronomic reduction of intraspecific competition could improve nitrogen use efficiency. Agronomic and breeding innovations are essential to support grain production whilst avoiding over-fertilisation and excess reactive nitrogen in some agroecosystems, and chronic under-fertilisation and mining of soil organic matter in others. Based on the well-established negative correlation between yield per unit land area and intraspecific competitive ability, we hypothesised that the yield-nitrogen curve at the centre of fertiliser decisions mirrors the competition-nitrogen curve. A factorial study combining six wheat cultivars, two locations, two sowing dates and four nitrogen rates supported our hypothesis in early-sown crops where intraspecific competition for nitrogen decreased, and competition for radiation and water increased with increasing availability of nitrogen. In late-sown crops, high temperature favouring fast development, short plants and smaller canopies overrode competition for resources as the driver of grain yield. The implication is that genetic and agronomic reduction of intraspecific competition can improve yield per unit available nitrogen. [ABSTRACT FROM AUTHOR]

• Defoliation was largely neutral for grain yield and WUE. • Defoliation improved harvest index and net income by 7–15%. • Defoliation improved translocation of WSC to grain. • Dual-purpose wheat was more profitable at low seeding rate and high initial soil water. Dual-purpose wheat has been adopted in many farming systems, but interactions between management, supply of resources, and seasonal conditions are still not clearly elucidated. Two experiments were established in the Loess Plateau of China to measure yield and its components, evapotranspiration, water-use efficiency (yield per unit evapotranspiration), accumulation and apparent remobilisation of stem water soluble carbohydrates (WSC), and economic benefit of dual-purpose winter wheat. Experiment 1 combined factorially three defoliation treatments, i.e. winter defoliation (DC23), spring defoliation (DC29) and untreated control, two seeding rates (currently recommended, and 125% recommended), and over four seasons. Experiment 2 combined factorially two defoliation treatments (spring defoliation and control), two nitrogen rates (low: 120–150 kg N ha−1, high: 180–200 kg N ha−1), three levels of soil water at sowing (low: rainfed; medium: rain +67 mm; high: rain +133 mm), and over three seasons. Defoliation was largely neutral for grain yield and water-use efficiency, and improved translocation of WSC to grain by 8%, harvest index by 7% and net income by 15% across conditions. Grain yield was unaffected by the interaction between defoliation and seeding rate, but significantly impacted by interactions of defoliation × initial soil water level and defoliation × nitrogen rate. Defoliated wheat yield was greater at high than at medium and low initial soil water content, and at low than at high nitrogen rate. Spring defoliation produced similar yield as winter defoliation but the former increased forage income. Increasing seeding rate or nitrogen rate increased forage income but reduced net income due to lower grain income and higher cost. Thus, dual-purpose winter wheat was more profitable (i) when defoliated in spring, (ii) at the lower seeding density, (iii) under the lower nitrogen rate, and (iv) with higher soil water content at sowing. Apparent translocation of stem WSC partially mediated the effect of defoliation on grain yield. It is concluded that dual-purpose winter wheat is feasible under straw mulching in semiarid environment. [ABSTRACT FROM AUTHOR]

• Excel x Kaspa RILs screened in dry, hot environment (yield 149 g m-2) and a wet, mild environment (477 g m-2). • Ranking of RILs was consistent between environments for pod wall ratio, the weight ratio between the pod wall and the whole pod including seeds. • A QTL for flowering time on chromosome 2 co-located with a QTL for a number of yield related traits including pod wall ratio. Trait-based selection to improve stress adaptation can complement direct selection for yield provided the trait meets six criteria: (1) it must be genetically correlated with yield in the target environments; (2) it should be less affected by the GxE interaction than yield; (3) it should not be associated with low yield in favourable conditions; (4) it must show genetic variation; (5) it must be genetically stable, persistent across generations and relevant in different genetic backgrounds, and (6) it must lend itself to rapid, cost-effective and reliable quantification. Against these criteria, this study focused on pod wall ratio, defined as the weight ratio between the pod wall and the whole pod including seeds. We explored the phenotypic and genetic associations of this trait with yield components in a field pea population of 102 recombinant inbred lines (RILs) from a cross between Excel and Kaspa grown in two environments: Roseworthy 2015 (average yield 149 g m−2) and Turretfield 2016 (477 g m−2). All three sources of variation, environment, line and their interaction, affected yield (all P < 0.0001). The ranking of RILs for yield varied between environments, reflecting the strong G x E. The ranking of RILs for pod wall ratio was maintained between environments. Broad-sense heritability was higher for pod wall ratio (≥ 0.83) than for yield (≤ 0.59). There was a narrow range of pod wall ratio, 0.07 to 0.25 at Roseworthy 2015 compared to 0.09 to 0.52 in Turretfield 2016. Pod wall ratio correlated with seeds per pod and harvest index in Roseworthy 2015, and with yield, seeds per pod and harvest index in Turretfield 2016. A QTL for flowering time on linkage group 2 co-located with a QTL for a number of traits including pod wall ratio, days to pod emergence, seeds per pod, seeds per m2, shoot biomass at harvest and grain yield. These markers are potentially valuable for breeding after validation in independent populations. [ABSTRACT FROM AUTHOR]

• Benchmarks of wheat N utilisation efficiency (NUtE) in Mediterranean conditions are needed. • We compiled a large set of data from Mediterranean and non-Mediterranean environments of Europe. • Mediterranean growing conditions narrowed N uptake contributing to lower final yields than in N Europe. • But they also reduced consistently NUtE (considering both average and maximum yields at each level of N uptake). • These effects on NUtE produced a trade-off with grain N concentration. Water and temperature stress during critical periods of grain yield formation are distinctive of wheat crops in Mediterranean environments. However, nitrogen (N) availability may also constrain grain yields in these environments. Benchmarks of yield response to N uptake in Mediterranean conditions are lacking, and extrapolation from non-Mediterranean environments is not warranted. We hypothesised that under Mediterranean environments (1) maximum N uptake would be lower, thus the range of N uptake would be narrower, and (2) N utilisation efficiency (NUtE, yield per unit N uptake) would be reduced along the whole range of N uptake than under non-Mediterranean conditions. To test these hypotheses, we compiled published data of yield and N uptake from Mediterranean (n = 340) and non-Mediterranean environments (n = 563) of Europe. Wheat in Mediterranean environments had lower average grain yield (4.1 vs 7.1 Mg ha−1), lower average N uptake (131 vs 166 kg N ha−1), lower average NUtE (33 vs 47 kg grain kg N−1), and higher average grain N concentration (2.4 vs 1.8%) than crops in non-Mediterranean environments. Boundary functions relating yield and nitrogen uptake captured the lower yield of wheat along the whole range of N uptake as hypothesised; these functions could be used for benchmarking wheat crops in Mediterranean regions of Europe, and possibly other Mediterranean environments. [ABSTRACT FROM AUTHOR]

Interactions between nitrogen and water may vary between N 2 fixing species and species that rely only mineral soil nitrogen. Here we compared above ground biomass accumulation (W), nitrogen uptake (N), evapotranspiration (ET) of alfalfa ( Medicago sativa L.) and tall fescue ( Festuca arundinacea Schreb.) during regrowth periods under contrasting supply of water (irrigated vs non-irrigated) and N (for non-fixing species). Using previously published data, we estimated the dynamics of the two components of ET, evaporation from soil (E) and transpiration (T), in order to analyse the impact of E/T, of the transpiration efficiency (TE = W/T) and the role of crop N nutrition on water use efficiency (WUE= W/ET). In tall fescue, limiting N supply reduced WUE by both increasing E/T ratio and decreasing TE. Water limitation in both alfalfa and tall fescue led to crop nitrogen deficit. This drought-induced N deficiency resulted in a proportional reduction in TE irrespective of the source of N for the plant. We propose that the ratio N/T, representing the apparent N concentration of water transpired by the crop, is relevant for analysing N-water interactions. Comparisons of dynamics of N/T ratio must be done at similar biomass or similar transpiration because N and T are related allometrically. [ABSTRACT FROM AUTHOR]

Yield gap analyses of individual crops have been used to estimate opportunities for increasing crop production at local to global scales, thus providing information crucial to food security. However, increases in crop production can also be achieved by improving cropping system yield through modification of spatial and temporal arrangement of individual crops. In this paper we define the cropping system yield potential as the output from the combination of crops that gives the highest energy yield per unit of land and time, and the cropping system yield gap as the difference between actual energy yield of an existing cropping system and the cropping system yield potential. Then, we provide a framework to identify alternative cropping systems which can be evaluated against the current ones. A proof-of-concept is provided with irrigated rice-maize systems at four locations in Bangladesh that represent a range of climatic conditions in that country. The proposed framework identified (i) realistic alternative cropping systems at each location, and (ii) two locations where expected improvements in crop production from changes in cropping intensity (number of crops per year) were 43% to 64% higher than from improving the management of individual crops within the current cropping systems. The proposed framework provides a tool to help assess food production capacity of new systems ( e.g. with increased cropping intensity) arising from climate change, and assess resource requirements (water and N) and associated environmental footprint per unit of land and production of these new systems. By expanding yield gap analysis from individual crops to the cropping system level and applying it to new systems, this framework could also be helpful to bridge the gap between yield gap analysis and cropping/farming system design. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated the relationships between yield components considering phenotypic plasticity. [•] Grains per m2 and spikes per m2 were coarse regulators while all components may be responsible for fine regulation of yield. [•] We showed that the rankings of responses of yield components depend on the nature of the driver, i.e. genotype or environment. [•] Strong trade-offs between components were found for small changes in yield or in grains per m2 for both environmental and genetic factor. [•] For large changes, trade-offs were weaker, but much stronger for components of yield than of grains per m2, particularly for genetic drivers. [Copyright &y& Elsevier]

• We assessed variation in grain-N removal as a result of grain nitrogen concentration (GNC). • We collected data from crops grown with current management in the US North Central region. • Grain yield differences explained much more variability than GNC in grain-N removal. • Variation in GNC was associated with temperature, water balance, and N fertilizer rate. • Estimates of grain-N removal were more reliable when aggregated at climate-soil domain. Accurate estimation of nitrogen (N) balance (a measure of potential N losses) in producer fields requires information on grain N concentration (GNC) to estimate grain-N removal, which is rarely measured by producers. The objectives of this study were to (i) examine the degree to which variation in GNC can affect estimation of grain-N removal, (ii) identify major factors influencing GNC, and (iii) develop a predictive model to estimate GNC, analyzing the uncertainty in predicted grain-N removal at field and regional levels. We compiled GNC data from published literature and unpublished databases using explicit criteria to only include experiments that portray the environments and dominant management practices where maize is grown in the US North Central region, which accounts for one-third of global maize production. We assessed GNC variation using regression tree analysis and evaluated the ability of the resulting model to estimate grain-N removal relative to the current approach using a fixed GNC. Across all site-year-treatment cases, GNC averaged 1.15%, ranging from 0.76 to 1.66%. At any given grain yield, GNC varied substantially and resulted in large variation in estimated grain-N removal and N balance. However, compared with GNC, yield differences explained much more variability in grain-N removal. Our regression tree model accounted for 35% of the variation in GNC, and returned physiologically meaningful associations with mean air temperature and water balance in July (i.e., silking) and August (i.e., grain filling), and with N fertilizer rate. The predictive model has a slight advantage over the typical approach based on a fixed GNC for estimating grain-N removal for individual site-years (root mean square error: 17 versus 21 kg N ha−1, respectively). Estimates of grain-N removal with both approaches were more reliable when aggregated at climate-soil domain level relative to estimates for individual site-years. [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]

Over-fertilization is economically and environmentally undesirable, and under-fertilization contributes to yield gaps. In dryland cropping systems, where precipitation is a major source of variation in yield, matching fertilizer to precipitation is critical. The aim of this study was to outline and test a method to match nitrogen (N), phosphorus (P), and potassium (K) fertilizer rate to precipitation for dryland winter wheat in the Loess Plateau of China. Based on field experiments at 52 sites from 2009 to 2013, the grain yield of winter wheat was found to increase quadratically with the precipitation in two periods: summer fallow, and summer fallow until jointing stage. The shoot N, P, and K nutrient uptake were linearly correlated with grain yield. Basal fertilizer requirement was calculated from target grain yield estimated as a function of fallow precipitation. The need for topdressing was determined by re-estimating target grain yield as a function of precipitation during summer fallow until jointing stage. Validation of this method using an additional dataset from long term studies in the same area suggested that adjusting fertilizer rates to summer fallow and summer fallow until jointing precipitation could correct the over application for N and P fertilizer, and deficient application for K fertilizer in the Loess Plateau. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is the primary driver of increased global food supply, but has environmental consequences from both under- and over-fertilisation. While over-fertilisation and reactive nitrogen release onto the environment is widespread in North America and Europe, under-fertilisation and soil mining prevail in South American croplands, calling for novel nitrogen-balancing strategies. The encroachment of soybean-centric, over-simplified cropping systems has eroded ecosystem services in South America. Here we compare the current soybean-centric system in Argentina with seven crop sequences in two long-term experiments started in 2008. Our aim was to identify alternative, more diverse crop sequences to maintain productivity and profitability with a close to neutral apparent N balance of the agroecosystem in two contrasting soils, i.e., a Mollisol and a Vertisol. Crop sequences combined locally adapted crops – soybean, maize and wheat for grain, field pea as cover crop – in a range from monocultures to complex sequences including all four crops. Crop sequence returned a 2.2–3.1-fold variation in productivity (from 4.7 to 10.9 Mg ha-1 in the Mollisol and from 3.4 to 9.9 Mg ha-1 in the Vertisol), 1.5-fold variation in profitability (from 0.92 to 2.14), variation in nitrogen balance from soil mining at − 35 kg N ha-1 year-1 to excess at 17 kg N ha-1 year-1, and a variation in nitrogen use efficiency at crop sequence level (NUE s) from 0.7 to 1.2 in both soil types. High soybean proportion reduced the NUE s and grain productivity of crop sequences. More complex crop sequences, i.e. including three/four crops, showed an N surplus and a similar grain yield than maize monoculture in both soils. The inclusion of maize into crop sequences with high cropping intensity increased both yield and NUE s. We identify new crop sequences that meet three conditions: high productivity and profitability, a close-to-neutral nitrogen balance, and a high nitrogen-use efficiency. These insights allow for alternatives to the current, unsustainable trajectories of simplified soybean-based systems that also avoid the path of over-fertilisation followed by cropping systems elsewhere. • We compare soybean monoculture with seven crop sequences in two long-term experiments in Argentina. • We identify crop sequences with high productivity, profitability, and nitrogen-use efficiency of the system (NUEs). • Most crop sequences had a negative apparent N balance, indicating soil mining. • High soybean proportion reduced the NUEs and grain productivity of crop sequences. • The use of maize in intensified cropping sequences increased both yield and NUEs. • More intensified cropping sequences increased N demand. [ABSTRACT FROM AUTHOR]

Annual crops accommodate environmental variation through grain number, whereas grain weight is more stable. Grain number is determined in a species-specific window which has been established for many crops, but not for oat. Field trials were established at two sites in southern Australia and in one site in southern Chile where successive, single 14-d shading periods were applied from crop establishment to maturity to identify the developmental window when the crop is most responsive to stress. Three oat varieties were compared in Australia (Mitika, Williams and Wintaroo) and two in Chile (Mitika and Yallara). Unshaded controls yielded from 327 g m −2 in Australia to 747 g m −2 in Chile. The overall pattern of yield response to time of stress was similar to that of wheat; it spanned the period from stem elongation (GS31) to about 10 days after anthesis. In line with theory, most of the yield response was mediated through response in grain number; further, the two environments in Australia where reduction in grain number in response to stress shortly before anthesis was larger, individual grain weight increased with shading. Grains per panicle was more responsive to stress than panicles per m 2 , in contrast to other cereals. The critical period is often assumed to be species-specific. However, our limited comparison of varieties suggests that there might also be varietal differences in oat. Interaction between time of shade and variety was significant for harvest index in all locations. Hence, we propose genotype-dependent response to time of stress is worth exploring. [ABSTRACT FROM AUTHOR]

Information regarding the pattern of sulphur (S) accumulation in shoots is scarce for field crops and few comprehensive analysis were performed on N:S stoichiometry. Particularly, the need to study the patterns of uptake, allocation and stoichiometry of S and N in soybean is two-fold. First, the main areas for soybean production in the world have been recently reported as S-deficient. Second, S concentration (%S) and N:S ratios are relevant for diagnosing S deficiency. The aim of this work was to analyze, in a gradient of S availability, the dynamics of nitrogen concentration (%N), %S and N:S ratio in soybean lamina, stem and shoots during vegetative growth. Experiments were performed at Balcarce, Argentina during two growing seasons. Two soybean cultivars were evaluated: DM2200 (maturity group II) and DM4970 (maturity group IV), sown in optimum dates for the region (mid-November). DM2200 was also sown late (early January). We sampled crops between biomass ≈ 1 Mg ha −1 and R5. Shoots were separated in lamina, stem and petiole, and pod. The adjusted S dilution curve for S-sufficient treatments was attenuated in soybean (S = 2.8 W −0.11 ), with no differences among cultivars of maturity groups II and IV, and sowing dates from November to January. For the same treatments, the N:S ratio was stable in shoots during vegetative growth (N:S = 12.2), supporting the use of a unique threshold for diagnosing the S status during this period. Sulphur concentration in stems was more responsive to the availability of S than%S in lamina. In addition, the concentration of N in stem tended to be constant with variation in %S while %N and %S correlated in lamina. This produced a greater response of N:S in stem than in lamina. Thus, the determination of%S and N:S in stem are good candidates as indicators of S status of soybean. [ABSTRACT FROM AUTHOR]