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Background and aims: During the fallow period, non-legume cover crop species can capture mineral nitrogen (N) and thus decrease nitrate leaching, whereas legume cover crop species can provide a green manuring service that increases N availability for the subsequent crop. The aim of our study was to investigate the ability of bispecific mixtures to simultaneously produce these two services of N management in relation to their interspecific interactions. Methods: Three field experiments were conducted at contrasting sites from summer to autumn to evaluate 25 mixtures and 10 sole crops. We measured biomass, N acquisition, C:N ratio and soil mineral N. Ecosystem services were assessed using both experimental data and simulation model predictions. Results: Overall, prediction of N mineralized from cover crop residues was significantly higher for mixtures than for non-legume sole crops. Predictions of nitrate leached after mixtures did not differ significantly from those after non-legume sole crops and remained significantly lower than those under bare soil, especially for mixtures with turnip rape which benefitted greatly from being in mixtures. Conclusions: Some of the mixtures provided a choice of compromises between the two ecosystem services, which helps define solutions for adapting mixture choice according to the site's soil and climate characteristics and to fallow period management. [ABSTRACT FROM AUTHOR]

France suffered, in 2016, the most extreme wheat yield decline in recent history, with some districts losing 55% yield. To attribute causes, we combined the largest coherent detailed wheat field experimental dataset with statistical and crop model techniques, climate information, and yield physiology. The 2016 yield was composed of up to 40% fewer grains that were up to 30% lighter than expected across eight research stations in France. The flowering stage was affected by prolonged cloud cover and heavy rainfall when 31% of the loss in grain yield was incurred from reduced solar radiation and 19% from floret damage. Grain filling was also affected as 26% of grain yield loss was caused by soil anoxia, 11% by fungal foliar diseases, and 10% by ear blight. Compounding climate effects caused the extreme yield decline. The likelihood of these compound factors recurring under future climate change is estimated to change with a higher frequency of extremely low wheat yields. [ABSTRACT FROM AUTHOR]

• Recent French bread wheat cultivars have an effect on Nitrogen Use Efficiency. • The genetic and agronomic indicators to assess it are consistent between them. • Cultivars differ in their capacity to achieve both yield and grain protein concentration for a given nitrogen rate. • Combined indicators to assess this cultivar capacity at the optimum nitrogen rate are proposed. Nitrogen (N) is an essential compound for the production and grain quality of bread wheat, which must respect market requirements. Improving nitrogen use efficiency (NUE) is a priority to better manage nitrogen for the benefit of farm economy and the environment. Among all the available levers to do this, the choice of the right cultivar is crucial. To this end, an accurate NUE cultivar characterization is needed both for breeding programmes and for agronomic extension services dedicated to advise farmers. These two fields of expertise (genetic and agronomy) do not share exactly the same protocols and indicators to assess the impact of cultivar on wheat NUE. Moreover, although some recent NUE genetic studies have been conducted on cultivars currently available in France, no recent NUE agronomic studies have been made on current French wheat cultivars. Moreover, the latest agronomic studies to date on cultivar effect on wheat N requirement (coefficient "b" used in France) were conducted without considering the need to reach a grain protein concentration of 11.5% (French bread wheat market requirement) in addition to the objective of achieving the yield potential. By using a classical agronomic protocol (network of 12 field trials over 3 years testing bread-wheat cultivars along a complete nitrogen response curve), the presented study aimed to address three specific NUE related topics by characterizing recent French cultivars with a large range of NUE indicators used by geneticists and/or agronomists. Firstly, we demonstrated that N rate and recent French cultivars had a significant effect on NUE and its components (nitrogen uptake efficiency – NupE and nitrogen utilization efficiency – NutE), as well as on apparent fertilizer recovery (AFR). Secondly, we showed that NupE and AFR were strongly correlated, allowing us to compare genetic studies (mainly using NupE) and agronomic studies (mainly using AFR) without any difficulty. Thirdly, we designed a set of new N requirement indicators (coefficients "bc" and "bq") helping the farmer to grow each bread wheat cultivar with a dual objective of optimum yield and grain protein content in line with the market requirements. This could be achieved without significant impact on nitrogen post-harvest losses. The presented study provides a large set of results, usable for breeding and agronomic research programs. [ABSTRACT FROM AUTHOR]

Key message: Clustering 24 environments in four contrasting nitrogen stress scenarios enabled the detection of genetic regions determining tolerance to nitrogen deficiency in European elite bread wheats. Increasing the nitrogen use efficiency of wheat varieties is an important goal for breeding. However, most genetic studies of wheat grown at different nitrogen levels in the field report significant interactions with the genotype. The chromosomal regions possibly involved in these interactions are largely unknown. The objective of this study was to quantify the response of elite bread wheat cultivars to different nitrogen field stress scenarios and identify genomic regions involved in this response. For this purpose, 212 elite bread wheat varieties were grown in a multi-environment trial at different nitrogen levels. Genomic regions associated with grain yield, protein concentration and grain protein deviation responses to nitrogen deficiency were identified. Environments were clustered according to adjusted means for grain yield, yield components and grain protein concentration. Four nitrogen availability scenarios were identified: optimal condition, moderate early deficiency, severe late deficiency, and severe continuous deficiency. A large range of tolerance to nitrogen deficiency was observed among varieties, which were ranked differently in different nitrogen deficiency scenarios. The well-known negative correlation between grain yield and grain protein concentration also existed between their respective tolerance indices. Interestingly, the tolerance indices for grain yield and grain protein deviation were either null or weakly positive meaning that breeding for the two traits should be less difficult than expected. Twenty-two QTL regions were identified for the tolerance indices. By selecting associated markers, these regions may be selected separately or combined to improve the tolerance to N deficiency within a breeding programme. [ABSTRACT FROM AUTHOR]

Nitrogen fertilization has been widely studied in wheat ( Triticum aestivum L .), with a view to maximizing local yields and obtaining high grain protein contents. It has long been accepted that nitrogen nutrition must be non-limiting throughout the crop cycle for these targets to be reached. However, studies over the last 20 years have shown that some periods of N deficiency are detrimental, whereas others have no impact on grain yield. There is, therefore, still a need to define the precise N deficiency path that can be tolerated. Nitrogen nutrition index (NNI) is an appropriate indicator of N deficiency. Based on experiments with wheat crops showing various patterns of NNI dynamics from the start of stem elongation to flowering, we aimed to identify a minimum nitrogen nutrition path, including periods of N deficiency, defining the threshold above which there is no detrimental impact on wheat crop yield. We used experimental data from 18 site-year experiments, each including 1–14 cultivars and 2–8 fertilization strategies, with determinations of crop NNI at four growth stages (Z30, Z32, Z39 and Z60 on the Zadoks scale). Experimental treatments were assigned to two groups: those with and without yield loss due to N fertilization strategy, relative to the maximum yield in each trial. Using receiver operating characteristics curve analysis, we identified the NNI path best distinguishing between the two groups of treatments. We found that the lowest acceptable NNI value (i.e. the lowest value for which there was no yield loss), increased during the crop cycle. We characterized, for the cultivars studied, periods of N deficiency during vegetative growth that did not lead to a decrease in yield or grain protein content, and even some periods in which the deficiency improved nitrogen use efficiency. Finally, we concluded that references in NNI should be revised for more efficient N management and the threshold NNI path could be used to determine timing of N fertilizer application on the basis of real-time crop N status monitoring. [ABSTRACT FROM AUTHOR]

The growing world population and global increases in the standard of living both result in an increasing demand for food, feed and other plant‐derived products. In the coming years, plant‐based research will be among the major drivers ensuring food security and the expansion of the bio‐based economy. Crop productivity is determined by several factors, including the available physical and agricultural resources, crop management, and the resource use efficiency, quality and intrinsic yield potential of the chosen crop. This review focuses on intrinsic yield potential, since understanding its determinants and their biological basis will allow to maximize the plant's potential in food and energy production. Yield potential is determined by a variety of complex traits that integrate strictly regulated processes and their underlying gene regulatory networks. Due to this inherent complexity, numerous potential targets have been identified that could be exploited to increase crop yield. These encompass diverse metabolic and physical processes at the cellular, organ and canopy level. We present an overview of some of the distinct biological processes considered to be crucial for yield determination that could further be exploited to improve future crop productivity. [ABSTRACT FROM AUTHOR]

Plant scientists and farmers are facing major challenges in providing food and nutritional security for a growing population, while preserving natural resources and biodiversity. Moreover, this should be done while adapting agriculture to climate change and by reducing its carbon footprint. To address these challenges, there is an urgent need to breed crops that are more resilient to suboptimal environments. Huge progress has recently been made in understanding the physiological, genetic and molecular bases of plant nutrition and environmental responses, paving the way towards a more sustainable agriculture. In this review, we present an overview of these progresses and strategies that could be developed to increase plant nutrient use efficiency and tolerance to abiotic stresses. As illustrated by many examples, they already led to promising achievements and crop improvements. Here, we focus on nitrogen and phosphate uptake and use efficiency and on adaptation to drought, salinity and heat stress. These examples first show the necessity of deepening our physiological and molecular understanding of plant environmental responses. In particular, more attention should be paid to investigate stress combinations and stress recovery and acclimation that have been largely neglected to date. It will be necessary to extend these approaches from model plants to crops, to unravel the relevant molecular targets of biotechnological or genetic strategies directly in these species. Similarly, sustained efforts should be done for further exploring the genetic resources available in these species, as well as in wild species adapted to unfavourable environments. Finally, technological developments will be required to breed crops that are more resilient and efficient. This especially relates to the development of multiscale phenotyping under field conditions and a wide range of environments, and use of modelling and big data management to handle the huge amount of information provided by the new molecular, genetic and phenotyping techniques. [ABSTRACT FROM AUTHOR]

Wheat occupies a special role in global food security since, in addition to providing 20% of our carbohydrates and protein, almost 25% of the global production is traded internationally. The importance of wheat for food security was recognised by the Chief Agricultural Scientists of the G20 group of countries when they endorsed the establishment of the Wheat Initiative in 2011. The Wheat Initiative was tasked with supporting the wheat research community by facilitating collaboration, information and resource sharing and helping to build the capacity to address challenges facing production in an increasingly variable environment. Many countries invest in wheat research. Innovations in wheat breeding and agronomy have delivered enormous gains over the past few decades, with the average global yield increasing from just over 1 tonne per hectare in the early 1960s to around 3.5 tonnes in the past decade. These gains are threatened by climate change, the rapidly rising financial and environmental costs of fertilizer, and pesticides, combined with declines in water availability for irrigation in many regions. The international wheat research community has worked to identify major opportunities to help ensure that global wheat production can meet demand. The outcomes of these discussions are presented in this paper. [ABSTRACT FROM AUTHOR]

Cover crops are used during fallow periods to produce ecosystem services, especially those related to N management such as (i) capturing mineral-N from soil to reduce nitrate leaching, and (ii) improving N availability for the next main crop (green manuring). Bispecific mixtures consisting of legume and non-legume species could simultaneously produce these two services of nitrate saving and green manuring. The magnitude of these services can be estimated from indicators of agroecosystem functions such as crop growth rate, crop N acquisition rate and the C:N ratio of the cover crop. We developed a conceptual model for each indicator which was described using general linear models. A three-step procedure was used: (1) represent the behavior of each species based on a sub-model and calibrate each species in bispecific mixtures; (2) validate the complete-mixture models, corresponding to the sum of the two species sub-models, and the proportion of each species in the whole cover, and (3) validate the generality of sub-models and complete-mixture models to predict the agroecosystem function indicators of species in mixture not used for calibration. The combined use of (i) potential agroecosystem functions measured in sole crop in non-limiting conditions, (ii) difference in leaf functional traits, as indicators of plant strategies and (iii) environmental factors, was efficient in fitting and predicting the level of agroecosystem functions provided by a cover crop species in mixture in actual conditions. The models fitted for bispecific mixtures were efficient to represent the behavior of each species in mixture and to estimate the legume proportion which expressed the species dominance. The models were evaluated as satisfactory for crop growth rate and C:N ratio for their generality in predicting the agroecosystem functions provided in mixtures by other species not used in the model calibration step, which illustrates the relevance and robustness of the approach. [ABSTRACT FROM AUTHOR]

A growing world population as well as the need to enhance sustainability and health create challenges for crop breeding. To address these challenges, not only quantitative but also qualitative improvements are needed, especially regarding the macro‐ and micronutrient composition and content. In this review, we describe different examples of how the nutritional quality of crops and the bioavailability of individual nutrients can be optimised. We focus on increasing protein content, the use of alternative protein crops and improving protein functionality. Furthermore, approaches to enhance the content of vitamins and minerals as well as healthy specialised metabolites and long‐chain polyunsaturated fatty acids are considered. In addition, methods to reduce antinutrients and toxins are presented. These approaches could help to decrease the 'hidden hunger' caused by micronutrient deficiencies. Furthermore, a more diverse crop range with improved nutritional profile could help to shift to healthier and more sustainable plant‐based diets. [ABSTRACT FROM AUTHOR]

Wheat phenology allows escape from seasonal abiotic stresses including frosts and high temperatures, the latter being forecast to increase with climate change. The use of marker-based crop models to identify ideotypes has been proposed to select genotypes adapted to specific weather and management conditions and anticipate climate change. In this study, a marker-based crop model for wheat phenology was calibrated and tested. Climate analysis of 30 years of historical weather data in 72 locations representing the main wheat production areas in France was performed. We carried out marker-based crop model simulations for 1019 wheat cultivars and three sowing dates, which allowed calculation of genotypic stress avoidance frequencies of frost and heat stress and identification of ideotypes. The phenology marker-based crop model allowed prediction of large genotypic variations for the beginning of stem elongation (GS30) and heading date (GS55). Prediction accuracy was assessed using untested genotypes and environments, and showed median genotype prediction errors of 8.5 and 4.2 days for GS30 and GS55, respectively. Climate analysis allowed the definition of a low risk period for each location based on the distribution of the last frost and first heat days. Clustering of locations showed three groups with contrasting levels of frost and heat risks. Marker-based crop model simulations showed the need to optimize the genotype depending on sowing date, particularly in high risk environments. An empirical validation of the approach showed that it holds good promises to improve frost and heat stress avoidance. [ABSTRACT FROM AUTHOR]

While concerns about human-induced effects on the Earth's climate have mainly concentrated on carbon dioxide (CO2) and methane (CH4), reducing anthropogenic nitrous oxide (N2O) flux, mainly of agricultural origin, also represents an opportunity for substantial mitigation. To develop a solution that induces neither the transfer of nitrogen pollution nor decreases agricultural production, we specifically investigated the last step of the denitrification pathway, the N2O reduction path, in soils. We first observed that this path is mainly driven by soil pH and is progressively inhibited when pH is lower than 6.8. During field experiments, we observed that liming acidic soils to neutrality made N2O reduction more efficient and decreased soil N2O emissions. As we estimated acidic fertilized soils to represent 37% [27–50%] of French soils, we calculated that liming could potentially decrease France's total N2O emissions by 15.7% [8.3–21.2%]. Nevertheless, due to the different possible other impacts of liming, we currently recommend that the deployment of this solution to mitigate N2O emission should be based on local studies that take into account agronomic, environmental and economic aspects. [ABSTRACT FROM AUTHOR]

Improved assessment and prediction of net nitrogen mineralization (NNM) from soil organic matter in field conditions are essential for a better management of nitrogen (N) in arable cropping systems and an accurate simulation of its seasonal dynamics. The first objective of this study was to quantify accurately NNM rates by combining measurements of soil water and mineral N contents in soil profile, daily weather data and the LIXIM calculation model (Mary et al., 1999). The second objective was to develop a predictive model of in situ NNM rates based on basic soil properties and to evaluate if additional factors related to cropping history, organic matter fractions or microbial biomass could improve the model performance. We selected a set of 65 field experiments representative of arable cropping systems in France which were carried out in bare fallow soils without recent addition of crop residue (minimal delay of 4 months) or organic amendment. In these experiments, soil water and mineral N contents were monitored over the soil profile (0–90 to 0–150 cm depth, 3 to 5 layers) during 100–555 days (median value of 272 days). LIXIM was able to satisfactorily simulate water ( EF = 0.58) and mineral N contents ( EF = 0.80) in the several layers, allowing to disentangle the two main processes involved in mineral N changes: NNM (occurring in the upper soil layer) and nitrate transfer (through the whole soil profile). The actual NNM rates varied widely between sites from 0.13 to 1.10 kg N ha −1 day −1 . The potential NNM rates ( Vp ), calculated under standard conditions of water and temperature, varied between 0.17 and 1.67 kg N ha −1 nday −1 (nday = “normalized” day at 15 °C and field capacity). A novel model with a multiplicative structure and a sequential approach was developed by including functions explaining the relationship between mineralization rate Vp (predicted variable) and explanatory variables. Soil organic N (SON) was the most correlated variable with Vp ( r = 0.51, p < 0.001) and the first variable introduced in the model as a linear function. Non-linear functions of soil clay content, pH, C/N ratio and CaCO 3 content were successively introduced, leading to a “soil model” based on five basic soil parameters that allowed explaining 61% of the variance in Vp . Two functions relative to the frequency of rapeseed and legumes in rotations were found to further improve the predictive quality of the soil model, explaining finally 72% of Vp variance (“soil-history model”). Organic matter fractions (particulate or extractible organic matter) did not explain significantly more variance of Vp due to their strong correlations with SON. Microbial biomass explained only 2% additional variance in Vp compared to the “soil-history model”. The predictive error of prediction ( RMSEP ) varied between 0.22, 0.19 and 0.17 kg N ha −1 nday −1 for the “soil” ( n = 65), “soil-history” ( n = 65) and “soil-history-biological” ( n = 47) models. This multiplicative, non-linear approach performed better than a multiple linear regression approach which explained 10–15% less variance of Vp when using the same explanatory variables. The models based on soil properties and cropping history could be further implemented in multidisciplinary soil-crop models and decision support systems in order to enhance the prediction of N dynamics in soils and improve fertilizer recommendations. [ABSTRACT FROM AUTHOR]

Agricultural management practices including soil tillage exert strong control on soil organic matter (SOM) turnover and its interactions with global C cycle through different mechanisms. One control mechanism is the priming effect (PE) which consists in stimulating SOM mineralization with the addition of fresh, energetic plant material. In this study, we quantified C mineralization and PE in soils sampled in two contrasted long-term (40 years) tillage treatments which deeply modified soil properties (e.g. organic C concentration, microbial biomass, pH). We hypothesized that soil tillage might affect these processes through changes in C addition rates, nutrient availability, and long-term variations in SOM content and microbial communities. We investigated the relationship between PE intensity, tillage and nutrients availability in soil samples taken in no till (NT) and full inversion tillage (FIT) in two layers (0-5 and 15-20 cm). Soils were incubated with or without addition of 13C labeled cellulose and mineral nutrients. Potential C mineralization and primed C were measured during 262 days. Unlabeled soil microbial biomass C was determined at the end of the experiment to separate apparent and real priming effect. Basal cumulative C mineralization in the control soil ranged from 363 to 1490 mg kg−1 soil at day 262. It was strongly correlated with soil organic carbon (SOC) concentration. Specific mineralization rates were 44.8 and 68.8 g kg−1 SOC in the 0-5 cm layer for the FIT and NT treatments, respectively and were strongly linked with the particulate organic matter content (r = 0.99***). These results suggest that SOC was more active in the upper layer of the NT treatment due to the high concentration of readily-decomposable, particulate organic matter. The cellulose was entirely metabolized after 60 days and its kinetics of mineralization was affected neither by tillage, depth nor nutrients. The percentage of cellulose C released as CO2 represented 55-61% of the added cellulose-C at day 262. A positive PE was found in all treatments and its kinetics was parallel to that of cellulose mineralization. The cumulative PE significantly varied with nutrients level but not tillage, ranging from 73 to 78 mg kg−1 under high nutrients level and from 116 to 136 mg kg−1 in low nutrients level. No significant differences were found in unlabeled microbial biomass C between control and amended soil, suggesting no apparent priming effect. We conclude that the priming was mainly controlled by nutrient availability but not tillage, in spite of strong tillage-induced changes in SOC concentration and microbial biomass. Since PE is known to depend on C addition rate, tillage is expected to affect in situ PE through variations in the ratio of fresh carbon to nutrient concentration along the soil profile. [ABSTRACT FROM AUTHOR]

Highlights: [•] 40 years of full inversion, shallow or no-tillage lead to similar SOC stocks over the ploughed layer or down to 60cm. [•] In the reduced tillage treatments, SOC accumulated in the upper layer (0–10cm) but declined continuously below 10cm. [•] The amount of C sequestered due to reduced tillage followed a non-monotonic pattern over time. [•] Changes in SOC over time in the upper layer of no-till were negatively correlated with the water balance. [•] C sequestration rate was positive in dry periods and negative in wet conditions. [ABSTRACT FROM AUTHOR]

Catch crops can effectively decrease nitrate leaching in arable cropping systems but their long-term impacts on nitrogen mineralization are not well known. This study quantified the effects of continuous catch crops on net N mineralization, crop N uptake, crop N use efficiency and N leaching in three long-term (13-17 years) field experiments in northern France. Mustard was grown every year at Boigneville, radish every year at Thibie and ryegrass every 2 years at Kerlavic. The mean N content of catch crop residues at these sites was 33, 36 and 35 kg ha yr and their mean C:N ratio was 13, 17 and 28, respectively. Net mineralization was calculated with a mass balance of soil mineral N using measured inputs and outputs. Catch crop establishment enhanced annual mineralization by on average 26, 18 and 9 kg N ha yr respectively during the 13-17 year period. The difference in mineralization rate between catch crop and control treatments (extra mineralization) was positive from the first year at Boigneville, whereas it was negative or nil during the first 3-5 years at Thibie and Kerlavic. At the latter sites, the extra mineralization rate increased significantly over time at a rate of 2.0 and 2.6 kg N ha yr. At the end of the experiment, cumulative extra mineralization represented 72%, 60% and 23% of the total N added by catch crop residues at Boigneville, Thibie and Kerlavic, respectively. Repeated catch crops significantly increased N uptake and N use efficiency by main crops at Kerlavic and Thibie, but not at Boigneville. The efficiency of catch crops in reducing N leaching persisted over the years at all sites. A model simulating C and N dynamics during catch crop decomposition was able to reproduce the pattern of extra N mineralization kinetics with the various catch crop species, but underestimated the range of variation between sites. Better predictions were obtained when C or N inputs due to catch crops were increased by 10-57%, suggesting that the actual inputs could be markedly greater than those measured in catch crop residues. According to the model, the C:N ratio of catch crop residues largely explained differences in mineralization due to different catch crop species. [ABSTRACT FROM AUTHOR]