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Maintaining high crop yield and meanwhile reducing the risk of environmental pollution are of paramount importance for food security and sustainability. The aims of this study were (i) quantify soil NO3− -N buffer capacity under wheat-maize cropping system in Northern China, and (ii) establish agronomic optimum and environmentally safe N rates to guide N recommendation for the region. We compiled data of 76 sets of wheat and 73 sets of maize experiments spanning about 20 years, where N rate experiments conducted and soil NO3− -N content were measured immediately after crop harvest under conventional practice. By applying linear-plateau and plateau-linear models, we computed the soil NO3− -N buffer capacity, agronomic optimum N rate and environmentally safe N rates. Soil NO3− -N buffer capacity ranged from 10 to 221 kg ha−1 for wheat season and from 14 to 212 kg ha−1 for maize season, which were mostly less than 100 kg ha−1 in the region. The agronomic optimum N rates for wheat and maize were 46–221 and 44–250 kg N ha−1 with means of 110 and 127 kg N ha−1, respectively. The environmentally safe N rates were 19–248 kg N ha−1 with mean of 107 kg N ha−1 for wheat, and 36–209 kg N ha−1 with mean of 99 kg N ha−1 for maize. It was found that agronomic optimum N rates from 61% of wheat and 52% of maize were higher than the environmentally safe N rates, implying that current N recommendation had the high potential risk of nitrate leaching. Hence, it is suggested that N recommendation should consider not only the agronomic optimum N but also environmentally safe N rate, especially in areas where are vulnerable to nitrate leaching the latter should be placed at the top priority.

Management of nitrogen (N) fertilizer is critical to avoid the environmental consequences of both over-fertilization and excess reactive N in the system, and chronic under-fertilization and soil mining. Split N application seeks to improve nitrogen use efficiency in both small-holdings and large-scale mechanized farms, but lack of conclusive evidence on its benefits restricts the adoption of this practice. Here we report a global meta-analysis of split N application in wheat using 129 studies with 2661 comparisons. Split N in 3–4 applications improved yield by 7.0 % and grain protein by 5.2 % in relation to single application. The effect of split N on yield was larger for winter wheat than for spring wheat, while split N improved grain protein in both winter and spring wheat. Its effects on both yield and grain protein were larger under conventional tillage, in humid climate especially for winter wheat, in coarse textured soils, on less fertile soils, and at high N rate. Splitting N in 3–4 applications would increase annual production of winter wheat by 12.9 M t grain and 1.3 M t protein globally. By identifying the conditions where split N application is more likely to deliver agronomic benefits, our study would contribute to the targeted adoption of this practice.

Long-term (over 15 years) winter wheat (Triticum aestivum L.)–maize (Zea mays L.) crop rotation experiments were conducted to investigate the accumulation of phosphorus (P) at five sites differing geographically and climatically in China. The results showed that, in soils without P added, the concentration of soil P extracted by 0.5 mol L−1 NaHCO3 at pH 8.5 (Olsen-P) decreased with cultivation time until about 3 mg kg−1, afterwards it remained constant. The trend of decrease in Olsen-P in soils without P added could be described by an exponential function of time. The concentration of Olsen-P in soils with P fertilizers increased with cultivation time and the model of accumulation of Olsen-P in soils could be described using P application rate, crop yield and soil pH. The accumulation rate of Olsen-P in the long-term wheat–maize crop rotation experiments was 1.21 mg kg−1 year−1 on average. If the target yield of wheat and maize is 10 ton ha−1 in the soil with pH 8, the increasing rates of Olsen-P in soils as estimated by the model will be 0.06, 0.36, 0.66, 0.95, 1.25 and 1.55 mg kg−1 year−1 when P application rates are 30, 40, 50, 60, 70 and 80 kg P ha−1 year−1, respectively. The models of accumulation of Olsen-P in soils were validated independently and could be used for the accurate prediction of accumulation rate of Olsen-P in soils with wheat–maize rotation systems. Also the application of the model was discussed for best management of soil P in agricultural production and environment protection.

This study assessed changes in nitrogen (N) and phosphorus (P) uptake and partitioning in response to selection for yield in milestone varieties of Chinese winter wheat (Triticum aestivum L.). We established a factorial trial combining 11 nutrient–water regimes with three (2013–14) and five (2014–15) varieties released from 1970 to 2005. Grain yield increased at a rate of 0.46% year–1, with no apparent increase in the uptake of nutrients. Nitrogen harvest index did not change, and P harvest index increased at a rate of 0.15% year–1. Consequently, yield per unit N uptake and yield per unit P uptake increased at similar rates (0.4% year–1) at the expense of nutrient concentration in grain, which declined at a rate of 0.47% year–1 for N and 0.31% year–1 for P. No trends in N nutrition index were found. Selection for yield in wheat increased the yield per unit nutrient uptake at the expense of grain nutrient concentration. Further gains in yield need to be matched by increasing N uptake to maintain grain protein. Dilution of P in grain needs to be considered in terms of the putatively undesirable role of phytate for human nutrition, and the need for P reserves in seed for crop establishment.