Marginal nitrate leaching around the recommended nitrogen fertilizer rate in winter cereals

Optimum nitrogen (N) fertilization, which aims for high productivity while minimizing N losses to the environment, requires a better understanding of the N leaching behaviour around the recommended N rate. A study was conducted with increasing N fertilization levels over 3 years (2016-2019) with early and timely sown winter cereals (rye and wheat) at two sites in Denmark with different climatic conditions. For winter rye N fertilizer application rates ranged from 0 to 258 kg N ha(-1), and for winter wheat from 0 to 300 kg ha(-1). Grain yields did not respond much to the N application above the recommended rate. Nitrate (NO3) leaching was very low in the first period, but increased in the second and third period. The effect of a potential N carry-over on marginal N leaching (defined as the additional N leaching per unit of additional N fertilizer applied) is large. Under early sown winter rye, marginal N leaching is reduced from 36 to 14 kg N ha(-1) in the third period following N fertilization of the recommended rate of 170 kg N ha(-1) when carry-over was accounted for, and under the timely sown winter rye from 68 to 24 kg N ha(-1). Our results show that marginal N leaching around the recommended rate is almost linear at the study site, when carry-over is accounted for. Thus, the use of precision agriculture, with lower fertilization application rates to areas with high residual soil N, is less effective compared with sites, which have an exponential leaching behaviour.

Automated summary

This study conducted a three-year experiment in two different climatic conditions in Denmark to investigate the effects of nitrogen fertilization levels on grain yield and nitrogen leaching. The results showed that marginal nitrogen leaching around the recommended rate is almost linear with nitrogen carry-over.