Soil testing at harvest to enhance productivity and reduce nitrate residues in dryland wheat production

The excessive application of fertilizer can inhibit the crop yield and decrease the nutrient use efficiency, as well as leading to nitrate-N residues in soils and other economic and environmental issues. In this study, an optimized method for fertilizer recommendation was developed based on soil testing at harvest of the previous crop. Multi-site and fixed location field experiments were conducted to assess this method from 2013 to 2016 in the typical dryland winter wheat (Triticum aestivum L.) production area of the Loess Plateau in China. Compared with the conventional fertilizer application (CFA), optimized fertilizer application (OFA) decreased the fertilizer application rates by 96 kg N ha−1 and 43 kg P2O5 ha−1, and the nitrate-N residues by 120 kg N ha−1 in the 0-100 cm soil layer, as well as increasing the winter wheat grain yield by 386 kg ha−1 and the economic returns by $ 230 ha−1 averaged across sites and years. Furthermore, the OFA method caused no changes in nitrogen (N), phosphorus (P), and potassium (K) uptake in wheat compared with CFA, but increased the harvest index by 4%, 3%, and 7% for N, P, and K, respectively. Averaged across years and sites, compared with CFA, the internal efficiency rate of N, P, and K under OFA were increased by 9%, 4%, and 8%, respectively, and the corresponding partial factor productivity for these nutrients also increased by 85%, 61%, and 31%. Thus, soil testing at harvest and determining fertilizer recommendations according to the proposed OFA method can decrease the fertilizer rates, as well as achieving a balance among the conflicting aims of environmental protection, crop yield increases, nutrient use efficiency, and improved economic benefits in dryland farming areas where the over-application of fertilizers occurs.