Effect of different agricultural measures on soil water and NO₃^–-N leaching and accumulation in cropland of the Loess Plateau

Objectives Fertilization and plastic film mulching affect soil water and fertilizer use efficiencies, the NO₃^–-N leaching as well as winter wheat yields. This study compared the effects of different measurements to provide support to pursue suitable measures for sustainable development in the Loess Plateau.

Methods A winter wheat field experiment was conducted in the dryland in Weibei since 2002. Seven treatments were tested, i.e., no fertilization control (CK), N and P fertilization (NP), NPK fertilization (NPK), NP plus biochar (NPB), NP and full plastic film mulching in summer fallow period (NPFFT), NP and full plastic film mulching in growth period (NPFGT), and NP and full plastic-film mulching in a whole year (NPFWT). Plowing after harvests and before winter wheat sowing was performed in all seven treatments. Accumulation of soil NO₃^–-N at the winter wheat harvest stage for 15 years and soil water contents in the growing season were investigated.

Results Compared with the CK, the NP significantly increased the accumulation of NO₃^–-N in 0–300 cm soil layers, which was 6.1 folds of the CK. Compared with the NP, the NPFGT, NPB, NPK and NPFWT significantly reduced soil NO₃^–-N accumulation by 78.7%, 73.2%, 66.0% and 59.7%, respectively. Although the soil NO₃^–-N accumulation of the NPFFT was not significantly different from that of NP, it also decreased by 19.2%. Compared with the CK, the NP had no significant effect on water recharge and depletion in 0–300 cm soil layers. Compared with the NP, the NPK and NPB had also no significant effect on water recharge and depletion in 0–300 cm soil layers, while the NPFFT, NPFGT and NPFWT significantly increased soil water recharge, of which the only NPFFT significantly increased soil water depletion. Nitrate accumulation in soil was affected by soil water movement, and its accumulation in soil increased with the increase of water recharge. Soil water movement significantly affected the distribution of NO₃^–-N in soil profile. The effect was that the NPFGT and NPB were mainly distributed in 0–20 cm soil layer, the NPK and NPFWT were mainly distributed in 0–100 cm soil layers, while the NP and NPFFT mainly distributed in 0–200 cm soil layer, of which the NPK, NPFWT, NPFFT and NP exhibited nitrate-nitrogen accumulation peaks.

Conclusions Different agricultural cultivation measures could reduce the leaching of NO₃^–-N by controlling soil water content, and thus improve the nitrogen utilization efficiency. The NPFGT effectively reduced the leaching and accumulation of NO₃^–-N and regulated soil water movement, which was an appropriate measure for improving the condition of soil water and fertilizer, and increasing winter wheat yields in the dryland.