Effects of digested biogas slurry applicationmixed with irrigation water on nitrate leaching during wheat-maize rotation in the North China Plain

Abstract

Nitrate leaching is an important pathway for nitrogen loss in soil and is becoming a public issue worldwide. The increasing application of both synthetic chemical fertilizers and digested biogas slurry (DBGS) as sources of nitrogen to farm fields in rural China has created new challenges regarding nitrate leaching. This study evaluated the effects of conventional fertilizers replaced by different nitrogen concentrations of dairy-sourced DBGS on nitrate leaching. A three-year field experiment from October 2013 to October 2016 on wheat-maize crop rotation was conducted using five levels of nitrogen application: a control (no nitrogen added), three concentrations of DBGS, and conventional chemical fertilizers. DBGS was applied through mixed with different percentage of fresh water to irrigate. Grain yield, soil nitrate accumulation, nitrate leaching loss, and the overall nitrogen budgetwere monitored. Yields of wheat and maize were generally increased with the increase in DBGS concentration amount up to the medium level, after that no significant increase in yield was found with further increase in DBGS application. Annual nitrate leaching reached 46-53 kg ha−1 from chemical fertilizer but declined by 20–32% using the medium DBGS concentration. Nitrate leaching mainly occurred after irrigation and heavy rainfall. The nitrate concentration in leachate and the nitrate leaching flux both increased with the increase in DBGS concentration, generally peaking 7–10 days after application. The results showed that the overuse of nitrogen resulting in the high net mineralization and nitrification and together with irrigation management, seasonal rainfall and soil texture influenced the nitrate leaching losses in this double cropping system. Using medium concentration of DBGS to replace chemical fertilizers is an reasonable approach to ensure high crop yields, high nitrogen use efficiency and reduced nitrate leaching losses.