Biogas slurry topdressing as replacement of chemical fertilizers boosts water and nitrogen use efficiency and yield in semiarid rainfed field crops

Biogas slurry (BS) is used as an organic liquid fertilizer for basal fertilization in semiarid regions. However, a single fertilization with basal fertilizer may reduce water and nitrogen use efficiency, which could negatively affect overall crop yield. This study proposes an innovative approach to enhance the water and nitrogen use efficiency and crop yield in semiarid areas by substituting chemical fertilizers with BS topdressing (SCFT). Based on the premise of equal nitrogen substitution, a maize field experiment was conducted in Shanxi Province, a typical semiarid region of China, using five concentrations of biogas slurry as nitrogen fertilizer (substitution ratios=0 %, 25 %, 50 %, 75 %, and 100 %) for topdressing. Quantified measurements of soil water and nitrogen content, crop physiological growth indicators, and yield in 2021 and 2022.The results showed that the soil moisture content was significantly increased within 5 %, and the content of ammonium nitrogen and nitrate nitrogen in maize root layer was also increased in the short term after topdressing. However, ammonium nitrogen content tends to align with soil moisture content, and significant changes will occur only in the short term after topdressing. SCFT could significantly promote the growth and development of maize, especially with 100 % is used, which showed the most significant effects. Compared to pure chemical fertilizer, SCFT increased plant height, diameter and leaf area index by approximately 10 %, and improved SPAD value, dry matter quality, and nitrogen uptake by approximately 50 %, 30 % and 20 %, respectively. These changes increased crop yield, water-use efficiency, and nitrogen use efficiency by 16.86–26.47 %, 4–6 kg/(ha·mm) and 16.86–26.47 %, respectively. SCFT can improve water and nitrogen use efficiency as well as crop yield in semiarid regions, and the positive effects of SCFT were demonstrated to have an annual cumulative impact. • Applying BS topdressing is a new technique in organic fertilizer management. • Substituting chemical fertilizers with BS topdressing can enhance yield and improve water and nitrogen use efficiency. • Substituting chemical fertilizers with BS topdressing increased soil moisture content in the main root zone. • Substituting chemical fertilizers with BS topdressing prolongs the growth cycle of maize. • Substituting chemical fertilizers with BS topdressing exhibits an annual cumulative effect.