Objectives In order to seek an environmentally friendly strategy that takes into account the improvement of grain yield and the utilization of agricultural waste resources, this study combined the application of water and fertilizer integration technology in arid and semi-arid areas, systematically evaluated the effect of biogas slurry instead of chemical fertilizer on nutrient balance, accumulation and yield of maize by drip irrigation, and provided a theoretical basis for the utilization of biogas slurry.

Methods A field experiment was conducted at the National Field Scientific Observation and Research Station of Shouyang Dryland Agricultural Ecosystem in Shanxi Province for two consecutive years. Under the same total nitrogen, phosphorus and potassium input and equal nitrogen topdressing amount, three treatments were set up : pure biogas slurry topdressing (BS); 50% chemical fertilizer topdressing + 50% biogas slurry topdressing (BC); pure chemical fertilizer topdressing (CF) and no topdressing (CK) were set up at V6 and V12 stages of maize. Leaf length, leaf width and relative chlorophyll content ( SPAD ) were measured, dry matter (DM) and N, P and K contents of aboveground organs were measured at different growth stages of maize. Leaf area index (LAI), nutrient stoichiometric ratio and nutrient use efficiency were calculated, and yield was measured at maturity stage.

Results Compared with CF treatment, BS and BC treatments significantly increased LAI and SPAD during the growth period of maize, and the LAI and SPAD of BS treatment at multiple growth stages were also significantly higher than those of BC treatment. During the two-year trial period, the maize yield, grain N, P and K contents of BS treatment were 20.56%, 19.76%, 46.05% and 55.07% higher than those of CF treatment, respectively, and Compared with CF treatment, BC treatment increased maize yield, grain N, P and K contents by 11.09%, 6.47%, 7.66% and 9.02%, respectively. The BS treatment was significantly higher than BC and CF treatments. BS and BC treatments significantly promoted the accumulation of dry matter and N, P and K nutrients in multiple organs during the growth period of maize plants, reduced the N/P stoichiometric ratios of leaves at V6 and V2 stages, and the N/P stoichiometric ratio of grains at maturity stage, indicating that the application of biogas slurry reduced the risk of N limitation in the vegetative period and increased the nitrogen storage capacity of grains at maturity stage, compared with the application of chemical fertilizer. Correlation analysis showed that N/K was significantly negatively correlated with yield and grain N content in the whole growth period (P<0.05), and N/P was significantly positively correlated with yield in R6 period (P<0.05), indicating that lower N/K in vegetative growth period was beneficial to the construction of photosynthetic organs, while suitable N/P in R6 period guaranteed the synergistic accumulation of grain nutrients, and N/K was the key stoichiometric factor regulating the yield formation of dryland maize.

Conclusions The application of biogas slurry instead of chemical fertilizer is more conducive to increasing the chlorophyll content and leaf area index of maize leaves as soon as possible, prolonging the leaf function period, greatly improving the agronomic efficiency and nutrient recovery rate of N, P and K nutrients, reducing the risk of nitrogen limitation during the growth period, and thus increasing the yield of maize. The yield increase and nutrient absorption and utilization effect of pure biogas slurry topdressing were better than that of 50% biogas slurry instead of chemical fertilizer topdressing. Therefore, it is not only an effective measure for topdressing with the help of water and fertilizer integration equipment in arid and semi-arid areas, but also an efficient way to reduce chemical fertilizer application and realize the recycling of agricultural waste resources.