Response of yield and nitrogen use efficiency of maize with plastic mulching to straw returning and nitrogen reduction in the dryland region of the Loess Plateau of Gansu eastern

This study was conducted to investigate the effects of straw return with nitrogenous fertilizer reduction on the yield, soil nitrogen forms, and nitrogen use efficiency (NUE) of film-mulched maize to identify strategies for reducing nitrogen fertilization while increasing the efficiency of agricultural green development in the dryland region of the Loess Plateau of eastern Gansu Province. The 5-year long-term fixed field experiment involved six treatments with three replicates: no nitrogen and phosphate fertilizer and no straw return (control, CK); 225 kg·ha⁻¹ and no straw return (F); straw return and no nitrogen (TS); 225 kg·ha⁻¹ and straw return (F + TS); 180 kg·ha⁻¹ and straw return (80%F + TS); and 135 kg·ha⁻¹ and straw return (60%F + TS). Results showed that the 80%F + TS treatment increased the grain yield by 22.1% in the second year but decreased the grain yield from the third to fifth year, while the 60%F + TS treatment increased the grain yield in the first three years but reduced the grain yield in the fourth year. The 80%F + TS treatment significantly increased (P < 0.05) the cumulative grain yield by 6.8% compared with the F + TS treatment. Compared with the F + TS treatment, the 80%F + TS treatment also significantly increased (P < 0.05) the nitrate nitrogen content, significantly decreased (P < 0.05) the organic matter and NO₃⁻-N content, significantly decreased (P < 0.05) the contents of total nitrogen and NO₃⁻-N content, significantly increased (P < 0.05) the organic matter and nitrate nitrogen content in deep soil (20 − 40 cm), but did not significantly change the total nitrogen content in the topsoil (0 − 20 cm) (P > 0.05). In addition, the 80%F + TS treatment improved (P < 0.05) the N use efficiency by 23.7% and 22.1% in 2019 and 2020 compared with the F + TS treatment, respectively. Therefore, straw return in the amount of 9000 kg·ha⁻¹ could be used to replace 20% of the chemical nitrogen fertilizer use, which represents the optimal mode for reducing fertilization while increasing efficiency in the dryland region of the Loess Plateau of eastern Gansu Province.