Incorporating straw-derived biochars enhances soil nitrogen accumulation and mitigates nitrogen leaching to facilitates crop productivity of mulching farmland in semiarid regions

The long-term use of film mulching and conventional chemical fertilizers in semiarid regions has resulted in soil degradation and suboptimal fertilizer utilization, necessitating a reevaluation of agricultural practices to enhance resource utilization efficiency and ensure the sustainability of dryland crop production. We conducted a 5-year study (2017–2021) field experiment in northwest of China, to assess the impact of straw or biochar incorporation on soil water accumulation, crop nitrogen transport, and maize yield under film mulching field. The experiment had six treatments (flat planting without mulching [NN], flat planting with straw incorporation [NS], flat planting with biochar incorporation [NB], film mulching [MN], film mulching with straw incorporation [MS], and film mulching with biochar incorporation [MB]). We undertook a comprehensive assessment over the two growing seasons in 2020–2021. The film mulching and straw/biochar treatments improved soil water storage. The MB treatment significantly decreased 60–200 cm soil NO₃⁻-N content by 28.37% compared with MN. Biochar incorporation significantly increased soil total and alkali-hydrolyzable N contents, whereas MS decreased soil alkali-hydrolyzable N content compared with MN. The maize plant N transportation and grain contribution rates were significantly higher under MS (17.46% and 29.84%) and MB (28.00% and 31.69%) than under MN, respectively. Straw and biochar incorporation significantly increased water use efficiency, nitrogen fertilizer recovery efficiency, and maize yield, on average, by 9.62%, 9.14%, and 14.6%, respectively. In conclusion, incorporating biochar, in particular, positively mitigated N losses, enhanced N utilization efficiency, and increased maize yield in long-term film mulching farmland in semiarid region.