Ridge-furrow film mulch with nitrogen fertilization improves grain yield of dryland maize by promoting root growth, plant nitrogen uptake and remobilization

Soil mulch has been widely applied to enhance crop yields in (semi-)arid and semi-humid regions on the globe. However, how different mulch practices influence root growth, plant nitrogen (N) uptake, remobilization and allocation remains unclear, especially under different N fertilization rates. A two-season (June–October in 2021 and 2022) field experiment was performed on dryland summer maize in a semi-humid but drought-prone region of northwest China. There were six mulch practices: flat cultivation without mulch (Flat), flat cultivation with straw mulch (Flat-Straw), flat cultivation with black film mulch (Flat-Film), flat cultivation with transparent film mulch (Flat-Trans), ridge-furrow cultivation with black film mulch on the ridge (Ridge-Film), ridge-furrow cultivation with transparent film mulch on the ridge (Ridge-Trans), and two N fertilization rates: 0 kg N ha−1 (N0) and 180 kg N ha−1 (N1). The results showed that film mulch significantly (p<0.05) improved root morphological parameters compared to Flat. Plant N uptake significantly (p<0.05) increased due to improved root growth under film and straw mulch, with grain N uptake increasing by 78.2% under Ridge-Film, 66.2% under Ridge-Trans and 39.6% under Flat-Film compared to Flat. The significant (p<0.01) increases in pre-anthesis N remobilization and post-anthesis N uptake under film and straw mulch compared to Flat achieved synergistic increases in grain yields. The contributions of total N remobilization to grain N dramatically increased by 31.2%, 27.5%, 17.0% and 11.2% under Ridge-Film, Ridge-Trans, Flat-Film and Flat-Trans compared to Flat, respectively. Meanwhile, film-mulched practices significantly (p<0.01) reduced soil nitrate-N residual due to improved plant N uptake, by 21.7% under Flat-Film, 16.9% under Flat-Trans, and 33.6% under Ridge-Film compared to Flat. The contributions of various mulch practices to grain yield ranked as Ridge-Film > Flat-Film > Ridge-Trans > Flat-Trans > Flat-Straw. The Ridge-Film with N fertilization significantly (p<0.05) increased N use efficiency, N agronomic efficiency, N recovery efficiency, N harvest index and grain yield by 10.8%, 124.9%, 147.1%, 19.8% and 120.0% compared to FlatN0, respectively. The structural equation modeling indicated that the differences in post-silking N uptake and pre-silking N remobilization caused by different mulch practices and nitrogen rates could directly explain at least 48.0% and 52.0% of grain yield differences. The ridge-furrow cultivation with film mulch, especially black film mulch, along with 180 kg N ha−1 is favorable for improving grain yield and N use efficiency of dryland summer maize in the semi-humid but drought-prone region of northwest China.