Ridge–furrow planting with film mulching and biochar addition can enhance the spring maize yield and water and nitrogen use efficiency by promoting root growth

Promoting root growth is essential for improving crop yields and the efficient use of soil nutrients, especially in dryland areas of the Loess Plateau in China where water resources are scarce and nitrogen utilization is low. Adding biochar is a potential strategy to enhance root growth and consequently increase crop productivity. In this study, we investigated the effects of adding biochar at 0.0 t ha–1, 4.5 t ha–1, and 9.0 t ha–1 on the growth and activity of roots, yield, and water and nitrogen use efficiency in spring maize under flat planting without film and ridge–furrow planting with film mulching. Adding biochar increased the root length density in spring maize by 7.1–13.8 %, root dry weight density by 4.8–9.2 %, root surface area density by 6.7–13.8 %, and root sap bleeding rate by 7.1–18.9 %, where the effects increased as the biochar application rate increased. Compared with flat planting without film mulching, the effect of adding biochar on the growth and activity of roots was more significant under ridge–furrow film mulching (P < 0.05), especially with biochar applied at 9.0 t ha–1. Ridge–furrow planting with film mulching and adding biochar at 9.0 t ha–1 increased the spring maize yield by 28.3 % and water use efficiency by 40.0 %. This method also increased the total nitrogen content of plants by 25.8 %, reduced the mineral nitrogen residue level in the 0–200 cm soil layer during the harvest period by 35.0 %, and increased the nitrogen use efficiency by 34.9 %. Therefore, the combination of ridge–furrow film mulching and adding biochar at 9.0 t ha–1 can be used as an efficient soil management practice for improving the utilization of water and nitrogen to possibly improve yields and facilitate the efficient utilization of resources in dry farmland areas of the Loess Plateau.