Plastic film mulching and biochar amendment enhance maize yield and nitrogen fertilizer use efficiency by reducing gaseous nitrogen losses

Simultaneously increasing the crop yield and nitrogen use efficiency in maize is challenging. Efficient management strategies such as plastic film mulching or biochar amendment are recognized as potential methods for overcoming this problem. However, no comprehensive studies have quantified how the addition of biochar combined with plastic film mulching might affect the crop productivity and N flow in agroecosystems. Therefore, we conducted a field experiment from 2018 to 2021 in the Loess Plateau region of China to evaluate the effects of adding biochar at two rates under traditional planting without mulching and plastic film mulched farmland (CK: no mulch or biochar; CKL: 4.5 t ha–1 biochar with no mulch; CKH: 9.0 t ha–1 biochar with no mulch; PM: plastic film mulch with no biochar; PML: plastic film mulch with 4.5 t ha–1 biochar; and PMH: plastic film mulch with 9.0 t ha–1 biochar) on the soil mineral nitrogen residual quantity (NO3–-N and NH4+-N), gaseous nitrogen loss (N2O and NH3), maize yield, and nitrogen use efficiency (NUE) in an agroecosystem. The results showed that plastic film mulching plus biochar amendment increased the maize yield by 13.9–45.1% and NUE by 12.1–74.8%, reduced the soil residual mineral nitrogen in the 0–200 cm soil layer at the maturity stage, and effectively decreased ammonia volatilization. Plastic film mulching increased the N2O flux by 12.1–26.9%, whereas biochar amendment decreased the N2O flux by 7.9–26.0%. Adding biochar at 9.0 t ha–1 (N2O: 14.9–29.1%; NH3: 16.4–28.6%) was more effective at reducing the N2O flux and NH3 volatilization than adding biochar at 4.5 t ha–1 (N2O: 6.9–13.7%; NH3: 3.0–16.0%). Among all of the treatments, plastic film mulching combined with biochar at 9.0 t ha–1 was most effective at increasing the maize yield and NUE, as well as decreasing ineffective N losses (gaseous N loss and N leaching), thereby reducing the risk of nitrogen losses from farmland. Mainly because the mulching measures and biochar amendment significantly promoted the growth of maize and the absorption of soil nitrogen. This soil management practice can achieve sustainable high yields with high efficiency in the Loess Plateau and regions with similar agroecosystems.