Effects of a Single Biochar Application on Soil Carbon Storage and Water and Fertilizer Productivity of Drip-Irrigated, Film-Mulched Maize Production

Biochar is a widely recognized soil amendment used to improve soil physicochemical properties and crop productivity. However, its compositive effects on soil water, fertilizer, and carbon in cropping systems are not extensively understood. A two-year field study was conducted to investigate the influence of integrating maize-residue-derived biochar on evapotranspiration, water and fertilizer utilization efficiency, soil organic carbon (SOC) content, and soil carbon emissions in maize farming, employing drip irrigation in conjunction with film mulching. The treatments included the following three biochar amendments: 15 (B15); 30 (B30); and 45 (B45) t ha⁻¹. Biochar was exclusively incorporated prior to sowing during the initial year of the experiment, and no biochar was used as a control (CK). After two years, the biochar amendments, especially B30, improved crop water productivity and the partial factor productivities of nitrogen, phosphorus, and potassium fertilizer. Relative to CK, the biochar amendments significantly reduced soil CO₂ and CH₄ emissions during crop growth by 17.6–40.6% and −1.21–268.4%, respectively, averaged across two years. The best treatment effect was achieved by adding 15 t ha⁻¹ of biochar. The biochar needed replenishing in the third year for B30 and in the fourth year for B45 to increase the SOC content by 20 g kg⁻¹. An application rate of 22 metric tons per hectare of biochar is proposed to optimize water and fertilizer utilization efficiency, alongside augmenting the soil organic matter content, within maize farming under drip irrigation and mulching practices on sandy loam soil. However, the biochar must be added at 20 t ha⁻¹ in the third year to counterbalance soil carbon losses and improve SOC.