Regulation Effect of Biochar Combined with Slow-Release Fertilizer on Soil Water Use in Oasis Irrigation Area

To address water scarcity in oasis irrigation areas and issues such as excessive nitrogen fertilizer application and low water use efficiency in maize production, this study investigated the effects of biochar combined with slow-release fertilizers on maize soil water use characteristics under reduced nitrogen application, so as to provide the practical evidence for high maize yields and efficient water resource utilization.

A split-plot design was employed. The main plots featured soil conditioner (biochar (B)) and no conditioner (C). Split plots included two nitrogen fertilizer types: traditional chemical nitrogen fertilizer (T) and slow-release nitrogen fertilizer (S). Sub-split plots tested two nitrogen application rates: traditional nitrogen application rate (N2: 360 kg·hm^-2), and a 30% reduced traditional nitrogen application rate (N1: 252 kg·hm^-2). This study investigated the effects of biochar combined with slow-release fertilizer on maize yield, water consumption, and water use efficiency under reduced nitrogen application during the 2023-2024 growth season.

Applying biochar with slow-release fertilizer to reduce nitrogen application (BSN1) increased pre-sowing soil water storage capacity in nitrogen-reduced maize and lowered maize water consumption throughout its entire growth stage. Regarding pre-sowing soil water storage, biochar increased by 5.3%-6.5% compared with no conditioner; no significant differences were observed between slow-release fertilizer and traditional chemical nitrogen fertilizer, nor between reducted nitrogen application and traditional nitrogen application rates (P>0.05). Compared with traditional chemical nitrogen fertilizer application rate without soil conditioner (CTN2), BSN1 increased pre-sowing soil water storage by 11.1%-12.5%. Biochar reduced water consumption during the maize sowing to jointing stage and the big flare to flowering stage by 6.4%-6.7% and 4.6%-5.5%, respectively, though the evapotranspiration modulus showed no significant differences. Slow-release fertilizer reduced maize water consumption from sowing to maturity by 8.1%-10.0%, but only lowered the evapotranspiration modulus during the sowing to flowering stage. Reduced nitrogen application decreased water consumption during the big flare stage to flowering stage by 6.3%-7.5%, with no significant difference in the evapotranspiration modulus. Comprehensive analysis of soil conditioner, nitrogen fertilizer type, and nitrogen application rate showed that BSN1 reduced maize water consumption by 21.4%-29.5% and the evapotranspiration modulus by 6.3%-7.6% compared with CTN2 during the sowing to flowering stage, water consumption decreased by 8.0%-9.9% during flowering to maturity stage, while the evapotranspiration modulus showed an upward trend. The combination of biochar and slow-release fertilizer effectively coordinated water supply and demand during different growth stages of nitrogen-reduced maize. Consequently, maize under BSN1 exhibited a 13.6%-14.8% reduction in total water consumption compared with CTN2, with grain yield and water use efficiency increasing by 8.6%-9.1% and 24.1%-24.7%, respectively.

The application of biochar combined with slow-release fertilizer and reduced nitrogen rates significantly increased maize grain yield and water use efficiency compared with traditional chemical nitrogen fertilizers without soil conditioners at traditional nitrogen application levels. This approach served as a viable technology for nitrogen-saving, yield-enhancing, and water-efficient maize production in the Hexi Oasis irrigation areas.