Application of biochar in saline soils enhances soil resilience and reduces greenhouse gas emissions in arid irrigation areas

Abstract

Quantifying soil health is crucial for evaluating and guiding soil management strategies. Soil salinization has become one of the main threats to soil health. However, the effects of biochar application on the improvement of saline soils and greenhouse gas emissions remain controversial. This study focused on spring maize fields in the Hetao Irrigation District and conducted a two-year field experiment from 2021 to 2022. Biochar derived from maize stalks at a pyrolysis temperature of 400℃ was a evenly spread over the soil surface, manually incorporated, and then rotary tilled to ensure thorough mixing within the 0–30 cm soil layer. Five field treatments were set up: CK (no fertilizer), BC0 (0 t ha⁻¹ biochar), BC7.5 (7.5 t ha⁻¹ biochar), BC15 (15.0 t ha⁻¹ biochar), and BC22.5 (22.5 t ha⁻¹ biochar). The results showed that appropriate biochar (15.0 t ha⁻¹) addition increased soil profile nitrate nitrogen content, 0–40 cm soil organic carbon and total nitrogen, 0–120 cm soil water storage (SWS) and electrical conductivity, as well as maize plant height, leaf area index, dry matter accumulation, grains per row, 100-grain weight, yield, and water use efficiency (WUE). However, excessive biochar application (22.5 t ha⁻¹) reduced the effectiveness of soil water storage, led to salt accumulation, decreased soil profile nitrate nitrogen content, and increased maize water consumption. Additionally, biochar application reduced N₂O emission peaks, N₂O emission factors, and cumulative emissions, while promoting soil CH₄ absorption. Biochar reduced cumulative soil CO₂ emissions, but excessive application (22.5 t ha⁻¹) increased CO₂ cumulative emissions. Sole nitrogen fertilizer application significantly increased global warming potential (GWP) and greenhouse gas emission intensity (GHGI), but the combination of nitrogen fertilizer and biochar significantly reduced GWP and GHGI. These findings provide a theoretical basis for improving the health of saline soils and mitigating climate change.