Impact of Biochar Application and Nitrogen Fertilization on Soil Aggregates and Aggregate Organic Carbon in Irrigated Areas of Northern Xinjiang

This study evaluates the impact of applying biochar alongside nitrogen fertilizer on soil aggregates and aggregate-associated carbon through a two-year experiment under irrigated conditions in North Xinjiang. In 2021, a randomized block design established 36 experimental plots. The experiment employed a factorial design with three levels of nitrogen fertilizer and four levels of biochar. Measurements of soil aggregates and aggregate-associated organic carbon were taken in 2022. This study’s objectives were to quantify biochar’s effect on soil aggregation and stability and to determine the distribution of SOC across different aggregate sizes. The results indicated that macroaggregates (>2 mm and 0.25–2 mm) were most common (N2B1, N2B2, and N2B3), making up 75.57–78.46% of all aggregates. In treatments with reduced nitrogen and biochar (N2B1, N2B2, and N2B3), soil aggregate refractory organic carbon content was significantly higher compared to other treatments. Generally, applying reduced nitrogen with moderate biochar (N2B2) significantly increased soil organic carbon and refractory organic carbon levels, aiding carbon fixation and improving soil carbon storage. Thus, biochar application effectively enhances carbon storage in agricultural soils, offering valuable insights for improving soil fertility in irrigated regions of northern Xinjiang.