Effects of Biochar Application before and after Freeze-Thaw on Soil Hydrothermal and Cotton Growth under Drip Irrigation

Abstract

Biochar as an organic soil conditioner has colossal application potential. Many recent studies revealed the influence of biochar on the soil during the crop growth period. However, few studies considered the effect of seasonal freeze-thaw on biochar’s improvement effect. Therefore, we conducted a field experiment to observe the impact of biochar on soil and cotton (Gossypium hirsutum L.). We used four biochar application rates (0.33%, 0.66%, 1.00%, and 1.33% of soil mass fraction) and applied biochar in the cotton field before and after seasonal freeze-thaw, respectively. The results showed that applying biochar after freeze-thaw was more effective on soil water storage and soil temperature preservation during the cotton growth period. Moreover, applying biochar with 0.66% soil mass fraction after freeze-thaw improved the cotton biomass by 5.31~36.13%, leaf area index by −10.82~32.52%, and seed cotton yield by 3.88~21.98%. Based on the principal component analysis of cotton fiber quality, we found that 0.66% biochar application after freeze-thaw improved cotton fiber most significantly. In total, applying biochar at 0.66% soil mass fraction after freeze-thaw was the most optimal application mode for improving soil hydrothermal conditions, cotton growth, and fiber quality. Our study can provide a scientific reference for applying biochar in northern Xinjiang, China.