Characterization of Cotton Stalk Biochar Using Fast and Slow Pyrolysis and Its Effect on Soil Water Holding Capacity

Biochar was prepared by fast and slow pyrolysis methods using Xinjiang cotton stalk as biomass at the pyrolysis temperature of 300∼700 ℃. The effects of fast and slow pyrolysis methods on the morphology, structure, functional groups, pH value, and elemental composition of biochar have been studied. The effect of biochar prepared under different conditions on soil moisture capacity was studied using indoor soil column experiments. The results showed that: 1) The biochar yield decreased, the pH value and the porosity increased with increasing pyrolysis temperature. Fast pyrolysis biochar has the advantages of well-developed pores, high aromaticity, and strong stability. 2) The soil water holding capacity increases with the increase of biochar addition and pyrolysis temperature. When the amount of biochar addition was 0.03 g/g, the soil water holding capacity was 51.7% and 49.7%, respectively, which was 32.5% and 27.4% higher than that without biochar. 3) The water retention of soil with biochar addition is much higher than that of pure soil. The soil added with biochar still retains 40.3% water retention after 15 days. The soil water retention of biochar added soil prepared by fast pyrolysis is higher than that of slow pyrolysis.