Effects of Straw and Biochar Returned to the Soil on Soil Physical Properties and pH Value in Cold Rice Region

[Objectives] In order to explore the feasibility of using straw and biochar returned to the soil to improve soil physical properties and pH value in cold rice regions of China. [Methods] the effects of straw directly returned to the soil and charred straw (biochar) returned to the soil on soil bulk density, porosity, temperature and pH value of cold paddy soil were studied in this paper. [Results] The results showed that compared with conventional production, straw (6 t/ha), a small amount of biochar (2 t/ha) and a large amount of biochar (40 t/ha) returned to the soil reduced paddy soil bulk density at different growth stages by 6.02%-11.86%, 2.69%-6.67% and 8.58%-11.32%, respectively, increased total porosity by 7.41%-14.93%, 3.19%-8.38% and 9.81%-14.27%, respectively, and increased aeration porosity by 22.28%-192.11%, 17.80%-92.11% and 52.44%-157.11%, respectively. Straw and a small amount of biochar returned to the soil had no significant effect on soil temperature and pH value of paddy field, but a large amount of biochar returned to the soil could significantly increase soil temperature by 5.13%-8.79% and pH value by 3.15%-5.96% in the later stage of rice growth. [Conclusions] The straw and biochar returned to the soil could reduce soil bulk density, increase total porosity and aeration porosity, and only a large amount of biochar returned to the soil could significantly increase soil temperature and pH value.