Effect of wheat straw burning on soil organic matter
accumulation and microbial activity

【Objectives】Open burning of agricultural waste is practiced to clear the surface biomass from land, to control pests and diseases, and to return some nutrients. Emissions from field burning activities deteriorate local air quality and seriously impede agricultural development. Recently many studies had been conducted to assess air pollution caused by straw burning. However, data are relatively limited in change of soil physical and organic subsequent to straw burning. Topsoil of different straw burning quantity was collected to study the immediate effect of straw burning on content of soil organic matter and soil microbial activity. 【Methods】 A field experiment was established in June 2012. The experimental treatments included 4 levels of amount of burned wheat straw: no burning (CK), decrement group (0.24 kg/m2, A1), normal group (0.48 kg/m2, A2) and increment group (0.72 kg/m2, A3). The wheat straw was put evenly over soil surface and then was burned, and the remained wheat straws were additionally burned in order to make straw burnt completely. After five hours, when soil temperature had returned to normal, soil samples were collected from 0-5, 5-10 and 10-20 cm depth of soil in each treatment and analyzed through laboratory experiment. To elucidate the specific effect of burning wheat straw on soil environment, change of indicators, soil organic matter content, moisture content, microorganism quantity and enzyme activities in each layer of soil, were analyzed. 【Results】 Burning wheat straw had significant influence on topsoil. The indicators of soil constituents were reduced with different degrees in different treatments. In the layer of 0-5 cm, the content of soil organic matter and moisture was reduced by 6.37%-19.47% and 22.15%-39.19% respectively. The quantities of bacteria, fungi and actinomyces were respectively decreased by 52.26%-75.25%, 45.21%-63.29%, 46.87%-68.26%. Activities of sucrase, urease, catalase and phosphatase were decreased by 14.19%-30.75%, 7.81%-25.48%, 9.63%-39.53% and 11.36%-40.44% respectively. There were significant differences between most combustion treatments and the control, while there was no significant difference in the 5-20 cm soil layer. The content of each indicator was decreased in the order of A3A2A1. The combustion treatments with different amount of straw mostly had significant difference between each other. The correlation analysis indicated that amount of straw burning had significantly negative correlations with soil organic matter content, moisture, soil microbial quantity and soil enzyme activity. 【Conclusions】 The results indicated that wheat straw burning significantly reduced soil organic matter content and soil microbial activity in topsoil (0-5 cm) in a short time, and the impact strength was proportional to the amount of burned straw. In the layer of 5-20 cm, the effect of the straw burning was small. The correlation analysis indicated that straw burning amount had significantly negative correlations with soil organic matter content, moisture, soil microbial quantity and soil enzyme activity. Due to long-term effect of straw burning on soil fertility and the complexity of the effect on the physical and chemical properties in soil environment of straw burning, long-term in-situ study should be carried out to better assess effect of wheat straw burning in field.