Studies on Chemical Pretreatment of Straw for Enhancing Soil Structure Formation and Stability

The direct straw incorporation to soils can lead to problems of slow decomposition, diseases and pests, and nitrogen immobilization by microorganisms competing with crop uptake. We examined how straw pretreatments (either comminution, addition of liquid urea or blending with ferric hydroxide) aimed at decreasing these risks affected aggregation, bulk density, porosity and water evaporation of amended soils. Results showed that comminuted and urea treated straw significantly improved soil aggregation and increased soil porosity. Whereas a direct incorporation of straw had no impact on aggregate stability or porosity. Pretreatment of the straw doubled the MWD measured with wet sieving method and increased porosity by up to 12%; the application of ferric hydroxide effectively improved soil porosity distribution and further controlled the soil water evaporation; the combined application of ferric hydroxide and straw had a better effect on soil water conservation. The above results provided a theoretical basis for the selection of an optimal straw-returning method.