Effect of ammoniated straw returning on soil pore structure

【Objectives】 Property of soil pores reflects the adaptability of soil structure. Addition of organic materials into soil can improve soil structure, soil permeability, soil water holding capacity and nutrient retention capacity. The objective of this study was to investigate effects of addition of ammoniated straw on soil pore distribution and soil pore structure, especially soil total porosity, residual porosity, matrix porosity and structural porosity relative to amounts of ammoniated straw addition.【Methods】 Incubation method was used and the ammoniated straw was added inpercentages to the soil weight 0% (CK), 0.384% (S1), 0.575% (S2) and 0.767% (S3)). In 0, 60, 120 and 180 dof incubation, soil water content were measured and soil water retention curve (SWRC) were set up.Based on SWRC, the double-exponential water retention equation (DE model) was used to calculate soil residual porosity, matrix porosity and structural porosity, with which to evaluate effects of ammoniated straw on various grades of soil porosities. Meanwhile, the differential equation of the DE model was used to calculate distributions of different soil pores. 【Results】The root mean square errors of the measured and estimated SWRCs vary in the range between 0.0036 and 0.0041 cm3/cm3, the coefficients of determination R2 vary in the range between 0.998 and 0.999, and the measured and estimated water contents of SWRC are close to the line of 1 ∶1, which indicates that the DE model is good enough to be used to fit the measured SWRCs of soils mixed with ammoniated straw and to efficiently estimate the changes of different soil porosities with time. The ammoniated straw has less effect on the soil residual, matrix and structural porosities within 120 d. On the 180 d, the soil structural porosities are increased with the increase of ammoniated straw. Meanwhile, the S3 treatment has less effect on the soil residual pore, significantly decreases the soil matrix porosities (P0.05) and significantly increases the structural porosities (P0.01). All the treatments with ammoniated straw significantly increase the ranges and quantity of soil structural pores compared with CK on the 180 d. The quantity of soil structural pores is increased with the increase of ammoniated straw in the soil pore distribution, and the peak value of soil structural pores in the soil pore distribution is moved forward with the increase of ammoniated straw. The ammoniated straw significantly promotes soil pores tending to bigger ones, and the effect could be enhanced with the increase of the ammoniated straw. In addition, the ammoniated straw could increase the soil organic matter content. There is a significant positive correlation between the soil organic matter content and the soil structural porosity and as well as the soil total porosity. The relationships between the soil organic matter content and the soil residual or matrix porosities are unclear. The ammoniated straw promotes the development of soil pore structure by increasing soil organic matter content that could bond and aggregate soil particles. The ammoniated straw increases the soil total porosity by increasing soil structural porosity, and the effect becomes more significant with the time. 【Conclusions】 The ammoniated straw could promote the development of soil pore structure by increasing soil organic matter content, and significantly increase soil structural porosity and total porosity, which is of great significance in improving soil fertility and soil workability.