Soil wet expansion and dry shrinkage characteristic curve and hysteresis effect under different irrigation and fertilization mode

Abstract: Farmland soil is often in alternating wet and dry state, which seriously affected the change of soil composition and properties, and thus changed soil hydraulic properties. During the course of alternation of wetting and drying, along with the change of water content, soil bulk density would change accordingly. The experimental investigations of this paper were carried out in irrigation field of Jiangxi province irrigation experiment station. The rice planting field trials were launched by employing experimental treatment with two irrigation modes including flooding, intermittent irrigation and four fertilization mode including no nitrogen fertilizer, nitrogen-containing compound fertilizer, controlled-release nitrogen fertilizer, organic and inorganic nitrogen fertilizer. Through analyzing change of soil specific volume with water content of all the tested soil undisturbed soil, the method of statistical analysis was used to fit the soil quality index curve model of water content and soil specific volume relationship. And main influence factors of soil wetting expansion and drying shrinkage were obtained by gray correlation analysis. The results showed that the index model can be used to describe the soil expansion process and shrinkage process under different irrigation and fertilization modes. a (dry soil, reciprocal of dry soil volume mass) and b (the natural logarithm unit value of soil specific volume change when unit water content change) values in soil shrinkage characteristics curve index models of different irrigation and fertilization mode were not the same with responding expansion curve index models. Soil shrinkage curve and expansion curve were two mutually non-coincident curves, b values and their differences in two curves were also different and lag phenomenon was existed. Soil wet expansion and dry shrinkage characteristics were affected by a variety of soil properties, which was mainly reflected through the effect of pore structure in soil and water holding properties.