Effects of microsized rice straw on soil clay dispersibility

Abstract

The incorporation of straw into soil has been encouraged as an alternative straw-disposal strategy to the on-site burning that occurs in many paddy regions. However, this practice may lead to changes in the colloidal properties of soil clays that potentially intensify clay and nutrient losses. This study aimed to demonstrate the effect of engineered microsized straw powder on the colloidal properties of two soil clays, that is, illitic and kaolinitic soil clays. Dynamic light scattering was coupled with the test tube method to evaluate timeresolved changes in the particle size, zeta potential and dispersibility for the suspensions of straw powder and its mixtures with illitic and kaolinitic soil clays. Data from kinetic experiments over a time span of 20 days revealed that straw powder remarkably increased the dispersibility of soil clays. It was found that straw particles carried negative charges; thus, the introduction of straw powder into the clay suspensions increased the number of negative charges in the system, thereby increasing internal repulsive forces and eventually favouring clay dispersion. Moreover, certain mutual processes, that is, the biodegradation and dissolution of phytoliths (silica in straw), resulted in the release of dissolved organic matter and silicon, which aggravated clay dispersibility. In addition to the "traditional" awareness of the impacts of straw incorporation, for example, creating toxic, reduced environments or increasing CH 4 emissions, the changes in the colloidal properties of soil clays should also be highlighted. We propose that the incorporation of straw requires additional solutions for the prevention of clay loss. Highlights • Straw powder was examined for possible effect on colloidal properties of soil clays • It was found that straw particles carried negative charges • Introduction of straw powder increase repulsive forces and favor clay dispersion • Microorganism, B. amyloliquefaciens, enhances the effect of straw powder