Yan-Ping WANG Ren-Kou XU Jiu-Yu LI. Effect of Fe-Al Hydroxides on Desorption of K⁺and NH⁺₄from Two Soils and Kaolinite.Pedosphere 201323(1): 81–87.

Abstract

Potassium (K) and nitrogen (N) are essential nutrients for plants. Adsorption and desorption in soils affect K⁺ and NH⁺₄ availabilities to plants and can be affected by the interaction between the electrical double layers on oppositely charged particles because the interaction can decrease the surface charge density of the particles by neutralization of positive and negative charges. We studied the effect of iron (Fe)-aluminum (Al) hydroxides on desorption of K⁺ and NH⁺₄ from soils and kaolinite and proposed desorption mechanisms based on the overlapping of diffuse layers between negatively charged soils and mineral particles and the positively charged Fe-Al hydroxide particles. Our results indicated that the overlapping of diffuse layers of electrical double layers between positively charged Fe-Al hydroxides as amorphous Al(OH)₃ or Fe(OH)₃ and negatively charged surfaces from an Ultisol an Alfisol and a kaolinite standard caused the effective negative surface charge density on the soils and kaolinite to become less negative. Thus the adsorption affinity of these negatively charged surfaces for K⁺ and NH⁺₄ declined as a result of the incorporation of the Fe-Al hydroxides. Consequently the release of exchangeable K⁺ and NH⁺₄ from the surfaces of the soils and kaolinite increased with the amount of the Fe-Al hydroxides added. The greater the positive charge on the surfaces of Fe-Al hydroxides the stronger was the interactive effect between the hydroxides and soils or kaolinite and thus the more release of K⁺ and NH⁺₄. A decrease in pH led to increased positive surface charge on the Fe-Al hydroxides and enhanced interactive effects between the hydroxides and soils-kaolinite. As a result more K⁺ and NH⁺₄ were desorbed from the soils and kaolinite. This study suggests that the interaction between oppositely charged particles of variable charge soils can enhance the mobility of K⁺ and NH⁺₄ in the soils and thus increase their leaching lsos.