Evolution of soil surface charge in a chronosequence of paddy soil derived from Alfisol

Abstract

Limited information is available on the changes in surface electro–chemical properties of paddy soils during pedogenesis. This study evaluated the category, evolution and origin of soil surface charge along an Alfisol–derived paddy soil chronosequence. Ammonium acetate adsorption, as well as cesium (Cs+) adsorption and sequential desorption methods were applied to reveal the surface charge evolution along a paddy soil chronosequence. Results indicated that organic matter increased by 52.79%, 84.90%, 144.35%, and 126.52% in the surface paddy soils after 3, 8, 30, and 70 years of rice cultivation, respectively. The main phyllosilicates in Alfisol and Alfisol–derived paddy soils were montmorillonite and illite, which increased with paddy cultivation over time. Soil negative charge, as determined by ammonia (NH4+) adsorption, was strongly correlated with data from Cs+ adsorption methods. The negative charge on the surface paddy soil, as estimated by NH4+ adsorption, increased by 16.41%, 33.21%, 56.49%, and 31.68% after 3, 8, 30, and 70 years of rice cultivation, respectively. Further investigations revealed that an increasing variable surface charge is mainly attributed to soil organic matter accumulation. Also, hydroponics cultivation was shown to prompt the destruction and weathering of primary minerals and formation of soil secondary phyllosilicate minerals, which are mainly responsible for increasing permanent surface charge along the paddy soil chronosequence. Thus, the nutrients holding capacities of paddy soils are maintained or even improved, thereby increasing agricultural productivity, when compared with upland soils.