Long-Term Effect of Fertilizer and Rice Straw on Mineral Composition and Potassium Adsorption in a Reddish Paddy Soil

摘要

Increasing K+adsorption can be an effective alternative in building an available K pool in soils to optimize crop recovery and minimize losses into the environment. We hypothesized that long-term fertilization might change K+ adsorption because of changes in the chemical and mineralogical properties of a rice (Oryza sativa L.). The aims of this study were (i) to determine clay minerals in paddy soil clay size fractions using X-ray diffraction methods and a numerical diagram-decomposition method;(ii) to measure K+adsorption isotherms before and after H2O2 oxidation of organic matter, and (iii) to investigate whether K+adsorption is correlated with changes in soil chemical and mineral properties. The 30-yr long-term fertilization treatments caused little change in soil organic C (SOC) but a large variation in soil mineral composition. The whole-clay fraction (<5μm) corresponded more to the fertilization treatment than the fine-clay fraction (<1μm) in terms of percentage of illite peak area. The total percentage of vermiculite-chlorite peak area was significantly negatively correlated with the total percentage of illite peak area in the<5μm soil particles (R=-0.946, P<0.0006). Different fertilization treatments gave significantly different results in K+adsorption. The SOC oxidation test showed positive effects of SOC on K+adsorption at lower K+concentration ( 120 mg L-1) and negative effects at higher K+concentration (240 mg L-1). The K+adsorption by soil clay minerals after SOC oxidization accounted for 60-158%of that by unoxidized soils, suggesting a more important role of soil minerals than SOC on K+adsorption. The K+adsorption potential was significantly correlated to the amount of poorly crystallized illite present (R=0.879, P=0.012). The availability of adsorbed K+for plant growth needs further study.