General chemical fertility and chemical processes of grey degraded soils as a problem soil in Viet Nam

Abstract

General chemical properties were analyzed for profile samples of four grey degraded soils collected at the sites different in land use, landform, and parent material, in Viet Nam. The chemical fertility of grey degraded soils was found to be commonly poor in organic matter, the nitrogen and phosphorus status, and exchangeable "bases". The vertical movement of free iron oxides was observed for the paddy soils and the simultaneous movement of organic components and free iron oxides was suggested for the forest soil. Reduction and oxidation was considered to the paddy soil while podzolization was to the forest soil as mechanisms of the eluviation-illuviation of the chemical compounds. The mechanism of the clay degradation was reevaluated: decomposition of clay particles in addition to leaching and accumulation was suggested to the paddy soil, while leaching and accumulation was proposed as a main mechanism to the forest soil. The careful management such as regular addition of organic amendments and split dressing of chemical fertilizers, in addition to application of iron-supplying material, was recommended to the cultivation of paddy rice in the degraded paddy field.