Present Soil Chemical Status and Constraints for Rice-Based Cropping Systems in Vientiane Plain and Neighboring Areas, Lao PDR

Soil chemistry and nutrient status of soil were surveyed in an attempt to improve the productivity of rainfed lowlands—which would include crop diversification and improved rice yields—in the semi-mountainous areas near Nameuang village (NV) and in the Vientiane plain (VP), Lao PDR. The soil survey revealed soil acidity, deficiency in exchangeable Ca and Mg and in available P despite the its being in a calcareous zone. The nitrogen; phosphorus and potassium fertilities in NV were not notably unique to those in the neighboring districts. In addition, it became apparent that in NV there was a risk of aluminum toxicity. In order to determine appropriate soil management, the effects of liming on non-rice crops and on rice plants were studied in pot experiments using soils collected from NV. Liming was usually effective for enhancing the growth of the tested non-rice crops. Under submerged conditions, soil pH increased naturally despite the strong pre-flooding acidity. Although liming plus chemical fertilizer was effective for increasing rice yields, the effect of liming was not positive when only liming was applied. Although soil amendments are required to mitigate aluminum toxicity on non-rice crops in lowland double cropping systems, it was necessary to consider the influence on rice yields, particularly under a condition without fertilization.

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