Phosphorus pool in an alfisol following three years of fallow using different types of legumes

Abstract

Leguminous crops not only supply N to the soil but also phosphorus (P). The availability of P in the soil however highly depends on the P fractions, which constitute the overall P pool in soils. A field study was carried out to determine the effect of five leguminous crops namely Sesbania, Cajanas, iron clay, lablab and mucuna on the P pool as signified by the P fractions in a degraded soil that have been cropped for thirty (30) years. Sesbania effectively increased the labile P form in the pool as well as Ca-P. Cajanas increased the labile P forms in the P pool as well as the moderately organic and inorganic P pools. Mucuna on the other hand was only effective in increasing the labile organic P form in the P pool of the degraded soil. However, lablab increased the two extracted non-labile P forms in the soil. These results in the overall signify that the P forms that constitute the P pool is dependent on the leguminous crop used for a fallow period. From this study, for an increase in the labile P forms in the P pool in a degraded soil, the use of leguminous crops such sesbania, cajanas and mucuna is recommended and this will invariably increase the plant available P level.