ABSTRACT
In many tropical ecosystems, phosphorus (P) is a scarce limiting nutrient. The supply of nitrogen and phosphorus controls organic carbon mineralization in tropical topsoil and subsoil and hence indirectly affects climate change. In tropical soils, P is almost always a limiting factor for crop yields, the acid-weathered soils of the tropics and subtropics being particularly prone to P-deficiency. Producing fixed P in the soil up to the fixing threshold is referred to as “quenching.” The excess after quenching is plant-available P. Extreme phosphorus-deficiency due to strong P-sorption caused mainly by high levels of aluminum and iron oxides prevail in Terra Rossa clayey soils of the humid tropics. Cajanus Cajan, a multipurpose species, is extensively used as a food grain and a green manure crop for soil fertility amelioration in several cropping systems. Pigeon pea can be grown in a wide range of soil textures, from sandy soils to heavy clays.
