Reactions of phosphate fertilizers and by-products in soils

Abstract

Fertilizers and by-products (manures) containing phosphorus (P) are applied to soils with the main purpose of increasing the bioavailable supply of orthophosphate to the roots of food and fiber-producing plants. For P fertilizers to be effective they, or their reaction products in soil (e.g., decomposition of organic manure), must have larger solubility products than the natural phosphates already present in soils. This chapter discusses the key processes and factors influencing the type of reactions occurring and the nature of the fertilizer-soil reaction products formed, with respect to soluble P fertilizers, directly applied phosphate rocks and by-products (biosolids and manures). For some by-products, in particular sewage sludges and animal manures, it considers disposal rates of application and the impact these and their reaction products have on soil and water quality.