Soil phosphorus fertility under organic nutrient management
Organic nutrient management, involving applications of animal manures and composts, provides both organic matter and plant available nutrients to soils. These amendments affect the chemistry of soil phosphorus, altering both the amount and distribution of the various phosphorus fractions. It has been reported that most of the phosphorus in manures and composts is inorganic phosphorus. A substantial proportion of the organic phosphorus fraction is inositol phosphate, which reacts strongly in soils to form stable phytate complexes. In manures and composts, the amount and distribution of organic and inorganic phosphorus forms varies widely depending on its source, animal physiology and diet, bedding material, and the method of storage and preparation.
The objectives of this study were to quantify the forms of phosphorus in animal composts, and to measure the kinetics of their transformation in soils. The transformations of various phosphorus forms during an18-week incubation were analyzed in an organically-managed calcareous soil amended with either turkey litter compost or water soluble inorganic phosphorus (KH2PO4). A sequential phosphorus fractionation method was used to assess these transformations. Soil organic phosphorus pools were extracted in NaOH–EDTA and organic phosphorus was characterized by solution 31P NMR spectroscopy.
The study showed that the majority of phosphorus in turkey litter compost and soils amended with turkey litter compost was inorganic phosphorus. The organic phosphorus pools were not significantly different among treatments. Amendment with KH2PO4 affected brushite (labile phosphorus) most, while the effect of turkey litter compost amendment was on the octacalcium pool. A soil phosphorus mineral species model predicted that octacalcium phosphate would become plant available in soils amended with turkey litter compost when total phosphorus in soil solution decreases. Octacalcium phosphate might play an important
role in phosphorus fertility in organically-managed soils.
Proceedings of Organic Phosphorus 2013 Integration across Ecosystems. Smithsonian Tropical Research Institute, Republic of Panama. 4-7 February 2013.