The effects of P fertilizer addition on P transformations on high-P fixing and grassland soils



Journal Title

Journal ISSN

Volume Title


Kansas State University


Although phosphorus (P) is an essential nutrient for the growth of plants, it is one of the most limiting nutrients in terms of availability as a high proportion of applied P rapidly transforms into insoluble forms with low solubility in soils. To further understand the fate of P applied to soils, two separate but related studies using three high P-fixing soil types each were used for which the objectives were to investigate the mobility, availability, and reaction products from two granular and one liquid P fertilizer alone or plus a fertilizer enhancement product. Energy dispersive spectroscopy showed a substantial amount of P remained in the granule following a 5-week incubation. At the end of the 35-day incubation period there was evidence that the fluid fertilizer was superior over the granular sources in terms of enhanced diffusion and extractability of P for three calcareous soils with varying levels of CaCO₃. Phosphorus x-ray absorption near-edge structure (XANES) spectroscopy results in conjunction with resin-extractable P indicated a strong negative correlation between Ca-P solids formed and P extractability, suggesting that degree of Ca-P formation limits P solubility. For the three acidic P-fixing soils the results were complex. In two out of three acid soils, liquid P treatments diffused farther from the application point than the granular treatments. Phosphorus XANES results suggested that Fe-P or Al-P interactions control the overall P solubility. Integration of pH, resin extractable-P and XANES results suggested the P retention mechanism was either dominated by adsorption or precipitation depending on soil pH. More acidic soil conditions favored precipitation. The objectives of the third study were to observe how long-term (14 years) addition of P with or without N influences the inorganic and organic P pools in a native grassland soil using sequential fractionation, XANES, and ³¹P-nuclear magnetic resonance (NMR) spectroscopy. The overall results suggested that P and N fertilization and associated changes in plant productivity induced significant changes in soil P pools such as Ca-P, phytic acid, monoesters, and residual forms of P. The addition of P alone induced formation of inorganic P forms while the addition of P and N induced transformation of residual P forms into more labile and/or organic P forms.



Soil phosphorus, High phosphorus-fixing soil, Soil phosphorus cycle, High phosphorus-fixing acid soil, High phosphorus-fixing calcareous soil, Tall grassland soils

Graduation Month



Doctor of Philosophy


Department of Agronomy

Major Professor

Ganga M. Hettiarachchi