Kinetics of phosphorus forms applied as inorganic and organic amendments to a calcareous soil

Abstract

Under organic management soil fertility is maintained using amendments of animal manures and composts as alternatives to synthetic phosphorus (P) fertilizers. These amendments can directly affect the chemistry of soil P by altering the amounts, distribution and transformations of P forms. The amounts of various P fractions in the control and soils amended with either inorganic P fertilizer or turkey litter compost were analyzed after 1, 4, 8, 11, and 18weeks by a sequential fractionation method. The addition of inorganic P fertilizer increased the labile/moderately labile P, while the compost increased the moderately labile P the most. Transformations of the labile/moderately labile P into more stable P occurred slowly during an 18-week incubation period. This study showed that P applied as either inorganic or organic amendments was recovered in different P fractions in a calcareous soil, and therefore it is expected that P source effects on soil P chemistry and potential for loss would differ. Fertilizer-P addition results in more labile P initially, with faster net transformation to a moderately labile form that may potentially lower the risk of P movement over time. With compost, the P enters more stable fractions initially and so it is less susceptible to loss shortly after application, but it could potentially remain a greater source of P for loss later on.