Kinetics of phosphorus forms applied as inorganic and organic amendments to a calcareous soil II: effects of plant growth on plant available and uptake phosphorus

- Compost affected soil P chemistry differently from that of synthetic P fertilizer.
- Ryegrass growth was greatest in soil amended with compost.
- Net transformation of the moderately labile P fraction was faster in compost-treated soil.
- Weak acid extractable P provided a good indicator of plant available P.

The forms of phosphorus (P) in animal manure composts are different from that of synthetic P fertilizers, and this affects how soil P chemistry will be altered when they are used as P amendments. This study is an extension of a previously reported incubation study, where the net changes in the nature and dynamics of plant available P forms applied either as inorganic P (KH2PO4) or turkey litter compost (TLC) without plant growth were analyzed. The objective of this study was to analyze the net changes in the nature and dynamics of plant available P forms with plant growth in the greenhouse. The amounts of various P forms dependent on their solubility in soils were measured by a sequential fractionation method after 4, 8, 12 and 16 weeks incubation. The majority of TLC-P (brushite and newberyite) was recovered in the moderately labile P extracted with a weak acid. Though the labile P fraction in the TLC-treated soil was smaller than that in the fertilizer-treated soils, ryegrass growth was greater. Net transformation/plant uptake of the labile/moderately labile P was faster in the TLC-treated soil than the fertilizer-treated soil. A weak acid extractable inorganic P fraction should be considered as plant available P, especially in the compost-treated soil, which would be converted into plant available P through direct and/or indirect root-induced acidification in the rhizosphere.