Compost in pellet form and compost moisture content affect phosphorus fractions of soil and compost
Takahashi, Shigeru | Ihara, Hirotaka | Karasawa, Toshihiko
Phosphorus (P) bioavailability depends on the forms of inorganic and organic P (P ᵢ and P ₒ). Our objectives were to investigate the effects of compost forms (pellet or non-pellet) on soil P forms, and to characterize the mineralization of P ₒ and the changes in P forms in compost of different moisture contents. Laboratory incubation experiments were conducted; (1) pelletized and ground pelletized poultry manure composts were applied to an Andosol and incubated for 56 d, and (2) poultry manure composts were prepared with five levels of moisture content (0.2, 0.4, 0.6, 1 and 2 kg kg ⁻¹-dry matter). Phosphorus forms in the soil and compost were determined by sequential fractionation. Compost amendment increased Truog P and labile P ᵢ in the soil. A greater increase in Truog P and labile P ᵢ (anion-exchange membrane (AEM)-P ᵢ + NaHCO ₃-P ᵢ) was observed in the soil amended with pelletized compost compared with the soil amended with ground compost. Phosphorus mineralization of poultry manure compost was enhanced at higher moisture contents. Moisture contents of pelletized compost were above 1 kg kg ⁻¹ under standard soil moisture conditions. Above compost moisture contents of 1 kg kg ⁻¹, labile P ᵢ levels reached a maximum at 26 d and subsequently remained stable. The increase in labile P ᵢ was mainly attributable to a decrease in HCl-P ₒ. These results indicate that compost in pellet form and compost moisture content strongly affect bioavailability of compost P.
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