Phosphate Amendments to Compost for Improving P Bio-Availability

Abstract

This study was conducted to investigate changes in P-fractions, bio-available P (CAL-P), citric acid extractable P, acid phosphatase activity and microbial biomass C and N during incubation of mature biogenic compost (MBC), immature biogenic compost (IBC) or immature sheep manure compost (ISC) not amended with P or amended with rock phosphate (RP, 7.6% P) or triple-superphosphate (TSP, 19.5% P). Incubation was performed at 20 °C in darkness under aerobic conditions. Samples were collected for laboratory analysis at the start of incubation (D-0) and after one, six and 26 days during incubation (D-1, D-6, D-26). Addition of soluble P fertilizer (TSP) led to a threefold increase in all P fractions in comparison to compost without TSP; even a “priming effect” could be observed, promoting conversion of non-labile to labile P. Moreover, addition of TSP lowered biological activity, especially acid phosphatase activity (P-ase), due to already high concentrations of readily available P. In general, P fractions (bicarbonate extractable P_i (NaHCO₃-P_i) and bicarbonate extractable P_o (NaHCO₃-P_o) and sodium hydroxide extractable P_o (NaOH-P_o)) increased during incubation until day 6 at the expense of NaOH-P_i fraction, which decreased. Generally, RP-derived P showed little or no effect on P fractions during the entire incubation period and only led to slightly increased CAL-P and Citric-acid-P levels. Fertilizer effects on labile P fractions were most enhanced with ISC. IBC enhanced microbial growth and P-ase, thereby enhancing conversion of labile into moderate labile NaOH-P_o.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Becas Chile Bicentenario Grant 74090022 from CONICYT (Comisión Nacional de Investigación Científica y Tecnológica de Chile).