Phosphorus availability and fractions in a humic soil amended with poultry manure and lime
NP Mkhonza, Nkosinomusa Buthelezi-Dube, Pardon Muchaonyerwa
Abstract
Phosphorus (P) availability in highly weathered soils is limited. The objective of this study was to determine the effects of poultry manure (PM) and lime on P availability in humic soils. The soils were amended with lime and PM, separately and in combination, and incubated at field capacity moisture in a dark room at 25 °C. Destructive sampling was done after 0, 7, 14, 21, 28, 42, 56 and 84 days and analyzed for extractable P. Soil microbial biomass phosphorus (SMB-P) was analyzed at days 14, 28 and 84 while other soil P fractions were determined after day 84 only. The PM alone had significantly higher extractable P than lime alone and co-application, and some mineralized P from PM was fixed with no contribution of resident soil organic matter (SOM). Higher P availability was observed at 0–10 cm than at 10–20 cm depth. Application of PM and lime increased P availability and SMB-P and decreased Al-P and Fe-P. The SMB-P decreased with increased incubation time in all treatments. These findings imply that the addition of PM and lime increase P availability and SMB-P, reduce fixation of P in humic soils, and that PM addition reduces contribution of resident SOM to available P.