Poultry litter phosphorus: From microscale to macroscale

Knowledge of the plant availability of P from manures is important for the proper management of poultry wastes. The purpose of this research was to investigate the effect of previous history of waste applications on the plant availability of poultry waste P. The first phase of the research was to assess the affect of previous waste applications on soil phosphatase activity. There was no consistent relationship between phosphatase activity and history of manure application. The second phase was to develop an extraction, preparation and analytical procedure for the analysis of organic P compounds in 0.25M NaOH + 0.05M EDTA turkey litter extracts. The NMR analytical technique was found to be optimum when longitudinal relaxation times, T1, were 860 ms; a gated one-pulse technique with the proton decoupler turned on during signal acquisition was used; the sample was treated with Chelex 100 to remove paramagnetic ions; samples were adjusted to pH 10.0 and subsequently analyzed at 20°C. Phase three involved monitoring, in a 20-week laboratory incubation, the P mineralization process in a previously manured and previously non-manured soil using phosphatase assays and direct measurement of organic P concentration by quantitative NMR. There was a net increase in phosphomonoesterase activity from week 0 to 20 in both the previously manured and previously non-manured soils that were amended with poultry litter. The concentration of organic P compounds decreased from the time of poultry litter incorporation until week 20 whereas orthophosphate concentration increased. Phase four was a 20-week laboratory incubation to investigate the effects of temperature (10, 25 and 40°C) and previous history of waste application on the Mehlich III-extractable P from six poultry waste materials. Results showed temperature had no significant effect on the P recovered by Mehlich III extraction. The effect of previous waste history was observable in five of the eight sampling dates with P recovery being greatest in a soil that had been manure amended for eighteen consecutive years prior to initiation of the experiment.