Anika Molesworth, Wendy C. Quayle, John Hornbuckle
Centre for Rural and Regional Futures, Deakin University, Hanwood, NSW 2680, Australia
Quantifying in-situ patterns of poultry litter (PL) mass decomposition and changes over time in NO3-N, NH4-N and Colwell P when applied alone or in combination with urea fertiliser helps farmers to synchronise nutrient additions to the soil with crop requirement. Using a buried litterbag technique in the field, decomposition and nutrient changes followed a two-phase pattern suggesting labile and recalcitrant PL components. Twenty-five days after burial (DAB), PL at 10 cm in loam soil contained64% dry matter (DM), 66% NO3-N, 16% NH4-N, and 69% Colwell P compared with initial concentrations at burial. After 27 DAB, PL in a clay loam had 73% DM, 8% NH4-N and 85% Colwell P remaining compared with initial concentrations, with increases of 6 times in NO3-N. Using an exponential model to estimate PL remaining values from day of burial until final excavation in the loam, it was determined there was 63% DM, 6% NO3-N, 5% NH4-N and 55% Colwell P remaining. After another 43 days buried in the clay loam, there was 63% DM and 2% NH4-N remaining of initial PL values, a 1.2 increase in NO3-N, while Colwell P had returned to starting levels. The rate of PL-N:urea-N had significant effect on NH4-N in phase 2, with greater concentration with higher litter ratio. Since only ~5% of starting PL NH4-N remained at the end of the experimental period on both soil types, the data indicates timely application of PL is required to synchronise any short-term N fertiliser benefit to a developing crop. The free-draining nature of the loam compared with the heavier clay loam are likely to be the main drivers of difference in PL decomposition and nutrient change observed between soil types. The patterns suggest that PL may better fulfil the expectations of a slow release nutrient source in a clay loam than a loam.