Rainfall Timing and Alum Effects on Nutrient Losses from Grasses Fertilized with Broiler Litter.

Amending broiler litter with alum has been shown to improve the N:P ratio in broiler litter and reduce P in runoff when grasslands were fertilized with alum amended broiler litter (BL).  More work however is needed in understanding the effect of rainfall timing on nutrient losses in runoff from grasslands fertilized with alum-amended BL.  We rained on grassland plots fertilized with BL and alum-amended BL (5000 kg litter ha-1) at time of application (wk0), 2 weeks after application(wk2), or 4 weeks after application (wk4).  Overall alum-amended BL plots had more N in runoff than BL plots.  For plots fertilized with alum-amended BL, significant (p<0.01) reductions of NH4-N (wk2, 76% and wk4, 78%), NO3-N (wk2, 70% and wk4, 48%) and TKN (wk2, 73% and wk4, 73%) losses in runoff were identified when comparing losses from wk0  vs either wk2 or wk4.  This was not the case for P, where alum-amended BL significantly reduced P in runoff all weeks compared to BL. However, significant (p<0.01) reductions of DRP (wk2, 43% and wk4, 57%) and TKP (wk2, 47% and wk4, 57%) losses in runoff were identified  for  BL (no amendments)  treatments rainfall, 2 weeks and 4weeks after BL application compared to BL application immediately prior to rainfall.