Utilization of poultry manure phosphorus for corn production

There is uncertainty about the need for supplemental P fertilization after applying poultry manure for corn [Zea mays L.). This study evaluated the effects of manure and fertilizer P on com by establishing 17 on-farm trials in Iowa. Manure from broilers, egg layers [Gallus gallus domesticus), or turkeys [Melleagris gollopavo) was used at each site. Replicated treatments were the combinations of three manure rates (0,53, and 104 kg P ha^-1 on average across sites) and four triple superphosphate rates (0-75 kgP ha ^-1). Initial Olsen P (15-cm depth) was 5 to 23 mg P kg^-1 across sites. Uniform rates of 168 kg N ha^-1 and 56 to 112 kg K ha^-1 were applied. Measurements were early plant dry weight (DW); P concentration and P uptake (V5-V6 stage): and grain yield, P concentration, and P removal. Increases in plant DW and P uptake were unrelated to soil-test P, were more frequent for manure, and only one site that was responsive [P ≤ 0.10) to fertilizer was not responsive to manure. Phosphorus fertilization in addition to manure increased plant DW at four sites and P uptake at eight sites. Both P sources increased grain yield at eight sites with < 15 mg Olsen P kg^-1, only manure increased it at another site, and supplemental fertilization did not increase yield at any site. The results provided no evidence for lower P availability of poultry manure P than fertilizer P for com yield and showed no need for supplemental P fertilization at prevailing manure rates used by farmers.