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 corn 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 on average across sites) and four triple superphosphate rates (0-75 kg P 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 OW 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 OW 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 corn yield and showed no need for supplemental P fertilization at prevailing manure rates used by farmers.