Liquid Swine Manure Phosphorus Utilization for Corn and Soybean Production

There is uncertainty about manure P availability for crops and need for P fertilization when manure is applied. This Study evaluated effects of liquid swine (Sus scrofa domesticus) manure and fertilizer P on early plant growth and P uptake, grain yield, and grain P removal for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Sixteen trials were conducted in Iowa from 2000 to 2002. Replicated treatments were the combinations of three manure rates (0, 29, and 57 kg total P ha(-1) on average across sites) and four 11 fertilizer rates (0 to 30 kg P ha(-1)). Initial soil Bray-P-1 (15-cm depth) was 9 to 89 mg P kg(-1). Fertilizer rates applied across all plots were 168 kg N ha(-1) for corn and 56 to 120 kg K ha(-1) for both crops according to soil-test K. Measurements were early plant dry weight (DW) and P uptake (V5-V6 stage), grain yield, and grain P removal. Increases in plant DW, P uptake, and grain P removal were unrelated to soil-est P (STP), and were more frequent to manure than to fertilizer. Yield increases (P <= 0.05) were observed at six sites with Bray-P-1 <= 20 mg P kg(-1), with response only to manure at one site and to both manure and fertilizer at five sites but to fertilizer only when manure was not applied. The Study provided no evidence of lower crop-P availability from liquid swine manure than fertilizer P for corn or soybean in these lowa fields.