Effect of Poultry Manure Phosphorus Applied for Corn on Post-Harvest Soil Phosphorus and Grain Yield of a Following Soybean Crop.

High P concentration in relation to N concentration for most poultry manures makes them ideal sources to supply crop P needs in 2-year corn-soybean rotations.  We studied effects of poultry manure and fertilizer P applied for corn on soil P and yield of following soybean crops at 16 Iowa fields.  Manure treatments for corn were a control and rates that on average across sites applied 64 and 122 kg total P ha^-1 and 133 and 256 kg total N ha^-1.  Fertilizer treatments for corn were 0, 25, and 50 kg P ha^-1.  An additional treatment applied 25 kg Pha^-1 before corn and 25 kg P ha^-1 before soybean.  A previous presentation showed results for corn yield and P removal.  Measurements for this portion of the study were soil P after corn, soybean grain yield and P removal, and soil P after soybean.  High K rates were applied to all soybean plots.  On average, soil P before soybean was 14 and 28 mg Mehlich-3 P higher than the control for the low and high manure rates, respectively.  Residual P from manure or fertilizer applied to corn increased soybean yield significantly at six sites, all of which initially tested optimum or less (< 21 mg kg^-1) in soil P.  Soybean grain P removal was also increased at these sites.  Additional P fertilizer for soybean after manure applied for corn never increased yield further.  On average, soil P after soybean was 9 and 17 mg Mehlich-3 P higher than the control for the low and high manure rates, respectively.  Additional P fertilizer for soybean was not needed even when poultry manure for corn applied as little as one-half the crop-available N needed by this crop.