SURFACE APPLICATION OF LIQUID SWINE MANURE - CHEMICAL VARIABILITY

The determination of manure loading rates for crop production is compl icated by the temporal variability in manure nutrient concentrations a nd the difficulty in obtaining representative samples on which to base application rates. The variation in nutrient concentrations in liquid swine manure obtained from an agitated anaerobic lagoon was examined during application to experimental plots. Grab samples were collected from a lagoon approximately two to four weeks prior to application and analyzed for nitrogen (N), phosphorus (P), and potassium (K). Based o n the preliminary P analyses, swine manure application rates were comp uted. Manure from the lagoon was surface-applied to corn plots to prov ide P rates of 15, 30, and 60 kg P/ha. During application, each tanklo ad of manure was sampled to determine P rates for each plot. The solid s content of each manure load was highly variable as were the total co ncentrations of manure N and P. Potassium content of the manure was al so related to the solids content, although not to the same extent as N and P. Manure application resulted in P rates of 17, 32, and 49 kg P/ ha in 1992, while the 1993 rates were 5, 11, and 22 kg P/ha. The inabi lity to achieve target P rates resulted from changes in nutrient conce ntrations between the time of initial manure chemical characterization and manure application. Variability in the solids content was identif ied as the major factor influencing nutrient concentrations among spre ader tankloads.