Impact of Feedlot Manure and Nitrogen Additions on Forage Yields, Nutrient Balance and Soil Nitrate, Phosphate and Salinity

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ABSTRACT Safe disposal of feedlot manure is an increasing problem throughout the world. A field experiment was established on a duplex sandy loam soil (Alfisol) in Northern NSW, Australia to determine the dry matter (DM) crop response and the fate of nutrients derived from cattle feedlot manure and inorganic fertilizer applications. The five treatments imposed over a three year period were no manure or inorganic fertilizer (NM), a moderate annual manure application (20–25 t DM ha−1) -/+ N (MA, MAN) a high initial application in year 1 (60 t DM ha−1 + N, HIN) and an inorganic fertilizer treatment (single superphosphate, KCl, urea, I) applied in each year. Vegetative yields of forage sorghum (Sorghum bicolor cv. Super-Dan) and triticale (Triticosecale spp. cv. Madonna) were recorded in crops grown in sequence over a three-year period. A mass balance approach was used to quantify nutrient gains to, and losses from the system. Total crop yield was 14.22 t dry matter (DM) ha−1 in the NM treatment with an approximate threefold increase with HIN and I. Removal of nutrients (kg ha−1) in harvested forage was highest for N, K and S in the I treatment (767 N, 1447 K, 76 S) and highest for P in the HIN treatment (189 P). There was no accumulation of NO3 in the soil layers to the B horizon in the manure treatments which contrasts with I. In the manure treatments there was a 6 to 8 fold increase over the initial value in Colwell bicarbonate extractable P in the 0–10 cm soil horizon in the MAN and HIN treatments, a decline in exchangeable K, an increase in EC and a loss of P sorption capacity. Supplemental inorganic nitrogen has been found to increase the nutrient benefits of feedlot manure. Accumulation of soil phosphate and salts, and a decline in soil K was found and needs to be closely monitored to maintain productivity and the environment.