Effects of soil type and landscape on yield and profit maximizing nitrogen rates for switchgrass production

Previous work has found yield-maximizing nitrogen (N) rates in switchgrass production and results have varied widely. Little attention, however, has been given to estimating profit-maximizing N rates. The objectives of this research were to determine the (1) yield- and (2) profit-maximizing N rates for producing switchgrass on four soil types/landscapes in Tennessee. Mixed models were used to perform an analysis of variance on the effects of four N rates on average yield and average net returns for switchgrass grown on the four soil types/landscapes. Data were analyzed from a switchgrass experiment conducted at Milan, Tennessee over a six-year period on: (1) a moderately- to well-drained level upland (WDLU), (2) a moderately- to well-drained flood plain (WDFP), (3) a moderate-to somewhat poorly-drained eroded sloping upland (MDSU), and (4) a poorly-drained flood plain (PDFP). The N rates that maximized average yield were 67, 134, 134, and 200 kg N ha(-1) for the WDFP, WDLU, MDSU, and PDFP soil types/landscapes, respectively. The profit-maximizing N rate was estimated by soil type/landscape using three prices of switchgrass and three prices of N. Results demonstrated that yield- and profit-maximizing N rates can be different, and the yield- and profit-maximizing N rates across different across the soil types/landscapes. The profit-maximizing N rate was sensitive to the price of N and the price of switchgrass across all soil types/landscapes, but sensitivity to price changes were not equal for all soil types/landscapes. Published by Elsevier Ltd.