Switchgrass Yield Response Functions and Profit‐Maximizing Nitrogen Rates on Four Landscapes in Tennessee

Abstract

Little is known about how yield‐ and profit‐maximizing N rates of switchgrass (Panicum virgatum L.) respond to environmental influences. The objective of this research was to determine the most suitable yield response functions and profit‐maximizing N rates of switchgrass grown on four landscapes in Tennessee. Research was conducted in West Tennessee during a 7‐yr period on four landscapes including: (i) a well‐drained level upland (WDLU), (iii) a well‐ to moderately well‐drained floodplain (WDFP), (iii) a moderate to somewhat poorly drained eroded sloping upland (MDSU), and (iv) a poorly drained floodplain (PDFP). The yield response functions considered were the quadratic, the quadratic‐plus‐plateau, the linear response plateau, and the linear response stochastic plateau. The most suitable response function for each landscape was used to calculate the profit‐maximizing N rate. The linear response stochastic plateau function was the most suitable for the WDFP, WDLU, and MDSU landscapes, and the quadratic function was the most suitable for the PDFP landscape. The most suitable yield response function and the yield‐ and profit‐maximizing N rates for switchgrass were sensitive across landscapes. Overapplication of N and a decrease in farmers’ net returns were predicted when a less suitable response function was selected to determine optimal N rates.