Biomass yield of warm-season grasses affected by nitrogen and harvest management

Authors: WEERASEKARA, C - University Of Missouri; Kitchen, Newell; JOSE, S - University Of Missouri; MOTAVALLI, P - University Of Missouri; BARDHAN, S - University Of Missouri; Mitchell, Robert - Rob

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2018
Publication Date: 3/22/2018
Citation: Weerasekara, C.S., Kitchen, N.R., Jose, S., Motavalli, P.P., Bardhan, S., Mitchell, R. 2018. Biomass yield of warm-season grasses affected by nitrogen and harvest management. Agronomy Journal. 110(3):890-899. doi:10.2134/agronj2017.04.0196.
DOI: https://doi.org/10.2134/agronj2017.04.0196

Interpretive Summary: Warm-season grasses like switchgrass, big bluestem, and Indiangrass are native to the US Midwest and have drawn interest as bioenergy crops. These grasses generally have high productivity with minimal amounts of nitrogen fertilizer and are adapted to a wide range of soils, including degraded soils. Further, because they are deep-rooted perennials and store soil carbon they are credited with multiple environmental benefits. Nitrogen fertility and harvest timing are critical management practices of these grasses that are not well understood when growing them on degraded soil landscapes. A study was conducted at four field locations in central and west-central Missouri over two years to evaluate the impact of N fertilizer rate and timing along with the harvest date on biomass yield. Results indicated delaying harvest until late fall or after killing frost (typically November or later) generally gave the best yields. Within the late fall harvest, rates of 60 lbs of N per acre or more produced the most biomass. In contrast, harvesting in summer and early fall (a two cut management system) or just early fall resulted in lower biomass yield. In a few situations, the optimal nitrogen fertilizer rate varied by harvest timing, but there was no consistent interaction between these two management practices. These results will aid researchers and practitioners in identifying optimal management practices when growing warm-season grasses as bioenergy crops on marginal soils.

Technical Abstract: Perennial warm-season grasses have drawn interest as bioenergy feedstocks due to their high productivity with minimal amounts of inputs while producing multiple environmental benefits. Nitrogen (N) fertility and harvest timing are critical management practices when optimizing biomass yield of these grasses. Our objective was to quantify the impact of N fertilizer rate and application timing in combination with the harvest date on warm-season grass dry matter yield. Research was conducted in 2014 and 2015 on a total of four field-plot locations in Missouri. The experiment was a split-plot design with three replications where N rate and harvest timing were main-plot and sub-plot treatments, respectively. Nitrogen was applied at rates of 0, 34, 67, and 101 kg/ha at two application times, all N early spring and split N (early spring and following 1st harvest). Harvest timing treatments included two single harvests (in September and November) and two double harvests (a June harvest followed by either a September or a November harvest) per year. In both years, delaying harvest until November increased yield at each site. Within the November harvest N rates = 67 kg/ha improved biomass yields. Although N fertilization improved yield, partial factor productivity (PFP) of applied N did not increase with N rates > 34 kg N/ha/yr. Nitrogen fertilization at 67 kg N/ha/yr provides an opportunity to maintain a balance between yield and efficiency of N inputs. Our results highlight the simultaneous implications of N fertilization and harvest management for optimizing warm-season grasses grown as bioenergy feedstocks.