PS8-2. Agronomic Impact of Interseeding Red Clover into Intermediate Wheatgrass Cultivars in Dual-use Systems.

Abstract Intermediate wheatgrass (Thinopyrum intermedium; IWG) is a perennial grain crop with additional potential for forage production for livestock but may require additional resources such as nitrogen for optimal production. With increasing prices of inorganic N, interseeding legumes such as red clover (Trifolium pratense L.; RC) may be a viable alternative source of N. However, introducing legumes into IWG for this purpose has not been thoroughly evaluated. The objective of this study was to determine the effect of either applying N fertilizer or interseeding RC into commercial and experimental cultivars of IWG grown as a dual-purpose forage and grain crop. This 3-year study was conducted as a split-plot design with four replicates using six IWG cultivars (whole-plot factor) that were randomized across the experimental area. Subplot treatments were IWG either interseeded with RC or fertilized with inorganic N. Data were statistically analyzed using a mixed model in SAS with year, treatment and year x treatment interactions as fixed effects, and block, block x year, and block x treatment interactions as random effects. Grain production was lowest (P < 0.01) for the ‘Rush’ IWG cultivar (mean 295.5 ± 194.5 kg ha-1) which was specifically bred for forage production, whereas the other cultivars were bred for grain production (mean 744.1 ± 194.5 kg ha-1). Grain production was negatively impacted (P < 0.01) by inclusion of RC (882.0 vs. 456.7 ± 194.5 kg ha-1 for monoculture and interseeded, respectively) likely due to competition for resources such as soil nutrients and water. Total herbage accumulation varied by cultivar but was not improved (P > 0.10) beyond the forage cultivar ‘Rush’, even when interseeded with RC (mean 5,455.0 ± 686.3 kg ha-1). Nutritive value (CP, NDF, TDN) of the sward was improved (P < 0.01) with inclusion of RC due to the addition of the higher-quality legume. Percentage of IWG in the sward was greater for monocultures (P < 0.01) due to dilution by RC in interseeded plots. Weed pressure was lower (P < 0.01) in interseeded swards due to RC outcompeting weeds; however, no treatment exceeded 7% weeds, likely due to use of chemical suppression prior to planting. This study concluded that while inclusion of RC into IWG improved nutritive value, grain production and herbage accumulation may be impacted due to competition for resources such as fertility, sunlight, and water. Future research should evaluate economic tradeoffs between grain production and forage production for livestock feed when considering IWG as a dual-purpose crop.