Maintaining grain yields of the perennial cereal intermediate wheatgrass in monoculture v. bi-culture with alfalfa in the Upper Midwestern USA

Abstract

Intermediate wheatgrass (Thinopyrum intermedium; IWG) is a perennial cereal crop undergoing development for grain production; however, grain yield declines of >75% are often observed after year 2 of the perennial stand and may be linked to soil nutrient depletion. Intercropping IWG with a perennial legume such as alfalfa (Medicago sativa) could benefit nutrient cycling while increasing agroecological diversity. Intermediate wheatgrass was established at five environmentally diverse sites in Minnesota, USA in (1) bi-culture with alfalfa, (2) non-fertilized monoculture and (3) monoculture fertilized annually in the spring with 80 kg N/ha. At northern sites where alfalfa growth was favoured, IWG grain yields were reduced in year 2 by growing IWG in bi-culture with alfalfa, relative to the monoculture systems. Across all sites IWG grain yield decreased by 90% in the non-fertilized monoculture, 80% in the fertilized monoculture and 65% in the bi-culture from year 2 to 4 and plant macronutrient concentrations decreased by 25–70%. In year 4, IWG grain yield was similar or greater in the bi-culture than the fertilized monoculture at three of the five sites and alfalfa biomass was correlated positively with grain yield, harvest index and nutrient uptake in the year 4 bi-culture. Chemical-nitrogen fertilization increased grain yields in year 2 but did not mitigate the decline in yields as stands aged. Intermediate wheatgrass in the bi-culture had similar yields and nutrient uptake and lower yield declines than the chemically fertilized stand at sites where alfalfa growth was maintained throughout the life of the stand.

Effective weed suppression in dual‐use intermediate wheatgrass systems

“…Since the weed‐free treatment was not imposed in first year of grain production, the extent to which grain yields were reduced as a result of weed competition is unclear in that first year. However, grain yields in the first production year were similar to those that were observed in other studies where weeds were controlled with herbicides and where other agronomic management factors were similar to those in our study (Jungers et al., 2017; Tautges et al., 2018). In the first production year, the majority of the crop–weed competition likely occurred while the IWG was in its vegetative stage early in the growing season, and by the time of crop anthesis and grain fill, the majority of the winter annual weeds had senesced which likely reduced the overall level of yield loss.…”

“…Grain yields of IWG were relatively low compared with other cereal grains but forage biomass yields were relatively high compared to other perennial forages, which suggests that dual‐use grain and forage IWG cropping systems may be economically profitable for farmers. Consistent with previous research, IWG grain yields were greatest in the first production year and decreased over time (Jungers et al., 2017; Pugliese et al., 2019; Tautges et al., 2018) under these management practices. Given that aboveground biomass did not change over time, the cause of grain yield decline is not related to biomass productivity, weed competition, or nitrogen availability.…”

“…To date, research on IWG has focused on forage yield (Jungers et al., 2017; Liebig, Hendrickson, Berdahl, & Karn, 2011; Wagoner, 1990; Wang et al., 2014), forage quality (Favre et al., 2019; Jungers et al., 2017; Karn, Berdahl, & Frank, 2006), grain yield (Jungers et al., 2017; Lee, Owens, Boe, & Koo, 2009; Tautges, Jungers, DeHaan, Wyse, & Sheaffer, 2018), and grain quality (Zhang, Ohm, Haring, DeHaan, & Anderson, 2015). However, there is a lack of scientific information relative to many aspects of agronomic management in IWG cropping systems.…”

Effects of defoliation and row spacing on intermediate wheatgrass II: Forage yield and economics

“…Straw production was high and relatively consistent, with yields in the upper half of the previously reported range (Jungers et al., 2017; Pugliese, 2017; Tautges et al., 2018; Wang et al., 2014). Straw yield declined as the row spacing increased in 2015 and 2016.…”

“…Here, we will focus on the forage potential of the straw. Straw yields at grain harvest can reach over 12 Mg ha −1 and are typically in the range of 3 to 10 Mg ha −1 (Jungers et al., 2017; Pugliese, 2017; Tautges, Jungers, Dehaan, Wyse, & Sheaffer, 2018; Wang et al., 2014).…”