Intermediate wheatgrass [IWG; Thinopyrum intermedium (Host) Barkworth & D.R.Dewey] is a cool-season perennial forage grass bred for higher seed yield. It is the first perennial grain crop in the United States, commercialized as Kernza since 2015. Managing IWG as a dual-use grain and forage crop could provide several ecosystem services including conserving soil and clean water while increasing economic income to growers. However, little is known about the weed management risks associated with IWG. Therefore, we studied weed community composition, biomass, IWG grain, and aboveground biomass in a factorial experiment with two weed management treatments, two nitrogen fertilization rates, and four forage harvest schedules (no harvest, summer only, summer + fall, and spring + summer + fall).Over three production years, weed biomass decreased by 88% regardless of treatment, and the weed community composition changed from predominantly winter annual to perennial species. In the second and third production years the weed community composition remained relatively stable. Grain yield was 16% greater with 135 kg N ha −1 than 90 kg N ha −1 but was not affected by in-season forage harvest or weed management treatments in the second and third years. Grain yield decreased from 763 to 371 kg ha −1 over three years, while aboveground biomass remained stable. Weed presence did not affect yields in second and third years. Dual-use IWG cropping systems effectively suppressed weeds and IWG is a promising grain crop alternative for farmers interested in diversifying their cropping systems under similar conditions. Abbreviations: AIC, Akaike's Information Criterion; IWG, intermediate wheatgrass.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

IntroductionKernza intermediate wheatgrass (IWG) is a perennial grain and forage crop. Intercropping IWG with legumes may increase the forage yields and nutritive value but may compromise Kernza grain yields. The interaction between IWG and legumes depends on planting season, row spacing, and legume species. Our aim was to evaluate the effects of those management practices on Kernza grain yield, summer and fall forage yield and nutritive value, weed biomass and, the profitability of the cropping system in Wisconsin, USA.MethodsIn the spring and fall of 2017, we planted eight cropping systems at 38 and 57 cm of row spacing: four IWG monocultures [control without N fertilization or weed removal (IWG), hand weed removal (hand weeded), IWG fertilized with urea at rates of 45 or 90 kg ha−1], and four IWG-legume intercrops (IWG with alfalfa, Berseem clover, Kura clover, or red clover).Results and discussionMost of the intercropping systems were similar to IWG monoculture in grain (ranging from 652 to 1,160 kg ha−1) and forage yield (ranging from 2,740 to 5,190 kg ha−1) and improved the forage quality. However, for spring planted IWG, intercropped with red clover or alfalfa, the grain and forage yields were lower than the IWG monoculture (~80 and 450 kg ha−1, respectively). The best performing intercrops in the first year were Kura clover in the spring planting (652 kg Kernza grain ha−1, 4,920 kg IWG forage ha−1 and 825 kg legume forage ha−1) and red clover in the fall planting (857 kg Kernza grain ha−1, 3,800 kg IWG forage ha−1, and 450 kg legume forage ha−1). In the second year, grain yield decreased 84% on average. Overall, the profitability of the IWG legume intercropping was high, encouraging the adoption of dual-purpose perennial crops.

Intermediate wheatgrass [IWG; Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] is a perennial cereal and forage crop marketed for its grain, Kernza. Lodging, which is correlated with plant height, can reduce IWG grain yield. Our goal was to determine the effects of the plant growth regulator trinexapac-ethyl (TE) application rate; forage harvest timing; and N rate on IWG plant height, lodging, aboveground biomass, grain yield, and harvest index. The experiment was established in 2015 in southern Wisconsin using a population of IWG bred for increased grain yield. The experimental design was randomized complete blocks with three replications of a factorial arrangement of three factors: TE rate (0, 0.22, 0.66 kg a.i. ha −1 ), forage harvest timing (unharvested, summer, summer + fall, spring + summer + fall), and N rate (90 and 135 kg N ha −1 ). Responses were measured in the second (2017) and third (2018) production years of IWG. Lodging was not observed. No interactions among treatment factors were detected. Plant height was 6% lower, grain yield was 26% higher, and harvest index was 48% higher in the low TE rate treatment compared to non-treated, averaged across other factors. Harvesting forage in the spring + summer + fall reduced plant height by 7% compared to unharvested control but reduced grain yield by 11%. The high N rate increased plant height by 4% and grain yield by 26%.Using TE can be a viable strategy to reduce plant height and increase grain yield in IWG dual-use (grain and forage) production systems.Abbreviations: GDD, growing degree days; IWG, intermediate wheatgrass; TE, trinexapac-ethyl This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Barkworth & D. R. Dewey subsp. intermedium] is being domesticated as a perennial grain crop. Advanced grain‐type IWG populations display variability in key physiological parameters related to seed development, making it difficult to determine grain harvest timing. A quantitative literature review of cool‐season grasses informed the modeling of IWG field trial data. Results revealed that multiple species exhibited a consistent multiphase dry‐down pattern from anthesis to a stabilized moisture content, which often included a rapid dry‐down phase that presaged maximum seed dry matter and gave insight into the relationship between floret shatter and maximum seed yield. A field trial was conducted at three locations in which IWG spikes were repeatedly sampled postanthesis and divided into three fractions to measure physiological patterns over growing degree days (GDDs). Similar to literature review results, IWG demonstrated a rapid dry‐down phase that started when seed moisture content was between 44.7 and 52.8% and decreased at a rate of −0.12 to −0.20% GDD−1 during this phase. At all locations, florets began shattering before seeds reached maximum dry matter, which resulted in reduced floret site utilization. Seed from distal fractions reached 95% dry matter 135 GDDs earlier than seed from basal fractions, while basal seeds were 21% larger than distal seeds. Timing of maximized seed yield per spike ranged from 530 to 701 GDDs after mid‐anthesis provided a starting point for estimating optimum IWG seed harvest timing under high and low shattering conditions and also supports the importance of repeated measurement of seed moisture to pinpoint optimal harvest time.