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Increasing intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] grain yield and maintaining yield over the life of a stand will be critical to the economic viability of Kernza (The Land Institute) grain production. Research on perennial grasses has shown that seed yield can be enhanced by (a) mechanically defoliating the stand for hay production and (b) increasing row spacing. We evaluated the interacting effects of row spacing and defoliation across the 4‐yr life of an intermediate wheatgrass (IWG) stand in St. Paul, MN. We measured grain yield, harvest index, lodging, and yield components including grain mass and number of tillers, spikes, and grains. Data was analyzed with linear mixed models and partial least squares path analysis. Overall, grain yield declined substantially over time, from a mean of 880 kg ha−1 in 2015 to 276 kg ha−1 in 2018. Wider row spacings tended to increase grain yield. Defoliation increased grain yield in the first 2 yr, but may have decreased stand vigor in later years. Neither management practice fundamentally mitigated yield decline. The main cause of yield decline was the reduction in grain number per high‐yielding spike, which dropped by roughly half after the first year. The proportion of spikes that were high yielding also declined over time. Increasing competition among reproductive units likely contributed to yield decline, but there is also evidence that resource allocation to reproduction declined over time. Future research in IWG breeding and management should focus on maintaining high grain number, reducing intra‐stand competition, and increasing resource allocation to reproduction.

Aims Perennial crops with more extensive and deep root systems could access deep stored water and build resilience to water shortage. In the context of human nutrition, perennial grain crops are very interesting. However, it is still questionable whether they are effective in using subsoil water. We compared intermediate wheatgrass (Kernza®) Thinopyrum intermedium , a perennial grain crop, to alfalfa Medicago sativa , a forage crop, for subsoil root growth and water uptake. Alfalfa was chosen because of its deep root system and agronomical interest as a companion crop. Methods Using TDR sensors, deuterium tracer labelling, minirhizotrons and the Hydrus-1D model we characterised the root distribution and water uptake patterns of these two perennial crops during two cropping seasons under field conditions down to 2.5 m soil depth. Results Both crops grew roots down to 2.0 m depth that were active in water uptake but alfalfa was deeper rooted than intermediate wheatgrass. All experimental methods concluded that alfalfa used more water from below 1.0 m depth than intermediate wheatgrass. However, simulations predicted that intermediate wheatgrass used more than 20 mm of water after anthesis from below 1 m soil depth. Simulations confirmed the advantage of deep roots in accessing deep soil water under drought. Conclusions In regions with high groundwater recharge, growing deep-rooted perennial crops have great potential to exploit deep soil water that is often left unused. However, the road to a profitable perennial grain crop is still long and breeding intermediate wheatgrass (Kernza®) cultivars for increased root growth at depth seems to be a worthy investment for the development of more drought tolerant cultivars.

Intermediate wheatgrass [IWG, Thinopyrum intermedium (Host) Barkworth & D.R. Dewey, trade name Kernza] is a widely adapted, cool‐season forage grass, actively bred for perennial grain production. Most of IWG's net primary productivity is directed to nonreproductive structures, so dual‐use strategies to harvest both grain and forage represent a potentially viable pathway to increase its productivity and profitability. We conducted a 3‐year trial at nine diverse environments across North America to evaluate grain and forage yields and forage nutritive value of an early IWG breeding line under contrasting forage harvest managements. These included control (no forage harvest), summer forage harvest immediately after grain harvest, and summer forage harvest with spring or fall forage harvests. Across all sites, IWG grain yields averaged 745, 296, and 221 kg ha−1 for the first, second, and third years, respectively. Grain yields were influenced more by stand age than site. Summer forage mass after grain harvest averaged 6.0, 4.5, and 5.7 Mg ha−1 respectively for the first 3 years. Forage mass was less influenced by stand age, and more by site and forage harvest frequency. Fall forage harvest increased grain yields while spring forage harvests decreased grain yields and both treatments increased total relative feed nutritive values. Collectively, our results demonstrate that harvesting forage can improve both grain yield and forage nutritive values. Farmers growing IWG as a perennial grain can benefit from dual‐use management by harvesting both grain and forage. Core Ideas Different forage harvest frequencies were imposed on intermediate wheatgrass (IWG) in nine sites across North America. Grain yields were largest in the first year and sharply declined with stand age. Fall and summer forage harvests increased grain yields. Increasing forage harvest frequency did not impact total annual forage mass but increased nutritive value. Harvesting forage is an important strategy to increase IWG productivity and profitability.

Management systems that produce both grain and biomass coproducts could enhance the profitability of the novel perennial grain crop Kernza intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] (IWG). Harvesting IWG for grain typically results in a straw harvest; in addition, vegetative biomass can be cut in spring, fall, or both for hay production. We evaluated the interacting effects of defoliation and row spacing on yield, forage quality, and economic return across the 3‐yr life of a conventionally managed IWG stand in St. Paul, MN. We measured straw and hay yield and forage quality and then used recent hay auction results to model forage price and total potential value. We then used estimated production costs to calculate potential net return from straw production alone and with additional hay harvests. Overall, straw was more valuable than hay, despite being of much lower quality, since yields were 3–4 times greater. Straw potential value was similar to the cost of producing both straw and grain, greatly reducing the financial risk in Kernza grain production. Hay production was almost always profitable. Straw and hay yield and value were greater in 15‐ and 30‐cm rows than in 61‐cm rows. Defoliating in both spring and fall led to lower hay and straw yields in the third year. Our results indicate that the best strategy for achieving consistent high net return to biomass production is to plant in 15‐ or 30‐cm rows and only cut hay in the fall.

Purpose Perennial crops have been suggested as a more sustainable alternative to the currently most common cropping systems. Compared with annual plants, perennial plants produce more biomass and have deeper roots, and are expected to lead to higher soil organic carbon (SOC). This hypothesis, however, has not been well tested for grain crops. Methods Using perennial intermediate wheatgrass (IWG, Thinopyrum intermedium ) and annual winter wheat ( Triticum aestivum ) as focal species, and native grassland as reference, we quantified the SOC accumulation via a process-based model, describing water and heat exchanges and carbon-nitrogen cycling in the canopy and soil to a depth of 2 m. The model includes C fixation via photosynthesis, plant biomass growth and litter production, physical protection of SOC, depolymerisation, C mineralisation, nitrification, denitrification, microbial growth, and necromass turnover in the soil. While of general applicability, we considered a sandy loam under warm-summer humid continental climate. Results Following a conversion from native grassland, IWG reduced SOC losses by at least 38%, especially in the particulate organic carbon (POC) pool, within the top 2 m of soil, compared with annual wheat. Soil microbial biomass and soil respiration were higher in IWG than annual wheat. Shifting from annual wheat to high photosynthetic capacity IWG increased SOC by about 33 g C m −2 y −1 (averaged over a 4-year continuous IWG cropping), with a large fraction of SOC gain stemming from restoring POC. Conclusion Compared with annual grains, perennial grains can increase soil carbon sequestration and maintain SOC at levels nearer to that of native grasslands.

Intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Barkworth & Dewey] is the first commercially produced perennial grain crop in the United States. Intercropping legumes with IWG has the potential to enhance dual‐purpose grain and forage production and contribute to weed control in organic management systems. We compared IWG with annual winter wheat (Triticum aestivum L.) in monoculture and intercropped with red clover (Trifolium pratense L.) in a 3‐yr experiment in central New York. Grain yield of IWG was lower than wheat in all years, partly due to lower tiller fertility and seed size in IWG. Compared with grain yield of 1,212 kg ha–1 in the first year, IWG grain yield was 83% (202 kg ha–1) and 64% lower (441 kg ha–1) in the second and third years, respectively. Intermediate wheatgrass straw production increased 40% from 5,541 to 7,785 kg ha–1 over 3 yr while wheat straw yield declined from 5,167 to 3,533 kg ha–1. Red clover did not affect grain or straw yield of either crop but reduced weed biomass and weed species richness. Weed communities in IWG plots were dominated by perennial grasses by the second year of production, whereas annual weeds were dominant in wheat throughout the experiment. Preventing establishment of perennial weeds that will persist in perennial grain cropping systems should be a management priority. High forage production observed when comparing IWG and wheat suggest opportunities for including IWG in integrated crop–livestock systems where IWG's higher forage yield and quality has higher utility. Core Ideas Grain yield of intermediate wheatgrass (IWG) was substantially lower than winter wheat over three harvests. Straw yield of IWG was higher than winter wheat and increased over the same period. Red clover increased total biomass production and suppressed weeds in both crops. Weed communities in IWG plots were dominated by perennial grasses within 2 yr. High straw yield and low grain yield of IWG highlights opportunities for dual‐use systems.

Perennial crops have the potential to provide food, feed, fuel, and fiber while promoting multiple ecosystem services. Intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Buckworth & Dewey] is a perennial grass being bred for grain production. Because the development of IWG as a grain crop is still in its infancy, basic agronomic management practices needed to maximize grain yield and profitability remain unclear. We conducted an experiment to test the effect of N fertilizer rate and type (synthetic vs. organic) and planting density on grain and forage yield of IWG at two sites in Minnesota over 3 yr. Nitrogen application had no effect on grain yield in Year 1 but increased yields in Years 2 and 3. Reducing planting density from 145 to 36 seeds m−2 reduced grain yield in Year 1 but increased grain yield in subsequent years, particularly when coupled with inorganic N fertilizer applied at 80 kg N ha−1. A high proportion of fertile tillers was the best predictor of high IWG grain yield, suggesting that shifts toward vegetative growth over sexual reproduction in the years following establishment are associated with grain yield declines. Generally, biomass yield responded positively to increasing N application rates and planting density across all years. Our results indicate that optimizing plant breeding and agronomic practices that promote fertile tiller production will be critical to the future management of IWG as a perennial grain crop.

Key messageAnalysis of multi-year breeding program data revealed that the genetic architecture of an intermediate wheatgrass population was highly polygenic for both domestication and agronomic traits, supporting the use of genomic selection for new crop domestication.Perennial grains have the potential to provide food for humans and decrease the negative impacts of annual agriculture. Intermediate wheatgrass (IWG, Thinopyrum intermedium, Kernza®) is a promising perennial grain candidate that The Land Institute has been breeding since 2003. We evaluated four consecutive breeding cycles of IWG from 2016 to 2020 with each cycle containing approximately 1100 unique genets. Using genotyping-by-sequencing markers, quantitative trait loci (QTL) were mapped for 34 different traits using genome-wide association analysis. Combining data across cycles and years, we found 93 marker-trait associations for 16 different traits, with each association explaining 0.8–5.2% of the observed phenotypic variance. Across the four cycles, only three QTL showed an FST differentiation > 0.15 with two corresponding to a decrease in floret shattering. Additionally, one marker associated with brittle rachis was 216 bp from an ortholog of the btr2 gene. Power analysis and quantitative genetic theory were used to estimate the effective number of QTL, which ranged from a minimum of 33 up to 558 QTL for individual traits. This study suggests that key agronomic and domestication traits are under polygenic control and that molecular methods like genomic selection are needed to accelerate domestication and improvement of this new crop.

Core Ideas Alfalfa–grass mixtures are good alternative to alfalfa and grass monocultures. In the establishment year, alfalfa dominated the mixture, whereas as stands got older, grasses increased their contribution to the biomass. Alfalfa had higher crude protein, whereas grasses had higher fiber digestibility. Alfalfa–grass mixtures improved forage seasonal distribution. The most common binary mixture in the northern Great Plains is smooth bromegrass (Bromus inermis L.) (SBG) with alfalfa (Medicago sativa L.). However, other mixtures might have advantages over SBG–alfalfa. The objective was to compare forage yield, nutritive value, seasonal distribution, and persistence of grasses in monoculture or binary mixtures with alfalfa. A field experiment was established in 2010 in Fargo, Prosper, and Carrington, ND, and results were evaluated until 2013. Several wheatgrass species not commonly used in alfalfa–grass mixtures were tested. All grass species produced higher forage yield in binary mixtures with alfalfa than in monoculture. Binary mixtures had higher persistence in normal rainfall conditions and improved forage nutritive value. Alfalfa contributed with higher crude protein, whereas grasses had higher digestibility of the fiber. Intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], not commonly included in mixtures with alfalfa, had greater biomass yield than many of the grasses in mixture with alfalfa, although not significantly different from SBG–alfalfa mixture. In the establishment year, alfalfa dominated the mixture (77–99% of total biomass), whereas as stands got older, grasses increased their contribution to the harvested biomass. In the third production year, grass in the mixtures was, on average, 50% of the total biomass. Alfalfa–grass mixtures with grasses other than SBG had similar or greater yield than SBG–alfalfa, increasing the number of potential grass choices that can be used in mixtures. In general, alfalfa–grass mixtures had greater forage yield and nutritive value than grass monocultures.

The slowly establishing salt‐tolerant perennial grasses reduced nitrous oxide (N2O‐N) emissions from saline/sodic soil compared to barren areas. Other salt‐tolerant species may accelerate vegetative establishment and reduce N2O‐N emissions. In a greenhouse study, barley (Hordeum vulgare L.), Florida broadleaf mustard (Brassica juncea L.), and Kernza intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D. R. Dewey] were grown for 63 days to compare shoot biomass and chemical composition, N2O‐N emissions, and the soil microbiome between saline/sodic and productive (non‐salt impacted) soils. Emissions were measured six times daily from 1 to 22 and 42 to 63 days after planting (DAP). Shoot and soil microbial biomass and communities were quantified 63 DAP. N2O‐N emissions were 87% greater from no‐plant saline/sodic than no‐plant productive soil (p < 0.05). N2O‐N emissions were reduced from planted treatments soon after plant emergence. N2O‐N emissions reductions from saline/sodic soil during the first 22 DAP were 84%, 76%, and 61% for barley, mustard, and Kernza, respectively. Barley had the greatest shoot biomass and impact on the soil microbial community, increasing the fungi to bacteria ratio from 0.063 to 0.094 in the productive soil and from 0.056 to 0.076 in the saline/sodic soil. Plant‐induced changes to the soil microbiome, and decreased soil inorganic N and water, contributed to N2O‐N emission reductions. Archived field samples from grass‐established saline/sodic soil areas had a fourfold increase in nos‐Z gene copy number compared to no‐plant controls, which may, in part, explain decreased N2O‐N emissions. Establishing these vigorous species may aid in restoring multiple ecosystem services to saline/sodic areas. Core Ideas Barren Northern Great Plains saline/sodic soils provide few ecosystem services. Barley, Florida broadleaf mustard, and Kernza wheatgrass reduced N2O‐N emissions from saline/sodic soil soon after emergence. N2O‐N emission reductions were attributed to plants decreasing soil water and N and changing the soil microbiome.