Forage harvest management impacts “Kernza” intermediate wheatgrass productivity across North America

Abstract

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.

Maintaining grain yield of Th. intermedium across stand age through constant spike fertility and spike density: Understanding its response to various agronomic managements

“…While reducing tiller density at grain harvest, the autumn defoliation had no impact on grain yield as compensation, with higher TKW, was reported. These results are in line with previous studies where forage harvest, when performed in summer (i.e., after grain harvest) or in autumn (Zimbric et al, 2021) didn't impact grain yield or even increased it (Pugliese et al, 2019;Culman et al, 2023). In addition, the study of Dick et al (2018) highlighted that the grazing of residues increased seed yield and harvest index compared to the removal or chopping of residues.…”

“…However, in denser swards, a strong trade-off has been observed between tiller density and fertility, especially as stand ages (Jungers et al, 2017;Hunter et al, 2020a), so that total densities exceeding roughly 1000 tillers m -2 were detrimental to grain yield. Additionally, there is a marked trend of yield decline as stand ages, leading to a drop in the harvest index as high as 50 % (Culman et al, 2023;Duchene et al, 2023). Different productivity dynamics have been observed in previous studies, with yields peaking the first or the second year of cultivation before dropping down (Jungers et al, 2017;Tautges et al, 2018;Bajgain et al, 2020;Bergquist et al, 2022).…”

“…Such crop is proposed for dual-purpose use, with both forage and grain for human consumption. While grain and straw are harvested in summer, additional cut or grazing operations could be performed in autumn or in early-spring for forage production (Culman et al, 2023;Favre et al, 2019;Hunter et al, 2020b). Grown for several years, the extended belowground activity and the yearround soil cover can provide important benefits for soil protection, carbon storage or water quality (Culman et al, 2013;de Oliveira et al, 2018;Sprunger et al, 2019).…”

“…intermedium, various management options have been studied to improve grain yield in young stands or to maintain yield in aging stands including crop defoliation in summer (i.e., just after grain harvest), in autumn or in spring, either by grazing (Dick et al, 2018) or mowing. As the spring mowing tends to decrease grain yield (Zimbric et al, 2021;Culman et al, 2023), the summer and autumn mowing can increase grain yield compared to no forage harvesting (Pugliese et al, 2019;Culman et al, 2023), but without mitigating yield decline with stand age (Hunter et al, 2020a).…”