Rhizodeposition and roots play opposite but complementary roles for building mineral-associated and particulate organic carbon.

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.

Forage crops have the potential to serve multiple functions, providing an ecological framework to sustainably intensify food production, i.e., ecological intensification. We review three categories of forages (annual forages, perennial forages, and dual-use perennial crops/forages) we believe hold the greatest promise for ecologically intensifying food production. Annual cover crops can provide additional forage resources while mitigating nutrient losses from agricultural fields when they are intercropped with, interseeded into, or following an annual crop, for instance. The integration of perennial forages either temporally, such as annual crop rotations that include a perennial forage phase, or spatially, such as the intercropping of perennial forages with an annual cash crop, provide weed suppression, soil quality, and yield and crop quality benefits. Dual-use crops/forages can provide forage and a grain crop in a single year while providing multiple ecological and economic benefits. However, tradeoffs in balancing multiple functions and limitations in reducing the risks associated with these practices exist. Advancing our understanding of these systems so we can overcome some of the limitations will play a critical role in increasing food production while promoting positive environmental outcomes.

Kernza intermediate wheatgrass (Thinopyrum intermedium) is the first commercially developed perennial grain crop in North America, with multiple environmental and economic benefits. One of the major challenges for adoption of this dual-use forage and grain crop is the decline in grain yield in subsequent harvest years. Post-harvest management practices (e.g., chopping, burning, chemical, and mechanical thinning) could reduce the intraspecific competition for light and maintain Kernza grain yields over time. We aimed to identify management practices that improve light penetration and propose a conceptual model to explain the mechanisms contributing to Kernza grain yield. We applied 10 management practices after the first Kernza grain harvest in a randomized complete block design experiment with three replications, at two different locations in Wisconsin, USA. Light penetration increased when post-harvest management practices were applied. Mechanical or chemical thinning had relatively lower lodging and increased yield components per row, but not per area due to a reduction in the number of productive rows. Threshed grain yield per area in the second year of Kernza was similar among the treatments despite the differences in vegetative biomass generated. Further research is needed to optimize management practices to maintain Kernza grain yield over time.

Introduction: Kernza 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.Methods: In 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 discussion: Most 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.