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

Abstract

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.Abbreviations: ADF, acid detergent fiber; CP, crude protein; Ctrl, no defoliation; Fa, defoliation only in fall; GDD, growing degree days; IWG, intermediate wheatgrass; NIRS, near-infrared reflectance spectroscopy; NDF, neutral detergent fiber; RFV, relative feed value; Sp, defoliation only in spring; SpFa, defoliation in spring and fall.

Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants

“…While they did not report yield plant -1 , similar decreases over time in yield spike -1 , seed mass, seed dimensions, florets spikelet -1 , and stem width were observed, though whether this decrease occurred between the second or third year was variable depending on the trait. A study of IWG yield components in sward environments also reported a 50% reduction in grain number per spike after the first year (Hunter et al, 2020).…”

Effects of defoliation and row spacing on intermediate wheatgrass I: Grain production

“…However, the reduction in grain yield following defoliation in 2017, which likely resulted from a reduction in spikes/tillers and grains spike −1 , suggests that repeated defoliation may ultimately diminish stand vigor and grain yield. This may be due in part to depletion of N reserves (see Hunter et al., 2020).…”

“…The reason for this is unclear, since these well‐established stands should have required lower investment in root growth than the first‐year stand. This suggests that reproductive growth may be declining due to other factors, such as genetic control, nutrient limitation (see Hunter et al., 2020), or disease burden.…”

“…For instance, the decrease in spikes/tillers following defoliation in 2018 may be because defoliation resulted in greater tillers m −1 , diluting resources for spike production, likely nutrients. There is evidence that by 2017 this stand was experiencing N stress, especially in the defoliated treatments, and that P and K concentrations in the fall vegetative biomass were near the critical values for perennial grasses (Hunter et al., 2020).…”

“…This study also provides the first detailed report of management effects on intermediate wheatgrass grain yield components. The effects of defoliation and row spacing on forage production, forage quality, and economic returns are reported in a companion paper (Hunter et al., 2020).…”