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

Abstract

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.Abbreviations: Ctrl, no defoliation; Fa, defoliation only in fall; HI, harvest index; IWG, intermediate wheatgrass; R/FR, red/far red; Sp, defoliation only in spring; SpFa, defoliation in spring and fall; TKW, thousand kernel weight; YC, yield component.

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

“…The defoliation treatments were continued in 2018, as reported in Hunter et al. (2020), but complete forage yield data was not collected.…”

“…Straw yield was sampled annually at grain harvest on about 4 August. Straw sampling methods are described in the companion paper (Hunter et al., 2020). Spring and fall hay samples were collected by harvesting all vegetation 7.5 cm above the soil surface in two separate 2‐m lengths of row per split plot.…”

“…Spring defoliation occurred prior to stem elongation on 8, 2, and 5 May and fall defoliation occurred prior to senescence on 20, 5, and 26 October in 2015, 2016, and 2017, respectively. In the 30‐ and 61‐cm row spacings, both straw and hay yields were adjusted to account for the colonization of interrow space that occurred in 2017 (see Hunter et al., 2020).…”

“…As discussed in the companion paper (Hunter, Sheaffer, Culman, & Jungers, 2020), mechanical defoliation for forage harvest stimulates tiller production in grasses by increasing both the intensity and the red/far red ratio of the light at the plant base (Aamlid, Heide, Christie, & McGraw, 1997; Deregibus, Sanchez, & Casal, 1983; Ugarte, Trupkin, Ghiglione, Slafer, & Casal, 2010; Youngner, 1972). Defoliation can improve sward density and help maintain an optimal leaf arrangement for photosynthesis (Youngner, 1972).…”

“…We conducted this study across the 3‐yr life of an IWG stand. A companion paper (Hunter et al., 2020) discusses the effects of defoliation and row spacing on IWG grain yield and yield components.…”