Legume species not spatial arrangement influence cover crop mixture effects in strip‐tilled organic cabbage

Abstract

Management constraints in reduced tillage organic vegetable production may be alleviated by combining strip tillage (ST) with overwintering cereal-legume cover crop mixtures. Field studies in Michigan and New York over 6 site-years evaluated the effects of preceding cover crops, including cereal rye (R; Secale cereale L.), hairy vetch (V; Vicia villosa Roth) and crimson clover (CC; Trifolium incarnatum), on N availability, weed management, and yields in ST organic cabbage (Brassica oleracea L. var. capitata). Cover crop treatments included R-legume mixtures (RV and RCC) planted under two spatial arrangements, standard full-width mixed [-M] vs. segregated strips [-S] (legumes planted in-row and R between-row), and R and V monocultures. Cover crop aboveground biomass (5-10 Mg ha -1 ) and N content (>90 kg N ha -1 ) were not different among RV and RCC but the C/N of RCC was 58% greater than RV. Cabbage yields after RCC-M were lower than RV-M in five of six cases with yield reductions ranging from 22 to 41%. Spatial arrangement had no effect on cabbage yield after RV but improved yields after RCC from 23 to 39% in one, relatively dry, site-year. Without N fertilizer, yields after RV and V were equivalent to or greater than R-S with 134 kg N ha -1 in seven of nine and four of four cases, respectively. Legume species and spatial arrangement had little or no impact on the efficacy of in-row mechanical cultivation, hand-weeding time or weed biomass.Overall, N supplied from V and RV mixtures was an important driver of ST organic cabbage yields across different soil types and weather conditions.

Strip-tillage and Zonal Cover Cropping Effects on Organic Squash Production

“…Higher observed weed densities in strip-till treatments compared with full-till treatments (Fig. 5) were also expected and consistent with those of several previous studies with similar levels of rye-vetch residue (Maher et al 2021). In strip-till mixed treatments, the rye-vetch biomass ranged from $4000 to 6500 kg/ha, which was consistent with the results of previous studies that examined rye-vetch productivity in northern climates (Keene and Curran 2016;Mohler and Teasdale 1993;Ryan et al 2011); however, it was considerably less than the 8000 kg/ha of rye-vetch mulch considered necessary to effectively suppress weeds in agronomic crops such as corn or soybeans (Mirsky et al 2013;Teasdale and Mohler 1993;Teasdale and Mohler 2000).…”

“…Various approaches have been evaluated to address weed and N management challenges in strip-till systems through adjustments in complementary cover cropping practices, including variations in the spatial arrangement of cover crops relative to future crop rows (Lowry and Brainard 2016;Maher et al 2021). For example, several studies have evaluated the impact of segregated or zonal plantings of grass-legume cover crop mixtures in which the legume component is planted only in the in-row zone (where subsequent striptillage and crop planting will occur) and the grass component is sown only in the untilled between-row zone (Elhakeem et al 2019;Gilley et al 1997;Lowry and Brainard 2016Maher et al 2021;Ofori and Stern 1987).…”

“…Various approaches have been evaluated to address weed and N management challenges in strip-till systems through adjustments in complementary cover cropping practices, including variations in the spatial arrangement of cover crops relative to future crop rows (Lowry and Brainard 2016;Maher et al 2021). For example, several studies have evaluated the impact of segregated or zonal plantings of grass-legume cover crop mixtures in which the legume component is planted only in the in-row zone (where subsequent striptillage and crop planting will occur) and the grass component is sown only in the untilled between-row zone (Elhakeem et al 2019;Gilley et al 1997;Lowry and Brainard 2016Maher et al 2021;Ofori and Stern 1987). The primary hypothesized benefits of these zonal plantings in reduced tillage systems include the following: improved N use efficiency because the N-fixing legumes are concentrated in the zone closest to early crop root growth; improved crop establishment because more recalcitrant grass residue is excluded from the zone where it might interfere with crop planting; enhanced weed suppression between crop rows because grass residues are generally more weed-suppressive than legumes; and lower total seed costs because more expensive legume seeds may be sown at a lower rate in segregated than in fully mixed plantings (Lowry and Brainard 2016).…”

“…Zonal plantings may also improve the overall cover crop productivity or quality when interspecific competition between component species is greater than intraspecific competition (Elhakeem et al 2019;Fujita et al 1992;Lowry and Brainard 2016). However, observed benefits of zonal cover crop plantings for subsequent crops, including sweet corn (Lowry and Brainard 2016 and cabbage (Maher et al 2021), have been few and inconsistent. Zonal planting of rye-vetch reduced the ratio of carbon (C) to N of cover crop residue concentrated in the row, and increased soil inorganic N in the root zone of subsequent crops in some cases; however, it had little impact on the subsequent yield or weed suppression, partly because of the cover crop and N mixing across zones or the plasticity of crop and weed root N-foraging across zones (Lowry and Brainard 2017;Maher et al 2021).…”

“…However, observed benefits of zonal cover crop plantings for subsequent crops, including sweet corn (Lowry and Brainard 2016 and cabbage (Maher et al 2021), have been few and inconsistent. Zonal planting of rye-vetch reduced the ratio of carbon (C) to N of cover crop residue concentrated in the row, and increased soil inorganic N in the root zone of subsequent crops in some cases; however, it had little impact on the subsequent yield or weed suppression, partly because of the cover crop and N mixing across zones or the plasticity of crop and weed root N-foraging across zones (Lowry and Brainard 2017;Maher et al 2021). Row spacing of winter squash is typically twoto three-times greater than that of other crops evaluated in zonal planting systems (Egel et al 2019).…”