Agronomic Comparisons of Organic and Conventional Soybean with Recommended and High Inputs during the First 4 Years of Organic Management

Abstract

Organic soybean hectares will increase in the Northeast United States of America (USA) because of demand by the expanding organic dairy industry. We evaluated organic and conventional soybean with recommended and high inputs (high seeding rate + organic seed treatment in organic system) from 2015 to 2018 in New York, USA to determine if high input management could reduce the yield penalty in organic soybean. Organic compared with conventional soybean yielded similarly in 2015 and 2016 but ≈ 11% lower in 2017 and 2018. Organic compared with conventional soybean had similar early and harvest plant densities in 2017 but lower early and harvest plant densities in 2018 when both densities correlated with yield (r = 0.33 and 0.36, respectively). Weed densities in organic soybean were low (<0.77 weeds/m2 in all years). Nevertheless, organic compared with conventional soybean in 3 of 4 years had greater weed densities, which had significant negative correlations with yield in 2015 (r = −0.36), 2017 (r = −0.53) and 2018 (r = −0.36). Organic compared with conventional soybean mostly had fewer pods/plant and greater seed weight but yield components showed no consistent correlations with yield. Organic soybean had similar weed densities and yield with recommended and high input management in all years indicating that growers should probably plant organic soybean at recommended seeding rates (370,500 seeds/ha) during the first 4 years of organic production under similar environmental conditions of this study.

High Seeding Rates and Low Soil Nitrogen Environments Optimize Weed Suppression and Profitability in Organic No-Till Planted Soybean

“…Partial returns to the soybean seeding rates were maximized at $2,238 ha −1 with 527,800 seeds ha −1 . The profit-maximizing seeding rates in this study were greater than soybean seeding rate recommendations for tilled organic (370,500 seeds ha −1 ; Cox et al, 2019) and conventional (321,000 seeds ha −1 ; Orlowski et al, 2012) soybean systems, respectively. Despite greater weed biomass, especially of annual species, in plots with added nitrogen, soybean yield was not affected by nitrogen treatment.…”

“…nitrogen treatments (P > 0.05) and profit optimization occurred at $2,238 ha −1 with 527,800 seeds ha −1 . Soybean seeding rates at the economic optimum are higher than recommended seeding rates in tilled organic (370,500 seeds ha −1 ; Cox et al, 2019) and conventional (321,000 seeds ha −1 ; Orlowski et al, 2012) systems. Higher recommended seeding rates compared to the tilled systems may be due to a greater reliance on cropdensity based weed management in the absence of tillage.…”

“…Conversely, increasing the seeding rate of no-till planted soybean is a proactive weed management strategy that suppresses weeds through faster canopy closure (Weiner, 1990;Schwinning and Weiner, 1998), increased light interception (Steckel and Sprague, 2004), and greater crop-weed size asymmetries (Bastiaans et al, 2008). Recommended soybean seeding rates in tilled organic production are 370,500 seeds ha −1 (Cox et al, 2019) but higher seeding densities are desirable for organic no-till planted soybean production. In organic notill planted soybean, weed suppression increased with soybean seeding rates between 195,000 and 914,000 seeds ha −1 (Liebert and Ryan, 2017).…”

Optimizing organic no‐till planted soybean with cover crop selection and termination timing

“…At lower within‐row plant densities, soybean has been shown to maintain yield per unit area by producing a greater number of lateral branches, pods, and seeds per plant, among other forms of compensatory growth (Board, 2000; Cox et al., 2010). Still, research has shown that increasing soybean density well beyond planting rates recommended for tillage‐based organic or conventional soybean production (Cox et al., 2019) can result in yield gains (Liebert & Ryan, 2017; Menalled et al., 2021).…”

High seeding rates, interrow mowing, and electrocution for weed management in organic no-till planted soybean

“…The SR was chosen to be slightly above the organic, no-till recommended feed-grade soybean rate (530,000 pure live seeds ha– 1 ) (Menalled et al 2021), while minimizing risk of soybean lodging and disease at high rates (Cooper 1971; Mohler et al 2021). The baseline seeding rate (432,000 pure live seeds ha– 1 ) is closer to rates used in tillage-based organic production (370,500 seeds ha– 1 ) (Cox et al 2019; Delate et al 2003), although the baseline rate may be considered a high rate compared with recommended seeding rates for conventional production (296,000 to 345,000 seeds ha– 1 ) (Conley and Santini 2007; Rees et al 2019).…”