Influence of Integrated Agronomic and Weed Management Practices on Soybean Canopy Development and Yield

The role of weed suppression by the cultivated crop is often overlooked in annual row cropping systems. Agronomic practices such as planting time, row spacing, tillage and herbicide selection may influence the time of crop canopy closure. The objective of this research was to evaluate the influence of the aforementioned agronomic practices and their interaction with the adoption of an effective preemergence (PRE) soil residual herbicide program on soybean canopy closure and yield. A field experiment was conducted in 2019 and 2020 at Arlington, WI as a 2×2×2×2 factorial in a randomized complete block design, including early (late-April) and standard (late-May) planting time, narrow (38 cm) and wide (76 cm) row spacing, conventional tillage and no-till, and soil-applied PRE herbicide (yes and no; flumioxazin 150 g ai ha−1 + metribuzin 449 g ai ha−1 + pyroxasulfone 190 g ai ha-1). All plots were maintained weed-free throughout the growing season. In both years, early planted soybeans reached 90% green canopy cover (T90) before (7 to 9 d difference) and yielded more (188 to 902 kg ha−1 difference) than the standard planted soybeans. Narrow-row soybeans reached T90 earlier than wide-row soybeans (4 to 7 d difference), but yield was similar between row spacing treatments. Conventional tillage had a higher yield when compared to a no-till system (377 kg ha−1 difference). The PRE herbicide slightly delayed T90 (4 d or less) but had no impact on yield. All practices investigated herein influenced the time of soybean canopy closure but only planting time and tillage impacted yield. Planting soybeans earlier and reducing their row spacing expedites the time to canopy closure. The potential delay in canopy development and yield loss if soybeans are allowed to compete with weeds early in the season would likely outweigh the slight delay in canopy development by an effective PRE herbicide.

Effects of Planting Density of Spring Soybean on Canopy Photosynthetically Active Radiation and Yield in Northeast China

Soybean is an important legume crop. Planting density of soybean directly affects the distribution of photosynthetically active radiation (PAR) in the canopy, which affects the physiological changes, such as photosynthesis of soybean, and leads to the change of yield. In this experiment, soybean variety Heinong 84 was adopted, and five planting densities were set as 200,000 plants/ha (D20), 250,000 plants/ha (D25), 300,000 plants/ha (D30), 400,000 plants/ha (D40) and 500,000 plants/ha (D50). The canopy PAR intensity was measured based on photosynthetically active radiation recorder, and the effects of different densities on soybean canopy PAR and yield were studied systematically. According to the results, with the extension of growth period, the PAR above and within the canopy of soybean decreased first and then increased, and the rules were consistent under different densities. During each growth period, PAR was above that of canopy > growth point > middle stem > cotyledon scar and decreased with the increase of density. The growth point changed significantly, followed by middle stem, but no significant change happened in cotyledon scar. The absorption photosynthetically active radiation (FPAR) showed a unimodal trend with the increase of density at V4 and R2 and had an upward trend at R4 and R6. The number of effective pods per plant and 100 seed weight of D20 are the highest, and the yield of D25 is the highest.

Breeding strategies for soybean canopy structure optimization in dry regions

Water supply is one of the key factors limiting soybean yield. Coming from the monsoon climate region, soybean lacks effective means of leaf surface growth restriction and is prone to produce excessive leaf area that leads to undesirable transpiration increase. Reducing branching rate and, correspondingly, leaf number per plant is usually proposed to decrease leaf area. However, as far as branching ability is generally a useful trait contributing to yield stability, we have undertaken a search for possible alternative ways of leaf area reduction. Soybean canopy structure was studied in our germplasm nursery in Kursk region. We have updated an express method of soybean trifoliate leaf surface calculation. A regression index for soybean trifoliate leaf surface by central leaflet length and width product characterizes leaflet shape and depends from its length to width ratio. In the sampling studied, trifoliate leaf surface varied from 79 to 150sq. cm. Leaf area index (LAI) varied from 4.0 to 8.6 sq. m/sq. m, with optimal LAI equal to 6.0 sq. m/sq. m. Excessive LAI (over 7.7 sq. m/sq. m) decreased yield by 20 %. Optimal LAI may be achieved by various combinations of leaf size and leaf number per plant. Lines possessing good branching rate but remaining within optimal LAI values due to small leaf size were revealed. Thus, lamina size reduction may be proposed as an alternative breeding direction to solve a conflict of bushy plant type and drought tolerance.

Effect of Deposition Aids Tank-Mixed with Herbicides on Cotton and Soybean Canopy Deposition and Spray Droplet Parameters

The adoption of auxin-tolerant crops has increased awareness regarding herbicide off-target movement. Deposition aids are promoted as a possible solution to off-target movement, although their effect on spray canopy deposition are not well understood. Studies were conducted to determine the impact of deposition aids tank-mixed with herbicides on spray droplet size and canopy deposition. Commonly used herbicides were applied on soybean and cotton in combination with deposition aids (oil, polymer, and guargum). Interactions between herbicide solution and deposition aid influenced droplet size parameters for both cotton and soybean herbicides tested herein (p ≤ 0.0001). Generally, the addition of polymer and guargum deposition aids increased spray droplet size, whereas the addition of oil deposition aid decreased droplet size for some treatments. When herbicides were combined, the inclusion of deposition aids did not influence overall spray deposition on cotton (p = 0.82) and soybean (p = 0.72). When herbicide solutions were evaluated individually, the advent of deposition aids had inconsistent results with cotton and soybean spray deposition being unaffected, increased, or even decreased depending on the herbicide solution tested. For example, the polymer-based deposition aid increased spray deposition on cotton for applications of glyphosate + dicamba + S-metolachlor resulting in 1640.6 RFU (relative fluorescence units). However, the same deposition aid decreased spray deposition on cotton for applications of glyphosate + dicamba + acetochlor (1179.3 RFU). Although deposition aids influenced spray deposition on cotton and soybean for some herbicide combinations, their use should be determined on a case-by-case scenario.

Impact of postemergence herbicides on soybean injury and canopy formation

Field studies were conducted in 2017 and 2018 in Arkansas to evaluate the injury caused by herbicides on soybean canopy formation and yield. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron alone and in combination with glufosinate were applied to glufosinate-resistant soybean at the V2 growth stage. Soybean injury resulting from these labeled herbicide treatments ranged from 9% to 25% at 2 wk after application. This level of injury resulted in a 4-, 5-, 6-, and 6-d delay in soybean reaching 80% groundcover following fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, respectively. There was a 2-d delay in soybean reaching a canopy volume of 15,000 cm3 following each of the four herbicide treatments. The addition of glufosinate to the herbicide applications resulted in longer delays in canopy formation with every herbicide treatment except glufosinate + fomesafen. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, each applied with glufosinate, delayed soybean from reaching 80% groundcover by 2, 7, 8, and 9 d, respectively, and delayed the number of days for soybean to reach a canopy volume of 15,000 cm3 by 2, 3, 2, and 2 d, respectively. No yield loss occurred with any herbicide application. A delay in percent groundcover in soybean allows sunlight to reach the soil surface for longer periods throughout the growing season, possibly promoting late-season weed germination and the need for an additional POST herbicide application.