Effect of Tillage Practice on Cover Crop Termination Timing on Soybean Production

• Determining when to terminate a cover crop while getting the most benefit out of the cover crop and maintaining the yield potential can be impacted by the tillage practice.
• The objective of this trial was to determine the interaction between cover crop termination timing and tillage practice, as well as the effect on soybean stand, weed suppression, and yield.

• This trial was designed as a split-plot with cover crop termination timing as the whole plot and tillage practice (strip-till or no till) as the sub-plot.
• The cover crop species used was winter wheat which was drilled at 120 lbs of seed/acre on 11/11/2021.
• On 4/12/2022 the trial had a base fertilizer application of 29 lbs of nitrogen (N)/acre, 60 lbs of phosphorus (P)/acre, 25 lbs of sulfur (S)/acre, and 0.25 lb of zinc (Zn)/acre. The fertilizer was applied with a strip-till machine in the strip-tilled plots and banded on the soil surface of the no-till plots.
• All treatments were planted in 30-inch row.
• Each termination timing of 1, 3, and 5 weeks before planting (WBP), was paired with no-till and strip-till (Table 1).
• Cover crops were terminated using Roundup PowerMax® herbicide at 32 fl oz/acre with a spray volume of 15 gal/acre (Table 2).

Table 1. Treatments with cover crop termination timings and tillage practice treatment combinations.

Table 2. Herbicide applications made during the 2022 growing season. 

• Pre-plant, burndown, and post-emergence herbicide applications are listed in Table 2. All plots had identical weed management but differed in cover crop termination timing.
• A total of 6.48 inches of precipitation accumulated during the soybean growing season. An additional 8 inches of water was applied by sprinkler irrigation which was a limited amount, leading to lower-than-normal yields.
• Weed suppression and early soybean stand were assessed when the crop reached the V1-V2 growth stage, prior to the first post-emergence herbicide application. Late stand assessment notes were recorded close to soybean harvest time.
  • Primary weed species evaluated in this trial were Palmer amaranth (Amaranthus palmeri) and volunteer corn.
• The trial was harvested with a plot combine, measuring grain moisture content, test weight, and total grain weight to determine yield.

• Winter wheat biomass accumulation took off after April 25th due to dry weather in the fall of 2021 and spring of 2022. By the time 1 WBP was terminated, the cover crop canopy cover was 45.5% of the soil, compared to 1.2% and 0.5% in the 3 WBP and 5 WBP, respectively. Therefore, there was no significant cover crop growth in the 3 WBP and 5 WBP treatments (Figure 1).

• Weed pressure in this trial was high and required four herbicide applications to achieve effective weed control. Weed suppression was greater (66%) when the cover crop was terminated 1 week before soybean planting (1 WBP) compared to 3 WBP and 5 WBP (Figure 2). The increased cover crop biomass accumulation in treatment 1 WBP helped building canopy closure to compete against weeds in the area. No difference in weed suppression was found between tillage practices.

• There was an advantage of strip-till compared to no-till for early stand of soybean which could be due to the increased seed bed quality that is provided by strip-tilling (Figure 3).

• No-till and strip-till reached similar soybean late stands, with the exception of the cover crop termination timing 1 week before soybean planting (1 WBP) in the no-till system (Figure 4). That is likely due to the increased cover crop biomass that impacted soybean emergence (Figure 1).

• In general, soybean yield was better with no-till than strip-till. On average, soybean yields in no-till were 46.4 bu/a compared to 44.2 bu/a in the strip-till treatment (Figure 5).
• There were no significant soybean yield responses due to cover crop termination timing (Figure 5).
• Although the soybean stand in the strip-till treatment was better than the no-till, the no-till plots had higher yields. This emphasizes the ability of soybean to adapt to population reductions.

• Winter wheat cover crop helped to increase weed suppression (mostly Palmer amaranth) when terminated 1 week before planting (WBP) soybean. Cover crop canopy is key to providing soil coverage and could be used as a weed management tool.
• The strip-till treatments had higher early emergence and final stand than no-till, but soybean plants have the ability to adapt to adverse growing conditions and can produce similar yields with a reduced stand when the growing conditions are favorable.
• In a dry year like 2022, soil moisture preservation is key to achieving better yields. In this scenario, no-till treatments yielded better likely due to more soil moisture present. The strip-till plots possibly lost moisture by having the soil exposed to the environment due to the strip-till machine removing residue cover from the row. In addition, cover crops can use moisture and must be terminated timely. In this study we saw a trend of lower yields (not significant) when cover crops were terminated at 1 WBP.
• The soybean yields were similar across the cover crop termination timings likely due to irrigation application.

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