Assessment of soil management strategies for sustainable crop production, weed management and mitigation of herbicide carryover

Herbicide Carryover Study

Experiments were conducted over the 2019 and 2020 growing seasons at the Arlington Ag Research Station (Arlington, WI), the Lancaster Ag Research Station (Lancaster, WI), and the University of Nebraska Havelock Farm (Lincoln, NE). Both corn and soybean experiments were conducted at all sites during both years, and new fields with no recent use of residual herbicide products were selected for each growing season. These sites were selected based on their representation of local soils used for crop production and to expand this research across the Midwest. Experiments were established in randomized complete block design with four blocks of 3x9.1 m plots, and a five by three factorial treatment structure that included five herbicide treatments (1/4 rate and 1/2 rate each of two herbicide products and a non-treated control) and three soil management practices (conventional tillage, no-till, and a cereal rye CC terminated prior to crop planting). Residual herbicides used prior to corn included imazethapyr (17.5 and 35 g a.e. ha^-1, Pursuit, BASF, Research Triangle Park, NC) and fomesafen (65.9 and 131.8 g a.i. ha^-1, Reflex, Syngenta, Greensboro, NC); herbicides used prior to soybean included mesotrione (26.3 and 52.6 g a.i ha^-1, Callisto, Syngenta, Greensboro, NC) and clopyralid (35.75 and 71.5 g a.e. ha^-1, Stinger, Corteva, Indianapolis, IN). Herbicides treatments were applied in the fall with soil management practices being implemented following application. Applying reduced herbicide rates in the fall was done to simulate herbicide which had partially degraded from application in the previous crop, such as would occur from a Summer post-emergence herbicide application.

               The cereal rye CC (in Wisconsin, Guardian Winter Rye, La Crosse Seed, La Crosse, WI; in Nebraska, Elbon Cereal Rye, Green Cover Seed, Bladen, NE) was drilled at 67 kg ha^-1 with 19 cm row spacing 3.2 cm seeding depth in the fall following the harvest of the previous crop and residual herbicide application. The CC termination with glyphosate (1261.6 g a.e. ha^-1, Roundup PowerMAX, Bayer Crop Science, St. Louis, MO) occurred 4-7 days prior to crop planting. Glyphosate was also used for a post-emergence application in all studies to keep experiments weed-free. Wisconsin sites were chisel plowed in the fall following residual herbicide application and field cultivated in the spring prior to crop planting; in Nebraska, an offset disk was used in the Fall following residual herbicide application. Fertility was managed in each experiment according to Wisconsin and Nebraska fertilizer recommendations for optimum nitrogen, phosphorus, and potassium (Laboski and Peters, 2012; Shaver, 2014). Crops were planted with a row-crop planter at 76 cm row spacing and a 3.8 cm seeding depth. The corn hybrid P0339AM (Pioneer, Johnston, IA) was used and it was planted at 80,300 seeds ha^-1 in Wisconsin experiments and 79,000 seeds ha^-1 in the Nebraska experiment. This hybrid was selected for its sensitivity to ALS herbicides. The soybean variety P22T1R2 (Pioneer, Johnston, IA) was used and it was planted at 345,900 seeds ha^-1 in Wisconsin experiments and 370,000 seeds ha^-1 in the Nebraska experiment.

               Sampling for this research included CC biomass sampling at termination timing, visual ratings of crop injury from herbicide carryover, photos for observing potential crop canopy differences, and crop yield. Aboveground CC biomass was sampled by collecting three subsamples from a 0.09 m² quadrat, drying samples at 50 °C until constant weight, and recording sample mass. Visual ratings of injury from herbicide carryover were collected at the V3-V4 crop stage in both corn and soybean along with photos for canopy comparisons. Six soybean plants or corn ears were sampled from each plot to assess potential differences in yield components (seed count, seed density, pods/plant, and seeds/pod). Crop yield was collected from the center two rows of each crop with a plot combine.

Soil Management Systems Study

Experiments were conducted over the 2019 and 2020 growing seasons at the University of Wisconsin’s Arlington Ag Research Station and Lancaster Ag Research Station in Wisconsin (Table 1). Both corn and soybean experiments were conducted at both sites over both years. These sites were selected because they represent two distinct areas of agriculturally productive soil in Wisconsin. Fields used were managed with predominantly no-till in recent years which provided a stable soil with predictable weed presence to begin these experiments. Experiments were established in randomized complete block design with four blocks of 3x9.1 m plots, with a six by two factorial treatment structure that included six soil management practices and two pre-emergence (PRE) herbicide treatments (yes PRE or no PRE). Soil management practices included conventional tillage (CT), no-till (NT), and four cover crop termination timings/methods (early termination [CCET] two weeks prior to crop planting, plant termination [CCPT] at the time of crop planting, forage harvest [CCFH] at the time of crop planting, and late termination [CCLT] two weeks after crop planting). Forage harvest of a CC is becoming more common in Wisconsin intending to provide additional feed sources for Dairy farms. Soil management was retained in respective plots as individual experiments progressed in a corn-soybean rotation so that the effects of soil management over time could be studied.

Table 1. Field site background information for experiments conducted in 2019 and 2020 growing seasons at the Arlington Agricultural Research Station and the Lancaster Agricultural Research Station in Wisconsin.

^aOM%, soil organic matter %

^bCC, cereal rye cover crop

The cereal rye (Guardian Winter Rye, La Crosse Seed, La Crosse, WI) CC was drilled at 67 kg ha^-1 (Smith et al., 2019) in the fall following the harvest of the previous crop with a 3.2 cm seeding depth and 19 cm row-spacing. Tillage was completed in CT treatments using a chisel-plow in the fall and field cultivator in the spring prior to crop planting. All experiments were broadcast fertilized annually in the spring, prior to crop establishment, according to Wisconsin fertilizer recommendations for optimum nitrogen, phosphorus, and potassium (Laboski and Peters, 2012). Glyphosate (1261.6 g a.e. ha^-1, Roundup PowerMAX, Bayer Crop Science, St. Louis, MO) was used for chemical termination of all CC soil treatments and for a burndown herbicide application at the time of crop planting in NT treatments (Table 2). Crops were planted at 3.8 cm depth using a row-crop planter with 76 cm row-spacing. Corn was planted at 80.3k seeds ha^-1. Soybean was planted at 345.9k seeds ha^-1. In corn, a pre herbicide mix containing bicyclopyrone, mesotrione, and S-metolachlor (44.9, 179.4, and 1603.6 g a.i. ha^-1, respectively. Acuron Flexi, Syngenta, Greensboro, NC) was used for treatments which included a PRE herbicide (Table 2A); in soybean, a PRE herbicide mix containing sulfentrazone and metribuzin (201.9 and 302.8 g a.i. ha^-1, respectively. Authority MTZ, FMC Corporation, Philadelphia, PA) was used (Table 2B). Herbicide applications for CC termination, NT burndown, and PRE herbicides were made using a CO₂ pressurized backpack sprayer at 140 L ha^-1 and a 3 m boom with six TTI110015 nozzles (Spraying Systems Co., Wheaton, IL). A tractor-mounted sprayer was used to apply POST herbicide applications at 140 L ha^-1 with a 6.1 m boom with 12 TTI11003 nozzles (Spraying Systems Co., Wheaton, IL) approximately 30 days after crop planting (Table 2A and 2B).

Table 2 Pre-emergence (PRE) and Post-emergence (POST) herbicide application information for corn (A) and soybean (B).

^aNT and CC, no-till and cover crop

^ba.i. and a.e, active ingredient and acid equivalent

^cAMS, ammonium sulfate

^aNT and CC, no-till and cover crop

^ba.i. and a.e, active ingredient and acid equivalent

^cAMS, ammonium sulfate

note: Intact (Precision Laboratories, Waukegan, IL), FS Certain (GROWMARK FS, Bloomington, IL)

               Data collection from this study included aboveground cereal rye CC biomass for each termination timing, weed density and biomass at the plant termination timing, visual weed cover control ratings (0-100% with 100% indicating complete control of weed cover) at the post-emergence herbicide application timing, and crop yield.