Cover crops can retain nutrients, increase organic matter, and reduce erosion. In addition, cover crops may help to increase cash crop yields. Zeroing in on cover crop benefits, what happens to weed suppression and corn yield the longer the cover crop grows? Would more cover crop biomass suppress weeds better? Would that suppression of weeds improve yield or would the thick cover crop mulch cause cooler soil conditions and shade out the young corn seedlings suppressing crop growth?
We set out to answer these questions by implementing an experiment that compares treatments of three cover crop termination dates with no cover crops. On October 5, 2020, winter rye was planted at 70 lbs/acre. In the spring of 2021, cover crops were terminated with an herbicide on three separate dates: 3 weeks before planting (planting brown), 8 days before corning planting (planting green/brown), and 4 days after corn planting (planting green) (Image 1). A bare treatment (no cover crop) served as the control. All treatments were planted on May 18th. Corn was harvested for grain on October 20th. Weed biomass was collected from each treatment just prior to cover crop termination and also when the corn was at the fifth leave stage (V5). Corn seedling vigor was evaluated when corn plants in the plots reached the third leaf stage (V3).
So, what did we find?
Early Season Cover Crop and Weed Biomass: As to be expected, the later the cover crop was terminated, the higher the cover crop and weed biomass. Cover crop biomass at termination was significantly different among the treatments. The first treatment to be terminated, planting brown (1,500 lbs/acre), was 1,810 lbs/acre lower than the planting green/brown (3,340 lbs/acre) and 7,141 lbs/acre lower than planting green (8,671 lbs/acre) (Figure 1). Overall weed pressure was low in the cover crop treatments and was less than 4% of the total harvested biomass.
Corn Vigor: The time of cover crop termination impacted the growth and development of corn. The bare and early terminated cover crop (planting brown) were the most advanced in corn stage, averaging near (V3) (Figure 2). The planting green treatment, was significantly behind the other treatments by nearly a growth stage or more. Image 2, taken 2-July illustrates the delayed growth observed between treatments with no cover crops and those planted green. . There is a high correlation between cover crop biomass and vigor with vigor higher in treatments with lower cover crop biomass. This indicates, that early in the season more cover crop biomass stunted corn growth.
Mid-Season Weed Biomass: So, did early season weed biomass trends translate into later season weed biomass? Weed biomass remained low throughout the season and there were no differences observed amongst the treatments (Figure 3).
Grain Corn Yield: But then the question remains, does any of the delayed growth early in the season compromise corn yields? Average yield ranged between 118 bu/acre in the planting green treatment to 121 bu/acre in the planting brown treatment. The yield range of the treatments was narrow and there were no significant yield differences among the treatments (Figure 4). This indicates that cover crop termination date or cover crop biomass did not impact grain corn yield.
Preliminary results indicate that although later cover crop termination did impact early season corn growth and development, this did not translate into reduced grain yields. Additional years of data need to be collected to confirm this first year of data. This trial will continue in subsequent years and with more data we can have higher confidence in the impact of cover crop termination date on corn yield. Additional research would also be needed to assess impact of cover crop termination date on corn silage yield.
This study is conducted in 16 states as part of the Precision Sustainable Agriculture Network (PSA). This work is supported by the Agriculture and Food Research Initiative’s Sustainable Agricultural Systems Coordinated Agricultural Projects [award no. 2019-68012-29818] from the United States Department of Agriculture (USDA) National Institute of Food and Agriculture.