Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Agronomy, Horticulture, and Plant Science

First Advisor

Dwayne Beck


A major concern of farmers implementing cover crops into a crop rotation is a potential reduction in soil moisture and nutrients available for the following cash crop. If soil moisture or nutrients are limited, the following cash crop yield suffers. One option to conserve soil moisture is to terminate cover crops with herbicides prior to a killing freeze. The purpose of this study is to develop a better understanding of the impact of cover crops and termination timing to the water and nutrient cycles and furthermore, the agronomic impact to the following cash crop (corn). Field experiments were conducted in 2019 through 2020 at the Dakota Lakes Research Farm (Pierre, SD) and on a producer’s field near Canning, SD. Three different cover crop mixes (Grass-M1 (grass dominated blend), Brdlf-M2 (broadleaf dominated blend), and Blend-M3 (equally weighted by rate of grass and broadleaves)) were planted on 2019-07-25 at Dakota Lakes and 2019-08-08 at Canning. A chemical fallow treatment was implemented as a control. Cover crops were terminated with herbicides at different times in the fall of 2019. Plant available water (PAW) was calculated using field gravimetric soil moisture percentage measurements for the 0-90 cm soil profile. At Canning, on 2019-11-15 PAW was impacted by cover crop mixture (p=0.086) with Grass-M1 containing 62 mm, Blend-M3 containing 59 mm, and Brdlf-M2 containing 49 mm. This difference was not present in the spring. The Control treatment contained significantly more PAW than the cover cropped treatments at Dakota Lakes and Canning in the fall of 2019 and again in April 2020. By June, when the corn crop is starting to use a significant amount of soil water, the Control contained more PAW than all other cover cropped treatments at Canning, but not at Dakota Lakes. At Dakota Lakes, spring soil nitrate-nitrogen was numerically lower in the cover cropped treatments than the Control. At Canning, spring soil nitrate-nitrogen was significantly lower in the cover cropped treatments than the Control (p<0.001). Corn grain yield was higher in the Control treatment than most cover cropped treatments at both locations. It is likely that the reduction in corn grain yield is a function of both reduced soil moisture and nitrogen. Earlier terminated cover crops resulted in a higher yielding corn crop as compared to those last terminated. The cover crops terminated later in the season produced more cover crop biomass but reduced the corn grain yield the following year. Terminating cover crops proved to be an effective practice. This approach saved a portion of the grain yield in the following cash crop, while still accomplishing some of the benefits from cover cropping. Drawbacks of early termination are reduced cover crop biomass production and reduced length of time that a living root is in place.



Number of Pages



South Dakota State University


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