Document Type

Thesis - Open Access

Award Date

2021

Degree Name

Master of Science (MS)

Department

Agronomy, Horticulture, and Plant Science

First Advisor

Jason Clark

Abstract

Cover crops have recently gained attention in the U.S. Midwest because of their potential to increase soil organic matter and protect overall soil health. This study was conducted to determine the effects of different cover crop mixtures on soil health measurements and corn grain yield at increasing nitrogen (N) rates. Cover crops were planted in the fall after small grains harvest as a dominantly grass mixture, dominantly broadleaf mixture, or a 50/50 grass and broadleaf mixture with a no cover crop control. Soil and cover crop biomass samples were collected in the fall before winter cold termination and in the spring before chemical termination of the cover crops. Soil samples were analyzed for permanganate oxidizable carbon (POXC), potentially mineralizable nitrogen (PMN), and soil respiration. Cover crop biomass samples were oven-dried and weighed to determine cover crop biomass. After spring cover crop termination, fertilizer-N was applied before planting corn at six rates: 0, 45, 90, 135, 200, and 225 kg ha-1. The inclusion of cover crops did not improve soil health measurements with no statistical differences in soil health measurements among the different cover crop mixtures. However, there were differences among soil health measurements among siteyears. Soil organic matter had a positive linear relationship with fall and spring POXC. The pH had a positive linear relationship with spring PMN and a negative linear relationship with fall soil respiration. Precipitation had a positive linear relationship with fall soil respiration and a negative linear relationship with fall PMN. When including a cover crop compared to the control, there were no differences in corn grain yield at economic optimum N rate (EONR), EONR itself, and economic return 55%, 42%, and 52% of the time, respectively. The economic profit was reduced most often when planted under a blend cover crop (mean decrease = US$235 ha-1), then a grass cover crop (mean decrease = US$265 ha-1), and then a broadleaf cover crop (mean decrease = US$296 ha- 1). The inclusion of cover crops did not improve soil health measurements compared to the no cover crop control. In the first year of comparing any species of cover crop mixture, growers should not expect to find differences among soil health measurements. However, a long-term trial to show the growing effects of cover crops is needed to fully compare these cover crop mixtures. In general, corn grain yield was not reduced by cover crop composition at EONR and did not change the amount of nitrogen needed for maximum corn grain yield. In conclusion, growers can plant cover crops regardless of composition in the fall after small grains harvest and terminate them in the spring before corn planting to maintain soil health without reducing corn grain yield at EONR or economic profit.

Number of Pages

107

Publisher

South Dakota State University

Rights

Copyright © 2021 the Author

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