The effects of winter rye cover crop on corn seedling disease, corn growth and development in respects to winter rye seeding spacing

Abstract

The United States is the largest producer of corn (Zea mays L.) and Iowa contributes to approximately18 percent of corn in the U.S. In the corn-soybean (Glycine maxx L.) crop rotation system, erosion and nitrate leaching are problems and encouragement for farmers to produce crops sustainably is increasing. Cover cropping is a sustainable option to enhance agricultural production systems by improving soil and water quality. In Iowa, approximately 2 million acres were planted to cover crops (CCs) in 2018, which is far less than the 12.5 million acres goal called for by Iowa’s Nutrient Reduction Strategy. Winter rye (Secale cereale) is the most commonly planted CC in Iowa due to its good establishment in the fall and winter hardiness. However, many studies and farmers have reported reduced corn yield after a winter rye CC, which discourages farmers from planting a winter rye CC. Proposed reasons for corn yield loss after a winter rye CC include nitrogen immobilization, reduced water availability, allelopathy, and seedling disease. Corn and winter rye can be infected by some of the same pathogens including Pythium spp. Studies have shown that Pythium spp. overwinter in winter rye roots thereby creating a ‘green bridge’ effect. Moreover, seedling disease in corn increased when corn was planted into winter rye residue compared to corn planted into no CC. Seedling disease can cause damping-off and delay emergence, resulting in uneven stands and reduced plant vigor that negatively affects yield. Previous research recommends terminating a winter rye CC 10 to 14 days before planting corn; however, this may be challenging in some years due to weather constraints. Cold, wet weather in the spring can delay termination of the rye CC and/or planting corn. This research focuses on spatially separating winter rye residue from corn to reduce seedling disease. We hypothesize planting corn at a distance from winter rye residue would decrease seedling disease and benefit corn growth and development. A growth chamber study, experimental field plot study, and an on-farm study were conducted to test our hypothesis. In the growth chamber study (Ch. 2) winter rye was planted on one side of 23 cm diameter pots. After winter rye was terminated, corn was planted into the winter rye residue and 8 to 10 cm away from the winter rye residue. Seedling disease and growth parameters of the corn were collected at corn growth stage V1 to V2. Root rot severity was numerically