Date of Award
Master of Science
Plant Pathology and Microbiology
Alison E Robertson
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 greater in corn planted in the winter rye residue compared to corn planted 8 to 10 cm away from rye residue but not significantly different (Run 1, P = 0.1177; Run 2, P = 0.1939). However, there were greater Pythium clade B populations in the roots of corn planted into winter rye residue compared to corn planted away from winter rye residue (Run 1, P = 0.0233; Run 2, P = 0.004). Additionally, corn shoot dry weight, radicle length and shoot length were greater in corn planted 8 to 10 cm away from winter rye residue compared to corn planted into winter rye residue. The experimental field plot study (Ch. 3) consisted of four treatments; no CC control, broadcast planted winter rye, 3 rows of rye drilled 19 cm apart in the corn interrow, and one row of rye drilled 76 cm apart in the corn interrow. Thus, corn was planted within the winter rye residue, 19 cm and 38 cm away from winter rye residue. Corn root rot ratings at growth stage V3, growth parameters, and yield were collected. Additionally, soil samples were collected to understand populations of Pythium spp. in the soil spatially and temporally. Radicle and seminal rot severity differed among treatments in 2020 (P = 0.0898; P = 0.0565, respectively). And effect of winter rye treatments on Pythium clade B populations in the radicles was detected (2019, P = 0.0455; 2020, P = 0.0209). Furthermore, winter rye treatments affected corn yield (2019, P = 0.0002; 2020, P = < 0.0001). In general, as distance between winter rye and corn increased root rot decreased and corn growth parameters and yield improved. Results from the soil samples demonstrated that Pythium clade B populations differed temporally but not spatially when winter rye is planted at different distances from the corn row. The on-farm study consisted of three treatments; no CC control, 38 cm drilled winter rye, and 76 cm drilled winter rye. Corn root rot ratings and growth parameters at growth stage V3, and yield were collected. Soil samples were collected to understand spatial distribution of Pythium spp. populations in the soil; however, difference among treatments and sample location were not detected. In both years, radicle rot severity was highest in corn planted in 38 cm drilled winter rye compared to corn planted in 76 cm drilled winter rye and no CC (2019, P = 0.0514; 2020, P = 0.0016). Growth parameters and yield of corn did not differ among treatments in both years. There are likely many factors that contribute to corn yield reduction after a winter rye CC. Further research is needed to fully understand the factors that play a role in reducing corn yield after a winter rye CC. This research demonstrated that spatially separating a winter rye CC from corn reduced seedling disease and benefited corn growth, development, and yield. An additional recommendation for incorporating a winter rye CC into the corn-soybean production system may include planting winter rye in the interrows to create a distance between the winter rye and corn.
Sarah Maria Kurtz
Kurtz, Sarah Maria, "The effects of winter rye cover crop on corn seedling disease, corn growth and development in respects to winter rye seeding spacing" (2021). Graduate Theses and Dissertations. 18534.