NUTRIENT LEACHING AND YIELD DYNAMICS FROM VARYING FERTILIZER TREATMENTS AND WINTER WHEAT, CEREAL RYE, AND FALLOW ROTATIONS WITHIN A CORN-SOYBEAN SYSTEM

Author

• Julianna Mariano, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2026

Degree Name

Master of Science

Department

Forestry

First Advisor

Williard, Karl

Abstract

Recent declines in global waterbody health have been attributed to excess nutrient loads from non-point sources such as urban and agricultural land uses. In 2015, the state of Illinois developed the Illinois Nutrient Loss Reduction Strategy (NRLS) to specifically reduce nitrogen and phosphorus entering local waterbodies. Sustainable agricultural techniques suggested include using cover crops, which are planted during traditionally fallow seasons to provide benefits such as nutrient management and erosion control. Cereal rye is the most common cover crop planted within the Mississippi River Basin, and it is best known for its ability to scavenge for nitrate. Double crops are also planted during winter seasons, and their primary benefit is through the financial incentive of harvest. Unlike cover crops, there is limited knowledge as to whether double crops, like winter wheat, can provide environmental benefits. This randomized complete block design study in Carbondale, IL incorporated winter wheat and cereal rye into a traditional two-year, corn-soybean rotation on a non-tile drained field. There were three varying fertilization intensities across plots that include winter wheat. Pan, suction cup, and ion exchange resin (IER) lysimeter soil water data were collected to determine nitrate-N and dissolved reactive phosphorus (DRP) leaching loads. The primary objectives were to determine how winter wheat could potentially reduce nitrate-N, total nitrogen (TN), and DRP leaching compared to cereal rye and fallow and analyze how fertilization intensity impacted both wheat yields and nutrient leaching.Winter wheat and cereal rye both significantly reduced nitrate-N loads after 3-years of rotation. In winter 2023-24, fallow plots experienced up to four times as much nitrate-N leaching compared to each of the winter covers, and the three winter wheat treatments leached significantly less nitrate-N on average compared to cereal rye. Winter wheat plots cumulatively leached an average of 25 kg nitrate-N ha-1 or between 50-80% less than fallow plots in winter 2023-24. DRP nutrient loads also decreased significantly over the course of the study, but there were no differences between individual treatments. Loads decreased between 85-98% between winter 2021-22 and summer 2024. Wheat yields were unaffected by fertilization intensity across all seasons, but they were impacted by seeding rates and planting dates. Winter 2021-22 had a seeding rate nearly 40% lower than winter 2023-24 due to lower seeding rate recommendations, and winter 2023-24 winter wheat grain yield was nearly two times greater than the following season. Soybean yields experienced a potential yield penalty from winter wheat in summer 2022 with winter wheat plots yielding 0.401 Mg DW ha-1 on average. This pattern was not consistent in the following summer 2024 season. There were also no differences in yield-based TN leaching in the winter wheat seasons or the summer 2022 season. In summer 2024, cereal rye was most effective at reducing TN leaching under the greatest soybean yield. Incorporating winter wheat into a corn-soybean rotation resulted in significant water quality benefits and no cash crop yield penalties, and it should be considered by Midwestern agricultural producers as a viable option to increase revenue and help reach water quality goals.