Due to the shorter growing season, northern Illinois has fewer cover crop options than the central and southern parts of the state. Winter rye, and to a certain extent, winter wheat, are adapted and grown as winter cover crops in northern Illinois.

It has long been known that the grain yield of corn, following winter rye, can be negatively impacted. To document and refine this impact on grain yield and to measure the forage quality and quantity of rye and wheat, a three year (2005-2007) study was conducted at the Northern Illinois Agronomy Research Center near Shabbona by University of Illinois.

Rye and wheat were planted in late September to early October following soybean harvest. Corn was planted from May 6 to May 9. Roundup herbicide was applied to the rye and wheat 30, 20, and 10 days before planting (dbp) corn. A fourth treatment was tillage (disking 2 to 3 times) 2 dbp corn. A forage sample was collected prior to each treatment.

Results included the following. Rye produced more forage dry matter than wheat at each sampling and averaged 0.7 ton per acre more overall. The quality of the wheat forage, as measured by crude protein and relative feed value, was higher than rye.

Even though corn harvest population (plants per acre or ppa) was acceptable across treatments and cover crops, it was more consistent following wheat. Lowest population (31,200 ppa) was with tillage 2 dbp following rye.

Corn grain yield was the highest when cover crops were sprayed with the herbicide 30 or 20 dbp. Tillage 2 dbp had the lowest grain yield of any treatment. Overall, rye lowered grain yields about 14 bushels per acre more than wheat.

The tradeoff between grain yield and forage yield was largely dependent upon the price of corn and forage plus the individual farm situation. Soil moisture, the tendency of cover crops to dry out the soil, and the amount, location, and management of cover crop residue are critical factors contributing to year-to-year variation in grain yield.

Further details on the study are available by contacting Jim Morrison, Extension Crops Educator, 815-397-7714, morrison@uiuc.edu