Agronomic and Economic Benefits of Rotating Corn with Soybean and Spring Wheat under Different Tillage in Eastern Canada.

Agronomic and economic performance of the corn (Zea mays L.)--soybean [Glycine max (L.) Merr.] rotation is well documented, but few studies have investigated the addition of spring wheat (Triticum aestivum L.) to this rotation, particularly at the northern limit of corn and soybean production in North America. A 6-yr field study was initiated in 1999 on a clay soil in eastern Canada to identify the best crop rotation (continuous corn, continuous soybean, corn--soybean, corn--corn--soybean, corn--soybean--spring wheat, or corn--spring wheat--soybean) under moldboard plow (MP) and reduced tillage (RT) in terms of grain yield, soil aggregate distribution, and annual net returns. To isolate the effect of annual climatic conditions, all crop phases of each rotation were present each year for a total of 13 rotation sequences within each soil tillage practice. Corn grown in rotation had greater yield (+0.6 to +0.9 Mg ha^-1) than continuous corn or second-year corn regardless of soil tillage. Soybean grown once every 3 yr had consistently greater yields (+0.20 Mg ha^-1) than continuous soybean. The addition of spring wheat in the rotation improved both corn and soybean yields compared with either continuously cropped. The RT management did not affect crop yield but increased the soil macro-aggregation only when corn was present in the rotation. Economic analysis revealed that continuous soybean, the 3-yr corn--soybean--spring wheat with wheat straw being sold, and the 2-yr corn--soybean were the most profitable and most efficient rotations when averse risk is considered. [ABSTRACT FROM AUTHOR]