Biological Activity in a Wheat-soybean Double-cropping System.

Wheat-soybean double cropping is a popular practice in mid-southern USA that requires effective and careful time management for adequate production of soybean. Soybeans are planted immediately following wheat harvest, thus presenting difficulty in handling wheat residue properly while seeding the crop in a timely matter. In most farms of the region, field preparation consists of burning wheat residue followed by conventional tillage. Burning is a practice that has been adapted as part of the norm in the agricultural area of the Mid-south. However, burning has negative impacts on air quality and potentially on the soil quality. Burning wheat stubble not only destroys valuable organic matter (OM) but also causes air pollution through the carbon dioxide (CO₂) released into the atmosphere.  The objective of this study was to evaluate the long term effects of alternative management practices of a wheat-soybean double crop system on soil biological activity. We evaluated the biological properties of each wheat-residue management practice: burn vs. no burn, till vs. no till, irrigated vs. non-irrigated and high wheat residue vs. low wheat residue to distinguish the treatment that will provide effective nutrient cycling needed for optimal growth and a high-yielding harvest. Our results indicated that the practice of tilling and burning failed to show any significant difference in soil enzyme activity and crop yield. However the study did indicate that the high nitrogen residue level treatment imposed higher enzyme concentration (b-glucosidase, acid phosphatase, and arylsulfatase) and the highest yield.