Impact of Tillage and Residue Burning on Carbon Dioxide Flux in a Wheat–Soybean Production System

Burning of wheat ( Triticum aestivum L.) residue followed by plowing is a common management practice in wheat–soybean [ Glycine Max (L.) Merrill] production systems in the mid‐southern USA. However, this residue management practice is not environmentally friendly and may not be sustainable. The objectives of this study were to (i) evaluate the effects of N fertilization of wheat, residue burning, and tillage on soil surface carbon dioxide (CO 2 ) flux in a wheat–soybean double‐crop production system, and (ii) evaluate the role of soil temperature and soil moisture in controlling CO 2 flux in a relatively warm, subhumid environment. Soil surface CO 2 flux was measured nine times between June 2002 and October 2003 during the soybean growing season under all combinations of conventional‐ (CT) and no‐tillage (NT) at high and low N fertilization levels with and without residue burning at two locations in the Mississippi River delta region of eastern Arkansas. Soil surface CO 2 flux was 37.6% higher ( P < 0.01) from CT than from NT and 6.1% higher ( P < 0.05) from the low than the high N rate treatment at one location, but not at the other. Burning did not affect soil surface CO 2 flux except for a significant burning × N rate ( P = 0.016) and burning × time interaction ( P = 0.032) at one location, but not at the other. Both soil temperature and moisture parameters were significantly negatively correlated with temperature‐normalized soil surface CO 2 flux, but soil temperature, particularly at the 10‐cm depth, explained more of the variation than did soil moisture parameters. The results of this study indicate that tillage and N fertilization of prior wheat, but not residue burning, affect the loss of C as CO 2 from the soil and that there are additional soil and/or environmental factors, other than near‐surface soil moisture and temperature fluctuations, perhaps microbial biomass, that contribute to controlling soil surface CO 2 flux in wheat‐soybean production systems in the subhumid region of southern USA.