Long-Term Rice Rotation and Tillage Effects On Soil Surface CO2 Flux.

The flux of carbon dioxide (CO₂) from the soil is a major process in the global carbon (C) cycle and is a portion of the terrestrial C budget. Soil aeration pertains to the condition and bioavailability of gases in the soil and the exchange of these gases between the soil and the atmosphere, and since the 1750s, the global CO₂ concentration in the atmosphere has steadily increased from an average of 280 parts per million (ppm) to over 388 ppm in 2010. Furthermore, CO₂ emissions represent roughly 77% of the total anthropogenic greenhouse gas emissions annually. The unnatural enrichment of CO₂ in the atmosphere is partly due to fossil fuel combustion and in part due to land-use changes, such as soil cultivation, expansion into natural ecosystems, and the mineralization of soil organic C. A study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) in the Mississippi River Delta region of eastern Arkansas to evaluate the long-term effects of rice (Oryza sativa L.)-based crop rotations [with corn (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)] and tillage [conventional tillage (T) and no-tillage (NT)] after 10 and 11 years of consistent management on soil surface CO₂ flux. In addition, soil temperature at the 2- and 10-cm depths and soil volumetric water content (VWC) in the top 6-cm of soil were measured and their correlations to soil surface CO₂ flux were evaluated. Results showed greater CO₂ flux in rotations that contained soybean every other year when compared to rotations with corn or continuous rice. As expected, soil temperature and VWC were directly correlated with soil surface CO₂ flux. No-tillage management had a greater CO₂ flux than tillage at cooler soil surface temperatures; however, CO₂ flux was greater under tillage than in NT at warmer soil temperatures. Knowing the influences different agricultural management practices have on the quantity of greenhouse gas emitted from the soil is critical for formulating innovative agricultural practices, economic policies, and energy conservation strategies that will affect civilization for generations to come.