Carbon dioxide mitigation potential of conservation agriculture in a semi-arid agricultural region

The Texas High Plains (THP) region is one of the largest upland cotton (Gossypium hirsutum L.) producing regions in the world. Cotton is a versatile crop with uses for both food and fiber products. Conservation management practices such as no-tillage and cover crops have been used to reduce wind erosion on the THP but are also associated with mitigating and reducing greenhouse gas (GHG) emissions from soil. Although row-crop agriculture has been linked to GHG emissions across the world, cotton production in the THP ecoregion has not been thoroughly evaluated for its contribution to GHG production. This research quantified the soil flux of carbon dioxide (CO₂-C) from continuous cotton production systems on the THP after implementing three tillage practices: (1) no-till with a winter wheat cover crop (NTW); (2) no-till winter fallow (NT); and (3) conventional tillage winter fallow (CT). In addition, the timing of nitrogen fertilizer application was evaluated within each tillage system. Five N treatments were implemented: (1) an unfertilized control; (2) 100% pre-plant (PP); (3) 100% side-dressed (SD); (4) 40% PP 60% SD; and (5) 100% PP with a nitrogen stabilizer product (STB). Tillage practice affected CO₂-C flux rates in spring 2016 and 2017 with the NTW system having greater CO₂-C flux than the NT and CT systems. In summer 2017, the NTW system had a greater flux of CO₂-C than the NT or CT systems. In fall/winter 2016, the NTW and CT systems had a greater CO₂-C flux than the NT system. Cumulative emissions of CO₂-C were affected by N treatment in 2016, with later season applications of N fertilizer increasing emissions compared to the STB treatment and the control. In 2017, cumulative emissions of CO₂-C were greater in the NTW system than in the NT and CT system. However, a greater amount of CO₂-C was assimilated by the wheat cover crop from the atmosphere than was lost from the soil which reduced net C losses from the system. With continued use of no-tillage and a cover crop, lower net soil CO₂-C losses should result in a greater rate of soil organic C gain, positively impacting the sustainability of cotton production in the THP.