Soil health management in cotton monocultures on the Texas High Plains
Burke, Joseph Alan
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The Texas High Plains (THP) is a semi-arid ecoregion with soils susceptible to wind erosion. Soil conservation management practices like reduced tillage, residue management, and cover cropping have been shown to reduce wind erosion potential. In other regions of the United States, conservation management practices such as no-tillage and cover cropping have been shown to provide additional benefits to cash crops and improve soil health but have not been thoroughly evaluated on the THP. Adoption of these conservation management practices have been limited in this region due to limited knowledge in adoptable practices and concerns regarding water-use and potential limitations, like nutrient immobilization and pest pressure. The overall objective of these series of experiments was to identify potentially adoptable practices for improved soil health management under the typical practice of cotton monocultures on the Texas High Plains. For example, the effects of no-tillage and cover cropping on soil C dynamics, nutrient availability, microbial respiration, soil aggregation, stored soil moisture, cotton yield, cropping system economics and sustainability were assessed. With field studies, soil organic C (SOC) increased 57% using conservation tillage and a mixed species cover compared to conventional tillage in sandy soils of this region. Additionally, SOC and potassium permanganate oxidizable C (POXC) were greatest during periods of active cotton and cover crop root growth. Soil organic C and POXC were significantly correlated (R2=0.75), but SOC and POXC were poorly correlated to microbial respiration (R2=0.3 and 0.12, respectively). Conservation management practices did not appear to have an impact on inorganic N fractions or soil aggregation. Stored soil moisture was reduced with cover crops but was greater than the conventional system following termination prior to planting the cotton (Gossypium hirsutum L.) cash crop. Deeper in the profile, stored soil moisture replenishment was greatest following cover crops. Decreased cotton lint yields in the no-tillage with rye cover treatment resulted in reduced lint revenue, gross margins, and sustainability compared to the conventional system; however, there were no significant differences between the conventional and no-till mixed species cover systems. Conservation management practices such as, no-tillage and cover crops increased SOC and POXC especially during winter fallow periods, improve infiltration and decrease evaporative potential, and helped improve several sustainability indicators including water-use efficiency and quality, soil conservation, and energy use. These conservation management practices demonstrated the potential to improve several ecosystem services, like nutrient cycling, under cotton monoculture production systems on the THP. Our results suggest further research is necessary to better understand yield differences under long-term conservative management scenarios.