Understanding benefits to soil health using no-till and stubble management for irrigated cotton in a semi-arid environment

The Southern High Plains of Texas (SHPT) is an economically important area that produces around 25% of cotton of the United States. However, climate variability in the area is increasing the vulnerability of several agricultural goods produced in this area that has historically benefitted from stable climatic patterns. Droughts have become more frequent and stronger, rainfall events are more spaced, and daily temperatures have reached higher records during the growing seasons. These environmental conditions have negative effects especially on agricultural soils managed with conventional techniques that are already known to be detrimental for soil health. There are however land management strategies that mitigate the negative environmental effects consequence of climate variability while promoting several physical, chemical, and biological factors that influence soil health. Such soil health practices include crop rotations, use of cover crops and reduced tillage or no-till, and although the implementation of these strategies is on the rise in the SHPT, the use is not yet widespread. My dissertation focuses on describing how environmental factors like soil temperature variability and water content affect soil health characteristics related to chemical (Soil Organic Matter - SOM, Cation Exchange Capacity - CEC, NH4+-N, NO3--N and Labile Carbon) , and biological (Microbial Biomass Carbon - MBC, FAME profiles and Enzyme Activity) factors in three center-pivot irrigated fields where soil health management like no-till has been implemented for 13 years, and one field subjected to conventional management practices. Measurements of all fields were conducted monthly across the growing season from 2017 to 2019. Volumetric Water Content (VWC) was observed to be significantly higher among no-till fields, suggesting that no-till fields had increased water holding capacity. However, temperature variability (DTR) was over all observed to be similar across both land management types due to the increased heat capacity that water from irrigation provides to soil. This suggested that over-all, environmental conditions were similar throughout all fields despite the differences that tillage normally produce. No-till fields had increased SOM levels, CEC and lower Labile Carbon amounts. Although no significant differences were observed in MBC, FAME indicators, and NH4+-N and NO3--N, among land management types, strong negative relations between these factors were observed only in the conventional-till field, suggesting that nitrogen dynamics are driven by abiotic controls instead of by biotic factors. Significantly higher levels of Labile Carbon observed in the conventional-till field were an indicator of increased organic matter degradation rates, consequence of tillage burying crop residue, which results in a decreased carbon storage capacity of soil. No significant differences were seen in enzyme activity and FAME markers among land management types. Knowing that soil moisture is an important driver of soil microbial communities and metabolic activity, irrigation could override potential benefits of no-till and stubble management and climatic constraints that would otherwise affect microbial community structure and enzyme activity. Over the longer term, key soil health indicators were less variable under the no-till and stubble managed system with increases in soil organic matter under no-till and stubble management being a major indicator of future progress for developing a healthy soil in this semi-arid region. For irrigated semi-arid agroecosystems, moving towards a no-till and stubble management approach resulted in a better relationship between the microbial communities and carbon and nitrogen dynamics and developing a positive trajectory in soil health.