A Comprehensive Study of Yield Components, Nutrient Uptake, Root Characteristics, and Cover Crops for Alabama Cotton Production

Abstract

This study has yielded crucial findings across multiple aspects of cotton agronomy and breeding by systematically evaluating 20 upland cotton (Gossypium hirsutum L.) cultivars released over the past 65 years (1953-2018). The first component of the research investigated the biomass partitioning and yield performance of the cotton cultivars. The results revealed a substantial increase in lint yield, averaging 11.7 kg ha⁻¹ yr⁻¹ in 2020 and 12.6 kg ha⁻¹ yr⁻¹ in 2021, driven primarily by improvements in lint harvest index and total aboveground biomass. However, the study cautions that merely increasing total biomass without concomitant enhancements in reproductive partitioning could lead to decreased lint yield, as total biomass had a direct negative effect on lint yield. The findings underscore the importance of prioritizing improvements in the efficiency of partitioning aboveground biomass into the economically valuable lint fraction to achieve further yield gains. Alongside the aboveground traits, the research also explored the evolution of nutrient dynamics in these twenty cotton cultivars. Over the 65-year period, the study observed a steady increase in total nutrient uptake (N, P, and K) and internal nutrient use efficiency. While nutrient concentrations in the vegetative growth either decreased or remained unchanged, there was an increase in nutrient concentration in the seed. This shift in nutrient partitioning suggests an indirect improvement in allocating essential minerals to the economically valuable seed component. Averaged over all tested nutrients, modern cultivars released in 2018 were 27% more efficient in producing lint per unit of nutrient uptake than the 1950s, highlighting the potential for further advancements in nutrient management strategies. iii Complementing the aboveground analyses, the research also delved into the root traits of the cotton cultivars. The investigation revealed significant cultivar differences in carbon isotope discrimination (Δ13C), a proxy for water use efficiency, and variations in root architectural characteristics, such as total root length, root surface area, and root crown attributes. Interestingly, the total root crown surface area exhibited a linear increase with the year of cultivar release, suggesting that breeding efforts to enhance aboveground performance have indirectly improved certain root parameters. Furthermore, the distribution of root surface area across different soil depths showed changes, with modern cultivars allocating a higher proportion of roots in the topsoil compared to older cultivars. These findings underscore the untapped potential for improving cotton's root system architecture and water use efficiency through targeted breeding strategies, which could contribute to developing climate-resilient cultivars. In addition to the cultivar evaluation, the research also explored methodological advancements in root phenotyping. Specifically, the study investigated the influence of X-ray computed tomography (CT) system voltage on the penetration capability in diverse soil types and container sizes. The results demonstrated that increasing the voltage enhances image quality up to a certain plateau, providing valuable guidance for researchers utilizing X-ray CT to study root growth and development in complex soil environments. Finally, evaluating six years of continuous cover crop systems in the southeastern United States provided insights into their effects on soil organic carbon and cash crop performance. While the results varied across sites and years, adopting high-biomass cover crop species, such as rye and crimson clover, showed the potential to improve soil carbon content and enhance cash crop yields, particularly under irrigated conditions. These findings underscore the importance of continued iv research and the development of region-specific recommendations for integrating cover crops into existing cotton production systems. Collectively, this comprehensive research program has explained the key drivers of historical improvements in cotton lint yield, the evolving nutrient dynamics of modern cultivars, the untapped potential of belowground traits, the optimization of imaging techniques, and the impacts of cover cropping. These insights can inform the strategic development of future cotton cultivars and management practices, ultimately contributing to the sustainable intensification of cotton production to meet the global demand for this vital fiber crop.