Crop residue and no-till as management tools to enhance soil microbial community dynamics in a dryland cotton system in the southern High Plains

Agricultural production systems across the Southern High Plains face significant challenges due to increasing climate variability interacting with conventional practices that can decrease soil health. Therefore, there is an urgent need for improvement of soil health for cotton production systems by implementing conservation agriculture management practices, such as crop residue and no-till, that will increase the activities of soil microbial communities and mitigate the environmental impacts resulting in a more sustainable agriculture across the region. The purpose of this research was to assess the effects of conservation management practices, such as crop residue management combined with no-till practices, to enhance the soil microbial community dynamics and crop production in a dryland monoculture cotton production system in the Southern High Plains. The research was carried out over four growing seasons (2014 to 2017). For the 2014–2015 growing seasons, 2 treatments were established: 1) using erosion blankets to mimic stubble (shade), and 2) sorghum or wheat residue (stubble) and control (no stubble) with 6 replicate plots in each treatment and control. For the 2016–2017 growing seasons, the shade treatment was not included. Soil samples were collected before planting and over the growing season (monthly) to evaluate environmental and nutrient parameters, microbial community size and structure, function, diversity and composition. Over the four years the addition of stubble reduced daily soil temperature range (DTRsoil) by approximately 6 °C on average at the soil surface and approximately 3 °C at 15-cm below the surface during the hottest months. Soil moisture was increased by 33 % and 49 % in the last two years when compared to the control. The combined effects of reduced DTRsoil and increased soil moisture had a positive effect on microbial activities. Overall, microbial biomass carbon increased across all growing seasons except in 2015 under stubble. Total bacterial FAME levels were higher in all growing seasons under stubble except in 2016. Total fungal FAME levels were higher in all growing seasons under stubble. Both fungal and bacterial FAME levels were influenced by changes in daily temperature variability with stubble application. NH4+-N and NO3--N levels decreased in the stubble in 2014 and 2016, and SOM increased substantially in 2014 and 2017 in the stubble. Overall, all enzyme activities increased under stubble, except β-glucosidase in 2016. Bacteria functional diversity using BIOLOG increased over time, with the greater differences in 2016 and 2017 when compared to the control. Both enzyme activity and bacterial functional diversity were correlated. Fungal functional diversity decreased over time except for a substantial increase in 2016 and was correlated with β-glucosaminidase and arylsulfatase activities. Fungal community composition as assessed by whole-community DNA sequencing was dominated by Ascomycota and Basidiomycota phyla, with the highest relative abundance of Basidiomycota under the stubble. The main fungal genera observed in the dryland systems were Fusarium, Phoma and Alternaria. The implementation of conservation management practices, such as crop residue and no-till, mitigated the climate variability with the reduction in daily soil temperature variability and increase of soil moisture, which positively affected the dynamics of microbial communities and their functions. Although the benefit from no-till and stubble management was not observed every year, the gradual improvement of microbial community dynamics will increase soil health, thus leading to a productive and sustainable agriculture in the long term.