Soil microbial community response to management in improved pastures of the semi-arid Texas Southern High Plains

The Southern High Plains (SHP) of the USA agriculture (crop and livestock production) is faced with many challenges such as limited water for irrigation, due to declining water levels of the Ogallala Aquifer. The insufficient and irregular rainfall, coupled with strong gusting winds that increase evapotranspiration worsens the situation. In addition, the soils in this region are highly degraded with < 1% soil organic matter (SOM). There’s a need for producers to adopt novel pasture-livestock management practices that are water efficient and that promote soil health and environmental sustainability such as the use of compost manure, use of legumes and limited irrigation coupled with grazing. Multiple research experiments were conducted in this thesis research to assess how alternative nutrient sources such as composted manure addition and legume forages (alfalfa and yellow sweetclover) interseeded with the WW-B. Dahl [WW-B. Dahl; Bothriochloa bladhii (Retz.), S.T. Blake perennial pasture impact soil biota and soil health in the SHP. In addition, we evaluated forage utilization practices: grazing contrasted with haying effect on soil’s biological, chemical and physical properties. Three pastures systems with different ages, past, and present management systems were evaluated. Key research conclusions include: Compost amendment increased total microbial biomass and changed the soil ecology as indicated by Non-metric multidimensional scaling (NMS) plots showing differences in microbial communities in compost and no compost treatments based on the selected phospholipids fatty acid (PLFA) biomarkers in fall 2018. Compost amendment increased soil total C, N, and SOM concentrations. Use of cattle manure could, therefore, be a sustainable and cost-effective way to enhance soil microbial communities, soil health and potentially increase forage yield in the SHP. The grass-legume mixture pasture system with long grazing history with no synthetic fertilization had higher total phospholipid fatty acid (PLFA), higher total C, N, SOM concentrations, and forage yield when contrasted with young grass-legume mixtures and pure stand grass pasture systems. The grass-legume mixture pasture system with long grazing history with no synthetic fertilization was ecologically different from young grass-legume mixtures and pure stand grass pasture. An interaction between year and grazing revealed that grazed treatment plots had a higher total carbon concentration indicating that grazing enhances soil organic carbon concentration. The grass-legume pasture had a higher N concentration than grass only suggesting that legume might have helped in N fixation. Overall, all the novel pasture management practices above, compost amendment, legume inclusion, and grazing are promising in enhancing soil microbial communities, promoting soil health and improving forage yield to sustain the economically important livestock industry in the SHP.