Differences in Soil Microbial Communities in Dryland Forage Production Systems in Semi-arid Texas High Plains

The declining water supply for irrigation in the semi-arid Texas High Plains is encouraging some growers to transition their continuous cotton (Gossypium hirsutum L.) land to dryland production of forages for grazing cattle and hay. These changes can modify soil water dynamics, which might affect soil microbial communities. The objective of this study was to determine changes in soil microbial communities following the transition from cotton to dryland annual forages at 0‒5 cm and 5‒15 cm over time. Soil water content was greater (P ≤ 0.05) in fall 2018 than in fall 2016 at both depths. Soil microbial biomass carbon (MBC) was greater (P < 0.001) at 0‒5 cm and numerically greater (P = 0.10) at 5‒15 cm in fall 2016 compared to fall 2018. In contrast, fall 2018 had greater soil microbial biomass nitrogen (MBN) than fall 2016 at both depths, but not significantly (P ≥ 0.15). Soil microbial community structure showed no sampling-time effect on total fatty acid methyl esters (FAMEs) nor on total fungal and bacterial populations at both depths. Soil microbial communities were generally at least maintained in dryland annual forage production systems even after several years of transitioning from irrigated cotton to annual dryland forages.