Assessing the role of interseeding alfalfa into grass on improving pasture soil health in semi-arid Texas High Plains

The rapid decline in water supply for irrigation in the Texas High Plains is encouraging some growers to convert their irrigated cropland to production of drought-tolerant forages such as `WW-B.Dahl' cultivar of Old World bluestem [OWB, Bothriochloa bladhii (Retz) S.T. Blake]. This perennial, warm-season pasture grass protects the soil surface from erosion; however, it needs nitrogenous fertilizer from an external source or by interseeding a nitrogen (N)-fixing legume to maximize productivity and quality of the pasture. Alfalfa (Medicago sativa L.) is a relatively drought-tolerant and high quality forage legume which is compatible with perennial grasses and enhances dietary protein supply for grazing cattle and improves pasture soil health. The aim of this study was to assess the value of interseeding alfalfa into established OWB grass on improving pasture soil health in relation to OWB grown in a monoculture stand. We investigated the microbial and chemical properties of soil taken at 0-10 cm in March of 2019 from OWB and OWB-alfalfa as a preliminary information for understanding the potential role of alfalfa on improving soil health. At this early assessment of the introduction of alfalfa into OWB, soil microbial biomass carbon (MBC) and nitrogen (MBN) were greater (P < 0.05) in OWB-alfalfa than in OWB. There were no forage treatment effects on soil organic carbon (SOC), total N, and the potential combined enzyme activity associated with C, N, P, and S transformations. The analysis of soil microbial community structure showed that forage treatments were not significant for total fatty acid methyl esters (FAMEs), arbuscular mycorrhiza fungi (AMF), and protozoa, but OWB-alfalfa had greater abundances. Saprophytic fungi were greater in the soil under OWB-alfalfa (P = 0.048) compared to that of under OWB. The bacterial markers for Gram + , Gram-, and actinobacteria were not significantly different. It is not clear whether the elevated soil microbial community in OWB-alfalfa in the current study was solely because of alfalfa, but enhanced soil microbial biomass and saprophytic fungal populations in OWB-alfalfa are at least partially caused by alfalfa. Results indicated that the OWB-alfalfa is a promising forage species combination for stimulating pasture soil health through enhanced soil microbial biomass and fungal populations.