Low-density alfalfa improves semiarid grassland without soil water depletion

Semiarid grasslands produce high quality forage in spring and early summer to support beef cattle at low cost. In the late summer and fall, forage protein content and digestibility decrease, triggering costly supplement addition to forager diets. Interseeding alfalfa can improve the forage quality of native grasslands by adding a high-protein species but risks accelerating soil water depletion in water-limited environments.

In an article recently published in Agronomy Journal, researchers in the Texas High Plains evaluate changes in soil water depletion, evapotranspiration (ET), plant water status, and root biomass with alfalfa interseeded into native grasses at narrow (36 cm) or wide (71 cm) row spacing.

Compared with the non-interseeded control, narrow spacing caused more soil-water depletion and ET than wide spacing due to denser root mass. Grass water potentials were depressed in narrow rows relative to wide rows and the control, indicating that the denser presence of alfalfa intensified competition with the grass for water. The wide-row treatment had negligible effects on grass water stress.

Wide-row spacing achieved a favorable compromise between slightly enhanced water use and greatly improved stand productivity and quality. Results suggested that alfalfa at wide rows can improve native-grass pastures in rainfed, semiarid environments, potentially helping farmers reduce supplement costs and increase forage quality.