Herbage dynamics and nitrogen cycling in two rangeland ecosystems on the Edwards Plateau, Texas

Vita.This study was conducted on the Sonora Research Station near Sonora, Texas, in the southwestern portion of the Edwards Plateau. The objective of the study was to determine the effects of two long-term grazing systems on vegetation structure and nitrogen cycling in a semi-arid grassland. The study sites were small, gauged watersheds of 3.0 and 1.8 ha. One site was located within a heavily stocked (5.4-4. 6 ha AU ⁻¹) continuously-grazed pasture, the other within one pasture of a 4-pasture deferred-rotation system (5.2 ha AU⁻¹). Data were collected through the 1975 and 1976 growing seasons. The two pastures had different soil depths to bedrock. In the continuously-grazed pasture, 86 % of soil depths were less than 30 cm, while 87% of the soil depths in the rotation pasture were greater than 30 cm. Percent bare soil was 30.5% for the continuous pasture and 10.9 % for the rotation pasture, while rock cover on the soil surface was 16.6 and 2.7% respectively. The different grazing regimes and soil depths in each watershed influenced the amount and type of vegetation present. Herbaceous vegetation cover was 18.5% for the continuous pasture and 41.5% for the rotation pasture. The continuous pasture was dominated by short grasses, while the rotation pasture had a more diverse assortment of short- and mid-grasses. Common curlymesquite (Hilaria belangeri) was the dominant herbaceous species in both pastures and provided 68.6% of the total species composition in the continuous pasture and 70.9% in the rotation pasture.