Aboveground biomass and concentration of nutrient contents of semiarid rangeland plant species: Influence of grazing and soil moisture

This study investigated spatial and temporal patterns of aboveground biomass and nutritive value of rangeland species in perspective of influence of grazing and soil moisture. The research was conducted over two years at Tomagh Research Station, near Sanjawi, Ziarat District, Balochistan, Pakistan. This area is protected from grazing since 1998; however, some of the area is open for grazing. Three sites were selected for research purpose; protected plain, protected hilly, and unprotected plain area. Sampling was carried out during spring, summer and autumn seasons. Results reveal that soil moisture was greater in protected sites as compared to unprotected site. The aboveground plant biomass was 66% to 76% lower at unprotected site as compared to protected sites. The biomass of annual plant species was nearly 0 at grazed site. In the grazed area the concentrations of all nutrients were higher than un-grazed and hilly area and this pattern was consistent over all species sampled. This finding indicates for lower nutrient use efficiency of plants in grazed site as compared to the plants at protected sites. This research provided evidence that besides having a negative influence on aboveground plant growth, grazing also impacted emergence/growth of annual plants and also reduced the nutrient use efficiency of native plant species. Moreover, 11 years of protection from grazing increased significantly the biomass of plants, enhanced their nutrient use efficiency and allowed annual plants to grow.