Above-Ground Biomass and Nitrogen Quantities in a Big Sacaton (Sporobolus wrightii) Grassland

Abstract

Live and standing dead biomass, standing crop, and total nitrogen, within each component, were measured in a big sacaton (Sporobolus wrightii Monro) grassland in southeastern Arizona for 3 years to determine annual fluctuations in above-ground biomass and nitrogen. Mean live biomass varied from 150 kg/ha in February to 2,000 kg/ha in August. Standing dead biomass accumulated after the summer growing season and rapidly disappeared following either fall, winter, or summer moisture, but was the predominant vegetative component for about 49 weeks of each year. Standing crop (live plus standing dead) was greatest in August and averaged 4,450 kg/ha. Total nitrogen varied from 2 to 31 kg/ha in live biomass, from 5 to 15 kg/ha in standing dead biomass, and from 9 to 40 kg/ha in standing crop. The rapid disappearance of standing dead suggests that stocking rates should be based on standing crop just prior to the grazing period rather than peak standing crop after the summer growing season.