Increasing plant species richness is often associated with an increase in productivity and associated ecosystem services such as soil C sequestration. Here we report on a 9-yr experiment to evaluate the forage production and C sequestration potential of grazed pastures sown to either a two-species cool-season grass-legume mixture or a five-species mixture of grasses, legumes, and a non-legume forb. We hypothesized that forage production and soil C sequestration would be greater in the five-species compared with the two-species mixture. We also evaluated the effects of rainfall and temperature on the difference in forage production between mixtures. When averaged across years, the five-species mixture produced 31% more forage biomass than the two-species mixture, and the difference between mixtures tended to be greater in wet than in dry summers (R2 = 0.42, P = 0.06). There was no relationship between growing season temperature and differences in biomass production. Soil C accumulation to 100 cm depth in the five-species mixture was 1.80 vs. 0.50 Mg ha-1 yr-1 for the two-species mixture (P = 0.15) with significant increases in the five-species mixture occurring at the 10 to 20 cm (P = 0.06) and 20 to 30 cm (P = 0.03) depths. Increased productivity in the five-species mixture persisted throughout the experiment despite changes in species composition that resulted in similar composition between the mixtures by the last 2 yr of the study. Increased soil C possibly had a positive feedback effect on forage production permitting the five-species mixture to out-yield the two-species mixture even after differences in species composition had largely disappeared.
All Science Journal Classification (ASJC) codes
- Agronomy and Crop Science