Yield and soil carbon sequestration in grazed pastures sown with two or five forage species

Authors: Skinner, Robert; Dell, Curtis

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2016
Publication Date: 4/29/2016
Citation: Skinner, R.H., Dell, C.J. 2016. Yield and soil carbon sequestration in grazed pastures sown with two or five forage species. Crop Science. 56:2035-2044.

Interpretive Summary: Pasture management options are needed that both increase forage production and provide ecosystem services such as increased soil carbon sequestration. One possible management practice could be to increase the number of plant species sown in a pasture since increased species numbers have been shown to increase the productivity of many plant communities. Most of the earlier studies, however, have been relatively short so that the long-term impact is not as well known. In this study we monitored pastures that had been sown to either two or five forage species for nine years. Over the entire nine years of the study, the five-species mixture had 31% greater forage yield than the two-species mixture. Yield benefits from the five-species mixture were greatest in years with high rainfall and were greater than average the last two years of the study, suggesting that the effects were long-lived. The five-species mixture also sequestered three times as much soil organic carbon as the two-species mixture. Increased soil carbon sequestration possibly had a positive feedback effect on forage production, permitting the five-species mixture to continue to out yield the two-species mixture during the last two years of the study when species differences between mixtures were not as great as when originally sown. This study showed that increasing the number of sown species can have multiple, long-term benefits for temperate pastures.

Technical Abstract: Increasing plant species richness is often associated with an increase in productivity and associated ecosystem services such as soil C sequestration. In this paper we report on a nine-year experiment to evaluate the relative 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. Our hypothesis was that forage production and soil C sequestration would both be greater in the five-species compared with the two-species mixture. We also evaluated the effects of environmental variability, particularly rainfall and temperature, on relative differences in forage production between mixtures. The five-species mixture had the greatest yield in eight of the nine years and when averaged across years produced 31% more forage biomass than the two-species mixture. The difference in yield between mixtures tended to be greater in wet than in dry summers (R**2 = 0.42, P = 0.06). There was no relationship between growing season temperature and differences in yield between mixtures. Increased productivity in the five-species mixture persisted throughout the experiment despite that fact that species changes over time resulted in very similar species composition between the two mixtures by the last two years of the study. The five-species mixture accumulated 180 ± 42 g C m**-2 yr**-1 (R**2 = 0.86, P = 0.02) vs. 60 ± 46 g C m**-2 yr**-1 (R**2 = 0.36, P = 0.29) for the two-species mixture. Increased soil C sequestration possibly had a positive feedback effect on forage production, permitting the five-species mixture to continue to out yield the two-species mixture even after differences in species composition had nearly disappeared.