|WHITWORTH, WHITNEY - University Of Arkansas|
|MONGOMERY, GREGORY - University Of Arkansas|
|BECK, PAUL - University Of Arkansas|
Submitted to: Journal of Animal Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2012
Publication Date: 7/24/2012
Citation: Gunter, S.A., Whitworth, W., Mongomery, G., Beck, P. 2012. Cool-season annual pastures with clovers to supplement wintering beef cows nursing calves. Journal of Animal Science and Biotechnology. 3:25.
Interpretive Summary: Manufacturing nitrogen fertilizer consumes fossil fuel, resulting in a net increase in green-house gas emissions. The processes of nitrogen fixation by Rhizobium bacteria in legumes uses photosynthetically-derived carbon, and it is a green-house gas neutralizing system because it also increases the plants photosynthetic activity beyond the carbon consumed. Grazing systems using only cool-season annual grasses require additional nitrogen to promote sufficient grass production. Normally this nitrogen is supplied by commercially produced fertilizers. However, planting clovers with cool-season annual grasses during the winter on the Coastal Plains has the potential to substantially reduce the need for nitrogen fertilizers compared to all grass systems. An experiment was conduct in southern Arkansas to examine the possibility of using clovers to fix atmospheric nitrogen and eliminate the need to apply nitrogen containing fertilizers. This experiment showed that by adding clovers to winter-annual pasture mixtures overseeded in to warm-season pastures, it effectively supplemented a beef cow herd, improved weaning weight per cow exposed, reduced the need to fertilize with nitrogen, and maintained sufficient forage production. Additionally, using these clovers to fix atmospheric nitrogen and supply the grasses with supplemental nitrogen resulted in decreased green-house gas emission with this grazing system.
Technical Abstract: Every December, for 3 years, 87 beef cows, nursing cows, (594 ' 9.8 kg; calving season, September to November) were stratified by body condition score, body weight, cow age, and calf gender. They were divided randomly into 6 groups and assigned to 1 of 6 cool-season annual swards (0.45 hectares/cow) that had been interseeded into a dormant bermudagrass/dallisgrass sod. All groups had ad libitum access to grass hay (12% crude protein; 58% total digestible nutrients). Swards contained 1 of the following 3 seeding mixtures (2 mixtures/pasture): 1) wheat (101 kg/hectare) and ryegrass (25 kg/hectare; WRG), 2) wheat and ryegrass plus red clover (9 kg/hectare; WRR), or 3) wheat and ryegrass plus white (4 kg/hectare) and crimson (12 kg/hectare) clovers (WRW). The second week in December, cow estruses were synchronized and were subsequently artificially inseminated, then, in late December, a bull was placed with each group for 60-day. Data were analyzed by analysis of variance with year as a random effect and pasture as the experimental unit and contrasts were used to compare WRG versus the average of WRR and WRW, and WRR versus WRW. Body weight and condition scores did not differ (P ' 0.27) among cows between February and June. Calf birth weights or average daily gain did not differ (P = 0.17) among treatments; however, calves grazing pastures with clovers did tend (P = 0.06) to weigh more than calves grazing grass only. Weaning weight per cow exposed to a bull was greater (P = 0.02) for WRR and WRW (211 kg) than WRG (173 kg). Cows grazing winter-annual pastures containing clovers tended to wean more calf body weight per cow exposed than cows grazing the grass only pastures.