|Skinner, Robert - Howard|
Submitted to: International Grasslands Congress
Publication Type: Proceedings
Publication Acceptance Date: 3/26/2005
Publication Date: 7/4/2005
Citation: Sanderson, M.A., Soder, K.J., Brzezinski, N., Goslee, S.C., Skinner, R.H., Wachendorf, M., Taube, F., Muller, L. 2005. Diverse forage mixtures effect on herbage yield, sward composition, and dairy cattle performance. In: Murphy, J. J., editor. Proceedings of a satellite workshop of the 20th International Grasslands Congress. June 26-July 1, 2005, Dublin, Ireland, p. 162. Interpretive Summary: An interpretive summuary is not required.
Technical Abstract: Greater plant diversity in grasslands has been linked to increased primary production, greater stability under disturbance, and reduced weed pressure. Thus, managing complex mixtures of plants to take advantage of spatial and temporal variability in land and climate may be one ecological approach to increase productivity of pastures. We tested the hypothesis that complex mixtures of forage species would yield more dry matter and reduce weed competition compared with a simple grass-legume mixture in grazed pastures. Four diverse forage mixtures were established in replicated 1-ha pastures at University Park, Pennsylvania, USA in the autumn of 2001: 1) orchardgrass (Dactylis glomerata L.)-white clover (Trifolium repens L.); 2) orchardgrass, white clover, chicory (Cichorium intybus L.); 3) orchardgrass, tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pratense L.), birdsfoot trefoil (Lotus corniculatus L.), and chicory; and 4) six species mix plus white clover, alfalfa (Medicago sativa L.), and bluegrass (Poa pratensis L.). The experimental design was a randomized complete block with two replicates. The pastures were subdivided into smaller paddocks and stocked rotationally with lactating Holstein cows during April to August in 2002 and 2003. Four cows grazed each treatment. Herbage allowance was 25 kg dry matter cow-1 day-1. Cows were fed a 13% crude protein corn-based concentrate (1 kg/4 kg milk) in two equal feedings after milking. Cows were moved to a fresh paddock after morning and afternoon milking. Herbage intake was estimated by the chromic oxide technique during May, June, July, and August in each year. Lactating cows were not available after August 1 of each year, therefore, pastures were mob grazed with 21 dry cows for one day in mid August (2003) and early September (2002 and 2003) to complete the grazing season. Animal performance was not measured on the dry cows. Pregrazing and post-grazing herbage mass was measured twice each week during the grazing season with a calibrated rising plate meter. The botanical composition of each pasture was measured during each grazing cycle by hand separating clipped samples before and after grazing. In 2002, forage yield was significantly lower on the orchardgrass-white clover mixture compared with the more complex forage mixtures. In 2003, with much greater rainfall, there were no significant differences among mixtures. The largest increase in forage yield in 2002 occurred with the inclusion of chicory in the three-species mixture, indicating that the yield increases with increasing seeded species richness resulted from adding a highly productive species, an example of the 'sampling effect' mechanism for explaining plant species diversity effects. The percentage of weeds differed among the four sward mixtures. Weed proportions were similar for the two- and three-species mixtures, whereas the six- and nine-species mixtures had lower weed populations than the simple mixture. Sown species composition of the pastures changed greatly during the experiment, with the complex mixtures simplifying to fewer species. Complex forage mixtures were more productive than simple grass-legume mixtures during drought and also had reduced weed pressure. Individual animal performance was similar among simple and complex mixtures. Increasing plant species diversity on pastures may be a short-term way to increase forage productivity and reduce weed competition. Stability of species composition in complex mixtures, however, may be a problem in the long term.