Dispersão de sementes de leguminosas forrageiras tropicais através das fezes de bovinos

Abstract

Legumes have some characteristics which make them able to improve pasture productivity, since they act as green manure and prevent soil erosion by weather agents. They contribute, furthermore, to maintaining or increasing soil organic matter level, since they draw carbon and fix atmospheric Nitrogen, so mobilize and recycle nutrients, increasing microbiological soil activity. Considering the useful potential of these forage plants the seed dispersal of five legume species (Pueraria phaseoloides, Neonotonia wightii, Calopogonium mucunoides, Macrotyloma axillare and Stylosanthes cv. Mineirão) through bovine feces in an established pasture of B. decumbens was studied in two trials. In the first one seeds mixed with concentrate were offered in the late afternoon to five crossbred (Holsten-Zebu) heifers weighing 250 kg. This experiment was carried out in a crop-pasture rotation system with five paddocks occupied for 4 days. Field evaluation were made from 12 to 30 hrs after seed ingestion, consisting in marking with sticks of different colors the sites of animal droppings in order to discriminate legume species. After 73 days of pasture vacancy was made the first evaluation in order to set the number of sprouts in the research field and Pueraria phaseoloides (puero) showed the best results, followed by Macrotyloma axillare (archer) and Calopogonium mucunoides (calopo). We accessed, in addition, the drought resistance after 266 days of pasture closure counting the survival legume plants in the pasture. The best performance for plant survival after dry season was observed in archer, followed by calopo. Concerning germination after the dry season of seeding made at the beginning of the experiment, best results were found by perennial soybean, despite its low results during the dry season. A second experiment was conducted using only archer seeds as they showed the best results concerning drought persistence. Five heifers were fed with 40 g of archer seeds; the animals were kept grazing for four days at the paddock in the crop-pasture system. At the first evaluation of this experiment we observed 215 archer plants in the research field. At the second evaluation the botanical composition analysis was made revealing the presence of 6,4% of the research area covered by archer plants (global mean of 380 plants).