Influência da adubação sobre a composição botânica e sobre a produção de pastagens

The effect of liming and fertilization of pastures established in low lying areas was studied. Rates of 1 ton of limestone, 150 kg of ammonium sulphate and 300 kg of rock phosphate/ha were applied on pastures which had been established 5 years previously and subjected to poor management. The pastures were composed of several species which were classified in 3 groups; more useful, intermediate and less useful. During the first 2 years the pastures were grazed by woolless sheep and botanical composition and animal production data were collected. During the third year the pastures were grazed by yearling calves and only animal production was measured. The proportion of molasses grass ( Melinis minutiflora ) , common Bermuda grass ( Cyno dom dactylon ) and legumes increased in the fertilized pastures, while Bahia grass ( Paspalum notatum ) , "Batatais" strain, increased considerably in the unfertilized pastures. In the unfertilized pastures there was an invasion by Sape ( Imperata brasiliensis ) an important weed-grass in South-Central Brazil. For sheep the daily gain in live weight per animal on the fertilized pastures was 37 g with a carrying capacity of 6 head/ha and a production of 77.7 kg of live weight/ha/year. On the unfertilized pastures, these values were 24 g/animal/day, 3.5 head/ha and 30.7 kg of live weight/ha/year. Five sheep from unfertilized pastures died. The sheep utilized in this experiment showed poor capacity for gain and for this reason economic analysis was not made for this period. In the third year, calves were maintained on the pastures for a period of 224 days during the summer. The calves on the fertilized pastures had a daily gain/animal of 399 g live weight with a carrying capacity of 2.66 head/ha and a total production of 237.7 kg of live weight/ha. On the unfertilized pastures, daily gain per animal was 100 g of live weight with a carrying capacity of 2.44 head/ha and a production of 54.7 kg of live weight/ha for the period. During this period the difference in animal production gave a return of 21% above the costs of fertilization.