Submitted by Leticia Schettini (leticia@ufrrj.br) on 2016-10-04T14:27:06Z No. of bitstreams: 1 2005 - Ricardo Martinez Tarr?.pdf: 741184 bytes, checksum: 1a3cc666f5aa519958cd7cacafdbd30f (MD5) / Made available in DSpace on 2016-10-04T14:27:06Z (GMT). No. of bitstreams: 1 2005 - Ricardo Martinez Tarr?.pdf: 741184 bytes, checksum: 1a3cc666f5aa519958cd7cacafdbd30f (MD5) Previous issue date: 2005-03-11 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior-CAPES / The experiment was conducted at the Experimental Station of CEPLAC, located in the South of Bahia State (CEPLAC/CEPEC/ESSUL), set as a entirely randomized design with 6 treatments and 3 repetitions. The treatments consisted of 2 pastures, one of grassonly Brachiaria humidicola (Rendle) Schweickt, and the other of B. humidicola consorted with Desmodium ovalifolium Wall cv. Itabela, each grazed at 3 different stocking rates of 2, 3 and 4 animals per hectare. Estimates of animal intake under grazing were made at two occasions during the year (August and November of 1995). Six oesophagus-fistulated steers were used for sampling of the consumed forage, and 36 animals were fed with 10 g of Cr2O3 each day, for 21 days. The ?in vitro? digestibility of dry matter, total nitrogen, and natural abundance of 13C were analyzed in the fistula samples. At the same time, the productivity of the pastures and their botanical composition was measured. The presence of the legume D. ovalifolium in the pastures of B. humidicola increased the protein content of the forage ingested by the animals by 64%. The dry matter intake was affected negatively by the presence of the legume due to its low palatability, however the proportion of the legume in the diet was quite significant (27 to 62%), being highest in the higher stocking rates due to the more restricted selectivity of the grazing animals. At the lower stocking rate there was a larger proportion of the legume in forage on offer. The total protein intake by the animals was higher in mixed pastures, but that didn't provide a better animal performance due to low digestibility of the legume. The rate of decomposition was very rapid (k ~ -0.081 and 0.060g g-1 day-1) P and K, and annual rates of P turnover through the litter pathway were between 13.7 and 13.2 kg P ha-1 year-1. In the grass-only pastures, as stocking rate increased from 2 to 3 head ha-1, P recycled in the litter decreased by 11%, but a further increase to 4 head ha-1 decreased P recycling by 6%, suggesting that beyond a certain critical level higher grazing stocking rates would lead to pasture decline if there was no N addition. High stocking rates decreased proportion of the legume in the sward, but at all rates the concentration of P in both the green and dead grass, in the forage on offer and in the litter, was higher in the mixed sward. The presence of legume in the litter resulted in increases in P and K recycled via litter deposition varying from 12.5 to 14.3 kg P ha-1 year-1 and 25.0 to 37.6 kg K ha-1 year--1. / Esse experimento foi conduzido na Esta??o Experimental de Zootecnia do Extremo Sul da Bahia (ESSUL/CEPEC/CEPLAC) obedecendo a um delineamento experimental inteiramente casualizado, com 6 tratamentos e 3 repeti??es. Os tratamentos foram estabelecidos segundo um fatorial 2 x 3, com 2 pastagens, Brachiaria humidicola (Rendle) Schweickt em monocultura e B. humidicola consorciada com Desmodium ovalifolium Wall cv. Itabela, e 3 taxas de lota??o, 2, 3 e 4 cabe?as por hectare. A estimativa do consumo animal em pastejo foi avaliada em 2 ?pocas do ano (agosto e novembro de 1995). Utilizaram-se 6 animais bovinos es?fago-fistulados para a retirada das extrusas (dietas consumidas) e 36 bovinos foram dosados com 10 g de Cr2O3 por dia, durante 21 dias. A digestibilidade ?in vitro? da mat?ria seca e a abund?ncia natural do 13C foram analisadas nas extrusas. Paralelamente, foram avaliadas a produtividade das pastagens e a sua composi??o bot?nica. O consumo de mat?ria seca foi afetado negativamente pela presen?a da leguminosa D. ovalifolium nas pastagens de B. humidicola devido ? sua baixa palatabilidade, por?m a propor??o da leguminosa na dieta consumida foi bastante significativa, sendo maior nas taxas de lota??o mais elevadas onde a seletividade dos animais foi mais restrita, apesar do fato de que na menor taxa de lota??o havia uma maior propor??o da leguminosa na forragem em oferta. O menor consumo de forragem observado nas pastagens consorciadas, n?o proporcionou menor desempenho animal, provavelmente devido ? maior oferta de prote?na oferecida pela leguminosa. As altas taxas de lota??o provocaram uma diminui??o na propor??o de leguminosas na forragem em oferta, entretanto em todas as taxas de lota??o a concentra??o de P na gram?nea verde e seca da forragem em oferta e da liteira foi maior nas pastagens consorciadas. A taxa de decomposi??o da liteira foi muito elevada, cerca de 0,081 e 0,060 g g-1 dia-1, para P e K respectivamente, acarretando uma deposi??o anual de P pela liteira entre 13,2 e 13,7 kg P ha-1 ano-1. Nas pastagens em monocultura, os aumentos na taxa de lota??o de 2 para 3 animais ha-1 e de 3 para 4 animais ha-1 causaram decr?scimos na reciclagem de P na liteira de respectivamente, 11 e 6%.Provavelmente essas altas taxas de lota??o provocam um decl?nio das pastagens devido ? menor adi??o de P ao sistema solo. A presen?a da leguminosa nas pastagens provocou um aumento significativo na reciclagem de P pela deposi??o da liteira variando de 12,5 a 14,3 kg P ha-1 ano-1 e 25,0 a 37,6 kg K ha-1 ano-1.