ASTRACT. This study evaluated the effect of increasing levels of leucaena forage in sorghum: forage. In addition to pure sorghum, it was evaluated different levels of inclusion of leucaena (15, 30 and 50%) at the time of ensiling. Forage was ensiled in PVC tubes (100 mm diameter, 500 mm length) under the density of 500 - 600 kg m-3, a total of 20 silos were prepared, which were opened 35 days after ensiling. There was no effect (p > 0.05) of leucaena inclusion levels for pH, water activity (Aw) and total ammonia nitrogen (total NH3-N). There was an increasing linear effect (p < 0.05) for the content of dry matter (DM), crude protein (CP) and lignin that increased from 33.47 to 34.75%, 7.82 to 16.05% and from 7.29 to 9.93%, at the levels from 0 to 50% inclusion of leucaena, respectively. There was a decreasing linear effect (p < 0.05) for neutral detergent fiber corrected for ash and protein (NDFcp) and hemicellulose, which reduced from 56.65 to 48.37% and from 24.07 to 17.67% at the levels of 0 and 50% inclusion, respectively. For the ash content, there was a quadratic effect (p < 0.05), with a maximum at 8.3% with 8.9% inclusion of leucaena. The inclusion of up to 50% leucaena into sorghum silage is recommended, because, in addition to maintaining the fermentation quality, it also improved nutritional quality of sorghum silage.

Objetivou-se por meio deste estudo avaliar as características estruturais, produtivas e o valor nutritivo do capim-Tifton 85 adubado com duas doses de nitrogênio em quatro idades de rebrota. Foi utilizado delineamento em blocos casualizados seguindo esquema fatorial 4 x 2, com 4 idades de rebrota (28, 35, 42 e 49 dias) e duas doses de nitrogênio (100 e 300 kg ha-1) com seis repetições, totalizando 48 unidades experimentais de 25 m² (5x5m) cada. O critério de blocagem foi à variação na área experimental. A produção de matéria seca incrementou linearmente, em média 56.4%, à medida que avançou a idade de rebrota de 28 para 49 dias (P<0,01). Entre as doses de N, houve aumento de 17.2% na produção de matéria seca quando adubado com 300 kg ha-1 de nitrogênio. A altura das plantas (P<0,01), assim como o número de folhas vivas (P<0,01), número de folhas expandidas (P<0,01) e o comprimento final da folha (P<0,01) aumentaram linearmente com o avanço da idade corte. A adubação do capim Tifton 85 com 100 kg ha-1 de N, manejado a cada 35 dias melhora a produção de matéria seca, características estruturais e valor nutricional da forragem para corte e/ou pastejo.

The objective of this study was to evaluate the structural, productive and nutritional value of Tifton 85 grass fertilized with two nitrogen doses at four regrowth ages. The experimental design was a randomized block in a factorial 4 x 2, with four regrowth ages (28, 35, 42 and 49 days) and two levels of nitrogen (100 and 300 kg ha-1) in six replicates, totaling 48 experimental units, of 25 m² (5x5m) each. The blocking criterion was the variation in the experimental area. Dry matter production increased linearly, on average 56.4%, as the regrowth age increased from 28 to 49 days (P<0.01). Among the N rates, there was a 17.2% increase in dry matter yield when fertilized with 300 kg / ha of nitrogen. The height of the plants (P <0.01), as well as the number of live leaves (P <0.01), number of expanded leaves (P <0.01) and the final leaf length (P <0.01) increased linearly with the advancement of cut age. Fertilization of Tifton 85 grass with 100 kg ha-1 of N, managed every 35 days improves the dry matter production, structural characteristics and nutritional value of forage for cutting and / or grazing.

RESUMO. Objetivou-se avaliar a produção, o valor nutritivo e a degradação ruminal potencial do feno de capim-Tifton 85 (Cynodon spp.) colhido em quatro idades de rebrota (28, 35, 42 e 49 dias) e adubado com duas doses de nitrogênio (N; 100 e 300 kg N ha-1). O delineamento foi o em blocos ao acaso, arranjado em esquema fatorial 4 x 2, com seis repetições. A área experimental foi o critério de blocagem. A adubação nitrogenada incrementou (p < 0,01) a produção de matéria seca e a produção de matéria seca digestível do feno e também os teores de lignina (p = 0,01) e proteína bruta (p = 0,01). Os teores de fibra em detergente neutro corrigida para cinzas e proteína (p = 0,01), fibra em detergente ácido (p = 0,01) e celulose (p = 0,02) ajustaram-se ao modelo quadrático de regressão em função das idades de rebrota. Para degradabilidade ruminal potencial do feno foi observado efeito quadrático (p = 0,01), com valor máximo de 73,1% aos 37 dias de rebrota. O feno de capim-Tifton 85 adubado com 300 kg ha-1 de N e colhido até os 37 dias de rebrota resulta em maior produção de matéria seca de feno, maiores teores de proteína bruta, melhor degradabilidade ruminal potencial da matéria seca.

ABSTRACT. The objective of this study was to evaluate the yield, nutritional value and potential ruminal degradation of Tifton 85 hay (Cynodon spp.) harvested at four regrowth ages (28, 35, 42 and 49 days) and fertilized with two nitrogen doses (N; 100 and 300 kg N ha-1). The experimental design was a randomized block design, arranged in a 4 x 2 factorial scheme, with six replications each. Nitrogen fertilization increased (p < 0.05) dry matter yield and digestible dry matter production of hay and also lignin and crude protein contents. Nitrogen fertilization increased (p < 0.01) the dry matter yield and the digestible dry matter production of hay, as well as lignin (p = 0.01) and crude protein (p = 0.01). The neutral detergent fiber corrected for ash and protein (p = 0.01), acid detergent fiber (p = 0.01) and cellulose (p = 0.02) adjusted to the quadratic function regression model of the regrowth ages. For potential rumen degradability hay, it was observed quadratic effect (p = 0.01) with maximum value of 73.1% at 37 days of regrowth. Tifton 85 hay fertilized with 300 kg ha -1 of N and harvested up to 37 days of regrowth results in higher hay dry matter yield, higher crude protein content, and better dry matter rumen degradability.