ABSTRACT The objective of this research was to characterize the nutritive value of corn silage made on intensive dairy farms and demonstrate the nutritional variations between silages located at the top and at the center of a bunker silo. Thirty-two dairy farms were visited in four Brazilian states. One corn bunker silo of each farm was chosen and samples were collected from the top and center parts. The nutritive value, fermentation end-products, and microbial counts were assessed. The predicted milk was determined by Milk2006 spreadsheet. The mean, standard deviation, maximum, minimum, and 95% confidence interval of all data were calculated. The ash, neutral detergent fiber (NDF), starch, in vitro NDF, and dry matter (DM) digestibility data were compared with reference value. Both statistical procedures were performed through the PROC MEANS of SAS. The mean values found at the center for NDF, starch, total digestible nutrients (TDN-1x), and estimated milk were 503 g kg−1 DM, 308 g kg−1 DM, 583 g kg−1, and 1,124 kg t−1, respectively. The top silages presented a mean TDN-1x and predicted milk of 559 g kg−1 and 1046 kg t−1, respectively. For NDF digestibility and starch concentration, 53.1% and 62.5% of the center samples presented a value equal to or above the reference value (500 g kg−1 and 300 g kg−1 DM for NDF digestibility and starch concentration, respectively). Overall, the corn silage produced on intensive dairy farms in Brazil has satisfactory nutritive value, especially in terms of starch concentration. Some parameters, such as the concentration of fiber and its digestibility, should be improved. This study also shows that a silo may contain two different types of silage: top and center. This alerts nutritionists and farmers when feeding and sampling corn silage from bunker silos.

Gradual reduction of legumes in mixed tropical pastures requires periodic oversowing. Exploiting the carrying capacity of grass for an extra year after the disappearance of legumes can be economically advantageous to the farmer. This study aimed to evaluate the productivity of Xaraés palisadegrass (Brachiaria brizantha) pastures in response to its historical association with stylo (Stylosanthes guianensis) under two canopy heights to determine whether different grazing management conditions affect the defoliation pattern left by grazing animals. The split-plot experimental design was used, with the historical botanical composition (HBC) (24, 34, 45 and 52 % legume composition) corresponding to the main plots and the canopy frequency of defoliation determined at heights of 30 and 45 cm for Xaraés palisadegrass corresponding to the subplots with two replicates (500 m2) grazed by Tabapuã cows. Pastures with over 34 % stylo in the botanical composition remained productive for one year after legume disappearance, accumulating more than 8 mg ha−1 of forage per year. Xaraés palisadegrass pastures at a height of 30 cm provided better canopy structure, with 64 % less stem production and 43 % less dead material. The 30-cm pre-grazing canopy height provided a grazing environment conducive to forage intake by animals that resulted in efficient use of the pasture. In response to the improved canopy structure, the cows grazed an average of 60 fewer minutes. A HBC greater than 34 % of legumes in the pastures allows for the postponement of legume oversowing until the next growing season.

O objetivo deste trabalho foi avaliar as respostas morfogênicas e estruturais de duas espécies e cinco cultivares de braquiária a intensidades de desfolhação. As cultivares Marandu, Xaraés, Arapoty, Capiporã (Urochloa brizantha) e Basilisk (U. Decumbens) foram desfolhadas mecanicamente a 15 e 7,5 cm de altura, durante o verão e o inverno. Utilizaram-se unidades experimentais de 9x4 m, irrigadas e adubadas com 220 kg ha-1 por ano de N e K2O. As características morfogênicas avaliadas foram: filocrono e senescência, duração de vida e taxas de aparecimento e alongamento de folhas. As características estruturais foram: número de folhas vivas por perfilho, comprimento final das folhas expandidas e de colmos, relação senescência/crescimento e densidade populacional de perfilhos. Variações nas condições meteorológicas, em cada estação, promoveram aumentos nas taxas de aparecimento e alongamento, diminuição do filocrono e duração de vida das folhas. As características estruturais mais responsivas ao gradiente promovido pelas alturas de corte foram o comprimento final de folhas expandidas e a densidade populacional de perfilhos. A altura de corte mais baixa exerceu maior impacto na dinâmica de crescimento do que na senescência, em perfilhos individuais. As cultivares Xaraés e Capiporã foram as mais produtivas, em razão das maiores taxas de alongamento foliar e maior densidade populacional de perfilhos.

The objective of this work was to evaluate structural and morphogenetic responses of two species and five cultivars of brachiaria to defoliation intensities. The cultivars Marandu, Xaraés, Arapoty, Capiporã (Urochloa brizantha), and Basilisk (U. decumbens) were mechanically defoliated at 15 and 7.5 cm, in mid-summer and mid-winter. The experimental units (9x4 m plots) were irrigated and fertilized with 220 kg ha-1 per year of N and K2O. Morphogenetic characteristics measured were: phyllochron, leaf senescence and life span, and leaf appearance and elongation rate. The structural characteristics evaluated were: number of leaves per tiller, final leaf length of fully expanded leaves, stems length, senescence/growth ratio, and tiller density. Variations in meteorological conditions of each season promoted increasing of the appearance rates and leaf elongation, and decreasing of the phyllochron and leaf life span. The structural features most responsive to the gradient promoted by harvesting heights were the final leaf length of expanded leaves and tiller density. The lower harvest height had the greatest impact on growth dynamics in comparison to senescence, in individual tillers. The cultivars Xaraés and Capiporã were more productive due to higher leaf elongation rates and higher tiller density.

O objetivo deste trabalho foi quantificar a fotossíntese foliar, durante o período de rebrotação, e estimar a fotossíntese de dosséis de duas espécies e cinco cultivares de braquiária, com base na arquitetura foliar e no ambiente luminoso no verão e inverno. Foram avaliadas quatro cultivares de Urochloa brizantha (Marandu, Xaraés, Arapoty e Capiporã) e uma de U. decumbens (Basilisk). Utilizou-se o delineamento de blocos ao acaso, com quatro repetições. As parcelas foram irrigadas e adubadas com 220 kg ha-1 por ano de N e K2O. Foi avaliada a taxa de assimilação de carbono nas folhas no dossel, o índice de área foliar (IAF) e a interceptação luminosa (IL). A fotossíntese foliar não variou entre cultivares ou estações, e houve assimilação de 0,91 mg m-2 s-1 de CO2 . Na fase inicial de rebrotação, o potencial fotossintético dos dosséis de verão e inverno foi baixo (0,80 mg m-2 s-1 de CO2); entretanto, dosséis forrageiros no inverno apresentaram maior aumento da assimilação de carbono por unidade de IAF. A fotossíntese de dossel, no final do período de rebrotação, foi 15% menor no inverno em comparação ao verão, e as correlações entre fotossíntese foliar e de dossel com a produção de forragem foram baixas. O IAF influencia fortemente os resultados do modelo de simulação da fotossíntese de dossel de espécies de braquiária.

The objective of this work was to quantify the leaf photosynthesis during forage regrowth and to estimate the canopy photosynthesis of two species and five Cultivars of brachiaria, based on leaf architecture and light environment in the summer and winter. Four cultivars of Urochloa brizantha (Marandu, Xaraés, Arapoty e Capiporã) and one of U. decumbens (Basilisk) were evaluated. It was used a randomized complete block design with four replicates. The plots were irrigated and fertilized with 220 kg ha-1 per year of N and K2O. Carbon assimilation in leaves and canopies, leaf area index (LAI) and light interception (LI) were evaluated. Leaf photosynthesis did not vary among cultivars or seasons, and there was assimilation of 0.91 mg m-2 s-1 CO2. In early regrowth, the canopy photosynthetic potential in the summer and winter was low (0.80 mg m-2 s-1 CO2); however, winter canopies showed greater increase in carbon assimilation per unit increase of LAI. Canopy photosynthesis at the regrowth end was 15% lower in the winter, in comparison to the summer, and the correlations of both leaf and canopy photosynthesis with forage production were low. The leaf area index has a strong impact on the simulation model results of canopy photosynthesis of brachiaria.