ABSTRACT. Ergot is a fungal disease and causes reductions in seed productivity and quality. We aimed to identify promising genotypes of brachiaria evaluating: (1) seed production potential (number of tillers, racemes per inflorescence, spikelets per raceme, raceme length, weight and number of seeds, and germination) and (2) resistance of seeds to Ergot (infected tillers, infected seeds). Five genotypes of Brachiaria grasses, four non-natural hybrids named BH1619, BH1810, BH1516 and Mavuno Palisadegrass (Urochloa brizantha x Urochloa ruziziensis), and Marandu Palisadegrass (U. brizantha Hoechst cv. Marandu) were evaluated. The BH1619 hybrid, despite the high weight of seeds, produced less viable, pure seeds. The hybrid BH1516 had a lower percentage of flowered tillers (42%) and seeds infected with ergot (8%). Marandu Palisadegrass had a higher percentage of infected tillers (95%) and infected seeds (38%). The hybrid BH1516 was the most resistant to ergot, followed by Mavuno Palisadegras sand BH1619. Among all materials, Mavuno Palisadegrass and BH1516 have a higher potential for seed production due to the higher percentage of flowered tillers and production of pure seeds with high germination capacity. The BH1516 hybrid was resistant to ergot, making it a better choice for use in infected areas used for seed or forage production.

ABSTRACT The objective of this study was to evaluate milk production and ingestive behavior of Holstein cows and the structural characteristics of Mulato II, a hybrid Brachiaria grass CIAT 36087 (B. ruziziensis × B. decumbens × B. brizantha), and Marandu (Brachiaria brizantha cv. Marandu) pastures under rotational stocking. The experiment was conducted from December 2011 to April 2012 after 10 months of adaptation to the grazing management objectives (25 cm pre-grazing height and 15-20 cm post-grazing height). An area of 4 ha was divided into 28 paddocks: 14 with Mulato II pasture and 14 with Marandu pasture. The treatments consisted of the two grasses and a completely randomized design of the grazing variables with six repetitions each (paddock of evaluation) was used. For the animal variables, a randomized matched pairs design of 20 Holstein cows forming 10 blocks of two animals with similar production each was used. The forage mass or accumulation rate did not differ between grasses. Mulato II pastures had a higher tiller population density (822 tillers m−2) and crude protein content (143.5 g kg−1) than Marandu pastures (636 tillers m−2 and 130.3 g kg−1 crude protein). Cows kept on Mulato II exhibited shorter nighttime grazing activity (234 and 246 min in summer and autumn, respectively) than animals kept on Marandu (273 and 394 min, respectively). The average milk yield during the experimental period was higher for Mulato II (15.3 kg cow−1 day−1) compared with Marandu (14.3 kg cow−1 day−1). Both grasses have potential to be used in milk production systems for the grazing management objectives evaluated.

O índice de área foliar é a principal característica do dossel relacionada com os processos de interceptação e competição por luz em comunidades de plantas. O objetivo deste experimento foi quantificar e avaliar a composição da área foliar dos perfilhos em pastos de capim-marandu (Brachiaria brizantha cv. Marandu) submetidos a estratégias de lotação intermitente. O experimento foi conduzido em Piracicaba, SP, Brasil, de outubro/2004 a dezembro/2005. Os pastejos foram realizados quando o dossel atingia 95 ou 100% de interceptação luminosa (IL) até as alturas pós-pastejo de 10 e 15 cm, seguindo um arranjo fatorial 2 ' 2 com 4 repetições e um delineamento de blocos completos casualizados. Foram estimados o índice de área foliar, site filling, área foliar específica e a relação adimensional entre área foliar e volume dos perfilhos (R), além da participação relativa de perfilhos basais e aéreos na composição dessas variáveis. No início de primavera os valores de índice de área foliar e área foliar específica foram baixos, e pastos manejados com 95% de IL apresentaram maior site filling e área foliar específica que pastos manejados com 100% de IL. Isso resultou em maior perfilhamento e aumento no índice de área foliar no final de primavera, indicando rápida recuperação e retorno precoce dos pastos manejados com 95% de IL a condições de crescimento. Os perfilhos aéreos corresponderam a uma importante adaptação morfológica do capim-marandu para aumentar sua habilidade competitiva. O tratamento 100/10 resultou nos maiores e o 95/15 nos menores valores de R, sugerindo um padrão alométrico de crescimento dos perfilhos durante a rebrotação para compensar baixa densidade populacional e otimizar o índice de área foliar. Práticas de manejo do pastejo podem se beneficiar desse conhecimento propiciando condições ideais de dossel para maximização e aceleração do crescimento.

Leaf area index is the main sward characteristic related to the processes of light interception and competition in plant communities. The objective of this experiment was to quantify and evaluate the composition of the leaf area on tillers of marandu palisadegrass (Brachiaria brizantha cv. Marandu) subjected to strategies of intermittent stocking. The experiment was carried out in Piracicaba, state of São Paulo, Brazil, from October/2004 to December/2005. Swards were grazed at 95 and 100% canopy light interception (LI) to post-grazing heights of 10 and 15 cm, following a 2 ' 2 factorial arrangement with four replications in a randomised complete block design. Estimates were made of sward leaf area index, site filling, specific leaf area and the dimensionless ratio between tiller leaf area and volume (R), as well as the relative contribution of basal and aerial tillers to these variables. In early spring, values of leaf area index and specific leaf area were low when compared to the other seasons, and swards grazed at 95% LI presented higher site filling and specific leaf area than those grazed at 100% LI. This resulted in higher tillering activity and increase in leaf area index in late spring, indicating quick recovery and early return of swards grazed at 95% LI to growing conditions. Aerial tillers corresponded to an important morphological adaptation of marandu palisadegrass to increase its competitive ability. Treatment 100/10 resulted in the highest and 95/15 in the lowest R values throughout the experiment, suggesting an allometric pattern of growth of tillers during regrowth in order to compensate low tiller population and optimise the leaf area index. Grazing management practices can benefit from this knowledge by promoting ideal sward conditions to maximise and accelerate growth.

Estratégias de pastejo alteram a área foliar dos pastos, interferindo em seus padrões de crescimento e afetando o acúmulo e a utilização de forragem. O objetivo desse experimento foi avaliar o crescimento de pastos de capim-marandu (Brachiaria brizantha cv. Marandu) submetidos a estratégias de lotação intermitente. O experimento foi realizado em Piracicaba, SP, Brasil, de Outubro/2004 a Setembro/2005. Os pastejos foram realizados quando o dossel atingia 95 ou 100% de interceptação luminosa (IL) até as alturas pós-pastejo de 10 e 15 cm, seguindo um arranjo fatorial 2 × 2 com 4 repetições e um delineamento de blocos completos casualizados. Avaliaram-se a taxa de crescimento da cultura, a taxa de crescimento relativo, a taxa de assimilação líquida, a razão de área foliar e a razão de peso foliar. No início e final de primavera a maior taxa de crescimento da cultura foi registrada para o tratamento 95/15 (11.2 e 10.1 g m-2 dia-1, respectivamente), associada a altos valores de taxa de assimilação líquida (4.4 e 6.9 g m-2 dia-1, respectivamente), razão de área foliar (0.0095 e 0.0103 m-2 g-1, respectivamente) e razão de peso foliar (0.56 e 0.56 g g-1, respectivamente). Para compensar reduções em taxa de assimilação líquida a planta se ajustou morfológica e fisiologicamente aumentando a razão de área foliar e razão de peso foliar. A taxa de crescimento relativo e a taxa de assimilação líquida foram, respectivamente, 26% e 50% superiores nos pastos manejados com 95% relativamente àqueles com 100% de IL. No início de primavera os tratamentos 100/10 e 95/15 resultaram na maior taxa de crescimento relativo (0.086 e 0.059 g m-2 dia-1, respectivamente). O tratamento 95/15 resultou no padrão mais favorável de crescimento (taxas de crescimento da cultura, crescimento relativo e assimilatória líquida), particularmente durante o período de transição entre inverno e primavera.

Grazing strategies alter sward leaf area patterns of growth, affecting herbage accumulation and utilisation. The objective of this experiment was to evaluate the growth of marandu palisadegrass (Brachiaria brizantha cv. Marandu) swards subjected to strategies of intermittent stocking. The experiment was carried out in Piracicaba, São Paulo, Brazil, from October/2004 to September/2005. Swards were grazed at 95 and 100% canopy light interception (LI) to post-grazing heights of 10 and 15 cm, following a 2 × 2 factorial arrangement with four replications in a randomised complete block design. The response variables evaluated were: crop growth rate, relative growth rate, net assimilation rate, leaf area ratio and leaf weight ratio. In early and late spring, the highest crop growth rate was recorded for treatment 95/15 (11.2 and 10.1 g m-2 day-1, respectively), along with high values of net assimilation rate (4.4 and 6.9 g m-2 day-1, respectively), leaf area ratio (0.0095 and 0.0103 m-2 g-1, respectively) and leaf weight ratio (0.56 and 0.56 g g-1, respectively). To compensate reductions in net assimilation rate plants made some morphological and physiological adjustments increasing leaf area and leaf weight ratio. Relative growth rate and net assimilation rate were 26 and 50% higher, respectively, on swards grazed at 95% than at 100% LI. In early spring treatments 100/10 and 95/15 resulted in the highest relative growth rate (0.086 and 0.059 g m-2 day-1, respectively). Treatment 95/15 resulted in the most favourable pattern of growth (crop growth rate, relative growth rate, net assimilation rate), particularly during the transition period between winter and spring.

O objetivo deste trabalho foi avaliar o efeito de estratégias de pastejo rotativo sobre a composição morfológica da forragem consumida por bovinos de corte em pastos de Brachiaria brizantha cv. Marandu. Os pastejos foram realizados sempre que o dossel atingia 95 ou 100% de intercepção luminosa (IL) até as alturas pós-pastejo de 10 e 15 cm. Foi avaliada a composição morfológica das extrusas coletadas de animais fistulados no esôfago em três etapas ao longo do rebaixamento dos pastos. À medida que o rebaixamento progrediu, a proporção de lâminas foliares na extrusa diminuiu e a de colmos e de material morto aumentou. Pastejos iniciados com 100% de IL ou realizados até a altura pós-pastejo de 10 cm resultaram em menor proporção de lâminas foliares e maior de colmos e de material morto. O tratamento 95/15 foi consistente entre os tratamentos que apresentaram as maiores proporções de lâminas foliares e menores de colmos e de material e, mesmo no final do rebaixamento, apresentou, ainda, mais de 50% de proporção de lâminas foliares na extrusa. Os resultados obtidos indicam que, durante o rebaixamento do dossel, pastejos mais freqüentes e menos severos proporcionam aos animais a obtenção de dietas com elevada proporção de lâminas foliares, o que deve aumentar o valor nutritivo da forragem consumida.

The objective of this work was to evaluate the effect of rotational grazing strategies on the morphological composition of the herbage consumed by beef cattle in Brachiaria brizantha cv. Marandu swards. Grazings were carried out when swards achieved 95 and 100% of light interception (LI) until postgrazing heights of 10 and 15 cm. Morphological composition of the herbage consumed was determined from extrusa samples harvested from oesophageal-fistulated animals in three occasions, during the grazing down process. As sward height decreased from the pre-grazing condition, the proportion of leaf laminae in the extrusa decreased, and that of stems and dead material increased. Grazing at 100% LI or at 10 cm postgrazing height resulted in lower proportion of leaf laminae and higher proportion of stems and dead material than grazing at 95% LI or 15 cm postgrazing height. The treatment 95/15 ranked consistently among those with the highest proportions of leaf laminae, lowest proportions of stems and dead material; and, at the end of the grazing session, it still had 50% of leaf laminae in the extrusa. In general, the results indicate that more frequent and less severe grazings favour animal to feed on forage with a high proportion of leaf laminae, which increases diet nutritive value.

Foram avaliadas características do sistema radicular (pré e pós-pastejo) dos capins aruana e tanzânia submetidos a doses de nitrogênio (150 e 300 kg ha-1 de N) e pastejados por ovinos em lotação rotacionada com três a sete dias de pastejo e período de descanso variável. O delineamento experimental foi o de blocos completos casualizados (dois) com duas repetições, em esquema de parcelas subdivididas (parcelas =capins e subparcelas=doses de N) e medidas repetidas no tempo. No pré-pastejo, o capim-tanzânia, na média entre doses de N e períodos de pastejo, apresentou maior quantidade de massa seca da matéria orgânica (MSMO) (1,7 mg cm-3 de solo) que o capim-aruana (1,2 mg cm-3 de solo), além de maior comprimento de raízes (119,1 cm cm-3 de solo e 68,7 cm cm-3 de solo, respectivamente). A dose de 300 kg ha-1 de N contribuiu para maior comprimento do sistema radicular (107,1 cm cm-3 de solo) que a dose de 150 kg ha-1 de N (80,7 cm cm-3 de solo). O crescimento radicular pós-pastejo demonstrou similaridade de comportamento entre as variáveis mensuradas, de modo que o crescimento de raízes se tornou mais evidente após a segunda semana de rebrotação. Na média de capins, doses de N e idades de crescimento, no período equivalente ao outono/inverno, o crescimento de raízes (em MSMO foi de 3,9 mg 100 cm-3) aumentou para 12,9 mg 100 cm-3 no inverno, caiu para 4,7 mg 100 cm-3 na primavera e elevou novamente para 17 mg 100 cm-3 no verão. Comportamento semelhante foi observado para comprimento e superfície de raízes, coincidindo os períodos de maior crescimento com os de maior pluviosidade. A dose de 150 kg ha-1 de N promoveu maior crescimento em comprimento e superfície de raízes que a dose de 300 kg ha-1 de N nos períodos de maior pluviosidade.

The root system (pre and post grazing) characteristics of aruanagrass and tanzaniagrass under two nitrogen rates (150 and 300 kg ha-1 N year) grazed by sheep in variable rotational stocking (three to seven grazing days) and variable rest period were evaluated in this study. The treatments were assigned to a complete randomized block (two) design with two replicates (plots = grasses and split-plots = nitrogen rates)within repeated measures. In the pre-grazing tanzaniagrass, averages within nitrogen rates and grazing period showed higher amount of dry matter of organic matter (DMOM) (1.7 mg cm-3 of soil) than aruanagrass (1.2 mg cm-3 of soil) and greater root length (119.1 cm cm-3 of soil x 68.7 cm cm-3 of soil). The 300 kg ha-1 N rate contributed to a higher root system length (107.1 cm cm-3 of soil) than the 150 kg ha-1 N rate (80.7 cm cm-3 of soil). Post-grazing root growth showed similar behavior among the variables measured and was more evident after the second regrowth week. Considering averages within grasses, nitrogen rates and growth age, in the period equivalent to Autumn/Winter, the DMOM growth root was of 3.9 mg 100 cm-3, increased by 12.9 mg 100 cm-3 in Winter, decreased by 4.7 mg 100 cm-3 from Winter to Spring, and increased by 17 mg 100 cm-3 on Summer. Similar behavior for both root length and surface was observed, when the periods with higher growth coincided with the ones with higher rainfall. The 150 kg ha-1 N rate promoted higher length and surface than the 300 kg ha-1 N in the periods with higher rainfall.