RESUMO

Dry mass production and persistence of Panicum maximum pastures depends on nitrogen supply. Defoliation influences N uptake and allocation patterns yet its effects on plasticity of N dynamics in P. maximum have not been investigated. Stable isotopes of N (15N) were used in order to test the hypothesis that defoliation in terms of proportion of the leaf area removed effects N mobilisation, uptake and allocation patterns in P. maximum. The plants were initially cut weekly to a height of either 0.15 m or 0.30 m for seven weeks. Eight weeks after the first defoliation, all plants were defoliated for a final time to remove 0, 25, 50, 75 or 100 % of the area of each individual leaf blade of the main tiller. Root N uptake was reduced when all leaf area was removed, but more lenient defoliation improved N uptake due to a positive effect on specific N uptake. Young leaves, side tillers and roots were the main sinks for N from root uptake. Roots of P. maximum became a net source of N for mobilisation immediately after severe defoliation. Root uptake was the main source of N for new growth in P. maximum plants. Allocation pattern of mobilised N was different from that of N derived from root uptake. It was concluded that adaptation of P. maximum to defoliation is related to plasticity of N uptake, mobilisation and allocation, but changes in N dynamics did not offset negative impacts of complete defoliation of the plants.

RESUMO

Dry mass production and persistence of Panicum maximum pastures depends on nitrogen supply. Defoliation influences N uptake and allocation patterns yet its effects on plasticity of N dynamics in P. maximum have not been investigated. Stable isotopes of N (15N) were used in order to test the hypothesis that defoliation in terms of proportion of the leaf area removed effects N mobilisation, uptake and allocation patterns in P. maximum. The plants were initially cut weekly to a height of either 0.15 m or 0.30 m for seven weeks. Eight weeks after the first defoliation, all plants were defoliated for a final time to remove 0, 25, 50, 75 or 100 % of the area of each individual leaf blade of the main tiller. Root N uptake was reduced when all leaf area was removed, but more lenient defoliation improved N uptake due to a positive effect on specific N uptake. Young leaves, side tillers and roots were the main sinks for N from root uptake. Roots of P. maximum became a net source of N for mobilisation immediately after severe defoliation. Root uptake was the main source of N for new growth in P. maximum plants. Allocation pattern of mobilised N was different from that of N derived from root uptake. It was concluded that adaptation of P. maximum to defoliation is related to plasticity of N uptake, mobilisation and allocation, but changes in N dynamics did not offset negative impacts of complete defoliation of the plants.

RESUMO

The objective of this experiment was to verify the outcome of the grazing above the productivity and the persistence of three accesses of Paspalum. The experiment was developed on Southeastern Cattle Embrapa, in São Carlos, SP, in the period of January to December 2005. Three genotypes of Paspalum (Paspalum. Guenoarum BRA-006572, Paspalum malacophyllum - BRA-003077 and Paspalum atratum BRA-011681) and two controls (Brachiaria decumbens and Paspalum atratum cv. Pojuca) were compared under two grazing intensities (1500 and 3000 kg MS/ha of post-graze residue). Plots were mob grazed (1-day grazing followed by 27-day rest (water period) and 1-day grazing followed by 55-day rest (dry period) and stocking rate was adjusted according to the herbage mass available and the treatment grazing intensity. The following variables have been evaluated: total herbage mass before and after grazing; proportion of leaf, stem and dead material; occurrence of weeds and tiller density and occurrence of diseases and symptoms of mineral toxicity or deficiency. For both grazing intensities the Paspalum atratum demonstrated positive characteristics of production and persistence indicating that these are promising genotypes for use in intensive systems of pasture.  KEY WORDS: Intensity of grazing, pasture, production of forage, tillers.

Desenvolveu-se o experimento na Embrapa Pecuária Sudeste, localizada em São Carlos, SP, no período de janeiro a dezembro de 2005, objetivando verificar o efeito do pastejo sobre a produtividade e a persistência de três acessos de Paspalum (Paspalum guenoarum BRA-006572, Paspalum malacophyllum BRA-003077 e Paspalum atratum BRA-011681) comparados com duas testemunhas (Brachiaria decumbens e Paspalum atratum cv. Pojuca), em dois níveis de desfolha (1.500 e 3.000 kg MS/ha de resíduo pós-pastejo). O ensaio foi do tipo mob grazing, em que se utilizou o método de pastejo rotacionado com 27 dias de descanso e um dia de ocupação (período das águas) e 55 dias de descanso e um dia de ocupação (período das secas). Ajustou-se a taxa de lotação animal das parcelas de acordo com a massa de forragem disponível antes do pastejo e com o nível de desfolha previsto pelos tratamentos. As variáveis foram: massa de forragem antes e após o pastejo; proporções de folhas, hastes e material morto; densidade de perfilhos; incidência de plantas invasoras; observações relativas à susceptibilidade a pragas e doenças, sintomas de toxidez e deficiência mineral. O Paspalum atratum BRA-011681 apresentou características positivas de produção e persistência, tanto na altura de pastejo de 0,15 m como na de 0,30 m, evidenciando que essa espécie é promissora para uso em sistemas intensivos de pastejo.  PALAVRAS

RESUMO

The objective of this experiment was to verify the outcome of the grazing above the productivity and the persistence of three accesses of Paspalum. The experiment was developed on Southeastern Cattle Embrapa, in São Carlos, SP, in the period of January to December 2005. Three genotypes of Paspalum (Paspalum. Guenoarum BRA-006572, Paspalum malacophyllum - BRA-003077 and Paspalum atratum BRA-011681) and two controls (Brachiaria decumbens and Paspalum atratum cv. Pojuca) were compared under two grazing intensities (1500 and 3000 kg MS/ha of post-graze residue). Plots were mob grazed (1-day grazing followed by 27-day rest (water period) and 1-day grazing followed by 55-day rest (dry period) and stocking rate was adjusted according to the herbage mass available and the treatment grazing intensity. The following variables have been evaluated: total herbage mass before and after grazing; proportion of leaf, stem and dead material; occurrence of weeds and tiller density and occurrence of diseases and symptoms of mineral toxicity or deficiency. For both grazing intensities the Paspalum atratum demonstrated positive characteristics of production and persistence indicating that these are promising genotypes for use in intensive systems of pasture.  KEY WORDS: Intensity of grazing, pasture, production of forage, tillers.

Desenvolveu-se o experimento na Embrapa Pecuária Sudeste, localizada em São Carlos, SP, no período de janeiro a dezembro de 2005, objetivando verificar o efeito do pastejo sobre a produtividade e a persistência de três acessos de Paspalum (Paspalum guenoarum BRA-006572, Paspalum malacophyllum BRA-003077 e Paspalum atratum BRA-011681) comparados com duas testemunhas (Brachiaria decumbens e Paspalum atratum cv. Pojuca), em dois níveis de desfolha (1.500 e 3.000 kg MS/ha de resíduo pós-pastejo). O ensaio foi do tipo mob grazing, em que se utilizou o método de pastejo rotacionado com 27 dias de descanso e um dia de ocupação (período das águas) e 55 dias de descanso e um dia de ocupação (período das secas). Ajustou-se a taxa de lotação animal das parcelas de acordo com a massa de forragem disponível antes do pastejo e com o nível de desfolha previsto pelos tratamentos. As variáveis foram: massa de forragem antes e após o pastejo; proporções de folhas, hastes e material morto; densidade de perfilhos; incidência de plantas invasoras; observações relativas à susceptibilidade a pragas e doenças, sintomas de toxidez e deficiência mineral. O Paspalum atratum BRA-011681 apresentou características positivas de produção e persistência, tanto na altura de pastejo de 0,15 m como na de 0,30 m, evidenciando que essa espécie é promissora para uso em sistemas intensivos de pastejo.  PALAVRAS

RESUMO

This study had the objective of evaluating the yield production of Panicum maximum cv. Tanzania using a production system with and without irrigation. The experiment was carried out at Embrapa Pecuária Sudeste, São Carlos, São Paulo State, from December 2003 to January 2005. The size of the experimental area was six ha, being three ha used without irrigation and three ha irrigated by conventional aspersion system. For both areas, the production system was the rotational grazed using holstein frisian cows, with a day of occupation and twenty-seven days of rest period. The pasture productivity was evaluated by the following variables: forage mass before and after the grazing, forage accumulation rate, and forage structures. For the total residue of post-grazing and leaves it was not observed significant effects of cycle grazing, treatment, and the interaction grazing cycle x treatment. As general, the total mass of forage before grazing and the stem mass before and after grazing were greater in the summer/autumn period and lower during the winter/spring time. The rate of forage accumulation was greater in the spring/summer and lower in the autumn/winter. The rate of stems accumulation was higher at february/2004 and january/2005. The experimental design was a replicated time measuring model analyzed by the Statistical Analysis Systems (SAS). The treatment with irrigation leaded t

O objetivo desse experimento foi avaliar a produtividade do Panicum maximum cv. Tanzânia sob pastejo de lotação rotacionada com e sem irrigação. O experimento foi conduzido na Embrapa Pecuária Sudeste, em São Carlos/SP no período de dezembro de 2003 a janeiro de 2005. Foi utilizada uma área de 6ha, sendo metade irrigada por aspersão convencional, pastejadas por vacas em lactação da raça holandesa, em sistema de pastejo rotacionado, com um dia de ocupação e vinte e sete dias de descanso. A produtividade do pasto foi avaliada por meio das variáveis: massa de forragem antes e após o pastejo, taxa de acúmulo e estrutura da forragem. Para o resíduo pós-pastejo total e de folhas não houve efeito significativo de ciclos de pastejo, tratamento e a interação ciclo de pastejo x tratamento. De modo geral, a massa de forragem total antes do pastejo e a massa de haste tanto antes quanto após o pastejo foram mais elevadas no período de verão/outono e mais baixas durante o inverno/primavera. A taxa de acúmulo de forragem foi mais elevada na primavera/verão e mais baixa no outono/inverno. A taxa de acúmulo de hastes foi elevada em fevereiro/04 e janeiro/05. O delineamento utilizado foi um modelo de medidas repetidas no tempo com o auxílio do pacote estatístico SAS (2001). O tratamento irrigado propiciou uma produção maior de forragem, com destaque para o período verão inverno e no período prim

RESUMO

This study had the objective of evaluating the yield production of Panicum maximum cv. Tanzania using a production system with and without irrigation. The experiment was carried out at Embrapa Pecuária Sudeste, São Carlos, São Paulo State, from December 2003 to January 2005. The size of the experimental area was six ha, being three ha used without irrigation and three ha irrigated by conventional aspersion system. For both areas, the production system was the rotational grazed using holstein frisian cows, with a day of occupation and twenty-seven days of rest period. The pasture productivity was evaluated by the following variables: forage mass before and after the grazing, forage accumulation rate, and forage structures. For the total residue of post-grazing and leaves it was not observed significant effects of cycle grazing, treatment, and the interaction grazing cycle x treatment. As general, the total mass of forage before grazing and the stem mass before and after grazing were greater in the summer/autumn period and lower during the winter/spring time. The rate of forage accumulation was greater in the spring/summer and lower in the autumn/winter. The rate of stems accumulation was higher at february/2004 and january/2005. The experimental design was a replicated time measuring model analyzed by the Statistical Analysis Systems (SAS). The treatment with irrigation leaded t

O objetivo desse experimento foi avaliar a produtividade do Panicum maximum cv. Tanzânia sob pastejo de lotação rotacionada com e sem irrigação. O experimento foi conduzido na Embrapa Pecuária Sudeste, em São Carlos/SP no período de dezembro de 2003 a janeiro de 2005. Foi utilizada uma área de 6ha, sendo metade irrigada por aspersão convencional, pastejadas por vacas em lactação da raça holandesa, em sistema de pastejo rotacionado, com um dia de ocupação e vinte e sete dias de descanso. A produtividade do pasto foi avaliada por meio das variáveis: massa de forragem antes e após o pastejo, taxa de acúmulo e estrutura da forragem. Para o resíduo pós-pastejo total e de folhas não houve efeito significativo de ciclos de pastejo, tratamento e a interação ciclo de pastejo x tratamento. De modo geral, a massa de forragem total antes do pastejo e a massa de haste tanto antes quanto após o pastejo foram mais elevadas no período de verão/outono e mais baixas durante o inverno/primavera. A taxa de acúmulo de forragem foi mais elevada na primavera/verão e mais baixa no outono/inverno. A taxa de acúmulo de hastes foi elevada em fevereiro/04 e janeiro/05. O delineamento utilizado foi um modelo de medidas repetidas no tempo com o auxílio do pacote estatístico SAS (2001). O tratamento irrigado propiciou uma produção maior de forragem, com destaque para o período verão inverno e no período prim