A. B. Bendahan

Produtividade de forragem e composição química de Stylosanthes capitata cv. Lavradeiro sob níveis de fósforo

The effects of phosphorus levels (0, 40, 80 and 120 kg of P2O5 ha) on green dry matter (GDM), chemical composition and nodulation of Stylosanthes capitata cv. Lavradeiro were evaluated under field conditions in Roraima ́s savannas. Phosphorus fertilization increased significantly (P<.05) GDM yields, nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg) and potassium (K) concentrations and number and dry weight of nodules. Maximum GDM yields and Ca, Mg and K contents were obtained with the application of 89.4; 56.2; 113.1 and 75.6 kg of P2O5 ha, respectively, while the N and P contents and number of nodules were directly proportional to P levels. The P critic level, related to 90% of GDM maximum production, was estimated at 2.43 g kg. The P efficiency utilization was inversely proportional to the P rates applied.

Produtividade de forragem e micorrrização de pastagens de Trachypogon plumosus sob adubação fosfatada

The effect of phosphate fertilization (0, 30, 60, 90 and 120 kg of P2O5 ha) on green dry matter (GDM) yield and the occurrence of arbuscular mycorrhiza fungi (AMF) of Trachypogon plumosus pastures was evaluated under field conditions of Roraima’s savannas. Phosphate fertilization positively and significantly (P<0.05) affected GDM, phosphorus concentrations and extraction, but linearly reduced spore numbers and root colonization rates by AMF. Maximum GDM yields, phosphorus concentrations and uptake were obtained with the application of 91.8; 76.7 and 82.6 kg of P2O5 ha, respectively. The phosphorus efficiency utilization was inversely proportional to the phosphorus rates applied.

Características morfogênicas e estruturais de Megathyrsus maximus cv. Tanzânia-1 sob intensidades de desfolhação.

O efeito de intensidades de desfolhacao (20, 30, 40 e 50 cm acima do solo) sobre a producao de forragem e caracteristicas morfogenicas e estruturais de Megathyrsus maximus cv. Tanzânia-1 foi avaliado nos cerrados de Roraima.

Dinâmica do acúmulo de forragem e morfogênese de Urochloa brizantha cv. Xaraés sob períodos de descanso.

The effects of rest periods (14, 21, 28, 35, 42 and 49 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Urochloa brizantha cv. Xaraés were evaluated under natural field conditions. GDM yields and regrowth, medium blade length, leaf elongation and leaf senescence rate increased consistently with highest rest periods however the nitrogen, phosphorus, calcium, magnesium and potassium contents and leaf appearance rate decreased. Maximum GDM yields, number of leaves tiller-1, leaf elongation rate and leaf area index were obtained with rest periods at 40.8; 40.2; 26.2 and 48.2 days. These data suggest that grass grazing at 35 to 42 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Produtividade de forragem, composição química e morfogênese de Megathyrsus maximus cv. Mombaça sob períodos de descanso

The effects of rest periods (14, 21, 28, 35, 42 and 49 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Megathyrsus maximus cv. Mombaça were evaluated under natural field conditions. GDM yields and regrowth increased consistently with highest rest periods. The leaf appearance and leaf expansion rates are inversely proportional to the rest periods, occurring the inverse for average leaf length, leaf area index and foliar senescence rate. Maximum GDM yields, regrowth yields, number of leaves tiller, average leaf length and leaf area index were obtained with rest periods at 36.4; 39.2; 40.8; 39.6 and 41.3 days. These data suggest that grass grazing at 35 to 42 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Adubação nitrogenada e consorciação de Trachypogon plumosus com Stylosanthes capitata cv. Lavradeiro sob diferentes densidades de semeadura

The effect of nitrogen levels (0, 40, 80, 120, 160, and 200 kg of N ha1) on pure pastures of Trachypogon plumosus and the sowing densities of Stylosanthes capitata cv. Lavradeiro (1.0; 2.0; 3.0 and 4.0 kg of seeds ha-1) on forage yield, botanical composition and apparent fixation and transfer of nitrogen (N) was evaluated under field conditions. Nitrogen fertilization quadratically affected grass forage yields and its nitrogen content, and the maximum values were estimated by the application of 154.6 and 155.7 kg N ha-1, respectively. The legume forage yield was directly proportional to the densities of its sowing, occurring the opposite for the grass forage yield. The forage yields of the grass-legume mixture, independently of legume sowing density, were higher than those showed by the grass grown alone and for all doses of N evaluated. The use of legume sowing densities between 2.0

Acúmulo de forragem e morfogênese de Brachiaria ruziziensis sob níveis de desfolhação

The effect of defoliation levels (10, 15, 20, 25 and 30 cm above soil level) on green dry matter (GDM) yield and morphogenetic and structural characteristics of Brachiaria ruziziensis were evaluated under field conditions in Roraima ́s savannas. The effects of defoliation levels on the GDM yields, number of leaves plant, leaf area index, leaf appearance and elongation rates were quadratics and maximum values recorded with cutting at 22.2; 17.7; 22.5; 17.1 and 25.2 cm above soil level, respectively. The population tiller density was inversely proportional to the level of defoliation, while the opposite occurred for to medium blade length and leaf senescence rate. Apical meristem removing percentage was higher with increasing defoliation level. Aftermath regrowth showed close negative correlation with defoliation level.

An ABM to Monitor Landscape Dynamics and to Undertake Collective Foresight Investigations in the Amazon

By seeking for alternative land uses in the Amazon, we designed an Agent-Based Model (ABM) containing a set of rural practices for small-scale farmers. In order to reach a more sustainable development, we analyze the benefits and the constraints of these practices. By comparing various production activities starting from the same initial conditions, we test several strategies and their efficiency faced to different initial conditions and environmental laws. Our study does not compare solely the financial profits of the agricultural activities. But it seeks to better understand and assess the feasibility of new activities in terms of family labor management, availability of land and economic profitability. Our first results conclude that a strict compliance with the law is not economically sustainable if the farmers still apply their standard land use strategies. We hope that this model could become a useful tool for the small farmers. By easily modifying the behavior of an agent, they could virtually invent and assess the efficiency of new practices on their farm. We also hope that this tool could become a means to facilitate dialogue between different stakeholders in the Amazon, in order to achieve more sustainable development.

Acúmulo de forragem e eficiência de utilização da radiação em pastagens de Axonopus aureus, durante o período seco, nos cerrados de Roraima

O efeito da idade de rebrota (21, 28, 35, 42, 49, 56, 63 e 70 dias) sobre a produtividade de materia seca (MS) e a eficiencia de utilizacao da radiacao (EUR) de Axonopus aureus, durante o periodo seco, foi avaliado em condicoes de campo. O aumento da idade de rebrota resultou em maiores rendimentos de forragem, taxa absoluta de crescimento, taxa de crescimento da cultura, taxa de crescimento relativo e area foliar. As relacoes entre idade de rebrota, rendimento de MS, taxa absoluta de crescimento e EUR foram ajustadas ao modelo quadratico de regressao, sendo os maximos valores registrados aos 62,6; 47,8 e 51,7 dias de rebrota, respectivamente. A resposta da produtividade de forragem a RFA incidente foi quadratica e o maximo valor estimado em 487,7 MJ/m2, o qual correspondeu a 796,7 kg de MS/ha. Visando conciliar produtividade de forragem da graminea com a maximizacao da EUR, o periodo de utilizacao mais adequado de suas pastagens situa-se entre 49 e 56 dias de rebrota.