Pedro Gomes da Cruz

Modelos empíricos para estimar o acúmulo de matéria seca de capim‑marandu com variáveis agrometeorológicas

The objective of this work was to test empirical linear regression models, to predict dry matter accumulation rates (DMAR) of Urochloa brizantha cv. Marandu, using agrometeorological variables. To generate the models, the average dry matter accumulation under rainfed conditions, between 1998 and 2002, was used. The evaluated variables were: minimum, maximum and average temperatures, global radiation (GR), degree-days, actual (AET) and potential evapotranspiration (PET) obtained from the water balance, photothermal units (PU) and the climatic growth index (CGI). Except for the PU, the univariate and multivariate regressions showed good predictive ability. The best results were for the multivariate regression, with Tmin, GR and AET: R 2 , 0.84; root mean square residual (RMSR), 14.72; and Akaikes information criterium (AIC), 222.5. In the univariate regression, the following variables stood out: corrected degree-days (R 2 , 0.75; RMSR, 17.84; CIA, 242.6), corrected minimum temperature (R 2 , 0.75; RMSR, 17.82; AIC, 244.1); and CGI (R 2 , 0.74; RMSR, 17.85; AIC, 236.9). The correction of the agrometeorological variables using the relation between real and potential evapotranspiration (AET/PET) enhances, in general, the model prediction of DMAR.

Dry matter production of Tanzania grass as a function of agrometeorological variables

o 11, CEP 13418‑900 Piracicaba, SP, Brazil. E‑mail: fcmendon@esalq.usp.br, lc_araujo@yahoo.com.br Abstract - The objective of this work was to develop and validate linear regression models to estimate the production of dry matter by Tanzania grass (Megathyrsus maximus, cultivar Tanzania) as a function of agrometeorological variables. For this purpose, data on the growth of this forage grass from 2000 to 2005, under dry‑field conditions in Sao Carlos, SP, Brazil, were correlated to the following climatic parameters: minimum and mean temperatures, degree‑days, and potential and actual evapotranspiration. Simple linear regressions were performed between agrometeorological variables (independent) and the dry matter accumulation rate (dependent). The estimates were validated with independent data obtained in Sao Carlos and Piracicaba, SP, Brazil. The best statistical results in the development and validation of the models were obtained with the agrometeorological parameters that consider thermal and water availability effects together, such as actual evapotranspiration, accumulation of degree-days corrected by water availability, and the climatic growth index, based on average temperature, solar radiation, and water availability. These variables can be used in simulations and models to predict the production of Tanzania grass.

Response mechanisms of Brachiaria brizantha cultivars to water deficit stress 1

Two cultivars of Brachiaria brizantha (Hochst ex. A. Rich) Stapf. (Syn. Urochloa) were evaluated for their adaptation to water deficit and the stress response mechanisms in a greenhouse experiment. The experimental design was in completely randomized blocks with a 2 × 2 × 4 factorial arrangement. The Marandu and BRS Piata cultivars were evaluated under two water availability conditions, with or without water restriction. The harvests were carried out 0, 7, 14 and 28 days after the start of water restriction. For both cultivars, the water deficit stress caused a reduction in shoot biomass and leaf area and an increase in the percentage of roots in the deeper soil layers. The B. brizantha cv. Marandu reached critical levels of leaf water potential in a shorter period of water restriction than did the B. brizantha cv. BRS Piata. The osmoregulation and deepening of the root system are mechanisms of adaptation to water stress observed in both Marandu and BRS Piata cultivars. Besides that, the Marandu cultivar also increases its leaf senescence and, consequentially, decreases its leaf area, as a response to water deficit.

Mudanças Climáticas Globais e a Pecuária: Cenários Futuros para o Semiárido Brasileiro (Global Climatic Changes and Animal Production: Future Scenarios for the Brazilian Tropical Semiarid)

Os sistemas de producao animal no Semiarido brasileiro podem ser vulneraveis as mudancas climaticas. Cenarios futuros para a producao de Brachiaria brizantha, Panicum maximum, Cenchrus ciliaris e Opuntia ficus indica foram analisados para a identificacao de areas mais vulneraveis. A partir dos modelos ja disponiveis, foram identificadas algumas areas de maior vulnerabilidade, o que possibilitou a indicacao de alternativas de adaptacao dos sistemas de producao para mitigacao de possiveis impactos negativos das mudancas climaticas globais sobre a producao animal do Semiarido brasileiro. O desenvolvimento de tecnicas para o uso sustentavel da Caatinga como pasto nativo contribuira para reduzir a degradacao deste bioma e os riscos de desertificacao da regiao. Novas variedades de plantas forrageiras, tanto de exoticas quanto de especies nativas, melhor adaptadas para as condicoes de cenarios climaticos futuros poderao ser desenvolvidos atraves do melhoramento vegetal. O uso de irrigacao de pastagens e o aproveitamento de co-produtos na alimentacao dos animais contribuirao para o aumento de produtividade e para a reducao da pressao sobre a vegetacao nativa. Diversos grupos de pesquisa tem desenvolvido modelos melhores para projecao regionalizada de chuva e de temperatura. O desenvolvimento desses modelos permitira uma investigacao mais precisa dos possiveis impactos das mudancas climaticas globais sobre a pecuaria no semiarido brasileiro.

Relationship between thermal comfort indices and internal temperature of grazing lactating Holstein × Gyr cows in western Amazonia

The relationship between the indices of thermal comfort and internal temperature in lactating cows was evaluated inRondônia, western Amazonia in a 2 × 2 crossover trial carried out with eight Girolando cows, 1⁄2 Holstein × 1⁄2 Gyr (n=4) and 3⁄4 Holstein × 1⁄4 Gyr (n=4), grazing palisade grass supplemented with or without soybean oil concentrates. Data logger thermometers adapted to intravaginal devices (hormone free) were used to measure internal temperatures (IT) every 10 min over 48 h. Concomitantly, environmental parameters (air temperature, relative humidity, wind speed, and solar radiation) were collected for the estimation of the temperature-humidity index (THI), equivalent temperature index (ETI), and predicted respiratory rate (PRR). Supplementation with soybean oil did not affect the internal temperature of the cows. IT varied significantly between the genetic groups, with the highest mean observed at night in the 3⁄4 Holstein × 1⁄4 Gyr cows, compared with that in the 1⁄2 Holstein × 1⁄2 Gyr cows (39.54 °C vs 39.06 °C, respectively). THI, ETI, and PRR were significantly and positively correlated with the IT of the Girolando cows; however, the PRR was not found to be adequate in indicating the night-time heat stress in cows.