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Campina Grande, Brazil

Pereira D.D.R.,Federal University of Vicosa | Martinez M.A.,Federal University of Vicosa | de Almeida A.Q.,UFS | Pruski F.F.,Federal University of Vicosa | And 2 more authors.
Engenharia Agricola

Hydrological models are important tools that have been used in water resource planning and management. Thus, the aim of this work was to calibrate and validate in a daily time scale, the SWAT model (Soil and Water Assessment Tool) to the watershed of the Galo creek, located in Espírito Santo State. To conduct the study we used georeferenced maps of relief, soil type and use, in addition to historical daily time series of basin climate and flow. In modeling were used time series corresponding to the periods Jan 1, 1995 to Dec 31, 2000 and Jan 1, 2001 to Dec 20, 2003 for calibration and validation, respectively. Model performance evaluation was done using the Nash-Sutcliffe coefficient (ENS) and the percentage of bias (PBIAS). SWAT evaluation was also done in the simulation of the following hydrological variables: maximum and minimum annual daily flowsand minimum reference flows, Q90 and Q95, based on mean absolute error. ENS and PBIAS were, respectively, 0.65 and 7.2% and 0.70 and 14.1%, for calibration and validation, indicating a satisfactory performance for the model. SWAT adequately simulated minimum annual daily flow and the reference flows, Q90 and Q95; it was not suitable in the simulation of maximum annual daily flows. Source

Bezerra J.R.C.,Pesquisador da Embrapa Algodao | de Azevedo P.V.,Federal University of Campina Grande | da Silva B.B.,Federal University of Campina Grande | Dias J.M.,Pesquisa da Embrapa Algodao
Revista Brasileira de Engenharia Agricola e Ambiental

Field experiments were carried out at the EMBRAPA, Barbalha, CE, during the growing seasons of 2003 and 2005 with the objective of estimating the evapotranspiration and crop coefficient of irrigated BRS-200 Marrom cotton cultivar. For this sensors of solar radiation, net radiation, dry and wet bulbs air temperature and wind speed at the 0.30 and 1.50 m levels above crop canopy and soil heat flux were installed and data were collected by a data acquisition system. Crop (ETc) and reference (ETo) evapotranspiration were estimated by the Bowen ratio and Penman-Monteith methods, respectively, while the crop coefficient (Kc) was estimated by the ratio of ETc to ETo. The ETc changed throughout the phonological cycle of the cotton crop, with mean values of 3.8 mm d-1 in the period from emergence to 10% of soil cover (phase I), 5.0 mm d-1 in the period of vegetative growth (phase II), 5.9 mm d-1 in the period of reproductive development (phase III) and 5.4 mm d-1 in the maturation period (phase IV). The Kc may be estimated as a function of the days after emergence (DAE) as: Kc =-0.00006 DAE2 + 0.009 DAE + 0.632. Source

Cardoso G.D.,Assistente de Pesquisa da Embrapa Algodao | Aguiar Alves P.L.d.C.,Sao Paulo State University | de Macedo Beltrao N.E.,Pesquisador da Embrapa Algodao | do Vale L.S.,Federal University of Paraiba
Revista Ciencia Agronomica

This study aimed to determine the late-season presence of weeds in reddish brown cotton (cultivar BRS Safira) and the critical times for removing weeds. The experiment was carried out in the area of Embrapa in Missão Velha-CE, Brazil, located at 7°42'07" S latitude and 39°24'18" WGr. longitude, during the 2007/2008 season. The treatments consisted of two control groups: weed-free crop during the initial period after crop emergency, and crop kept with weeds during initial period after plant emergency. Both consisted, 0; 20; 40; 60; 80 e 120 days after crop emergency (DAE), the weed community was evaluated by two phytosociological indices (relative dominance and relative importance). Regression analysis was performed as the model of sigmoidal Boltzman, using data from productivity separately within each type of competition, to identify the critical periods of competition, considering 2; 5 and 10% reduction in yield. The community of weeds was composed by 21 species, standing out among them: Richardia grandiflora, Amaranthus deflexus, Eleusine indica, Merremia aegyptia, Eragrotis pilosa, Cenchrus echinatus and Waltheria indica. Considering 2; 5 and 10% reduction in yield fiber as acceptable, the critical period before weed interference were, respectively, 8; 14 and 20 DAE. The critical period of weed interference, for those same levels of losses, were respectively, 100; 82 and 60 days. Source

De Lima R.L.S.,Brazilian National Council for Scientific and Technological Development | Severino L.S.,Pesquisador da Embrapa Algodao | Pereira W.E.,Federal University of Paraiba | De Lucena A.M.A.,Brazilian National Council for Scientific and Technological Development | And 2 more authors.
Revista Brasileira de Engenharia Agricola e Ambiental

Jatropha curcas is traditionally propagated by seed. However, in several situations the vegetative propagation is an important alternative and its technology needs to be developed. The objective of this study was to evaluate how the length and the portion of the branch from where the cuttings are extracted, influence the rooting and growth capacity of Jatropha cuttings. The treatments were arranged in a 3 x 4 factorial design, with three cutting positions (apical, middle and basal) and four cutting lengths (10, 15, 20, and 25 cm). A completely randomized design with four replications and ten cuttings per plot was adopted. At 70 days after planting, the cuttings were evaluated for the number of sprouts and branches, branch length, number of leaves, leaf area, number of roots, and dry mass of shoots and roots. The position from where the cuttings are extracted (apical, middle or basal) did not influence its capacity for rooting and the growth of the seedlings. The cutting length influences the initial growth, and the best growth was obtained in cuttings of around 22 cm. Source

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