Water and energy fluxes in cowpea and castor beans cultivated in northeast Brazil / Fluxos de Ãgua e de energia em feijÃo macassar e mamona no nordeste do Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The castor beans and cowpea are crops of enormous economic and social importance for the farmers in northeast Brazil, whereas the extracted oil of seeds of castor beans is used for production of biodiesel and the cowpea is the main food for poor population. Independent of crop type, the knowledge of water amount removed from soil by vegetation is of great interest, mainly, for the studies about the use of water by evapotranspiration, as well as for the dynamic absorption of nutrients. However, up to now, few researches exist that consider the transfer of water and energy in these crops, mainly, for the castor beans. It is known that the biophysical processes involved in water and energy exchanges are numerous and complex: transfer in unsaturated zone, infiltration, water extraction by the root plant system, in addition to the turbulent flux above and inside the vegetal cover, which complicates its direct measurement in large areas, in a continuous form and in a large period of time, owing to the large number of required equipment and finatial resources. Models have been conceived describing the exchange of mass and heat in the soil-vegetation-atmosphere system, called SVAT models. The SiSPAT (Simple Soil-Plant-Atmosphere Transfer model) is one of these models and it has been very used for the environmental conditions in Europe and Africa; however, it has never been used for the environmental conditions in the Northeast Brazilian. Thus, the present work has the objective of studying and simulating the water and energy fluxes, through the SiSPAT model, in a mountain region cultivated with castor and cowpea. The required data were obtained in a 4 ha area at the Experimental Station of the Agricultural Sciences Center, of the UFPB, municipality of Areia, PB (6o 58â S, 35o 41â W e 620 m). The area was instrumented with an automatic micrometeorological tower, which allowed estimation of the components of energy balance by the Bowen ratio Energy Balance method, and evapotranspiration from the castor and the cowpea. In addition, sensors had been installed for the measurements of soil water content and temperature profiles. The model was used in representative periods of the phenological phases of the crops, for the castor and for cowpea. It was found, from the sensitivity analysis, that output variables presented sensitivities in the following order: latent heat flux, cumulative evapotranspiration, soil heat flux, sensible heat flux and net radiation. Through the validation process, it was observed that SiSPAT model demonstrated excellent performance when simulating the components of the energy balance (net radiation, latent heat flux, sensible heat flux and soil heat flux) and the cumulative evapotranspiration in the phenological phases of the castor beans and cowpea, in the most varied atmospheric condition and soil water content. The SiSPAT model also adequately simulated the temporal evolution of the soil water content, in periods without any rainfall and with high rainfall. The same occurred for the temporal evolution of soil temperature.

ASSUNTO(S)

characterization thermal evapotranspiration caracterizaÃÃo hÃdrica energia nuclear characterization hydria sispat model evapotranspiraÃÃo anÃlise de sensibilidade engenharia nuclear modelo sispat analyses of sensibility

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