Evapotranspiração real em cultivo de milho no agreste alagoano

Abstract

Corn is a grass, witch its diverse applicability and its high power of adaptation from adverse weather is grown in virtually every places of the world. This cereal has very high nutritional value for the reason that its high starch concentration, at times, the population food basis. Food industries use corn as the main ingredient to produce several products, such as oils, soft drinks and other. It is widely used for animal meal production and currently it has been framed in the market of bio-fuels for ethanol production. Seasonal environmental changes, in a specific area, are the major factor in agricultural productivity, in this context, the study of environmental factors, such as rainfall, air temperature and solar incident radiation on the surface, become indispensable. Real evapotranspiration indicates how many water a vegetated surface lost in a given time, so their knowledge will subsidize the determination of the amount of water needed to restore the culture. That will mean absence of water stress and consequently higher productivity and better use of natural resources. Based on the predicted, this study aimed to evaluate the methods of Penman-Monteith original and the Culture Simple coefficient to estimate real evapotranspiration (ETR), respectively associated with schemes to determination of the culture resistance and the reduction coefficient of soil water, to determine the real needs of water in each stage of corn cultivation and during its cycle. The study was based on data from an experimental área installed at São José Villa, located in Arapiraca city, Alagoas (09 ° 38 '35.3 "S, 36 ° 40' 15.5" W, 260 m) during June-September 2005. The variety of maize used was BR 106 grown in rainfed conditions. Daily real evapotranspiration was determined with soil water residue balance, with variation of the water content obtained in the soil profile 0 to 0.30 m. The sub-culture resistance models evaluated were proposed by Ortega-Farias (Ortega-Farias et al., 2004) and the sub-model as a leaf resistance function to water vapor diffusion parameterized by the leaf area index. The second sub-model was considered two leaf resistances i) rs = 100 s m-1 proposed by Monteith (1965) and ii) rs = 73.2 m s-1, obtained from field measurements with infrared gas analyzer. The influence of soil water availability in evapotranspiration was determined by the water reduction soil coefficient estimated by three methods, i) logarithmic decay method, ii) FAO 56 bulletin method, linear decay from easily available water and iii) hyperbolic decay. The results demonstrated that ETR estimated value by the hyperbolic sub-model water reduction coefficient in the soil (Ks), embedded in the simply culture coefficient method showed low dispersion, with determination coefficient between observed values (water soil balance) and (r2) estimated 0.561, and satisfactory agreement, with root mean square error (RMSE) of 0.71 mm d-1. Dispersion and similar agreement was obtained with the sub-model that parameterize the culture strength by Leaf Area Index (LAI) applied to Penman-Monteith original and the hyperbolic water reduction coefficient in soil, being prominent when used leaf resistance to water vapor diffusion (rs = 100 s m-1) suggested by Monteith (1965) (r2 = 0.602 and RMSE = 0.70 mm d-1). Based in the predicted models, was found that increased water consumption by the vegetated surface occurred at the intermediate stage (55-95 DAP), ranging between 106.8 and 122.6 mm.