EVAPOTRANSPIRAÇÃO E BIOMASSA DE CULTURAS AGRÍCOLAS EM SISTEMA CONVENCIONAL E PLANTIO DIRETO VIA SENSORIAMENTO REMOTO EM URUÇUÍ - PI

Abstract

Remote sensing contributes with several other sciences. Agronomy is very benefited with remote sensing, allowing the physical barrier to be broken, that is, to make analysis without being in the field, through satellite image analysis. In the present study, we aimed to determine the Net Primary Production - NPP and the water use of soybeans (no-tillage and conventional systems), corn, eucalyptus and pasture fields using remote sensing products, in the municipality of Uruçuí- Piauí, at 2012/2013 harvest. OLILandsat 8 orbital images were used (path/row 220/66), obtained in clear sky condition, i.e., free of clouds over the interest area. So, scenes from May to October 2013 were applied. The Normalized Difference Vegetation Index – NDVI from the Landsat scenes was applied to determine basal crop coefficients - Kcb. Data from a National Meteorological Institute station were used to characterize the weather conditions and to compute the reference evapotranspiration. The light use efficiency (ε) and NPP were were obtained from the NDVI images and air temperature data. The maximum values of NDVI and Kcb in corn and soybean fields peaked in May and later regressed after senescence in June. Eucalyptus field showed the lowest values of NDVI and Kcb in September. The pasture area remained with vegetation cover throughout the whole period, so there isn´t a marked reduction in NDVI and Kcb values. For all crops, Kcb values was close to those values reported by the FAO Manual 56. The highest light use efficiency and NPP for pasture and eucalyptus were found at the end of the rainy season (May 19), and lower values in September, comprising the dry season. Soybean in no-tillage system showed a higher biomass production (211 kg ha-1 day-1) compared to conventional system (200 kg ha-1 day-1), although both crops have almost the same values from light use efficiency. The corn crops showed the biggest light use efficiency, 3.83 g. MJ-1 and consequently bigger biomass production, 322.74 kg ha-1 day-1. The estimated values of productivity for corn, soybeans in conventional system and soybeans in no-tillage system were 3133 kg ha-1, 1303.57 kg ha-1 and 1.714 kg ha-1 respectively, with good agreement for soybean crop, compared to the real field productivity. Remote sensing allows to monitor productivity and water use of crops with good accuracy.