Determinação do coeficiente de cultivo e da biomassa do algodoeiro irrigado por meio de imagens TM – Landsat 5.

Abstract

The determination of actual evapotranspiration – ETa of irrigated crops is extremely important in arid and semi-arid, since ETa has great influence in water resources management. The use of remote sensing techniques and satellite images have become powerful, efficient and economical tool for estimation of ETa and crop coefficient – Kc curves at the regional scale. Such techniques have also been used for determining the biomass of irrigated crops, characterizing their development and yield through of Monteith’s model, used for calculation of absorbed photosynthetic active radiation (APAR); the Carnegie Institution Stanford model, used for determining the light use efficiency, and the METRIC algorithm, used in determination of the energy balance. Therefore, the objectives of the present study were the estimation the daily and seasonal ETa, the Kc and biomass of cotton crop irrigated by center pivot system, varieties Delta Opal and Delta Penta. TM – Landsat 5 images, corresponding to different phenological stages of the crop and additional data collected by an automatic weather station installed on the Busato Farm (13 ° 15 'S, 43 ° 25' W, 436 m), were used in determining the energy balance components and reference ET according to Penman-Monteith-FAO, respectively. The results showed that the period of full development of culture, 13% of net radiation – Rn was used for heating the soil – G, 7% for heating the air – H and 80% of Rn was used as latent heat flux – LE. The maximum daily ETa in the same period was approximately 6 mm day-1 and an averaged seasonal ET of 850 mm, for an average cycle of 200 days. The Kc of cotton ranged from 0.39 to 1.12 among the phenological stages considered. In turn, the maximum biomass was over 200 kg ha-1 in the period of full development of culture and the validation showed an average error of 12% between the estimates and measurements. These results showed that the methods used in this research resulted in reliable estimates of ETa, curves of Kc and biomass, which are very important in irrigated projects and sustenable use of water.