ESTIMATION OF CASSAVA WATER REQUIREMENTS BY USING GEOSPATIAL DATA IN CHON BURI, THAILAND

Abstract

Water is one of the most important factors in agriculture. Moreover, the plants have different water requirements depending on their species, climate, and soil condition. In this research, the estimation of the water requirement of cassava was from application of remote sensing by satellite image cassava cultivation areas in Bang Lamung District, Chon Buri Province, Thailand. To study the best correlation between vegetation indices obtained from Sentinel-2 satellite image and crop coefficients referenced by the Royal Irrigation Department (RID), with linear regression analysis. In addition, to calculate cassava evapotranspiration by the Penman-Monteith method. The vegetation indices are Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Soil-Adjusted Vegetation Index (SAVI), and Normalized Difference Red Edge index (NDRE) were evaluated in this study. The results showed that the vegetation index has correlated with the crop coefficient (Kc) of cassava as referenced by RID, divided into critical periods of crop water requirement for cassava according to the equation, the age range of 1-6 months (R2 = 0.82) is obtained from the equation Kc = -011 + (0.94*SAVI) and 7-12 months (R2 = 0.98) is obtained from the equation Kc = -3.21 + (-3.24*GNDVI) + (-3.16*NDVI) + (11.94*SAVI). The comparison of crop evapotranspiration estimated using Kc predicted from the vegetation index with ET calculated by using Kc referenced from the RID. Where crop evapotranspiration was calculated using crop coefficient from Kc predicted and was found to be 26.08 mm/day while the crop evapotranspiration value of cassava calculated using crop coefficient referenced by the Royal Irrigation Department was 25.81 mm./day. As a result, the estimated values were quite near to the real values with a Root Mean Square Error of 0.15 indicated that were of significant and reliable correlates.

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