Geospatial technologies for assessing seasonal variability in crop coefficient for efficient irrigation scheduling in cashew

Abstract

In India, cashew is generally grown as rainfed crop mainly along the coast in low fertile soil. The productivity levels of cashew are low in India compared to other producer countries. Water limitation during critical periods of growth stages is one of the major constraints in realizing higher productivity in cashew. The common approach for irrigation scheduling is by estimating evapo – transportation demand by estimating reference evapo-transpiration and crop coefficients. Crop coefficients can be highly variable depending on the condition of canopy. Reliable estimation of crop coefficient and scheduling of irrigation is possible by combining the weather information and biophysical parameters derived from vegetation indices obtainable from remote sensing imageries in GIS. The present study was carried out for estimating the crop coefficient and crop evapotranspiration for a cashew plantation of 10 year. The study was performed in the cashew plantations of Karnataka Cashew Development Corporation near Savanoor, Puttur, Dakshina Kannada, Karnataka. The region experiences tropical monsoon climate with dry season from January to May. The multispectral images used for this study was Landsat 8 satellite for the months of December 2016, January to May 2017. Satellite imageries were processed in ERDAS Imagine 9.2. Digital Elevation Model by Cartosat was used in GIS and by performing hydrological modeling a watershed of interest in the study area was delineated. Subset image of each satellite imageries was prepared using watershed boundaries in Arc Map 10.2. The potential evapo-transpiration of the study area was worked out from the climatic data using FAO Penman-Monteith method. Vegetation index map prepared was used to derive crop coefficient for each months. Finally the crop evapo transpiration was computed by combining potential evapotranspiration with crop coefficient. The highest crop coefficient (0.42) was recorded for May 2017 with corresponding Etc of 3.69 mm. The lowest Kc values were recorded in April 2017 (0.24) along with the lowest Etc values (1.23 mm) among the six months of study. The study revealed the usefulness of geospatial technologies in irrigation management in cashew.