ABSTRACT
A study was carried out to determine the water requirement of main crops in the perumal tank irrigation command area in Cuddalore district. The main crops include rice, groundnut, and sugarcane. The crop water requirements were determined using 15 year climatic data using CROPWAT 8.0. The seven crop growth stages (nursery,nursery/land preparation,land prepearation,initial,development,mid season,late season) and three decades (I,II,III) were considered for all crops. Crops were planted during 2012 kuruvai season and the crop coefficient was determined for each crop. Reference Crop Evapotranspiration (ETo) was determined using the FAO Penman Monteith method and the effective rainfall was calculated using USDA S.C. Method. The study shows that for the study area, reference evapotranspiration (ETo) varied from 3.67 to 6.42 mm/day and the effective rainfall varied from 12.8 to 166.8 mm. Crop evapotranspiration (ETo) and the crop water requirement for Rice varied from 0.74 mm/day to 6.23 mm/day and 0.0 mm/dec to 244 mm/dec, for groundnut 2.4 mm/day to 5.03 mm/day and 0.0 mm/dec to 29.2 mm/dec, for Rice (Navarai) 0.45 mm/day to 6.49 mm/day and 0.0 mm/dec to 152.5 mm/dec, for Groundnut (Navarai) 1.78 mm/day to 5.79 mm/day and 4.1 mm/dec to 54.8 mm/dec and for Sugarcane 2.07 mm/day to 6.57 mm/day and 0.0 mm/dec to 63.9 mm/dec respectively. The peak water requirement was 1.11 l/s/ha or 9.6 mm/day with an application efficiency of 70%.