Assessment of Irrigation Scheduling in Pelwatte Seed Cane Plantation

Abstract

Sugarcane (Saccharum officinarum L) is mainly grown in the dry zone of Sri Lanka wherethe major soil group is well drained Reddish Brown Earth. Pelwatte Sugar Industries Limitedcultivates more than 4,000 hectare of sugarcane. Uneven and unpredictable rainfall in the dryzone makes it necessary of the irrigation. This research project was conducted to develop analternative system to overcome weaknesses of the existing irrigation system. Irrigationinterval, irrigation time and net irrigation depth was measured via a number of equations,which used in irrigation scheduling. Distribution uniformity was found by three can tests forexisting and suggested spacing and those tests were helpful to find irrigation rate. Othermiscellaneous practices are equal for both suggested and existing systems. Irrigation intervalof the existing system is around 10 to 14 days. Irrigation time is 3 hours. Irrigation rate of thesystem is 6.30 mm hr-1. Net irrigation depth is 18.7 mm; hence water requirement per hectareis 186.75 m3. Spacing used in existing sprinkler system is 18 m × 18 m and averagedistribution uniformity is 55.71%. Area covered in a day is 1.7 hectare. Fuel cost per hectareis Rs. 3,395.00. Suggested irrigation interval of the study was 14 days. Net irrigation depthwas 33.2 mm. Two spacing systems were suggested, 18 m × 12 m spacing system and 12 m ×12m system. Distribution uniformity and discharge rate increment of the two systems wasstatistically significant over existing system. Their values and corresponding p values are70.8%, 0.026 and 10.427 mm hr-1, 0.002 for 18 m × 12 m system and 83.5%, 0.007 and 16.6mm hr-1, 0.014 for 12 m × 12m system respectively. Irrigation time, area covered within aday, water requirement per hectare and fuel cost per hectare for 18 m × 12 m system areconsecutively 3 hours and 11 minutes, 1.2 hectare, 332.49 m3 and Rs. 6,034.00 and for 12 m× 12 m system are 2 hours, 1.1 hectare, 332.49 m3 and Rs. 5,060.00. It can be concluded thatboth suggested systems were improved distribution uniformity and irrigation ratesignificantly. Moreover, net irrigation depth of the new system was almost twice compared toexisting system, which explains the inadequate wetting of the existing system. 12 m × 12 msystem is superior over both 18 m × 12 m spacing and existing system.