<![CDATA[Land use changing in Way Ketibung Irrigation Area from rice field cropping to rubber and palm oil planting were one of causes to decline rice field production at its irrigation area. The changing of land use were caused by lack of water availability . Therefore, it is necessary efforts to optimize irrigation area in order to increase rice production. Based on cropping schedule which used by Way Ketibung Irrigation Area the farmer had define cropping season, rainy cropping season (rendeng, MT I) and dry cropping season (gadu, MT II). The 1 st class of rainy cropping season was started on 1 st week of September and on 1 st week of Jan- uary to the 1 st class of dry cropping season. Whereas, the 2 nd class of rainy season began on 2 nd week of September and on 2 nd week of January to the 2 nd class of dry season. Cropping pattern which based on its cropping schedule that the farmers have done was not suitable, because only a few one could apply the schedule to crop rice field. It is due to the water availability could not serve the amount of water to its cropping pattern. Field observation and hydrologic analysis using suitable approach methods produced the opti- mized cropping pattern that approximated by reliable discharge has 80 % probability in occurs (Q 80 ) and Net Farm Requirement (NFR). The optimized cropping pattern of Way Ketibung Irriga- tion Area defines the cropping season. The 1 st class of rainy cropping season begins on 2 nd Decem- ber and 2 nd April to 1 st class of dry cropping season. Whereas, The 2 nd class of rainy cropping sea- son begins on 1 st January and 1 st May to 2 st class of dry cropping season. Water balance analysis describe surplus and deficit of water, therefore could be generated cropping pattern rotation as; The rainy cropping season (MT I) : 1 st class begin on 2 nd week of December with 821 hectares (100 %), 2 nd class begin on 1 st week of January with 612 hectares (100 %). The dry cropping season (MT II) : 1 st class begin on 2 nd week of April with 50 % of 821 hectares, 2 nd class begin on 1 st week of May with 50 % of 612 hectares.]]>
