Application of FAO-CROPWAT software for modelling irrigation schedule of rice in Rwanda

The overall objectives of the present research are the study of weather, soil, discharges in the irrigation channels crop water requirement and irrigation scheduling of rice in Muvumba-8 marshland of Nyagatare district in Rwanda. The specific objective is to study the crop water requirement and irrigation scheduling of rice in the marshland. The average infiltration rate of the soil in the experimental field was 12.8 mm/hour. The average discharge in the primary channel is 7.94 m3/sec. The average reference crop evapotranspiration for the site was 3.89 mm/day. It varies from 3.51 to 4.38 mm/day. The maximum reference crop evapotranspiration was recorded in August and the minimum was May. The difference between maximum and minimum of reference crop evapotranspiration was observed to be 0.87 mm/day. CROPWAT derived the maximum effective rainfall of 80.3 mm in the month of October and the minimum of 20.9 mm during July. The total irrigation water requirement for rice crop for the season from Sept. to March was 412.7 mm. This low water requirement for rice is mainly due to higher effective rain fall in the experimental site from Sept to Dec. It was also inferred that the higher irrigation is needed from Dec to Feb because effective rainfall is lesser during that period. The moisture depletion pattern during the irrigation schedule varies from 59 to 71% with an average depletion of 64.8%. The net irrigation supplied to the field varies from 11.3 to 14.7 mm with an average net irrigation requirement 13.2 mm. The gross irrigation water requirement was varying from 16.2 to 21 mm with an average gross irrigation requirement of 18.96 mm. The average flow rate of water to the field was worked out to be 0.6 liter/sec/ha and it varies from 0.33 to 0.78 0.6 liter/sec/ha. The total gross irrigation was 906.9 mm and the total net irrigation was 634.8 mm.Keywords: CROPWAT, rice field, water requirement, irrigation schedul