Water balance and loss assessment of the Upper Pampanga River Integrated Irrigation System (UPRIIS) and Magat River Integrated Irrigation System (MARIIS) under the program smart farming-based nutrient and water management for rice and corn production

This study aimed to assess the conveyance and application losses in UPRIIS [Upper Pampanga River Integrated Irrigation System] and MARIIS [Magat River Integrated Irrigation System], validate crop coefficient (Kc) of commonly used varieties of rice and corn, and recommend measures to increase water use efficiency. Inflow-outflow method was used to determine farm ditch and application losses, respectively. Lysimeters were used to validate Kc of corn and rice. Results showed that conveyance losses from UPRIIS an MARIIS ranged from 0.175 to 1.65 m3/s while conveyance efficiency ranges from 41.3% to 81.0%, which are less than the values set by FAO for adequately maintained canals. Percolation losses range from 2-7 mm/day which were significantly different with paddy fields and soil types and generally higher than NIA design percolation losses for each soil type. The measured farm ditch losses range from 0.09 to 23.87 lps/km with considerable variations attributed to condition and maintenance of the ditches. Using measured losses and secondary data, the average storage, conveyance, and on-farm efficiencies of the UPRIIS were computed as 93%, 60%, and 76.8% (dry) and 36.4% (wet), respectively, making the overall system efficiency of UPRIIS at 32%, which is about the same as that of many systems based on FAO studies. Reduction losses in irrigation systems improve water use efficiency thereby increasing the irrigated area and crop production. Six indicators were used to further assess the performance of the two systems. For the five Divisions of UPRIIS, relative water supply (RWS) values (1.09 to 3.06 m3/ m3) indicate sufficient water supply with no water deficits. The values of irrigated area performance (F) (78.6% to 98.0%) were generally higher in dry season than in wet season. The high values of (gross irrigation water quota) M and RWS indicated that the supply of water is enough and there is no problem in water delivery. As such the yields were found to be higher than the national average of 4,430 kg/ha, using only 2.6 m3 (dry) and 2.4 m3 (wet) of water produce 1 kg of palay. For the four Divisions of MARIIS, computed RWS (0.41 to 0.82 m3/ m3) suggest that the amount of water supplied to the farm is less than the demand. High values of F (78.6% to 98.0%) despite low values of RWS indicted that large areas in MARIIS practiced deficit irrigation. High values of M (17, 001 to 30, 350 m3/ha) and low values of RWS indicated problems in the water delivery, which indicates high conveyance and water losses. And yet, the yield per unit area (Y) in MARIIS averaged 4,860 for dry and 4,484 kg/ha for wet season, with the yield per unit quantity of water (Yw) indicating that farmers used 4.4 m3 (dry) and 5.2 m3 (wet) of water to produce 1 kg of palay. The computed average Kc values for IPB Var13 corn variety were 0.43, 0.69, 0.92 and 0.70 during the initial, development, mid-season and late season stages, respectively. For PSB Rc18 rice variety, the computed Kc values during the initial, vegetative, reproductive, and late stages for rice were 1.02, 1.15, 1.14 and 0.78, respectively. The estimated Kc values are very close to FAO recommended values. The results of the isotopic technique to determine actual crop evapotranspiration and partitioning of evaporation and transpiration have not yet been completed by the PNRI.