Actual evapotranspiration and crop coefficients for tropical lowland rice (Oryza sativa L.) in eastern India

• Published in: Theoretical and applied climatology 2021-10, Vol.146 (1-2), p.155-171
• Main Authors: Chatterjee, Sumanta, Stoy, Paul C., Debnath, Manish, Nayak, Amaresh Kumar, Swain, Chinmaya Kumar, Tripathi, Rahul, Chatterjee, Dibyendu, Mahapatra, Smruthi Sagarika, Talib, Ammara, Pathak, Himanshu
• Format: Article
• Language: English
• Subjects: Agriculture; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Climate science; Climatology; Coefficients; Crop development; Crop growth; Crop water; Crops; Dry season; Earth and Environmental Science; Earth Sciences; Eddy covariance; Energy balance; Evaporation; Evapotranspiration; Evapotranspiration measurements; Growing season; Heat transport; Humid climates; Irrigation; Irrigation scheduling; Methods; Original Paper; Pan evaporation; Potential evapotranspiration; Rainy season; Regional planning; Rice; Seasons; Tropical climate; Tropical climates; Waste Water Technology; Water Management; Water Pollution Control; Water requirements; Wet season
• ISSN: 0177-798X; 1434-4483
• DOI: 10.1007/s00704-021-03710-0

Accurate measurements of actual evapotranspiration (ET a ) and crop coefficients (K c ) are essential to know crop water requirements and to improve irrigation scheduling. The eddy covariance (EC) technique is increasingly being used to do so. Precise information on K c for lowland rice is essential for local- and regional-scale irrigation planning but it is lacking for tropical humid climates such as those found in eastern India. We used the EC technique to measure ET a and K c —the ratio of ET a to reference potential evapotranspiration (ET 0 )—of tropical lowland rice in eastern India over 2 years. ET 0 was estimated by four different approaches—the Food and Agriculture Organization-Penman–Monteith (FAO-PM) method, the Hargreaves and Samani (HS) method, the Mahringer (MG) method, and pan evaporation (E pan ) measurements. Measurements were taken when rice was grown in the dry season (January–May) and wet season (July–November) and in between growing seasons when the field was kept fallow. The magnitude of average ET a during dry seasons (2.86 and 3.32 mm d −1 in 2015 and 2016, respectively) was higher than that of the wet seasons (2.3 and 2.2 mm d −1 ) in both the study years. Of the four methods tested for ET 0 estimation, the FAO-PM method best-represented ET 0 in this region of India. The energy balance was found to be more closed in the dry seasons (75–84%) and dry fallow periods (73–81%) as compared to the wet season (42–48%) and wet fallow (33–69%) periods of both years of study, suggesting that lateral heat transport was an important term in the energy balance. The estimated K c values for lowland rice in dry seasons by the FAO-PM method at the four crop growth stages, namely, initial, crop development, reproductive, and late-season, were 0.23, 0.42, 0.64, and 0.90, respectively, in 2015 and 0.32, 0.52, 0.76, and 0.88, respectively, in 2016. The FAO-PM, HS, and MG methods produced reliable estimates of K c values in the dry seasons, whereas E pan performed better in wet seasons. The actual K c values derived for tropical lowland rice in eastern India are different from those suggested by the FAO implying revision of K c values for regional-scale irrigation scheduling.