Abstract:
Local level calibration of crop coefficient (Kc) values is critical for regional level
planning and allocation of water resources for irrigation. Hence, a research was conducted at the
eastern block of instructional farm of Kelappaji College of Agricultural Engineering and
Technology, Tavanur, during the month of October - December, 2017 to estimate the crop
coefficient values of Okra for the humid tropical region. An improved crop variety - Varsha
Upahar was used for the study. A lysimeter water balance study was conducted in the field for
the determination of actual crop evapotranspiration (ETc). The reference crop evapotranspiration
(ETo) was computed from the weather data using the three empirical models which were found
most suitable for the humid tropical region of Tavanur in earlier studies and widely used in
Indian conditions. The three models were FAO-56 Penman Monteith (1991) model, FAO-24
Open pan(1977) model and Christiansen pan evaporation (1968) model.
Among the three models, Penman-Monteith model gave higher ETo values than the other
two models. However the other two models gave nearly same values. The seasonal cumulative
ETc of Okra was found as 224.56 mm from the lysimeter water balance study. Then, crop
coefficient values (Kc) were estimated as the ratio of actual crop evapotranspiration to reference
crop evapotranspiration for different growth stages. The Kc values of Okra obtained from
different ETo models for initial, mid-season and late season stages ranged from 0.43-0.75, 0.73-
1.30 and 0.51-0.77 respectively. The maximum Kc value was found during the mid-season stage
and the lowest was found during initial stage for all the three models. The Penman-Monteith
model gave relatively lower Kc value than the other two methods. But it was found that the Kc
value obtained from FAO-56 Penman-Monteith model (0.43, 0.73 and 0.51) showed quite good
agreement with the Kc values recommended by FAO (0.38, 0.74-0.98 and 0.49). Therefore, the
average crop coefficient values of Okra obtained in this study would be helpful for computing
the water requirement and irrigation scheduling of Okra in the humid tropical region.
