Towards Accurate Estimation of Crop Water Requirement without the Crop Coefficient K_c: New Approach Using Modern Technologies

Abstract

Modern technologies to measure actual evapotranspiration, ET a , were implemented at an experimental farm near Bologna, Italy. Large-aperture scintillometer and eddy covariance instruments were installed. The results showed significant differences between actual evapotranspiration measured by eddy covariance and scintillometer when compared with the potential reference evapotranspiration, ET 0 , calculated from meteorological data using the Penman-Monteith equation and the crop potential evapotranspiration, ET c , which is based on the ET 0 and the crop coefficient, K c . The ET c and ET 0 showed higher values than those of ET a obtained by eddy covariance and scintillometer. On average the actual evapotranspiration measured by eddy covariance and scintillometer for the cropping seasons 2014 and 2015 represented 45 and 35% of the ET 0 or the ET c , respectively.The ET 0 , or the ET c , represent the atmospheric water demand while, fundamentally, the crop water requirement should be based on crop water demand better represented by the actual evapotranspiration. At present, the results indicate that the actual crop water requirement based on modern technologies could save at least 50% of irrigation water for this region. Another benefit is that these modern technologies do not need the crop coefficient K c , which for many irrigation practitioners is difficult to obtain. Copyright © 2017 John Wiley & Sons, Ltd.

Improving water saving, yield, and water productivity of bean under deficit drip irrigation: Field and modelling study using the SALTMED model*

“…The fact that irrigating with 80% ETc was close to the100% ETc confirms the findings of Ragab et al . (2017). These findings indicated that the actual crop water requirement based on actual evaporation is significantly less than the crop water requirement based on ETc calculated from the potential evapotranspiration equations, which is the case in this study.…”

Enabling policy environment for water, food and energy security

“…Results of Water4Crops project in Southern Europe, 10 showed significant reduction of actual crop water requirement differences when compared with the present practice. On average, obtaining a better understanding of the actual crop water requirement based on the modern technologies could save at least 50% of irrigation water for this region (Ragab et al, 2017a).…”

“…New technologies for estimating water needs at different times of the season and crop growth stages include scintillometers and eddy covariance to measure actual evaporation values that represent the real crop need for water. Results of the Water4-Crops project in southern Europe 8 showed that at least 50% of irrigation water could be saved by better quantification of actual crop water requirements using modern technologies (Ragab et al, 2017a). In the same project the cosmic ray soil moisture sensor (COSMOS), which uses non-invasive, non-destructive natural atmospheric cosmic rays, was shown to accurately sense soil moisture for an area of 300-700 m radius from 0 to 60 cm depth; this solves the problem of spatial variability and can be used to avoid harmful water stress under irrigation (Ragab et al, 2017b).…”

Development of Simple Software for Irrigation Scheduling of a Crop

“…In the recent past, new technological approaches are being considered for accurate estimation of actual crop evapotranspiration. For instance, [3] used large-aperture scintillometer and eddy covariance instruments and reported that the actual evapotranspiration thus obtained is lesser by 35% of the crop evapotranspiration obtained using Penman-Monteith method for an experimental farm at Italy. Their results corroborate the previous findings by researcher [4] who after studying many methods including FAO Penman-Monteith, Penman, Blaney -Criddle, Hargreaves etc reported that the estimated evapotranspiration by these methods are on the higher side when compared to those obtained using instruments like lysimeter.…”

“…Hence, there is a need to develop simpler software which can give irrigation scheduling details with lesser meteorological information without adversely affecting the accuracy. Of many methods available, in this study, the estimation of evapotranspiration is implemented in the developed software using Blaney Criddle method [2,3] as a default option primarily because it uses minimum number of meteorological parameters and is widely used by many engineers. The proposed software also incorporates the facility for forecasting the temperature during the crop growth period based on the historical mean temperature time series.…”