Updated single and dual crop coefficients for tree and vine fruit crops

Abstract

The present study reviews the research on the FAO56 crop coefficients of fruit trees and vines performed over the past twenty years. The main objective was to update information and extend tabulated single (K c ) and basal (K cb ) standard crop coefficients. The selection and analysis of the literature for this review have been done to consider only studies that adhere to FAO56 method, computing the reference ET with the FAO Penman-Monteith ET o equation and field measuring crop ET with proved accuracy. The crops considered refer to vine fruit crops, berries and hops, temperate climate evergreen fruit trees, temperate climate deciduous fruit trees and, tropical and subtropical fruit crops. Papers satisfying the conditions expressed above, and that studied the crops under pristine or appropriate eustress conditions, were selected to provide for standard K c and K cb data. Preference was given to studies reporting on the fraction of ground cover (f c ), crop height (h), planting density, crop age and adopted training systems. The K c and K cb values obtained from the selected literature generally show coherence relative to the crop biophysical characteristics and reflect those characteristics, mainly f c , h and training systems. The ranges of reported K c and K cb values were grouped according to crop density, particularly f c and h, and were compared with FAO56 (Allen et al., 1998) previously tabulated K c and K cb values, as well as by Allen and Pereira (2009) and Jensen and Allen (2016), which lead to define update indicative standard K c and K cb values. These values are aimed for use in crop water requirement computations and modeling for irrigation planning and scheduling, thus also aimed at supporting improved water use and saving in orchards and vines.

Transpiration and Water Use of an Irrigated Traditional Olive Grove with Sap-Flow Observations and the FAO56 Dual Crop Coefficient Approach

“…The K cb non-growing and K cb ini values obtained in this study are comparable to those obtained by [5] in a super-intensive hedgerow olive orchard. Moreover, the calibrated K cb values are in the range of those reviewed by [14] and confirm the values proposed by [33]. The values of the depletion fraction p are equal to those proposed by [12] and similar to those previously adopted in other studies [5,17,18,23].…”

“…The time-averaged K c mid values varied little, from 0.54 to 0.56, for the three study years, resulting in similar values to those reported in [23]. The K c mid values are higher than the standard values proposed in [14], which may result from the high number of wetting events in the current study. The K c mid values are also larger than those proposed in [33] after using the A&P approach.…”

“…r l r typ (14) where r l and r typ are, respectively, the mean leaf resistance and the typical leaf resistance (s m −1 ) for the vegetation in question, ∆ is the slope of the saturation vapor pressure vs. air temperature curve, kPa • C −1 , and γ is the psychrometric constant, kPa • C −1 , both relative to the period when K cb full is computed. The original version of that equation was established with a fixed r typ = 100 s m −1 , a common value for annual crops, but default F r values were recently reviewed for trees and vines and several annual crops [33].…”

“…Thus, ET c is split into crop transpiration (T c = K cb ET o ) and soil evaporation (E s = K e ET o ). The standard tabulated K c and K cb values for trees and vines were recently reviewed and updated [14].…”

“…For sparse vegetation systems, the dual crop coefficient approach has to be considered more accurate than the single K c because it allows for the separate estimation of T c and E s , thus accounting for the effects of wetting events and soil management practices on the different terms of the water balance [5]. A wide review on crop coefficients for trees and vines [14] has shown that the variability in K c values is large and much greater than the variability in K cb values, particularly by the end season, as well as in the initial and the late seasons, which results from rainfall events occurring during these periods. Aiming at ET partitioning [16], studies have been carried out based on soil evaporation, measured in mi-crolysimeters; actual crop transpiration, determined with sap flow sensors [5,17,18]; and/or actual crop evapotranspiration, obtained using eddy covariance techniques [4,19,20], as reviewed by Pereira et al [21].…”