European Journal of Agronomy 13 2000 155 – 163
Measurement and modeling of evapotranspiration of olive Olea europaea L. orchards
F.J. Villalobos
a,b,
, F. Orgaz
a
, L. Testi
a
, E. Fereres
a,b
a
Instituto de Agricultura Sostenible, CSIC, Apartado
4084
,
14080
Cordoba, Spain
b
Dep. Agronomı´a, Uni6ersidad Co´rdoba, Apartado
3048
,
14080
Cordoba, Spain Received 19 February 1999; received in revised form 6 July 1999; accepted 4 February 2000
Abstract
Efficient irrigation management requires a good quantification of evapotranspiration. In the case of olive orchards, which are the dominant crop in vast areas of southern Europe, very little information exists on evaporation.
Measurements of aerodynamic conductance and evaporation above and below an olive orchard allowed the calibration of a transpiration model of olive trees based on the Penman – Monteith equation. The model was
combined with Ritchie’s soil evaporation model and tested against an independent data set, indicating its validity unless a substantial fraction of the soil surface is wetted by irrigation emitters, which is not taken into account by the
model and deserves further research. Simulated crop coefficients of olive orchards in southern Spain changed during the year in response to changes in vapor pressure deficit VPD and evaporation from the soil surface. The average
annual crop coefficient 0.62 was rather low due to the low ground cover and to the enhanced control of canopy conductance by stomatal responses to VPD. According to our results the crop coefficient will vary among locations
and even among years, depending on rainfall and temperature. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Evaporation; Evapotranspiration; Olive; Olea europaea L.; Eddy covariance www.elsevier.comlocateeja
1. Introduction
Olive orchards are the main component of agri- cultural systems in many semiarid regions around
the Mediterranean, with more than 2 million ha in Spain and around 5 Mha in the whole European
Union Civantos, 1997. Most olive orchards are rainfed, with yields limited mainly by water sup-
ply. Traditional olive orchards in Spain have typi- cally around 100 trees per ha with ground cover
rarely exceeding 25. Modern orchards are usu- ally drip-irrigated, with 200 – 300 trees per ha and
ground cover of 40 – 50. Drip irrigation has also extended to numerous traditional orchards using
groundwater of poor quality and uncertain supply.
Good irrigation management requires an accu- rate quantification of olive evapotranspiration.
The most common approach to calculate evapo- transpiration ET has been as the product of
Corresponding author. Tel.: + 34-957-499234; fax: + 34- 957-499252.
E-mail address
:
aglvimafuco.es F.J. Villalobos. 1161-030100 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 1 1 6 1 - 0 3 0 1 0 0 0 0 0 7 1 - X
reference grass ET ET
o
by the crop coefficient K
c
= crop ETgrass ET, which depends on ground
cover and crop characteristics FAO method, Doorenbos and Pruitt, 1977; Allen et al., 1998. In
the case of olive the information on K
c
is scarce and obtained mainly from ET measurements us-
ing the soil water balance e.g. Mickelakis et al., 1994. Orgaz and Fereres 1997 reported crop
coefficients from 0.45 to 0.75 in different locations which are far below the values of annual crops,
typically from 1.0 to 1.2 Doorenbos and Pruitt, 1977. The variability of K
c
measured at different locations makes it difficult to apply the FAO
method to locations where no experimental infor- mation exists. An alternative approach to deter-
mine olive ET is to calculate its two components, transpiration E
p
and evaporation from the soil surface E
s
, independently, with an E
p
model based on the equation of Penman – Monteith
Monteith, 1965 and an E
s
model like the one proposed by Ritchie 1972. The E
p
model re- quires a parameterization of canopy conductance
G
c
as a function of environmental variables e.g. Stewart, 1988 which has to be based on accurate
measurements of evaporation at short time steps e.g. Dolman et al., 1988.
The objectives of this work were a to develop a joint E
s
– E
p
model to determine evapotranspira- tion of intensive irrigated olive orchards, and b
to analyze temporal variations in the crop coeffi- cient.
2. Materials and methods
