Articles
CROP LOAD AS A MODIFYING FACTOR IN CROP EVAPOTRANSPIRATION MODEL FOR IRRIGATION SCHEDULING
Article number
618_44
Pages
379 – 382
Language
English
Abstract
Accurate irrigation scheduling is the most important factor to avoid drought stress of plants or water wasting in irrigated orchards.
Many irrigation scheduling models include an irrigation threshold based on the drought sensitivity or water demand of the orchards.
Using correct crop coefficient is critical for real estimation of plant water use in evapotranspiration models.
The aim of this study was to determine the real crop coefficient in an apple orchard Florina/M.26 in two consecutive (on and off) years.
The average foliage area was 5.6 m2/tree in 1998, and it was 15,0 m2/tree in 1999, while the crop load was 15.0 and 3.0 kg/tree, respectively.
Crop evapotranspiration was calculated by Penman-Monteith FAO equation using Kc=0.9, the proposed value for apple.
Using the crop evapotranspiration, it was possible to estimate the soil water depletion (DRi). It was clear, comparing these estimated DRi with measured soil water values, that the model overestimated the evapotranspiration.
To determine the right Kc value, the crop evapotranspiration was calculated using lower crop coefficient, and iterative calculation was proceeded to Kc=0.45 in 1998 and Kc=0.50 in 1999, when estimated and measured soil water values did not differ significantly.
Foliage area (or the leaf area index) is the most common factor considered as a water demand factor in irrigation scheduling models.
However, in commercial orchards (mainly in orchards established with alternate bearing varieties) crop load is one of the main factors modifying actual growth vigour of trees.
Fruits have a great influence on tree water balance by means of direct (increasing water demand) and indirect (decreasing vegetative growth) ways, so considering crop load is essential for proper irrigation scheduling in orchards.
Many irrigation scheduling models include an irrigation threshold based on the drought sensitivity or water demand of the orchards.
Using correct crop coefficient is critical for real estimation of plant water use in evapotranspiration models.
The aim of this study was to determine the real crop coefficient in an apple orchard Florina/M.26 in two consecutive (on and off) years.
The average foliage area was 5.6 m2/tree in 1998, and it was 15,0 m2/tree in 1999, while the crop load was 15.0 and 3.0 kg/tree, respectively.
Crop evapotranspiration was calculated by Penman-Monteith FAO equation using Kc=0.9, the proposed value for apple.
Using the crop evapotranspiration, it was possible to estimate the soil water depletion (DRi). It was clear, comparing these estimated DRi with measured soil water values, that the model overestimated the evapotranspiration.
To determine the right Kc value, the crop evapotranspiration was calculated using lower crop coefficient, and iterative calculation was proceeded to Kc=0.45 in 1998 and Kc=0.50 in 1999, when estimated and measured soil water values did not differ significantly.
Foliage area (or the leaf area index) is the most common factor considered as a water demand factor in irrigation scheduling models.
However, in commercial orchards (mainly in orchards established with alternate bearing varieties) crop load is one of the main factors modifying actual growth vigour of trees.
Fruits have a great influence on tree water balance by means of direct (increasing water demand) and indirect (decreasing vegetative growth) ways, so considering crop load is essential for proper irrigation scheduling in orchards.
Authors
T. Lakatos
Keywords
apple, crop coefficient, sap flow rate, soil water
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