Articles
Determining orchard specific crop coefficients for improved irrigation management in citrus
Article number
1335_9
Pages
79 – 86
Language
English
Abstract
Crop coefficients are widely used for both irrigation planning and scheduling, largely due to the simplicity and accuracy of the approach.
However, for tree crops these crop coefficients are orchard dependent and there is a need to derive orchard specific crop coefficients.
The challenge is therefore to adjust crop coefficients for specific orchards and this often starts by partitioning evapotranspiration into transpiration (T) and evaporation and using a dual crop coefficient approach.
Measurements of transpiration conducted across multiple seasons, growing regions and tree size revealed that canopy size was a major determinant of transpiration, on both a daily and seasonal basis for Valencia orange orchards.
A number of descriptors of canopy size (volume, leaf area index (LAI) and fractional interception of photosynthetically active radiation intercepted by the canopy (fIPAR)) were regressed against transpiration crop coefficients (Kt) in order to find the best parameter for adjusting Kt values for specific orchards.
Simulated daily and average monthly fIPAR showed a strong positive correlation with Kt, with a satisfactory R2 of > 0.7. However, both LAI and canopy volume resulted in rather poor relationships with Kt values.
These results demonstrate that the amount of light intercepted by a citrus canopy is important in determining T under non-water limiting condition.
The strong correlation between fIPAR and Kt suggests that Kt could be predicted from measured fIPAR for different orchards in which T measurements are not available and of particular importance is the consistency of the relationship for all the orchards in which measurements were made.
This latter aspect was particularly important as it means that perhaps one relationship exists for citrus.
Therefore, Kt values for citrus can be estimated from the fIPAR of the canopy.
The one factor limiting the widespread use of this approach would be accurate estimates of fIPAR.
However, for tree crops these crop coefficients are orchard dependent and there is a need to derive orchard specific crop coefficients.
The challenge is therefore to adjust crop coefficients for specific orchards and this often starts by partitioning evapotranspiration into transpiration (T) and evaporation and using a dual crop coefficient approach.
Measurements of transpiration conducted across multiple seasons, growing regions and tree size revealed that canopy size was a major determinant of transpiration, on both a daily and seasonal basis for Valencia orange orchards.
A number of descriptors of canopy size (volume, leaf area index (LAI) and fractional interception of photosynthetically active radiation intercepted by the canopy (fIPAR)) were regressed against transpiration crop coefficients (Kt) in order to find the best parameter for adjusting Kt values for specific orchards.
Simulated daily and average monthly fIPAR showed a strong positive correlation with Kt, with a satisfactory R2 of > 0.7. However, both LAI and canopy volume resulted in rather poor relationships with Kt values.
These results demonstrate that the amount of light intercepted by a citrus canopy is important in determining T under non-water limiting condition.
The strong correlation between fIPAR and Kt suggests that Kt could be predicted from measured fIPAR for different orchards in which T measurements are not available and of particular importance is the consistency of the relationship for all the orchards in which measurements were made.
This latter aspect was particularly important as it means that perhaps one relationship exists for citrus.
Therefore, Kt values for citrus can be estimated from the fIPAR of the canopy.
The one factor limiting the widespread use of this approach would be accurate estimates of fIPAR.
Authors
N.J. Taylor, J.T. Vahrmeijer, N. Shongwe, J.G. Annandale
Keywords
fractional interception of photosynthetically active radiation, leaf area index, canopy volume
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