DISAGREEMENT BETWEEN TREE SIZE AND CROP COEFFICIENT IN ‘CONFERENCE’ PEAR: COMPARING MEASUREMENTS BY A WEIGHING LYSIMETER AND PREDICTION BY CROPSYST

Accurate prediction of a crop coefficient (Kc) is necessary for proper irrigation management.
We explored the use of a computer-based model, CropSyst, for determining irrigation requirements of ‘Conference’ pear trees and we assessed the accuracy of Kc predictions.
Values of Kc were compared to those obtained, over 2002-2010, from lysimeter-grown trees.
Lysimeter data over the years indicated weak Kc response to the increase of tree size with age.
CropSyst predicted irrigation require¬ments using tree light interception and water uptake sub-model components.
The most important parameters in CropSyst to determine Kc are: full canopy Kc (Kc,fc), and canopy porosity.
Parameters of the model were adjusted using data obtained from the lysimeter in 2010. Using the parameterization of 2010, we found poor agreement between simulated and measured Kc over different seasons (2002-2009). The main reason for poor agreement was attributed to yearly changes in the Kc,fc parameter.
When Kc,fc was yearly adjusted so that differences between observed and simulated Kc were minimized, it was observed that Kc,fc decreased with tree age.
Therefore the lack of agreement between tree size and Kc was attributed to a decreased capacity for consuming water with tree age.
In conclusion, irrigation scheduling methods to be applied to ‘Conference’ pear orchards shouldn’t only rely on canopy light inter¬ception.

VII International Symposium on Irrigation of Horticultural Crops

J. Marsal, J. Casadesus, G. Lopez , J. Girona, C.O. Stöckle

simulation models, transpiration, leaf area, ground cover

https://doi.org/10.17660/ActaHortic.2014.1038.36