Production Practices and Quality Assessment of Food Crops. Vol. 1

64 M. Génard and F. Lescourret
tactical decisions about peach tree irrigation and based on an indicator of water stress
is first presented. A more complex model useful to study kiwifruit orchard management
in terms of strategic decisions is then presented and used to analyse the
effects of several combinations of technical operations on fruit size.
5.1. WASIF: a model using WAter Stress Indicator in Fruit management
A micromorphometric technique has been developed to measure the water status
of the plant and schedule irrigation (Li et al., 1989). This technique measures
trunk shrinkage (Plate 1) which is an indicator of the plant water status as it varies
similarly to the water content of the tree (Simonneau et al., 1993). This method helps
to determine the water needed to maintain growth of the tree, but do not help per
se to produce good size fruit. To overcome this difficulty, it can be chosen to use
trunk shrinkage and to connect this bio-indicator with a model of fruit growth.
Such an approach will be presented hereafter for peach. It can be extended to other
aspects of fruit quality such as sugar content (Génard and Huguet, 1999).
5.1.1. WASIF main principles
The aim of this model is to simulate the growth of individual peaches during the
expansion of flesh cells as a function of water availability. Water availability,
Plate 1. Trunk shrinkage is measured using a linear variable differential transformer (LVDT) mounted
on an INVAR frame.