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

68 M. Génard and F. Lescourret
5.2. SIMTECK: a SImulation Model for TEChnical operations in Kiwifruit
5.2. orchard management
Kiwifruit size is highly variable, especially within vines (Habib et al., 1991; Smith
et al., 1994). Accordingly, SIMTECK attempts to account for fruit size variability
by considering variation factors occurring at different levels of organisation (flower,
cohort of flowers, cane, vine, and plot). The model is made up of sub-models that
describe the flowering process in female (Agostini et al., 1999) and male vines,
pollination and fertilisation of flowers, and the growth of individual fruits (Lescourret
et al., 1998b, c). We will present these submodels, explain their relationships and
focus on the way technical operations are incorporated into the global model
(Lescourret et al., 1999). By incorporation, we mean the effect of technical decisions
on the biological processes. Apart from technical operations, inputs include
climatic series (temperature, rainfall, and potential evaporation rate). The output
is the size, for a chosen harvest date, of each fruit of an orchard. Time-step in the
model is one day. The general principles are presented below. More details can be
found in the papers quoted above.
5.2.1. Flowering model
Kiwifruit is a fruiting vine that only crops on new shoots originating from oneyear-old
stems called canes. The flowering model of female kiwifruit works at the
cane level, canes being independent units within the plant. It simulates the number
and time-distribution of flowers which bloom. The components of the number of
flowers are:
– the number of overwintered buds on the cane;
– the number of buds that have burst and will produce shoots. The maximal rates
of bud break depend on the location of the buds on the cane (basal, medium
and apical), and on their orientation (upwards, sideways or downwards pointing);
– the number of flowers remaining per shoot after abortion.
The time-distribution of flowers which bloom is modelled by a stochastic approach.
As the architecture is more complex in male vines than in female vines, the model
operates at the plant level. Another difference is that bud break triggering is based
on an estimated bud break rate, without any positional effect.
5.2.2. Pollination and fertilisation model
The fertilisation of individual kiwifruit flowers was described as the combination
of four random processes:
– a Poisson distributed deposition of pollen on the stigmas. The intensity of the
process is computed for each cohort (populations of flowers with the same day
of anthesis) in each vine. It is the sum of the pollen produced by all the pollen
sources of the orchard (male vines) and received by the targets (the stigmas of
the flower) during the effective pollination period. Pollen production, which is