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

72 M. Génard and F. Lescourret
few seeds were removed. However, the difference was negligible, and the overall
yield was slightly better when lateral flowers were not thinned (36 vs. 34.4
tonnes/ha).
Two simulated tactics of irrigation were analysed. In the first one, a fixed amount
of water (30 mm) was supplied each time the accumulated plant water demand
exceeded 30 mm (a) resulting in no water-stressed vine. In the second one, irrigation
was triggered each time the accumulated plant water demand exceeded
30 mm and only 65% of the water demand accumulated since the last irrigation
was supplied (b) resulting in water stressed vines. In (b), total irrigation water
amounted to 427 mm versus 570 in (a), and water demand was frequently unsatisfied.
Comparing the effects of irrigation tactics (a) and (b) yielded significant
differences, with the distribution of fruit sizes left-shifted for (b) (Figure 11f). In
this case, the mean fruit size was 90 g vs. 98 g with no water-stress, and the
corresponding yield was 15.7 tonnes/ha versus 17.2 tonnes/ha.
5.2.5.2. Use of SIMTECK to evaluate management decisions
This section intends to illustrate how the model can be used to address issues
about technical operations and crop performance. For example, it could be useful
to evaluate how operations such as pruning and thinning can be managed to make
the crop performance of two plots characterised by different planting schemes as
close as possible. Using SIMTECK, several technical situations were simulated.
Yields and yield values were calculated, the latter was based on a series of prices
for year 1997.
In case A, the planting ratio was 1:5. This situation was highly favourable to
pollination. It was decided to keep as many fruits as possible on vines, anticipating
that the reducing effect of vine crop load on fruit growth would be largely
compensated by the large number of seeds that is a major factor of fruit size. Thus,
pruning was rather light (60% of replacement canes were kept) as was thinning (only
aberrant shaped flower buds were removed). Total yield was 24.6 tonnes/ha and both
the percentage and the number of fruits were high in the best grades (Table 2).
The yield value was 4900 /ha.
In case B, the planting ratio was 1:10, which is unfavourable to pollination.
Situation B1 consisted in trying to compensate the effect of the anticipated poor
pollination on fruit growth by reducing as much as possible the vine crop load.
Table 2. Distribution of fruit numbers (percentages by rows in brackets) among size grades for three
simulated technical situations.
< 70 g 70–90 > 90
A 01086 (1) 09382 (10) 88288 (89)
B1 04018 (6) 14315 (21) 49192 (73)
B2 10977 (9) 48200 (38) 67000 (53)
70 and 90 g are the EEC thresholds for ‘First’ and ‘Extra’ grades. The planting ratio was 1:5 for A
and 1:10 for B; the ratio of replacement canes kept at pruning was 60%, 40%, and 70% for A, B1,
and B2, respectively; thinning concerned the aberrant shaped flower buds for A and B2, as well as
the lateral buds for B1.