HETEROGENEITY IN A GLASSHOUSE TOMATO CROP AND ITS EFFECT ON CROP MANAGEMENT .1. EFFECT OF HETEROGENEITY ON YIELD

Experiments were set up to characterise the heterogeneity of individual vegetative states within a greenhouse soilless tomato crop, and to study its effects on yield. The heterogeneity of the planting date, for individuals sown at the same date, enabled us to create 2 types of plants. The 'weak' and the 'vigorous' types differ in the development rate, the weight of vegetative part, and the diameter of stem. Thus, their yield is different (number of fruit and mean fruit weight). The differences between the types persist throughout the crop cycle. In a heterogeneous population (ie vigorous and weak types mixed), the vegetative growth of weak plants is much smaller than that of the same plants in a homogeneous population. On the contrary, vigorous plants have a larger growth than in a homogeneous population. These results show a strong interplant competition. Within the range of studied cases, heterogeneity has no effect on yield per area because of the compensating phenomenon between vigorous and weak types. On the contrary, heterogeneity reduces the quality of the production, because the fruit grade distribution is more scattered than in a homogeneous population.