YIELD DEVELOPMENT IN POTATOES AS INFLUENCED BY CULTIVAR AND THE TIMING AND LEVEL OF NITROGEN-FERTILIZATION

Path-coefficient analysis based on an ontogenetic model was used to st udy the relationships between tuber yield and yield components as infl uenced by cultivar and nitrogen fertilization. Four experiments were c arried out from 1987 to 1989 in Granada, southern Spain. Two of these experiments used six potato cultivars with a single N rate, while the other two experiments used one cultivar and nine levels of N, split be tween planting and top-dressing. Variation in tuber yield between cult ivars resulted mainly from differences in stem number per m2 followed by tubers per stem and, to a lesser extent, average tuber weight. In N experiments, however, average tuber weight was the only yield compone nt that showed a significant direct effect on yield, while the number of stems per m2 and tubers per stem had negligible direct effects. In addition, the ontogenetic model used indicated compensatory mechanisms during the formation of the three yield components in the potato, whi ch resulted stronger in the N experiments.