Improvement in the efficiency of N application can be achieved by synchronizing the plant demand with N supply during the potato cycle. The objective of this study was to determine the optimum values of nitrogen indexes over the cycle of potato grown in a greenhouse, using different propagative materials such as seed tuber, minituber, and sprout tuber, common in the pre-basic seed tuber production. The indexes, determined in the fourth (FL) and the oldest (OL) leaf, were green color intensity, measured by chlorophyll meter and color chart, and agronomic characteristics as leaflet length, width, area and number. Three experiments were carried out in pots in a greenhouse at the University Federal of Viçosa. In each experiment, arranged in a randomized block design with four replications, there was evaluated six nitrogen rates (0, 25, 50, 100, 200 and 400 mg dm-3). The indexes were determined every 10 days, starting 20 days after plant emergence (DAE). With each propagating material, the SPAD index measured in both the FL and the OL responded differently to the increase in N and reached the optimal values of 41.3, 40.5, 37.0, 35.8, 36.0, 31.9 and 29.8 g.kg-1 from 20 to 80 DAE, respectively when seed tuber was used. In all the propagating material, plant age significantly affected all variables except number of stems or the number of leaves, when it is used sprout tuber or minitubers, respectively. Optimum values of variables over the potato cycle depended upon propagation material and time of evaluation.
Chlorophyll meter; color chart; critical level; diagnosis; propagation; Solanum tuberosum L
