Top-dressing nitrogen management decision in potato using the UFV-80 color chart and SPAD readings

The chlorophyll meter (SPAD‐502) and “UFV-80” color chart can be used to diagnose the nitrogen (N) nutritional status of potato plants to determine the need for fertilizer‐N topdressing. The present investigation was focused on how chlorophyll meter and “UFV-80” color chart help in determining optimal N management through real time N application for improving yield and profitable rate in potato crop. The experiments, in two planting seasons (dry and wet), were carried out a split-plot design in a randomized complete blocks with four repetitions. In the whole plot, five N fertilization rates (0, 50, 100, 200 and 300 kg ha-1 of N) were applied before planting. In the half of plot area, N fertilization rates (42, 152, 152, 152 and 152 kg ha-1 of N at dry season and 133, 93, 69, 58 and 205 kg ha-1 of N in wet season) were or did not applied in top-dressing, depending on the UFV-80 color chart reading and SPAD chlorophyll meter reading in the terminal leaflet of the fourth leaf, at 21 day after the plant emergency (DAE). At 77 and 70 DAE for the dry and wet seasons, respectively, the plants were harvested to determine the commercial tuber yield. The SPAD chlorophyll meter reading and “UFV-80” color chart can be used to determine N nutritional status in potato crops in both planting seasons. Both planting seasons, the commercial production was not influenced by the N fertilization rates in pre-planting and top-dressing.   Key words: Solanum tuberosum L. fertilization, diagnosis, profitable rate.