N-Nh4+ and N-NO3- uptake by potato in the tuber seed production

Abstract

The nitrogen is the structural constituent of proteins, several metabolites involved in the synthesis and transference of energy, and also of nucleic acids. It is absorbed by plants in the nitrate (NO3 –) or ammonium (NH ) form. The nitrate uptake varies with cultivar and light intensity. The objective of this research was to determine the preferential form of N (N-NH4+or N-NO) absorbed by the potato plants in seed tuber productions, using 15 3 –N isotope. The experiment was carried out in the greenhouse of Centro de Energia Nuclear na Agricultura (CENA) / USP, Brazil, using 2.3 l plastic pots, with expanded clays as substrate. The experimental design used was completely randomized with five treatments,  corresponding to the labeled NH(15 NH4 or 15NO) application time: 14, 28, 42, 56, and 70 days after transplanting (DAT), and three replicates. An IAC nutrient solution was used, modified to supply N, K and Ca, substituting calcium nitrate and potassium nitrate by ammonium nitrate labeled with 3 preferential forms of nitrogen absorption at the initial developing stage was the ammonium, changing to nitrate
after 56 DAT (tuber formation). The N utilization by the plants, however, was always higher with ammonium form applied in all stages, with the exception at 28 DAT and at the end of cycle.