EFFECT OF MINERAL NITROGEN CONCENTRATION IN SOIL AND IRRIGATION ON NO₃ CONTENT IN POTATO TUBERS

Soil mineral nitrogen affects NO₃ content in addition to potato yields. The objective of the present study was to investigate the effect that mineral nitrogen from organic and mineral fertilizers has on potato yield and tuber NO₃ content (mg.kg^-1) with and without irrigation.

For this purpose, an experiment was established on a calcareous chernozem using the split-plot design. The main plot involved two separate trials: 1. Control trial (no irrigation), and 2. Trial in irrigation conditions (the lower limit of optimum soil moisture was 70% of the FWC). Each trial included eight different fertilization treatments: Control (no fertilization), N₈₀, N₁₂₀, N₁₆₀, N₂₀₀, 40 t.ha^-1 of barnyard manure, 40 t.ha^-1 of barnyard manure+N₈₀, and 40 t.ha^-1 of barnyard manure+N₁₂₀. Each of the treatments included P₂O₅ and K₂O, 80 kg.ha^-1 of each.

In the no-irrigation control treatment, the average mineral nitrogen content in the 0–120 cm layer before fertilization was 103.23 kg.ha^-1, while in the no-fertilization control it was 79.39 kg.ha^-1.

Under irrigation conditions, the average mineral nitrogen content in the 0–120 cm layer was 114.43 kg.ha^-1. In the control treatment (no fertilization), the mineral nitrogen content was 138.93 kg.ha^-1.

After fertilization, soil mineral nitrogen increased linearly and the correlation coefficients were highly significant.

Tuber NO₃ content depended on the amount and, even more importantly, distribution of mineral nitrogen through the soil layers. This was particularly evident under conditions of insufficient water supply (trial without irrigation), especially in the medium late variety Desirée.