Effect of nitrogen and phosphorus fertilization on growth components, yield and tuber quality characteristics of two potato cultivars grown under organic production system

The effect of two levels of nitrogen (Ν1=1.3 and N2=2.0 g Ν plant^‑1) and two levels of phosphorus (P1=3.1 and P2=5.2 g P₂O₅ plant^‑1) on the growth, yield and tuber quality of two potato cultivars (‘Voyager’, ‘Spunta’), grown during spring season at Kalamata, Greece was studied. Seed tubers were planted in 11-L pots containing a mixture 1:1 (v/v) of peat (pH=6, no additional inorganic nutrient elements) and perlite. In all plants the same amount of PatentKali (0-0-30 + 10% MgO + 42% SO₃) was applied (6.6 g K₂O and 1.3 g MgO plant^‑1). In order to meet the fertilization treatments, the organic fertilizers Biosol (7-0.5-0.3), Phosphorite (0-27-0) and Acadian 1-1-16 were used. In both cultivars, the higher N-dose increased the fresh weight of leaves, shoots, tubers, and shoot N-content. It also increased N-content of tubers when phosphorus was applied at the lower dose. In both cultivars, the higher P-dose increased the fresh weight of shoots, tubers N-content when nitrogen was applied at the lower dose. Phosphorus did not affect tuber yield in ‘Spunta’, but in ‘Voyager’, the higher P-dose increased tuber yield. In addition, the higher P-dose increased leaf N-content in ‘Voyager’ when nitrogen was applied at the lower dose. However, fertilization treatments did not affect dry matter content, P-content and K-content of leaves, shoots and tubers. We concluded that, in organic farming system, tuber yield is favoured by nitrogen fertilization in both ‘Spunta’ and ‘Voyager’ and by phosphorus fertilization in ‘Voyager’, however, tuber quality characteristics were not affected by nitrogen or phosphorus fertilization.