The nitrogen fertiliser use of the world multiplied during the last decades. The improvement of the conversion rate of applied fertilisers could result in a significant economic advantage and a favourable environmental impact. For this reason, it is especially important to get to know the N demand of the produced varieties, as well as to explore the difference in genotypes concerning N use.

The analysis of the N conversion of the varieties and breeding lines of the Potato Research Centre of Keszthely has recently been launched under field circumstances. To continue this work and in order to analyse the components of N conversion more thoroughly, a greenhouse pot experiment was established with the Keszthely varieties White Lady, Katica, Hópehely and Chipke, as well as the S440 breeding line. The experiment was established in a sand culture medium with three replications and a randomized design. Crops were irrigated with a Hoagland nutrient solution modified to the different nitrate concentrations (7.50 mmol; 3.00 mmol; 0.75 mmol). Treatment was launched at three weeks of age and harvest took place 42 days after the first treatment. During the treatments, the chlorophyll content of leaves was measured and different morphological and yield parameters, as well as the N content of potatoes and the crops’ Harvest index were determined during harvesting.

The chlorophyll content of the examined varieties responded differently and with a different curve as a result of N treatments. The obtained results of the examined genotypes were significantly different in terms of the root-shoot ratio. The genotypes of S440, Katica and Hópehely showed the lowest root-shoot ratio in the 3.00 mmol treatment, while White Lady had the highest value in the same treatment. As regards Chipke, the root-shoot ratio proportionally decreased with decreasing nitrogen doses. As regards the tuber yield, S440 and White Lady responded similarly to N-deficient treatments by producing a higher number of lower weight tubers. The varieties Chipke and Katica showed a contrasting response by producing a lower number of tubers which were larger at the same time. No difference was found in the harvest indexes and the nitrogen content of the tubers, but the strength of responses was different in each genotype.

During the statistical evaluation of the results of analysis, it was concluded that there is a significant difference between the tested potato genotypes in terms of the examined parameters of N conversion ratio. These results can be used subsequently in the practice of potato production and they can contribute to fertilisation synchronized with production purposes and to the more economical and environmental friendly optimisation of fertiliser doses in accordance with production purposes.

Keywords: potato, Solanum tuberosum L., N treatment, chlorophyll content, N content of tubers, N conversion ratio