In the years 1987 to 1989 exact field trials have been established with the late commercial variety Kamyk in which the relation of the soil nitrogen content was studied as affected the nitrogen accumulation in the potato plant. The variants of fertilizing were selected in such a way that nitrogen rates were gradated within 0 to 160 kg of N per ha (variants 1 to 4). In other variants to the basic nitrogen rate (120 kg of pure nutrients of N per 1 hectare), phosphorus was higher (variant 5), potassium (variant 6), phosphorus and potassium (variant 7) and in the variant with the nitrogen level 160 kg of pure nutrients of N(+PK) per 1 hectare the inhibitor of nitrification N-serve (variant 8) was used. Soil and plant samples were taken in all variants at the onset of bud formation, at the onset of anthesis, for 21 days following the second sampling and during harvest. The plants were divided into aboveground part (tops), roots and tubers. Inorganic nitrogen content (total nitrate and ammonia nitrogen) was affected highly significantly by the year. The effect of variants was not manifested, solely in the first sampling in the variants with gradated nitrogen content it was gradually higher in dependence on the level of nitrogen fertilizer. Increased phosphorus rate had not unambiguous effects. Increased potassium rate, however, reduced on average the content of soil nitrogen in decisive stages of the growing season but during the harvest there was an opposite tendency. Neither the effect of nitrification inhibitor was unambiguous. It can be summed up that the content of inorganic nitrogen (and its forms as well) was fluctuating during the growing season and was not significantly influenced by the difference in rates of N(+PK) fertilizers. The relation between soil nitrogen and potassium content in the tops was unambiguously positive. However, the variant close to the boundary of significance was recorded only in the second sampling (F = 2.29) in highly significant influence of the year on the content of nitrogen in tops and mainly with respect to the results of limit variants (on average of the variant 7 - 3.55 % and variant 5 - 2.93 %). It is evident from the comparison of nitrogen content in roots and soil nitrogen content that in the first and second samplings the same dependence was recorded as with the former indicator. In the third sampling this relation was not yet significant. The effect of variants on nitrogen content in roots was always insignificant. The effect of the year acted-highly significantly, except for the third sampling (F = 2.35). Nitrogen content in tuber dry matter was not practically affected by gradated nitrogen rates. During the growing season the tendency of reducing the content of total nitrogen prevailed, while the highest intensity of reduction was found between the first and second samplings. In unambiguously highly significant effect of the year the variants were applied with the success solely in the second sampling. This was due to significantly lower level of variant 1 (1.0 %) compared to variants 4 and 8 (i.e. in variants where higher nitrogen rate was applied). A close correlation followed from comparison of inorganic nitrogen content in soil and from total nitrogen content in tubers for the first to third samplings, i.e. for a decisive part of the growing season.
