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A long-term crop rotation experiment was established in Central Lithuania (Skėmiai, Radviliškis region) in 1971 (lysimeters were installed in 1976) on a sandy loamy Endocalcari-Endohypogleyic Cambisol (CMg-n-w-can). The effect of regular fertilisation with different rates and combinations of NPK fertilisers in a crop rotation (winter wheat → sugar beet → spring barley → spring rape → annual grasses and perennial grasses) on the concentrations of cations (Ca , respectively. Low levels of potassium leaching had little effect on potassium balance in the soil. Sodium leaching level did not exceed 7.67 kg ha -1 Na + in winter and 3.39 kg ha -1 Na + in summer. Application of mineral fertilisers resulted in sodium leaching increase by 5.77 kg ha -1 Na + on an average; potassium fertilisation encouraged the process of sodium leaching. As a result of intensive fertilisation the concentrations of calcium and magnesium ions in lysimeter water sampled at 80 cm depth were slightly higher than in the lysimeter water at 40 cm depth, the concentration of potassium ions -lower, and the concentration of sodium ions -about the same.

The aim of this work was to investigate the interdependence of mineral nitrogen (N min ) content in 0-60 and 0-90 cm soil layers and in 0-30 cm soil layer in order to see whether it would be possible to predict the N min content in the deeper soil layers based on the N min content determined in 0-30 cm soil layer and thus to get a possibility to skip the soil sampling from the deeper layers of soil. Higher levels of N min were found in the soils of heavier texture as well as in the soils of plots treated once with N min fertiliser at the rates not lower than 90 kg ha -1 . significant correlations were determined between the N min content in 0-60 or 0-90 cm soil layers and in 0-30 cm soil layer: in spring r 2 = 0.837, P < 0.01 and r 2 = 0.687, P < 0.01, respectively, in autumn r 2 = 0.833, P < 0.01 and r 2 = 0.723, P < 0.01, respectively. The ratios of N min content (as dependent on the N min content in 0-30 cm soil layer) in the 0-60 and 0-90 cm soil layers were calculated; when the content of N min in 0-30 cm soil layer increased from 6 to 12 mg kg -1 , the 0-60 and 0-30 cm soil layer N min content ratio decreased from 0.85 ± 0.25 to 0.75 ± 0.13 in spring and from 0.87 ± 0.21 to 0.82 ± 0.17 in autumn. These ratios or regression equations can be used for the calculation of N min content in the deeper soil layers based on the available data on the N min content in 0-30 cm soil layer. Strong correlations were determined between the nitrate N and N min contents in 0-60 and 0-90 cm soil layers in spring and in autumn; the corresponding ratios were calculated. The content of nitrates in soil increases as the N min level in soil rises.

The monitoring of mineral nitrogen (N min ) concentration in Lithuanian soils was conducted during the period 2005-2014 in 206 test sites of 20 × 20 m size located in 15 different soil regions considering the appropriate geographical units. The soil regions are distinguished from one another by relief, soil type, soil texture, climatic conditions as well as the specialisation and intensity of agricultural activities. It was found that soil N min concentration in spring differed not only between years, but also between the geographic climatic zones of Lithuania. The most important factors and their interactions affecting the soil N min concentration in spring were crops and pre-crops, soil texture, winter air temperatures and precipitation levels. The lowest N min concentration in 0-60 cm soil layer in spring was recorded in perennial grass fields and pastures, in fields where pre-crops were spring cereals and spring rape, in sandy loam and particularly sand soils, when precipitation levels during the November-March period were high and especially when this level exceeded 250 mm, when predominant winter air temperature was above 0°C. The soil N min concentration tests taking into account the territorial division of Lithuania into 15 soil regions enabled us to assess the long-term fluctuation of this indicator as affected by the local conditions. The accumulated and processed multiannual data can be used as a reference for the assessment of the results of the future tests.