A vegetation pot experiment was established to explore the effect of two doses of nitrogen (0.6 and 0.9 gN in the form of ammonium sulphate) and two doses of sulphur (20.6 and 30.6 mg/kg of soil) on the yields and quality of spinach and pepper in comparison with a natural level (7.85 mg/kg). The results of the experiments confirmed that the application of sulphur by means of (NH₄)₂SO₄ in combination with nitrogen had a positive effect on yields and also on the quality of the vegetables. In the sulphur-free variants of spinach the effect was statistically significant and also when the levels of S in the soil were higher. Lower doses of nitrogen under increased levels of sulphur increased the yields statistically significantly (on average by 47%) and the sulphur concentration in the plants increased. The N:S ratio became narrower in proportion with the level of sulphur, particularly under a lower N level. The nitrate content in spinach corresponded with the applied dose of nitrogen and the nitrogen concentration. The sulphur level did not influence the content of C vitamin, but had a positive effect on the content of the essential amino acids cysteine and methionine. A mean level of S₁ in combination with a N₁ dose significantly increased pepper yields, narrowed the N:S ratio and was reflected in dry matter production per 1 g of N. The highest pepper yields were achieved with a dose of S₁, which resulted in the highest dry matter production in the fruit per1 g of N under both levels of N. At the same time increasing the sulphur level reduced the content of nitrate and increased the level of cysteine from 0.11 to 0.305 g/kg.

 In 1999, the effect of increasing levels of nitrogen at the initial (13.9 mg.kg^–1) and increased (40 mg.kg^–1) level of watersoluble sulphur (S_wat) was studied in winter rape (cv. Lirajet) grown in pots. A synergetic effect of nitrogen on concentrations of Ca and Mg was demonstrated in the growth stages DC 20–29 and 31–39. Levels of P and K were balanced. In variants with a low content of S_watin soil to 40 mg.kg^–1of soil S concentration increased. With the increasing dose of N the content of S decreased from 1.00% to 0.78% and from 0.68% to 0.38% in DC 20–29 and DC 31–39, respectively. An increased level of S in soil changed the ratio N/S. In variants with a natural (i.e. low) content of S in soil, this ratio widened with the increasing dose of N from 8.06 to 25.15 while in variants with an increased level of S in soil it ranged from 3.24 to 5.85 in the growth stage DC 20–29. Increasing doses of N widened the ratio N/P regardless to concentration of S in plants. In individual growth stages the ratio P/S was markedly narrowed by changing contents of S in soil. The highest yields were obtained in the variant with an optimum concentration of all elements in plants and S contents above 0.6% and/or about 0.4% in growth stages DC 20–29 and DC 31–39, respectively. The obtained yields demonstrated a highly significant effect of N and S on seed yields. At a low concentration of sulphur in plants the yield of seed increased only to the dose N₃(i.e. 0.9 g N per pot); thereafter, it gradually decreased. An increased level of S in soil showed a positive effect on seed yields. Higher doses of N widened the ratio straw/seeds from 2.46 to 7.69; at higher levels of S in soil, an opposite trend was observed. In variants with a low content of S the number of branches and pods increased proportionally with increasing doses of N. On the other hand, increased levels of S reduced the number of branches and pods. At a low level of S in soil the total weight of seeds per pod decreased with the increased supply of N from 69.9 mg to 20.4 mg. At increased levels of S the weight of seeds per pod increased from 61.9 mg to 79.8 mg. Results of field experiments in four different localities corroborated a positive effect of S (in interaction with N) on its concentration in plants. The seed yield was significantly increased. In 2000, results from all localities were markedly influenced by climatic conditions; however average results of all experiments showed that S increased seed yields depending on the dose of N by 2.5 and 5.9%. An optimum nutrition of plants with all elements (including S) results in improved utilisation and increased yields.

The efficiency of partial doses of nitrogen applied to poppy (Papaver somniferum L.) plants, cv. Opál, was followed in a pot experiment. The ammonium nitrate was applied either in a single dose at the beginning of growing season or in two split doses with the second application at the stage of flowering. With the increasing dose of nitrogen the number of capsules per a plant during the harvest and their volume increased irregularly. The separated application of an optimum dose of N (i.e.0.9 g N/pot) showed a statistically highly significant positive effect on the yield of poppy seeds compared to the same single dose of N made this figure increased by 25.6%. The morphine content in the capsules increased with the increasing supply of N from 0.85 to 1.01%. The term of nitrogen application influenced the number of capsules per a plant and their volume and morphine content irregularly.

Selenium is a trace element which in small amounts is necessary for human and animal nutrition. In a living organism, it helps a number of antioxidant enzymes to function normally. In many parts of the world, including the Central European region, its content in agricultural products is very low. Attempts are therefore made to increase its content and cover human requirements with biologically valuable products by incorporating selenium into the system of plant nutrition. In a vegetation trial established in 2008 and 2009, we explored the effect of foliar applications of Se(IV) on yields and on its content in seeds and the uptake of selenium by a poppy (Papaver somniferum L.) stand. Selenium was applied at a rate of 300 g ha-1 during the stage of the end of elongation growth and after the fall of blossoms. Poppy yields were significantly influenced by the weather in the experimental years. In the dry year of 2009, poppy production was 40.6% lower than in 2008. Selenium application at the end of elongation growth reduced poppy seed yields by an average of 11.5%. Late supplementary nutrition at the stage after blossom fall also reduced yields (by 11.8%). Owing to the effect of extra-root Se nutrition, the content of selenium in poppy seeds increased highly significantly from 139 µg kg-1 to 757 µg kg-1 of seeds. Also the uptake of selenium by the poppy stand was significant and after foliar application it increased 4.8 times.

In the years [2001][2002][2003] in field trials we studied the effects of the conditions of year, fore-crops (winter wheat, sugarbeet, grain maize) and optimalization of the nutritional status on the yield and crude protein content in the grain of spring barley. From the analysis of the plants we can see that dry ma�er production and nutrient concentration in the plants were influenced by the conditions of the year and the fore-crop. A�er sugar beet, the growth of the dry ma�er was intensive and the concentrations of nutrients per one plant were higher as early as in the initial stages of vegetation. The yields in the years 2001 and 2002 corresponded with these results while the highest yields were seen a�er the sugar beet. Due to the extreme lack of precipitation, the best fore-crop in 2003 was maize. While the dose of 50 kg N/ha increased the yields a�er maize, a�er wheat it reduced the yields and increased the crude protein content in the grain.