Sweet basil (Ocimum basilicum L.) is an annual plant belonging to the plant family Lamiaceae. There are many varieties of basil, with leaves of colour from green to purple and with small white or pink flower. In field experiment conducted in the years 2007–2008 there was investigated the effect of nitrogen fertilization in the doses of 50, 150 and 250 kg N·ha^-1and irrigation on yielding and nutritional status of basil of ‘Red Rubin’ cultivar grown from transplants. Basil positively responded to irrigation and the increase in its yield under the influence of irrigation amounted from 97.37% to 25.36% in subsequent years of cultivation. Also the dose of nitrogen did advantageously affect basil herb yield. The highest yields were recorded at the dose of 150–250 kg N·ha^-1. The highest amount of nitrates ranged from 697.00 to 938.00 mg·kg^-1 f.m. was determined in plants fertilized with nitrogen dose of 250 kg N·ha^-1. The level of macroelements depended both on irrigation and on nitrogen doses. Irrigation caused decreased amounts of phosphorus, potassium and calcium, while content of magnesium increased. The highest quantities of phosphorus and magnesium were obtained at nitrogen dose of 150 kg N·ha^-1, while for the highest values of potassium and calcium nitrogen dose was 250 kg N·ha^-1.

Phenolic compounds which occur in red cabbage, have strong antioxidant activity, and can be used as substances protecting human cells from oxidation. Field experiment conducted in the years 2007–2009 in Department of Horticulture at Wroclaw University of Environmental and Life Sciences involved research on the effect of different nitrogen doses on yield, chemical composition and antioxidant activity of red cabbage. Nitrogen, in the form of ammonium saltpeter, was introduced in the following doses: 50 kg N·ha^-1; 150 kg N·ha^-1 and 250 (150+100) kg N·ha^-1. In the third decade of April red cabbage seeds of ‘Langendijker’ cv. were sown into multipots. The seedlings were planted on 5 m² – area plots at the end of May. Harvesting took place in the second week of September, when there was assessed marketable and total yield. In samples of red cabbage heads there were estimated the content of nitrates, vitamin C, total and reducing sugars, polyphenols, anthocyanins, as well as dry matter and soluble solids. In order to investigate antioxidant activity there were applied DPPH and ABTS tests. In experiment optimum nitrogen dose for red cabbage was 150 kg N·ha^-1. The highest amount of anthocyanins were determined in the leaves of red cabbage fertilized with moderate N dose up 150 kg N·ha^-1. The highest antioxidant activity proved to characterize edible parts of red cabbage fertilized with nitrogen in the dose of 50 kg N·ha^-1, while the level of total polyphenols featured the lowest values in the conditions of intensive nitrogen fertilization amounting 250 kg N·ha^-1.

Very important element of proecological vegetables cultivation it is cover plants applied. They have favourable influence on the soil environment, indicated the possibility of limiting mineral fertilizer use and also reduce an application of herbicides, allow to keep soil fertility and in this same achieve high and good quality of yield. An experiment was carried out in 2002–2005 at the Experimental Farm in Zawady belonging to University of Podlasie. The objective of the study was the effect of cover plants (phacelia, spring vetch, serradella and oat) ploughed down in the autumn, spring or retained on the soil surface as a cover crop on the yield of red and savoy cabbage, and dry matter and vitamin C contents in white and savoy cabbage was investigated. The effects of covers were compared to the uncovered control. White cabbage cv. 'Masada F₁', red cabbage cv. 'Koda' and savoy cabbage cv. 'Wirosa F₁' were cultivated. Irrespective of the date of ploughing down of cover plants, serradella was the best plant cover preceding red cabbage, and phacelia was most beneficial when preceded savoy cabbage. Oat cover ploughed down in the autumn favoured dry matter accumulation, when spring-incorporated, stimulated vitamin C in white cabbage. The autumn-incorporated phacelia cover resulted in the greatest dry matter and vitamin C contents in savoy cabbage.

Abstract: Swiss chard is recognized as valuable leafy vegetable species with short growing period suitable for cultivation as forecrop and aftercrop in crop rotation .Till now is still a minor crop in Poland and there are not existing any data describing the response of this species to nitrogen fertilization and the effect of this nutrient on plant composition. In a field experiment conducted in 2004–2006, the influence of nitrogen fertilization applied as a single or split dose in the amounts of 50, 100, 100 + 50, 150, 150 + 50 and 200 kg∙ha^-1 on yield and crop quality of Swiss chard was examined. Seeds of Lukullus cv. were sown directly into the field in the half of April in spacing 45 × 25 cm, and single harvest of leaf rosettes was conducted on 8–10 July. In separate samples of leaf blades and petioles there was evaluated the content of dry matter, vitamin C, sugars, total N, nitrates, P, K, Ca, and Mg. Results of the study indicate that the increment of N dose from 50 to 100 kg∙ha^-1 had positive effects on Swiss chard yield but the efficiency of higher nitrogen doses was rather small and not significant. Heavy nitrogen fertilization caused the increment of total N and nitrates in both edible parts and magnesium in leaf petioles, while reduction the sugar content in leaf blades. On the average blades contained higher amounts of dry matter, sugars, total N and Mg, while petioles – calcium and nitrates.

A number of research studies investigating melon production technologies in various macroregions of Poland characterized by different climate conditions have been initiated to investigate the effect of perforated PE film and non-woven PP fabric covers as well as soil mulching with organic and mineral material on the melon growing process. A two-factorial field experiment was conducted in the years 2004–2008, in the Garden of the Research and Experimental Station of the University of Warmia and Mazury in Olsztyn. The first experimental factor were four Polish melon cultivars, Malaga F₁, Melba, Oliwin and Seledyn F₁, recommended for open ground and forced cultivation. The second factor were types of soil cover and plant cover. Apart from the control treatment (without protective cover), the effect of the following types of cover on the growth rate and yield of melon plants was determined in a five-year cycle: perforated PE film with 100 holes per m², non-woven PP fabric with surface density of 17 g·m^-2, black PE film for soil mulching; black PE film for soil mulching + perforated PE film with 100 holes per m², black PE film for soil mulching + non-woven PP fabric. An analysis of the chemical composition of melon fruit showed that the concentrations of dry matter, L-ascorbic acid and total carbohydrates were higher in the edible parts of heterotic cultivars. The type of plant cover and soil cover had a significant effect on the dry matter content of the edible parts of melon, but it caused no considerable changes in the levels of the remaining organic compounds. In the majority of cases, the nitrate content of melon fruit was below the allowable standards. The lowest quantities of nitrates were accumulated by melon fruit of cv. Oliwin in the control treatment.

Asahi SL stimulates plant’s vital processes like growth and development, affects physiology and biochemistry, what often leads to increased biomass accumulation and yield. However, common is opinion that application of this preparation could be beneficial only, when treated plants are grown under unfavorable conditions. Therefore the aim of this work was the assessment of the stimulatory effect of Asahi SL on Arabidopsis thaliana L. and ornamental amaranth plants grown under optimal conditions. Plants treated with Asahi SL were higher and more advanced in development, particularly generative. Biomass accumulation was greater after biostimulator application mainly due to better photosynthetic apparatus efficiency, which was manifested by (i) greater leaf area, (ii) higher total chlorophyll content and (iii) increased intensity of photosynthesis. Effect of Asahi SL on chlorophyll a fluorescence was marginal. Despite of higher transpiration and lowered stomatal resistance the RWC was almost unchanged in biostimulator treated plants what was attributed to increased water uptake. Obtained results clearly showed that Asahi SL applied on plants can also be effective and beneficial when they are grown under optimal conditions.

Plant fertilization with iodine may be an alternative source of this element in human diet. Iodine influence on nitrogen metabolism in plants has not yet been thoroughly described. Thus, there is an urgent need to determine the effect of iodine application on nitrate(V) accumulation in plants. The aim of the study was to determine the influence of soil and foliar application of iodine forms (I^-, IO₃^-) on nitrate accumulation and concentration of selected compounds in radish plants. The following treatments were applied in the experiment: 1 – control (without application of iodine), 2 – foliar application in KI form, 3 – foliar application in KIO₃ form, 4 – soil fertilization in KI form, 5 – soil fertilization in KIO₃ form, 6 – soil fertilization in KI form + foliar application in KI form, 7 – soil fertilization in KIO₃ form + foliar application in KIO₃ form. Soil fertilization with iodine was carried out before radish sowing to the level of 15 mg I·dm^-3 soil. Foliar application of this element was performed twice using iodine solution in a concentration per pure element of 0.2%, in dose of 0.4 dm³· m^-2. In all tested combinations with iodine treatment an increase of ammonium ion content in radish roots was observed in comparison to the control. Both, foliar nutrition with KI as well as nitrogen fertilization with KIO₃ (combination 2 and 6, respectively) resulted in a significant increase of free amino acids concentration in radish roots. No significant influence of tested factors was noted for the root and leaf content of: dry mass, nitrates(V), nitrates(III) as well as root level of total soluble sugars and leaf concentration of photosynthetic pigments and ammonium ions in radish.

Shallot is one of the vegetables, which are especially abounding in flavonoids, phenolic acids and other compounds with antioxidative properties. Among Allium vegetables it is also distinguished with good storage ability. The studies conducted in the years 2007–2009 included the assessment of dry matter, flavonoids and phenolic acid contents in shallot bulbs immediately after harvest and drying off, as well as after long-term storage (5 months in the temperature 0–1^oC and humidity of 86%). The studies concerned 3 cultivars of shallot: ‘Ambition F₁’, ‘Bonilla F₁’ and ‘Matador F₁’. The bulbs of these cultivars were obtained from seedlings planting. For chemical analyses bulb samples with the diameter of 25–30 mm were selected, as such constituted the greatest participation in the obtained yield. The contents of total and reducing sugars, flavonoids (converted into quercetin), as well as phenolic acids (converted into coffeic acid) were determined in fleshy scales, whereas in dry scales only the contents of flavonoids and phenolic acids were determined. The dry matter of fleshy scales in the examined shallot cultivars was on average 16.65%. From among three examined cultivars the bulbs of ‘Bonilla F₁’had significantly greater dry matter (18.03% on average). The contents of total sugars in shallot bulbs was on average 6.32% immediately after harvest and 5.71% after 5 months of storage. Similarly as in the case of dry matter, the bulbs of ‘Bonilla F₁’ cultivar turned out to be the most abounding both in total and reducing sugars. The examined cultivars significantly differed in the contents of flavonoids and phenolic acids both in dry and fleshy scales. In all the cultivars the dry scales contained more than 50 times more flavonoids and more than 34 times more phenolic acids, as compared with fleshy scales. Long-term storage of shallot bulbs significantly affected the decrease of flavonoid contents, slight decrease of total sugars, but a significant increase of phenolic acids. From among the examined cultivars ‘Ambition F₁’ was characterized with the lowest contents of all the analyzed components.

Endive, like another leafy vegetables, as an annual plant with short time vegetation is prone to nitrate accumulation. The aim of research conducted in the years 2007–2009 was the assessment of the effect of diversified nitrogen doses on growth, yielding and nutritive value of two ‘Excel’ and ‘Cigal’ –endive cultivars. There were compared the effects of two kinds of fertilizer: ammonium saltpeter and Entec 26 containing DMPP nitrification inhibitor. On the basis of the results obtained it was possible to prove that ‘Excel’ endive cultivar gave marketable yield higher, average, by 19.4% as compared to Cigal cv. Significantly increased marketable yield of endive, regardless its variety, resulted from a single application of Entec 26 fertilizer, especially in the doses of 90 and 135 kg N·ha^-1. The experiments also pointed to the fact that the method of fertilization, as well as nitrogen doses did considerably affect biological value of the examined endive varieties Excel cultivar characterized higher degree of nitrates accumulation and higher content of carotenoids, while Cigal cultivar featured increased content of vitamin C (average by 8.8%), dry matter and chlorophyll.

Spaghetti squash is an interesting novelty in Poland. Popularization of spaghetti squash cultivation in our country requires development of agricultural recommendations. The size and the quality of yield is highly affected by the sowing date and plant population. The paper presents the results of a four-year study on the effect of the sowing date (5, 15 and 25 May) and plant spacing (1 × 0.6 m, 1 × 0.8 m and 1 × 1 m, ie. 16,668, 12,500 and 10,000 plants per ha) on the yield of spaghetti squash (‘Makaronowa Warszawska’ and ‘Pyza’) under the soil and climatic conditions of central-eastern Poland. The highest yield per hectare and the largest number of marketable fruits per plant was obtained while sowing on 5 May. Delaying the sowing date resulted in a decrease in the yield per hectare and of the number of marketable fruits per plant, although the average weight of a marketable fruit sown on 15 and 25 May did not significantly differ in comparison to sowing on 5 May. Increasing the spacings between plants from 1 × 0.6 m to 1 × 1 m resulted in decreasing the yield per hectare, but the number of marketable fruits per plant was larger. Plant spacing did not have a significant effect on the average weight of a marketable fruit. The yield per hectare for the ‘Pyza’ was larger in comparison to the ‘Makaronowa Warszawska’. The number of marketable fruits per plant did not significantly differ, but the weight of the ‘Pyza’ fruit was higher.