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A field experiment was carried out at the Experimental Station of the Aleksandras Stulginskis University in 2011 with the objective to establish the influence of spring oilseed rape (Brassica napus L.) crop density (50-100, 100-150, 150-200, 200-250, 250-300, 300-350, 350-400, 400-450 plants m -2 ) on plant root biomass and soil enzymes urease and saccharase activity.It was found that the highest plant root biomass in the 0-10 and 10-20 cm soil layers was formed at a plant density of 100-150 plants m -2 . With rape crop density increasing from 150 to 450 plants m -2 , a decreasing trend of plant root biomass in both soil layers was detected. Statistically significant dependencies were determined between the dry biomass of oilseed rape roots in the 0-10 cm soil layer and the content of potassium in the soil (r = 0.76, P < 0.05), and between the dry biomass of rape roots in the 10-20 cm soil layer and soil pH (r = 0.74, P < 0.05). With increasing rape crop density, compared with the thinnest crop, the activity of urease in the soil did not change significantly. At a rape crop density of more than 100 plants m -2 the activity of saccharase significantly increased (by 31-56%) in comparison with saccharase activity in the thinnest crop. The soil urease activity depended on the spring rape crop density (r = 0.81, P < 0.05) and the content of available phosphorus (r = 0.75, P < 0.05). The soil saccharase activity was influenced by the rape crop density (r = 0.79, P < 0.05) and soil pH (r = 0.72, P < 0.05).

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As the consumption of plant products grown under regulated-climate conditions intensifies, its production also intensifies. Peat substrate as a growing medium is widely used due to its desirable physical, chemical, and biological properties. Peatlands play an important ecological, economic, and cultural role in human well-being, but their resources are decreasing, so wood fiber can be used as a substitute for peat substrate. Cucumbers (Cucumis sativus L.) were cultivated in growing media (Factor A) of peat substrate and wood fiber: (1) peat substrate (PS); (2) wood fiber (WF); (3) WF and PS 50:50 v/v; or (4) WF and PS 25:75 v/v. To evaluate the amount of additional nitrogen, four fertilization rates were used (Factor B): (1) conventional fertilization (CF); (2) N13; (3) N23; or (4) N30. The yield of cucumbers grown in wood fiber depended on the amount of additional nitrogen. When plants were fertilized with the highest rate of additional nitrogen, N30, their yield increased by 22% compared to the yield of cucumbers that were grown in wood fiber using conventional fertilization. Chlorophyll synthesis was the most intense in the leaves of cucumbers grown in wood fiber when the plants were additionally fertilized with N23 and N30, and in mixtures of wood fiber with peat substrate in ratios of 50:50 and 25:75, fertilized with N23 and N13, respectively. In summary, it can be argued that cucumbers can be grown in wood fiber and in a mixture with peat substrate in a ratio of 50:50, but additional nitrogen is needed to compensate for the amount of nitrogen immobilized in the fiber.