Biogas production from manure and other organic matter, or combinations thereof, is part of the circular economy, and the use of the digestate from biogas production for plant nutrition and thus for soil fertility restoration and organic carbon (C) sequestration completes the circular economy cycle. The use of digestate from biogas production in agriculture is one of the sustainable ways to manage manure or organic waste, an alternative to conventional chemical fertilizers, and a means to achieve the objectives of the European Green Deal. To this end, two two-factor pot experiments were carried out in 2019–2020. Factor A—1. Control (without fertilization), 2. Liquid cow manure 170 kg ha⁻¹ N (N₁₇₀), 3. Digested manure 170 kg ha⁻¹ N (N₁₇₀), 4. Digested manure 140 kg ha⁻¹ N (N₁₄₀), 5. Digested manure 110 kg ha⁻¹ N (N₁₁₀); Factor B—1. Plants not cultivated, 2. Plants cultivated. The experiments determined the effect of digestate on the changes in soil nitrate (NO₃-N), ammonium (NH₄-N) and mineral (NO₃-N + NH₄-N) nitrogen, and available phosphorus (P₂O₅) and potassium (K₂O) in the soil without plants as well as with plants cultivated and evaluated the risk of migration of macronutrients into deeper soil layers. The results showed that the application of the highest allowed rates under the Nitrates Directive (N₁₇₀) and N₁₄₀ digestate is accompanied by the addition of high levels of ammonium (NH₄-N) nitrogen, which alters the balance of ammonium (NH₄-N) and nitrate (NO₃-N) nitrogen in the soil, and the extent of their migration to the deeper layers. These results suggest that the application of digestate to agricultural land enhances the migration of nitrogen and, in phosphorus-rich soils, of phosphorus (PO₄-P) compounds to deeper layers (>25 cm). In order to achieve environmental objectives, digestate rates should be based on the agrochemical properties of the soil and the needs of the plants and should not exceed 65% of the nitrogen needed by the plants from mineral fertilizers.

Super hardy kiwifruit [Actinidia kolomikta (Maxim. & Rupr.) Maxim.] accumulate large amounts of biologically active compounds, but it is possible to store ripe fruit for a very short time, only 2 weeks at 0–5 °C. Therefore, it is necessary to determine optimal storage conditions to prolong fruit storage time. The aim of this research was to analyse changes in the basic chemical composition of fruit during ripening in controlled atmosphere chambers. Fruit was stored for 6 weeks at a constant temperature (0 °C) and humidity (90%) in different air compositions (No. 1—21% O₂, 78% N₂; No. 2—0.5% O₂, 98.5% N₂, 1% CO₂; No. 3—1.5% O₂, 95.5% N₂, 3% CO₂; No. 4—2% O₂, 93% N₂, 5% CO₂). The chemical composition of the fruit was determined at harvest, after 2, 4 and 6 weeks of storage. Dry matter, soluble solids, ascorbic acid, total chlorophyll and carotenoid contents were analysed. The greatest increase in the contents of dry matter and soluble solids after 6 weeks of storage was found in the chamber where O₂ was 2% and CO₂ was 5%. The ascorbic acid content decreased during the fruit ripening process regardless of the air composition. Most of the ascorbic acid remained in fruit stored in the chamber with 1.5% O₂ and 3% CO₂. The concentration of total chlorophyll and total carotenoids in the fruit increased as development progressed. The different air parameters in the storage chambers had different effects on the synthesis of pigments in fruit, but the content of pigments increased most in fruit stored in the chamber with atmospheric parameters 0.5% O₂ + 1% CO₂.

Nitrogen is one of the main factors that shapes soil fertility and the productivity of crops, although its abundance can also cause damage to the environment. The aim of this study is to evaluate the influences of different forms of nitrogen fertilizers, soil temperature, and precipitation on the changes of nitrogen compounds (N-NH₄⁺, N-NO₃⁻, and N_min) in two soil layers. Two pot experiments are performed, involving simulated precipitation levels of 10- and 20 mm. Urea and ammonium nitrate fertilizers are used for fertilization. The soil samples are stored in pots in a climate chamber at different temperatures of 5, 10, 15, and 20 °C. After seven days, the changes of nitrogen compounds (N-NH₄⁺, N-NO₃⁻, and N_min) in 0–15 and 15–30 cm soil layers are analyzed. This study shows that the amount of N-NH₄⁺ nitrogen in the soil depends on the fertilizer form and soil temperature. In the temperature range of 5–20 °C, significantly more N-NH₄⁺ nitrogen is present in urea-fertilized soil. The migration of N-NH₄⁺ into the deeper 15–30 cm soil layer at both the 10- and 20-mm simulated precipitation levels is negligible. The N-NO₃⁻ contents in the 0–15 cm soil layer in the temperature range of 5–20 °C are 1.7–2.3 times lower in the urea-fertilized soil than in the ammonium nitrate-fertilized soil at a 10-mm simulated precipitation level and 1.6–2.2 times lower at 20 mm. The N_min contents in soil are directly dependent on the fertilizer form and soil temperature for both levels of simulated precipitation.

Plant fertility and soil quality are determined by many environmental factors