Natural organic mulch eventually breaks down and adds organic material to the soil. The increase of the amount of soil organic carbon (SOC) is regarded as the main advantage of organic mulches. The aim of our investigation was to evaluate the effect of different organic mulches and different thicknesses of the mulch layer on the content of SOC. The field experiment was carried out in the Pomological Garden of Aleksandras Stulginskis University (54°53 ¢N, 23°50¢E) in a certified organic field. The soil was Calc(ar)i-Endohypogleyic Luvisol. The following treatments were applied: factor A – mulch: (1) without mulch, (2) straw, (3) peat, (4) sawdust, and (5) grass. Factor B – thickness of mulch layer: (1) 5 cm and (2) 10 cm. The influence of organic mulches was investigated in 2004–2009 and their residual effect in 2010–2011. In the article the data of 2008–2011 are presented. A higher content of SOC was established in all mulched experimental plots compared with the unmulched plots. A significant influence of peat mulch was observed during the whole period reported. Sawdust mulch significantly increased the content of SOC (2008–2009) but its residual effect (2010–2011) was not significant. The influence of straw mulch on the content of SOC was significant only in 2009. The thicker (10 cm) mulch layer significantly (by 0.35–0.52 percentage points) incresed the content of SOC compared with the thinner (5 cm) layer. A very strong positive linear correlation (r = 0.994, P £ 0.01) between the amount of organic C carried into the soil with mulch and the content of organic C in the soil was established.

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.

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

In recent years, farmers across the country have been using intensive farming systems to increase yields and profits. As the number of livestock farms has declined, so has the use of organic fertilizers. The use of mineral fertilizers alone, combined with the increased use of pesticides, has led to a decline in soil bioactivity, humus content, and soil fertility. It is therefore particularly important to use fertilizers enriched with humic acids, which are characterized as growth promoters – they stimulate root development, the growth of the vegetative part of the plant, the chlorophyll content of the leaves, the intensification of respiration and photosynthesis, and the germination of the seeds. These acids make plants more resistant to adverse environmental conditions and increase their yield. To this end, an experiment was conducted in 2022 at the Experimental Station of Vytautas Magnus University Agriculture Academy (54° 53' 6.17", 23° 50' 14.8"). The research was carried out on a Calcari-Endohypogleyic Luvisol. The soil is slightly alkaline (pH 7.1–7.2), highly phosphatic (P2O5 227 mg kg-1), and moderately calcareous (K2O 135 mg kg-1). The fertilizers used in the study were: 1) Without humic acids and silicon and 2) With humic acids and silicon. The results show that the use of plant fertilizers with humic acids and silicon stimulates the photosynthetic potential of plants. There is a significant increase in the content of photosynthetic pigments: chlorophyll a (19.3% at flowering and 13.6% at maturity), chlorophyll b (33.9% and 19.8%, respectively), and total pigments (12.8% and 10.1%, respectively). Humic acids with silicon increased the productivity of spring wheat. Significantly higher aboveground and root mass, leaf area, the number of leaves, and total plant mass were observed with the use of humic acids and silicon fertilizer. The use of humic acids improved the quality of spring wheat grain.

Pastaruoju metu Lietuvoje išplito netvaraus agroekosistemų, kurios užima per 53% šalies teritorijos, naudojimo tendencijos. Siekiant kuo didesnių derlių ir trumpalaikės naudos, sparčiai išaugo žieminių kviečių ir rapsų plotai, nesilaikoma tinkamos augalų kaitos principų, labai padidėjo azoto bei cheminių augalų apsaugos priemonių naudojimas, nepaisoma realios augalų mitybos ir sveikatingumo būklės bei geros žemdirbystės praktikos principų. Tai anksčiau ar vėliau veda prie dirvožemio degradacijos, humuso praradimo ir biologinės įvairovės mažėjimo, dirvožemio rūgštėjimo, taršos didėjimo. Mokomojoje knygoje nuosekliai aprašyti praktiniai tvarių agroekosistemų formavimo žingsniai, dirvožemio valdymo ir jo kokybės vertinimo principai. Recently, trends of unsustainable use have spread in agroecosystems, which occupy over 53% of the total territory in Lithuania. To achieve the highest possible yields and short-term benefits, the areas of winter wheat and rapeseed have increased rapidly, the principles of proper crop rotation are ignored, the use of nitrogen and pesticides for plant protection has increased significantly, the real nutrition and health status of crops and the principles of good agricultural practices are ignored. This sooner or later leads to soil degradation, loss of humus and reduction of biological diversity, soil acidification, and an increase in pollution. The textbook consistently describes practical steps to reach agroecosystems sustainability, principles of soil management and soil quality assessment.