Modern agricultural technologies have contributed to a significant reduction in the amount of soil organic matter. Brown coal waste (BCW), with low energy content, can be used to neutralize this process, contributing to the recuperation of soil fertility and to environmental protection. More studies need to be conducted on organomineral fertilizers based on BCW and applied to soils with low humus content. Apart from increasing soil production capacity in arable fields, BCW could be used for the reclamation of industrially contaminated areas and degraded soils, in the vicinity of motorways and in soilless agriculture. It can also be used as a sorbent of gases emitted from slurry during its storage such as NH₃, H₂S, mercaptans, volatile fulvic acids (FAs); as a component of sewage sludge compost; as a natural additive to calf feed; and for the production of adsorbents for sewage and wastewater treatment.

This paper examines the effect of mineral fertilizers and waste lignite, the latter applied to the preceding crop, on the enzymatic activity of soil. The research was conducted between 2014 and 2016 at the Agricultural Experimental Station of the Siedlce University of Natural Sciences and Humanities in Zawady (Poland). The following treatment combinations were involved: 1—control; 2—NPKMgS; 3—NPKMgS + 20 N; 4—NPKMgS + 40 N; 5—NPKMgS + 60 N. Three varieties of maize grown for silage constituted the second research factor. Mineral fertilizers were applied at the following doses (pre-sowing): N-100, P-35, K-125, Mg-12 and S-14 kg ha⁻¹. Nitrogen was additionally applied as top dressing with 3, 4, and 5 treatment combinations at 20, 40, and 60 kg ha⁻¹. Waste lignite was applied to the preceding crop on two plots (3 and 4), in 1 and 5 t ha⁻¹ doses. In the subsequent years, the significantly highest content of soil organic carbon was recorded on the NPKMgS + 60 N plot (1.12%; 0.98% and 1.16%). With 49.25 and 51.95 mg NH₄-N h^–1 kg^–1 DM, urease activity in the soil treated with NPKMgS + 20 N and NPKMgS + 40 N was 56.95% and 65.55% higher than in the control plot soil. Throughout the experimental years, acid phosphatase activity did not vary much and amounted to 3.51–3.53 mmol PNP h^–1 kg^–1 DM. Mineral fertilizers significantly increased the activity of alkaline phosphatase and dehydrogenases in relation to the control. To ensure the high enzymatic activity of the soil and a high biochemical index of soil fertility, pre-sowing fertilizers at the level of 100 kg N, 35 kg P, 125 kg K, 12 kg Mg, and 14 kg S per hectare and top dressing of 20 kg N or 40 kg N per hectare are recommended. At the same time, it is advisable to use 1 t ha^–1 or 5 t ha^–1 of waste lignite of low energy value on the preceding crop.

The field experiment was conducted in the central-eastern Poland. The aim of the research was to determine the effect of low-energy lignite organic matter applied to the preceding crop in the form of an organomineral fertilizer on the treatment optimization of Zea mays L. maize grown for silage. Two factors were taken into account in the research: factor I—five fertilization plots control plot—without fertilization (1), NPKMgS (2), NPKMgS + N1(3), NPKMgS + N2 (4), NPKMgS + N3 (5); factor II—three varieties of Zea mays L. Nitrogen was applied as fertilizers 3, 4 and 5 at doses of N1-20, N2-40 and N3-60 kg per hectare. In the spring each year, selected plots were pre-sown with mineral fertilizers at doses of 100 kg·N, 35 kg·P, 125 kg·K, 12 kg·Mg and 14 kg·S per hectare. Organomineral fertilizer based on low-energy lignite was applied to the preceding crop (maize grown for silage) on two plots, in 1 and 5 t·ha⁻¹ doses. Mineral fertilizers used in research significantly reduced the content of nitrogen, phosphorus, potassium, magnesium and sulphur in the dry matter of plants. The uptake of the nutrients reached the highest values for maize treated with NPKMgS + N1, NPKMgS + N2 and NPKMgS + N3. The agronomic efficiency (AE) of nitrogen, phosphorus, potassium, magnesium and sulphur, all of which were applied in the form of the polyfoska^® fertilizer, M-MAKS (NPKMgS), potassium salt and urea, reached the highest values for plots treated with NPKMgS + N1 and NPKMgS + N2. In turn, the treatment of NPKMgS and NPKMgS + N3 with nitrogen, phosphorus, potassium, magnesium and sulphur resulted in the highest values of physiological efficiency (PE). Based on the three-year research carried out with the use of polyfoska^® M-MAKS (NPKMgS), potassium salt and urea in the fertilization of maize grown for silage, it is possible to recommend the optimal dose of NPKMgS + N1 mineral fertilizers (100-35-125-12-14 pre-sowing, 20 kg top dressing N) and NPKMgS + N2 (pre-sowing 100-35-125-12-14, top dressing 40 kg·N). The low-energy lignite applied to the preceding crop in doses of 1 t and 5 t at the NPKMgS + N1 and NPKMgS + N2 plots contributed to the achievement of the analyzed parameters (uptake, AE and AE) at a high level.