Enzymatic Activity of Soil after Applying Mineral Fertilizers and Waste Lignite to Maize Grown for Silage

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.