Number of melanin-synthesising microorganisms under mineral fertilisation and liming of Albebeluvisoil

The study of the main patterns of distribution of microorganisms that synthesise melanins, which are precursors and components of humus molecules in agrocenosis soils is an urgent scientific task. The purpose of this study was to determine the influence of agrochemical factors on the number of melanin-synthesising microbial species and bacteria in grey forest soil. Microbiological, laboratory and analytical, and statistical methods were employed in the study. It was found for the first time that the number of melanin-synthesising micromycetes is minimal in the soil of the variant without fertilisers, liming with one dose according to hydrolytic acidity contributes to an increase in their number by 86.8%, application of mineral fertilisers in a dose of N30Р30К45 – 2.0 times, compatible use of lime and mineral fertilisers – 2.94 times. A 1.5-fold increase in the dose of mineral fertilisers leads to a 2.54-fold increase in the number of colony-forming units (CFU) of melanin-synthesising microbial species compared to a single dose of fertilisers, and a 2.0-2.62-fold increase in the dose of fertilisers, which coincides with the results of the analysis of the humus content in the soil of these variants – it exceeds the humus content in the variant with a single dose of fertilisers by 26.5% and 16.3%, respectively (correlation coefficient is 0.811). The number of melanin-synthesising bacteria in grey forest soil is 2-3 orders of magnitude higher than the number of melanin-synthesising micromycetes. However, the patterns of influence of anthropogenic factors on their number coincide with those established for micromycetes: liming with one dose of hydrolytic acidity leads to an increase in the number of melanin-synthesizing bacteria by 26.1%, application of mineral fertilizers in a dose of N30Р30К45 – 2.03 times, combined use of lime and mineral fertilisers – 2.48 times. A 1.5-fold increase in the dose of mineral fertilisers leads to a 5.8-fold increase in the number of melanin-synthesising bacteria compared to a single dose of fertiliser, while a 2.0-fold increase in the dose of fertiliser leads to a 13.3-fold increase, respectively. The correlation coefficient between the number of melanin-synthesising bacteria and the humus content in the soil is 0.417. The findings of the presented research can be used to develop recommendations for measures to increase the humus content of agricultural soils