QUALITATIVE CONCENTRATION OF HUMUS OF CHESTNUT SOILS CONSIDERING MANY-YEAR FERTILIZING

The results of long-term agrochemical experiments highlight quantitative and qualitative changes in the humus status of chestnut soil when applying organic and mineral fertilizers. When fertilizers were not applied, the initial humus concentration in the soil was reduced and on average reached its minimum level of 0.94 ± 0.03% in the 48th year of research. During the whole period in the unfertilized variant, the soil lost 28.3% of the initial amount of humus, or 11.0 t/ha, with an average annual loss of 228 kg. Kinetic parameters of humus reducing in the soil of the control variant reached k = 0.008 year -1 in rapid manifestation. When mineral fertilizers were applied, the humus concentration was higher than in the control variant and reached 1.17 ± 0.05% by the last date of determination. The reduction rate in the variant of applying mineral fertilizer was k = 0.003 year -1. The average annual inflow of root and stubble residues when applying mineral fertilizes compensated humus losses and stabilized its concentration after 30 years of research. Reducing of humus reserves in the soil revealed in a corresponding reduction of annual losses, which reached 131 kg/ha in the first 16 years, with further decrease of 107 kg/ha in 14 years, followed by their absence and slight decrease in the last 7 years - 41 kg/ha. Deficient and positive balance of humus was provided by the variant with manure application. The humus concnetration in the soil for 48 years of applying fertilizers reached 1.50 ± 0.04% and significantly exceeded the initial concentration. On average, during the research period the soil multiplied its reserves on 5.6 t/ha with an average annual growth rate of 117 kg/ha. Kinetics of humus concentration increase in soil in the variant with manure application had a growth rate constant k = 0.002 per year. Ranking of positive quantitative (S gen, %) and qualitative (HC: FC) changes of humus in soil according to estimation variants in dynamics of perennial series occurs in a row: no fertilizers (0.56 % and 0.75) → complete fertilization NPK (0.69 % and 0.79) → manure (0.86 % and 0.92).

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