Stability of microbiological activity of the sod-podsolic soil when applying diatomite and zeolite

At present, the analysis of the state of soil biotic complex when using non-traditional materials, such as high-silicon rocks is an important problem in the field of agronomic soil science. The aim of this research was to assess the state of the basic microbial participants of the L-selection survival strategy (ammonifying and amylolytic consortia) in conjunction with hydrolase enzymatic activity of the sod-podzolic soil under high doses of diatomite and zeolite rocks with subsequent assessment of the stability of the considered part of microbiota. We studied the effect of different doses (3, 6 and 12 t/ha) of diatomite of the Inzensky deposit (Ulyanovsk region) and zeolite of the Hotynetsky deposit (Oryol region) on the number of ammonifying and amylolytic microorganisms and on hydrolase enzymatic activity of soil in a microfield experiment (2015-2017) carried out in the sod-podzolic light loamy soil (WRB - Retisols) of Nizhny Novgorod region (56°31'13.00"N 44°06'57.37"E). Field experiments were conducted according to the generally accepted rules for small-plot field studies (the registration area of the plot was 1 m², the location of the plot was randomized, and replication was fourfold). Analytical studies included the number of microorganisms with Koch's pour plate method using beef-extract agar (BEA) and Inorganic Salt Starch Agar (ISSA), protease enzymatic activity using the ninhydrin spectrophotometric method, invertase using the gravimetric method with Fehling's solution, the intensity of carbon dioxide gas transpiration from soil by standard gasometrical method, and the biomass of microorganisms in the soil by rehydration method. The stability of the soil microbial pool was assessed by a two-phase method, in which the inactivated state characterizes the soil capacity to preserve a certain microbial niche (microbiological resistance), and the mobilized phase describes the potential microbiological activity in the soil, that is the most possible biochemical “reserve” of the microbial consortium under study. The results of our three-year microfield experiment with the use of diatomite showed that, on average, during a three-year microfield experiment with the use of diatomite, the number of inactivated ammonifying microorganisms maximally increased up to 42%, and that of mobilized ones up to 13% (See Table 1). A similar, but a less active pattern was observed in the mobilized samples. When using zeolite rock, we observed a tendency to optimize both phases of the ammonifying group of microorganisms. The number of inactivated amylolytic microorganisms decreased by 34% when using diatomite and by 13% when using zeolite, and when mobilizing the soil, there was a decrease to 17% and 8% respectively. The activity of the proteolytic enzyme system of the soil was found: on average, over 3 years the activity of protease enzymes increased up to 38% due to the use of diatomite and up to 11% of zeolite rock (See Table 2). The activity of invertase enzymes began to decline in the second year of the study with an increase in the dose of each of the rocks and was prolonged to the end of the experiment. The measure of decline turned out to be more significant in the variants with diatomite material (up to 8-11%) than with zeolite (up to 3-6%). The use of both rocks reduced the value of the mineralization coefficient of the organic matter of C_M (See Fig. 1). In inactivated samples, the degree of their impact on the indicator was more significant. The smallest C_M values were established in the variants with 6 and 12 t/ha of application in the soil, where the decline reached 54% in the variants with diatomite and up to 24% with zeolite. The use of diatomite rock, especially in high doses, contributed to a decrease in the activity of microbiological processes of decomposition of organic matter in the soil (inactivated part of the microbiota), while maintaining the potential of this function (the level of the mobilized part). The application of zeolite in the soil slightly reduced the indicator under consideration, but it definitely did not contribute to an increase in potential microbiological activity in the transformation of organic components. The degree of microbiological resistance of the soil, depending on the dose of diatomite, increased by 17-27% in ammonifying function and decreased by 21-23% in amylolytic one. The index of microbiological transformation of nitrogen-containing organic matter increased up to 58-60% relative to the control group (See Fig. 2). In variants with the use of zeolite, on average over 3 years of research, we observed a similar trend but with an insignificant activity. Here, the exponent of N-microbiological resistance (DMS_N) increased by 12-14% in variants with the 2nd and 3rd doses of rocks. The coefficient of soil microbiological cultivation DMC_N showed (See Fig. 3) that against the background of a general increase in soil microbiological activity (more than 2 times in variants with diatomite and by 12-29% in tests with zeolite) the persistence of potential microbial reserve of L-strategies significantly increased (by 19-31% in tests with diatomite and by 7-14% in variants with zeolite). We demonstrated (See Fig. 4) that in the variants with the use of diatomite rock with a gradual annual increase in carbon of the microbial mass in the soil (from 5% to 11% with D1, from 6% to 16% with D2 and from 7% to 15% with D3) the activity of carbon dioxide release from it decreased. The tests with the application of zeolite showed a similar tendency: a weak one with respect to the microbial biomass (on average, for 3 years by 4%, regardless of dose) and significantly sharp with respect to CO₂transpiration by 11-21%. Due to the above-described change in the number of basic saprotrophic soil microorganisms, its hydrolase activity, soil microbial biomass and its “respiration” under the influence of diatomite, as well as due to shifts in microbially-dependent indicators of the organic matter mineralization, microbiological stability and soil cultivation, components are subject to change under its action, are directed towards complication and are actively and directly involved in the microbial metabolism. The latter, undoubtedly, has a positive meaning in terms of active participation of the microbial pool in the formation of humic substances in the soil. The paper contains 4 Figures, 2 Tables and 35 References. Acknowledgment: The authors are grateful to AG Pushkov, General Director of “Elithoz” LLC (Borsky district, Nizhny Novgorod Region) for the given opportunity to carry out microfield studies: a field site and high-quality crop seeds.

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