Аннотация:An increasing anthropogenic impact on agricultural land results in soil deterioration
processes mainly due to soil structure degradation. Degradation of the soil structure of the
arable horizon has been marked in the vast areas al over the world. The latter led to
drastically reduced soil fertility due to poor conditions of crops growing. Therefore,
searching for new methods of soil improvement aimed primarily at improving soil structure
is of a great importance. An introduction the humic acids (HA) modified with siloxanes (so
called silsesquioxane humic systems, Si-HA) seems to be one of the most promising
approach. Despite the fact that the possibility of using Si-HA has already been shown
earlier [1], there are still no studies aimed at comprehensive evaluate their ameliorative
properties. So, the goal of our work was to conduct a comprehensive evaluation of Si-HA
ameliorating properties including both evaluation of their effect on soil structure, their
sorption on soil and their toxicity assessment towards higher plants and soil microflora as
well.
To reach this goal, a model experiments with soil samples of arable horizon of sodpodzolic
soil (pH 5.3, OC 1.83%, N 0.12%) were saturated with HA or Si-HA at different
rates followed by estimation of HA or Si-HA desorption from soil, measuring soil substrateinduced
respiration (SIR) according to [2], estimation of stable microaggregates using
laser analyzer of particle size Microtrac Bluewave (Microtrac, USA) and bioassay of soil
water extracts using wheat seedlings. To follow alteration of soil humus composition, a
ratio of CHA/CFA was also measured. Samples saturated with distilled water were used as
blank ones. Si-HA was synthesized based on coal HA using (3-aminopropyl)triethoxysilane
(APTES) according [1].
Our results demonstrated that additional stable microaggregates in the soil in the
presence of Si-HA formed when the rate of Si-HA was 0.75% by weight of the soil or
higher. That rate corresponded to humus content ca. 4% that is usually considered as
optimum humus content in terms of humus’ properties as“soil glue” [3]. Si-HA sorbed
mainly irreversible by soil, and the amount of desorbed organic carbon did not exceed
10% of the input. That finding was consistent with the concept of adsorption Si-HA due to
the formation of siloxane bonds. The latter was indirectly confirmed also by closeness of
CHA/CFA ratio in case with soil saturation with Si-HA to the blank values (0.760.03 for Si-
HA versus 0.620.03 for blank), while soil saturation with unmodified HA resulted in
significant increase in CHA/CFA ratio (1.080.19). Si-HA stimulated SIR (probably, due to
release of nitrogen of amino groups of APTES) and were not toxic for wheat seedlings up
to the rate 1.25% by weight of the soil.
So, the obtained results allowed to conclude that further study of Si-HA as
ameliorating soil agents is of great promise.
References
1. Volikov A.B. et al. // Catena. 2016. 137:229–236.
2. Ananieva N.D et al. // Pochvovedenie. 2009. 9:108–1116. (in Russian)
3. Antipov-Karataev et al. // Soil aggregate and methods of its study. Academy of
USSR Publisher. 1948. (in Russian)
This research was supported by the Russian Science Foundation grant 16-14-00167.