The paper is devoted to the development and performance testing of a soil conditioner based on leonardite humic substances (LHS) modified with 3-aminopropyltriethoxysilane (APTES). The modified HS were obtained by adding APTES to LHS solution at different mass ratios of LHS and APTES, followed by the investigation of siloxane structures using ³¹Si NMR spectroscopy. The Urbic Technosol was used as a model soil. The size and amount of water-stable soil aggregates were estimated using wet sieving and laser diffraction, respectively. Toxicity was evaluated by monitoring microbial substrate-induced respiration (SIR) and seedling bioassay. Laboratory column experiments demonstrated an increase in water-stability of the 3–5 mm soil aggregates after LHS-APTES application. Field tests showed an increase in the average weighted diameter of micro aggregates (from 59 to 73 μm) and water-stable macroaggregates (from 1.6 to 2.9 mm) due to the LHS-APTES amendment. A substantial increase in SIR from 5 to 9 mg CO₂ (kg h)⁻¹ was detected. Better survival of seedlings was observed. The obtained beneficial results indicate that APTES-modified HS can be successfully used as a soil conditioner. The formation of extended siloxane networks was suggested as the main mechanism of the observed improvement in the structure of the amended soils.

Humic acids (HAs) possess diverse functionalities, endowing them with multiple applications as bioactive compounds in agriculture. Alkaline extraction is key to obtaining HAs from their source material. The presence of oxygen during extraction can lead to oxidative changes in the humic structure. The extent of HA transformation depending on their origin remains poorly understood, and the effect of alkaline extraction on the HA biological activities is yet to be estimated. Here, we compare the physicochemical properties of HAs extracted from fresh organic material, compost, in air (HA-O₂) and under nitrogen (HA-N₂). We also assess the antioxidant properties of HAs-O₂ and HAs-N₂ from compost (HAC), Retisol (HAR), and Chernozem (HACh) and relate them to the HA biological activities. Changes in the HAC properties were analyzed using the following techniques: elemental composition, ultraviolet–visible and infrared spectroscopy, ¹³C nuclear magnetic resonance (¹³C-NMR), electron paramagnetic resonance (EPR), gel filtration using Sephadex G-75 gel, and potentiometric titration. The HA antioxidant properties were explored using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay (antiradical activity) and phosphomolybdenum assay (total antioxidant capacity). The HA biological activity was estimated by priming radish and wheat seeds (0.5 g L⁻¹ HAs, 25 °C, 5 h for radish and 14 h for wheat), followed by germination tests. Alkaline extraction of HAC in air vs. nitrogen resulted in a 1.2-fold increase in the O/C ratio and optical density at E₄₆₅, oxidation of aliphatic fragments, a 2-fold increase in the contents of functional groups, and a 1.2-fold increase in the number of paramagnetic centers. All HA-O₂ preparations have demonstrated an enhanced antiradical activity (1.3–1.6 times) and total antioxidant capacity (1.1–1.3 times) compared to HA-N₂. The Vigor Index of seeds primed with HA-O₂ was 1.1-to-1.8-fold higher than those treated with HA-N₂, depending on the HA origin. We demonstrate that alkaline treatment in air benefits the antiradical and biological activities of HAs, making such preparations more attractive for use as natural antioxidants and priming agents. This opens up new perspectives for using O₂-modified HAs as innovative plant stimulants in agriculture.

The goal of this work was to conduct a systematic review and meta-analysis of domestic and international data (a total of 687 data points) on the effect of

The study aimed to perform a systematic study and meta-analysis of national and foreign data (687 data points in total) on the eff ect of humic preparations (HPs) on crop yields. Specific objectives included evaluating the effi ciency range of HPs (yield increase as a percentage of the control) accounting for statistical uncertainty estimated via absolute median deviation, and assessing the infl uence of HPs characteristics, crop types, and soil properties on this metric. HPs effi ciency varied from -59% to +540% (mean 18%) and followed a non-normal distribution. The median effi ciency was 12 %, with lower and upper quartiles at 5% and 21%, respectively, and uncertainty of 99 %. Kruskal-Wallis test revealed that soil granulometric composition and HPs enrichment with trace elements did not signifi cantly aff ect efficiency of HPs. Key infl uencing factors included: cation salts of humate in HPs (Na salts were the least eff ective); HPs application method (combined soil and foliar application was most eff ective); soil acidity and humus content (higher efficiency at pH > 6.6 and humus content < 1%). Plants in the aster family showed the greatest responsiveness to HPs, while legumes and nightshades exhibited signifi cantly lower effi ciency. Under nitrogen defi ciency, HPs effi ciency rose to 22%, and most studies reported increased nitrogen and/or protein content in crop products. Th ese fi ndings suggest that HPs primarily enhance fi eld yields by improving plant nitrogen assimilation. The results indicate that promising future research should evaluate HPs eff ectiveness against reduced nitrogen fertilizer rates. Given rising fertilizer costs, even modest eff ects could prove economically viable. Further field studies should optimize HPs use conditions and methods, prioritizing identification of factors driving effi ciency uncertainty - preliminarily, application method and soil conditions (pH, humus content, and available nitrogen).

The increasing use of silver nanoparticles (AgNPs) as nanoagrochemicals raises important environmental and toxicological considerations of their usage. AgNPs influence soil microbiome functioning, which regulates essential nutrient availability. However, their effects on key chemical soil health indicators remain unclear, with existing studies limited to concentrations ≥10-fold above predicted environmental levels. The aim of the work was to evaluate the effect of AgNPs at a realistic concentration of 10 μg/kg on the principal chemical soil health indicators, including acidity, redox potential, electrical conductivity, contents of NPK, and soil organic carbon (SOC). In addition, dissolved organic carbon and nitrogen (DOC and DON) and water-extractable elements (Al, Ca, Fe, K, Mg, Na, P, S, and Si) were also examined. The laboratory experiment was carried out for 3 months on Retisol, Chernozem, and Solonetz. AgNPs stabilised with carboxymethylcellulose (AgNP-CMC) or polyvinylpyrrolidone (AgNP-PVP) were used. AgNP-induced changes exhibited non-monotonic patterns, peaking at 2–3 months of incubation. A statistically significant effect observed across all soils following AgNPs application included only increased water-extractable Fe. In addition, AgNPs increased nitrate content 1.1–1.4-fold in Retisol and Chernozem, while available phosphorus increased 1.4-fold in Solonetz. However, changes were transient, indicating no pronounced long-term impact on soil properties. Partial Least Square (PLS) analysis revealed that chemical soil health indicators and water-extractable elements do not reliably discriminate between control soils and soils amended with AgNPs. Although our study shows that AgNPs had neither markedly negative nor positive effects on chemical soil health indicators or water-extractable element contents, future research should prioritise field trials. Model experiments under optimised microbial activity conditions limit direct extrapolation to field scenarios.