Chromatographic characteristics (HPLC, HPSEC) of humic acids of soil fertilised with various organic fertilisers

Abstract

The aim of this study was to determine the effect of the size of the soil particle containing organic matter, the type of organic fertiliser (cattle manure, vermicompost, straw) and the decomposition time of these fertilisers in soil on the hydrophilic–hydrophobic properties and polydispersity of humic acid molecules. In the model incubation experiment, organic fertilisers (cattle manure, vermicompost and wheat straw) were mixed with soil material (sandy texture). The soil was sampled for testing after one and three years of incubation. Each sample was separated into two fractions according to graining, grain diameter>0.1 mm (sand fraction) and<0.1 mm (silt and clay fraction), and humic acids (HAs) were isolated. For the HAs isolated, hydrophilic–hydrophobic properties were defined using RP-HPLC, and the division was made into low- and high-molecular-mass fractions (HPSEC). It was demonstrated that introducing organic fertilisers into soil resulted in an increase in the proportion of hydrophobic and high-molecular mass fractions and a decrease in the proportion of hydrophilic and low-molecular mass fractions in the HA molecules. Highest values for the ratio HIL/ΣHOB and lowest values for S1/S2 were noted for HAs of soil mixed with straw. HAs isolated from the fine-grained soil fraction demonstrated a higher degree of ‘maturity’ than HAs from the coarse-grained fraction, which was seen as higher values for HIL/ΣHOB and lower values for S1/S2.

Keywords:

• organic fertilisers
• humic acids
• polydispersity
• hydrophilic and hydrophobic fraction