Properties of Humic Acids in Meadow Soils Irrigated with the Slope-and-Flooding System

Abstract

The still-advancing soil degradation and the related losses of soil organic carbon stocks due to the limited inflow of organic residues in agro-ecosystems encourage more and more soil protection. Establishing meadow ecosystems is one of the key methods of agricultural land use preventing losses of organic carbon in soils. Based on the research on the properties of humic acids, it is possible to determine the advancement of the processes of transformation and decomposition of soil organic matter. The obtained results may allow for the development of a soil protection strategy and more effective sequestration of organic carbon. Therefore, the aim of the research was to determine the properties of humic acids defining the quality of organic matter of meadow soils irrigated for 150 years with the slope-and-flooding system. The research was performed based on the soils (Albic Brunic Arenosol) sampled from Europe’s unique complex of permanent irrigated grasslands (the same irrigation management for 150 years), applying the slope-and-flooding system: the Czerskie Meadows. The soil samples were assayed for the content of total organic carbon (TOC) and the particle size distribution. HAs were extracted with the Schnitzer method and analysed for the elemental composition, spectrometric parameters in the UV-VIS (ultraviolet-visible) range, hydrophilic and hydrophobic properties and the infrared spectra. The research results showed that the HAs properties depend on the depth and the distance from the irrigation ditch. The HAs of soils sampled from the depth of 0–10 cm were identified with a lower “degree of maturity” as compared with the HAs of soils sampled from the depth of 20–30 cm, reflected by the values of atomic ratios (H/C, O/C, O/H), absorbance coefficients, and the FT-IR (Fourier transform infrared) spectra. The mean values of the H/C ratio in the HAs molecules of soils sampled from the depth of 20–30 cm were lower by 8.2% than those from the depth of 0–10 cm. The mean values of the absorbance coefficient A4/6 in the HAs molecules of soils sampled from the depth of 20–30 cm were lower by 9.6% than in the HAs molecules of soils sampled from the depth of 0–10 cm. The HAs molecules of the soils sampled 25 m from the irrigation ditch were identified with a higher degree of humification, as compared with the HAs of the soils sampled 5 m from the irrigation ditch. The results identified that humic acids produced in the many-year irrigated sandy soils were identified with a high degree of humification, which proves the relative stability of the soil’s organic matter. It confirms the importance of meadow soils for the carbon sequestration process. It should also be emphasized that the research area is interesting, although hardly described in terms of organic matter properties. Further and more detailed applicable research is planned, e.g., monitoring of total organic carbon content and comparing the properties of irrigated and non-irrigated meadow soils. Continuity of research is necessary to assess the direction of the soil organic matter transformation in such a unique ecosystem. The obtained results may allow for the development of, inter alia, models of agricultural practices that increase carbon sequestration in soils. In the long term, this will allow for greater environmental benefits and, thus, also increased financial benefits.

Humic acids in permanent grasslands of the Czersk Meadows Complex, north Poland

“…The results confirm the relationship found in previous studies of HAs in meadow soils conducted by Banach-Szott et al (2021a).…”

“…The percentage of clay fraction (<0.002 mm) was very low, ranging from 0.2% to 0.7% (Table 1). The results confirm previous research by Banach-Szott et al (2021a) for soils sampled in the same area but continuously irrigated by the slope-and-flooding system. Moreover, with depth, the amount of sand was seen to decrease and the amount of clay to increase (Table 1).…”

“…The pH values of the studied soils ranged from 5.2 to 6.9 (Table 1) and were similar to the soil pH values obtained in previous studies (Banach-Szott et al, 2021a) and in peat soils of northeastern Germany (Heller and Zeitz, 2012). Soil samples were characterized by an increase in pH with depth, with soils collected from 10-20 cm differing significantly from those taken from 20-30 cm (P=0.029, Table 2).…”

“…On the other hand, the levels of TOC and Nt in continuously irrigated soils were highest in the soil samples taken from the 10-20 cm layer and lowest in the 0-10 cm layer, 49.5 and 14.7 g kg -1 respectively (Banach-Szott et al, 2021a). This proves that mineralization processes dominated over humification processes in the 0-10 cm layer.…”

“…It is a continuation of research being carried out on the Czersk Meadows. In the previous studies (Banach-Szott et al 2021a), continuously irrigated soils were analysed. The total organic carbon content (TOC), total nitrogen content (Nt) and grain size composition were determined in soil samples.…”