Organo-Mineral Interactions Involved in Herbicide Sorption on Soil Amended with Peats of Different Maturity Degree

José Dorado,Gonzalo Almendros

doi:10.3390/agronomy11050869

Abstract

The sorption of three herbicides (alachlor, atrazine and linuron) on samples from six peats of progressive degree of maturity (fibric, hemic or sapric types) and soil samples (dryland agricultural Calcic Luvisol amended with the peats) was determined. The extent of the sorption was examined in terms of peat maturity (up to 220 analytical descriptors of the peat material). In most cases, a sorption enhancement effect was observed in the peat–soil system compared with the sum of the sorption in peat and soil alone, i.e., a positive interaction leading to an increase in soil matrix reactive sites. The analytical characteristics of humic and bitumen peat subfractions were useful in forecasting sorption performance. This was the case for high molecular weight hydrophobic fractions, the extent of the alkyl domain in humic substances and oxygen-containing groups. Correspondence analysis illustrated how different characteristics of the peats played a distinct role in sorption in the herbicide–peat system or in the soil–peat–herbicide system. In the former system, there was a relevant bearing of parameters indicating low peat maturity, whereas in the second the sorption was mainly explained by peat colloidal properties, including the concentration and base saturation of oxygen-containing functional groups.

Highlights

The role of soil organic matter in enhancing the sorption of a wide variety of low molecular weight organic compounds incorporated into agricultural soils as pesticides has been the subject of several studies [1,2]
A general observation was that the highest sorption values were obtained in systems with the comparatively least decomposed organic matter, characterized by the dominance of fibers consisting of plant tissues, or by a low degree of association between humic substances and the mineral fraction
It is remarkable that the sorption values of herbicides were substantially different when studied on isolated organic matter and when studied on organic matter applied to the soil

Summary

Introduction

The role of soil organic matter in enhancing the sorption of a wide variety of low molecular weight organic compounds incorporated into agricultural soils as pesticides has been the subject of several studies [1,2]. Humic-type organic matter, of a highly variable nature depending on its origin, displays sorption properties highly dependent on the reactivity of its surfaces, and on diffusion processes, i.e., dependent on the microporosity of the sorbate [10]. In this regard, the total content of soil organic matter, and its chemical structure, systematically has a significant effect on its environmental properties. There are still few studies on the importance of the composition and structure of soil organic matter in its role in the retention of pesticides [13,14,15] and, in particular, on the extent to which the organo-mineral interactions can regulate the sorptive behavior of organic matter in the function of different types of soils [16]

Methods

Results

Conclusion