Die Bodenkultur - Journal for Land Management, Food and Environment

A. Voelkner and R. Horn:

Influence of anaerobic digestates on dispersion of soils – impact of soil texture and cations of different valence

Summary

The by-products of the biogas production are digestates, which are used as nutrient-rich organic fertilizer on agricultural soils. The applied digestates add besides polyvalent ions, also vast amounts of monovalent cations (e.g. sodium and potassium) and carbon (lignin, hemicellulose) to the soil matrix. Especially the monovalent salts can induce soil dispersion and, thus, contribute to the weakening and degradation of an intact soil structure. To quantify the vulnerability of a soil to disperse after the application of digestates, the amount of readily dispersible clay (RDC) can be used. From the amount of RDC, it is possible to deduce the soil stability at the particle-scale. The consequences of soil dispersion are crusting, colloid leaching and erosion of soil surfaces. Therefore, the aim of this study was to assess the impact of a medium amount of digestates (equivalent to 30 m³ ha-1) of maize and sugar beet silage on clay dispersion and the cation exchange capacity (CEC) of a Cambic Luvisol and a Podsol at different scales. The digestates were applied at the surface of homogenized and structures lysimeters. The results showed dispersing but also aggregating processes, especially in the structured soil (up to fivefold higher amounts of RDC were found). The application of digestates from maize monofermentation containing more sodium resulted in inceased dispersion of soil particles. Nevertheless, besides the amount of monovalent cations, the accessibility of sorption sites of soil particles appeared to be the most important factor for the development of soil dispersion. Key words: Anaerobic digestates, dispersion, readily dispersible clay (RDC), cation exchange capacity, soil stability.