Abstract
The objective of this study was to analyse the influence of tillage on soil aggregate stability using the ultrasonic dispersion method with different levels of energy. Experiments are performed with self-developed equipment at low vibration amplitudes of 0.5 μm, 2 μm and 5 μm. Ultrasonic power is 0.7 W, 8.9 W and 22.3 W for the three amplitudes. Samples of aggregates 2 000 - 250 μm of a degraded loamy silt Chernozem, a loamy clay Cambisol and a loamy sand Cambisol from eastern Austria were collected under different tillage regimes: conventional tillage (CT) with mechanical weed control and no tillage (NT) with inter cropping in winter. Measuring Soil Aggregate Stability (SAS) according to DIN norm showed that the stability decreased in the sequence loamy clay Cambisol &gt; loamy sand Cambisol &gt; loamy silt Chernozem. Influences of tillage could be observed with SAS for the last two samples mentioned. Ultrasonic dispersion tests at vibration amplitude 0.5 μm and 2 μm show higher stability of the Cambisol soils. Significant influences of soil tillage on aggregate stability for the loamy clay Cambisol and the degraded Chernozem were observed after short ultrasonic dispersion times and absorbed energies of 1 - 1.7 J ml<sup>-1</sup>. The measured aggregate stability decreased in the following order: Cambisol NT &gt; Cambisol CT &gt; Chernozem NT &gt; Chernozem CT. Differences in loamy sand Cambisol could not be detected with the ultrasonic method due to a low aggregation level of the macro aggregates. This study highlights the importance of quantifying the energy output of the ultrasonic equipment when analysing changes in soil aggregate stability, for the evaluation of tillage treatments. A more comprehensive analysis of aggregate stability can be obtained when using both, the wet-sieving SAS method and ultrasonic dispersion at low energy levels.
Highlights
The breakdown of soil into smaller aggregates and particles can be accomplished using ultrasonic equipment
Kirchberg no tillage (NT) has 42 % stable aggregates followed by Kirchberg conventional tillage (CT) (33 %) and Pixendorf NT (23 %)
The present results demonstrate the influence of low vibration amplitude on the dispersion of the macro aggregate fraction 2 000 - 250 μm of two soil types under agricultural use
Summary
The breakdown of soil into smaller aggregates and particles can be accomplished using ultrasonic equipment. According to the aggregate hierarchy theory, breakdown occurs when sufficient mechanical stresses are applied to overcome the attractive forces within the aggregates (Raine 1998). Acoustic pressure waves are emitted into the soil water solution, which cause cavitation, stressing of soil aggregates and breaking of aggregate bonds. Higher pressure waves occur and particle disruption is accelerated (Mentler et al 2004). The focus of this paper is the stability of the soil macro aggregate fraction in the range of 2 000 - 250 μm, coarse and medium sand included. Roots and hyphae stabilize the aggregates, inhibit erosion and are affected by soil utilisation (Tisdall and Oades 1982; Tippkötter 1994). A good soil structure is needed which in turn depends on the presence of stable soil aggregates (Amézketa 1999)
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