Abstract
Only little is known about the rate and extent of structural evolution under the combined influence of tillage and wheeling. Whereas some quantitative information on the regeneration of compacted soils is available, the course and potential of structure formation and recovery under the absence of wheel traffic – as made possible by Controlled Traffic Farming (CTF) systems using permanent traffic lanes – are not well investigated and understood. Therefore the effects of tillage practices and field traffic organization on soil structure were studied in a crop sequence under practical soil management conditions on a loamy orthic luvisol at Tänikon, Switzerland (1187 mm mean annual precipitation, 8.0 °C mean annual temperature). From 2000 to 2008 the effect of no-till on soil structure evolution was studied on a formerly ploughed field and compared to continuously ploughed plots. Since 2008 the previous random field traffic organization was maintained in the ploughed and no-till plots, but changed to controlled traffic in plots formerly under shallow tillage and consecutively managed by no-till. Soil structure evolution was described by repeated samplings of undisturbed soil cores in the top- (10-15 cm) and subsoil (35-40 cm) and subsequent analysis of porosity, permeability and strength characteristics in the lab. In situ measurements of parameters characterizing soil water regime (volumetric water content, matric potential) and the soil environment (O2- and CO2-concentrations in soil air, oxygen diffusion rate, redox potential) under field conditions were done quasi continuously at several soil depths. Results show a slow evolution of structural properties in the subsoil and a limited structure formation in the absence of tillage measures in the topsoil. Soil structure evolution can be followed up in short-term cycles covering individual vegetation periods as well as in medium-term cycles covering crop rotation periods. In situ measurements of water retention characteristics and properties of soil environment revealed consistent but minor effects of field traffic organisation on processes depending on soil structure as well as on weather conditions.
Highlights
Soil structure is considered one of the key elements of soil quality, controlling many soil processes - thereby influencing many other soil properties - and defining exchange processes between soils and atmosphere, hydrosphere or biosphere
1.0 Cn 10 cm Cm 10 cm Ci 10 cm Conclusions The monitoring of structural properties demonstrated that soil structure evolved in at least two different cycles: The short-term cycle over one vegetation period was reflecting immediate impacts of mechanical loosening and wheeling on soil structure and is substantially depending on the prevailing weather conditions
The mechanical loosening of compacted soil structures and the compaction of the loosened soil by the impact of heavy vehicles is leading to high amplitudes and magnitudes of structural topsoil parameters in both the short- and medium-term cycles of structure evolution
Summary
Soil structure is considered one of the key elements of soil quality, controlling many soil processes - thereby influencing many other soil properties - and defining exchange processes between soils and atmosphere, hydrosphere or biosphere. Direct effects of soil structure on processes mostly depend on the pore system characteristics and are affecting the water and air regime of a soil, changing transport and storage processes for water and air [1]. Modified transport characteristics as a consequence of changes in soil structure influence the availability of oxygen in the soil. The consequences are impaired soil processes (e.g. mineralization) and chemically reduced metabolites such as N2, N2O, Mn(II) or Fe(II) [3]. These adaptations of metabolic pathways change the redox status of the soil environment, thereby for instance altering the chemical properties of nutrients and pollutants, which has consequences for their mobility, availability and toxicity [4,5]
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