Influence of tillage methods on soil water content and geophysical properties

Abstract

This paper focuses on the development of a geophysical methodology as a tool for agricultural soil research particularly concerning the impact of different tillage. Geophysical interest laid on the suitability (practically and technically) resolution limits of the applied methods; on the reliability of the data on small horizontal and vertical scales (cm–dm) in volumetric water content (VWC) determination as well as consequences for the interpretation in terms of water retention capacity.In parts of the investigated area a large field was divided into sub‐fields, each of them subjected to different tillage since about 15 years: normal tillage (field I, with a 0.3 m deep impact plough), conservative tillage (field II, zero tillage, just seeding) and mulch tillage (field III, just the uppermost 0.1 m ploughed). Measurements were performed on two parallel profiles with geoelectrics, radar, induced polarization and nuclear magnetic resonance.The contrast of VWC and electrical resistivity was always larger between fields I and II on profile 1 as well as on profile 2 but for one exception: for the ground‐penetrating radar (GPR) data of August 2004 on profile 2 the largest contrast was between fields I and III, nevertheless the contrast between fields I and II was nearly as large as between fields I and III. How could the type of tillage of fields I and II be distinguished by the contrast of their physical parameters? Whereas on profile 1 field I was dryer and field II the wetter, on profile 2 field I was the wetter and field II the dryer one. On the other hand the laboratory samples from profile 2 showed a similar behaviour as the field data from profile 1. This (apparent) contradiction may have come from the respective precipitation history. Whereas some of the measurements have been performed during and shortly after a rain event, other measurements were performed after a longer dry period. During and directly after precipitation the soil on the unploughed field II could take up more, whereas the soil on the ploughed field could not hold as much water.The first layer of field I was more inhomogeneous than the first layer of field II and the second layer of field I was more homogeneous than the second layer of field II. The differences in homogeneity were caused by destructive process of the plough, which loosens the soil and exposes the soil to the weathering.