SOIL PREPARATION

CHAPTER 3

A more modern instrument for determining root restricting layers in the soil than those mentioned above is the EM38 (Figure 3.8). It generates small fluctuating electric currents in the soil that cause magnetic fields. These magnetic fields are then detected by a receiver placed at a specific distance from the transmitter. The instrument measures the bulk electrical conductivity that is affected by many factors such as salinity, water content, temperature, bulk density, and clay type and clay content. A calibration of the EM38 is necessary to determine the dominant variable factor in the field e.g. compacted soil layers.

FIGURE 3.8: EM38 apparatus used for determining the variation in various soil properties, amongst others also soil compaction (Photo: W. de Clercq, Stellenbosch University).

In Australia this instrument is being used to determine vineyard soil variability in, amongst other soil properties, soil depth (White, 2009) and in Italy to map homogeneous zones in vineyards (Priori et al ., 2011). The EM38 can e.g. indicate the transition from soil to a rock layer where this transition occurs within 1.5 m depth. This depth (1.5 m) is the measuring range of the instrument when placed in an upright position. In South Africa the EM38 has been used in a similar capacity for advisory purposes on wine farms. The authors could, however, find no results of EM38 use in formal experiments to detect soil restrictions in vineyard soils.

SOIL PREPARATION | 43