SOIL PREPARATION

CHAPTER 4

Root distribution of grapevines using core sampling and the subsequent recovering of the roots and measuring of root lengths were compared to results of the profile wall method in South Africa (Brink, 2005). This researcher found a reasonable good correlation (R 2 = 0.86) between the two methods. In practice, however, the profile wall method is much quicker and less labour-intensive than the core method and should therefore be the preferred technique for root studies for advisory purposes. The core method is less destructive to research plots and will therefore be a better method for researchers when root studies are required frequently, e.g. several times per season. In such cases, the use of mini-rhizotrons (Figure 4.4), consisting of underground transparent tubes and a camera system, would, however, be preferable since it is a non-destructive method that can be used to study chronological changes in root development in situ in a vineyard (McClean et al ., 1992; Bauerle et al ., 2008; Lehnhart et al ., 2008; Linsenmeier et al ., 2010). However, soil disturbance due to installation of mini-rhizotron observation tubes may cause root proliferation artefacts (Smart et al ., 2005). Consequently, these authors recommend a six month waiting period before reliable quantitative information regarding root dynamics can be collected.

FIGURE 4.4: Mini-rhizotron tube installed at an angle (typically 30⁰ or 45⁰ to the vertical) below the soil surface (left) and roots photographed inside the tube (right); white roots are actively growing (Photos: E. Lotze, Stellenbosch University).

Due to the sparse root distribution of grapevines compared to annual plants, estimates of spatial root distribution using mini-rhizotrons did not correlate with the monolith method (Linsenmeier et al ., 2010). Their work showed that it is difficult to quantitatively measure root length density using mini-rhizotrons.

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