SOIL PREPARATION

CHAPTER 3

FIGURE 3.1: A thorough evaluation and classification of the soil as well as soil sampling is essential well before soil preparation is carried out. Soil evaluation will indicate which implement to use while the analyses of soil samples will determine which, and how much, ameliorants to apply (Photo: J.E. Hoffman, Stellenbosch University). Samples from the different horizons should be kept separate, but samples from the same depths at different profile pits within a uniform soil can be pooled to obtain representative samples. During the inspection and sampling of the soil, thickness of the soil horizons should be recorded. In the case of stony soils where the stones are too large to include in the samples, an estimate of the volume of stones should be made. Such information should be supplied to the soil analytical laboratory since adaptations based on the volume of stones will be made to the ameliorant recommendation (Raath, 2016b). Profile pit inspections and soil sampling must be done well before (more than six months) the intended soil tillage operation. This will allow time for analyses of the soil to be completed as well as for finding a contractor to do the soil preparation. 3.2 Soil physical parameters The interrelationship between soil compaction, soil strength, water retention, aeration and root growth have been well-studied (Hillel, 1980) and methods exist to measure all of these. Soil strength increases drastically with a decrease in soil water content (Figure 3.2), and consequently measurements associated with soil strength, using instruments such as penetrometers or vane testers, must be done at water contents close to field capacity.

SOIL PREPARATION | 35