SOIL PREPARATION

SUMMARY DETECTION OF COMPACTION

• Digging and inspection of pro- file pits before soil preparation is imperative to detect root im- pediments and decide which soil preparation methods to use. At the same time, soil samples for analyses must be taken in the profile pits. This should be done at least six months before the deep tillage to allow enough time for soil analyses and procuring of a soil preparation contractor. • Soil compaction can be deter- mined using several methods. These include, amongst others, bulk density, penetrometer resis- tance, soil shear strength, water infiltration rate, and unsaturated hydraulic conductivity. • Field and pot studies on grape- vines found penetrometer mea- surement of soil strength to be the most practical, easiest and quickest method to detect the degree, position and extent of soil compaction. Generally these studies showed a decrease in root

penetration with increasing bulk density and penetrometer resis- tance. Based on South African and other studies, a penetrometer re- sistance of 2 000 kPa is accepted as the critical value above which grapevine root growth becomes seriously impeded. • Penetrometer resistance was successfully used to determine re-compaction in soils, detect large clods due to ineffective soil preparation, compare the effec- tivity of different implements, and also to identify the cause for the decline of grapevines in patches in vineyards. • An instrument that measures the bulk electrical conductivity of the soil, namely the EM38 apparatus, is also increasingly used to deter- mine root restricting layers in the soil. More formal experiments are, however, needed to determine its effectivity in detecting and quanti- fying root restrictions in vineyard soils.

44 | DETECTION OF ROOT IMPEDIMENTS