FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

also be noted. For soil preparation of vineyards, it is desirable to collect samples from the topsoil and subsoil separately. It is also often desirable to sample underlying clay material separately, since salts can move upwards to the overlying soil layers during dry periods. Sample labels must include the depth of sampling. A sample of 1 kg is enough. Sampling in existing vineyards The first samples ought to be taken shortly after soil preparation to establish whether optimal soil conditions have been created. Samples must be taken per management unit. To ensure that samples are representative of the management unit, they must constitute sub-samples taken from different places from within the unit. In instances where soil has been ridged, samples should only be taken from the ridge.  For maintenance fertilisation, soil samples must be taken at least every three years. However, in very sandy or stony soils, where extensive leaching of nutrients occurs, samples must be taken every two years. These samples are taken in the vine row. Because soil composition can vary drastically over short distances, long-term soil trends are best determined when samples are collected at more or less the same place each time. This is achieved by marking vines where samples are taken. Areas of the vineyard that are growing poorly should be sampled separately. Cultivation actions will often disturb the transition between soil layers, samples should therefore always be collected at the same fixed depths, in order to compile a historical record. These results can then be correlated with fertiliser applications. If the person who is responsible for the recommendations does not have records of previous analyses, more than one soil layer should be sampled. Because lime and phosphate fertilisers do not react immediately, samples should preferably be collected at depths of 0 – 150 mm and 150 – 450/500 mm. Taking into account that few roots are found at deeper soil levels, it is not necessary to sample more deeply. If the soil is shallower than 450 – 500 mm, sampling should be limited to above the restricting layer, because the presence of underlying clay in the sample, may lead to meaningless results. Stony Soil If the soil is very stony and the stones are so large that they cannot be sampled, an estimate of the incidence of stones must be made, i.e. indicate the volume occupied by stones. This information can have a significant effect on the fertiliser recommendation and must accompany the soil samples to the laboratory. A stone correction is used in the estimation of gypsum, lime, potassium and phosphate fertiliser requirements.

14 | COLLECTION OF SOIL AND LEAF SAMPLES