Crops differ in terms of their soil requirements in order to perform optimally.

It is therefore important to analyse the soil to determine the chemical and physical properties before the crop, especially perennial crops such as fruit trees and vines, are planted. Soil acidity and low soil nutrient levels cannot be corrected overnight. It is also important to identify soils with high concentrations of soluble salts (saline soils), and soils in which the levels of certain nutrient elements may be excessive for the particular crop. After planting, soils should be analysed every two to three years. The water holding capacity of a soil, which is essential for irrigation scheduling, need only be determined once.

How should soil samples be taken

Soil sampling must be done correctly and the sample should be truly representative of the site in order to obtain accurate and reliable recommendations. There is no specific time for soil samples to be taken, but must preferably be analysed before fertilizers are applied.

Soils should be sampled separately where:

  • Significantly different types of soils are identified on one unit of land
  • The vigour of the trees or vines varies in the same block

Samples may be taken by means of an auger or with a spade. The sample should be taken from within the drip zone of the tree/vine, midway between two plants, after having first removed any surface debris. Normally it is only necessary to sample the top 60 cm of soil, since few roots are active below this depth. If the soil depth is restricted to less than 60 cm due to the presence of some limiting factor, such as a clay layer or water table, only the material above the limiting horizon need to be sampled. The topsoil (0-30 cm) and the subsoil (30-60 cm) should be sampled and analysed separately.

Wynboer - March 2002 - Soil Sampling For Nutritional And Irrigation Recommendations

Routine sampling

For routine purposes in existing blocks, each orchard, vineyard or unit of land should be sampled at no fewer than 6 uniformly distributed locations. All the topsoil samples from these separate locations should be combined in a clean bucket and mixed thoroughly. Approximately 2 kg of this mixture should be transferred to a clean plastic bag, sealed and labelled. Rock and stone fragments form part of the soil and should therefore not be removed from the sample. If the soil contains a large amount of stone the mass of the sample, which is to be sent to the laboratory, will need to be increased to at least 3 kg. The sub soils should be treated similarly. The samples are then sent to the laboratory for analysis.

Sampling for soil preparation

When samples are taken prior to the establishment of a new orchard/vineyard, it is necessary to dig profile holes in uniformly distributed locations. The holes must be deep enough to show any restricting layers. The placing of the holes must represent the different soil types. Mark the 0-30, 30-60 and 60-90 cm zones and chisel a sample from the side of each zone into a clean plastic bag. It is important not to mix the soil from the different zones. Each sample bag must be labelled.

For the purpose of sampling for soil preparation, the samples from the different holes should not be combined.

The label should contain the following information:

  • Owner’s name and surname
  • Farm name and postal address
  • Orchard/vineyard and sample name or block number (profile hole number)
  • Sample depth (e.g. 0-30 cm)

The following additional details will be needed if fertilizer recommendations are required:

  • Whether the recommendations are needed for soil preparation or for an existing orchard/vineyard
  • The age of the trees/vines
  • Fruit kind and cultivar
  • Vigour of trees/vines (e.g. weak, normal or strong)
  • Plant spacing (m)
  • Estimated yield in the next season

The following details are needed if an irrigation recommendation is required:

  • Fruit kind
  • The age of the trees/vines
  • Plant spacing (m)
  • Potential root depth (cm)
  • Is the orchard/vineyard ridged or not
  • Type of irrigation system (e.g. drip, micro, over head, flood)
  • Emitter type (e.g. blue base, 360o, 12-hole)
  • Delivery rate of emitter (l/h)
  • Water pressure (kPa)
  • Emitter spacing (m)
  • Width of irrigated strip (m)

This information is essential for the interpretation of the analytical results and for the formulation of recommendations. The accuracy of the recommendations will depend on both the extent to which the sample is representative of the orchard/vineyard as a whole, and on the accuracy of the information that is supplied. No recommendations can be given if this information is inadequate.

ARC Infruitec-Nietvoorbij provides a comprehensive analytical and advisory service. For further information contact the Soil Science Department at ARC Infruitec-Nietvoorbij ( 021 – 809 3105 ).

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