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Soil Sampling and Analyses

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Soil sampling is possibly the most neglected step in soil testing, and the greatest source of error in the whole process. Since soil characteristics are variable both in time (temporal) and space (spatial), it is essential to get an accurate measurement of nutrients by adjusting the sampling strategy to adequately represent the variation in soil and land use. Bulking or mixing soil from several locations to create an average (or composite) sample is a common procedure. However, averages can hide problems if there is a big range in properties of the soil you have sampled.

Establishing a monitoring program

  1. Start by selecting at least 3-5 paddocks that will be regularly monitored.

    These should represent a range of cropping conditions on your farm such as:
    - paddocks at different points in a standard crop rotation (same soil type),
    - paddocks on different soil types under the same rotation,
    - paddocks with typically good vs. typically poor crop performance,
    - paddocks which represent different soil management practices (e.g. minimum vs. conventional tillage, with vs. without grazing).

    Avoid fences (especially headlands), gateways, tramlines, water troughs, shelterbelts and areas of double cultivation (e.g. paddock diagonals). Also avoid obvious dung and urine patches, stock camps and small areas of unusual crop growth (high or low).

  2. Determine the properties of the soil to be monitored in each paddock.
  3. Measure soil property indicators once each year, at about the same time each year and under approximately the same environmental conditions
  4. Follow a consistent pattern of sample collection and measurement on each paddock 
  5. Record results
  6. Identify paddocks with indicator values that fall outside the optimum range and determine a suitable course of action.
  7. For each indicator, note consistent patterns of change in the short term (2-3 years) and trends over the longer term (>3 years).

Soil monitoring can be carried out after crop harvest or before seeding in autumn, but before the paddock is cultivated. Sampling closer to sowing will better reflect nutritional status which may be affected by out of season rainfall. Do not monitor directly after the application of soil amendments or fertiliser application.

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