Beware Soil Type Sampling

April 10, 2005

Over the last 10 years SOYL have pioneered the use of GPS when soil sampling for nutrient management. We currently recommend the use of a technique called STRATEGIC SAMPLING. This approach combines the detailed information collected by a grid soil sampling system with additional sample points located where variation is more likely due to past management, soil type and yield variation. SOYL's preicison nutrient management service ensures that at least 1 sample location is taken in every hectare and at this location 16 sub-samples are taken. Sampling with maps and annual recommendations in this way costs a typical arable farm £5.00 per hectare per year.

From time to time over the last decade a number of suppliers have proposed a service that takes one soil sample location in each main soil type region of a field. This is sold on the basis that the soil type regions only need to be mapped once and that analysis cost are less. Services like this cost £2.80 - £5.00 per hectare per year. There are some serious drawbacks with this approach:

  1. The reduction in cost is not great
  2. P and K levels often do not correlate with soil type.
  3. P and K levels vary within soil type regions.
  4. Fields or part fields within even soil types still contain P and K variability.

By assuming that one soil test if reflective of a whole soil type region you may miss out some of the variation within that region leading to lost yield or less fertiliser savings.

Typically, soil zone sampling means you get one soil sample analysis per 5-8 hectare block. On a 400 hectare farm this means your fertiliser decisions are based on 80 analysis results compared with 400 analysis results using SOYL maps - an 80% reduction in accuracy.

Key points with SOYL

  • Small areas of deficiency ARE identified which can have a dramatic effect on yield.
  • Small areas of Mg deficiency are commonly found.
  • Service price includes; annual P, K, Mg and lime recommendations, advice and support, application maps for most GPS systems, no hidden additional charges and integration with yield maps where available.
  • Successful remapping results prove the SOYL approach works.

Sampling by soil zones may seem appealing due to lower initial costs but is not much better than W-pattern sampling.

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