The benefits of farm/paddock management zones

by

Todd Buck

Management zones for soil amelioration

Paddock or farm management zones can be an effective way to develop targeted sampling strategies that increase the value of your soil testing and may support variable rate amelioration.

The concept of using such zones for variable rate management is well established, but the various methods for creating them are often used interchangeably without explicitly considering the management actions that they will be used for.

The variability captured by management zone maps is defined by the data used to form the zone, rather than the characteristic that is being measured and managed. For example, yield maps are the result of multiple factors over the length of the growing season with Liebeg’s law of the minimum suggesting that the most severe constraint will determine the yield of any individual plant. Consequently, low yield in one part of a paddock may be due to an entirely different reason than the same low yield in another and require different management to achieve true yield potential. Put another way – because a yield map is driven by so many things, it may not correlate to any one underlying management factor.

If we wish to create zones that can effectively drive management, not just capture areas that look similar at a surface level, a more effective approach is to define our goal in agronomic terms and then select the most appropriate methods to measure and define the variability. For example, the data used to develop a VR lime strategy for surface acidity may be different from the data required for a VR phosphorus replacement strategy or a VR gypsum strategy to address sodicity through the soil profile.

ECa measured using EM38

Management zones and strategic sampling plan

The benefits of using EM38 to create management zones

Electromagnetic (EM38) surveys can be used to capture soil variability within fields and delineate soil management zones. An EM38 sensor measures the apparent electrical conductivity (ECa) of soils, which is dependent on the volume and type of water, salts, clay, and rock within the soil. Due to this range of variables, ground-truthing via soil testing within each zone is essential to understand the context of the spatial variation described by the maps.

EM38 results provide powerful insights into soil variability and create evidence-based and reliable management zones for more targeted management. EM38 can also be combined with elevation data to create soil management zones.

These soil management zones form a foundation for:

  • Establishing a geo-referenced deep soil sampling strategy,
  • identification of sub-soil constraints,
  • strategic soil nitrogen sampling,
  • VR seeding programs,
  • Development of VR Irrigation strategies,
  • along with the accurate location of soil moisture probes (required in some Carbon ERF projects)

As EM38 is conducted every 10 years, it is extremely cost-effective. At less than $20 per hectare, amortised it is < $2/ha.

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