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Variable Rate Crop Management

Variable Rate Technology (VRT) offers potential cost savings, provided there is sufficient paddock variability to manage.

What is VRT Management?

The independent management of variation within paddocks and across farms, to either reduce input costs or increase yield potential. The potential benefits of VRT come from two separate approaches.

A.          Correcting soil constraints such as pH, sodicity or subsoil compaction

    • This provides the greatest improvement in productivity and return on investment
    • Often requires amelioration once, or periodically.

Example:  Instead of applying lime at a blanket rate of 1.5 tonnes per hectare, targeting lowest pH areas with 3.0 tonnes and not applying any lime where it is not required.

B.          Optimising crop inputs for realistic yield potential

    • Ongoing differential management of inputs, based on underlying differences in yield potential across the paddock
    • Often the variation is based upon fundamental differences in soil type or topography, which cannot be altered.
    • Inputs are directed towards responsive and low risk areas within paddocks, away from areas that never perform, regardless of input levels.

Example:  Phosphorous replacement maps can be created from yield maps, so that Phosphorous fertiliser applications are targeted to those areas which produce the most grain, hence export the most Phosphorous.

How much variation is needed?

A recent CSIRO workshop suggested that a 1.0 t/ha difference in wheat yield between high and low performing zones was required to justify the time and effort to manage the variability. For many growers in southern NSW with uniform soils, there is insufficient variation within paddocks for VRT to provide significant benefits.

Steps for developing a VRT management plan

1.  Identify the variation

  • where are the boundaries?
  • do they change in wet/dry years?
  • do they change with crop type?
  • These can be determined using historical yield maps

2.  Quantify the variation between high and low areas

  • is the variation large enough to manage separately? i.e. 1.0 t/ha wheat yield difference from low to high areas.

3.  Determine the cause of the variation

  • is it something that can actually be managed?
  • rectifying a constraint such as pH will give much greater improvement than optimising fertiliser inputs.

4.  Devise management solutions and ground truth them

  • Additional information, tools and decision support systems can aid in decision making.
  • For example, deep soil Nitrogen testing, moisture probes and crop modelling programs such as Yield Prophet can be used to more accurately determine yield potential based on soil moisture and Nitrogen. This can help identify situations where Urea applications may not be necessary to achieve median yields.

5.  Create zones

  • This can be as simple as drawing lines onto satellite imagery. Software such as FarmWorks or Spatial Management System (SMS) can be used to create zones and prescription maps for VRT equipped machinery.

6.   Implement plan

  • Monitor and evaluate progress throughout the year and adjust accordingly.

Where sufficient variability exists, VRT management can help reduce costs by better matching crop inputs to realistic yields. Without significant variation across paddocks, VRT management can consume large amounts of time and effort for little gain. The process starts with the collection of high quality yield data, from properly set up and calibrated yield monitors. Assistance with this process can be obtained by contacting Rural Management Strategies.