Evolution of Variable Rate Equations

Knowing how variable rate equations have evolved and the customization that you have available to you, helps to differentiate you to Growers.

Variable Rate.  We've been hearing about Variable Rate Fertilizer for the last 25+ years.  It all starts with an Equation. However, how would you define it?  Here's one way to define it:

Equations?!?!  Series of conditions??!?!?!

Let's make this easier to understand, but not pretend that equations are simple in agronomic nature.

It really is just taking known pieces of information, or Attributes and the values associated with them, and manipulating them to accomplish a goal.

Level 1: Early Equations were designed to make the map 1 color. Mine the high areas and build up the low areas.

Pros:

• Better than whole field spread (flat rate).
• Attempts to account for crop removals.
• The yield goals can be adjusted to individual growers average yields.

Cons:

• The yield goals are a field average or yields the same.
• Does not account for productivity zones.
  
  
  

Level 2: Spatial Yield Goal

This type uses actual yield by soil type data to define spatial yield goals.

With a deep database, you can use the query tool to define yield goals by soil type.

Pros:

• Better than whole field yield goals.
• Soil types do have some correlation to yield.

Cons:

• Soil type does not always match yield.
• Does not account for productivity zones.

Level 3: Actual Crop Removals

This type uses a yield file allows for accounting for removal of nutrients at an even more precise level.

Pros:

• Ability to incorporate what was removed by the crop spatially.
• Growers can see the yield changes on their monitor and want to replace nutrient rates accordingly.

Cons:

• Does not account for productivity zones.
• Leaves Grower vulnerable to building fertility where a higher return is not possible.

Going Beyond Level 3 - Response Curves

A response curve tells us that at the lower fertility ranges there is a higher chance of a response to added fertilizer and the response is also larger.

Higher Productive areas have higher response.

Conclusions:

1. If you combine the A,B,C zones you will get the traditional curve.  It is just like taking a composite soil sample from a field.
2. If you look at each zone separately you will see that the A Zone doesn’t flatten out and continues to provide a high ROI while the C Zone levels off due to other factors like moisture.

Level 4: Incorporating Zone Management

Why Management Zones?

1. Historic yield data shows areas that consistently yield higher
2. Manage those areas independently (fertilizer, etc.)
3. Doesn't compromise the agronomy
4. A zones provide a high ROI
5. C zones have other yield limiting factors - do we need to build fertility as high?

Doesn't it make more sense?  Doesn't it look more complex?  But, it was easy to create!