What are Surfacing Parameters?

 Requirements:

• Farms, fields, and cropzones created.
• Soil test layer with data.
• Determine if you will use a calculator previously loaded in AgStudio, such as the Illinois, Iowa, Tri-State, or Custom, or if you will upload a user-created calculator.

Answer:

Whether or not you need to set surfacing parameters depends on how your soil samples were collected. If your soil samples were collected using polygons/zones, you will not need to surface. If your samples were collected using point samples, you will want to surface your recommendations on the Surface tab in Advanced Nutrient Recommendation.  The purpose of this tab is to create interpolation of the data to make a recommendation. By using the Surface Tab, you are telling Advanced Nutrient Recommendation to look at the sample points and then look at other values at a certain radius to mathematically determine the value for the unknown areas in between.  You can change the settings for the following parameters:

Cell Size:  
How much area the squares represent on a map.  Cell sizes can have a wide range. Generally, a smaller cell size “looks” prettier because it has more transitions that are useful for reports. The Rxs will be built upon the interpolated values and aggregated into the larger application cells.

Search Radius: 
How far away from each square do you want the AgStudio algorithm to look to find a data point.  Visualize putting a quarter on top of each square looking for data points.  

Weighting:
Determines how much influence one data point will have vs. another data point.  You can set a value to help calculate that influence mathematically.  For example, if you enter 2 in the Weighting field, that calculates the inverse square of the distance.  So, a measured value twice as far away receives ¼ the weight (i.e. 2 squared equals 4, of which ¼ is the inverse).

Plateau Radius:
How far out dense data should be pushed based on the size of the plateau.  Here’s a couple of use cases for using a Plateau Radius.  

• First, nearby measures could overwhelm values further away based on weighting, so you could set a plateau.
• The second is if you’re using yield data.  There are a lot of data points there, so you may need to minimize the effect of those data points.  You can minimize the value of the cell’s data. In essence, the harvest data from outside the cell will not influence the value of the cell if the Plateau Radius is set to the width of the header.  The number used for the plateau is typically equal to the width of the header.

Recommendations:

The following recommendations are based on research from Bob Gunzenhauser, Granular Agronomy Science Lead.

Cell Size:
Set cell size to the width of applicator.
Note: For maps being presented to the user, use a smaller cell size of 20 or 30 feet and set RX cell size to application width.

Search Radius:  Soil samples are taken on different intensities of grids such as 2.5 acre, 5 acre, or even 10 acre grids. On a 2.5 acre grid, each of the points are approximately 330 feet from each other. For any given location, in order to include the data from 10 points in the interpolation, a search radius of 600 feet would be suitable. This is based on picking a location in the field and drawing an ever increasing radius around the point until at least 10 sample points fall within the radius.  Use the following guidelines:

• If your grid is 2.5 acres, use 600 ft search radius.
• If your grid is 5 acres, use 900 ft search radius.
• If your grid is 10 acres, use 1200 ft search radius.

Weighting:
Use 2.
Note: This means the measured value twice as far away receives ¼ of the weight.
(ex: 2 squared equals 4, of which ¼ is the inverse)

Bob’s caveat: “We are interpolating in between known sample points, and the further we are between points the more error there can potentially be.  Interpolation will always produce inaccurate answers in between known sample points, but the goal here is to be “less inaccurate.”

Plateau Radius:
Use 0.
Bob’s interpolation analysis did not use a Plateau Radius, so he can’t confirm this would improve the results or not. The main use of Plateau Radius is used when surfacing yield data, or planting data; where you would set the plateau to the width of the header or planter.

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