Using Chlorophyll Maps to create N Prescription maps

From Wikiagro.com

In this tutorial, you can download a sample dataset with Chlorophyll Maps layers, and review sample applications, including:

Variability analysis → improves the knowledge about within-field variability, supporting management decisions, creating management zones, selecting areas for research, etc.
Support for directed sampling → Using the Chlorophyll Maps for directed sampling, the agronomist can find limiting factors.
Creating Prescription maps → Chlorophyll Maps can be used as base maps for N prescription maps.

Double click on the layer 'RE20090801...' to make it active and zoom to its extents.
Turn On Chlorophyll layers/maps for each of the dates in ascending order
Display the legend for the chlorophyll values, by clicking on the '+' sign to expand the legend to see how is the map classified
Values closer to green indicate higher levels of chlorophyll, which is rated from 1 to 8, where 8 is the highest.

Create an N Prescription map

After ground truthing the information, we've validated that there is a close relation between map values and N availability in the field.

Please review the GPS Module, and this tutorial: Plan your field visit and download points to your GPS device, to learn more about working with a GPS device for ground truthing purposes.

After the field visit, we then decide to do an in-season fertilizing operation, for chlorophyll classes 2, 3, 4, and 5 in the map.

We assume that we have applied a base rate of 100 pounds per acre, and now we'll apply additional N in a rate of 80 pounds in classes 3 to 6 , and 0 pounds in the rest. Since we are going to apply Urea (46% N), we need to apply 175 lbs/ac of Urea.

Open the Drawing Tools in the Left Panel, and then Select the Prescription tool to start the prescription wizard.
Select the reference layer, based on which the N prescription will be created. Click on Next >.
Define recommended input rates, entering the following values:
In the right side:
- Operation: N fertilizing
- Input: Urea
- Unit: lbs/ac

In the left side, enter 2 rates: 175 (lbs/ac), and 0 (lbs/ac), and their corresponding color, in the blue and yellow tones respectively.

Please note that if you are going to standardize rates in your operation, it's a good idea to use the Save option in the screen above to save the rates and colors definition for future use.
Next, assign the rates to the chlorophyll classes. Let's assign rates of 175 lbs/ac for areas with 2,3,4 and 5 levels, and 0 lbs/ac to the remaining areas.
Also, click on the 'Join polygons of the same class' option, so the polygons of the same class will be joined in the resulting layers
Next, enter the name of the layer where the prescription map will be saved:
- Name: N Fertilizing
- Group: [New Group], in the new group field enter: N Fertilizing
- Structure: Prescription (this value cannot be changed)
Click on Finish, and expand the 'N Fertilizing' layer just created.