Using Productivity Maps
In this tutorial, we review a case of Management Zone delineation using NDVI layers from past crop seasons.
In this case we also call the resulting layer as a 'Productivity Map', given that the resulting zones have an associated NDVI median value which has a correlation with yields.
The benefits of generating Productivity Maps, include:
- 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 productivity map for directed sampling, the agronomist can find limiting factors.
- Creating Prescription maps → Productivity maps can be used as base maps for prescription maps, to reduce inputs in areas with low potential, and optimize areas with high yields
- Can complement / replace more data intensive approaches for applying variable rate technologies, such as soil grid sampling, or definining management zones based on yield mapping history.
Prior to carrying out these exercises, it's recommended to review: 'NDVI Maps'
- 1 Download sample data
- 2 Exercise 1 - Review NDVI layers, related with the Productivity map
- 3 Exercise 2 – Directed sampling based on the productivity maps
- 4 Exercise 3 – Create a Prescription map based on producitivity zones
- 5 Exercise 4 – Share the Prescription map with the applicator or other team members
Download sample data
For these exercises we are going to use a sample dataset: 'Sample Farm_Remote Sensing'.
To create a project, importing this dataset, we can follow these steps:
- Start GeoAGro GIS
- the first time you Start GeoAgro GIS, the Projects Panel will be empty. Click on the Projects Main Folder, and then on Create, to create a new project
- Enter as the Poject Name: 'Sample_Farm-Remote_Sensing' -
! Please make sure to Check on the option "Retrieve startup data for your project", so you can download the sample dataset
- As the initial dataset, select 'Sample_Farm-Remote_Sensing', which can be found under the 'Tutorials_en' folder:
- Accept the next options, and your project should be setup.
The first step is to analyze all the information related with the sample productivity map.
Review crop history and Vegetation index (NDVI) from previous years
In the references panel, under the Base Map group, you will find Landsat imagery layers, and the processed NDVI layers for each Landsat image.
Double-click on one the NDVI layers that you'll find in the reference panel, to turn it on and zoom to its extents: 'ndvi_LANDSAT_20100701_024_032'
In the name: ndvi_LANDSAT_20100701_024_032:
- ndvi is Normalized Differential Vegetation Index
- LANDSAT, is the satellite system used, in this case images from the Landsat Program
- 20100701 is the date that the image was taken, in format yyyymmdd, where yyyy is the year, mm is the month, and dd is the day.
- 24_032 is the path and row, which indicates what landsat image area was used. For more information on path/row visit the Landsat Program world reference system
The NDVI for landsat imagery for 20100701 (Jul. 1st , 2010) is shown.
Also, crop history can help us to understand the resulting NDVI maps and variability in Productivity maps. See Why is crop history important
- Please download the crop history for the sample farms from this link , and open the table.
The layer ndvi_LANDSAT_20100701_024_032 corresponds to July 7th, 2010; we can see that fields 1,3,4, had Corn planted, and fields 2,5 had Soybeans planted.
- Turn off layer 'ndvi_LANDSAT_20100701_024_032' (see how to turn a layer on/off)
- Turn on layer 'ndvi_LANDSAT_20090628_024_032'; this layer corresponds to the crops in June 28th, 2009 , we can see that fields 2,3,4, 5 had Corn planted, and field 1 had Soybeans planted.
Review Productivity maps
Now let's review how each Productivity map was created.
- Click on the group Productivity Maps, to expand it and see the list of productivity maps for each field.
- Double click on layer 'ProductivityMap_Field_1' to make it active, visible and zoom to its extents.
- Click on the plus sign next to the layer name to see the legend. We can see that values range from 'very low' (light green) to 'very high' (dark blue)
- Go to the Query tool, and select the option 'Query data by layer'.
The attribute table for all the objects in the layer will open.
- move to the column “Descrip” to see which NDVI layers where used to obtain the productivity map in Field 1. You may use your mouse to widen the table display, and the width of column 'Descrip'
- The 'Descrip' column shows that NDVI from dates Jul. 1st, 2010, and Jul 27, 2008 were used to create the productivity map.
Exercise 2 – Directed sampling based on the productivity maps
Create a Soil Sampling layer
- Select the new layer tool to create a new Field Scouting layer. It opens the Layer Creation Wizard.
- Select 'Vector layer' and click on next
- In the Layer Creation Wizard, enter the following values:
Group: [New Group], in the new group field enter: 'Soil Sampling'
Structure: Sampling Lab Results (this structure contains fields where you can enter soil attributes values, such as Organic Matter – OM, SoilPH, P or K)
- Using the Edit Cartography and layer properties tool , change the appearance of the recently created layer, to points size 10, color purple
Mark field visit locations
In this exercise, you will mark some locations that you´d like to visit based on the variability in your field.
- Make sure the layer 'ProductivityMap_Field_1' is visible, to use it as a reference for selecting field visit locations.
- Make the layer 'Soil Sampling_Aug2010' Active by clicking on it:
- Click on the Edit layer objects panel, and select the Add New Object tool.
Enter some sample locations by double clicking on the map area for each point. Select locations where productivity is very low (light green areas), and very high, so we can evaluate these locations in the field
- To assign an identifier to each point in the "Soil Sampling_Aug2010" layer, first select all objects by using the Select by rectangle tool.
- Then, in the Edit toolbar, go and click on Edit Selected Object's Data tool.
A data table will open. Complete the “Sample” column with correlative numbers; and any other attribute you wish to add.
Export Points to the GPS Module
Now we will import the recently created points into the GPS
- Go to the upper left-hand tab and click on GPS. This will display the window for the GPS Module of Geoagro GIS.
- Go to the Tools toolbar on the right, and click on the Import from GIS Module button.
Select the “Field Visit_Aug2010” layer in the dialog box. Click on Accept.
- In the next dialog box, drag the field 'Sample', in the right side, which has the Sample Nr., to match the field 'Identifier' on the left side. This way, the Sample nrs. will be shown as the identifier in the GPS device. Click on Accept.
- The points in the “GPS Points” layer have been imported to the map.
Upload the Points to your GPS device
Please note that you need to work with a GPS model supported by GeoAgro GIS and make sure that it's properly connected.
- Connect to your GPS:
Click on the ‘Connect to GPS Device' button. Automatically, GeoAgro GIS will detect if your GPS device is connected
- After connecting to the GPS, click on the Upload Objects to GPS Device button. GeoAgro GIS will inform that points are being loaded to your GPS device, as in the figure below
Now the georeferenced points with their corresponding identifiers are stored in the GPS device and ready to be set out on site.
Exercise 3 – Create a Prescription map based on producitivity zones
For this example, we are assuming that based on soil lab results, Soil PH is the limiting factor for the lower yielding areas. We are going to create a prescription map to apply lime in those areas.
- 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 lime prescription will be created. Click on next.
- In the next step, define recommended input rates, entering the following values:
In the right side:
. Operation: Application
. Input: Lime
. Unit: tons/acre
In the left side, enter 2 rates: 2 (tons/acre), and 0 (tons/acre), and their corresponding color, in the green and yellow tones respectively.
Please note: 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 Productivity maps area. Let's assign rates of 2 tons/acre for areas with 'Low' to 'Very Low' Productivity, and 0 tons /acre to the remaining areas.
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:
Group: [New Group], in the new group field enter: 'Applications'
Structure: Prescription (this value cannot be changed)
- Click on Finish, and expand the 'Lime' layer just created. Use the transparency option to show the productivity layer underneath, and how it corresponds to the 'Lime' layer.
In this final step, you can use different options to share your recently created Prescription map:
- If you'd like to send it to the applicator for instance, you can export it as a shapefile, using the Export Layers tool
- If you'd like to share it with other GeoAgro GIS user in your team, you can export it as a .lay file, using the Backup Layers tool
- If you'd like to print it or save it as an image, you can use the Print tool. To practice this option, you may find this tutorial: Communicating with maps useful.