What is a planting prescription?

Friday, April 4, 2014

Seems like the 3-day rain has finally ended, with a total of 3.3″ (89mm) received.  We can use this rain-delay time to review the planting prescriptions that we created.

What is a planting prescription?  It is a map of a field that shows the areas that are assigned to different populations for use during the planting operation.  Here at Carnahan & Sons, we use a soil survey map as the basis of our soybean planting prescriptions.  Each soil type has an inherent productivity capability.  We categorize each of our soils into one of three productivity classifications, but if you desired to be more specific, you could assign a particular population to each of the different soil types.  This classification is based on a study of the properties of each soil, plus our experience with each of them.  Each of our fields has from one to nine different soil types.

Here is the map of soil types for our Steen Hill Field.   It is shown as open in our JD Apex software.

Here is the map of soil types for our Steen Hill Field, shown as opened in our JD Apex software.  Using the legend at the bottom, you can see Alford soils (with 3 different slopes)… as well as Birds, Iva, Sylvan, and Patton soil types.

Using the JD Apex software, we create the planting prescriptions in the office computer. With just a few clicks (about 30) of the mouse, the soil map is converted into a new map, showing the 3 population rates.  We logically assign red color for low population, yellow for average or medium population, and green for high population.

The soybean planter is calibrated in pounds per acre, not in seeds per acre.  Because each variety has a different number of seeds per pound, we must create a prescription for every variety that we anticipate may be going into every field.  We use approximately 140,000 seeds/acre for low, 165,000 for medium, and 190,000 for high.   The population rates are assigned in a counter-intuitive way, with the lower populations going to soils with higher productivity capabilities and vice versa.

Here you see the above soil map of the Steen HIll Field transformed into a new planting prescription map.  You can see the areas of the field with relatively high, medium, and low productivity.  This field is about 108 acres.

Here you see the soil map from the picture above transformed into a new planting prescription map. You can see the areas of the field we’ve assigned to high, medium, and low populations. This field is about 108 acres.

The maps are saved inside the Apex software.  It can then be transferred to the internal memory of the GreenStar3 2630 screen in the tractor in one of two ways.  Pre-2012 tractors receive this information by placing it on a USB thumb drive, and then plugging that into the 2630. In our 2012 and newer machines, the information can be sent wirelessly via JD Link and 2-way Remote Display Access… which involves an MTG antenna box in the cab and some type of cell phone signal.

Once we head to the field to plant soybeans, this technology operates like this:  As the satellite-guided tractor runs over the field, the GPS receiver reads its location.  The on-board computer inside the GS3 screen then utilizes this location information, and matches it to the planting population for that specific spot from the prescription.  This, in turn, sends commands to the planter’s (air cart, really) metering system to apply the corresponding seeding rate.  As the tractor moves from one population zone on the map to another, you can see the read-out on the GS3 change the population on-the-go.   This type of precision matches an optimum planting rate for the soil type.

The utility of these prescription maps makes them valuable to us.  A net result of this technology is a savings in the cost of soybean seed used, compared to using a single seeding rate for all acres.  Our experience has demonstrated a cost savings over the last decade that we have used this technology of 10%!   In 2014, that’s about $7 per acre.

We have used this variable-rate seeding for soybeans for many years.  In recent years, we have experimented with this technology in our corn planting.  The difficulty we have found is that we cannot quantify a cost savings or yield boost from using it for corn.  Therefore, we will not be using this variable-rate technology in corn for 2014.

We do utilize the map-based overlap control on our corn planter.  That will be a topic for later explanation, but in summary, it makes for cleaner headlands, and saves expensive corn seed.  Our best guess for this technology is a savings of 2% of seed cost, because all of our fields are irregularly shaped, and have ‘point rows’.

Have a good weekend.  Do you have a favorite in the NCAA Final Four?

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1 Response to What is a planting prescription?

  1. casifarm says:

    Reblogged this on Carnahan & Sons, Inc. and commented:

    Since we’re planting double-crop soybeans (DCB), I thought I’d offer this previous post about planting by prescription

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