Farm Progress

Yield maps considered entrance and final exam for precision agriculture

• Production variability always shows up in final yield numbers and yield monitors allow producers to capture this variability and see how they are addressing it in different parts of the field.

Paul L. Hollis

June 4, 2013

6 Min Read
<p> YIELD MONITORS AND yield maps have proven their worth is helping producers identify poor-performing parts of a field and in correcting any deficiencies in the field.</p>

No good cotton farmer likes to count his bales before they’re picked.

But it might not be too early — even during planting season — to start thinking about ways to map those yields to help increase efficiency and profitability in the fall.

Yield maps can be viewed as both an entrance and the final exam for precision agriculture, says Georgia Vellidis, University of Georgia crop & soil science professor.

Vellidis and other researchers have authored a publication funded by Cotton Incorporated that promotes the use of yield maps throughout the U.S. Cotton Belt.

Farmer-cooperators also contributed to the publication with on-farm case studies.

“The overall purpose is to promote the use of yield maps,” says Vellidis. “We created a booklet focusing on how yield maps can improve on-farm efficiency.

“We used case studies from working farms, and we wanted to show an economic benefit from taking information from a yield map and using it in your management to result in some kind of economic benefit.”

Production variability always shows up in final yield numbers, he says, and yield monitors allow producers to capture this variability and see how they are addressing it in different parts of the field.

Yield maps also allow growers to change their management practices to compensate for areas of a field that may need attention, he adds.

“In 1995, I produced my first peanut yield map in Georgia, and it showed the power of information from a yield map,” says Vellidis.

“There was a direct correlation between where nematode damage occurred and where lower yields occurred in the peanut field. This was clear evidence that the grower needed to apply nematicides.

“But peanuts were only one crop in a four-year rotation. So we started looking at how much yield he was losing to nematode damage and asked him to compare the loss in yield to the cost of a nematicide.

Bottom line

“The bottom line was that nematicides cost more than the yield gains he could expect by killing the nematodes. That’s the power of information and how you can make an operation more efficient.”

A yield map gives you an understanding of how much variability you have within a field, and whether it’s worth addressing that variability, he says.

“If the map shows you do have yield variability, and you manage it to address that variability, then the yield map at the end of that season or the following seasons will tell you how well you’ve done with your management practices. So it truly is the entrance exam and the final exam,” says Vellidis.

Yield maps also can show dry corners and major leaks in a center pivot irrigation system, he says. “Yield maps should have high resolution so that you can actually see the pivot tracks in fields.”

Vellidis says he encourages growers to go a step further and create “profit” maps from their yield maps.

“The profit maps are a basic tool to help a producer understand where a field is producing revenue, and where a field is causing losses.

“Areas of losses are shown in red on the map and greens show high profits. Areas that are red are net revenue losses in the field. The grower would have been better off by not farming those areas in the field.

“When you look at the budget for the entire field, more money could have been made by not farming those areas. But it’s not always feasible to completely leave out areas in a field.”

When engineers design yield monitors for farm equipment, they always conduct a design analysis to see where on the machine is the best location for a monitor, explains Vellidis.

“It’s clear that the best location for a yield monitor is somewhere in the ducts or somewhere in the basket, because that’s where the clean yield ends up.

“In the late 1990s when people were developing yield monitors, a lot of these studies were done. Several equipments companies researched this, and it turns out that the ducts are the best place to put these sensors.”

There are two types of sensors available on the market, and they all work on the same basic principle, he says.

“There’s the optical sensor, where you put an emitter on one side of a duct and a receiver on the other side of a duct, and you’re transmitting light beams across the duct.

“The light beams are then interrupted by the cotton bolls flowing up through the ducts.

“Some of them that remain on the market include AgLeader, which is compatible with many generations of AgLeader user interfaces.

Microwave energy

“John Deere’s cotton yield monitor uses microwave energy to measure the cotton’s flow into the ducts. The emitter and receiver are mounted behind the duct, and the reflectance of this microwave energy is used to count how much cotton is coming through the ducts. This requires plastic ducts to operate properly.”

Depending on the model of the yield monitor, sensors may be installed on two, four or six ducts. Cables from the sensors on the ducts lead to the cable of the picker where a user interface console is installed.

“The console receives and processes data from the sensors, displays yield information and yield maps in real time, and stores the data for later use.

Yield data is typically stored in pounds of seed cotton harvested per acre, although the user can choose to diplay yield data in many forms, including bales per acre.

One of the case studies used to illustrate the benefits of yield maps was from Paul Clark Farms in Courtland, Ala., in the Tennessee Valley region of the state. Clark reports as follows:

“We identified a low-yielding area approximately five acres in size in a 58-acre field from cotton yield maps created during 2003 and 2005.

“After the 2005 growing season, we decided to take this area out of production and apply chicken litter and gin trash to it for four years. The area also was planted to grass.

“In addition, we used the yield maps to develop a variable-rate corn seeding map for the field. For variable-rate seeding, we use three rates — 25,000, 27,000 and 29,000 seeds per acre — and planted fewer seeds in areas with lower yields and more seeds in areas with higher yields.

“Our normal seeding rate is 26,000 seeds per acre. We brought the five-acre area back into production during 2010.

“The 2010 corn yield map showed that most of the five-acre area produced about the same yield as the rest of the field. The field was in cotton during 2011, but we were not able to collect yield data.”

The cost of the yield monitor and associated mapping software for Clark was approximately $10,000. About $2,000 was invested for variable-rate seeding equipment.

“Yield maps and yield monitors are very valuable tools,” says Vellidis.

“You can’t document the effects of your management without yield maps. The best way to take advantage of the information provided by yield maps is to convert them to profit maps. This way, you can see the dollars and cents of your management practices.”

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About the Author(s)

Paul L. Hollis

Auburn University College of Agriculture

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