For decades Mark Chapman was aware of the differences within his fields.
“We’re known that we had high-yielding regions and lower-yielding regions,” says the Bowling Green, Ky., no-tiller. “Lots of times we knew why, but we weren’t able to do something about it.”
But that all changed once he was able to bring GPS onto the farm. With the ability to collect site-specific data, he can also take site-specific actions to address those issues using variable-rate technology (VRT).
At the 2021 National No-Tillage Conference, Chapman shared his strategy for variable-rating fertilizer and seed, and his advice to other no-tillers on successfully implementing the technology on their own operations.
Start with Why
The first step to using VRT, Chapman says, is to ask yourself why you want to use it in the first place. That means setting your goals.
Chapman’s journey into VRT began in 2008 when a fertilizer dealer encouraged him to try grid soil sampling and variable-rate dry phosphorus (P) and potassium (K). Chapman had been fertilizing for his fields’ averages: drawing down fertilizer on higher-yielding areas, while building up lower-yielding spots.
His goals at the time were to reduce his fertilizer bill, address pH variation, improve low-yielding areas, and apply inputs more efficiently for a more profitable return.
As he’s implemented the technology, his goals have become more focused and he now says his primary objective is to place fertilizer and seed where the probability of a return is the greatest and establish a profitable fertility level for each field by variable-rating P and K to maintain fertility levels.
“I use the word probability because we call it precision agriculture, but in many cases, it’s as much an art as it is science,” Chapman says. “We’re not aiming at a fixed target,” he says.
Along the way, Chapman realized he was spending too much money on grid soil testing and felt he could achieve the same goals with management zones. He also discovered his pH didn’t vary as much as he expected.
COMPARING TARGETS. Bowling Green, Ky., no-tiller Mark Chapman creates these tables for every hybrid he plans on using on his farm. Seeding rates are determined by whether the field is low-, average- or high-producing, as well as the percent an area will likely yield based on the field’s multi-year average. For example, if he’s seeding variety A on a high-producing field, he’ll push the population to 34,000 seeds per acre for the zones that yield 120% of the overall field’s average.
Gather the Right Resources
Once you’ve determined your goals, Chapman says the next step is determining what operational resources you need:
- Agronomic Expertise — If it’s not you, you need someone on your team who has an eye for agronomic recommendations and sorting through information to grow a great crop.
- Precision-Application Equipment — If you want to do variable-rate seeding, you’ll need a planter with those capabilities. If you’re interested in variable-rate fertilizing, you need to decide if that’s something you’ll do or if you’ll outsource it to someone who has VRT capabilities on their equipment. Chapman also includes the combine in this category because one of the keys to VRT is building data, “and that starts with really good yield data over time.” So it’s a good idea to consider whether your yield monitors need any adjustments.
- Precision-Capable Software — This is necessary for both data storage, analysis and creating variable rate prescriptions.
- Quality Operators — Whether it’s you or someone on your team, you need to trust whoever is in the tractor seat to know how to work the technology, not only to spot problems but also to correct them.
- Labor and Equipment — These two are necessary for timeliness in the season, Chapman says. “We can add a lot of high technology, but if you lose timeliness when it comes to planting, you may give up any yield potential that you gain,” he says. “You need to make sure that the infrastructure is there.”
- Time — Chapman spends a lot of time on analyzing his data and deciding, “How do I use what I know?” It’s not a one-time task. View it as a moving transition with a strategy.
Look at Soil and Yield Data
The next step is to establish a benchmark, Chapman says. This requires both good quality yield data — a minimum of 2-3 years — as well as soil test results.
Chapman’s current soil sampling protocol is to sample every 2 years around January and February after soybeans. Most of Chapman’s farm is on a 3-crop, 2-year rotation: corn, winter wheat, then double-cropped soybeans. But he does have a few fields in a corn-soybean rotation because they have fragipan soils, as winter wheat does not like wet feet.
BUILDING MANAGEMENT ZONES. Mark Chapman produced this map based on multi-year corn yield data. Creating these maps allows him to see where he has uniform areas, so he can manage those zones separately. He points out that areas don’t need to touch each other for them to be in the same zone. In this map, zone 11 is actually broken into three smaller areas. Because they act the same, they are managed the same.
He prefers a 2-year sampling program to a 3- or 4-year program because he feels the latter allows too much time to pass between management decisions. He also chooses that time of year because crop residue that is breaking down could be releasing fertility that wouldn’t show up if samples were pulled in the fall immediately after harvest.
Whenever a no-tiller chooses to soil sample, Chapman advises sticking with it so that data is more likely to be consistent.
Chapman manages his own soil sampling and typically pulls cores 4 inches deep, a depth recommended to him because he no-tills. But after consulting with his soil testing lab, he decided to pull 5-inch depths in 2020 to see if anything was different.
“If you want to look at something in a different way, it’s kind of nice sometimes to pick it up and look at it from different angles,” he says.
He also makes sure he doesn’t pull cores from overlapping areas. Because his fertilizer trucks spread on an 80-foot width, there’s a high probability that fertilizer will overlap on the headlands, borders, and along that 80-foot range, which would cause those samples to test higher.
He uses Bad Elf for enhanced GPS on the iPad he puts on his 4-wheeler for soil sampling, which gives him about a 3-foot accuracy. This pairs with Granular’s AgStudio, the software he uses to manage his soil data and create VRT prescriptions.
Usually within 48 hours of overnighting his soil samples, sometimes sooner, the results are available to download and he can pull them into AgStudio to start working on the numbers.
“That can be pretty handy if you get into a spring where something happens and you had to sample it later, and you still want to get a decision made on what you’re going to do before you plant,” Chapman says.
This is also where precision ag becomes more of an art than a science, he adds. He doesn’t obsess about the fine data points but instead looks at the overall trend — like if a zone suddenly jumped from 35 pounds of phosphate per acre to 64.
“Well, I know that didn’t happen in a year,” Chapman says. “So I’m comfortable saying, ‘Look at the whole field. Was there a trend that everything was going up? Maybe I want to go back out and re-pull the sample.’ But if you’ve got enough long-term data, you say, ‘I’ll just ride it out and I won’t look at that.’”
With a solid database of yield and soil test results, the next step is to determine how you’ll variable-rate your fertilizer and seed.
VRT Fertilizer Strategy
Chapman’s first step to variable-rating fertilizer was to build management zones based on field history, soil type, multi-year yield data and any water characteristics.
Field history is evaluating how the land was used and treated before. In his area of south-central Kentucky, it’s not uncommon to have fields that grew tobacco or were once cattle or hog lots. The key is to look for any obvious places to draw boundaries. On one of Chapman’s fields, he had combined two fields into one. One side was average-producing ground, but the other had been abused over time, so that was a natural spot to create his first boundary.
“I’ll spend at least 2 days a year doing seeding rates because I really want to look at that data…” – Mark Chapman
Chapman then considers soil type and multi-year corn yield data. He only uses corn yields because soybean and wheat yields can be skewed by weather.
“You could have an excellent bean crop, but the best-yielding ground is disappointing because it had too much water,” he says. “And freeze damage can cause the normally highest-yielding wheat areas to be the lowest. So I tend to stick to corn because there’s a really good correlation with corn and the quality of the soil.”
Stacking yield data from several years allows him to see where he consistently has higher or lower producing areas and determine whether he should manage them separately in their own zones.
Finally, he considers how water impacts the fields. Areas that have fragipan soils, have been tiled or are more prone to flooding should be looked at differently, he says.
Once his management zones are determined, Chapman starts creating his P and K prescriptions.
First he looks at whether his soil tests suggest the zones need to be fixed for P and K. He evaluates whether a zone is abnormally high or low in either nutrient. If it’s too high, he assesses whether he can mine its fertility and perhaps avoid spending more on a zone that’s not likely to bring a positive ROI.
“Maybe it’s that spot in the field where you think, ‘Man, this is good soil, I really ought to be able to push the yield better here but it’s not responding,’” Chapman says. “Well, perhaps it’s something that can be adjusted with your fertilizer application.”
He primarily bases his prescriptions on crop removal rates. He’s learned from soil testing that his fertility levels stay pretty well balanced this way — they’re not building up or drawing down.
But he’s also learned that you need to continue monitoring soil tests to make sure they’re accurate. He discovered that on his corn-soybean fields, P levels were dropping despite using crop removal rates. Over time he’s increased the crop removal rate of P for corn.
Now that he has his system in place, it doesn’t take Chapman too long to create his fertilizer prescriptions for crop removal, which is crucial because he’s usually harvesting corn in September and then seeding winter wheat in October. Unless there are any changes he wants to make, once he gets all of the harvest data from the combine into AgStudio, he can run the software scripts to create the fertilizer prescriptions based on crop removal rates. He says he can easily do his whole farm in 1-2 hours.
VRT Seeding Strategy
Chapman’s approach to VRT seeding is similar to his fertilizer strategy. Using his multi-year yield analysis, he comes up with field averages in AgStudio, which eliminates any outliers.
He does this every year because as the field changes from variable-rating and time spent under his management system, he sometimes finds areas that were once low-yielding have improved to average.
EVALUATING CORN HYBRIDS. In this map, which is Mark Chapman’s highest-yielding field, he shows what stacked crop removal data for potassium based on corn looks like. The block of green bordered off is a new hybrid he tried, which yielded 30-35 bushels higher than the one he planted in the rest of the field. “When you’re talking about that much difference in crop removal, I can go in and account for that with variable rate,” he says. “This is just a picture of what the potash removal was from that difference.”
That results in a map that shows him where his high-, average- and low-producing spots are in a field. From there, he can create a seeding rate map and tailor the seeding populations to those areas. In the example he shared, he would use a high seeding rate for the zones that yield more than 115% of the field average, and lower the rate for zones that produce 85% of the average.
“I can adjust where those breaks fall,” he says. “In a field that has a super high yield potential, I may want to up the seeding rate when the yields are 105% or higher. So I lower that down because I want to take advantage of that inherent high yield over the whole field.”
He also adjusts the seeding rate by the hybrid he’s planting. In the “Target Seeding Rate” chart, he shows an example of two varieties he created seeding rate charts for, based on whether a field is low-, average- or high-producing, and then breaks it down by the percent of the average yield.
For example, if he wants to seed Variety A on an average field and he expects one zone to yield less than 65% of that field’s multi-year yield average, then the seeding rate will be 28,000 seeds per acre. On the other hand, in a high-producing field, if a zone can yield 106-120% of the average, he bumps the rate up to 34,000.
Chapman says he makes a chart like that for every variety he anticipates using on the farm each year, and he recommends writing a prescription for all varieties that you might plant on each field. If your planting order changes due to a wet spring or equipment breakdown, you’ll be ready to go with multiple options.
He also recommends leaving a flat rate pass in the field as a check strip to evaluate your decisions. In 2012, he planted a test strip with 34,000 seeds per acre. Thanks to the drought, he discovered that under that stress, 34,000 seeds per acre yielded the same as 29,000.
“If it could yield, under that stress, at 34,000 the same it did with 29,000, then I’ve got a variety that’s pretty adaptable and the population’s not going to bite me so hard,” Chapman says. “Maybe it’s another variety that you begin to push populations and you hit a certain population and anything above that just flattens out. There’s not a response even in a high-yield year. And I’ve seen that as well.”
Creating seeding prescriptions takes more time than the fertilizer ones because Chapman likes to look at averages from different years. For example, since 2012 was more of an outlier, he’ll put it in and take it out of his multi-year yield analyses to compare how it changes his scripts.
“I’ll spend probably at least 2 days a year doing seeding rates because I just really want to look at that data,” he says. “Once I get that normalized yield set, then I can go in and just run the prescription according to the script and it’s going to kick out what I need. Once you get the scripts built, you don’t have to build them every year. I have to go in and tweak them as the varieties change, but it’s not like starting from scratch.”
Higher Yields Bring VRT ROI
Prior to 2008, Chapman only had one year where corn yields averaged over 200 bushels per acre. But since 2008, he’s had the best farming years of his life, averaging over 200 bushels in 6 out of the last 8 years.
“I don’t want to take credit for what the gift of rainfall gave me on yields, but I have done some regression analysis and there’s more going on than just the weather,” he says.
While genetics and pushing populations have been part of it, he believes the management changes from VRT have played a big role. His fertilizer use has gone up a little bit, but he’s more focused on applying it where he can get a response and backing off on areas where it won’t pay off.
“If my fertilizer bill is relatively the same and my yields are going up, then that’s where the payoff is,” he says.
