BRANDON – Nitrogen is a major cost, so the most logical way to make GPS and variable rate pay is to reduce or re-allocate nitrogen.
However, farmers are discovering that it doesn’t work that way and AgriTrend agronomist Chris Paterson isn’t surprised.
He said there’s a new way to look at how variable rate technology can make money for producers, and nitrogen is one part of the new approach.
AgriTrend agronomists are finding that nitrogen often ranks as low as fourth in terms of financial payback when it comes to precision farming, he added.
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“We make a major mistake assuming nitrogen is the first factor we set out to control in a precision farming or variable rate plan,” Paterson said.
“Here’s another problem. Variable rate N is the big deal being marketed today. Go to any major farm show and there’s always a pack of companies pushing variable rate nitrogen as if that’s all there is to making a profit. It’s an easy message to sell because it sounds so logical. But that doesn’t make it true.”
He said a grower’s first priority should always be to identify and manage the most limiting factor preventing maximum profit. Nitrogen may be a major input, but producers typically put on enough so it’s not the limiting factor.
“There are nearly always one or two or even three factors ahead of nitrogen. Drainage is often the biggest factor limiting production. Then we have salinity, nutrient imbalance, compaction, variable rate fungicides and other factors to examine.”
He said achieving nutrient balance is the most important contributor to extracting profit from a field.
“The potassium to magnesium is one ratio that’s very important. Calcium to sodium is a critical ratio. Boron to nitrogen and sulfur to nitrogen are also significant,” he said.
“So if all you’re doing is variable rate nitrogen and ignoring boron and sulfur, then your variable rate program isn’t working. If you keep adding N to prop up the crop, you’re upsetting the nutrient balance even further. You’re doing more harm than good and you’re spending money on nitrogen your crop can’t use.
“You’ve got to think like a plant. If all you’re looking at is nitrogen, well, that’s not how a plant thinks.”
Agronomists can use correlation analysis to figure out how a growing plant responds in a specific field. This statistical method measures the relationship between two distinct factors, such as plant growth and nitrogen, or plant growth and soil moisture.
“We determine the most relevant factor impacting yield on each field,” he said.
“It’s very rarely nitrogen related. We find that drainage is usually the number one limiting factor, even in flat areas like Swift Current where people generally don’t think about drainage.
A properly drained field lets the farmer get out there two weeks earlier, instead of waiting for those little ponds to dry up. He gets a more uniform crop and an earlier maturing crop.”
Paterson said healthy vegetation in undrained low spots is often deceiving because it’s salad instead of grain. While they may produce the best yields in a dry year, in most years all they produce is vegetation.
He said it has as much to do with nutrient imbalance as it does moisture. Better drainage and a better nutrient balance can turn that salad into grain.
Paterson said most producers don’t realize they have salinity problems unless their soil surface is white.
“There’s a slight degree of salinity in a whole lot of areas. It’s costing money because normal inputs are going into those spots, but normal yields are not coming off. It’s not always feasible to treat salinity areas or rectify the problem, but you can stop pouring money into them. Adding fertilizer is like adding salt on top of salt.”
He said the best course of action is to identify and map the saline spots. They can still be cropped, but the prescription map should turn off the fertilizer applicator when it goes over those areas. For large saline tracts, some producers put the land into forage.
Compaction is another hidden problems that isn’t obvious to the naked eye. Sometimes the compaction is caused by machinery, but it can also be caused by soil chemistry.
“High sodium and high magnesium soil are very prone to compaction,” he said.
“It’s natural compaction. The weight of the top soil can sometimes be enough to cause compaction.
“But we all know compaction also comes from big machinery. Bigger drills and air carts, heavier tractors, big grain carts, semis in the field.
“The worst offender is a big combine on a sloppy field. If it’s so bad that you need to bring out a tractor to pull the combine through the mud, then you’re driving the compaction five or six feet into the earth. It’s no longer just a surface problem.”
Paterson said soil amendments such as sulfur, gypsum and calcium can help.
Ripping solves the problem down to about two feet, but no deeper. At a cost of $100 per acre, he doesn’t recommend doing a whole field unless producers are certain the whole field needs it.
“A lot of times, a half section field might only have 25 acres of highly compacted soil. The approaches, driveways and headlands are the worst,” he said.
“So you basically apply the variable rate principle to ripping or soil amendments. Only do it where it’s needed. Ripping corner to corner doesn’t pay.”
Paterson said fungicide is one of the best ways to make variable rate pay. On a half section field, the full rate $20 per acre might be required only on 80 acres. Another 80 acres might only need a half rate application.
“There’s not only the financial saving of reducing your input cost, but a lot of producers figure they lose five to six percent yield when they drive the sprayer through the crop at that time of the growing season.
“If you have a good map showing where you need to spray and where you stay out of the crop, it’s going to make money for you.”
For more information, contact Chris Paterson at cpaterson@agritrend.com.
