VRT May Not Fit Every Farm

Marcel Van Staveren needs to see more research to convince him that variable rate fertilizer application technology (VRT) can produce any better results on his Saskatchewan farm than him just knowing the productivity of his own land.

Van Staveren says the concept of VRT has merit, but on his farm with fairly consistent yields on soils within the Moist Brown Soil Zone, he can manually adjust fertilizer application rates on those relatively few acres he knows have potential for lower yields.

“I certainly can’t make a blanket statement that variable rate technology shouldn’t be considered,” says Van Staveren, who farms with two brothers in the Griffin-Filmore area of southeast Saskatchewan. “But on my farm, the variability of soils isn’t that great. Maybe what we do is a bit primitive or maybe considered one of those cowboy farming techniques, but when we’re applying fertilizer and come to those lower producing sites, we can simply reduce the amount of fertilizer being applied or just shut it off.”

And, he points out, his field knowledge and visual observations don’t cost him $8 per acre to apply to his 13,000 acre farm. The $8 is an average rate some consulting services charge to develop variable rate technology prescriptions specific to an individual farm.

Different types of variable rate technology are available to Canadian producers, but all are geared toward improving fertilizer use efficiency. GreenSeeker technology, for example, using an optical sensing system, reads the amount of crop biomass in a field and will vary the amount of top-up nitrogen required in crop. Other VRT systems vary the amount of fertilizer that goes on at seeding by using a combination of soil test analysis, yield data and infrared photos of previous crop stands to come up with a fertilizer “prescription” that varies according to the productivity of different zones in a field.

While admittedly Van Staveren tends to apply fairly high rates of fertility to crops in his canola-flaxdurum rotation, he says if there is any excess nitrogen it isn’t lost. “The amount of nitrogen lost due to denitrification or volatilization is less than one per cent, so losses are relatively low,” he says. “If for example, for whatever reason the flax or the durum hasn’t used as much nitrogen as expected, it is there in the soil and can be used by canola the following year. And we can adjust fertilizer application rates accordingly.”

Van Staveren, who was on the board of the Indian Head Agricultural Research Farm (IHARF) for six years, isn’t anti-technology. But he does want to see more research supporting the value of VRT. At the recent Saskatchewan Soil Conservation Association conference, he spoke to a leading soil scientist from the University of Manitoba, a well known South

Dakota researcher, and three fellow Saskatchewan researchers. They all shared similar reservations toward the overall likelihood of success with variable rate application on rolling to flat fields, he says.

“If soils are highly variable in their productivity, then VRT may have a greater application,” he says. “But I haven’t seen anything in research conducted at IHARF that suggests VRT will produce anything but marginal results at best. In looking at other studies, some researchers say no one has been able to prove the merits of VRT. This is one piece of technology I don’t need to be first with. It is not costing me a lot if I am in the second or third wave of adopters.”


On his farm, Van Staveren applies nitrogen in the form of anhydrous ammonia. Rates vary depending on the crop and soil test recommendations. For canola he aims for about 115 pounds of nitrogen per acre, flax gets about 70 pounds of nitrogen and durum gets about 90 pounds.

“Our fields and our soils aren’t perfect,” he says. “As we come to areas that are saline, or solonetzic — areas we can visibly see have less crop residue and are therefore less productive — we can either switch to a reduced rate of nitrogen or just shut it off.” With a Raven controller on the anhydrous ammonia system, Van Staveren can apply the full rate, a reduced rate (which is about 20 pounds of nitrogen per acre) or none at all. He estimates about two sections of his farm have higher than average variability, with 30 per cent variability due to solonetzic and saline conditions.

Most proponents of VRT claim the system improves fertilizer efficiency and provides an input savings while still providing the same yields for wheat and durum. However, Van Staveren says they don’t often talk about the other valuable component, protein, with price premiums that can often pay for half of the nitrogen fertilizer bill.

“In our durum, for example, if we can bump the protein by one percentage point, that is a huge value for us,” says Van Staveren. “Our fertility rates are on the high side, but at the same time over the past four years our durum has averaged 50 bushels per acre with protein between 12 and 13 per cent. And that is a good barometer for us that we are supplying sufficient nitrogen. A general rule of thumb is if your protein is below 13 per cent you’re not applying enough nitrogen to maximize yields.”


Van Staveren says other management techniques and farming practices will make more of a difference in fertilizer-use efficiency, overall productivity and yields. These include continuing with a zero-till direct seeding system, an early weed control measures.

He points to research at IHARF and also at Jim Halford’s (founder of Conserva Pak seeding systems) farm, also at Indian Head, that show under a long term zero tillage regime higher soil organic matter levels increases both the nitrogen and phosphate supplying power of the soil. For early weed control, Van Staveren uses pre-or post-harvest treatments and timely spring burnoffs with residuals. “Controlling weeds helps to increased fertilizer use efficiency by removing weed competition on time or prior to absorption of valuable plant nutrients in the soil,” he says.

Long-time Agriculture Canada research Guy Lafond says the potential of variable rate technology can’t be discounted, but he says more research is needed to answer some of the basic questions.

“The whole idea of variable rate technology is to be much more precise with fertilizer application,” says Lafond, who specializes in production systems agronomy. “The challenge is how do you combine the spatial variabilities, which are the variabilities you find over a field, and the temporal variabilities, which are the variabilities you find from year to year.”

He says tools such as satellite imagery are useful for measuring plant biomass, which in turn is an indication of soil productivity. The more plant material you have, the more productive the site. “But once you identify the variabilities in plant characteristics, the question is what do you do about it,” he says.

Some prescriptions for variable fertilizer rates are based on how crops have grown on a field or certain soils in the past, but they can’t take into account current growing conditions or the year to year temporal variabilities.

He says the optical sensors, as used in GreenSeeker variable rate system, may be more accurate because it is a “real time” system based on what is currently growing in a field about one-third of the way through the growing season. The concept of GreenSeeker is to be able to top-dress nutrients based on crop growth.

“The merit of variable rate technology cannot be abandoned,” Lafond says. “The potential is there. It is a complex issue, but we need more research and we need to see more grower experience with this technology to answer these questions.”

Long-time soil fertility specialist John Harapiak in Calgary, says producers can’t expect variable rate technology to immediately solve all crop production problems.

“You need to base these prescriptions on a thorough assessment of soil quality and cropping history, because there can be so much variability in a field,” he says. “There are consulting services that can provide this thorough assessment and I have talked to a number of growers who seemed to be pleased with the results. That being said, it doesn’t mean everyone is going to have the same experience, and no matter how good your information is, Mother Nature can always throw you a curve. There can always be surprises. We have to keep in mind that this technology is in its embryonic stage.”

Lee Hart is field editor of Grainews, based in Calgary. Contact him at 403-592-1964 or by email at [email protected]

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.



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