Adoption rates of autosteer, sectional control and weigh cells in grain carts and air-seeder tanks are incredible. Auto guidance adoption, for example, was well above 50 per cent in the U.S. as of 2019 (McFadden et al., 2023). Nowadays, it is unusual to see crop rows that aren’t perfectly straight.

Crop lodging on headlands due to double rates of seed and fertilizer is becoming a thing of the past. The “final pass” with no seed or fertilizer applied due to an unknowingly empty tank is less common.

There is one commonality among most of these technologies — you can easily direct results and calculate their economic impact on the farm.

Precision ag technology to guide variable rate (VR) nutrients, though steadily climbing, has not had the same adoption rate. Recent surveys in Western Canada have put VR nutrient management in wheat and canola near 15 per cent adoption. In the U.S. it is slightly higher, with adoption rates as high as 40 per cent in corn, with other crops lagging, and significant variation by state.

Most surveys cite expense and data management as key reasons for lack of adoption, but really it comes down to poor understanding about the return on investment of VR fertility due to complexity. Every field is different. Every farm is different. Every region is different. VR benefits cannot be generalized, other than to say the goal is better return on investment of applied inputs. Perhaps most of all, VR benefits are often not easy to see, nor does it make logistics easier.

It is commonly said that there needs to be at least a 15 per cent difference in yield to visibly see the difference in the crop, but even a five per cent increase in yield can have a large effect on profitability. You just don’t “see” it unless you conduct a replicated trial and measure differences. Even then, what you see are just numbers on paper or a computer screen that don’t evoke the emotion of a strip of missing crop due to malfunctioned GPS.

Crop nutrition is complex, driven by multiple nutrient interactions, crop species, weather variability, soil types and other factors. A successful variable rate strategy is not as easy as saying, “Put more nitrogen here, and less there,” because other nutrients such as phosphate, potassium or even micronutrients all affect nitrogen use efficiency and can be more limiting than nitrogen. We need to look at the whole system and consider any factor as being potentially yield-limiting.

There are also long-term implications for fertility decisions. Highly responsive soils may take several years to build soil nutrition to non-limiting levels and increase yields, as evidenced by a recent study near Brandon, Man., by Agritruth Research. In this 10-year trial, the data suggests that higher rates of N and P with a positive N and P balance over the rotation eventually overcame limited soil N and P supply, resulting in higher yields. But it took several years to see it.

This situation is not as unusual as one would think. Our SWAT MAPS agronomy team has seen yield limitations from P, K, S, Zn, Cu, acidic soil and salinity in specific areas of fields in Western Canada. Many are not easily corrected in just one or two years. Variable rate fertilizer is simply not the type of technology to always give instant visual gratification like so many other technologies we use. But it can provide methodical, 4R, science-based gains that over time provide significant cumulative value to the farm. Perhaps as an industry we just need to do a better job of measuring and communicating that value.

The elephant in the room is logistical capability. What a farm should do versus what it can do are often two different things, and in most cases involves a compromise of optimum applied rates of each nutrient. In fact, to quote Jonathan Zettler, a trusted SWAT MAPS service provider based in Ontario, “optimum rate” should be the term rather than “variable rate.”

Nothing says that every crop input should be applied with variable rates. It’s simply a tool to achieve a better return on investment when it makes sense to do so. Optimizing rates of every single nutrient is a logistical challenge for many farms.

Technology that immediately makes tasks easier and has easily visible results will always have high adoption rates. But many management decisions have long-term benefits and very strong returns. It can just take a little more trust and patience in the process.

Further reading

10 years of reduced versus enhanced rates of N and P fertilizer. CLICK HERE.

Jonathan McFadden, Eric Njuki, and Terry Griffin. February 2023. Precision Agriculture in the Digital Era: Recent Adoption on U.S. Farms, EIB-248, U.S. Department of Agriculture, Economic Research Service. CLICK HERE.

Adoption of precision agriculture to reduce inputs, enhance sustainability and increase food production: A study of southern Alberta, Canada. 217. 327-336. 10.2495/SDP180301. CLICK HERE.

Which of your customers were early adopters of precision technology? CLICK HERE.

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The first thing I noticed at Joe’s farm was a difference in the stages of canola seedling emergence between his fields. Overall, five different fields totalling 1,000 acres were showing delayed emergence while another 2,000 acres appeared normal. The normal-looking fields were more advanced than the others, even though some of them had been seeded later.

Most of the plants in the fields showing delayed emergence were stalled at the one-leaf stage, whereas plants in the healthy fields were already at the three-leaf stage.

We had our work cut out for us; delayed seedling emergence like this could be the result of any of the following causes: seeding depth, fertilizer application, herbicide residue, seedling disease, or insects — to name a few causes. To complicate matters further, Joe had seeded three canola varieties, so seed lot and varietal differences also had to be considered.

Initially, Joe felt concerned that he may have seeded too deep with one drill, but I checked the seeding depth and reassured Joe it was fine. At this time, I also noticed the roots of the plants were a healthy white colour, ruling out seedling blight and wireworms as factors causing the damage in Joe’s fields, and I couldn’t find any evidence of cutworms.

There was no pattern to suggest the damage correlated to a specific seed lot or variety because all five of the affected fields were damaged in a similar manner.

That year, Joe’s application of fertilizer went off without a hitch. He had seed-placed 90 pounds of balanced fertilizer product including nitrogen, phosphate and sulphur, so fertility levels should have been adequate.

I could also rule out herbicide carryover as a cause of the damage to Joe’s canola plants because some of the affected fields had not had any residual herbicides applied the previous year.

I re-entered one of the affected fields for a closer examination of the plants. I noticed a few subtle symptoms on approximately 80 per cent of the seedlings — some of the leaves were cupped and growing abnormally, and the cotyledons were larger and thicker than I would normally see at this stage.

I wondered if Joe had added another herbicide to the glyphosate he had sprayed in the pre-seed burn-off application?

“Some fields had a lot of flixweed, so we threw in one jug of 2,4-D Ester per tank to heat it up,” he told me.

“I know what’s damaged your canola fields,” I said.

Crop Advisor’s Solution: Herbicide residues hamstring canola

Unfortunately for Joe’s emerging canola seedlings, 2,4-D Ester residue remains in the soil for a few days — enough to injure the seedlings.

This herbicide is valuable for controlling winter annuals in the spring, but not before seeding canola. It normally breaks down after a few days when moisture is present, but Joe’s fields remained dry for 12 days after spraying; therefore, when the canola plants emerged, there was enough residue left in the soil from the 2,4-D Ester to injure them. This herbicide should never be used before seeding sensitive crops such as canola or pulses.

On the bright side, adding 2,4-D Ester to his glyphosate to take care of the weed problem in his canola fields didn’t spell disaster for Joe. The affected plants slowly overcame the herbicide injury, but they matured several days later than normal. Joe’s yield decreased by roughly three to four bushels per acre.

This time Joe was lucky — the loss might have been worse had the weather been less cooperative while the fields were in the flowering stage. Together we developed a crop plan for Joe to follow for the rest of the year and into the coming spring in order to avoid a similar incident.

Wes Anderson is an agronomy manager at Richardson Pioneer Ltd. at Regina, Sask.

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