Go deep with immobile nutrients
By Madeleine Baerg, Farming Smarter
With low and no-till now common, more and more farmers are asking questions about how best to apply nutrients in zero tillage operations. Zero tillage tends to mean all the added nutrients land within the top two inches or so of the soil. Some worry this could promote a loss of the more immobile nutrients like copper (Cu), phosphorus (P) and potassium (K) and, perhaps, even a lessening of root depth in some crops or years.
For the past three years, SARDA Ag Research in Falher, AB, has been investigating whether there is a better way to apply immobile nutrients than our current system of annual shallow banding. While it’s still too early to be certain - results have not been tabulated for 2020 data - findings from 2018 and 2019 suggest periodic deep banding (ie: deep banding every three years) may offer operational benefits.
“Immobile nutrients are currently shallow banded annually. Some research in the past said farmers should deep band immobile nutrients to increase availability for plants. However, when you deep band, you have higher power requirements for equipment, you use more fuel and you create more soil disturbance. [The researchers] wondered if you could get the benefits of deep banding but decrease those costs by only applying every three years,” says Shelleen Gerbig, SARDA’s extension coordinator.
The study included three sites to replicate a cross-section of Alberta’s diverse growing conditions. SARDA managed the site in Falher; which offered dark grey soil and the shortest growing season. InnoTech Alberta managed a site in Vegreville with black soil and a mid-length growing season; and Farming Smarter managed the Lethbridge site in brown soil and the longest length growing season.
At each site, technicians applied a variety of treatments into fields planted to a canola, wheat and pea rotation. Treatments included no P, K or Cu; 1-3”-depth shallow banded P, K and Cu (both individually and together) at an annual rate; and 5-6”-depth deep banded P, K and Cu (again individually and together) applied at three times the annual rate in only the first year of three.
The first question researchers hoped to determine was: how much nutrient stratification exists in Alberta’s long-term crop soils? The short answer? A lot says Mike Gretzinger Farming Smarter’s Research Coordinator.
“We did a lot of soil testing and the stratification of nutrients was really apparent. You can see right off the bat that most of the P is in the 0-3” layer. The 3-6” layer didn’t have nearly as much.”
The second question researchers asked was whether, in fact, periodic deep banding improves nutrient availability and uptake in each of a three-year period? Their thought was that, whereas shallow banding limits nutrient availability to the very top layers of the soil, deep banding places key nutrients in the soil layer where the roots grow of most prairie annual crops. Gretzinger says the southern Alberta fields treated with deep banded phosphorus visually showed improved vigour. Most of the other fields showed no visual differences.
“The hope was that we’d see improved nutrient uptake in the form of a measurable difference in yield. It’s not tending to show that at this point, though we can only say ‘tend’ because we don’t yet have final results,” says Gerbig.
That said, she adds, “So far, it seems deep banding isn’t showing any detrimental effects either. What doesn’t happen can be just as important as what does happen.”
If the study ultimately shows that there is no production downside to periodic deep banding, producers might find ways to capture a range of economic and operational benefits by shifting away from annual application. In addition to less equipment wear-and-tear, less fuel cost, and less soil disturbance, applying non-mobile nutrients every three years would lighten producers’ workload in two out of three years and potentially allow for application to occur at non-peak work times (and at non-peak pricing). Also, savvy producers might translate a three-year investment to tax-planning advantage.
Gerbig cautions against making operational conclusions from incomplete research. For example, if crops with access to three years’ worth of nutrients used more than a one-year allocation in either or both of years one and two, detrimental yield impact might only appear in year three.
If it turns out crops use the nutrients more quickly than expected, “maybe a farmer could put down a little more – say 3.25 years worth – at once and it might still be cheaper than putting down three annual amounts. That will depend on the individual producer,” says Gerbig.
One thing is already certain: questions will remain even after this study wraps up. The three-year term of the study won’t answer long-term questions about nutrient stratification, a key factor in plant uptake and rate calculations. For example, deep banding could translate over time to seedlings facing starvation if soil’s upper layers become depleted of key nutrients and aren’t renewed via shallow banding.
“I like research that has a different element. This one is a totally right-field idea,” says Gretzinger. “We may not get all the answers, but it’s a starting place.