Optimize P and K in strip tilled fields

Optimize P and K in strip tilled fields
Apr 30, 2021

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Ontario-based research is investigating the impact of placement and timing of P and K with strip tillage on corn yield

By Jackie Clark
Staff Writer

An OMAFRA expert is investigating the impact of phosphorus (P) and potassium (K) fertility in strip and conventionally tilled corn fields.

Ben Rosser, OMAFRA’s corn specialist, designed the experiment to address “questions I was getting from growers that I didn’t have answers for a couple years ago,” he told Farms.com.

The experiment six treatments:

  • full tillage with no fertilizer
  • full width tillage with spring broadcast P and K
  • full width tillage with half spring broadcast, half planter banded P and K
  • fall strip tillage with shank placed P and K
  • fall strip tillage with half shank placed and half planter banded P and K
  • spring strip till with shank placed P and K

Rosser planted those treatments on low P and K testing fields at 10 sites over two years, so far. Studying the impact on low P and K testing soils helps identify yield responses in corn.

The first question Rosser addressed had to do with “broadcasted and incorporated fertilizer in a conventional till scenario, compared to putting fertilizer in the strip,” he explained. Growers want to know if there is an advantage to placing fertilizer near the seed.

“This work definitely showed that we saw a yield advantage for the strip fertilizer compared to where fertilizer was broadcast and incorporated with full width tillage,” he said. However, given the treatment setup, Rosser cannot definitively say whether tillage method or fertility alone caused the response.

“We were comparing fertilizer and we’re also comparing different tillage methods, but if I had to speculate, I think it’s fertility driving that response,” he said. A yield benefit exists when P and K fertilizer is put down with strip tillage, compared to broadcast with conventional, particularly if you’re in a low soil test situation.

Many growers also ask if “there is a better time to strip till and put fertilizer on comparing fall versus spring,” Rosser said. Producers may choose one or the other for reasons such as workflow timing or soil conditions and moisture, however some want to know if there is a strictly yield-based reason to choose fall or spring application and strip tilling.

“Again, there did seem to be an edge to that spring strip-till program. The spring strip and fertility tended to yield slightly higher than the fall strip and fertility system,” Rosser said.

Again, timing of fertility and tillage are confounding factors in the experiment, so researchers can’t statistically parse out which is driving response, but Rosser believes fertility is the main factor.

“On low fertility ground you seem to get a bit more response with those spring applications,” he said.

Finally, Rosser tested splitting applications, applying the same total amount of P and K, but with half at tillage and half at planting.

“In an ideal system from a logistics and efficiency perspective, it would be nice to put all the fertilizer on the strip-tiller, get your strip-tilling done and come back with your planter bare and just plant seed,” he explained. “Numerically we eked out a little bit of a yield response to that, it was less than two bushels on average, but when you ran the stats on it there was no significant difference.”

So, “this data would suggest that there was no benefit from moving fertilizer to the planter, and you were fine running the fertilizer in the fall in the strip,” he added.

Between the two years of data collected so far “the story was fairly consistent,” said Rosser. “The more fertilizer you’re putting closer to the seed on low-fertility soils, and the closer to planting you’re putting that fertilizer, we seem to get more response out of it.”

That trend was more pronounced in 2019 data than 2020. A few reasons could explain the difference.

“When I looked back at soil tests, the fields we were in for 2019 tended to be lower soil tests, especially for P,” explained Rosser. “So, maybe that’s part of it, we were just on more responsive soils.”

He also made small changes to the equipment between years.

“In 2019 I had two hoses coming off our air box to the shank, but I was having some trouble plugging in some rows, because of the two rows coming into one,” Rosser explained. “The only way that I could get around that was to put a second outlet behind the existing fertilizer outlet behind the shank, and then run one fertilizer hose to each of those, and then I had no plugging issues after that.”

However, “when I added that second outlet on the back, I don’t think I was getting that shallow band like I was with that single outlet, I think there was a bit more of a void behind the shank and fertilizer’s maybe falling in the bottom of that strip a bit more,” he added.

The less concentrated band of fertilizer in 2020 may have made the impact less dramatic.

At this point, that explanation is “purely speculation,” Rosser said. “I’m going to do some tests this spring to compare those two systems.”

The third and final year of this study is now in progress. Read the full report here. 

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