Ferrie: No-Till Farmer Asks at What Depth to Pull Soil Samples?
A question came in this week for Ken Ferrie to answer that he believes other no-till growers would benefit from knowing the answer to as well. The question asked: “As a no-till corn and soybean farmer, at what depth should I pull soil samples for nutrient evaluation?”
In this case, the grower, who has been no-tilling for upwards of 10 years, says he wants to evaluate phosphorus, potassium and pH levels in fields.
“I would still recommend a six-and-two-thirds-inch sample depth, but that’s without knowing what your fertilizer applications were in the past 10 years of no-tilling and what your fertility levels were before you started no-tilling,” replies Ferrie, Farm Journal Field Agronomist and owner of Crop-Tech Consulting, Heyworth, Ill. “I'd recommend you pull some stratification tests as well.”
Ferrie recommends carefully splitting the sample (core of dirt) and placing it in two different buckets for testing. The reason is after 10 years of no-till, the top three inches of the sample will likely be considerably higher in nutrient levels than the bottom three inches.
“This is due to stratification that comes from all the crops that have decomposed at the surface as well as broadcast fertilizers over the past 10 years,” Ferrie says “High levels of fertility in the top three inches is not a concern, but ultra-low levels in the bottom three inches is. If the bottom three inches are deficient in nutrients, that means it was probably that way when you started no-tilling,” he adds.
Drought Can Impact Nutrient Availability
Ferrie says in fields his team routinely samples, they don’t see a lot of movement in the lower three inches of a soil sample (core) in no-till growers' fields after decades of no-tilling. He adds that if the grower finds deficient fertility levels in the bottom three inches of the sample, he probably needs to address it.
“Ninety percent of the P and K we pick up comes out of the top six inches where the microbial activities are at. But if the top three inches get in trouble in a drought, like this year, your plants will need to feed on those lower three inches,” he says.
To weatherproof the soil it would likely be best to fix the fertility in the lower three inches.
“This could be done by knifing some fertility down there or adding some tillage and mixing the top three inches with the bottom three inches,” Ferrie says. “Once you’ve brought your bottom three inches into range, you can go back to no-till.”
Consider pH Levels
He adds that no-till farmers also need to pay attention to soil pH.
“This is an area where farmers get in trouble when they go into no-till and keep applying lime like they did when they were in tillage, using (those) three- and four-ton rates,” he says.
Ferrie advises farmers to treat limestone like they do P and K.
“If you have made big lime applications (in no-till), you'll probably find your surface pH is too high. I have seen surface pH in the mid sevens. This causes issues with nutrient tie-up, herbicide carryover and damage, and also nutrient and nitrogen volatility,” Ferrie says. “With stratification pH issues, the only option is to mix that soil, which can be a tricky step in highly erodible ground.”
Aviation Fuel Update
On December 15, the Biden administration released an update on the sustainable aviation fuel front, and what farmers can anticipate in the near term. In this week’s Boots In The Field podcast, Ferrie addresses how farmers are likely to be able to participate in the process and benefit financially.
“If the American farmer can get credit for building sustainable aviation fuel, guys, this will be a game changer. It could be a wild ride, at least until 2027 when these credits sunset,” he says.
Listen to Ferrie’s review on the aviation fuel opportunity here:
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