Making the most of nutrients

ST. CHARLES, Minn. — For Bill Powel-Smith, growing healthy crops in a sustainable, cost-effective manner comes down to three take-home practices: ditching monoculture for diverse, multi-family forage fields; understanding how soil moisture impacts nutrient availability; and applying manure onto green cover.

“The conventional system says we’ll provide you all the products to kill everything that’s there and then we’ll provide you with the products to feed your crop,” Powel-Smith said. “We kill off the weeds and kill off the insects, and we kill off everything else, and we plant the mono crop. … We’re promoting the growth of one species in the soil. … There’s no natural predation, there’s no competition and so we’re fighting Mother Nature.”

Powel-Smith owns his own soil health consulting business, LandCares Consulting LLC. Powel-Smith was the guest speaker for the Driftless Area Ag Alliance’s annual meeting Feb. 10 in St. Charles.

Healthy soil starts with a proper carbon-nitrogen ratio of the organic matter, which Powel-Smith said is 10:1.

“If I’m building a diet for a cow, I’m going to build it around protein and energy,” he said. “(If) I’m looking at building a healthy soil, I’m going to build it around the same two things. We just call it carbon and nitrogen.”

He said for many dairy farmers, their ratio is off because they remove carbon in the form of forages and apply nitrogen in the form of manure. This can lead to unbalanced soil with low organic matter and higher soil nitrogen.

Powel-Smith said farmers should consider planting their fields with multiple species of forages instead of monoculture alfalfa. One of the reasons for this is soil density. Alfalfa tightens soil by pulling out carbon. This is hard on the field. By growing other plants, the variety of nutrient needs keeps the soil more balanced and less compacted.

Powel-Smith said fields need not only species diversity but also plant family diversity. For example, this could look like a field containing grass, legumes and broadleaf plants.

“It’s the families that make a difference,” Powel-Smith said. “I get more families in there, I can start driving soil health better, build more structure.”

This soil structure can help retain water and limit erosion.

Powel-Smith said multispecies fields can feel like a mess that need to be sprayed and cleaned up.

“This is really what we’re looking for,” he said. “Not only do you bring diversity to your soil, but look at the diversity you bring into that rumen.”

The finished crop is dairy quality feed he said. With a multispecies field, the goal Powel-Smith said is to get similar yields while eliminating one cutting compared to monoculture alfalfa fields.

“The thing with cutting alfalfa is it’s hugely expensive,” Powel-Smith said. “It costs a fortune.”

Powel-Smith said planting cover crops helps with nutrient uptake from manure. He said rye, triticale and wheat are good options.

“These grasses are great for sucking up nutrients,” he said. “I don’t want nutrients moving to the soil profile. Get them tied up in your plants, and then let that cover crop break down in the summer.”

Powel-Smith said one of the best ways to capitalize on potential soil nutrients in manure is to apply it to green growing fields.

“I can terminate that crop, and it’ll release (the nutrients) as 100% plant available,” Powel-Smith said. “It didn’t go on that way, but it’ll come out that way.”

He said cutting cover crops while lush is a good idea because as cover crops grow larger, the nutrient availability to the next crop lessens.

“If you can get your nutrients held up on a cover crop and then released, that’s money in the bank,” he said.

Powel-Smith said farmers should plant shorter day corn and soybeans and reduce trait stacks to give themselves more time to manage their cover crops.

“The profit secret behind this whole thing is, as we go further down this road, we can simplify, simplify, simplify,” he said. “I need less treated traits. I need less cropping inputs. (That) doesn’t mean zero, but I just need less all the time as we build diversity.”

Powel-Smith also discussed nutrient availability and inputs. He challenges the idea of an add and subtract input system, because he said this does not take into consideration soil structure, moisture, and availability of nutrients.

This is why Powel-Smith said he is critical of variable rate nitrogen, because he said it assumes the exact amount, uptake and source of nutrients.

“It’s based on a model that says what you remove, you replace,” he said.

Powel-Smith said farmers should do comprehensive soil testing to understand the nitrogen and phosphorus in their soil as well as other nutrients.

“This isn’t available through voodoo, … it’s available if I can access and take advantage of it,” Powel-Smith said.

Powel-Smith said farmers should get manure analyses and track what manure is spread where.

He said he has been part of doing tissue samples on crops every three weeks to understand how the plants are utilizing nutrients as the season progresses. This is important because soil moisture and other factors can affect whether or not plants can access the nutrients in the soil.

For example, extremely wet, saturated soil can mean increased iron in the plants, which is toxic. The plant will try to compensate by using calcium to bring in aluminum to counteract the iron.

Or, if potassium is abundant, Powel-Smith said this can interfere with the uptake of calcium and magnesium. In fact, he said some research supports the possibility that abundant potassium causes luxury consumption which interferes with the availability of magnesium and calcium.

Overall, Powel-Smith emphasized in his presentation that a diverse field, with green applied manure, and with soil, manure and tissue sampling, will be on its way to providing healthy feed, a sustainable future, and economic viability.

“Cows don’t lie, soils don’t lie,” Powel-Smith said. “Forage quality will improve and become richer as the soil feeds and protects the crop.”