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Experts advise putting phosphorus and potassium fertilizer in the soil

Experts advise putting phosphorus and potassium fertilizer in the soil
Farmers question why phosphorus and potassium need to be placed in, not on, the soil.

Agronomist Justin Petrosino emphasized a point at a farmer meeting of Stewart Seed customers recently, and some of the farmers were surprised at what he said.

Petrosino is a member of the A.I.M. team that serves Stewart customers as agronomists, doing research on hybrids, varieties and crop production practices. A.I.M. stands for Agronomy In Motion.

Related: Get Phosphorus Fertilizer Under the Soil's Surface

Petrosino works in Ohio. The farmers were gathered in Columbus, Ind., and represented various parts of south-central Indiana. Here's how the conversation went.

Head start: Greg Lake in Allen County seeds cover crop and injects fertilizer at the same time, putting P and K under the surface. The rig belongs to the Allen County Soil and Water Conservation District, purchased with grants from the Great Lakes Initiative.

"You really need to put nutrients in the soil, not just on the soil," Petrosino emphasized. "We learned that a year ago with nitrogen tests. When N is left on the surface there is too much chance for loss."

Farmer: "You're talking about nitrogen, right?"

Petrosino: "I'm talking about nitrogen, phosphorus and potassium. I'm really talking about any fertilizer you're applying except what you might apply through irrigation."

Farmer: "I understand about getting nitrogen under the surface. But we've always been told it's OK to apply P and K on top of the soil. That's the normal practice."

Petrosino: "I work mostly in Ohio. Last summer there was an algae bloom in Lake Erie. The City of Toledo shut down its water plant for two days. The algae bloom was blamed on too much phosphorus in the water. I'm not getting into where the phosphorus comes from. What I am saying is that more people are looking at how phosphorus and potassium fertilizer are applied. In the case of phosphorus it turns out that part of it is in a readily available form that washes away if soil washes away. Soil particles carry it with them."

Farmer: "So you're saying we have to inject P and K too? That's slow."

Related: Why Conservation Groups Spend Money for Tools That Put Fertilizer Under Ground

Petrosino: "I understand it's much faster to have someone spread P and K on your fields. What I'm telling you is you may need to think about changing that approach in the future. There will be a move toward applying P and K in the soil, not on the soil."

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