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How seed-placed fertilizer may hurt your crops if not applied carefully and attentively

Reference: Decisive Farming

Placing fertilizer within the seed row has been long-standing practice for many farmers across the prairies. Having those nutrients close to the seed makes it easily accessible by the plant, and can help the crop out of the ground and into the sun.
Potash fertilizers and other nutrients, such as phosphate, are immobile fertilizers, meaning they don’t travel more than a half-inch through the soil. Placing these fertilizers close to the seed can be beneficial for plant growth.

But putting down fertilizer with your seed can negatively impact the germination and yield of the crop if not done carefully and attentively. Seed-placed nutrients can cause damage depending on the type of fertilizer, the rate it’s seeded, the soil’s composition, and the soil’s moisture levels.

Acid Burn Germination Damage

Seed-placed fertilizers can be problematic for growers by being directly toxic, or by creating a ‘salt effect’ in the seed row. Ammonia (NH3) from Ammonium-based fertilizers, such as Urea Nitrogen fertilizers, is an acid-based fertilizer, which can raise the pH levels in the soil along the seed-row.

A soil pH between 6.0 and 7.0 is considered optimal for the best crop yields, while a pH level too high or too low can cause germination damage.

Growers should be aware of their soils Ph levels when placing nutrients in the seed-row, as both Ammonium-based fertilizers (such as ammonium nitrate, ammonium sulfate and urea) and Sulfur-based fertilizers (such as elemental sulfur, iron sulfate and aluminum sulfate) are acidic.

“These acid-based fertilizers, when they dissolve, they create an acid,” said Garth Donald, Manager of Agronomy at Decisive Farming, “It’s the acid in that product that affects that root zone. It makes it hot.”

This can cause the roots to burn up and wither the plant. A similar reaction can be seen above ground when acid fertilizers are broadcast too heavily on the plant itself, burning and browning the leaves above.

“It’s kind of like turning on a hot tap, whether it’s lukewarm or smoking hot. When it’s lukewarm, it doesn’t hurt. But when it’s smoking hot, you get burned, right? You get some type of burn, and you are no different than your (crops) roots,” said Donald.

Soil Salinity Germination Injury

Aside from pH levels, another concern for growers is the ‘salt effect’ caused by seed placed fertilizers.

The salt effect is caused by salt fertilizers absorbing the moisture in the soil before the roots can absorb it, competing with the plant for water. Highly soluble fertilizers like urea will create a greater salt effect than less soluble fertilizers, such as phosphates.

When the soil is lacking moisture and precipitation is down, the salinity levels in the soil rise. Fertilizers, which are all salts, increase the salinity levels around the seed through dry conditions.

“This year, all the soil tests are coming back with high salinity over the previous year,” said Donald. “That’s because the water from below brings up the salt and deposits it up top.”

Finding solutions for the salt effect have come in an abundance of forms, such as humic acid and gypsum, but there is only one true way to solve the salt problem. Water.

“You’re not removing the salt. It’s staying in that band. You need moisture to move salt,” said Donald.

How to Spot Seed Injury

Donald says seed-placed nutrient damage is likely more common than most growers think, but it’s because they aren’t familiar with what it looks like.

“We’re not talking ‘death and destruction,’ like what’s been shown to us for the past 30-40 years,” said Donald. “That’s the issue with seed injury, is that’s what people think it’s supposed to look like, and that’s not what it is.”

Rather than total seed failure or the burning death of the plant in early stages, Donald says fertilizer damage is more subtle. So subtle, farmers may not realize it’s an issue.

“A lot of it is delayed maturity,” he said. “They’ll look at their crops and say ‘well, it’s a cold spring, the plants are just slow,’ but that’s usually how fertilizer damage represents. The plants are still growing, they’re just not quite as vigorous as ones that don’t have seed-placed nutrients. They’ll still produce a good crop, but on the maturity side, we’re seeing anywhere from seven to 10 days of delay.”

Doing plant counts to monitor germination rate, as well as using a variety of types and amounts of fertilizers and comparing yields can help farmers spot seed-placed fertilizer damage.

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