Slider for Fitting Foliars into the 4Rs article
The 4Rs of nutrient application may be slightly different than granular application, but they are just as important.

Applying 4R principles to foliar fertilizer application.

Choosing the right source, at the right rate, at the right time and in the right place works well in traditional soil fertilizer application, but can the principles of the 4R Nutrient Stewardship program be applied to foliar fertilizer?

The Right Source

Jarrett Chambers, president of ATP Nutrition, believes the 4R principles can work very well for the foliar application of fertilizer.

“I think 4R is a great program for the soil,” says Chambers. “I actually think they’re even more valuable for the foliar.”

The soil has a more complicated ecosystem than the foliage of a crop, says Chambers. For example, the soil tries to keep nutrients available for the plant for as long as possible. Crops benefit from foliar application quickly and make use of the nutrients within minutes of absorption. Chambers suggests using a foliar fertilizer with nutrients in a form that is the same as the plant needs for immediate use.

“Source is so important, probably more important than soil application because it’s important for every element,” says Chambers. “When it comes to plant nutrition on the leaf, every element, every nutrient we need to address in that plant has to be in the right source.”

The Right Rate

Blake Weatherald, regional manager for Saskatchewan and Manitoba at Nachurs Alpine Solutions, also believes that the 4R principles can be applied to foliar fertilizer application.

“I think it fits well in a balanced soil fertility program for sure,” says Weatherald. “I think it’s a great fit when you talk about the source, the rate, the time, and the placement of the foliar fertilizer.”

Weatherald typically uses soil or tissue sampling to decide at what rate he should apply the foliar fertilizer, which will depend on the product and the nutrient a farmer uses for the foliar. Tissue sampling can also measure how well a plant absorbs a foliar fertilizer’s nutrients.

"We’ll sample the plant before the foliar fertilizer application and five days to a week afterwards. We compare how much nutrients went into that plant and how it affected nutrient levels in the tissues,” says Weatherald. “If we can keep those nutrient levels high in the plant, the end goal will be a yield bump.”

When it comes to the right rate, Chambers says ag retailers should think about the right rate in the same way we think about human nutrition.

“When you sat down for breakfast this morning, do you eat this entire month’s meal at 8:00 a.m.? No.” says Chambers. “That’s the way we’ve got to think.”

For example, adding a season’s worth of nitrogen in one application might overwhelm and kill the crop, whereas seven to 10 days worth of nitrogen in a foliar fertilizer will provide the benefits the plant needs at the rate it can safely use.

The Right Time

Weatherald says the right time to place for foliar fertilizer will depend on its growth stage. Applying foliar fertilizer at the right time allows a farmer to update the nutrition program to what the plant needs at its stage in the plant life cycle.

“The foliar fertilizer allows you to get the plant what it needs when it goes through the reproductive stage,” says Weatherald. “Maybe the soil can’t keep up with supplying that plant with the nutrients. The foliar application can do that as well.”

When it comes to plant nutrition on the leaf, every element, every nutrient we need to address in that plant has to be in the right source.
Jarrett Chambers

Chambers also says farmers should consider the stages of plant growth, and retailers should work with farmers to find out what they want their crop to accomplish during the growing season. For example, consider applying foliar fertilizer during the vegetative stage to maximize the crop’s potential for healthy leaves and roots.

External factors like humidity, soil moisture level, and temperature can also affect how well the plant can absorb the fertilizer’s nutrients. Weatherald suggests applying the foliar fertilizer during a cool evening instead of mid-day as plants conserve their moisture in hot temperatures, which could make absorbing nutrients from foliar fertilizers more difficult.

The Right Place

Some of ATP’s collaborative work with the University of Hanover, Germany, involves research into plant nutrient uptake. Their findings suggest that the plant absorbs twice as much nutrition underneath the leaf than on top. Chambers says the top of the leaf has a waxy surface that works like a shield against UV rays, but underneath the leaf is hairier and is not as waxy, making it easier for the leaf to absorb the nutrients.

“Good coverage foliar fertilizer placement is critical,” says Chambers. “Full coverage on the top of the leaf and underneath the leaf would be ideal, including a large enough water volume so that it doesn’t dry up really quickly.”

Chambers and Weatherald both believe that while 4R Nutrient Stewardship can work well for foliar applications, they should only complement an already well-balanced granular fertilizer program guided by 4R, not replace it.

“It’s important for people to manage their expectations on what they will get out of a foliar nutrient application,” says Weatherald. “I wouldn’t necessarily look at it as a replacement for a good up-front soil fertility program.”


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