I have had a few recent conversations about liquid fertilizers that are either soil applied or foliar applied as well the questionable promotion that is being put out there. Have you heard of phrases like “using our product will increase your yields,” “our product is far superior to any other on the market,” or “I guarantee it will work.” (But no written guarantee is offered). And my favorite is, “You can reduce your purchased fertilizers by a third or maybe even half.”

Plain and simple, crops need a certain amount of nutrients and they come from the air, water, and soil. If there are not enough nutrients to obtain maximum yield, then we need to add supplements, i.e. – manures and fertilizers.  A 200 bu/acre corn crop needs about 74 lbs/acre P₂O₅ and 56 lbs/acre of K₂O and a 60 bu/acre soybean crop needs about 45 lbs/acre P₂O₅ and 56 lbs/acre of K₂O. These numbers do not reflect any addition requirements to account for low soil test values. 

 Let’s look at an example product that keeps coming up in my conversations. This example product is a 3-18-18 and is 11.7 lbs/gallon. The suggested use rate is 10 GPA in furrow with the planter and 2 GPA later in season as a foliar application.  This 12 gallon total will provide:

(All values are in lbs.)

When you compare the above numbers, the liquid program is not providing enough nutrients for the crop. Therefore, any additional nutrients must come from the soil. Then, over time, you will deplete that soil and yields will decline. I have seen it before, and it is just like going to the bank. You cannot continually make large withdrawals with very minimal deposits. Eventually, it will get you into trouble.

Here’s another scenario that has been mentioned. They are using a mix of 4 GPA of 3-18-18 (11.7 lbs/gallon) and 4 GPA of 0-0-30 (12.2 lbs/gallon). This mix is applied ahead of their corn and their soybeans with the planter. No additional P or K fertilizer is applied. Here’s what they are getting:

(All values are in lbs.)

I will not discuss how low these soil test values have reached, but in 2022 the average soybean yield on this farm was 32 bu/acre, which were considerably lower than what most producers saw in 2022.  Do not get me wrong, liquid fertilizer supplements are a great thing and can be a welcome part of an overall fertility program. But they are NOT a replacement. If you use products like these, calculate the amount of nutrients they provide and deduct that from your dry fertilizer amounts. Starter fertilizers containing N and P have consistently been shown to provide earlier season plant health in cool, wet soils. They should be considered since we are continually pushing the envelope for earlier and earlier planting.  However, potash is not needed is such high quantities at planting.  I also wrote a Starters/Pop-Up Fertilizer article several years ago when I was an ILSoyAdvisor Soy Envoy: Agronomy: Are Pop-Ups or Starters Really Needed for Soybean? – ILSoyAdvisor

Foliar Applied Nutrients

As for nutrient uptake, most are taken up through the root system and only a few passes directly into the leaf after they manage to get through the wax layer on the leaf surface. Most foliar applied nutrients run off the plant and enter through the roots. Yes, you can see a response to foliar applied nutrients by giving a quick boost of fertilizer at the base of the plant. The plant leaf is designed to shed some of the water back toward the stalk and that water and fertilizer can then run into the soil at the base of the plant and the foliar applied nutrients will enter here as well.  This is basically the concept behind the use of Y-Drop for applying N to corn.

Sugars

First, they are a waste of money.  Most people see a response simply because they need to versus admitting they paid for something that doesn’t work.  The sugar molecule is C₆H₁₂O₆.  This big molecule cannot penetrate the leaf and cannot enter the root.  So the sugar must be feeding the soil microbiology because the plant is not utilizing it as it is applied.  Sugar has to be broken down first into C, H, and O.  The plant already has a source for these nutrients from the air and soil and they are called Carbon Dioxide (CO₂) and Water (H₂O).

Calcium-Containing Products

There is some promotion to supply large amounts of calcium to the plants because it is one of the building blocks to cell walls in the plant.  True.  However, the best and cheapest way to supply calcium and magnesium to the plant is by applying limestone.  A well-managed limestone program will supply all the calcium that a crop needs without the need for “miracle products”.  Secondly, the liquid calcium products do not eliminate hydrogen (H⁺) or acidity from the soil; therefore, you’ll need limestone anyway. The favored environment is pH 6.8 to 7.0. The carbonate (CO₃^-2) in limestone is needed to eliminate the hydrogen (H⁺).  Carbonate (CO₃^-2) will react with 2 hydrogens (H⁺) to form a weak carbonic acid (H₂CO₃), which is very unstable and quickly converts to carbon dioxide (CO₂) and water (H₂O).  For the chemistry folks in the room:

2 H⁺         +        CO₃^-2          ➡️          H₂CO₃         ➡️         CO₂        +        H₂O

Soil                      From                        Carbonic                  Carbon             Water

Acidity                Lime                      Acid, Weak                 Dioxide           (H⁺ is eliminated)

Maintaining the soil pH in that 6.5 to 7.0 range is also beneficial to B. Rhizobium japonicum, the microbe that infects the soybean root, creates the nodules, and then supplies N to the soybean plant.  In some soils, there can also be a large amount of aluminum.  When it undergoes hydrolysis, additional H⁺ is released into the soil.  Therefore, soil testing is a must to look at both the water pH and buffer pH to account for the active and reserve acidity in the soil.

• Look at all these products.
• Look at the labels.
• Some may have a fit into a larger program and some may not.
• Ask questions, a lot of questions!
• Do the calculations to see exactly what you are getting per quart or per gallon.