April 26, 2018
This has been one strange spring! And because of it, I’ve gotten more than the usual number of calls from farmers who wonder if they need to apply starter fertilizer when they plant. Unfortunately, “It depends” is not the answer most farmers want to hear.
First, let’s take a look at the nutrients in most starter fertilizers. Most starters are primarily nitrogen and phosphorus. A common starter is 10-34-0 which contains 10% nitrogen (N) and 34% phosphate (P2O5). Some starters may also have potassium or sulfur and possibly other micro-nutrients, if requested.
There are two ways a starter fertilizer can improve early plant growth, and sometimes yields. The obvious way is the starter can supply a nutrient that is lacking in the soil. The less obvious way is it can supply a nutrient that is adequate in the soil, but the plant cannot take up enough of this nutrient, at least early in the growing season.
If you’ve been farming long, I’m sure you’ve seen springs when the corn has a purplish color on the leaves. Several things can cause this, but it is usually related to the plant’s inability to take up phosphorus from the soil. Some of our soils are deficient in phosphorus and require additional phosphorus fertilizer. Other soils may have adequate levels of phosphorus, but it’s not getting into the plant.
Usually we see this situation early in the season when the soil is cool and plants are not growing rapidly. When this happens, the corn roots may not be extensive enough to intercept the phosphorus in the soil. Cool soils also slow the movement or diffusion of nutrients in the soil to the plant roots. The other problem with cool soils is microbes in the soil that assist the corn plant in taking up nutrients are not as active.
These fields often look poor early in the season, but grow out of it once we get warmer weather and the soil temperatures warm which results in increased root growth and microbial activity. Starter fertilizer may reduce the purple color because a concentrated band of phosphorus is placed near the seed, but the boost in early growth is often because of the nitrogen that is also found in the starter.
Earlier I said starters may improve plant growth, but not yields. That’s why I tell farmers “It depends” if starter will pay for itself with increased yields. It depends on the nutrient levels in the soil and the weather after planting. If the soil was deficient in a nutrient in the starter or if the weather remains cool and plant growth is slowed, then you are more likely to see a yield response. But if the soil had adequate nutrient levels and growing conditions continue to improve after planting, you are less likely to see a yield response.
So conditions when you will be more likely to see a response from starter fertilizer on corn include:
• When a nitrogen application was not made last fall or this spring before planting
• When soil temperatures are cooler than normal
• Fields with poorly drained soils
• No-till fields with high residue cover, especially on corn following corn
The last thing to remember when applying starter fertilizers is the potential for injuring the germinating seed and reducing your stand if making an in-furrow application. The rule of thumb on corn is to apply no more than a total of 10 pounds per acre of nitrogen plus potassium and sulfur, if potassium and/or sulfur are in your starter. The risk of injury is greater if the soil is dry.
The risk of injury from an in-furrow starter application on soybeans is much higher than it is in corn. Avoid in-furrow starter applications with soybeans if at all possible. Consider dribbling starter on top of the row if you can adjust your planter to do so. If you must make an application in furrow, use a very low rate.
For more information on starter fertilizers, contact your local Nebraska Extension office.