I got an email from a grower in northern Illinois this past Christmas. He was concerned that if he applied an in-furrow starter in soybeans, the starter might ruin germination or injure soybean seedlings because of its salt content. He said he could apply it in-furrow or dribble on top just off center of the emerging row. Another option would be to place it in a 2×2 band to the side of the seed trench.
Applying starters has been a common practice in corn where growers routinely apply 5 gallons per acre of 10-34-0 or some other analysis. They put it in-furrow as a pop-up or they applied in a 2×2 (2” inches to the side and 2 inches below the seed trench) band. Corn isn’t as sensitive to the salt content in liquid fertilizer and a grower could easily apply it as a furrow or as a 2×2 band.
But agronomists and growers have all worried that it was too great a risk with soybeans. And it is true that it is a risk, but a manageable one if you know what you are doing.
Pop-up or 2×2 Band or Surface Dribbling: All the systems work, but the closer you are to the seed the greater the salt risk. In-furrow should be limited to a couple gallons. With banding or dribbling you can double the volume of liquid fertilizer because it will be diluted out in the soil and the soil exchanges sites will grab and hold many of the salts.
Fertilizer Analysis: So what should be in the starter? There are many starters available that can work such as 10-34-0, 7-7-7, 7-21-7, 28-0-0, etc. There are many commercial, proprietary blends available and some are featured as salt-free. When it comes to soybeans, as with corn, the analysis isn’t so important. What is important is provide a freshly available source of nutrients to the seedling roots. So what do soybeans need in the spring when soils are cool and there is little or no mineralization? A little nitrogen, phosphorus, sulfur, zinc and manganese. Don’t worry about applying potassium. Potassium isn’t mineralized and ample amounts are usually available from the stover left by the previous corn crop. However, if you buy a commercial starter blend, it may already contain potassium.
Salt Index: We don’t have to make this too hard as it is quite simple to estimate. Corn, for example, can tolerate 10 to 12 lbs. per acre of fertilizer salt, while soybeans are limited to 5 to 6 lbs. The fact is only nitrogen and potash are salts, while phosphate isn’t. So don’t include phosphate in your estimate. To estimate, calculate the lbs. of nitrogen and potash in a gallon (% nutrient times weight of gallon) and add up for the number of gallons applied. This is an easy estimate.
In corn you can add 5 gallons of 10-34-0 or other specialty starter liquids like 8-20-3-6S-.4Zn as long as your salt index doesn’t exceed 10 lbs. per acre. In soybeans I cut back that rate to 2 to 2.5 gallons of product per acre along with 2.5 to 3 gallons of water and a salt index of 3 or 4 lbs. per acre, which I consider safe. The 3 gallons of water are important because they dilute out the salt effect in the soil since the water helps redistribute it.
Adding starters to soybeans is a good way to add some early nitrogen, phosphate, sulfur, zinc and manganese. Adding starter with phosphate is especially important for soils testing low in phosphate or cold soils. It may help boost soybean growth and help the crop establish itself quicker if conditions are cool and damp or if the crop is no-tilled. Adding manganese helps correct glyphosate herbicide’s tying up manganese in the plant. Using starter works in at-risk seasons or at-risk areas of a field and serves as a good risk management tool to help the crop get established more quickly, just like in corn.
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at email@example.com.