Agronomy: Applying Starters on Soybeans

So, can you apply a starter fertilizer on soybeans and, if so, what are the rules?

Starter fertilizer is a small quantity of nutrients applied in close proximity to the seed at planting. Starter fertilizers enhance the development of emerging seedlings by supplying essential nutrients in accessible locations near the roots at a time when nutrients might not be available.

Yes, you can apply a starter on soybeans, but the rules are a bit different. I know that many university soil fertility specialists advise against it, but it can be done and any risk can be managed. With so many growers planting soybeans earlier and even at the same time as corn, using a starter begins to make sense. And if you no-till beans into cornstalks starters it makes even more sense. But if you apply a starter please account for it in your overall nutrient budget so that the dollars spent applying a starter means less should be spent elsewhere on your dry fertilizer budget. So if you are spending $12 to $20 per acre on starter, account for that in your overall fertilizer budget for soybeans.

Of course, I have to acknowledge that as farmers have gone to larger planters and wanting to plant more acres per day, they no longer want to plumb a large 24-row or 36-row planter or spend time tending fertilizer and carrying on that extra weight on the tractor and planter that can pinch the rows alongside tire tracks. But on the opposite side, the more often you can feed a plant, the better fertilizer use efficiency you will experience.

Soybeans do respond to starter, but generally when you plant later the response is often smaller or occurs less often. And soybeans are more sensitive to salt in fertilizer so you have to cut back the rates or band it away from the seed so the soil acts as a natural barrier and dilutes the salt effect. Also, since soybean planting generally happens when soils are warmer, root growth is faster, nutrients are more mobile in the soil and nutrients are being mineralized.

Regardless of crop, the same rules apply. If the soil test values are low, soils are sandy, soils are cool, planting early, or planting in no-conditions consider using a starter. However the risk of injury is lower if you band, use a low-salt starter, soils have a higher CEC, soil is moist or it rains a day after planting.

First, let’s talk about in-furrow starter or pop-up—this is where the most risk exists. In corn you can easily apply 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 the rate to 2 gallons of product per acre along with 3 gallons of water and a salt index of 3 or 4 lbs. per acre, which I consider safe. I also consider the 3 gallons of water important because it helps to dilute the salt effect in the soil. Of course that means carrying around 5 gallons of product per acre which means you have to tender your planter more often.

Of course if you apply in a 1-by-1-inch or 2-by-2-inch band away from the seed, that soil zone acts as major buffer against fertilizer damage. Nevertheless, I consider following my half-rate rule still important. So for corn I consider 20 lbs. the top rate for a 1-by-1-inch band and 45 to 50 lbs. top for the 2-by-2-inch band. In soybeans I would cut that back to 10 and 25 lbs., respectively.

Soybeans need phosphate and potash just like corn does so feeding some of it through a starter makes some sense. However, one may ask about applying nitrogen since most starters carry it. When it comes to making a nitrogen recommendation on soybeans, currently one of the few sound recommendations is to apply some nitrogen preplant or as a starter. The plant’s early growth can benefit, it can help with residue decomposition and most of that nitrate will be gone by the time nodules begin to form on the roots.

So what are your thoughts on applying a starter on soybeans? Have you done it successfully? Has it worked and given you a response? Has it damaged your crop and you said “never again”? If you like the practice, what is your recommendation for doing it?

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.