Pop-Ups or In-Furrow fertilizers are typically used on corn to supply a small quantity of N (Nitrogen) and P (Phosphorus) or micronutrients. This N and P is used for early season plant vigor or to satisfy a need determined by low soil tests. Nitrogen and K (Potassium) have a high salt index and should not be used in a pop-up situation or in limited quantities. Greater salt injury can occur in sandy or dry soils and less injury in clayey or wetter soils.
Products like urea, UAN solutions and ammonium thiosulfate should not be used in a pop-up situation. Years ago when I was conducting research at SIU-Carbondale, we observed severe root injury and stand reduction in corn at rates as little as 7.5 lbs./acre of polymer-coated urea placed in-furrow (unpublished data). Soybeans are much more sensitive to salt injury than corn.
Cornell University published an article regarding pop-up and starter fertilizer use. Below is a table from Cornell University on pop-up fertilization limits.
Starters, on the other hand, are placed 2 x 0 (two inches to the side of the seed) or 2 x 2 (two inches to the side and two inches below the seed) to supply larger quantities of N and P than In-Furrow amounts. This placement helps minimize potential injury to the root system from high salt index fertilizers. There are a myriad of products available on the market today and many have a much lower salt index than the old standard 10-34-0. Here is a second table from Cornell University on Starter Fertilization limits.
So, do we need to be applying pop-ups and/or starters on soybeans? It depends on a variety of factors, some of which may be (not in any particular order): planting date, soil textural class, soil test values, soil productivity index, soil type or soil order. The Aridisols or calcareous soils common in the western Corn Belt and Western States are much drier and have a naturally high soil pH. These soils benefit from high P containing starters. The dark, rich Mollisols and the lighter Alfisols found in the Midwest are more acidic in nature, much wetter in the spring and benefit from N and P containing starters.
Soybeans grown on low testing soils will benefit the greatest from starters, responding especially well to P. Even more so on medium testing soils in high productivity regions. Additionally, a small amount of K in the starter mix can greatly benefit soybeans by aiding in enzyme activation, root nodulation and biological N fixation. If you want to apply N, I would suggest no more than 10 lbs./acre of actual N. Some reports and research suggest 10 – 20 lbs./acre, but I am a little more reserved. Higher N rates can result in reduced nodulation, which in turn could potentially limit your N supply later in the season at peak demand.
I personally view Pop-Ups and Starters as a means of obtaining early season plant health and vigor when the soils are cool and wet. This will help the plant get out of the ground quicker and a healthier plant can fight off pathogen attack better. Also, they are a good option for supplying needed micronutrients, especially zinc and boron. Most of the time you will not see a dramatic yield increase, but you may see a 2 – 5 day earlier harvest which has value as well.
Remember with these lower commodity prices to figure the cost of all of these additional inputs. However, do not figure what these costs are up front. Ask and figure what these additional inputs will gain you at harvest time. Simply put … will I see a return on my investment?
To read the full Cornell article, click here.
Terry Wyciskalla is an independent crop and soils consultant based out of Nashville, Illinois. He specializes in soil sampling, fertility recommendations, precision ag services and crop problem diagnoses. He serves a 12-county area throughout Illinois. He earned his 4R Nutrient Stewardship certification in 2015 and is happy to be a part of the 2016 Soy Envoy team.