I am pleased to have this opportunity to post an editorial on ISA’s ILSoyAdvisor management website. Soybeans are a unique crop whose end product is the production of high levels of protein and oil. When a crusher buys your soybeans, he is less interested in your production level than in how many lbs. of oil and protein he can extract from a bushel.
While yields have increased over the last few decades, general protein levels have gone the other way. Much of the yield potential of new soybean varieties is rarely achieved in the field on a commercial basis without a lot of extra help. Today’s soybean crop presents new opportunities to build yields in ways much different and more time-specific than today’s corn production practices.
Increasing soybean yields requires insights into the unique properties of soybeans and the essential building blocks of protein. Protein production is dependent on having adequate supplies of nitrogen and sulfur during the reproductive stages of the soybean plant. However, adding high levels of nitrogen throughout the life of the soybean plant, or at the wrong time, tends to reduce the effectiveness of the nodule interaction which provides much of the needed nitrogen for normal yields. Timing of application is important. Indications are that supplementing nitrogen and sulfur levels in the right ratios early in the reproductive stage can increase both yield and protein. Supplemental applications of nitrogen alone won’t do the trick.
The most effective nitrogen sources need to be stable, readily available and nonvolatile. In fact, a literature review suggests that these properties may be most effective under lower rainfall conditions when the nodules struggle to fix nitrogen. If you remember back to 2014, soybean growth stalled out and plants took on a yellow hue due to wet conditions which adversely affected the nodules’ struggle to fix nitrogen.
However, the soil still needs a rain event in order to supply the plant with a needed, stable and accessible source of nitrogen. It is very helpful for the nitrogen source to be in the right form for rapid plant uptake and to overcome organic matter interaction or tie up. A balanced and appropriately proportioned application of ammonium nitrate and ammonium sulfate is an intriguing approach that has shown some significant responses in our limited trials.
There is a lot of interest in applying additional products to increase soybean yields—and more study is needed to define when nitrogen does contribute—but applying a balanced program of nitrogen and sulfur may just be the ticket to increasing crude protein and yield.