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Sponsored: Nitrogen Management in Soybeans
Which requires more nitrogen (N); corn or soybeans? The answer may surprise you. It’s soybeans. Soybeans require approximately 5 lb. of N to produce one bushel. A 60 Bu./A soybean yield would then require about 300 lb. of N. To drive higher yields in soybeans, we need to drive more N into the plant. The soybean plants get this N from mineralization and from bacteria that produce N through nodules. The question we must ask ourselves is, “How can we make the nodules produce more N?” Let’s review a few of the management practices we can put into place.
Plant Early: Nodules work best at temperatures of around 73°F. When you plant early and get quicker canopy closure, the shade provided by the plant will keep the ground cooler and the temperature moderate, making the nodules more efficient. This is one of the main reasons why early planted soybeans yield more than late planted soybeans. Trying to shade the ground quicker by increasing plant populations may help later planted soybeans, but is not needed for early planted soybeans.
Tillage: Many people no-till their soybeans. No-till can help retain more moisture, but it also keeps the soil temperatures cooler (and buffers temperature extremes), especially in hot years. This improves the efficiency of nodules.
pH: Soybeans grow best at a neutral pH of 6.5 to 7.0. The reason they like a neutral pH is that the Bradyrhizobia bacteria in the nodules work best at this pH.
Calcium: Higher calcium levels in the plant seem to make Bradyrhizobia more efficient.
Planting Depth: Soybeans begin to nodulate at the depth of planting. Nodules are more efficient at a consistent temperature and moisture, which occurs at a deeper depth. There needs to be a balance between depth to increase nodule efficiency and emergence. A planting depth of about 1.5 in. should be pretty close to adequate.
Many farmers have tried to apply N to increase yields with variable results. Approximately 50 percent of all studies in which N is applied show no yield increases, while the other 50 percent do show a statistically significant increase. The average yield increase for those studies which did respond to N was over 8 Bu./A. Why don’t we see more consistent results? If you have nitrate N in the zone where Bradyrhizobia form (approx. 1 to 4 in. below the soil surface), there will be fewer nodules that form. Research is being conducted to try and determine if there is an ideal timing, amount, or form of N to consistently increase yield.
In the meantime, we need to focus our attention on making the bacteria as efficient as possible.
Mark Apelt, CCA | Regional Product Specialist