Improve nitrogen fixation in soybeans to increase yield and crop performance
Maximizing soybean yield depends on meeting the crop’s nitrogen needs. Soybeans require about 3.5 pounds of nitrogen per bushel of grain, making proper nitrogen supply very important. Strong nodulation helps plants get enough nitrogen for healthy growth and high yield.
Nodulation occurs when rhizobia bacteria in the soil attach to soybean roots and form nodules. In this process, the plant provides energy to the bacteria, and in return, the bacteria convert nitrogen from the air into a usable form for the plant. This natural process supports crop development without relying fully on fertilizers.
“At [V1 or V2], I’m not overly worried about the top growth of this plant,” said Jonathan Rotz, Pioneer strategic account manager. “What I am really going to look at is what is going on below ground. One of the first places we want to look is the nodulation.”
Farmers should check nodulation early in the growing season. At the V2 or V3 stage, plants should have seven to 14 nodules. These nodules should appear pink or red when opened, showing that nitrogen fixation is working properly. Monitoring root health is more important than early top growth.
Several factors can reduce nodulation. These include low levels of rhizobia bacteria, poor soil oxygen due to compaction or excess water, weak seed treatments, drought stress, and high nitrogen levels in the soil. These conditions can affect the plant’s ability to fix nitrogen.
Poor nodulation can lead to nitrogen deficiency. If plants have five or fewer nodules or if nodules are not active, nitrogen supply may be limited. In such cases, adding supplemental nitrogen can help.
For better results, farmers should apply less than 44 pounds of nitrogen, as higher amounts do not increase yield. Urea with a urease inhibitor is recommended, while liquid nitrogen may damage leaves. Fertilizer should be placed between rows and applied at early flowering when plants can use it efficiently.
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