Soybean Side-Dress Trial This is the second year of testing in the soybean side-dress trial and continues to be one of our favorite trials on the farm. This trial is designed to evaluate the response to late season addition of phosphorus to soybeans. When we set up this trial a lot of people thought that we were crazy when we talked about side dressing soybeans with phosphates. The thought came from a research article that describes the soybeans need for phosphorus during the reproductive stages and results that indicated yield increases from these additions. Because phosphorus and zinc are taken up together we also added zinc to the trial then added QLF Boost and Terramar also to see if there was an advantage to that. We would expect the Boost to drive photosynthesis and the Terramar to aid in stress reduction, nutrient movement and photosynthesis. The side dress was added during cultivation in the early R1 growth stage. In 2021, we added the side-dress at late R2 to early R3. We observed a 5.1 bpa increase from the addition of 4 gpa of 10-34-0, however when we added zinc and QLF Boost, yields were increased over the check but not as dramatically as the 10-34-0 alone. We felt that this was because we did not have ample time to move the zinc through the plant. Once zinc reaches the leaf petiole it can take an additional 20 to 30 days to reach the leaf tip. For 2022, we moved the timing to the early R1 growth stage in order to allow more time for the zinc to move through the plant. Phosphorus (P) is an essential nutrient that enhances root development, photosynthesis and energy transport in soybeans. P is immobile in the soil and when loss occurs it is with soil loss by erosion and runoff, small amounts of water soluble P can be bad in water causing algae blooms when there is enough nitrogen also present. The immobility in the soil makes it very important to place P where the plant roots can acquire it in order to optimize yields. Placing P next to the plant with the cultivator makes great sense when thinking of adding P in season, in order to most efficiently supply additional nutrients. P reacts with other elements in the soil such as iron, calcium or aluminum that can leave it unavailable to the plant. We feel that this is another reason that we are seeing a response to additional P during the growing season. This is because 75-80% of the P is taken up by soybeans in the late vegetative to mid reproductive stages of the plant.
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