Description
Visual symptoms only tell part of the story. By the time nutrient deficiencies become obvious in a soybean field, yield potential may already have been affected.
In this episode of RealAgriculture's Soybean School, SGS Crop Science agronomist Jack Legg explains how tissue testing during the reproductive stages can help growers identify nutrient deficiencies, evaluate overall plant health, and make in-season management decisions before hidden problems become yield robbers.
While early-season tissue testing focuses on juvenile plant development, Legg says the approach changes once soybeans reach flowering and pod development. At this stage, growers should be evaluating the crop for subtle differences in colour, height, and vigour while using tissue tests to confirm whether nutrient uptake is keeping pace with crop demand.
"A soil test is always a good first start to see what the fertility of the soil is," says Legg. "However, that doesn't necessarily mean the crop will utilize all the nutrient."
Weather, soil compaction, and soil texture can all limit nutrient uptake, even when soil fertility is adequate. Tissue testing can identify deficiencies before visible symptoms develop, allowing growers to consider foliar nutrient applications where they are likely to provide a benefit.
Legg says manganese and potassium are two of the nutrients growers should be watching closely. Interveinal chlorosis can indicate manganese deficiency, while yellowing along the leaf margins may point to a potassium shortage.
Sampling also differs later in the season. Rather than collecting entire plants, growers should sample the newest fully developed trifoliate leaf—typically four or five leaves below the growing point—from representative areas across the field.
Beyond plant nutrition, Legg recommends digging plants to assess root health, nodulation, and potential disease issues. Healthy, pink nodules indicate active nitrogen fixation, while examining roots can also help identify disease problems. Where soybean cyst nematode is suspected, however, soil sampling remains the preferred diagnostic tool.
Perhaps the biggest value of tissue testing is its ability to uncover what Legg calls "hidden hunger"—nutrient deficiencies that have not yet produced obvious symptoms but may already be limiting yield potential. "We want to make sure that the plant nutrition is doing fine, and a tissue test does that," he says.
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