Plant analysis to test nutrient levels in corn
Plant analysis is an excellent in-season “quality control” tool. It can be particularly useful for managing secondary elements and micronutrients that lack reliable, high-quality soil testing, and for providing insight into how efficiently you are using applied nutrients.
Plant testing can be used by Kansas farmers in two basic ways: for diagnostic purposes and to monitor nutrient levels at a common growth stage. Diagnostics can be performed at any time and are particularly useful at the start of the season when corrective action can easily be taken. Monitoring is usually done early in reproductive growth.
General Sampling Guidelines:
• Plants less than 12 inches tall: Harvest the whole plant; cut the plant at ground level.
• Plants over 12 inches in height and up to the start of reproductive growth: Harvest fully expanded upper leaves (those with crowns).
• After the start of reproductive growth: Collect the leaves from the ear (under the upper developing ear), samples should be taken randomly in the field as the silks emerge.
Plant analysis for nutrient monitoring – for general monitoring or quality control purposes, plant leaves should be collected when the plant enters the reproductive growth stage. Sampling under stress conditions for monitoring purposes can give misleading results and is not recommended. Stresses such as drought or saturated soils generally limit nutrient uptake and cause an overall reduction in plant nutrient content.
What nutrients should be included in plant analysis? In Kansas, nitrogen (N), phosphorus (P), potassium (K), sulfur (S), zinc (Zn), chloride (Cl) and iron (Fe) are the most common nutrients. likely to be deficient. Recently, questions have been raised regarding copper (Cu), manganese (Mn), and molybdenum (Mo), although widespread deficiencies of these micronutrients have not been found in the state. Normally, the best values are the “bundles” or “packages” of tests offered by many laboratories. They can be as simple as N, P, and K, or can be any mineral element considered essential to plants. K-State offers a package that includes N, P, K, Ca, Mg, S, Fe, Cu, Zn, and Mn.
What will you remember from the lab? The data returned by the laboratory will be reported as the concentration of nutrients, or potentially toxic elements, in the plants. Units reported will normally be in “percentage” for primary and secondary nutrients (N, P, K, Ca, Mg, S and Cl) and in “ppm” (parts per million) for most micronutrients (Zn, Cu, Fe, Mn, B, Mo and Al).
Most labs/agronomists compare plant nutrient concentrations to published sufficiency ranges. A sufficiency range is simply the range of concentrations normally found in healthy, productive plants when investigated. It can be considered the range of optimal values for plant growth. The medical profession uses a similar range of normal values to evaluate blood tests. Sufficiency ranges change with plant age (they are usually higher in young plants), vary between plant parts, and can differ between hybrids. A value slightly below the sufficiency range does not always mean that the plant is deficient in this nutrient. This is an indication that the nutrient is relatively low. Values at the lower end of the range are common in extremely high yielding crops. However, if that nutrient is significantly below the sufficiency range, you need to have serious questions about the availability and supply of that nutrient.
To read the full article on the best way to harvest and ship plant leaves, learn more about plant stress and nutrient uptake, extreme nutrient levels and the range of nutrient contents considered as “normal” or “sufficient” at two growth stages of corn at www.cottonwood.ksu.edu
Stacy Campbell is the Agriculture and Natural Resources Officer for the Cottonwood Extension District. Email him at [email protected] or call Hays’ office at 785-628-9430.