Plant analysis is an excellent in-season “quality control” tool. It can be especially valuable for managing secondary and micronutrients that do not have high-quality, reliable soil tests available and for providing insight into how efficiently you are using applied nutrients.
Kansas farmers can use plant analysis in two basic ways: for diagnostic purposes and for monitoring nutrient levels at a common growth stage. Diagnostics can be done at any time but are especially valuable early in the season when corrective actions can easily be taken. Monitoring is generally done at the beginning of reproductive growth.
General sampling guidelines:
- Plants are less than 12 inches tall: Collect the whole plant; cut the plant off at ground level.
- Plants more than 12 inches tall and until reproductive growth begins: Collect the top fully developed leaves (those which show leaf collars).
- After reproductive growth starts: Collect the ear leaves (below the uppermost developing ear); samples should be collected randomly from the field at silk emergence.
Figure 1. Corn sampling during different growth stage. Photos by Dorivar Ruiz Diaz, K-State Research and Extension.
Plant analysis for diagnostic sampling
Collecting specific plant parts is less important when sampling for diagnostic purposes than obtaining comparison samples from good and bad areas of the field.
Plant analysis is an excellent diagnostic tool to help understand some of the variation among corn plants in the field. When using plant analysis to diagnose field problems, try to take comparison samples from both good/normal areas of the field and problem spots. This can be done at any growth stage.
Along with taking plant tissue samples, collecting a soil sample from both good and bad areas is also helpful when doing diagnostics. Define your areas, and collect both soil and plant tissue from areas that represent good and bad areas of plant growth. Soil samples can help define why a problem may be occurring. The soil sample may find certain nutrient levels are very low in the soil, helping to explain why a deficiency is occurring. However, other factors can also cause nutrient problems. Soil compaction, or saturation of soils, for example, often limits the uptake of nutrients, especially potassium, which are otherwise present in adequate amounts in the soil.
Plant analysis for nutrient monitoring
Plant leaves should be collected as the plant enters reproductive growth for general monitoring or quality control purposes. Sampling under stress conditions for monitoring purposes can give misleading results and is not recommended. Stresses such as drought or saturated soils will generally limit nutrient uptake and result in a general reduction in nutrient content in the plant.
How should you handle collected samples, and where should you send them?
The collected leaves should be allowed to wilt overnight to remove excess moisture, placed in a paper bag or mailing envelope, and shipped to a lab for analysis. Do not place the leaves in a plastic bag or other tightly sealed container, as the leaves will begin to rot and decompose during transport, and the sample won’t be usable. Most soil testing labs in the region provide plant analysis services, including the K-State Testing Lab. For questions about the plant tissue testing services at the K-State Testing Lab, email soiltesting@ksu.edu or call 785-532-7897.
What nutrients should be included in the plant analysis?
In Kansas, nitrogen (N), phosphorus (P), potassium (K), sulfur (S), zinc (Zn), chloride (Cl), and iron (Fe) are the nutrients most likely to be found deficient. Recently, questions have been raised concerning copper (Cu), manganese (Mn), and molybdenum (Mo), though widespread deficiencies of those micronutrients have not been found in the state. Normally, the best values are the “bundles” or “packages” of tests offered by many labs. They can be as simple as N, P, and K, or they can be all the mineral elements 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 get back from the lab?
The data returned from the lab will be reported as the concentration of nutrient elements, or potentially toxic elements, in the plants. Units reported will normally be in “percent” for the primary and secondary nutrients (N, P, K, Ca, Mg, S, and Cl) and “ppm” (parts per million) for most of the 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 during surveys. It can be thought of as the range of values optimum for plant growth. The medical profession uses a similar range of normal values to evaluate blood work. The sufficiency ranges change with plant age (generally being higher in young plants), vary between plant parts, and can differ between hybrids. A value slightly below the sufficiency range does not always mean the plant is deficient in that nutrient. It is an indication that the nutrient is relatively low. Values on the low end of the range are common in extremely high-yielding crops. However, if that nutrient is significantly below the sufficiency range, you should ask some serious questions about the availability and supply of that nutrient.
Remember that any plant stress (drought, heat, soil compaction, saturated soils, etc.) can seriously impact nutrient uptake and plant tissue nutrient concentrations. A low value in the plant does not always mean the soil is low in the nutrient and that the plant will respond to fertilizer. It may be that the nutrient is present in adequate amounts in the soil but is either unavailable or not being taken up by the plant for various reasons. Two examples are drought, which can reduce plant uptake of nutrients and cause low nutrient values in the plant, and high-pH soils, which can cause low iron availability.
Conversely, levels above “sufficiency” can also indicate problems. High values might indicate over-fertilization and luxury consumption of nutrients. Plants will also sometimes try to compensate for a shortage of one nutrient by loading up on another. This sometimes occurs with nutrients such as iron, zinc, and manganese.
Table 1 gives the range of nutrient contents considered normal or “sufficient” for corn seedlings below 12 inches tall and for the ear leaf of corn at silking. Remember, these are the ranges normally found in healthy, productive crops.
Table 1. The range of nutrient contents considered “normal” or “sufficient” at two growth stages in corn.
|
Nutrient |
Unit |
Whole Plant |
Corn Ear Leaf |
|
Nitrogen (N) |
% |
3.5-5.0 |
2.75-3.50 |
|
Phosphorus (P) |
% |
0.3-0.5 |
0.25-0.45 |
|
Potassium (K) |
% |
2.5-4.0 |
1.75-2.25 |
|
Calcium (Ca) |
% |
0.3-0.7 |
0.25-0.50 |
|
Magnesium (Mg) |
% |
0.15-0.45 |
0.16-0.60 |
|
Sulfur (S) |
% |
0.20-0.50 |
0.15-0.50 |
|
Chloride (Cl) |
% |
Not established |
0.18-0.60 |
|
Copper (Cu) |
ppm |
5-20 |
5-25 |
|
Iron (Fe) |
ppm |
50-250 |
20-200 |
|
Manganese (Mn) |
ppm |
20-150 |
20-150 |
|
Zinc (Zn) |
ppm |
20-60 |
15-70 |
|
Boron (B) |
ppm |
5-25 |
4-25 |
|
Molybdenum (Mo) |
ppm |
0.1-10 |
0.1-3.0 |
|
Aluminum (Al) |
ppm |
<400 |
<200 |
Summary
Plant analysis is a good tool for monitoring the effectiveness of your fertilizer and lime program and a very effective diagnostic tool. Consider adding this agronomic practice to your toolbox.
Dorivar Ruiz Diaz, Nutrient Management Specialist
ruizdiaz@ksu.edu
Tags: corn nutrient deficiency tissue testing nutrient anaylsis