Wheat producers may want to start planning soon for taking tissue samples of wheat for plant analysis. Sampling can be done at the tillering-jointing stage, or later in the season near boot to heading. The later-season sampling, once the flag leaf has emerged until flowering, is commonly used for routine monitoring or quality control. The process is fairly simple, but care needs to be taken to ensure the correct plant parts are taken and that they are handled properly to ensure the best information is obtained.
There are two primary ways plant analysis can be used: as a routine monitoring tool to ensure nutrient levels are adequate, and as a diagnostic tool to help explain some of the variability in wheat growth we see in fields this time of year. Keep in mind, however, that any plant stress (drought, heat, frost, etc.) can have a serious impact on nutrient uptake and plant tissue nutrient concentrations. Sampling under stress conditions for monitoring purposes can give misleading results, and is not advisable.
Sampling for routine monitoring
For monitoring purposes, early in the season, 40-50 whole plants, without roots, should be collected at random from the field. The plants 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 plants in a plastic bag or other tightly sealed container, as they will begin to rot and decompose during transport, and the sample won’t be usable.
Later in the season as the stem elongates and new leaves emerge, the top fully developed leaves with a leaf collar visible should be collected. Ideally, samples for routine monitoring would be the flag leaves during the heading to flowering stages. Again, 40 to 50 fully developed leaves would be collected, allowed to wilt to remove excess moisture, placed in a paper bag or envelope, and shipped to the lab.
The data returned from the lab will be reported as the concentration of nutrient elements, or potentially toxic elements in the plants tissue collected. 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 varieties. So a value slightly below the sufficiency range does not always mean the plant is deficient in that nutrient, but it is just an indication that the nutrient is relatively low. In many cases, very high yielding wheat that is growing efficiently will have nutrient concentrations at the low end of the sufficiency range. However, if a nutrient is significantly below the sufficiency range, then one should ask some serious questions about the availability and supply of that nutrient.
Levels above sufficiency can also indicate problems. High values might indicate over fertilization and luxury consumption. Plants will also sometimes try to compensate for a shortage of one nutrient by loading up on another. This occurs at times with nutrients such as iron, zinc, and manganese. In some situations very high levels of a required nutrient can lead to toxicity. Manganese is an example of an essential nutrient which can be toxic when present in excess.
Plant analysis as a diagnostic tool
Plant analysis is also an excellent diagnostic tool to help understand some of the variation seen 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. Collect soil samples from the same good and bad areas also. Don’t wait for the boot stage to take diagnostic samples. Early in the season (prior to stem elongation) collect whole plants from 20-30 different places in your sampling area. Later in the season take the upper most, fully developed leaves (those with leaf collars visible). Handle the samples the same as those for monitoring.
Sufficiency ranges
The following table gives broad sufficiency ranges for wheat early in the season, prior to jointing (Feekes 4-6), and later in the season, at boot to early heading (Feekes 9-10). Keep in mind that these are the ranges normally found in healthy, productive wheat.
|
|
|
Growth stage |
|
|
Nutrient |
Unit |
Whole plant at tillering-jointing |
Flag leaf at boot to heading |
|
Nitrogen |
% |
3.5-4.5 |
3.5-4.5 |
|
Phosphorus |
% |
0.3-0.5 |
0.3-0.5 |
|
Potassium |
% |
2.5-4.0 |
2.0-3.0 |
|
Calcium |
% |
0.2-0.5 |
0.3-0.5 |
|
Magnesium |
% |
0.15-0.5 |
0.2-0.6 |
|
Sulfur |
% |
0.19-0.55 |
0.15-0.55 |
|
|
|
Growth stage |
|
|
Nutrient |
Unit |
Tillering-jointing |
Boot |
|
Iron |
ppm |
30-200 |
30-200 |
|
Manganese |
ppm |
20-150 |
20-150 |
|
Zinc |
ppm |
15-70 |
15-70 |
|
Copper |
ppm |
5-25 |
5-25 |
|
Boron |
ppm |
1.5-4.0 |
1.5-4.0 |
|
Aluminum |
ppm |
<200 |
<200 |
In summary, plant analysis is a good tool to monitor the effectiveness of your fertilizer and lime program, and a very effective diagnostic tool. Consider adding this to your toolbox.
Dave Mengel, Soil Fertility Specialist
dmengel@ksu.edu
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