Wheat producers may want to start planning soon for taking tissue samples of wheat for plant analysis. Sampling can be done at tillering-jointing stage, or later in the season near the boot stage. If sampling is done early, this can allow time for corrective measures to be taken.

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 at tillering-jointing for routine monitoring

For monitoring purposes, 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.

The data returned from the lab will be reported as the concentration of nutrient elements, or potentially toxic elements in the plants. 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. However, if that 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. 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.