posted by Martin Botha on Sep 21

Sampling for Plant Tissue Analysis

Of the many factors affecting crop quality and yield, fertility is one of the most important. It is fortunate that producers can control fertility by managing the plant’s nutritional status. Nutrient status is an unseen factor in plant growth, except when imbalances become so severe that visual symptoms appear on the plant.

WHAT PLANT TISSUE ANALYSIS SHOWS

Plant tissue analysis shows the nutrient status of plants at the time of sampling. This, in turn, shows whether soil nutrient supplies are adequate. In addition, plant tissue analysis will detect unseen deficiencies and may confirm visual symptoms of deficiencies. Toxic levels also may be detected. Though usually used as a diagnostic tool for future correction of nutrient problems, plant tissue analysis from young plants will allow a corrective fertilizer application that same season.

Not all abnormal appearances are due to a deficiency. Some may be due to too much of certain elements. Also, symptoms of one deficiency may look like those of another. A plant tissue analysis can pinpoint the cause, if it is nutritional. A plant analysis is of little value if the plants come from fields that are infested with weeds, insects, disease organisms; if the plants are stressed for moisture; or if plants have some mechanical injury.

The most important use of plant analysis is as a monitoring tool for determining the adequacy of current fertilization practices. Sampling a crop periodically during the season or once each year provides a record of its nutrient content that can be used through the growing season or from year to year. With soil test information and a plant analysis report, a producer can closely tailor fertilization practices to specific soil-plant needs.

It also may be possible to prevent nutrient stress in a crop if the plant analysis indicates a potential problem developing early in the season. Corrective measures can be applied during the season or, if the crop is perennial, during the next year. Combined with data from a soil analysis, a tissue analysis is an important tool in determining nutrient requirements of a crop. By request, the following elements can be determined in a plant sample:
  

COLLECTING AND PREPARING THE SAMPLE

If you suspect a nutrient deficiency:
1) Sample when the symptom first appears (see table 2 for deficiency symptoms).
2) In the same field or area, collect similar samples of plant materials from plants that appear abnormal.
3) Make sure that the symptoms are not due to a factor unrelated to plant nutrition.

The parts of plants to sample depend on the plant and its growth stage. Table 3 lists the best parts to sample for common crops (see also fig. 1). More specific sampling strategies may be necessary for cotton and peppers (chile).

Instructions for leaf sampling may differ. Also, comparing samples from both a “good” and a “bad” area often helps in determining corrective action. If specific sampling guidelines are not given here, collect recently mature leaves just below the growing point from at least 10 plants.

When gathering the tissue sample in the field, use a clean container. A plastic pail or a paper bag works best. Never use a metal container because it can contaminate the sample.

If the plant samples have soil, fertilizer, dust, or spray residues on them, they will need to be cleaned. A dry brush works best, but for stubborn residues, wipe the samples with a damp cloth or wash them with distilled or deionized water. However, do not prolong the washing because it can leach nutrients out of the tissue.

Air-dry the samples in the shade, not in the sun. To prevent contamination, place the dried samples into clean paper bags or envelops for mailing to the laboratory. Never place fresh plant tissue samples in plastic bags for mailing. The plastic bags do not allow the samples to dry, so they may decompose. It is also a good idea to take a soil sample in the same vicinity as the plant sample because the soil test may help to interpret the plant tissue analysis readings.

Provide Information with the Sample
When mailing samples to the laboratory, be sure to provide the following information:

• Type of crop.
• Variety.
• Soil type (if known).
• Current crop fertilization and management practices (such as stand, kinds and rates of fertilizer, method of fertilizer application).
• Last year’s crop fertilization practices and yield.
• Irrigation frequency and quality of irrigation water.
• Visual appearance of crop.
• Insect and disease problems (if any).

This information is necessary for sound interpretation of the plant tissue analysis.

Things to Avoid
Do not sample the following:

• Young, emerging leaves; old, mature leaves; and seeds. These plant parts usually are not suitable because they are not likely to reflect the nutrient status of the whole plant.
• Diseased or dead plants.
• Plants that have insect or mechanical damage.

General symptoms of nutrient deficiency in plants.

Tissue sampling techniques for specific plants.