Plant Tissue Analysis
Plant tissue analysis complements soil testing by measuring the nutrients actually taken up by the plant. In addition, secondary nutrients and micronutrients that currently are not routinely measured in soils can be measured reliably in plants.
It should be noted, however, that plant nutrient content represents the effects of not only soil nutrient status but also all the factors controlling plant growth. Therefore, a single year’s information may not be useful for planning a soil fertility management program. But as results are accumulated over a period of years, the information will become more valuable.
Sample collection is very important. The nutrient concentration in a plant varies with the plant’s age and the part of the plant sampled. If plant analyses are to be meaningful, the appropriate plant part must be collected for the age of the plant, and a number of plants must be included to obtain a representative sample. Specific directions on plant sampling generally are available with each sampling kit from the plant analysis laboratory. Sampling instructions and sufficiency levels for corn, alfalfa, small grains, and soybeans can be found in the following table.
Plant part to be sampled, growth stage, and sufficiency levels for plant tissue analysis
At least 10 subsamples of the indicated plant part(s) should be taken at the indicated growth stage to make a complete sample for submission to the lab.
|Plant part:||Whole Plant
||Ear leaf||Leaves, top 33% of plant||Uppermost leaves||Uppermost full leaves|
|Time:||~12 inches tall
||Silking||Bud to 10% bloom||Before heading||Prior to or early flowering|
|Element||Sufficiency range¹ (percent)|
|Sufficiency range¹ (ppm)|
Plant tissue analyses may be useful in diagnosing crop nutritional problems. Take samples from the problem area and a nearby “normal” area for comparison. Then, use all available information to interpret the plant analysis for diagnosing a nutrient deficiency. Look carefully at symptoms on the plants, note any patterns in the field, and consider the timing of the problem’s appearance. Keep in mind that not all nutrient deficiencies in plants are the result of nutrient deficiencies in the soil.
Soil testing and plant analysis can confirm each other, but they also can indicate when the cause of the problem is something other than a nutrient deficiency in the soil. If the soil test level is optimum but the plants are deficient, some other factor is limiting the plant’s ability to take up available nutrients. Some areas to consider include:
- possible interactions with other cultural practices such as tillage or pesticide use
- pest injury such as rootworm feeding
- differences in varieties or hybrids
- soil physical conditions such as compaction.
Soil and plant sampling and mailing kits are available from your local extension office.