Plant analysis and soil testing are your best guides for most efficient fertilizer use.
High crop yields and quality depend on many factors-adequate water and nutrients, the correct plant population and variety, disease and insect resistance or control, etc. One of the most important is nutrient status of plants which reflects the nutrient supply of the plant at the time of sampling.
Nutrient status of plants is an "unseen" factor in plant growth, except when deficiencies become so acute as to appear visually as deficiency symptoms. Plant population can be counted, variety name can be read on the label, and rainfall measured with gauges. But the nutrient status of plants is measured by plant analysis in the laboratory.
Plant analysis shows the nutrient status of plants at time of sampling. In turn, this reflects sufficiency of soil nutrient supplies and applied fertilizers. Usually, plant analysis is most useful as a diagnostic too for future correction of problems, although, in the case of young plant samples, there is often time for remedial fertilizer application to crop. Combined with soil test information, results of plant analysis allow fertilizer practices to be fitted more closely to soil-plant needs.
Plat analyses usually identify status of the following elements:
| Nitrogen Phosphorus Potassium Calcium Magnesium |
*Sulfur Boron Copper Iron Manganese |
Zinc *Reported sometimes, or on request |
For accurate plant analysis, considerable care must be taken in collecting, preparing and sending the sample to the laboratory.
Parts of plants to sample vary with the plant and stage of growth. ITL provides instruction sheets which describe the part of plants to sample and at what growth stage sample should be taken. Also, these instructions indicate the number of plant parts needed for a sample. Use a clean plastic pail or paper bag, not metal, to collect the sample. A metal container may contaminate the sample.
If plant parts have soil, fertilizer, dust or spray residue on them they should be cleaned. Cleaning with a dry brush is best. If that isn't adequate, wipe sample with damp cloth. For stubborn residues, wash with water. Do not prolong washing. Air-dry samples in shade, not in sun. Clean paper bags or envelopes are best for mailing tissue samples to avoid contamination. Never place fresh tissue samples in plastic bags.
Request a mailing kit from Iowa Testing Laboratories. Read the instructions. Fill out the sample submission form. The more information you include, the better the interpretation of the plant analysis is likely to be.
CORN |
When to sample. Sometime between emergence from soil and silking. Do not sample after silks turn brown.
What part of plant. Seedling stage (6" to 12")-all the above ground portion. Sample 20 to 30 plants at random.
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Prior to tasselling. (Figure 1) Take the entire first mature leaf below the whorl-top of plant where emerging leaves coil or roll together. (A mature leaf is completely unrolled from stalk and fully elongated.) Do not include the leaf sheat-htat part attached to the stalk. From tasselling and shooting to silking. (Figure 2) Take the entire leaf at the ear node (or immediately above or below it). Again do not include the leaf sheath. |
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Amount to include in sample. Remove one leaf per plant from 15 to 25 plants selected at random in the field and/or problem area. Break off leaf aat base. (See Figure 1).
SOYBEANS
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When to sample. The ideal time to sample is when the first bloom appears. However, if problems develop prior to bloom, the seedling can be sampled. Do not sample after pods begin to fill.
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What part of plant. Seedling stage (6" to 12")-all the above ground portion. Sample 20 to 30 plants at random. Prior to pod filling-Select the two or three fully developed trifoliate leaves at the top of the plant (Trifoliate leaf includes three leaves on one stem or petiole). Do not use upper leaves which have not developed to full size. |
Amount to include in sample. Remove two or three trifoliate leaves per plant from 20 to 30 plants selected at random. Remove and discard stems as shown in figure 4. | |
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Sampling other crops
SAMPLING OTHER CROPS |
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| Stage of growth | Plant part to sample |
Number of parts needed |
| Alfalfa | ||
| Prior to or at bloom stage | The entire top half or top 6 inches of the plant | 30-35 |
| Sorghum-milo | ||
| Prior to or at heading | Second leaf from top of plant | 15-25 |
CAUTION |
Soil testing plus plant analysis provides your best fertilization guide. Contact Iowa Testing Laboratories for details.
Text prepared by:
Soil and Plant Testing Committee,
The Fertilizer Institute
Union Center Plaza
820 First Street NE
Suite 430
Washington, DC 20002
www.tfi.org
