Plant Testing & Sampling Service
From Agricultural Testing
Plant sampling guidelines: Proper plant sampling techniques are essential for meaningful evaluation of crop fertility. Be sure to use clean sample bags which breathe freely. Collect a sufficient number of samples to represent the field—at least 25 to 30. Collect the samples from representative parts of the field. Stay away from odd areas unless they are to be sample separately. Collect the correct portion of the plant.
If you suspect a nutrient deficiency:
- Sample when the symptom first appears (see Table 1 for deficiency symptoms).
- In the same field or area, collect similar samples of plant materials from plants that appear abnormal.
- Make sure that the symptoms are not due to a factor unrelated to plant nutrition.
Instructions for petiole or 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, wipes the samples with a damp cloth or washes 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 the plastic bags for mailing. The plastic bags do not allow the sample 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 reading
When mailing samples to the laboratory, be sure to provide the following information:
- Type of crop.
- 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).
- Young emerging leaves; old, mature leaves; and seed. 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.
- Nitrogen: Plant light green, lower leaves yellow to light brown, stalks short and slender, plants stunted.
- Iron : Young leaves are chlorotic, with principal veins typically green; stalks short and slender.
- Phosphorus : Plants dark green, often developing red and purple pigments; lower leaves sometimes yellow; plants stunted.
- Zinc : Leaf spots on older leaves, with spots rapidly enlarging and generally involving the area between the veins; thick leaves; stalks with shortened internodes.
- Potassium : Spots of dead tissue, usually at the tips and between the veins; marked margins of leaves.
- Boron : Young leaves of the terminal bud are light green at the base; the bud eventually dies.
- Magnesium : Mottled or chlorotic leaves, which typically redden; leaf tips and margins turned or cupped upward.
- Copper : Young leaves are permanently wilted, with spotty or marked chlorosis.
- Calcium : Young leaves of terminal bud hooded; with severe deficiency, dying buds; dying back at the tips and margins of the leaf.
- Manganese : Spots of dead tissue scattered over the leaf; smallest veins tend to remain green.
- Sulfur : In young leaves, veins and tissue between veins are light green.