Sampling for Plant Tissue Analysis

Guide A-123

Robert Flynn, Extension Agronomy Specialist Shane T. Ball, Extension Agronomy Specialist R.D.Baker, Extension Agronomist

College of Agricultural, Consumer and Environmental Sciences, New Mexico State University. (Print Friendly PDF)

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.

The only way to know whether a crop is adequately nourished is to have the plant tissue analyzed during the growing season.  

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:

Nitrogen Sulfur Boron
Phosphorus Iron Sodium
Potassium Copper Chlorine
Calcium Zinc Molybdenum
Magnesium Manganese  


Levels of elements such as cadmium, lead, arsenic, and selenium also can be examined. See table 1 for sufficiency levels of plant nutrients.

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). Also, many devices are available for a "quick test" of the plant nitrogen status. Chlorophyll meters for certain crops can be used to predict the cost/benefit of additional nitrogen fertilizer.

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, 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. Mail the samples to: Soil, Water, and Air Testing Laboratory / New Mexico State University / Gerald Thomas Hall, room 269 / P.O. Box 30003, MSC 3Q / Las Cruces, NM 88003.

A nominal fee will be charged. Your county Extension agent can provide further details.

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.

A single plant showing visual deficiency symptoms, unless it is possible to sample normal plants from an adjacent area in the field. Normal plants give a reference to help interpret the chemical analysis of the deficient plant sample.   

Table 1. Sufficiency levels of plant nutrients for crops at growth stages shown in table 3.*
  Sufficiency levels
Element Corn Grain sorghum Soybeans Small grains Peanuts Alfalfa Bermuda grass
Nitrogen, % 2.7-3.5 3.3-4.0 4.2-5.5 1.7-3.0 3.5-4.5 4.5-5.0 2.5-3.0
Phosphorus, % .25-.40 .20-.35 .26-.50 .20-.50 .20-.35 .26-.70 .26-.32
Potassium, % 1.7-2.5 1.4-2.5 1.7-2.5 1.5-3.0 1.7-3.0 2.0-3.5 1.8-2.1
Calcium, % .21-1.0 .30-.60 .36-2.0 .20-.50 1.25-1.75 .50-3.0
Magnesium, % .21-.60 .20-.50 .26-1.0 .15-.50 .30-.80 .30-1.0
Sulfur, % .15-.40 .20-.30 .26-.50 .15-.20
Boron, ppm 4-25 1-10 21-55 5-10 20-50 30-80
Copper, ppm 6-20 2-7 10-30 5-25 10-50 7-30
Iron, ppm 21-250 65-100 51-350 50-150 100-350
Manganese, ppm 20-150 8-190 21-100 25-100 100-350 31-100
Zinc, ppm 20-70 15-30 21-50 15-70 20-50 < 20-50
*Adapted from Soil Fertility Handbook, Oklahoma State University.
Table 2. General symptoms of nutrient deficiency in plants.
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.


Table 3. Tissue sampling techniques for specific plants.
Crop When to sample Where to sample Number to sample
Alfalfa Early bloom Top 6 inches or upper third of plant 12-30
Canola Before seed set Recently mature leaf 60-70
Clover Before bloom Upper 1/3 of plant 30-40
Corn/sweet corn  Seedling stage OR Before tasseling OR Tasseling to silking All above-ground portions First fully developed leaf from the top of the plant  Leaf opposite and below ear

15-20 15-20 12-20

Cotton  Full bloom Recently mature leaf from main stem 40-50
Grasses/forage mixes Stage of best quality (before seed emerges) Upper 4 leaves 30-40
Peanuts Before or at bloom Recently mature leaves 40-50
Small grains (barley, oats, wheat, rye, rice) Seedling stage  Before heading All above-ground portions  4 uppermost leaf blades 25-40 25-40
Sorghum (milo) Before or at heading 2nd leaf from top of plant 20-30
Soybeans Before or at bloom Recently mature, trifoliate leaves from the top of the plant 20-30
Sugar beets Midseason Recently mature leaf at center of whorl 25-30
Sunflowers Before heading Recently mature leaf Before heading Recently mature leaf 20-30
Crop When to sample Where to sample Number to sample
Asparagus Maturity Fern, 18-30 inches above ground line 10-30
Beans Seedling stage OR Before or at bloom  All above-ground portions Recently mature leaf 20-30 20-30
Broccoli Before heading Recently mature leaf 12-20
Brussels sprouts Midseason Recently mature leaf 12-20
Celery Midseason Outer petiole of recently mature leaf 12-20
Cucumbers    Recently mature leaf 12-20
Head crops(cabbage, cauliflower) Before heading Recently mature leaf at center of whorl  12-20
Leaf crops(such as lettuce, spinach) Midseason Recently mature leaf 12-20 
Melons  Before fruit set Recently mature leaf 12-20
Peas Before or at bloom  Leaves from 3rd node from top 40-60
Peppers Midseason Recently mature leaf 25-50
Potatoes Before or at bloom 3rd to 6th leaf from growing tip 25-30
Sweet potatoes  Midseason or before root enlargement 3rd to 6th leaf from tip center OR Mature leaves 20-30 25-35
Root/bulb crops(such as carrots, beets, onions)   Midseason before root or bulb enlargement Recently mature leaf 20-30
Tomatoes (field)  Midbloom 3rd to 4th leaf from growing tip 15-20
Tomatoes (trellis or indeterminate) Midbloom from 1st to 6th cluster stage Petiole of leaf below or opposite top cluster 2-20
Crop  When to sample Where to sample Number to sample
Carnations Newly planted Established 4th to 5th leaf pair from base 5th to 6th leaf pair from base 20-30 20-30
Chrysanthemums  Before or at bloom Top leaves on flowering stem 20-30
Ornamental trees and shrubs  Current year's growth Recently mature leaf 30-70
Poinsettias  Before or at bloom Recently mature leaf 15-20
Roses At bloom Recently mature compound leaf on flowering stem 25-30
Turf Active growth Leaf blades. Avoid soil contamination. 2 cups
Crop When to sample Where to sample Number to sample
Apples, pears, almonds, apricots, cherries, prunes, plums  Midseason(June-July) Leaves from current season's nonfruiting, nonexpanding spurs 50-100
Peaches and nectarines Midseason (June-July) Midshoot leaflets/leaves 25-100
Grapes At bloom Petioles or leaves adjacent to basal clusters at bloom 50-100
Pecans Midseason Midshoot leaflets/leaves 25-60
Pistachios Mid- to late season (August) Terminal leaflets from nonfruiting shoots 25-60
Raspberries Midseason Recently mature leaves from laterals of primocanes 30-50
Strawberries Midseason  Recently mature leaves 25-40
Walnuts (June-July) Terminal leaflets/leaves from nonfruiting shoots 25-40

Illustration of corn before tasseling.

Corn before tasseling. Collect the first fully developed leaves from the top of 15-20 plants. If the plant is less than 12 inches tall, collect all of the above-ground portion.

Illustration of alfalfa leaf collection.

Alfalfa. Collect the top 6 inches or upper third of the plant at early bloom.

Illustration of soybean leaf collection.

Soybeans. Collect recently mature trifoliate leaves from the top of 20-30 plants before or during bloom. (In the seedling stage, collect all of the above-ground portion of the plant.)

Illustration of corn leaf collection.

Corn from tasseling to silking. Collect the leaves below and opposite from the ear of 15-20 plants.

Illustration of sorghum leaf collection.

Sorghum. Collect the second leaf from the top of 20-30 plants before or at heading.

Illustration of pistachio leaf collection.

Pistachios and Walnuts. Collect terminal leaflets/s from nonfruiting shoots at mid- to late season.

Illustration of apple leaf collection.

Apples, Pears, Almonds, Apricots, Cherries, Prunes, Plums. Collect the leaves from the current season's nonfruiting, nonexpanding spurs at midseason.

Illustration of pecan leaf collection.

Pecans, Peaches, and Nectarines. Collect the midshoot leaflets/leaves at midseason.

Illustration of grape leaf collection. 

Grapes. Collect the petioles or leaves adjacent to basal clusters at bloom.

Illustration of small grains leaf collection.

Small grains. Collect the four leaf blades from the top of 25-40 plants. Sample should equal 2 cups. (In the seedling stage, collect all of the above-ground portion.)

Illustration of cotton leaf collection.

Cotton. Collect recent from the main stem on 40 to 50 plants selected at random at full bloom.

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July 1999, Las Cruces, NM