Soil and Plant Analysis

Deciding when to sample

• To monitor plant nutrient status most effectively, sample during the recommended growth stages of the specific crop.
• Take samples weekly or biweekly during critical periods, depending on management intensity and crop value.
• However, to identify a specific plant growth problem, take samples whenever you suspect the problem.
• The best time to collect samples is between mid-morning and mid-afternoon.
• Nitrate nitrogen varies with time of day and prevailing conditions but generally not enough to alter interpretation.
• Sampling during damp conditions is okay but requires extra care to prevent tissue from decomposing during shipping.
• Keep samples free of soil and other contaminants that can alter results.
• The appropriate part of the plant to sample varies with the crop, stage of growth, and purpose of sampling.
• When sampling seedlings less than 4 inches tall, take whole plants from 1 inch above the soil line.
• For larger plants, the most recent mature leaf is the best indicator sample.
• Taking a representative sample
• Proper sampling is the key to reliable plant analysis results. A sample can represent the status of one plant or 20 acres of plants. In general, a common-sense approach works well.
• In problem solving, take samples from both ‘good’ and ‘bad’ areas. Comparison between the two groups of samples helps to pinpoint the limiting element.
• Comparative sampling also helps factor to out the influence of drought stress, disease, or injury.
• Take matching soil samples from the root zones of both ‘good’ and ‘bad’ plants for the most complete evaluation.
• When monitoring the status of healthy plants, take samples from a uniform area.
• If the entire field is uniform, one sample can represent a number of acres.
• If there are variations in soil type, topography, or crop history, take multiple samples so that each unique area is represented by its own sample.
Choosing sample size

• The actual laboratory analysis requires less than one gram of tissue. However, a good sample contains enough leaves to represent the area sampled. Therefore, the larger the area is, the larger the sample size needs to be.
• Sample size also varies with the crop.
• For crops with large leaves like tobacco, a sample of three or four leaves is adequate. For crops with small leaves, like azalea, a sample of 25 to 30 leaves is more appropriate.
• For most crops, 8 to 15 leaves are adequate. For crops requiring petiole analysis, collect at least 15 to 20 leaves.


The table below shows the sampling guide for various crops

Crop	When to Sample	Where to Sample	Qunatity
Field Crops
Alfalfa	Early bloom stage	Upper 1/3 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 Before heading Tasseling to silking	All above ground portion Upper 4 leaves Opposite or below ear leaf	15 – 20 12 – 20 12 – 20
Grasses/forage mixes	Stage of best quality	Upper 4 leaves	30 – 40
Peanuts	Before / at bloom	Recently mature leaf	40 – 50
Small grains (barley, wheat, oat, rye, rice)	Seedling stage Before heading	All above ground portion Upper 4 leaves	25 – 40 25 – 40
Sorghum	Before / at heading	2nd leaf from top	23 – 30
Soybeans	Before / at bloom	recently mature leaf	20 – 30
Sugarbeets	Midseason	recently mautre leaf at center of whorl	15 - 20
Sunflower	Before heading	Recently mature leaf	20 – 30
Tobacco	Before bloom	Recently mature leaf	10 - 15
Vegetable crops
Asparagus	Maturity	Fern from 18 – 30 inches up	10 – 30
Beans	Seedling stage Before / at bloom	All above ground portion Recently mature leaf	20 – 30 20 – 30
Broccoli	Before heading	Recently mature leaf	12 – 20
Brussel sprouts	Midseaason	Recently mature leaf	12 – 20
Celery	Midseaason	Outer petiole	12 – 20
Cucumbers	Before fruit set	Recently mature leaf	12 – 20
Head crops (Cabbage / cauliflower)	Before heading	Recently mature leaf at center of whorl	12 – 20
Leaf crops (lettuce, spinach etc)	Midseason	Recently mature leaf	12 – 20
Melons	Before fruit set	Recently mature leaf	12 – 20
Peas	Before / at bloom	Leaves from 3rd node from top	40 – 60
Peppers	Midseason	Recently mature leaf	25 – 50
Potatoes	Before / at bloom	3rd – 6th leaf from growing tip	40 – 60
Root / bulb crops (carots, beets, onions etc)	Midseason before root or bulb enlargement	Recently mature leaf	20 – 30
Tomatoes	Mid – bloom	3rd – 4th leaf from growing tip	15 – 20
Tomatoes (indeterminate)	Mid-bloom from 1st to 6th cluster stage	Leaf below or opposite top cluster	12 – 20
Fruits and Nut crops
Apple, pears, almonds, apricots, cherries, prunes, plums	Midseason (June – July)	Leaves from current season’s non-fruiting non-expanindg spurs	50 – 100
Olives, peaches, Figs	Midseason (June – July)	Basal to mid- shoots leaves from current season’s non fruiting shoots	25 – 100
Blueberries	2 – 4 weeks before harvest	Mid-shoot leaves from current season’s shoots	50 – 100
Citrus	Late season (Aug.)	Terminal leaves from current season’s non-fruiting shoots	25 – 40
Grapes	Mid-bloom	Recently mature petioles or leaves adjacent to basal clusters	50 – 100
Kiwi fruit	Mid season	1st – 3rd leaf beyond fruit or mid-cane leaves if non-bearing	50 – 60
Pecans	Midseason	Paired mid-shoot leaflets from non-fruiting shoots	25 – 60
Raspberries	Midseason	Recently mature leaves from laterals of primo canes	25 – 60
Strawberries	Midseason	Recently mature leaves	25 – 40
Walnuts	Midseason (June – July)	Terminal leaflets from non-fruiting shoots	25 – 40
Oranamentals and flowers
Carnations	Newly planted Estabilished	4th – 5th pair from base	20 – 30 20 – 30
Chrysanthemums	Before / at bloom	Top leaves on floweirng stem	20 – 30
Ornamental trees and shrubs	Current years growth	Recently mature leaf	30 – 70
Roses	At bloom	Recently mature compound	15 – 20
Turf	Active growth	Leaf blades. Avoid soil contamination	2 cups


• In some specific cases, based on the nutrient to be analyzed, the sampling parts of the plant may vary.
• When leaves are sampled, recently matured ones are taken; both new and old growth is generally avoided.
• However, young emerging leaves are sampled for diagnosing iron chlorosis by determining ferrous (Fe++) content of fresh leaves and B content in certain crops.
• Plant samples should be transported to the laboratory immediately in properly labeled paper.
• If samples are very wet, air-dry to a workable condition before packaging. Otherwise, decomposition or molding will occur.
• Include a completed plant analysis information sheet or cover letter with instructions within the same package.
Graphic Sampling Guides for some Common Crops