IRRI SERVICE LABORATORIES
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Plant sampling guide
The most important aspect of plant analysis is knowing how to take a representative sample. Planning is an important step that must be done in order to address factors that need to be controlled. Sampling plan and method must be available during sampling and must be properly executed to ensure sample integrity. Results are only as good as the samples collected and the method used for its preparation. Because only a small amount of sample is used for any particular test, it is essential that sub-samples are carefully selected and thoroughly mixed, and the quantity prepared should be at least 10 times greater than the final sample analyzed.
To remove surface contamination, leaves are cleaned with a damp linen cloth or by gently brushing with a stiff-bristled brush, followed by brief rinsing with distilled water.
Shoots (from greenhouse experiments) contaminated with soil may be washed under running tap water. Washing must be done quickly to minimize loss of soluble constituents and should be followed by rinsing with distilled water and drying with a cloth or tissue paper.
Sand or soil adhering to roots can be washed away under running tap water, and then roots must be rinsed with distilled water and dried with a cloth or tissue paper.
Metabolic activity can alter the composition of plant tissue material. To keep metabolic activity to a minimum, keep the samples cold or frozen.
Leaves and other plant material are cut into small pieces before drying.
Contamination by dust should be avoided, especially when Fe, Mn, Cu, and Zn are to be determined.
Samples are placed in an oven and dried overnight at 80 ± 2°C. Longer drying times are required for materials high in silica.
How should plants be sampled?
Take all plants in each pot and make a composite sample. If that is not possible, take two predetermined plants per pot.
Sample all replications.
Exclude 2 border rows.
The number of plants per 3 x 5-m2 plot depends on variability. For rice, 4 tillers/hill are recommended as the minimum if the entire plant is used. If the sample is a single lead, use at least 10 plants. Make a composite sample. Quarter the sample if it is too bulky.
Locate plants using random pairs of numbers with the first number corresponding to the width and the second to the length of the plots for spaced plants. Pairs of such numbers, the first between 1 and 10 and the second between 1 and 20, are chosen from a table of random numbers. This set of random pairs can be used for each plot in a block. A new set is necessary for each block.
Do not sample plants attacked by insects or diseases or are injured mechanically or are under physical stress.
Do not include dead leaves in the sample except in straw samples at harvest.
Do not sample a plant adjacent to a missing hill.
For nutritional deficiencies or toxicities, sample 2 or 3 plants showing symptoms and 2 or 3 healthy plants at the same growth stage from an adjacent area. Avoid dead or nearly dead plants.
For nutrient surveys, divide the field into a suitable number of blocks of equal area and take a sample from the center of each block or depending on the experimental design.
What plant parts should be sampled?
Nutrient deficiencies and toxicities: The whole plant if the plant is small and the most recently matured leaf blade if the plant is large.
Pattern of nutrient uptake: The entire above-ground plant at different growth stages.
Total nutrient uptake: The entire above-ground plant, including panicle at maturity.
Detecting hidden hunger or toxicity: The whole plant at tillering phase.
Fertilizer recommendations: The whole plant before reproductive phase.
Total nutrient uptake: The whole plant at maturity.
Physiological studies: The whole plant at successive developmental stages.
Solution culture plants: Cut at the base with scissors, wipe the tops with dry muslin cloth, put a label on it, and then place in a labeled muslin cloth bag. If iron and manganese are to be determined, wipe the plant with a muslin cloth dipped in 0.2% Teepol, rinse rapidly with reverse-osmosis filtered water twice, and dry with a muslin cloth. If root analysis is needed, dry the roots with a muslin cloth, label it, and place in a labeled cheese-cloth bag.
Dry soil culture plants: Cut 3 cm above the soil and follow the same treatment previously mentioned above.
Wet soil culture plants: Cut 2 cm above the water mark on the plant and follow the same treatment previously mentioned.
Dry-land plants: Cut 5 cm above the ground, brush off soil at the base of the plant, and follow the same treatment previously mentioned.
Wetland rice: Cut 5 cm above the water mark and follow the same treatment previously mentioned.