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Plant tissue analysis is a useful diagnostic tool and can greatly help with fertility management. From emergence through the first six weeks of growth, plant analysis is helpful in identifying nutrient uptake. Testing corn leaf samples at this early stage may indicate where additional nitrogen should be applied. This is a way to determine the cost-effectiveness of the additional application of fertilizer.
Plant analysis may be utilized at the reproductive stage (full grown) to determine nutrient uptake for that season. This allows for determination of fertility requirements for the upcoming growing season. Tissue sampling and analysis is a key tool in determining the soil's ability to meet the sufficient nutrient requirements of the crop, thereby reducing any possible nutrient stress that may result in a potential yield drag or loss.
A variety of tests are available, including phosphorus, potassium, calcium, magnesium, sulfur, sodium, zinc, iron, manganese, copper, nitrogen, and boron.
Plant nitrates(NO3) can be added to any tests for a small charge
How to Sample
Remember: test results are only as good as the sample. The most common mistake in plant sampling is not obtaining enough tissue for an accurate analysis. Several leaves from several plants will ensure a more representative sampling and ensure enough plant material. Fertility management samples should be collected from representative areas of the field. Always take composite samples. One plant is not a sample.
Generally, select only upper mature leaves for your tissue sample. When samples are being collected for nutrient review, specific leaves are normally selected depending upon the plant. Here are a few examples:
- Corn - at tasseling, collect the leaf at the ear node
- Soybeans - at flowering collect the most mature trifoliant from the top of the plant
- Wheat and small grain - at beginning of head set collect the flag leaf (most mature leaf below the head)
- Alfalfa - at flowering collect the top 6 inches of the plant
When troubleshooting is the issue, it is extremely important to take leaves from several plants experiencing the same problem and use this composite for one sample (Sample #1). Compare this analysis with a composite sample taken from the non-affected area of the field (Sample #2). Sample #2 is the control sample. This gives the grower an idea of the sufficient nutrient level for that crop in that field at that sampling period.
For example: a portion of a corn field is exhibiting chlorosis (yellowing) and stunted growth. Plant tissue analysis is the best way to determine the reason for the chlorosis and abnormal growth. A composite sample (Sample #1) of upper mature leaves from 6 to 10 chlorotic plants and a composite sample taken from the upper mature leaves from 6 to 10 plants located in the non-affected area of the field (Sample #2) are submitted for analysis.
Where to Sample
Avoid leaves that were heavily preyed upon by insects or mechanically damaged. Avoid taking samples from areas located in border rows or heavy shade. Do not collect tissue that is already dead. Do not take samples from contaminated or chemically altered plants. Take diagnostic samples from the affected site for one composite sample and one from the non-affected area for a second composite sample. If the entire field is distressed, collect a composite sample over the entire area and note that the entire field is affected.
When to Sample
Timing of diagnostic sampling depends on the first sign of trouble. The earlier the problem is detected, the easier it is to treat with fertilizer or lime application. If nutrient application is not feasible due to plant growth, these results, along with soil analysis, can be used in fertilizer recommendations for the following growing season.
Fertility management sampling is done at the time of flowering or pollination (reproductive stage). Avoid taking samples too late in the growing season. Take a single composite sample at the onset of the reproductive stage to measure nutrient uptake throughout the growing season. Take samples when the plant is still viable and growing. It is too late once it has started to produce seed. These values determine the following growing season's fertility needs.
Submitting the Sample
Place each dried composite sample in a paper bag. Do not use plastic bags for plant samples because the plants mold. Label each bag with the field name and sample number. Please label them good, bad, affected or non-affected. Please include information that contains: name, address, telephone number, field names, number of samples per field and the type of test (Test #7, Test #8 etc.).
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