Monitoring Nutrient Status
Plant Analysis
Plant analysis can be a valuable tool in determining the general nutritional status of crops. It can be particularly helpful in diagnosing nutritional deficiency symptoms because various elements have similar visual symptoms. Plant analysis is a nutrient management tool most effectively used in conjunction with a regular soil-testing program. In some cases, symptoms that appear to be caused by nutrient deficiencies may actually be caused by other factors such as disease, herbicide residues, insects, high or low temperature, or too much or too little moisture.
Plant Tissue Analysis
Plant tissue analysis involves the determination of nutrient concentrations from a particular part or portion of a crop, at a specific time and/or stage of development. This, in turn, shows whether soil nutrient supplies are adequate. Plant tissue analysis has a diagnosis role, where it is used to confirm or dismiss the presence of limiting nutrients in soils that are highlighted by visual symptoms on plants; it also has a monitoring role, which ensures that growing crops always have adequate nutrients for consistent optimal growth; and it lastly has a supporting role, where it is used along with soil test results to make fertilizer recommendations. The advantage of plant tissue analysis is that it reveals the actual nutritional status of plants, which may at times tell a different story from what is expected from pre-existing soil nutrient conditions.
Plant Tissue Testing for Nitrate
A soil test does not always accurately reveal the nitrogen status of a crop. Nitrogen is a mobile element and is readily moved down into the soil by irrigation or precipitation. Nitrogen can also be tied up by soil microorganisms so that it is not available for crop uptake or because cooler soil temperatures limit nitrogen mineralization. Soil nitrate testing is most useful after the soil has been warm long enough for nitrate-N to accumulate. Testing nitrogen status in the plant rather than soil is a more reliable indicator of the crop’s nitrogen status. Several plant tissue tests are specifically designed to refine nitrogen management.
Cornstalk Nitrate Test: The end-of-season cornstalk nitrate test (CSNT) measures the nitrate content of the lower portion of mature cornstalks at harvest time.
Petiole-Sap Test: The petiole sap nitrate-N test is a rapid and effective method for growers to monitor the nitrogen status of plants throughout the growing season. This method can be used for tomatoes grown in the field as well as in high tunnels and greenhouses.
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