A plant analysis has three main applications:
- To confirm a suspected nutrient element deficiency when visual symptoms are present.
- To monitor the plant nutrient element status in order to determine whether each tested nutrient is in sufficient concentration for optimum yield.
- To serve as the basis, along with a soil test, for making fertilizer recommendations for fruit and nut crops.
The diagnostic role of a plant analysis has been well established. Confirm a suspected deficiency by a plant analysis before applying a corrective treatment. Numerous cases can be given where incorrect diagnosis in the field has led to crop failures, as well as costly and ineffective corrective treatments. Take care when sampling plants which are being stressed nutritionally. Plants that have been subjected to long periods of stress tend to develop unusual nutrient contents. Therefore, obtain samples as soon as symptoms appear. Dead tissue or tissue that is showing severe symptoms should not be included in the sample.
The monitoring role of a plant analysis or a series of plant analyses is not used extensively; however, it offers the opportunity to maintain high quality production with a minimum of nutrient deficiency problems. To provide a means of noting changes in nutrient content, sample each year on a regular basis and compare analytical results from one sample to the next. Study carefully upward or downward trends along with previous production inputs to warn of a potential nutrient deficiency or imbalance. Therefore, corrective treatments can be applied before significant losses in yield or quality occur.
Plant analysis has proved to be a very effective means of predicting fertilizer needs for orchard crops. It does not completely replace a soil test. Soil and plant analyses serve different purposes and when properly used they supplement and support each other. In the case of annual crops, soil analysis prior to planting enables the grower to determine whether limestone, phosphorus, potassium, magnesium or zinc applications will be needed. Plant analysis of the growing crop will indicate to the grower if the applied materials were effective and whether the preplant prediction by soil analysis was correct.
Soil analysis is very useful in appraising soil acidity where crops have failed and the need for limestone applications in established orchards. Plant analysis is particularly useful in determining the nutritional status of permanent deep-rooted crops such as apple, peach, or pecan trees, where soil samples of the plants' entire feeding zone are very difficult to obtain.
In fruit crops, nutrient imbalances may affect the fruit quality of otherwise normal appearing trees. Nutrient imbalances or low nutrient levels may seriously reduce crop yield and quality even in the absence of noticeable growth reduction. Therefore, when considering the adequacy of nutrition for fruit and nut trees, it is important that nutrient levels are sufficient to prevent abnormal growth and development of fruit.
Many of the deficiencies and excesses occurring in most fields and orchards are self-induced due to inadequate liming, excessive application rates of some fertilizer elements, improper timing of fertilizer applications, especially sidedress applications of nitrogen, and the failure to replace elements lost by crop removal. In Georgia, inadequate liming can lead to severe soil acidity in a short period of time, particularly under intensive cropping conditions. Magnesium deficiency, a frequently occurring deficiency in Georgia, is primarily associated with low soil pH and inadequate liming. Heavy rates of applied N fertilizer will generate acidic soil conditions faster than many realize. Vegetable, silage, and hay crops remove tremendous quantities of plant nutrients from the soil, which must be replaced by lime and fertilizer. Small excesses of P fertilizer applied each year can accumulate to eventually reach excessive proportions. Excessively high soil test P levels may induce Zn deficiency in Zn sensitive crops, such as corn, pecans, and possibly cotton. Heavy K and NH4-N fertilization may induce Mg deficiency when the soil test Mg level is on the borderline of being low. These deficiencies and imbalances can be avoided if the grower will use soil tests and plant analyses as monitoring tools.
Maintain a record of soil tests and plant analyses and refer to them each time a lime and fertilizer program is formulated. Evaluate upward or downward trends in pH or level of extractable plant food nutrients. Adjustments can be made to keep the nutrient content of the soil and plants within the sufficiency range for each tested element.
When used together, visual observations, knowledge of the site, a soil test, and the plant analysis provide an effective means of evaluating the nutrient status of the soil-plant environment. However, a plant analysis result may not solve every problem or uncover all unseen nutrient element deficiencies or excesses. When a nutrient deficiency is confirmed by a plant analysis, or an unseen deficiency is uncovered, a corrective treatment may not always be applicable to the sampled crop. Treatments may be specified for future growing seasons, or additional tissue and soil samples may be needed to fully evaluate the suspected deficiency.
A plant analysis may indicate that a nutrient deficiency or excess does not exist. Therefore, the cause for poor plant growth or visual symptoms needs to be sought elsewhere. Such directing can be invaluable and is not to be underestimated.
In order to use the plant analysis technique effectively, take care when collecting, preparing, and sending plant tissue to the laboratory. The following procedures should be carefully followed:
|What to Sample|
Proper sampling requires that a definite plant part be taken, such as a particular leaf, group of leaves, or portion of the plant (see Guidelines for Collecting Leaf and Plant Tissue). Instructions also include the number of individual parts and the number of plants to sample. This will ensure that a sufficient quantity of plant tissue is submitted for analysis and that the collected sample is statistically representative of the area under study. When sampling mixed stands, particularly forages and pastures, separate plant species. Similarly, the sample should be of only leaves, or petioles, or whole tops, and not mixtures.
When no specific sampling instructions are given for a particular crop, the general rule of thumb is to sample the uppermost recently mature leaves. Young emerging leaves, older mature leaves, and seed are not usually suitable plant tissues for analysis since they do not ordinarily reflect the general nutrient status of the whole plant. The recommended time to sample usually occurs just prior to the beginning of the reproductive stage for many plants. However, sampling earlier or even later than specified may be recommended for specific plants or circumstances. Sample plants which are showing a suspected nutrient deficiency symptom at the time or shortly after the visual symptoms appear. Do not sample or include plants under a nutrient stress for an extended period of time, dead plant tissue, or plants or tissue mechanically injured, diseased or insect damaged.
When a nutrient deficiency is suspected at a time other than specified for sampling, also collect similar plant parts from normal plants growing in the immediate or adjacent areas. Take care to ensure that the two sets of plants are at approximately the same stage of growth and have been treated the same. Comparative analyses are questionable when the two sets of plants are not at the same stage of growth, have not received the same treatment, or are not the same variety or hybrid. If the soil type varies between the two sites, tissue analyses would not be comparable. If all the proper conditions have been met, then a comparison of results between two sets of plant tissue samples can be invaluable to the interpreter. Do not mix or place the collected tissues in the same mailing kit. When soil test data is not available, take soil samples from both areas.
|Washing to Remove Contaminants|
Avoid dusty or soil-covered leaves and plants whenever possible. Under normal conditions, rainfall is frequent enough to keep leaf surfaces fairly free from dust and soil particles. However, when leaves are dusty, brushing or wiping with a damp cloth may be sufficient to remove the contaminants. If this is not effective, or when leaves are covered with spray materials, wash in a mild detergent solution (0.30%) and rinse in running water to remove most attached substances. Do not prolong the washing procedure or allow the plant material to "stand" in either the washing or rinsing baths. Wash and rinse briskly. Wash leaves which have been sprayed with nutrient solutions while they are still fresh. If iron is of primary interest, wash leaves regardless of their outward appearance. Wash whole plants sampled shortly after emergence to remove soil particles which are frequently attached to the new tissue
|What Not to Sample|
Do not include diseased or dead plant material in a sample. Do not sample or include plants or leaf tissue which have been damaged by insects or mechanically injured in a sample. When whole plants are sampled, remove the roots and wash the upper portion to remove soil particles. Do not sample plants which have been stressed extensively by cold, heat, moisture deficiency, or by excess moisture. Examine both the below ground as well as the above ground portion of the plant. The presence of nematodes or roots damaged by other insects or diseases should preclude the need to sample
|The Plant Submission Form|
The questionnaire serves as the means of communication between the sampler and the interpreter. Completion of the questionnaire is important if the interpreter is to properly evaluate the analysis and make a recommendation. Failure to supply all the information requested may limit the scope of the interpreter's evaluation of an analysis. For situations which require immediate corrective action, the time lost in order to obtain the desired information may make the applied corrective treatment less effective. The Plant Submission Form form is available in this publication.
|Packaging Plant Tissue|
Partially air dry plant tissue samples before shipment to the laboratory. When samples are placed in plant analysis kits, allow the sample to set in a warm place for one half-day with the end of the envelope open. This will generally remove excess moisture. It is not necessary to maintain the tissue sample in the fresh state unless the tissue will require washing in the laboratory. Never place fresh plant tissue in polyethylene bags or tightly sealed containers unless it is kept under refrigeration. When samples are shipped in polyethylene bags by routine mail, they have generally started to decompose by the time they are received for processing. Such samples are not analyzed, because erroneously high nutrient concentrations are measured.
|When to Soil Test|
A recent soil test result can be helpful when interpreting a plant analysis. When visual symptoms of a suspected nutrient deficiency are present, take a soil sample at the same time and in the area that the plant tissue is collected. In this way, an evaluation of the soil in the affected area can be made along with the plant analysis result. When tissue samples are collected from both good and poor areas in a field, soil samples should be collected from both areas also.