Plant Tissue Analysis

Plant tissue analysis measures the nutrient content within the plant tissue. This is one of the tools used to predict the optimum nutrient application rates for a specific crop in a specific field. This is important to identify if a specific nutrient is excessive, adequate or deficient during a growing season, and to correct immediately if they are deficient or if they are more than adequate.

Plant tissue analysis can be used to evaluate phosphorus, potassium, magnesium and manganese fertility. It is very useful in assessing the status of boron, copper, iron or molybdenum as these nutrients do not have reliable soil tests. Plant tissue analysis results for nitrogen and zinc are not always reliable.

Plant tissue analysis is most useful when it is combined with the soil test, along with a visual inspection of the crop and soil conditions. Results from plant tissue analysis are compared against established normal ranges for the crop, indicating whether a specific nutrient is deficient. For some nutrients, this can indicate whether the soil nutrient supply is adequate for optimum growth. If soil levels are known to be adequate, plant analysis may indicate other problems that are reducing nutrient uptake.

Sampling

Time of sampling has a major effect on the results of plant analysis. Nutrient levels within a plant vary considerably with the plant age and physiological stage.

Recommended sampling stages have been developed for most vegetable crops. Results are difficult to interpret if samples are taken at times other than those recommended.

If you suspect a plant is nutrient deficient, sample it as soon as the problem appears. Take tissue samples from a problem area rather than from the entire field. Collect and submit a separate sample from an adjacent, non-affected part of the field for comparison purposes.

Take leaves or petioles from at least 20-50 plants, depends on crops, distributed throughout the area chosen for sampling. Each sample should consist of at least 100 g (3.2 oz) of fresh material. For most crops, it is recommended to sample the most recently mature leaf from each plant. Very old and very young leaves often provide irregular test results.

Collect tissue samples into labeled paper bags. Plant tissues will rot if they are stored in plastic bags. Avoid contaminating the sample with soil. Even a small amount of soil will cause the results to be invalid, especially for micronutrients.

Collect and submit a soil sample from both affected and non-affected areas to accompany the tissue sample. This soil sample can help address whether the nutrient deficiency is a result of limited soil availability or due to another contributing factor.

Fresh plant samples should be delivered directly to the laboratory. If they are not delivered immediately, they should be dried at a low temperature to prevent spoilage.

Interpretation

Fertilizer recommendations based on plant tissue analysis have not been well established yet. However, when the nutrient levels are in the crop’s sufficiency range, increasing the nutrient concentration in the leaf is unlikely to result in increased crop growth. The objective of a good fertility program is to maintain tissue concentrations on the lower end of the range. Attempting to bring the nutrient analysis up to the higher end could possibly result in over fertilization and may not be cost effective.

Click the link below to view the nutrient sufficiency ranges for crops.

Plant analysis has limitations. Expert help in interpreting the results is often needed. Plant analysis does not usually indicate the cause of a deficiency, or the amount of fertilizer required for correcting it. The timing of plant analysis on many vegetable crops is difficult. Rapid growth and a relatively short growing season mean that yield loss may have already occurred by the time sample results are available. However, it is a valuable tool for diagnosing nutrient-related problem areas for future corrective measures.

Additional info on the plant tissue analysis can be found on OMAFRA Pub 611, Soil Fertility Handbook. In addition, crop specific soil nutrient ranges and fertilizer recommendations, can be found on OMAFRA Publication 363, Vegetable Production Recommendations, which is continues to be available until Pub 839 (the Ontario Field Vegetable Guide) is available.

Sap Analysis

Plant sap is the fluid extracted from conductive tissue, either xylem, phloem, or a mix, although there is no consensus yet about this definition in the scientific community. Nevertheless, the nutrients found in sap are readily available for the plant’s development; therefore, sap analysis is considered as a tree ‘blood test’.

Along with leaf and petiole analyses, sap analysis is a complementary technique that has the potential 1) to provide an early determination of the plant nutrient status, 2) to optimize fertilizer application, 3) to minimize environmental impacts, and 4) to improve sustainability in vegetables and perennial species. Sap analysis may enable to determine plant mineral levels, nutritional deficiencies, and excesses before they cause any damage to plant development and consequently fruit yield. However, inconsistency in the extraction and analysis methods and the lack of specific sufficiency ranges for horticultural crops are some challenges associated with this technique.

Use of Optical/Real-time Sensors

Application of optical/real-time sensors are considered as an advanced and non-destructive diagnosis of nutrient deficiencies in field and horticultural crops. This uses optical sensors to measure and quantify the variability of the crop, crop health or vigor. It can be handheld or can be mounted on farm equipment (i.e., sprayer or tractor) which works with most variable rate controller or delivery systems (e.g. N). A few challenges include high upfront cost, technological requirements, and accuracy of measurements that may require ground truthing (i.e., comparison against soil or plant tissue results).