Guideline Index

Chapter 9: Interpreting Soil and Tissue Tests

9.3 Interpreting plant tissue tests

Plant tissue testing is the preferred method for diagnosing trace element toxicities, deficiencies, and imbalances for plants. Tissue tests, also known as plant or leaf analysis, determine the chemical analysis of the nutrients present in plant tissue. Tissue tests are also used to confirm that plants are accessing the nutrients that have been applied and to confirm a diagnosis made by other means. Both the major nutrients and the micronutrients (trace elements) are covered in plant tissue tests (see the example in Figure 9.3a).

Plant tissue testing is also very useful to corroborate animal nutritional or deficiency problems such as copper (Cu), cobalt (Co) and selenium (Se). Both plant nutrient and animal health problems can be diagnosed by comparing results from healthy and unhealthy samples. However, the rapid growth and quick maturity of annual crops combined with daily management (e.g. irrigation, fertiliser), and the effects of grazing on pasture plants, can make assessments of subclinical deficiencies or toxicities difficult.

Tissue testing is carried out by comparing samples with standard results recorded in various publications (see references at the end of this section). However, where animal health is a concern, blood testing is often more useful and it is more cost effective to treat the animals directly.

Clover samples are generally used to diagnose trace element deficiencies in dairy pastures where clover is prevalent, however lucerne or ryegrass samples can also be used. Plant tests are also used to confirm that plants are accessing the nutrients that have been applied, and to confirm a diagnosis made by other means.

Interpretation of the results of a plant tissue test is complex and depends on a number of factors. It is therefore recommended that interpreting the results of plant tissue tests should be done by a trained professional. This is because actual adequate levels for any nutrient varies depending on species, plant part, time of year, and stage of growth.

When using plant tissue tests to determine nutrient levels in plants, it is vital to take the sample correctly and to provide as much information as possible to aid interpretation. Supplying relevant information will help the person interpreting the results to correctly calculate the level of nutrients in your sample. If possible, tissue samples of identical plant parts and age should be taken from ‘good’ and ‘poor’ areas to allow a direct comparison of tissue nutrient levels. See Chapter 8.4 for details on sampling for tissue tests.

Results from laboratories will be analysed by trained professionals who will take into account the information you have provided and will interpret the results. The results are usually shown with a number and an interpretation of this (for example, deficient, adequate, high). Based on this interpretation, you can then make decisions about nutrients required in your fertiliser program.

More information about interpretation of tissue test results can be found in Plant Analysis: An Interpretation Manual (Reuter and Robinson, 1986) and Plant Nutrient Disorders 4: Pastures and Field Crops (Weir and Cresswell, 1994). 

Figure 9.3a An example plant tissue test
Figure 9.3a An example plant tissue test

 

Figure 9.3b Explanation of an example plant tissue test
Figure 9.3b Explanation of an example plant tissue test