Plant and tissue analyses can supplement, but not replace, soil testing. Tissue sampling can be used to diagnose crop problems that may be nutritionally related and to identify any nutrients that may be limiting yields, but it does have serious limitations. Tissue nutrient levels vary significantly depending on stage of plant growth, plant parts sampled, and the time when samples are collected (e.g. time of day, timing relative to environmental stresses).
No reliable interpretative criteria exist for nutrient ranges in seedling canola. And because nutrient contents usually differ greatly between different plant parts and ages, the proper part must be sampled at the proper growth stage.
Each tissue testing lab will have slightly different requirements for taking and submitting samples. In general, select typical plants from the areas you want to compare, avoiding unusual, dead or stressed plants, as well as those covered with soil or recent sprays. Cut samples with a clean, rust-free knife or scissors.
Important tip. Send separate samples from good and poor areas within a field. It is best if the plants in each area are at the same growth stage. Comparing the plant analysis results from areas of a field that differ visibly in growth can be difficult to interpret because nutrient content differences can be confounded by growth differences. If the two areas differ mainly in deficiency symptoms, then comparative sampling can be useful. In this case, collect the samples soon after the symptoms appear and before major differences in growth and maturity occur.
Plant and tissue analyses measure the nutrient content of above ground plant parts during growth. The values are compared to established ranges for inadequate, adequate and excess levels. The Canola Encyclopedia has a table shows sufficiency levels for most plant nutrients in flowering canola.
LISTEN to a Canola Watch podcast on macronutrient deficiencies, which includes a conversation about tissue tests….