Tissue testing for high rainfall pastures

Page last updated: Thursday, 1 November 2018 - 3:57pm

Please note: This content may be out of date and is currently under review.

Tissue testing can identify plant nutrient deficiencies that affect plant health. In high rainfall areas, pasture productivity is high and the demand for macronutrients and micronutrients is also high.

We recommend tissue testing to assess the effectiveness of fertiliser and soil testing programs, and diagnose emerging macronutrient and micronutrient deficiencies that could cause production losses.

Why you should tissue test

The symptoms of plant nutrient deficiencies are often vague, and observation should not be relied upon to make fertiliser and micronutrient management decisions because yield reductions may occur before signs are obvious.

We recommend plant tissue testing because it:

  • is the most reliable way of confirming micronutrient deficiencies, and commercial tests can measure all the common plant micronutrients at one time
  • can monitor the effect on plants of a nutrient management program and soil fertility
  • can identify emerging deficiencies before they reduce yield
  • can identify luxury or toxic levels of nutrients
  • can be used to adjust or calibrate soil test results of the major nutrients for the site.

Soil testing is recommended for the major nutrients of phosphorus (P), potassium (K), nitrogen (N) and sulfur (S). Soil test results can be used to decide the major fertiliser applications before the growing season.

Sampling plant tissue

Reasons to tissue test

  • as part of a regular program of nutrient management (preferred)
  • when yield drops and nutrient deficiencies are suspected
  • when plants have symptoms of poor health (e.g. yellowing, spotting)
  • after liming
  • after adding macronutrients or micronutrients to correct deficiencies.

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When to sample

  • For clover, sample in early spring before flowering.
  • For ryegrass and kikuyu, sample 2–5 weeks after grazing.
  • Sample growing plants that have been grazed and are not senescent or rank.
  • Sample plants early in the day to avoid heat-stressed plants. 
  • Take samples early in the week so they can be sent to the laboratory to arrive before the weekend.
  • Do not sample soon after fertilising or spraying.

Preparation for sampling

  • Wear the disposable gloves provided in plant tissue test kits.
  • Use only the sample bags provided in the kit.
  • Sample only the plant tops to avoid any contamination with soil.

Where to sample

  • Select a representative sample at random across the paddock, avoiding the atypical sections, such as livestock camps, drainage lines or scalds.

What to sample

  • Sample the species that is of interest; do not sample weed species.
  • Sample the major desirable species showing symptoms of poor health or lowered productivity.

In the field

  • Include only one species of plant in each sample bag.
  • Sample the youngest or newly grown part.
  • Snap off a handful of tops at a time.
  • Carefully check each handful contains:
    • no roots or soil
    • no dying or diseased plants
    • no contamination with dust
  • Keep the samples cool.

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Using tissue test results

Tissue test results will identify micronutrient deficiencies, but the treatment is not as simple as adding more of the deficient nutrient. To avoid problems with nutrient interactions, problems with livestock and incorrect application, we recommend that you take advice from your advisers and make use of the information provided on this page:

Interpreting results

Tissue test results are shown as a proportion of the dried plant matter. Laboratory results can be compared to the levels of adequate nutrients in Table 1. This guide is only for tissue sampled in spring. 

Table 1 The approximate ranges of adequate nutrient levels from tissue testing during spring

Nutrients

Percentage of nutrient in subterranean clover (%)

Percentage of nutrient in

perennial ryegrass (%)

Percentage of nutrient in kikuyu (%)

Notes

Nitrogen 3.5–5.5 4.5–5.0 3.0–4.5  
Phosphorus
0.3–0.5
0.35–0.4 0.24–0.35 Use tissue test to calibrate and check soil test.
Potassium 2.0–2.4 2.0–2.5 2.3–3.8 Use tissue test to calibrate and check soil test.
Sulphur 0.27–0.47 0.27–0.32 >0.12  
Calcium 0.8–2.5 0.25–0.3 0.4–0.7  
Magnesium 0.15–0.5 0.16–0.2 0.3–0.58  

Zinc mg/kg

15–50 14–20 30

Can be reduced by liming.

Copper mg/kg 5–30 6–7 6–9

Care should be taken if copper is low; can be reduced by liming.

Molybdenum mg/kg 0.5–10 0.3–0.4   Care should be taken if molybdenum level is high; can be increased by liming.
Boron mg/kg 25–100 5–15 10 Seek advice to avoid toxicity.
Manganese mg/kg 25–300 50–300 70–90

Can be reduced by liming.

Iron mg/kg 50–65 50–60 50–70 Not commonly deficient and not usually associated with yield loss.
Cobalt mg/kg >0.04   >0.04 Associated with apparent nitrogen deficiency in legumes.

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Making better nutrient management decisions

We encourage grazing managers (dairy, beef, sheep) in the lower south-west of Western Australia to base any nutrient decisions on good evidence.

In addition to tissue testing, we recommend regular soil testing and consultation with FertCare-accredited advisers to plan profitable and responsible fertiliser use.

Contact information

Robert Summers
+61 (0)8 9535 4140
David Weaver