Monitoring plant nutrition levels

Plant tissue analysis is a valuable management tool which can be used to determine whether or not a plant is deficient in nutrients, particularly trace elements. Tissue testing reflects what the plants can take up at the time of sampling.

Mild purple pigmentation starts at the end of the leaf and progresses to the base on both sides of the leaf
Iron deficiency in wheat induced by heavy liming
Deficient plants are smaller, pale and poorly tillered.
Sterile boron deficient heads

It is not possible to rely on visual symptoms of nutrient deficiency as single element symptoms can often be confused with each other or with disease or other stresses. Also, once the deficiency has manifested itself by way of a symptom, the yield penalty may have already occurred.

In many cases plants will not show obvious signs of a deficiency even though crop growth may be restricted. Up to 50 per cent reduction in growth can occur before symptoms become obvious. This reinforces the need to undertake plant tissue testing as a regular means of monitoring crop growth and performance. The most important elements that can be monitored using plant tissue analysis include copper, zinc, manganese, sulphur and phosphorus.

Collecting plant tissue samples

All plant tissue testing kits have instructions provided which give full details on sampling and collection techniques for a range of crops being monitored. When collecting samples, the following procedures should be followed:

  1. Collect samples early in the week, so the lab analysing your samples can receive and process your samples within the week. Samples should also be collected and posted away the same day if possible.
  2. Allow 14 days after a herbicide application before sampling. Avoid sampling if the crop is stressed
  3. Sample at the specified growth stages. Identify and record the crop growth stage and date that the sample was collected.
  4. Sample appropriate plant parts for the main nutrients in question
  5. The start of tillering (approximately 4 weeks from sowing) to early jointing (approximately 12 weeks from sowing) is the preferred sampling stages for cereals. Samples should be taken when the deficiency is most likely.

Interpreting plant tissue analysis result

Plant weight, plant age and ratio with other nutrients are factors which need to be taken into account when interpreting laboratory results.

Recommended minimum plant nutrient levels for cereal crops at varying plant stages

Plant nutrient (%) Deficient Marginal Adequate Excess/toxic
Phosphorus (Z30) <0.3 0.3-0.37 >0.37 0.7
Phosphorus (Z30 - 32) <0.27 0.27-0.3 >0.3 0.7
Nitrogen (Z26) <4.5 4.5-5.5 >5.5 6.5
Nitrogen (Z30) <4.0 4.0-4.5 >4.5 6.5
Potassium (Z21 - 30) <1.5 1.5-2.3 >4.5 6.0
Sulphur (Z21 - 30) <0.2 0.2-0.23 >0.23 -
Magnesium (Z21-30) <0.10 0.1-0.12 >0.12 -
Calcium (Z21 - 31) <0.15 0.15-0.2 >0.2 -
Micronutrients (ppm) Deficient Marginal Adequate Excess/toxic
Molybdenum (Z21 - 30) <0.05 0.05-0.1 >0.1 -
Manganese (Z21 - 30) <15.0 15-20 >20 700
Iron <70.0 70-100 >100 -
Copper (Z21 - 30) <1.5 1.5-3 >3.0 -
Zinc (Z21 - 30) <16.0 16-25 >25.0 -
Boron (Z21 - 30) 3.0 3.0 >3.0 30-100

Recommended minimum plant nutrient levels for a range of pulse crops and canola

These are given for a range of pulse crops and canola during vegetative stages (seedling to budding).

Plant nutrient (%) Faba beans Lupins Field peas Canola
Phosphorus 0.35-0.45 0.2-0.3 0.25-0.4 0.25-0.3
Nitrogen 4.0 4 - 2.7-3.2
Potassium 2.0-2.5 1.2-1.5 1.5-2.0 1.3-2.8
Sulphur - 0.2-0.25 - 0.25-0.33
Magnesium 0.2 - 0.2 0.14-0.12
Calcium 0.6 - 0.6 1.0-1.4
Micronutrient (or trace elements) Faba beans Lupins Field peas Canola
Manganese (Mn) (mg/kg) 20-25 17-20 20-30 15-20
Iron (Fe) (ppm) - - - -
Copper (Cu) (mg/kg) >3.0 >1.2 >3.0 Whole shoots of young plants (seedling) below about 4mg/kg to 2.2mg/kg (rosette) and YEB levels below about 3mg/kg indicate copper deficiency
Zinc (ppm) >20-25 >12-14 20-30 Whole shoots of young plants (40 days) below about 23mg/kg and YEB levels below about 15mg/kg indicate zinc deficiency
Boron (mg/kg) (ppm) 10 15 10 15-22

Footnote: young leaves are recommended for micronutrient testing if suspected.

Where to go for expert help

Craig Scanlan
+61 (0)8 9690 2174
Page last updated: Wednesday, 12 July 2017 - 2:12pm