Leaf testing is an important tool to have in your nutrient management toolbox.

Leaf testing complements soil testing, evaluating the effectiveness of the fertiliser program.

Reasons to leaf test

Leaf testing enables nutrient trends on-farm to be identified and monitored over time. The data can also be used collectively to determine trends across a district, region or industry.

Leaf testing can be used as a diagnostic tool to:

  • Identify nutritional issues in poor growth areas
  • Confirm the effectiveness of fertiliser programs
  • Assess and evaluate nutrient imbalances being translated into the crop

Interpreting leaf tests

Caution is needed when interpreting the results of leaf test as other factors such as; age of the plant, variety, moisture stress and pest and disease damage can influence nutrient levels in a plant.

SRA CRITICAL LEVELS FOR THIRD LEAF ASSAYS – Australian Sugarcane Nutrition Manual, 2018

Third leaf assay


Critical level of assay

Nitrogen (N) % November to mid-January: 1.9

Mid-January to February: 1.8

March to May: 1.7

Phosphorus (P) % 0.19
Potassium (K) % 1.1
Calcium (Ca) % 0.2
Magnesium (Mg) % 0.08
Sulfur (S) % 0.13
Copper (Cu) mg/kg 2
Zinc (Zn) mg/kg 15
Manganese (Mn) mg/kg 15
Boron (B) mg/kg 1
Molybdenum (Mo) mg/kg 0.08

Silicon (Si)




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