Unusual symptoms in crops can indicate nutrient disorders. Visible symptoms tell you there is some kind of problem but are not enough to base a reliable diagnosis on.
Crop symptoms can be triggered by too little or too much of a nutrient, as well as a range of other constraints to growth. Tissue testing is an important tool for confidently identifying and excluding potential causes of the symptoms.
Early diagnosis is essential for any chance of addressing the problem in the current crop. The longer-term approach is to monitor the paddock for risks of nutrient disorders.
To confidently diagnose a nutrient disorder in a growing crop
- Monitor the crop by visual inspection at least fortnightly up to stem elongation in cereal, bolting in canola or first flower in legumes – after that, it’s probably too late to assist the crop.
- Take photos of any unusual symptoms in the crop. If you are posting on twitter mention us as @aucropnutrition.
- Identify any site-related factors that might be contributing to the symptoms such as:
- position in the paddock relative to headlands and previous windrows
- recent application of soil amendments, especially lime
- frost risk
- waterlogging or other soil constraints
- Collect two samples, one from an area of healthy growth, the other from a poor part of the paddock. Collect at least 100 youngest fully emerged leaves, while the sun is shining and quickly send them to a lab for analysis.
- Consider the soil conditions and growth stage at the time of sampling when interpreting the tissue test results, as these can change the concentrations expected in healthy plants.
To assess paddock risk of nutrient disorders
- Review soil test results, looking for any nutrients that are below or close to the lower limit of critical ranges.
- Check for visual symptoms – you can use the free IPNI nutrient deficiency app.
- Review tissue testing results from previous grain harvests, looking for levels of any nutrient that are below optimum.
eXtensionAUS Crop Nutrition
Plant tissue testing – an underutilised tool for diagnosing hidden hunger in crops by David Lester & Mike Bell, 2010.
Plant tissue testing a presentation by Rob Norton, ANZ IPNI
Wheat – nutrition a QDAF resource
Photo courtesy of IPNI.