Grain nutrient testing is a quick and easy way to see what nutrients are leaving the farm with the grain. Incitec Pivot trials at the Darling Downs, western Downs and in northern New South Wales have looked at sorghum grain test results from the last three years of summer crops. Nutrient removal rates varied widely:
- Nitrogen removal was up to double the assumed 18 kgN/tonne grain.
- Phosphorus removal was both higher and lower than the published average of 3.4 kgP/tonne grain.
- Potassium removal was 6–10 kgK/t, higher than the published average of 3.3 kgK/t.
Table 1. Grain nutrient test results in sorghum
|Trial data||Published data|
|N (kg/t)||36.6||18.6||23.2||18.0||9 – 26|
|P (kg/t)||4.0||5.6||2.9||3.4||1.4 – 4.0|
|K (kg/t)||10.3||6.0||7.3||3.3||2.6 – 4.1|
|S (kg/t)||2.1||2.2||2.0||2.4||0.9 – 3.2|
|Zn (g/t)||53.0||49.5||47.0||Up to 72||13 – 24|
|Mean grain yield (t/ha)||4.56||7.52||3.15|
Source: Data from Incitec Pivot Fertilisers’ trial sites. Grain tests conducted by Nutrient Advantage laboratory.
* Sourced from Pacific Seeds Nutrition Booklets (2015), More Profit from Crop Nutrition (2015), Australian Soil Fertility Manual (2000), Incitec Pivot Fertilisers’ data (unpublished).
+ Red emphasis added for removal rates higher than published data range.
Other reasons to test grain
Grain testing can also:
- be used (total N %) to estimate N removal where grain protein is not known
- show if that crop had a hidden hunger that may have limited yield
- document the degree of deficiency (if relevant)
- confirm its suitability to use as seed.
How to test grain
Collect about half a kilo of harvested grain from the back of the header, truck or silo. Send the sample to an accredited laboratory for analysis.
Combine grain test results with yield results to calculate actual nutrient export amounts by crop species, paddock or hybrid/variety. This provides a useful base to plan fertiliser rates for the next crop.