Author: Reily Menhenett – Technical Agronomist, Incitec Pivot Fertilisers  

With harvest underway in some areas, and fast approaching in others, now is the perfect time to round out nutrient budgets with grain testing.

Grain testing is available from IPF’s Nutrient Advantage® Laboratory and while it doesn’t replace the need to soil test, it is a quick and accurate way to determine exactly how much nutrient has been accessed by a crop and converted to grain.

This is important for growers who wish to understand their exact nutrient removal per hectare of grain. It can also assist with post-harvest reviews of fertiliser budgets, by providing an exact figure on how efficient nutrient assimilation was for a certain crop.

Nutrient budgets, and nitrogen (N) in particular, are often forgotten at harvest time, however taking the time to collect a grain sample will help with reviewing where a fertiliser strategy was optimal, and where it requires further attention for subsequent seasons.

What does this tell us?

A sample of just 400 grams of grain is all that is required, with test code G1 available for wheat, barley and other cereals, plus canola and pulse crops. Results are presented in mg/kg or percentage terms and scaled up to ‘nutrient removed per tonne of grain’ to gain a quick insight into crop removal.

Whilst reference tables can provide a rough guide for crops, submitting a grain sample will give insight into your own farming operation. Nutrient removal varies greatly both between and within paddocks, therefore capturing a precise figure will be far more meaningful than estimating from a standardised table.

A 2012 study comparing nutrient removal from southern National Variety Trials (NVT) sites found significant variability in uptake – particularly of phosphorus (P), which varied by up to 20% across all sites (Norton 2012).

Figure 1 shows the variance in P levels alone averaged by state. Also shown is the ‘standard’ value used for removal, based on Reuter et al. (1997).

Figure 1: Average P removal from NVT Sites (Wheat, 2012). Source: Norton 2012.

If assuming a wheat yield of 4t/ha in Victoria, using a ‘standard’ value, rather than confirming through grain testing could underestimate actual removal by 2kg/ha. If you’re aiming to replace P at sowing the following season, this represents a difference of 10kg/ha of MAP – significant if you’re trying to build or maintain Colwell P in the soil.

Seedling strength

Strong seed vigour has been found with greater than 500 nanograms of zinc (Zn) per seed (Rengel and Graham, 1995) and 130 micrograms of P per seed (De Marco 1990). Where wheat grain is below these benchmarks, growers may need to consider another seed source or additional fertiliser to support early growth.

Understanding potential seedling vigour before deciding on which grain to use as seed can save headaches when preparing for planting next season.

Step by step grain testing

  1. Collect samples by paddock, zone, crop or area as required.
  2. Record yield within the area/zones sampled.  Yield is multiplied by removal from grain analysis to calculate kg (or gms) /ha removed.
  3. Supply approximately 400 grams of threshed seed (no stalks), in a Nutrient Advantage plant tissue test bag.
  4. Submit to the laboratory under the code G1.
  5. Receive your report.

Your report will include:

  • Moisture percentage
  • Nutrient results (in mg/kg or % units)
  • Some important nutrient ratios
  • 1000 grain weight (for wheat only)
  • Seed Zn and P contents (for wheat only)
  • Nutrient removal scaled up to 1 t/ha yield.

Moisture percentage and 1000 grain weight are reported to allow an appropriate seeding rate to be accurately calculated.

Summary

Make grain testing a priority this harvest. It is a simple and inexpensive way to round out this season’s nutrient budget, and get a head start on planning for next season.

Addressing precise nutrient removal, and getting a head start on understanding seedling vigour, will assist decision making when seeding time rolls around again next year.

Further Information

For more information, contact IPF’s Technical Agronomist, Reily Menhenett at reily.menhenett@incitecpivot.com.au or 0474 093 167.

If plant sampling bags are required contact Nutrient Advantage on 1800 803 453.  

References 

Reuter DJ, Edwards DG and Wilhelm NS (1997). Temperate and Tropical Crops. In Plant Analysis: An Interpretation Manual. Eds DJ Reuter, JB Robinson. p 83-253. CSIRO Publishing, Melbourne.

Norton R (2012). Wheat grain nutrient analysis for south-eastern Australia. Agronomy Australia Proceedings. https://agronomyaustraliaproceedings.org/images/sampledata/2012/7984_5_norton.pdf

Rengel Z & Graham RD (1995) ‘Importance of seed Zn content for wheat growth on Zn-deficient soil’ Plant and Soil, 173: 259-266, 1995.

DG De Marco (1990) ‘Effect of seed weight, and seed phosphorus and nitrogen concentrations on the early growth of wheat seedlings’ Australian Journal of Experimental Agriculture, 30, 545-9, 1990.