Growing crops just is not an exact science

13 July 2001

Growing crops just is not an exact science

GRAIN is not a manufactured product – its a raw material and theres a great deal of variation within it, stresses Northants grain marketing specialist Charles Jackson.

"Agronomic factors affect quality. Stress from flooding, drought, chemical overspray, general fungicide policy and soil type all have an effect."

Banks Cargill grain director Richard Whitlock adds: "Growing crops is no more an exact science than anything else. The trouble is we try to make it so.

"Producers realise year-on-year variability exists. The dilemma arises where a bulk goes into two 1000t stores and comes out in 25-30t multiples."

Taking samples throughout a bulk and mixing them to represent the whole does not necessarily reflect the quality in each outloading because 90% may reflect that homogenous sample, but there can be 10% that falls outside, causing the grower and end user consternation, says Mr Whitlock.

Under scrutiny

Grain analysis then comes under scrutiny. "The difference between 13.0-13.7% protein wont have a financial implication for the grower, but a difference of 0.7% in the other direction may incur rejection.

"Quality analysis only becomes an issue when grain falls out of its contracted purchase bands."

Mr Jackson says it is borderline cases that matter. "In due course, growers will have to get their own analysis done and they must sample thoroughly. You cannot be too accurate."

But analysis is only as good as the samples presented, warns Mr Whitlock. Mr Jackson recommends growers take dry samples from trailers as they are tipped.

"We suggest segregating a store into bays, keeping a bucket and taking a dry sample from each trailer. Once the bay is full, bag and label a sample from the bucket for analysis," advises colleague Sarah Adams. If the grain is wet, apply a similar approach as it comes off the drier.

Test results

With test results received, a picture of average quality within each bay and extremes within the whole store will emerge to help marketing. "Sampling in situ is not ideal because the depth of grain may affect your ability to gain a true representation of the whole bulk," warns Ms Adams.

A minimum of one sample/50t is recommended and always use an NAMAS or TASCC-registered laboratory for testing. "An ISO standard will not do," says Mr Whitlock. "With that scheme you write your own standards, and as long as you complete them youre OK.

"NAMAS and TASCC have extra demands, including ring testing, staff training, repeatability and independent verification."


Discrepancies between laboratories have declined, but Mr Whitlock warns producers to remember test tolerances when selling. "No manufacturer of laboratory equipment guarantees it is correct to the extent of the minute claims we incur. Growers need to allow for a degree of tolerance. Who is to say we are wrong testing at 14.8% moisture when intake tests at 15% and the tolerance is +/- 0.2%?

"Years ago, farmers took grain samples to market. Then, as output increased, merchants wanting to secure new contracts offered sampling. Now its going full circle. Accurate sampling will help farmers with marketing, but they should take variability and test tolerances into account to ensure they dont oversell quality."

See more