picture

13 July 2001

More samples, better

picture

Understanding how grain

quality varies and sampling

accordingly can help avoid

marketing disappointments.

Amanda Dunn reports

IT is well known that grain quality varies within fields. But the implications for in-store sampling are not so well appreciated, says independent consultant Chris Dawson.

Soil type and moisture are key influences, he explains. "If you have more than one soil type yield and quality will probably vary across your fields."

Work in 1996 at Shuttleworth Farms with AGCO Fieldstar and Hydro Agri highlighted such fluctuation when a 12ha (30 acre) field of Consort wheat was sampled at 158 satellite-mapped points during combining.

Yield bands ranged from 6-7t/ha to 11-12t/ha and protein from 10-11% to 16-17% (old nabim scale). The whole-field average was 8.7t/ha at 13.6% protein.

High output and associated low proteins came from the heavier clay loam in the north of the field, while the opposite occurred at the lighter southern end.

"The protein variation wasnt that surprising," says Mr Dawson. "If yields are down proteins are generally better. Protein was obviously satisfactory, but the results illustrate the potential for in-field variability.

"The problem is how to manage it without spending a lot of money. If you are unsure about the need for extra nitrogen for protein, it may be most rewarding to apply it to areas of anticipated higher yield."

Then, when assessing quality at harvest, taking more than one sample is important, he explains. Trailers may already hold admixtures where combines have cut high and low yielding areas.

"An absolute minimum is one sample/trailer. You dont necessarily have to analyse all individually to get the overall picture. But without them, you dont have the choice."

Creating accurate variability maps requires at least 100 analysed samples, but the cost is unlikely to be justified. However, general values in specific areas can be determined by analysing a bulked sample of perhaps 16 sub-samples, he suggests.

PRACTICAL VARIABLITY

&#8226 In-field yield and quality ranges.

&#8226 Driven by soil type and moisture.

&#8226 High yields often mean low protein.

&#8226 Low output suggests high protein.

SAMPLING STRATEGY

&#8226 Divide store into bays.

&#8226 Collect samples from each trailer in bucket.

&#8226 When bay full, bag and test one sample from bucket.

&#8226 Use NAMAS or TASCC laboratory.

Shuttleworth field results

Range Average

Yield (t/ha) 6-7 to 8.7 11-12

Protein (%) 10-11 to 13.6 16-17

Specific wt 74-75 to 76.8(kg/hl) 78-79

TGW (g) 37.5-40 to 45.5 50-52.5