Selective grain harvesting

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By Rob Bramley

Generally grain is harvested paddock by paddock, a practice that results in good and poorer-quality grain being combined. While this natural blending may result in an acceptable average product, it might not result in the best return from the paddock. This is especially likely for crops such as malting barley and durum wheat, where there may be a substantial quality component in the price.

We have had considerable experience and success introducing selective harvesting to the wine grape industry, which has proved to be highly profitable. Calculations suggest selective harvesting could be highly profitable in the grains industry.

For example, if a 100-hectare barley paddock is conventionally harvested as a unit and yields 240 tonnes with an average protein of 9 per cent, it would be worth $37,360 or $374/ha.

If 60ha yielded 2t/ha at 10 per cent protein and 40ha yielded 3t/ha at 8 per cent protein, by differentially harvesting the return would increase to $43,360 or $434/ha – an increase of 16 per cent.

Working with three South Australian growers experienced in the use of precision agriculture (PA), we are exploring the feasibility and potential financial value of selective harvesting. The initial project, which started in 2009, is working with malting barley.

Malting barley can be downgraded to feed for a range of reasons including small seeds, high protein and stained or discoloured grains. The degree to which these problems arise varies at a paddock scale.
The use of zone-based management and harvesting is being investigated in this project. Using spatial data sets including yield, elevation, electromagnetic and radiometric soil maps, as well as normalised difference vegetation index (NDVI) imagery obtained through remote and/or proximal sensing, management zones will be established.

Hand sampling and protein analysis of the grain within these zones will be used to calibrate the protein sensor. Targeted soil sampling and analysis will be used to identify any possible soil-based drivers of variation in crop quality. Initially zones will be based on yield, but as more data is generated protein zones may be developed.

Protein data will be gathered on the harvester and patterns of spatial variation in protein will be examined in relation to the zones.

For example, immediately prior to the 2009 harvest, approximately 70 grain samples were collected from the trial paddocks on Yorke Peninsula and the Mid North of South Australia, across the full range of variation in the paddock. The mean and the range of variation in protein percentage was 10.7 per cent (8.8 to 14.4 per cent) in the Mid North and 10.6 per cent (8.1 to 13.5 per cent) on the Yorke Peninsula. Protein maps showed this variation to be spatially structured rather than random. These initial results therefore confirm the potential opportunity for selective harvesting.

In the first year of the trial, data was only successfully collected at harvest for two of the paddocks and considerable time was spent setting up and calibrating the protein monitors.

A cost-benefit analysis of the selective harvesting will be carried out for the duration of the project. This will include investigating additional storage and handling costs that could arise from selective harvesting. A range of price and cost scenarios will be examined to identify when it may or may not be profitable to selectively harvest.

A second objective of the project is to use targeted in-season management to minimise grain quality problems. Much of this part of the project will focus on improving the calibrations for active crop sensors in relation to barley protein response to additional nitrogen. However, it will also build on previous research to better understand how differences between management zones can be best managed to optimise the value of barley produced.

GRDC Research Code CSA00024
More information: Dr Rob Bramley, principal research scientist, CSIRO Sustainable Ecosystems, 08 8303 8436, email

GRDC Project Code CSA00024

Region National