RIM scenario– LWCW – Harrington Seed Destructor

The graphs below summarise the results of RIM scenarios for a Lupin / Wheat / Canola / Wheat rotation. The top graph shows the ryegrass seed bank ‘blowing out’ under a herbicide dominant regime. The addition of the Harrington Seed Destructor (HSD) leads to a big improvement in the ryegrass seed bank and the gross margin. The scale change on the second graph shows that where all crops are dry sown (green line) the HSD holds ryegrass numbers about level. The addition of crop competition (purple line) and spray swathing canola (light blue line) to the dry sown crops results in the greatest gross margin with a low ryegrass seed bank.

Scenario / 10 year Gross Margin
/ Herbicide dominant - including croptop lupin -knockdown for wheat & canola / $208
/ Herbicides + HSD every year – knockdown for wheat & canola / $217
/ Herbicides + HSD every year + dry sow all crops / $265
/ Herbicides + HSD + dry sow all crops + high wheat seed rate / $268
/ Herbicides + HSD + dry sow all crops + high wheat seed rate + spray swath canola / $272

Aspects to note:

Dry sowing of crops gives a 5 to 10% yield advantage in RIM hence the extra profit that results. The capital cost of the HSD in RIM was $200,000 compared to $70,000 for a chaff cart. There are also allowances made for extra fuel and maintenance of the HSD, however both remove 70% of ryegrass seed from the crop. Consequently, the ryegrass seed bank results are the same when comparing the chaff cart with the HSD but the gross margin of the HSD is always $5 to $6 /ha lower than the chaff cart due to the higher cost of the HSD.

Assumptions used in this RIM simulation

% Control
Trifluralin / 80
Sakura / 90
Boxer Gold / 85
Clethodim (some resistance) / 85
HSD (% removal of ryegrass seeds) / 70
Crop top lupin (% seed set reduction) / 75

Rotation: Lupin / Wheat / Canola / Wheat

Yield / Grain Price
Wheat / 2 t/ha / 250 $/t
Barley / 2 t/ha / 240 $/t
Lupin / 1 t/ha / 550 $/t
Canola / 1 t/ha / 240 $/t

About RIM

RIM is a hands on, user-friendly decision support software for farmers and advisors to evaluate the long-term cropping profitability of strategic and tactical ryegrass control methods.

RIM lets you test your ideas to run ryegrass down and profit up over a 10 year rotation.

For more information and to download RIM, visit www.ahri.uwa.edu.au/rim.