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Applied Horticultural Research :

Building soil wealth in Western Australia

On September 17th a field day on biofumigation at David and Lee East’s Bewray farm at Manjimup, WA attracted over 45 growers and industry specialists. The field day was held as part of Horticulture Innovation Australia’s (HIA) national Soil Wealth program, which aims to communicate information to farmers about practical and economically sound practices to improve soil health.

The field day speakers included grower David East, leading vegetable agronomist Mike Titley and 2015 AUSVEG Researcher of the Year, Dr Doris Blaesing.
Also speaking was Deb Archdeacon, a passionate advocate for sustainable agriculture who has promoted a range of effective approaches to improving soil wealth in the South West of WA for many years.

Four years ago David, began including a cover crop of Caliente mustard for green manure and biofumigation purposes into his cropping mix.

How Caliente mustard works as a biofumigant
In Caliente mustard these glucosinalates have been maximised. When the crop is mulched and incorporated, in the presence of moisture, the glucosinalates breakdown to produce the biofumigant ITC (Isothiocyanate).

It is this biofumigant that is active against weeds and many soil borne diseases including Pythium, Rhizoctonia, Fusarium, Verticillium and Sclerotinia. It also has a suppressant effect on nematodes.

Cropping Program
David and Lee East’s production season begins with first plantings of lettuce and baby leaf in late September and the final harvest is in late May.

Caliente is sown in April-May after the crop residues of the summer leaf program have been incorporated. It is generally a 120-130 day crop in the Southern Forest region of WA. The field day was timed to coincide with the incorporation of the Caliente crop into the soil so that visitors could witness this critical process that entails a three-pass operation.

The Process
The optimal stage to mulch the Caliente crop is when the crop is at around 20% flowering. This is when the beneficial fumigant compounds within the plant are at their peak.

The soil needs to be moist at the time of incorporation to obtain maximum benefit from the breakdown process. The crop is mulched down to ground level in a single pass and then has two passes with a speed cultivator before being rolled with a heavy roller to seal the soil.

Sealing the soil is important to ensure that the gases released during the breakdown of the crop are activated against weeds and plant pathogens in the soil. If the soil is not rolled much of the “active” moisture in the crop will evaporate and weaken the impact of the process. Importantly, the three passes need to be done within a total of twenty minutes.

Growing Caliente
Prior to planting the crop David deep rips his soil in both directions to a depth of around 50cm. The crop is seeded between early April and mid May. It is important to get the crop established whilst there is still some warmth so that it has enough bulk before the winter slows it down.

Crops were seeded this year at around 10kg/ha No fertiliser is added to grow the crop with David relying on the residues from his summer leaf cropping program.
No herbicides are necessary as the crop smothers all competition. It is then just a matter of timing of incorporation which will generally be in September or around 120-130 days from sowing.

Though David stresses that Caliente and will not solve all of a farmers soil problems, he has observed a range of beneficial effects.

David east said “Caliente is not a silver bullet but another safe and effective means by which farmers can increase their soil fertility as well as a tool for combatting soil borne pathogens and weeds”.

For more information:
Danny Fyffe
Applied Horticultural Research
Tel: +61 (0)437 353 748

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