A specially bred mustard variety, Caliente - when grown to full bloom, flail-mowed and then incorporated just before strawberries or raspberries are planted - has a significant biofumigation effect.
Plant Solutions' Rebecca Dawson explained the biofumigation process on a demonstration plot of Caliente mustard next to the company's stand at Fruit Focus.
Biofumigation refers to the suppression of soil-borne pests and pathogens by naturally occurring compounds - predominately isothiocyanate (ITC) released from brassica family plant tissues. When these plant tissues are damaged, glucosinolates and an enzyme are allowed to come together and in the presence of water produce ITC.
Caliente-brand mustards are not simple green manure crops, as they have been bred and selected at Italian ISCI research station to produce large quantities of biomass and contain the high levels of glucosinolates and enzymes required for the biofumigation process.
The benefits for soft fruit growers - whether growing organic or conventional crops - are twofold. Firstly, the green manure effect improves soil health. It is a good source of nutrients, particularly nitrogen, and gives improved root penetration. Secondly, it suppresses weeds, a range of soil-borne pathogens (including Verticillium and Fusarium) and a range of nematode species.