They call them “suppressive” soils because they suppress disease in crops. Scientists are racing to find out why. But they know 2 things:
- Soil microbes are responsible for them.
- Soil carbon increases are the key.
And “There are soils right across the country where the incidence or severity of disease is suppressed, even in the presence of the pathogen that causes it, a host plant and a favourable environment,” says Associate Professor Pauline Mele, LaTrobe University and principal research scientist, Department of Primary Industries Victoria (DPI).
“These disease-suppressive soils have been found to develop under management practices that supply higher levels of carbon inputs for more than five consecutive years. The carbon from plant roots and crop residues is biologically available and provides an important food source for soil biota, ” says CSIRO’s Dr Gupta Vadakattu in GRDC’s GroundCover 96 Soil Biology Supplement.
Disease suppression is the result of increased species density among microbial communities in soils associated with increased carbon levels. We know that, when soil carbon levels are rising, biodiversity increases and this has the effect of increasing resilience (or disease resistance). “We know the effect is due to the presence of a diverse range of ‘good’ micro-organisms,” says Professor Mele.
Three facts Dr Mele mentioned provide further evidence that soil carbon is a key influence:
- Balance in the microbial community is critical: “upsetting the balance or sterilising the soil can cause the disease to strike with a vengeance”.
- It is not soil type specific; it could therefore be a soil health agent – such as carbon – that is at work: “ we believe every soil has the potential to be suppressive”
- It is a feature of soil heavily influenced by a farmer’s management practices: “it’s just a matter of working out what management techniques will encourage it.”
The fact that a microbial community is a natural system and such systems exhibit ‘emergent properties’ as they become more complex. It is not one variable at work. However, reductionist science tends to look for the single factor. However the Professor says, “At this stage, though, we’re still trying to identify exactly what organisms, or combination of organisms, are doing the work.”
“HIGH rainfall zone (HRZ) grain growers stand to increase yields and save significant amounts of money on chemicals, if the secrets of suppressive soils can be unlocked,” reports The Land. Growers lose an estimated $250 million each year from root lesion nematodes alone. “Soil biology is tipped to be the ‘next big thing’ in terms of productivity gains and a five-year research program is currently being funded by the Grains Research and Development Corporation (GRDC) to address some of the knowledge gaps.” Having poured scorn on soil biology as “snake oil” and ‘witches brew’ for so long, the GRDC’s epiphany is welcome.
“The soil biological resource under our feet is seen as something of the ‘last frontier’ for the grains industry… We know it’s about competition for resources. If we create a habitat that favours one type of soil microbe, say through repeated use of the same management practice such as addition of fertiliser or sowing the same plant types, the community may end up with fewer types of biota present; thereby reducing the resilience of the system,” says Professor Mele.
The writing is on the wall for chemical companies. “Using biological suppression to reduce crop losses, without chemicals or with minimum chemical input, could improve the profitability of growers worldwide,” says the Professor.
More information about the Soil Biology Initiative II is available at www.grdc.com.au/soilbiology
. Research partners include the Victorian Department of Primary Industries (DPI Vic), Queensland Department of Agriculture, Fisheries and Forestries (DAFF), Department of Agriculture and Food WA (DAFWA), and CSIRO.