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Soil nutrient tests have been compared between each cropping system since the trial began. To date, very little soil nutrient differences have been observed in the top 10cm. We are however finding that continuous cropping rotations are showing higher P levels than the fallow rotations. This is to be expected, and is common experience for local paddocks.
One major variation that we are observing is the levels of Glomalin between the tillage systems.
Glomalin is a 'glue' like product found in the soil that is produced by arbuscular mychorrhizal fungi (AMF), and usually accounts for 15-20% of the organic carbon in undisturbed soils.
Glomalin has been found to increase soil agregate stability, reduce surface setting and erosion, and increase moisture storage and infiltration.
The fungi associated with Glomalin, AMF have also been shown to have a symbiotic relationship with plant roots, ie you scaratch my back and I'll scratch yours!! The fungi are able to access nutrients (particularly P) and moisture and supply these to the plant roots. The fungal hyphae are much better at extracting these nutrients and moisture from the soil than plant roots as they are much more plentiful within the topsoil than the plants root system. In return the plant roots supply the fungi with carbon. This is a win win situation.
A graph of the Glomalin levels are shown below.
Soil borne diseases are also starting to change, with the incidence of rhizoctonia and pratylenchus neglectus becoming more common in some treatments. This is measured by the Predicta B root disease test.
We are finding that these two soil pathogens are related, ie nematodes are allowing entry of rhizoctonia into plant roots.
The graph above shows that the continuous wheat system is allowing rhizoctonia levels to increase. Another point to note is the higher level of rhizoctonia under the minimum till system. This is because rhizoctonia levels are significantly reduced by cultivations. As expected, any cropping system following cereal has higher rhizoctonia levels in the following year.
The same trend is occurring for Pratylenchus neglectus. By adding a break crop such as peas, the risk of yield loss from these diseases is significantly less.
Note: These figures indicate the risk associated with each disease given the amount of inoculum in the soil. The actual disease incidence observed may vary according to the environmental conditions.
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