Opinion

Thought and planning needed in battle against erosion

WE HAVE been using zero or minimum tillage for nearly 30 years in our farming systems.

This is not big news to any of us, in our endeavours to retain surface stubble, reduce machinery and fuel costs and save job time.

These days many of us have worked out that having to spray a 1000 acre paddock takes much less time, than to mechanically work it.

You just have to go back over the last two years with our rampant Fleabane and Feather Top Rhodes populations that have needed some tillage control operations and hours on the tractor - even with guidance systems.

High quality soil takes something like 100 years to "formulate" from parent rock to a few millimetres of quality clay-based soil.

Yes, we got our paddocks looking cleaner hopefully and therefore did not add to the weed seed bank in these wet times.

However the seasons have turned back into drier times with extreme weather conditions of heavy rainfall events, increased sequential cold days and plenty of hot days in the coming summer.

Moisture is going to become our big deciding factor in our cropping regime again.

To be more specific, stored sub-surface moisture is going to be regaining the mantelpiece's top place for successful cropping in our farming endeavours.

On the Darling Downs we have already had examples of what lack of stubble and a heavy rain event of 60mm can do.

This all fell in less than one hour a few weeks ago.

It was a wild little storm with driving hail stones over some of the best soil in the world and on some mid-October-planted, and struggling, cotton, sorghum and maize crops.

As I travelled around the area some days later, I observed plenty of soil erosion.

And there were many previously cultivated strips that were still too dry to plant, even after the wild 240 points.

Add to this tonnes of cultivated stubble swept from paddocks into dams and waterways.

It was everywhere but where it should be.

High quality soil takes something like 100 years to "formulate" from parent rock to a few millimetres of quality clay-based soil.

So the good scientists from ASPRU calculated that losing .75 of an inch of soil over 100 years is equivalent to losing two tonnes per hectare of soil each year.

Given that many of our local regional soils over 10,000 square metres, down to only four inches deep, weighs in at around 1300 tonnes, or thereabouts, you can see that losing this minor amount of 2 t/ha, you would not even notice it, or would you?

I can assure you without any measuring devices, we would have lost a good deal more than 2 t/ha from the mid-November storm.

So the rate of soil regeneration is far exceeded by erosion events.

This is especially so now we have been tilling the soil in our cropping endeavours more than the original settlers did with grazing animals.

What can we do about arresting this trend?

Retain your upright stubble as long as you can and don't forget to factor in heavy storms this summer.

Cultivated country with little stubble will retain only 20% or less of heavy rainfall.

Compare this to the parallel block alongside with uncultivated standing wheat stubble.

As I recall from those ASPRU field days, the comparable water retention is 70 % or more.

Yes, we do have soils that are hard setting due to poor structure from previous years of cultivation events.

These blocks do require different management.

Surface roughness is a key to let the water pond and slowly infiltrate into the sub soil as the hours pass.

It's a bit of a vicious circle and a juggling act to improve soil structure and reduce erosion events. Zero till is a basic compound.

Yet, to let water soak into these harder soils, you may need top level roughness.

So your weed control decisions are going to come under a lot of pressure, and this is where some residual herbicides and a rotation plan will help immensely.

This erosion type scenario is occurring all over Queensland farmlands and unfortunately zero or even minimal tillage needs time to work its magic.

Topics:  columns, erosion, paul mcintosh, soil health


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