Eroding our future through farming practices

FOR nearly 30 years now, we have been practising zero or minimum tillage in our farming systems.

This is not 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 work it mechanically.

You just have to go back for the past two years, with our rampant Fleabane and Feather Top Rhodes populations that have needed some tillage control operations and how many hours it took on the old "round the clock on the tractor" scenario, even with guidance systems. 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 dryer times with heavy rainfall events, increased sequential cold days and, no doubt, plenty of hot days in the coming summer. So what I am alluding to is that moisture is again going to become the big deciding factor in our cropping regime. 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 this lack of stubble and a heavy rain event of 60mm - 240 points in my language - and this fell in less than one hour not two weeks ago.

As I travelled around the area some days later, I saw plenty of soil erosion, as well as many previously cultivated strips still too dry to plant and tonnes of cultivated stubble swept from paddocks into dams and waterways.

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

The good scientists from ASPRU calculated that losing only 0.75 of an inch of soil over 100 years is equivalent to losing only two tonnes per hectare of soil each year. Given that many of our local regional soils over 10,000 square metres (one hectare) down to only four inches deep weigh in at around 1300 tonnes or thereabouts, you wouldn't even notice losing this amount - or would you?

Without any measuring devices, I can assure you we would have lost a lot more than 2t/ha from that storm.

So the rate of soil regeneration is far exceeded by erosion events, especially 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?

None of you will be surprised to hear me say to retain your upright stubble as long as you can and don't forget to factor in this summer's heavy storms.

It all sounds easy, especially when you consider that armed with the knowledge that cultivated country with bugger all stubble will many times retain only 20% or less of your heavy rainfall event.

Compare this to the parallel block alongside uncultivated standing wheat stubble and, as I recall from those ASPRU field days, the comparable water retention is like 70% or more.

Yes, we do have soils that are hard-setting due to poor structure from previous years' cultivation events and these do require different management, with surface roughness a key to letting the water pond and slowly infiltrate into the subsoil as the hours pass.

It's a bit of a vicious circle and a juggling act for a start to improving your soil structure and reduction of erosion events, with zero till a basic compound and 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 by water is occurring all over Queensland farmlands and, unfortunately, zero or even minimal tillage needs many months to work its magic on our soils and their structure.

  • Paul McIntosh is a former manager of Landmark Emerald, now based on the Darling Downs.

Topics:  erosion paul mcintosh soil health

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