Soil Structure The Key To Big Yields

June 25, 1999 The Rural News

Well-structured soils in the higher rainfall areas of the southern wheat belt should be capable of producing 5-6 tonne/ha wheat crops "in a majority of years" while minimizing the risk of erosion, according to soil scientist with the Department of Land and Water Conservation, Ian Packer.

Conducting rainfall run-off experiments in Junee with the Department's Wagga based Innovative Farming officer, Sean Roberts, Mr Packer found that despite minimum tillage and direct drill techniques being carried out for years, many soils in the area showed 75 per cent run-off rates when 43 mm of simulated rain was applied over an hour.

This type of rainfall is relatively common in the area, occurring on a one in five year basis.

Run-off rates of 75 per cent are likely to be causing topsoil losses of around 1 tonne/ha, which is far above the rate of topsoil formation.
Well structured soil (without stubble protection) should produce little or no run-off at those rates (of rainfall) in these soil types, Mr Packer said, creating minimal erosion and storing moisture for following crops.

The key to well structured soils, he said, is not only direct drilling and stubble retention, but better management of stock and equipment

to prevent subsurface compaction, plough-pans and sealing of the soil surface from traffic.

"If you want to change the soil, you have to change the whole system," Mr Packer said.

Controlled Traffic Farming

"Think about lengthening both the pasture and cropping phases to eight to ten years each, keep stock off potential cropping paddocks when it rains, particularly paddocks which were sown to canola the previous year and definitely move into "controlled traffic farming".

"If you want to he even more radical do not stock the cropping paddocks at all or for only very short periods when the soil is dry to control weeds".

"Controlled traffic farming" is a system where machinery follows the same track each time an operation is carried out.

This greatly reduces compaction leading to better water infiltration rates, less power requirement to sow, less costs from better herbicide and fertilizer application and better accessibility after rain to allow more timely operations.

To establish controlled traffic a base width is used which is usually the tractor and sowing unit. Using this width other equipment is set up on this width or a multiple of it.

While it may not be economically feasible or possible to initially have every implement for controlled traffic, Mr Packer said it was important to target the equipment which is causing the most compaction.

"Boom sprays and urea spreading are some of the worst culprits, because of the weight involved and the fact they operate in winter on moist soils:' Mr Parker said.

"A lot of people are finding it is not that difficult to match their spraying gear to the base unit. It might just mean adding four to five nozzles on your boom spray.

"The other killers are chaser bins running all over the paddock — stick to the track." Mr Packer said the benefits can be large after only two to three years, particularly in marginal country.

Conservation Tillage

"There is often the attitude that conservation tillage means more work and less dollars. On a property near Cowra which is now basically no tillage, they averaged 5 tonne/ha of wheat amongst a variety of other crops over 2800 ha, double the district average last year in soils ranging from grey cracking clays to sandy loams. Their faba bean crop went 3 tonne/ha where most properties had a near failure." On some properties Mr Packer said "you can dig a post hole with a shovel in the middle of summer", the soils have become so well structured.

High rain infiltration rates and stubble retention are allowing conservation farmers to dry sow crops such as canola and pulses into stored moisture profiles, allowing germination irrespective of the timing of rainfall Mr Packer said.

Dry sowing has also been successful in situations with summer weed control and burning stubble late. Sufficient moisture was available to germinate the crop which was not available in cultivated paddocks.