Deep rip hard setting soils? Consider zero till long term

Deep-ripping increases infiltration and reduces surface ponding on a hard-setting soil on the Darling Downs, Qld. Deep-ripping helps water soak into a self-mulching soil on the Darling Downs, but also promotes evaporation.

TAILOR farming practices to the soils. That's the message from deep-ripping trials in the Jinghi catchment in the Darling Downs area of southern Queensland.

According to CSIRO researcher Neal Dalgliesh, growers wanted to identify the benefits of deep-ripping and reduced tillage for water capture and other soil properties on two of the soils found in the area - one a self-mulching brigalow soil and the other a hard-setting clay soil. The results were quite different for the two soil types.

surface cover under any tillage system = less run-off and crusting

"Many growers had already been ripping the hardsetting soils, and our aim was to quantify the benefits and to compare it against other options such as reduced tillage and stubble retention," says Mr Dalgliesh.

Fallow efficiency, which is the percentage of rainfall stored in the soil profile during a fallow, was one of the main indicators of the performance of deep-ripping and the minimum-till and no-till options that were tested.

Self-mulching clays

On the self-mulching soil, only 82 mm of rainfall stored (to a depth of 1.05 metres) were retained some 110 days after ripping, compared with 107 mm under the plots that weren't ripped. This gave fallow efficiencies of 20 per cent and 30 per cent respectively.

"Hie story is very different for the hard-setting soil, with the ripped treatment returning a fallow efficiency of 16 per cent, and the non-ripped treatment returning a fallow etticiency of only 12 per cent over the same period," says Mr Dalgliesh.

From these preliminary results from only one year of trials, Mr Dalgliesh suggests that there appears to be no benefit to ripping on the self-mulching soils and in fact ripping may be detrimental in terms of water capture.

Supported by growers and the Federal Government through the GRDC, and the Jinghi Catchment and the Brigalow Jimbour Floodplains Groups, the trials are based at two properties in the Jinghi catchment. Research support is provided by the CSIRO and Queensland Department of Natural Resources and Mines.

Grower response to the trials

Grower Bill Hoare, of 'Tarawera', was host to one part of the trials. With the mix of soil types on his property, he says his best option might be to deep-rip the hard-setting soils occasionally to improve soil structure, with a no-till approach in between.

"I see deep-ripping as a short-term solution. No-till could achieve the same thing, but it would take a few more years," says Mr Hoare.

Although he hasn't tried it out, Mr Hoare believes that if he used traditional tillage on those soils, he would find that he would need to be ripping every few years. This approach wouldn't fit easily into his hectic schedule of double-cropping wheat or barley with sorghum and other summer crops when the conditions are right.

The trials also set out to benchmark various properties of the soils, so that long-term changes under no-till and minimum-till systems can be measured.

"We hope to see signIficant changes in soil physical and chemical properties down the track, but it will take a few years to see any impact of these treatments. So far, the results are only interim," says Dr Dalgliesh.

"In the short term, however, it has become clear that increasing the level of surface cover under any tillage system on the self-mulching soils reduces run-off and crusting, with more water able to penetrate the surface during a rainstorm:' he says.

In contrast, water infiltration into the hard-setting soils was influenced by cultivation and surface cover, with all treatments reaching a similar low level of longer-term infiltration, which suggested some subsurface restriction.

With benchmarking studies continuing in the Jinghi catchment, Mr Dalgliesh and his team hope to build up a detailed picture of the economics of the tillage systems and the impact of farming systems on the physical, nutrient and water-holding properties of the soils in the area.

Program 3.5.1 Contact: Mr Neal Dalgliesh 07 4688 1376

Region North, South, West