*Note - this report may contain independently supported projects, which complement the work in this GRDC research program.

Introduction

Waterlogging and poor soil structure in southern Victoria are the biggest constraints to consistently achieving high yielding crops.

In 1995, the Southern Farming Systems began a project looking at three drainage systems suitable for broad area cropping.  Underground plastic pipes and moles, wide raised beds (20m) and narrow raised beds (1.5m) were the methods.

After one year, narrow raised beds were chosen as the system that offered the most potential to cheaply drain cropping land and provide an environment which could significantly improve soil structure.  Three hundred hectares on eight commercial farmers’ properties were installed in 1997.  Only two sites were marginally waterlogged and yield increases of 55% - 100% were achieved on these sites.  The other sites were not wet and yields on beds were equal or slightly superior to the flat comparison.

The success in installing 300 hectares without too many problems, combined with the extensive publicity, high profile demonstration areas and the continued success with the raised beds at SFS Gnarwarre, has resulted in the concept capturing the imagination of many farmers and contractors.  This has resulted in the installation of approximately 5,000 hectares spread throughout south west Victoria, Gippsland and Tasmania.

The small raised bed area at SFS, Gnarwarre is producing outstanding results.  Canola yielded 3.5t/ha (control 2.2t/ha) in 1996.  Franklin barley yielded 6.3t/ha (Malt2) (control 5.7t/ha) in 1997.  Improvement in soil structure of cropping land was one of our project’s original aims.  Soil tests were carried out in February, 1998 and the results and discussion is as follows. 

Discussion

These results must be interpreted with caution.  Our drainage demonstration is not a replicated scientific trial.  We do not have initial soil tests from each treatment - we certainly didn’t anticipate the success of the project and the public interest.

However the results do help confirm some of the dramatic effects we can see in the paddock. When we stop and think about what we have done it is not too hard to understand.  We have cultivated extensively in the narrow raised beds and placed the top soil (plus a small amount of clay subsoil) in aerated piles in rows.  This created excellent drainage where any excess water only had to find its way a maximum of 0.5m to the

furrow.  We applied a high rate of gypsum which as discussed before, ends up a higher rate on the beds because we didn’t apply it to the furrows.  The canola crop grown in 1996 averaged about 3.5t/ha over the whole drainage site.  If it is calculated on a per-square-metre basis, the raised beds themselves yielded around 5t/ha.  The Franklin Barley crop yielded between 6-7t/ha over the whole site, but once again if it is calculated over a per-square-metre basis, the raised beds themselves yielded close to 9.5t/ha.

The only vehicles travelling on the beds have been a windrower and a harvesting machine (twice).  These machines were operating when the beds were dry and although some compaction occurred, it is not serious but certainly significant.  Therefore controlled traffic has been observed in the narrow beds whenever possible and the sooner it is full controlled traffic, the better.

No animals have grazed the site and no other vehicle traffic has driven on the beds, but vehicles have traveled over the other treatments. (Sprayer, tractors, combines, windrowers, harvesters).

Soil pH.  The narrow beds have a lower pH than the other treatments.  This is probably a reflection of the gypsum application and the urea applied to the bed tops.

Electrical conductivity and Total Soluble Salts.  The soil chemists tell me the higher level on the narrow beds is almost certainly a reflection of the higher rate of gypsum and urea applied on a per-square-metre basis.  These are not sodium salts so not of concern.

Sulphur.  Probably a reflection on the higher initial dose via the gypsum to the top of the beds.

Dispersion / Slaking.  This is the area of most excitement.  The narrow raised beds have been given a perfectly clear bill of health for these physical tests.  The soil is in excellent physical condition, where the other treatments show slaking and varying degrees of dispersion.

Organic Matter.  Our chemists tell me it takes tonnes and tonnes of organic matter to measure a difference.

 With a soil weight of around 1400t/ha in the top 10cm it is easy to understand it will take a huge amount of organic matter to measure a % difference.  The chemists tell me you need over 250t/ha of organic matter to measure an appreciable difference.  I think we’ll forget measuring this so-called variable.

Ballarat University were also employed to carry out soil physical tests.  They selected three sites at random in the control area and in three of the beds.  At each site three areas 75mm high and 75mm diameter were taken.

Results Summary

• Bulk density significantly lower and total porosity significantly higher in narrow raised beds compared to control.
• Total porosity in raised beds is approximately 10% greater than in control.
• Air filled porosity in the raised beds is approximately 15% greater than in the control.
• Gravimetric moisture content higher in raised beds than in control.
• Volumetric moisture content is equivalent in raised beds and control.