Risky business

A cartoon portraying a very large cow with the comment: "I see Martin's been giving them lupins again."

We've got a lot more knowledge than we had 10 years ago, we've cut out the risk of total losses with management strategies but there are still losses. Farmers still look at lupins as being a difficult crop grow. I have confidence in contributing research dollars in the hope of making it a bit less risky. John Hutchinson, WA lupin grower.

Best bets for healthy lupins

Keeping the lupin crop reasonably safe from attack by brown spot and root rots is top priority for most growers of this tricky grain, especially in wetter areas known for disease. Production losses in the economically desireable 1:1 and 1:2 lupin-cereal rotations can amount to $10 million annually in Western Australia.

The advice from a major research project funded by growers through the GRDC is fourfold: stubble retention, sowing depth, phosphate nutrition and a surprisingly low rate of a good fungicide. These four strategies, together with a wide-row spacing approach to stubble mention, are 'best bet' techniques for the long haul in lupin growing, according project leader Mark Sweetingham of the Western Australian Department of Agriculture Division of Plant Industries. "Nothing is 100 per cent every year. Biological systems don't work that way," said Dr Sweetingham, noting the vagaries of weather and the importance of the right soils and soil conditions.

"But these findings are likely to have the most useful application where disease is most severe."

Dr Sweetingham and his team demonstrated that changes involving tillage and seeding machinery can dramatically reduce disease severity and increase yields by 30 per cent or more. They found that cereal stubble mulching reduces brown spot and that precise sowing at 5cm depth minimises Pleiochaeta root rot.

Increase row width

Growers have had trouble sowing into stubble with machinery designed for precise control of sowing depths. The response strategy, said Dr Sweetingham. is increasing row width.

'Handling stubble with tine, dramatically improved by increasing row spacing from the traditional 7" to 14"," he reports. "Unlike in cereals, yield is not depressed by wide spacing in lupins to offset the benefits of precise sowing depth with stubble retention."

He said the combination of the wide spacing with the stubble retention and sowing depth techniques had not been used extensively before. It was therefore the biggest news out of this research project.

Building on these results, Dr Sweetingham is leading a Departmental team in a new project, also with GRDC funding, to further improve establishment techniques.

This involves field trials at Wongan Hills to determine the most suitable rates of fungicide, the best sowing machines and establishment systems and the interaction between phosphorus nutrition and disease.

Less is just as good and cheaper

Trials with the dicarboximide fungicides Rovral and Sumislex measured their efficiency at rates varying from 12g to l00g active ingredient at 100kg of seeds. Following three years of trials testing all rates at low, mild and severe disease pressures, the result was always the same: 12g of fungicide per 100kg of seed proved just as effective as the currently recommended l00g per 100kg — reducing the cost to one-eighth of the present level.

Getting through the stubble

In collaboration with colleagues Ron Jarvis and Glen Riethmuller, Dr Sweetingham has been examining the problems of handling stubble on light soils with machinery designed for precise control of sowing depth.

The team compared the effectiveness of three kinds of seeding machine: combine, cultitrash and modified cultitrash (this had long tubes directed behind the back discs, for increasing the precision of seed placement).

In tests on the machines, the conventional cultitrash seeder fell short of the target depth, especially at the deeper settings, where it also attracted severe root rot in the vulnerable early life of the seedlings (at 4 weeks), due to the machine's tendency to invert the spore-laden surface soil and bury the spores below the seed. The modified cultitrash improved depth precision

The combine produced the best compromise, with similarly precise placement and the least root rot. Subsequent grain yields followed the same pattern.

Disease and phosphorus

The scientists are also testing the interaction between brown spot, Pleiochaeta root rot and phosphorus nutrition, in co-operation with Mike Boland of the Plant Nutrition Branch of the Division.

They found increasing the level of phosphorus nutrition has little preventative effect when brown spot attacks seedlings, but it can reduce the impact of brown spot epidemics that continue right through the winter and into early spring. Such persistent attack can severely limit grain yield, but adequate phosphorus makes the crop taller, denser and less exposed to rainsplash of the soil-borne spores.

Research is continuing to investigate the disease implications of deep-banding superphosphate. Early indications suggest that this will reduce brown spot severity more efficiently than topdressing or drilling with the seed. Each of those findings can reduce farmers' costs and/or crop losses. Collectively, they add considerably to the benefit:cost ratio of about 8:1 that the earlier GRDC-funded research enjoyed.