Wheat yields can be boosted considerably by sowing into paddocks where the stubble has been retained, according to the results of a long running trial by the Department of Agriculture of Western Australia.

The results of the ongoing 17-year trial at the Department's Merredin Research Station will be presented today at the Agribusiness Crop Updates, supported by the Grains Research and Development Corporation. 

During the last five wheat years of the trial, crops sown using no tillage methods with retained stubble had 10 per cent higher yields than those that had been burnt.

Department agricultural engineer Glen Riethmuller said the stubble had little effect on crops sown under conventional tillage methods, but the response was significant when combined with the no tillage system.

"Each year the same treatment is applied to the same plot of red sandy clay loam soil, which last year was sown to Wyalkatchem wheat," he said.

"In 1995 we changed to a no-till system and since then the yields have averaged 2.82 tonnes per hectare with stubble retained and 2.56 tonnes with burnt stubble, illustrating the benefits of stubble retention in the no-till system."

The trial also investigated other variables, including the effect of row spacing on wheat yields and ryegrass seed set.

The results showed a reduced yield of about 0.4 per cent for every centimetre that the row spacing increased more than 18 centimetres, with or without stubble.

"That equates to a yield loss of about 1per cent for every inch or 2.5 centimetres," Mr Riethmuller said.

"This is consistent with other work in Western Australia and is probably due to a number of factors that are not totally understood yet.”

In 2003, about five times more ryegrass seed was produced in the stubble retained plots compared to those that had been burnt, but the wheat yielded 20 per cent better with stubble retained.

"Once again, the results show the yield gains to be made from retaining stubble, even with a high amount of ryegrass present," Mr Riethmuller said.

The trial will continue this year with barley.