THREE YEARS of tri als have shown that a three-year lucerne ley increased organic carbon, but there was no change with water infiltration rates in a continuous cropping system on black cracking clay soils.
Based at the Jimbour Plains, 40 km north-west of Dalby in the Darling Downs of southern Queensland, the trials aimed to assess whether a lucerneley would be profitable in continuous cropping farming systems, and what effect it would have on subsequent crops. The trials were supported by growers and the Federal Government through the GRDC, as well as by CSIRO and Eastern Farming Systems.
According to CSIRO researcher Neal Dalgliesh, the first year of lucerne exhausted the subsoil moisture to a depth of 3 meters and the following years' rainfall could not adequate ly recharge the soil profile.
"This would he great for recharge control in areas affected by waterlogging and salinity," says Mr Dalgliesh. "but the problem for cropping here is lack of water when you need it."
As a result, growers hosting the trials could profit from the lucerne only in the first year ( 1997- 98), when there was enough growth to produce hay. In the second and third years, under conditions of low soil moisture and low rainfall , there was not enough growth to cut much hay and so there was no profit.
Play it by ear on rainfall
According to Mr Dalgliesh, there is no such thing as a ' normal ' year because the rainfall can vary so much. Compared with a long-term median rainfall of 622 mm, rainfall in the trial years was 750 mm (year 1), 425 mm (year 2) and 525 mm (year 3).
In this climate, growers have come to rely heavily on fallowing to store enough water for optimal production, and they double-crop when conditions allow. Controlled traffic and zero-till are standard practices for these growers in their efforts to maximise production by conserving soil and water.
As a result of the trials, growers now suspect that leys of two years in every ten might be financially viable. Scientists and growers continue to look for specific benefits a lueence ley brings to the following crops, and how long the ley phase should be. Benefits could include increased nitrogen and more macropores in the soil , which can affect the way plants access soil water.
Grower Jamie Grant of ' Kielli ' is on one of the trial sites. He says a two-year lucerne ley in one paddock was enough to give a decent sorghum crop on very limited moisture. He compares this to the so rghum crop in the neighbouring paddock that had similar starting moisture but which was a failure.
According to Mr Dalgliesh. the trial results suggest a possible reason for the yield benefits is the increases in plant - available water caused by improved soil structure, allowing roots to access more of the soil profile.
"The crops in old lucerne paddocks have been completely reliant on surface moisture, from rainfall. There hasn' t yet been enough rain to recharge the subsoil," says Mr Grant.
"Lucerne leys are an accepted part of th e cropping rotation in mixed farming systems through much of the northern grains zone," says Mr Dalgliesh. " But we still have some way to go to identify the best way to incorporate a lucerne ley phase into the continuous cropping systems on the Jimbour Plains."
Program 4 Contact: Mr Neal Dalgliesh 07 46881376
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