Grains Research and Development

Date: 01.09.2001

Lucerne supports wheat on salt scald by Caroline Peters

Salt scald December 1999 Before and after watertable lowered by >50 cm in under 12 months Same area July 2000 (right)

Growing lucerne near salt scalds on a Temora (NSW) farm lowered the watertable sufficiently in one year to allow wheat to grow in the scald where there had been 100 per cent crop losses in the previous year.

A saline scald first appeared on the farm in the late 1980s and 10 years later covered two patches with a combined area of almost 112 ha with a thin crust of salt. An electromagnetic survey revealed there was a further 20 ha affected by high subsoil salinity.

The scald was 50 m upslope from a road and at the foot of a 2 km long slope of about 2 per cent. Farmers in the Temora district believe they can partly control salinity using perennial pastures to lower the watertable.

At present there are few salt scalds in the area but with the Salinity Audit predicting a 60-fold increase in the area affected by dryland salinity in NSW over the next 50 years, farmers are keen to fix the problem.

Trials to test solutions were supported by graingrowers and the Federal Government through the GRDC.

Researchers lohn Angus and Matt McCallum from CSIRO Plant Industry, and jim Salmon from NSW Department of Land and Water Conservation, sowed various crops and pasture plants in transects across the salt scald and the surrounding areas.

Measuring farmer's success with lucerne

Lucerne was established in 1999 by undersowing with wheat over a 100 ha area adjacent to, and uphill from, the scald.

“The farmer had already tried lucerne in other salt-affected areas, with obvious visual success, so we thought it would be important to actually measure the extent of salinity, the level of the watertable and gauge plant establishment and production,” said Dr McCallum.

Plant establishment in 1999 was poor for most trial crop and pasture species within the scald and the growth and yield of surviving plants were limited. The exceptions were a sparse population of perennial grasses that became well-established productive plants.

However, in 2000, a wheat crop was successfully sown in areas of the scald where there had been no emergence or growth in 1999. Weeds (annual ryegrass and capeweed) grew in the middle of the scald for the first time in many years and there was vigorous growth of isolated perennial plants.

This indicated that the surrounding lucerne was having some impact on the scald.

Watertable drops

Between spring 1999 and autumn 2000 the watertable under the scald fell from the surface to a depth of 60 cm. Surface salinity levels also dropped as the salt was leached by winter rains.

However, following several weeks of rainfall in winter 2000, the watertable rose close to the surface under the scalds but not under the surrounding lucerne. The watertable again fell during the summer/autumn of 2000-2001, this time to a depth of 80 cm.

“Despite the rising watertable in winter, the wheat crop in 2000 still managed to yield 1 t/ha in an area which had not yielded anything in the past decade,” Dr McCallum said.

He said the watertable rise beneath the scald during late winter 2000 indicated that the lucerne established near the discharge area was insufficient for complete rehabilitation of the scald.

“A reduction in recharge upslope is also required. We need methods to identify the location and size of recharge areas,” he said.

Program 3.4.2 Contact: Dr Matt McCallum 02 6246 5531 email m.mccallum@pi.csiro.au