SEMINAR: Soil and Water seminar series, Weds May12, 4pm: Prof. Richard Bell

SEMINAR TITLE: "Soil properties and crop performance in salinised soils following deep drainage in the WA wheatbelt"

ABSTRACT: Deep drains are intended to lower watertables in salinised land, and to trigger changes in soil conditions that lead to increased plant productivity. However, drain effectiveness varies and impacts on soil properties and crop productivity remain poorly understood. During the seminar I will present results obtained between 2004 and 2009 on: change in soil properties at Beacon, Beynon Rd, Morowa, Pithara, and Wallatin Creek; and crop productivity trials at Beynon Rd, Beacon, and Wallatin Creek. After 4 years at Beynon Rd, decreases in EC1:5 levels were most readily observed in the 0-10 cm layer of the soil. Following deep drainage, down profile soil analysis at Beynon Rd indicate a decline in EC1:5 to 30 cm depth between 2004 (2 years after drainage) and 2006 (4 years after drainage) and a further decline by 2009 (7 years after drainage). At Wallatin Creek and Beacon, there was no indication that EC1:5 levels in the 0-40 cm layer had changed between pre-drain samples and post drain samples 3 years later. Based on change in water levels before and after drainage, all sites except Pithara and Morowa should experience a relief in waterlogging in the root zone. At Wallatin Creek, the draw down in water levels was to > 1.8 m. However, at Beynon Rd, Beacon and Morowa, the persistence of a saline water table at < 1.8 m from the soil surface may continue to discharge salts into the root zone. The observed changes in water levels may be due to the effects of either the drain or to seasonal rainfall or both. In 2007, the barley yields at Beynon Rd were 1.5-2 t/ha within 20-50 m of the deep drain. Hence 4.5 years after installation of the deep drain at Beynon Rd, a highly profitable barley crop was grown. By contrast, at Wallatin Creek, 2 years after the deep drain was installed, and despite the drop in water levels to > 1.8 m, there were still very low barley yields close to the deep drain. At Beacon, yields in 2008 were 1.4 to 1.0 t/ha, exceeding those obtained in the previous 2 years. Overall the results suggest that significant decreases in soil salinity in the surface 10-40 cm were measurable 3-5 years after installation of the deep drains, and the recovery of crop productivity to profitable levels occurred over a similar time frame.