Subsoil Physicochemical Constraints and Dryland Crop Growth on Alkaline Soils in Southeastern Australia.
James Gray Nuttall and Roger Armstrong. Department of Primary Industries, Victoria, Natimuk Road, Horsham, 3400, Australia
Alkaline soils used for dryland cropping across the semi-arid regions of southeastern Australia typically have high levels of salinity (ECe), sodicity (ESP), soluble boron (B) and chloride in the subsoil. These constraints are likely to operate simultaneously to decrease root growth and activity of crops thus limiting available water and subsequent crop yield. The current research is being undertaken to improve our knowledge of the relationship between physicochemical characteristics of these alkaline soils and the growth and water use of cereal, pulse and oilseed crops. A survey of representative alkaline soils of the southern Mallee and Wimmera regions of Victoria, comprising 130 profiles (solonized brown soils, solodized solonetz and grey clays), revealed high correlation between ESP and both ECe (r = 0.88) and B (r = 0.80). Boron and ECe (r = 0.68) and ESP and pH1:5 (r = 0.60) were also highly correlated. This intercorrelation between the various potential constraints to crop growth, makes ranking difficult. Ridge regression will be used to link soil and crop data, where this technique overcomes problems associated with collinearity. For solonized brown soils in the southern Mallee, the yield of wheat (cv. Frame) in 1999 was significantly reduced by subsoil sodicity (ESP). The probability of getting a 3.0-3.5 Mg/ha grain yield that year was 60% when ESP was less than 19% in the subsoil, but only 12% when ESP was greater than 19%. This approach is being expanded to develop links between physicochemical properties and a range of other crop species and soil types. This knowledge is being used to develop management guidelines for crop production in this region as well as assisting breeders to develop better-adapted crops for alkaline soils.