Mapping of salinity risk in the lower Namoi valley using non-linear kriging methods

Dryland salinity is on the increase in the upper catchments of central and northern New South Wales, Australia. Consequently, salts may be exported downstream, which could adversely affect irrigated-cotton farming systems. To assess the potential threat of salinity downstream, a simple salt-balance model is used to simulate the potential impact of salinisation due to the farming systems, by using progressively saline water (i.e. ECw 0.4, 1.4, 4.0 and 9.0 dS/m). We studied the problem in the lower Namoi valley of northern New South Wales and compared the various non-linear (indicator, multiple indicator and disjunctive) kriging methods to determine an optimal method for assessing the risk. Our results indicate that potential salinisation due to application of the water currently used for irrigation is minimal and may not pose any problems to sustainability of irrigated agriculture. The same results were obtained by simulation based on irrigation using slightly saline water (ECw 1.4 dS/m). However, simulations based on irrigation using saline water (i.e. ECw of 4 and 9.0 dS/m) shows potential salinisation, which will require management inputs for sustainable cropping systems, especially legumes and wheat, which are used extensively in rotation with cotton. In terms of producing the fewest misclassifications disjunctive kriging was found to be optimal compared to multiple indicator kriging and indicator kriging. Using non-linear geostatistical methods to spatially distribute the results of a simple salt-balance model it is possible to identify the locations where the risks of salinisation are greatest in the lower Namoi valley from the application of saline water.