The disposal of municipal and industrial wastewater to pastures over several decades in northern Victorian has resulted in the sodification of surface soils due to the predominance of sodium salts in the diluted wastewater used for irrigation. Attempts to improve the physical and chemical properties of regional sodic soils by gypsum (or phosphogypsum) applications have had only partial success and pasture yield response has frequently been negligible. Similarly, surface applications of organic material, added as dried, pulverized cow manure, have had no effect on soil or agronomic performance – presumably due to rapid oxidation of low molecular weight organic compounds under typical summer irrigation conditions.

A preliminary field experiment was established at Mooroopna in March 2002, to evaluate the effects of three commercially available organic amendments on soil properties with and without phosphogypsum applications (0, 5 t/ha). These organic amendments, applied at 20-60 t product/ha, were organic humate , derived from brown coal, composted supermarket waste and vermicast. Forty experimental plots of 3 m x 3 m were established on the site as a row by column factorial experiment comprising Omnia-HRL humate, UR-Coles supermarket compost, Swanpool vermicast, control with and without phosphogypsum treatments, in five replicates.

Chemical characteristics and analytical results of organic amendments and soils prior to and after treatments will be presented in this paper, including conventional analytical data in addition to organic chemistry identification by Fourier Infra Red and Solid State ¹³C Nuclear Magnetic Resonance Spectroscopy.