Ammonium Sulfate for Canola in Southeastern Australia

Two field sites were sown to canola with varying rates of N and S supplied either as ammonium sulphate or urea plus gypsum. The Mallee site had a soil S test level (to 10 cm) of 2.7 mg/kg (KCl40) while the Wimmera site had a S soil test of 2.1 mg/kg. At these levels, both sites should have been responsive to applied S for both canola and wheat, but the grain yield results showed a significant response to S only at the Wimmera site. This is likely a function of the higher soil S contents in the subsoil at the Mallee site.

At the Wimmera site, for both wheat and canola, the urea and gypsum treatment was similar to the ammonium sulphate treatments. And both of these were superior to urea alone, gypsum alone, or the control. Unlike the previous year, ammonium sulphate was not better than the urea and gypsum treatment at the Mallee site. In addition to the main treatments, the project evaluated a range of N management strategies including the use of nitrification inhibition, fluid N formulations, and topdressing applications, although there were only small and inconsistent effects among these treatments.

The N and S contents and uptakes are being estimated in the labs, as well as the proportion of N uptake from either urea or ammonium sulphate fertilizers using ¹⁵N stable isotopes. These data form a significant part of the Ph.D. studies of Mr. M.T. Khan, through the University of Melbourne. ANZ-03