Ammonium Sulfate for Canola in Southeastern Australia

In cropping systems, the importance of N and S nutrition has been clearly established, particularly for canola. The usual strategy has been to pre-spread gypsum and drill urea in at sowing to meet these demands. It was hypothesized that the use of ammonium sulfate along with urea may enhance both N and S efficiency in calcarosol. A field experiment was conducted in 2011 on a sandy soil at Walpeup in the semi-arid north west of Victoria, an area and soil type that has seen renewed interest for canola production. This experiment aimed to characterize the agronomic aspects of urea, gypsum, and ammonium sulfate under field conditions. Nitrogen and S were applied at different rates, in different ratios, and from different products at sowing.

The applied N significantly increased growth and seed yield, and the crop yield increased more with applied S in the urea plus ammonium sulfate compared to urea plus gypsum strategy. Urea plus ammonium sulfate significantly increased both agronomic N and S efficiency by 4% and 36%, respectively, compared to urea plus gypsum. Irrespective of whether derived from ammonium sulfate or urea, N significantly increased (p ≤0.05) biomass yield and grain yield at flowering stage and maturity stage, respectively. Sulfur responses were not seen at flowering, but ammonium sulfate showed significant increase of grain, straw, and grain yield at 20 kg S ha at maturity stage of canola compared to gypsum. Although two sources of N and S had little effect on growth and yield at the lower rates of N and S, the urea and ammonium sulfate when applied together increased grain yield (12%) over urea plus gypsum at highest level of N and S. There was no interaction between N and S rates indicating that the ratio at which these nutrients were applied was not important in this situation. This research is part of a PhD project undertaken by MT Khan through The University of Melbourne. ANZ-03