Ammonium Sulfate for Canola in Southeastern Australia

The importance of N and S in canola cropping systems is well established. However, in the past, urea and gypsum were the commonly used strategies for N and S nutrition. We hypothesized that the use of ammonium sulphate (AS) along with urea may enhance both N and S efficiencies in a Calcarosol growing canola. We conducted a field experiment to investigate the effects of combining urea and AS on canola growth, yield and nutrient uptake at Walpeup in southeastern Australia.

Irrespective of sources, N significantly increased aboveground biomass at flowering stage and grain maturity stage. Similarly, this was also reflected on a range of nutrient uptake. However, nutrient uptake (N, P, K, S, Ca, Mg, and micronutrients) at flowering stage was also significantly higher in the urea plus AS treatment compared to that observed in the urea plus gypsum treatments. Although a response to S was not seen at flowering stage, a significant S response occurred at grain maturity stage in urea plus AS compared to urea plus gypsum. Urea plus AS significantly increased agronomic N and S efficiencies by 3.6 and 35.6%, respectively, compared to urea plus gypsum. We hypothesize that the higher efficiency may be associated with lower ammonia volatilization and high acidification of the root zone in the alkaline calcareous soil, which enhanced nutrient uptake. Further results on N and S uptakes at maturity and N isotope studies of plant and soil under field micro-plots will be used to test our hypothesis. ANZ-03