Ammonium Sulfate for Canola in Southeastern Australia

Evaluation of ammonium sulfate as a S source for rainfed wheat and canola cropping systems.


29 Jan 2010

2009 Annual Interpretive Summary

This project is investigating the role ammonium sulfate (AS) can play as a fertilizer for cropping systems in southeast Australia. A pot experiment showed that after 42 days, compared to the control, AS gave a 104% growth response compared to urea/gypsum (61%) in canola. When a similar experiment was conducted using wheat as the test crop, AS and the urea/gypsum application produced similar responses. To test these effects, field trials were established at Pira and Nurrabiel, in western Victoria. Both sites were expected to respond to S and a range of fertilizers were compared. The control (no fertilizer) was compared to urea, gypsum, urea/gypsum together, and AS to supply 35 kg N/ha and/or 40 kg S/ha at sowing with 34 or 46 kg P2O5/ha.

The site at Pira showed a significant yield response to both applied S as gypsum with or without urea (+44%), but no significant response to urea alone. A large yield response was observed (+75%) when both N and S were supplied as AS. At Nurrabiel, neither urea nor gypsum alone, or in combination, gave a significant yield response, but when N and S were supplied together as AS, yields significantly increased by almost 30% (1.83 t/ha with urea/gypsum compared to 2.36 t/ha with AS). The urea/gypsum treatment was not significantly different from the control. None of the treatments had a significant effect on wheat grain yield at Nurrabiel. It seems that the S from gypsum was somewhat less available than the S from AS fertilizer at both these sites. There may also be synergy by placing N and S placed with AS, as similar effects have sometimes been noted with the co-placement of N and P fertilizers for cereals. The reasons for this could be a consequence of rhizosphere acidification, co-placement of N and S, or some other issue.

A clear understanding of why AS performed better than urea and gypsum will provide growers with guidelines about where this fertilizer can be reliably used. It is also possible that blending AS with other N sources could provide new types of mixed nutrient fertilizers for canola and other crops where N and S are in demand. ANZ-03