Ammonium Sulfate for Canola in Southeastern Australia

In alkaline-calcareous soils of southeastern Australia (Calcarosols), the main N fertilizer sources are either urea or ammonium sulfate (AS) in cereal and oilseed cropping systems. The relatively low N recovery in these systems is most likely associated with ammonia volatilization. In addition, S from AS may be immobilized by chemical precipitation with Ca, which may result in S deficiency, thereby reducing the N recovery further. Previous research showed that AS results in root zone acidification around the site of placement, which increased P availability, and could also reduce ammonia volatilization. To compare the effectiveness of N derived from urea with N derived from AS, a field ¹⁵N microplot study with canola as the test crop was conducted.

This study showed that when N was sourced from AS, N recovery in the grain was significantly higher than when the N was sourced from urea (31% vs. 23%, p=0.07). There were no differences in straw, root or soil recovery of the labelled N. Approximately 63% of N in total was recovered from AS, while 54% was recovered from urea. When AS and urea were used as a mixture, the recovery of N from either labelled urea-N or labelled AS-N was similar to the recovery from the straight AS. These data indicate that AS, either alone or in a mixture with urea, can increase the recovery of fertilizer applied N in canola.