Effectiveness of elemental S fertilizers on canola after three annual applications

Non-Peer ReviewedPlants feed on sulphate-S, but now elemental S fertilizers (which cost less per unit of S than the sulphate-S fertilizers) are available for commercial use. The effectiveness of elemental S fertilizers depends on how quickly the S is oxidized in soil for effective plant uptake. A 4-year field experiment was initiated in 1999 on S-deficient soils at two sites in northeastern Saskatchewan to determine the relative effectiveness of elemental S (ES-90 and ES-95) and sulphate-S (Agrium Plus containing both elemental S and sulphate-S, and ammonium sulphate) fertilizers on yield of canola seed. The S fertilizers were applied at 10 to 20 kg S ha-1 rates in the previous fall or in spring at sowing. At both sites, canola showed S deficiency and seed yields increased with the sulphate-S fertilizers in 1999, 2000 and 2001. In 1999, there was no significant increase in seed yield from the elemental S fertilizers, though fall application tended to give slightly greater yield than the spring application at one site. In 2000 and 2001, elemental S fertilizers usually corrected S deficiency on canola and increased seed yields significantly over the zero-S control, but yields were less than the sulphate-S fertilizers in most cases in 2000 and in many cases in 2001, especially when the S fertilizers were applied in spring. Fall-applied elemental S usually had greater seed yield than the spring-applied elemental S at both sites in 2000 and 2001, and in some cases seed yields tended to be equal to sulphate-S fertilizers. Fall-applied ammonium sulphate produced lower seed yield than spring-applied ammonium sulphate in some cases. In summary, the results suggest that the elemental S fertilizers were not as effective as the sulphate-S fertilizers in increasing canola seed yields on S-deficient soils after three annual applications, particularly when the S fertilizers were applied in spring at seeding time