Influence of four successive annual applications of elemental S and sulphate-S fertilizers on yield, S uptake and seed quality of canola

Abstract

The effectiveness of elemental S fertilizers in increasing crop yield in S-deficient soils depends on the rate at which S is oxidized to sulphate in soil for plant uptake. A 4-yr field experiment (1999 to 2002) was conducted with canola (Brassica napus L. or Brassica rapa L.) on a S-deficient loamy sand Gray Luvisol soil near Tisdale in northeastern Saskatchewan to determine the effectiveness of elemental S and sulphate-S fertilizers applied annually at different times and S rates on seed and straw yield, oil and protein concentration in seed, concentration and uptake of S in seed and straw, amount of residual sulphate-S in soil, and recovery of applied S in plant, soil and plant + soil. The S fertilizer treatments included granular types of two bentonite -elemental S fertilizers (ES-90 and ES-95), one sulphate-S (ammonium sulphate), one containing elemental S and sulphate-S (Agrium Plus), and a zero-S control. The S fertilizers were surface-broadcast at 10 or 20 kg S ha-1 rates in the previous autumn or in spring, and incorporated into the soil a few days prior to seeding in May. Canola plants in the zero-S control showed S deficiency in the growing season. Seed yield, straw yield, oil concentration in seed, and S concentration and uptake in seed and straw increased with the sulphate-S fertilizer in all years. There was no significant increase in seed yield from the elemental S fertilizers in 1999, though autumn application tended to give slightly greater seed yield than the spring application. Elemental S fertilizers usually increased seed yield and S uptake significantly over the zero-S control, but yield and S uptake were less than the sulphate-S fertilizer in most cases in 2000, in many cases in 2001 and in some cases in 2002, especially when the S fertilizers were applied in spring. Autumn-applied elemental S usually had greater seed yield and S uptake than the spring-applied elemental S in 2000, 2001 and 2002. On the other hand, autumn-applied ammonium sulphate produced or tended to produce lower seed yield and S uptake than spring-applied ammonium sulphate in some cases. There was little effect of S fertilizer application on protein concentration in seed. In summary, the results indicated that elemental S fertilizers were not effective in increasing canola yield and S uptake on the S-deficient soil in the first year of application. The elemental S fertilizers became effective in the second to fourth year, but seed yield and S uptake were still less than those obtained with sulphate-S fertilizer, particularly when the S fertilizers were applied in spring. The findings suggest the need for research on best management practices to improve effectiveness of elemental S fertilizers. Key words: Canola, elemental and sulphate S fertilizers, oil and protein concentration, seed yield, sulphur uptake