Effectiveness of sulphate-S fertilization at different growth stages for yield, seed quality and S uptake of canola
Authors: Malhi S. S. , Gill K. S. 
Published: April 2011

Canola ( Brassica napus L. and B. rapa L.) is an important cash crop in the Prairie Provinces of Canada. The majority of canola is grown in the Parkland zone where many soils are deficient or potentially deficient in plant-available S for optimum seed yield of canola. Because canola has high S requirements and S is immobile in plants, its deficiency can occur any time during the growing season and drastically reduce canola seed yield, particularly on soils fertilized well with N and P. The objective of this study was to assess the effectiveness of sulphate-S fertilizer (potassium sulphate) applied using various application methods at seeding and during the growing season for yield, seed quality and S uptake of canola on S-deficient soils. Six field experiments (two sites per year from 1998 to 2000) were conducted on Grey Luvisol soils in north-eastern Saskatchewan. Fertilizer treatments were no fertilizer, N (120 kg N ha-1) alone at seeding, S (30 kg S ha-1) alone at seeding, and N (120 kg N ha-1) at seeding + S (15 and 30 kg S ha-1) at seeding, bolting and flowering stages of canola. Methods of S application were surface broadcast and incorporated into the soil, sidebanded and seedrow placed at seeding, and topdressed and foliar sprayed at bolting and early flowering. Canola at all experimental sites showed severe S deficiency symptoms. Compared to N alone, N + S fertilization increased yield, oil content and S uptake of seed in all cases, increased yield and S uptake of seed + straw in most cases, while protein content of seed and S index (ratio of S uptake in seed to S uptake in seed + straw) were not influenced consistently. A trend of seeding > bolting > flowering time of S applications was generally shown by yield and S uptake of seed and seed + straw, and by S index. There were no noticeable differences among treatments applied at seeding. Topdressing at bolting and flowering tended to produce less seed yield than foliar-applied S in few cases and method of S application had no consistent effect on other parameters. Increasing the rate from 15 to 30 kg S ha-1 generally increased yield and S uptake of seed and seed + straw, but had no consistent effect on oil and protein contents in seed and S index. Fertilizer S alone tended to increase yield, oil content and S uptake of seed but had no effect on seed protein content. However, application of N alone tended to reduce yield, oil content and S uptake of seed while it had an inconsistent effect on yield and S uptake of seed + straw and S index. In conclusion, application of sulphate-S fertilizer on S-deficient soils improved yield, seed quality and S uptake of canola, with applications at seeding generally more effective than at bolting and early flowering stages. The results suggest that application of sulphate-S can correct S deficiency in canola if it occurs in the growing season, and restore seed yield substantially at bolting and moderately at early flowering. Key words: Application times, canola, placement methods, seed quality, S index, S rates