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

Influence of four successive annual applications of elemental S and sulphate-s fertilizers on yield, S uptake and seed quality of canola S. S. Malhi Agriculture and Agri-Food Canada, P.O. Box 1240, Melfort, Saskatchewan, Canada S0E 1A0 (e-mail: malhis@agr.gc.ca). Received 20 August 2004, accepted 30 April 2005. Malhi, S. S. 2005. Influence of four successive annual applications of elemental S and sulphate-s fertilizers on yield, S uptake and seed quality of canola. Can. J. Plant Sci. 85: 777 792. 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 Malhi, S. S. 2005. Incidence de quatre applications annuelles successives d engrais à base de S élémentaire et de S-sulfate sur le rendement, l absorption du S et la qualité des graines du canola. Can. J. Plant Sci. 85: 777 792. L efficacité avec laquelle les engrais à base de S élémentaire accroissent le rendement des cultures sur les sols carencés en S dépend de la rapidité avec laquelle le S s oxyde en sulfate avant son absorption par la plante. L auteur a entrepris une étude sur le terrain de quatre ans (de 1999 à 2002) sur la culture du canola (Brassica napus L. ou Brassica rapa L.). Le sol carencé en S était un sable loameux de type luvisol gris situé près de Tisdale, dans le nord-est de la Saskatchewan. L étude devait établir l efficacité des engrais à base de S élémentaire et de S-sulfate appliqués annuellement à des moments et à des taux d application différents sur le rendement grainier et le rendement en paille, sur la teneur en huile et en protéines de la graine, sur l absorption de S et sa concentration dans la graine et la paille, sur les résidus de S-sulfate dans le sol et sur la quantité de S récupérée dans la plante, le sol et les deux. Les engrais employés comprenaient deux engrais de bentonite et de S élémentaire sous forme granulaire (ES-90 et ES-95), un engrais S-sulfate (sulfate d ammonium), un autre contenant du S élémentaire et du S-sulfate (Agrium Plus) et un engrais témoin sans soufre. Les engrais ont été répandus à la volée en surface à raison de 10 ou 20 kg de S par hectare l automne précédent ou au printemps, puis incorporés au sol quelques jours avant les semis, en mai. Les plants de canola soumis au traitement témoin étaient carencés en S pendant la saison de croissance. L engrais S-sulfate a entraîné chaque année une hausse du rendement grainier, du rendement en paille, de la teneur en huile de la graine ainsi que de l absorption de S et de la concentration de cet élément dans la graine et la paille. Les engrais à base de S élémentaire n ont pas entraîné de hausse significative du rendement grainier en 1999, bien que leur application en automne ait tendance à l augmenter légèrement plus que leur application au printemps. En règle générale, les engrais à base de S élémentaire augmentent significativement le rendement grainier et l absorption de S comparativement au traitement témoin, mais la hausse était moins importante que celle obtenue avec les engrais S-sulfate dans la plupart des cas en 2000, dans Trade names in this publication are used only in the interest of accurate reporting. No endorsement of a product to the exclusion of other similar products is implied by Agriculture and Agri-Food Canada or its researchers. 777

778 CANADIAN JOURNAL OF PLANT SCIENCE beaucoup de cas en 2001 et dans quelques cas en 2002, surtout quand les engrais à base de S élémentaire sont appliqués au printemps. L application d engrais à base de S élémentaire à l automne a habituellement entraîné un meilleur rendement grainier et une plus forte absorption de S que l application au printemps en 2000, 2001 et 2002. D un autre côté, l application de sulfate d ammonium à l automne entraîne ou a tendance à entraîner dans certains cas une réduction du rendement grainier et de l absorption de S comparativement à son application au printemps. L application d engrais S agit peu sur la teneur en protéines de la graine. En résumé, les résultats indiquent que les engrais à base de S élémentaire n accroissent pas de manière efficace le rendement ni l absorption de S du canola cultivé sur un sol carencé en S la première année de l application. Ces engrais gagnent en efficacité de la deuxième à la quatrième année, mais le rendement grainier et l absorption de S restent inférieurs à ceux obtenus avec les engrais S-sulfate, surtout quand on les applique au printemps. Les résultats laissent croire qu on devrait entreprendre des recherches sur les pratiques de gestion idéales qui permettraient d accroître l efficacité des engrais à base de S élémentaire. Mots clés: Canola, engrais à base de S élémentaire et de S-sulfate, teneur en huile et en protéines, rendement grainier, absorption de soufre In the Prairie Provinces, there are about 3.5 million ha of agricultural land under canola production (Statistics Canada 2002). Canola is the major cash crop in the Parkland region. Being a high-protein oilseed crop, canola has high requirements for S (Grant and Bailey 1993; Jackson 2000). As S is immobile in plants, deficiency of S can occur at any growth stage and cause considerable reduction in seed yield. In order to prevent seed yield loss due to S deficiency, a constant supply of available S to canola plants is needed throughout the growing season. On soils marginally deficient in S, the use of high-yielding cultivars and application of higher rates of N and P fertilizers can result in faster depletion of S from soil, and increase instances and severity of S deficiency during peak growing periods of canola. Sulphate-S (SO 4 -S) is the only form available to plants. Now there is a wide variety of commercial fertilizers that contain elemental S, which may cost less per unit of S than sulphate-s fertilizers. However, the effectiveness of these fertilizers depends on how quickly the S is oxidized in soil to plant-available sulphate. The rate of conversion of S from elemental to sulphate form is influenced by soil properties (e.g., ph, texture, microbial activity), environmental conditions (e.g., temperature, moisture, aeration), and other factors that increase dispersion of elemental S fertilizer granules (e.g., particle/granule size, tillage, method and time of application) (Noellemeyer 1981; Bettany and Janzen 1984; Janzen and Bettany 1986, 1987a, b; Solberg 1986; Solberg et al. 2003; Nuttal et al. 1993; Slaton et al. 2001). In the Prairie Provinces, there are more than 4 million ha of agricultural soils deficient in plant-available S, and substantially greater areas are potentially deficient (Bettany et al. 1982; Doyle and Cowell 1993). Canola grown on S-deficient Gray Luvisol soils has been found to result in poor seed set (Nyborg et al. 1974; Nuttal et al. 1987). The S deficiency on canola can be eliminated by applying S fertilizers (Ukrainetz 1982; Janzen and Bettany 1984b). There are several studies on the relative effectiveness of elemental S versus sulphate-s fertilizers (Ukrainetz 1982; Karamanos and Janzen 1991; Janzen and Karamanos 1991; Nuttall et al. 1993; Grant et al. 2001) on canola in the prairies. However, in those studies, elemental S and sulphate-s fertilizers alone or in combinations were not applied to the same plots for a number of years. As long-term field research information on the time period for the elemental S fertilizers to become as effective as sulphate-s fertilizers is limited (Karamanos and Poisson 2004), the number of years a combination of sulphate-s and elemental S fertilizers has to be used on canola before considering switching completely to elemental S fertilizers without any risk of yield loss due to S deficiency needs to be investigated. The objective of this study was to compare the relative effectiveness of elemental S and sulphate-s fertilizers applied at different times and S rates on the yield, oil, protein concentration, and uptake of S in seed and the concentration and uptake of S in straw of canola. MATERIALS AND METHODS A 4-yr field experiment (1999 to 2002) was conducted on a S-deficient loamy sand Gray Luvisol (Typic Cryoboralf) soil near Tisdale (with 2.0 mg SO 4 -S kg 1 and 2% organic matter in the 0 15 cm soil) in northeastern Saskatchewan. Each treatment was replicated four times in a randomized complete block design. Individual plots were 1.8 m 7.5 m. The amount of precipitation over 4 mo from May to August was 230, 269, 90 and 250 mm, respectively, in 1999, 2000, 2001 and 2002. The precipitation for the 30-yr mean at the nearest meteorological station (Melfort) was 191 mm. The amount and distribution of precipitation during the growing season was above normal May, June and July in 1999 and 2000, below normal in 2001, and relatively drier moisture conditions in the early growing season and frost in August at seed filling in 2002. The treatments included two granular types of elemental S fertilizers (ES-90 and ES-95, both bentonite based and containing 90 and 95% elemental sulphur, respectively), one fertilizer containing 21.7% elemental S and 18.7% sulphate- S (16-0-0-40 marketed as Agrium Plus by Agrium), one sulphate-s fertilizer (ammonium sulphate, 20.5-0-0 24), and a zero-s control. Two brands of ES-90 were used, namely, Tiger90 in the autumn of 1999, and Tiger90CR in remaining years (Tiger Industries). The ES-95 was Sulfer95 brand in all years (Fernz SulFer Works). The S fertilizers were surface-broadcast at 10 or 20 kg S ha 1 annually in the previous autumn or few days prior to seeding in spring as specified in the treatments. All plots received a blanket annual application of 120 kg N ha 1 (as ammonium nitrate), 30 kg P ha 1 (as triple superphosphate) and 20 kg K ha 1 (as KCl muriate of potash). In treatments that did not receive ammonium sulphate, the amount of N was adjusted. All the plots were tilled to a depth of about 8

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 779 cm, with a rotovator, in the spring before seeding to incorporate all fertilizers into soil. A double-disc press drill was used to seed canola (Brassica rapa L. Fairview ) at 17.8 cm row spacing and seed rate of 9 kg ha 1. Data were recorded on seed and straw yield, oil and protein concentration in seed, concentration and uptake of total S in seed and straw, and residual sulphate-s in soil. Seed yield was determined by harvesting 1.25-m-wide and 7.0-mlong strips with a plot combine and straw yield was calculated from hand harvested samples collected from two 1-m long rows in each plot. The oven dry (60 C) samples were analyzed for oil, total N and total S in seed, and total S in straw. Oil concentration in canola seed was determined using crude fat method [Assocation of Official Analytical Chemists (AOAC) 1990]. Total S in seed and straw was determined by digestion of samples in nitric acid-hydrogen peroxide and measuring its concentration in the digest by ICP-AES (Huang and Schulte 1985). Total N in seed samples was determined by sample digestion and detection of N by thermal conductivity using a CNS combustion analyzer (AOAC 1995). Protein concentration was calculated by multiplying the total N with 6.25 (Williams et al. 1998). Percent recovery of applied S was calculated as: 100 [amount of S in fertilized treatment] [amount of S in the zero-s control]/[rate of applied S]. Soil samples in each plot were taken from the 0 15, 15 30 and 30 60 cm depths in the spring of 1999, 2000, 2001 and 2002, and at termination of the experiment in October 2002. Each sample was a composite of four cores (4-cm diameter) per plot. The soil samples were air dried at room temperature, ground to pass through a 2-mm sieve, and then analyzed for sulphate-s. Sulphate-S in soil was determined by extraction with CaCl 2 and measuring its concentration in the extract by ICP-AES (Combs et al. 1998). The data were subjected to analysis of variance (ANOVA) using GLM procedure (SAS Institute, Inc. 1993). For each parameter, the zero-s treatment data were used in the ANOVA to determine response of canola to the S fertilizer treatments in comparison to the zero-s control. The values for each parameter for the zero-s control are given in the next section in results and also as footnote in tables. Main and interaction effects of S fertilizer source (F), rate (R) and application time (T) were determined after excluding the data for zero-s treatment in order to achieve factorial combination of various factors. For each ANOVA, standard error of the mean (SEM) and significance are reported. Least significant difference (LSD 0.05 ) was used to determine significant differences between treatment means. RESULTS Fertilizer S versus Zero-S Control Canola plants in the zero-s control showed typical S deficiency symptoms (yellowing of new growth and cup-shaped leaves, purpling of stems) in all four growing seasons. There was a significant effect of S fertilizer on seed yield, straw yield, concentration of oil in seed, and concentration and uptake of S in seed and straw. Canola seed yield was exceptionally low in the absence of S fertilization in all years (Table 1). Ammonium sulphate and Agrium Plus increased seed yield significantly above the zero-s control at both rates and both application times in all years. For the elemental S (ES-90 and ES-95) fertilizers, significant increase in seed yield above the zero-s control was observed in some treatments in 2000, and in most treatments in 2001 and 2002. In the zero-s treatment, straw yields were much greater relative to seed yields (1940, 1140, 1161 and 2827 kg straw ha 1 vs. 14, 37, 65 and 418 kg seed ha 1 in 1999, 2000, 2001 and 2002, respectively). The response of straw yield to S application was similar but less pronounced than seed yield response (Table 1). In the zero-s control, in 1999, 2000, 2001 and 2002, respectively, oil concentration in seed was 305, 327, 324 and 376 g kg 1 ; protein concentration in seed was 219, 245, 289 and 250 g kg 1 ; S concentration in seed was 1925, 2150, 2700 and 2863 mg S kg 1 ; and S concentration in straw was 1303, 1300, 970 and 1883 mg S kg 1. Oil concentration in canola seed increased with application of S fertilizer, more so with sulphate-s than elemental S fertilizers. Application of S did not have a consistent effect on protein concentration in seed. There was a significant increase in S concentration in seed and straw with sulphate-s-containing fertilizers in all years, while elemental S fertilizers increased or tended to increase S concentration in 2000 to 2002. Like seed yield, uptake of S in canola seed was extremely low in the absence of S application. In the zero-s control, in 1999, 2000, 2001 and 2002, respectively, S uptake in seed was 0.03, 0.08, 0.18 and 1.21 kg S ha 1 ; S uptake in straw was 2.47, 1.43, 1.14 and 5.45 kg S ha 1 ; and S uptake in seed + straw was 2.50, 1.51, 1.32 and 6.66 kg S ha 1. Sulphate-S containing fertilizers, particularly ammonium sulphate, increased S uptake many times over the zero-s control in all years. Application of elemental S fertilizers caused little or no increase in S uptake in seed in 1999 and increased S uptake in 2000 to 2002. The effect of S application on S uptake in straw and seed + straw was similar to, but less pronounced than that for seed. Symptoms of S deficiency in canola plants in zero-s control in all the growing seasons plus significant effects of sulphate-s application in all years and elemental S application in 2000 to 2002 clearly showed that soil was unable to supply adequate S to canola crop in the absence of S application. Main and Interaction Effects of Fertilizers S Source (F), Rate (R) and Application Time (T) Main effects of fertilizer S source (F), rate (R) and application time (T) were significant in most cases, and interaction effects of F R, F T, and R T were significant in many cases, but interaction effect of F R T was significant only for yield and S uptake of seed in 1999 and for S concentration in seed in 2001. The data were thus averaged to present the main and first level interaction effects of F, R and T on different measurements of canola. Seed Yield Seed yield was greatest with sulphate-s and at the 20 kg S ha 1 rate, and the effect of application time was not consistent (Table 2). In 1999, ammonium sulphate produced significant-

780 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Seed and straw yield of canola with various elemental S and sulphate-s-containing fertilizers applied at two rates in previous autumn or in spring and incorporated into soil in spring at Tisdale in northeastern Saskatchewan Treatment x S fertilizer Time of Seed yield (kg ha 1 ) Straw yield (kg ha 1 ) source z (kg S ha 1 ) application 1999 2000 2001 2002 1999 2000 2001 2002 ES-90 10 Autumn 37 323 273 888 1996 1753 1722 3999 20 Autumn 59 609 414 908 2312 3013 1843 4871 10 Spring 15 68 170 566 1905 1188 1576 2941 20 Spring 20 131 261 686 1145 2062 1916 3944 ES-95 10 Autumn 59 270 224 617 2743 2605 1864 3383 20 Autumn 118 648 340 890 4272 3213 2444 3829 10 Spring 24 81 121 508 2109 1579 1754 4100 20 Spring 19 193 174 630 2111 2747 1865 3450 AP 10 Autumn 101 579 357 973 3112 3256 1941 3240 20 Autumn 278 922 470 1099 3805 3395 2570 4254 10 Spring 91 652 409 918 3705 2744 2326 3449 20 Spring 510 797 485 1048 4658 3011 2417 4500 AS 10 Autumn 120 704 459 961 2348 3468 2059 3739 20 Autumn 309 765 433 1100 3151 3885 2831 4095 10 Spring 383 784 411 975 4000 2676 1927 4431 20 Spring 865 956 464 1231 5638 3295 2707 4143 Control (no-s) 14 37 65 418 1940 1140 1161 2827 SEM y 41.3 *** 60.7 *** 35.5 *** 57.4 *** 668.1 *** 374.2 *** 323.5 0.06 317.2 *** LSD 0.05 116 173 101 163 1900 1064 920 902 y *** and 0.06 indicate the treatment effect being significant at P < 0.001 and P < 0.06, respectively. x In the zero-s control, in 1999, 2000, 2001 and 2002, respectively, seed yield was 14, 37, 65 and 418 kg ha 1 ; straw yield was 1940, 1140, 1161 and 2827 kg ha 1 ; oil concentration in seed was 305, 327, 324 and 376 g kg 1 ; protein concentration in seed was 219, 245, 289 and 250 g kg 1 ; S concentration in seed was 1925, 2150, 2700 and 2863 mg S kg 1 ; S concentration in straw was 1303, 1300, 970 and 1883 mg S kg 1 ; S uptake in seed was 0.03, 0.08, 0.18 and 1.21 kg S ha 1 ; S uptake in straw was 2.47, 1.43, 1.14 and 5.45 kg S ha 1 ; and S uptake in seed + straw was 2.50, 1.51, 1.32 and 6.66 kg S ha 1. ly greater seed yield than both elemental S fertilizers and Agrium Plus, and Agrium Plus showed significantly more yield than the elemental S fertilizers. Ammonium sulphate and Agrium Plus produced less seed yield when applied in autumn compared with when applied in spring, while both elemental S fertilizers tended (not significantly) to produce more seed yield with autumn than spring application. The significant F R T interaction effect indicated that seed yield with autumn-applied ammonium sulphate at both S rates and with Agrium Plus at 20 kg S ha 1 was significantly lower than their spring application at the same S rates. Overall, elemental S fertilizers were not effective in 1999, especially when applied in spring, and only the sulphate-s part of Agrium Plus appeared to be effective in increasing seed yield. In 2000, seed yield with all the S fertilizers was greater at 20 kg S ha 1 than at 10 kg S ha 1. Elemental S fertilizers gave much greater seed yield when applied in autumn rather than in spring, but ammonium sulphate had lower seed yield when applied in autumn rather than in spring, and Agrium Plus showed no effect of application time on seed yield. Irrespective of S rate or application time, seed yields were significantly lower with elemental S treatments than sulphate-s fertilizers. In 2001 and 2002, seed yield increased with change in S rate from 10 to 20 kg S ha 1 for all fertilizers, except for the ammonium sulphate in 2001 and ES-90 in 2002. Seed yield with spring application was less than autumn application of elemental S fertilizers, while application time did not influence seed yield with ammonium sulphate and Agrium Plus. Elemental S fertilizers usually produced less seed yield than ammonium sulphate, especially when the S fertilizers were applied in spring. Agrium Plus produced seed yield similar to ammonium sulphate, except for lower yield for spring application in 2002. Straw Yield Straw yield was significantly higher at 20 kg S ha 1 than at 10 kg S ha 1 in all years (Table 3). The main effect of S application time was significant only in 2000, when autumn application had more straw yield than spring application. Straw yield was usually greater with sulphate-s fertilizers than both elemental S fertilizers in 1999 and 2000, and ES-90 in 2001. The main effect of fertilizer source was not significant in 2002. In 1999, F R and R T interaction effects were not significant. Elemental S fertilizers tended to show more straw yield when applied in autumn compared with when applied

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 781 Table 2. Seed yield from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in north-eastern Saskatchewan Treatment y Seed yield (kg ha 1 ) x Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 26 196 222 727 20 40 370 337 797 ES-95 10 41 175 173 562 20 68 421 257 760 AP 10 96 616 383 945 20 394 859 478 1073 AS 10 251 744 435 968 20 587 861 448 1165 LSD 0.05 83 NS NS NS SEM 29.2 *** 43.9NS 22.7NS 40.2NS Fertilizer S source time of application ES-90 Autumn 48 466 344 898 Spring 18 99 215 626 ES-95 Autumn 88 459 282 753 Spring 21 137 148 569 AP Autumn 189 750 414 1036 Spring 300 725 447 983 AS Autumn 214 734 446 1030 Spring 624 870 438 1103 LSD 0.05 83 125 65 114 SEM 29.2 *** 43.9 *** 22.7 *** 40.2 *** time of application 10 Autumn 79 469 328 860 Spring 128 396 278 742 20 Autumn 191 736 414 999 Spring 354 519 346 899 LSD 0.05 59 88 NS NS SEM 20.7 ** 31.0 * 16.1NS 28.4NS Fertilizer S source ES-90 33 283 279 762 ES-95 55 298 215 661 AP 245 738 430 1009 AS 419 802 442 1066 LSD 0.05 59 88 46 81 SEM 20.7 *** 31.0 *** 16.1 *** 28.4 *** 10 104 432 303 800 20 272 628 380 949 LSD 0.05 42 62 32 57 SEM 14.6 *** 21.9 *** 11.4 *** 20.1 *** Time of application Autumn 135 602 371 929 Spring 241 458 312 820 LSD 0.05 42 62 32 57 SEM 14.6 *** 22.0 *** 11.4 *** 20.1 *** y In the zero-s control, seed yield was 14, 37, 65 and 418 kg ha 1 in 1999, 2000, 2001 and 2002, respectively. x Source of seed yield is Malhi et al. (2005). *, **, *** and NS refer to significant treatment effects in ANOVA at P 0.05, P 0.01, P 0.001 and not significant, respectively. in spring (significant effect for ES-95). But for ammonium sulphate and Agrium Plus, straw yield was lower (significantly for ammonium sulphate) with autumn than spring application. Autumn-applied Agrium Plus tended to produce greater straw yield than ammonium sulphate, but spring-applied Agrium Plus tended to produce less straw

782 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Straw yield from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in north-eastern Saskatchewan Treatment y Straw yield (kg ha 1 ) Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 1950 1471 1649 3470 20 1728 2537 1879 4407 ES-95 10 2426 2092 1809 3741 20 3192 2980 2155 3639 AP 10 3409 3000 2133 3345 20 4232 3203 2494 4377 AS 10 3174 3072 1993 4085 20 4394 3590 2769 4119 LSD 0.05 NS NS NS 613 SEM 482.1NS 268.5NS 235.9NS 215.2* Fertilizer S source time of application ES-90 Autumn 2154 2383 1782 4435 Spring 1525 1625 1746 3442 ES-95 Autumn 3507 2909 2154 3606 Spring 2110 2163 1810 3775 AP Autumn 3459 3325 2256 3747 Spring 4182 2878 2371 3975 AS Autumn 2750 3676 2445 3917 Spring 4819 2985 2317 4287 LSD 0.05 1373 NS NS 613 SEM 482.1 ** 268.5NS 235.9NS 215.2 ** time of application 10 Autumn 2550 2770 1896 3590 Spring 2930 2047 1896 3730 20 Autumn 3385 3376 2422 4262 Spring 3388 2779 2226 4009 LSD 0.05 NS NS NS NS SEM 340.9NS 189.8NS 166.8NS 152.2NS Fertilizer S source ES-90 1839 2004 1764 3939 ES-95 2809 2536 1982 3690 AP 3820 3101 2314 3861 AS 3784 3331 2381 4102 LSD 0.05 971 541 475 NS SEM 340.9 *** 189.8 *** 166.8 * 152.2NS 10 2740 2409 1896 3660 20 3387 3078 2324 4136 LSD 0.05 687 382 336 306 SEM 241.0 134.2 ** 117.9 * 107.6 ** Time of application Autumn 2967 3073 2159 3926 Spring 3159 2413 2061 3870 LSD 0.05 NS 382 NS NS SEM 241.0 134.2 ** 117.9NS 107.6NS y In the zero-s control, straw yield was 1940, 1140, 1161 and 2827 kg ha 1 in 1999, 2000, 2001 and 2002, respectively., *, **, *** and NSrefer to significant treatment effects in ANOVA at P 0.10, P 0.05, P 0.01, P 0.001 and not significant, respectively. yield than ammonium sulphate. This difference was probably due to lower effectiveness of the elemental S part of the Agrium Plus fertilizer when applied in spring. In 2000, F R, F T, and R T interactions were not significant. However, there was a tendency for increase in straw yield with increase in S rate from 10 to 20 kg S ha 1

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 783 for all fertilizers. Also, elemental S as well as sulphate-s fertilizers tended to give greater straw yield when applied in autumn rather than in spring. Similar to 2000, F R, F T, and R T interactions were not significant in 2001, and there was a tendency for increase in straw yield with increase in S rate from 10 to 20 kg S ha 1 for all fertilizers. But time of application showed no consistent trend for all fertilizers and both S rates. In 2002, F R and F T interactions were significant because only ES-90 and Agrium Plus showed significant increase in straw yield with increase in S rate from 10 to 20 kg S ha 1 and only ES-90 had greater (though not significant) straw yield with autumn than its spring application. There was no consistent effect of time of application on straw yield for both S rates. Oil and Protein Concentration in Seed Oil concentration in seed was significantly higher with sulphate-s-containing fertilizers than elemental S fertilizers, for 20 kg S ha 1 than 10 kg S ha 1, and for autumn rather than spring application of S in 1999, 2000 and 2001 (Table 4). In 2002, the effects of S source, time and rate were not significant. For elemental S fertilizers, oil concentration in seed was higher in most cases when the S fertilizers were applied in autumn rather than in spring, while application time had no consistent effect in the case of Agrium Plus and ammonium sulphate. Oil concentration in seed tended to be higher at 20 kg S ha 1 than the 10 kg S ha 1 rate of all fertilizers in 1999 and 2000, but it was not consistently influenced by S rate in 2001 and 2002. Averaged across the fertilizer sources, oil concentration in seed for both S rates tended to be greater with S application in autumn than in spring, mainly due to relatively better effectiveness of autumn-applied elemental S fertilizers. Protein concentration in seed did not show consistent effect of S fertilizer source, rate or application time in any year (data not shown). Sulphur Concentration in Seed and Straw In all years, concentration of S in seed was significantly higher with sulphate-s than elemental S fertilizers and for autumn than spring application, and it increased with increasing S rate from 10 to 20 kg ha 1 (Table 5). Concentration of S in seed was greater at 20 than 10 kg S ha 1 for different fertilizers in all years, except for elemental S fertilizers in 1999, indicating that elemental S fertilizers did not provide an available form of S to canola in the first year of application. Similarly, S concentration in seed increased or tended to increase with S rate from 10 to 20 kg S ha 1 for both autumn and spring applications. For elemental S fertilizers, autumn application usually had higher S concentration in seed than spring application in 2000, 2001 and 2002. On the other hand, S concentration in seed was higher with spring than autumn application of ammonium sulphate in 2000 and 2001. Application time of S had very little influence in the case of Agrium Plus. The F T interaction data showed greater differences between sulphate-s and elemental S fertilizers for spring application relative to autumn application. Concentration of S in straw showed a trend very similar to the S concentration in seed (data not shown). Briefly, concentration of S in straw was greater with sulphate-s than with elemental S fertilizers in most cases. The S concentration in straw was higher or tended to be higher with autumn applications than with spring applications for elemental S fertilizers, while there were no consistent differences between autumn and spring applications for sulphate-s fertilizer. Concentration of S in straw usually increased with increasing S rate from 10 kg to 20 kg S ha 1. Sulphur Uptake in Seed and Straw Uptake of S in seed was greater with sulphate-s fertilizers than with elemental S fertilizers and it increased significantly with increasing S rate from 10 to 20 kg S ha 1 in all years (Table 6). Spring application resulted in greater mean S uptake than autumn application in 1999, whereas the opposite was true in the following 3 yr. Elemental S fertilizers and Agrium Plus resulted in less S uptake in seed than ammonium sulphate at both S rates and application times in most cases. Ammonium sulphate had greater S uptake in seed than Agrium Plus. Autumn application had significantly greater S uptake in seed with elemental S fertilizers than spring application, but there was no consistent effect of application time for ammonium sulphate and Agrium Plus. An increase in S rate from 10 to 20 kg S ha 1 resulted in a significant increase in S uptake in seed and straw in all years and with both application times, except for elemental S fertilizers in 1999. The trends for S uptake in straw were similar to the S uptake in seed (Table 7). Amount of Sulphate-S in Soil Autumn application of S fertilizers increased the amount of sulphate-s in soil sampled in the spring of 1999, but the differences were not significant (data not shown). The amount of sulphate-s in soil tended to be more with ammonium sulphate than with elemental S fertilizers or the zero-s control in all soil depths, particularly in the 30 60 cm layer. This indicated downward movement of autumn-applied S as ammonium sulphate into the 15 30 and 30 60 cm layers. The amount of sulphate-s in soil with 20 kg S ha 1 autumnapplied ammonium sulphate was 14.6 kg S ha 1 (i.e., 73% of the amount of applied S), which suggested over-winter loss (27%) of sulphate-s from autumn-applied ammonium sulphate. The lower amount of sulphate-s in soil from autumn-applied ES-90 and ES-95 than ammonium sulphate suggested only partial conversion of elemental S to sulphate-s over the winter. The amount of sulphate-s in soil sampled in spring 2000 showed that there was no significant increase in sulphate-s in most S fertilizer treatments in all soil layers, except the 0 15 cm depth for autumn-applied ammonium sulphate at 20 kg S ha 1. In spring 2001, the amount of sulphate-s in soil was greater with autumnapplied ammonium sulphate at the 20 kg S ha 1 rate than the zero-s control in the 15 30 and 30 60 cm layers. In spring 2002, the amounts of sulphate-s in soil were greater in the 20 kg S ha 1 autumn-applied ammonium sulphate and Agrium Plus treatments over the zero-s control.

784 CANADIAN JOURNAL OF PLANT SCIENCE Table 4. Oil concentration in seed from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in north-eastern Saskatchewan Treatment y Oil concentration (g kg 1 ) Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 309 346 366 386 20 325 355 352 388 ES-95 10 324 340 339 387 20 332 350 354 393 AP 10 338 370 364 396 20 367 380 358 390 AS 10 350 375 367 398 20 376 378 358 383 LSD 0.05 NS NS 12 11 SEM 6.4NS 4.3NS 4.3 * 3.8 * Fertilizer S source time of application ES-90 Autumn 325 363 357 390 Spring 309 339 341 384 ES-95 Autumn 347 353 352 390 Spring 309 338 341 389 AP Autumn 361 373 361 397 Spring 344 377 361 388 AS Autumn 360 375 360 393 Spring 366 378 365 389 LSD 0.05 18 12 12 NS SEM 6.4 * 4.3 ** 4.3 3.8 NS time of application 10 Autumn 341 360 358 394 Spring 319 355 350 389 20 Autumn 356 372 357 391 Spring 345 360 354 386 LSD 0.05 NS NS NS NS SEM 4.5NS 3.1NS 3.0NS 2.7NS Fertilizer S source ES-90 317 351 349 387 ES-95 328 345 346 390 AP 352 375 361 393 AS 363 377 362 391 LSD 0.05 13 9 9 NS SEM 4.5 *** 3.1 *** 3.0 *** 2.7NS 10 330 358 354 392 20 350 366 355 389 LSD 0.05 9 6 NS NS SEM 3.2 *** 2.2 * 2.1NS 1.9NS Time of application Autumn 348 366 357 393 Spring 332 358 352 387 LSD 0.05 9 6 6 5 SEM 3.2 *** 2.3 ** 2.1 1.9 y In the zero-s control, oil concentration in seed was 305, 327, 324 and 376 g kg 1 in 1999, 2000, 2001 and 2002, respectively., *, **, *** and NS refer to significant treatment effects in ANOVA at P 0.10, P 0.05, P 0.01, P 0.001 and not significant, respectively. In soil sampled in the autumn of 2002, after four annual S applications and canola crops grown, the amount of sulphate-s in the 0 15 and 15 30 cm layers was significantly greater with 20 kg S ha 1 of autumn-applied ammonium sul-

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 785 Table 5. Concentration of S in seed from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in north-eastern Saskatchewan Treatment y S concentration (mg S kg 1 ) Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 1937 2387 3500 3505 20 1975 2675 4300 4313 ES-95 10 2013 2225 3175 3069 20 1987 2563 3650 3580 AP 10 1937 2775 4263 4373 20 2150 3950 5925 5407 AS 10 2150 3213 4925 4599 20 2650 4500 6113 5374 LSD 0.05 119 190 248 235 SEM 41.8 *** 66.6 *** 87.0 *** 82.6 * Fertilizer S source time of application ES-90 Autumn 1975 2813 4487 4417 Spring 1937 2250 3313 3400 ES-95 Autumn 2013 2550 3725 3535 Spring 1987 2237 3100 3114 AP Autumn 2100 3387 5150 4843 Spring 1987 3337 5037 4937 AS Autumn 2400 3700 5337 4969 Spring 2400 4013 5700 5004 LSD 0.05 NS 190 248 235 SEM 41.8 NS 66.6 *** 87.0 *** 82.6 *** time of application 10 Autumn 2037 2681 4050 4019 Spring 1981 2619 3881 3753 20 Autumn 2206 3544 5300 4863 Spring 2175 3300 4694 4474 LSD 0.05 NS 134 175 NS SEM 29.6 NS 47.1 61.5 *** 58.4 Fertilizer S source ES-90 1956 2531 3900 3909 ES-95 2000 2394 3413 3324 AP 2044 3363 5094 4890 AS 2400 3856 5519 4986 LSD 0.05 84 134 175 166 SEM 29.6 *** 47.1 *** 61.5 *** 58.4 *** 10 2009 2650 3966 3886 20 2191 3422 4997 4668 LSD 0.05 59 95 124 118 SEM 20.9 *** 33.3 *** 43.5 *** 41.3 *** Time of application Autumn 2122 3113 4675 4441 Spring 2078 2959 4287 4114 LSD 0.05 NS 95 124 118 SEM 20.9NS 33.3 ** 43.5 *** 41.3 *** y In the zero-s control, S concentration in seed was 1925, 2150, 2700 and 2863 mg S kg 1 in 1999, 2000, 2001 and 2002, respectively., **, *** and NS refer to significant treatment effects in ANOVA at P 0.10, P 0.01, P 0.001 and not significant, respectively. phate and Agrium Plus than the zero-s control (Table 8). It also tended to be greater in most cases for all the three layers of sampled soil with other sulphate-s fertilizer treatments. For the 0 60 cm soil, both autumn and spring applications of ammonium sulphate and Agrium Plus at 20 kg S ha 1 significantly increased sulphate-s amount over the

786 CANADIAN JOURNAL OF PLANT SCIENCE Table 6. Uptake of S in seed from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in north-eastern Saskatchewan Treatment y S uptake (kg S ha 1 ) Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 0.05 0.50 0.79 2.63 20 0.08 1.10 1.46 3.49 ES-95 10 0.09 0.40 0.55 1.75 20 0.13 1.14 0.98 2.77 AP 10 0.19 1.73 1.63 4.13 20 0.85 3.41 2.81 5.79 AS 10 0.54 2.41 2.14 4.45 20 1.58 3.89 2.72 6.26 LSD 0.05 0.21 0.50 0.41 NS SEM 0.07 *** 0.18 ** 0.15 0.22NS Fertilizer S source time of application ES-90 Autumn 0.10 1.37 1.54 3.97 Spring 0.03 0.23 0.71 2.15 ES-95 Autumn 0.18 1.22 1.07 2.71 Spring 0.04 0.31 0.46 1.80 AP Autumn 0.41 2.66 2.17 5.03 Spring 0.63 2.47 2.26 4.89 AS Autumn 0.55 2.75 2.38 5.14 Spring 1.58 3.55 2.48 5.57 LSD 0.05 0.21 0.50 0.41 0.62 SEM 0.07 *** 0.18 *** 0.15 ** 0.22 *** time of application 10 Autumn 0.17 1.33 1.38 3.53 Spring 0.27 1.19 1.17 2.95 20 Autumn 0.45 2.68 2.20 4.90 Spring 0.87 2.09 1.78 4.25 LSD 0.05 0.15 0.35 NS NS SEM 0.05 ** 0.12 0.10NS 0.15NS Fertilizer S source ES-90 0.07 0.80 1.12 3.06 ES-95 0.11 0.77 0.76 2.26 AP 0.52 2.57 2.22 4.96 AS 1.06 3.15 2.43 5.35 LSD 0.05 0.15 0.35 0.29 0.44 SEM 0.05 *** 0.12 *** 0.10 *** 0.15 *** 10 0.22 1.26 1.27 3.24 20 0.66 2.38 1.99 4.58 LSD 0.05 0.11 0.25 0.21 0.31 SEM 0.04 *** 0.09 *** 0.07 *** 0.11 *** Time of application Autumn 0.31 2.00 1.79 4.21 Spring 0.57 1.64 1.48 3.60 LSD 0.05 0.11 0.25 0.21 0.31 SEM 0.04 *** 0.09 ** 0.07 ** 0.11 *** y In the zero-s control, S uptake in seed was 0.03, 0.08, 0.18 and 1.21 kg S ha 1 in 1999, 2000, 2001 and 2002, respectively., **, *** and NS refer to significant treatment effects in ANOVA at P 0.10, P 0.01, P 0.001 and not significant, respectively. zero-s control. In the elemental S fertilizer treatments, there was little (nonsignificant) increase in the amount of sulphate-s in soil from applied S. For the amount of sulphate- S in the 0 60 cm soil depth, effect of S source and rate was significant, but interaction effects of F R, F T and R T were not significant. Ammonium sulphate, Agrium Plus and

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 787 Table 7. Uptake of S in straw from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in North-eastern Saskatchewan Treatment y S uptake (kg S ha 1 ) Fertilizer z (kg ha 1 ) Time of application 1999 2000 2001 2002 Fertilizer S source rate of S ES-90 10 3.02 2.50 1.80 8.83 20 3.31 4.43 2.81 15.16 ES-95 10 3.97 2.69 1.89 7.61 20 6.01 4.99 2.55 8.92 AP 10 5.81 4.94 2.94 10.95 20 8.34 8.84 5.51 19.57 AS 10 5.41 6.31 3.70 13.28 20 9.87 11.22 7.09 20.22 LSD 0.05 NS NS 1.31 2.49 SEM 1.06 NS 0.70 NS 0.46 * 0.87 ** Fertilizer S source time of application ES-90 Autumn 3.93 4.71 2.75 15.58 Spring 2.40 2.22 1.86 8.41 ES-95 Autumn 6.81 4.83 2.61 8.69 Spring 3.17 2.85 1.83 7.85 AP Autumn 7.86 7.70 4.01 13.87 Spring 6.28 6.08 4.45 16.65 AS Autumn 5.94 9.62 5.44 15.61 Spring 9.34 7.91 5.35 17.88 LSD 0.05 3.01 NS NS 2.49 SEM 1.06 * 0.70 NS 0.46 NS 0.87 *** time of application 10 Autumn 4.67 4.92 2.55 10.13 Spring 4.43 3.30 2.62 10.20 20 Autumn 7.60 8.51 4.86 16.74 Spring 6.17 6.23 4.12 15.19 LSD 0.05 NS NS NS NS SEM 0.75 NS 0.49 NS 0.32 NS 0.62 NS Fertilizer S source ES-90 3.17 3.46 2.31 11.99 ES-95 4.99 3.84 2.22 8.27 AP 7.07 6.89 4.23 15.26 AS 7.64 8.77 5.39 16.75 LSD 0.05 2.13 1.41 0.93 1.76 SEM 0.75 *** 0.49 *** 0.32 *** 0.62 *** 10 4.55 4.11 2.58 10.17 20 6.88 7.37 4.49 15.97 LSD 0.05 1.50 0.99 0.65 1.25 SEM 0.53 ** 0.35 *** 0.23 *** 0.44 *** Time of application Autumn 6.14 6.70 3.70 13.44 Spring 5.30 4.77 3.37 12.70 LSD 0.05 NS 0.99 NS NS SEM 0.53NS 0.35 *** 0.23NS 0.44NS y In the zero-s control, S uptake in straw was 2.47, 1.43, 1.14 and 5.45 kg S ha 1 in 1999, 2000, 2001 and 2002, respectively. *, **, *** and NS refer to significant treatment effects in ANOVA at P 0.05, P 0.01, P 0.001 and not significant, respectively. ES-90 had significantly greater amount of residual sulphate- S in soil than ES-95. Residual sulphate-s in soil increased with increasing S rate from 10 kg to 20 kg S ha 1. Time of application had no effect on residual sulphate-s in soil. Recovery of Applied S in Plant (Seed + Straw), Soil and Plant + Soil Percent recovery of applied S as total S in plant was significantly affected by S source and time of application, and the F

788 CANADIAN JOURNAL OF PLANT SCIENCE Table 8. Amount of SO 4 -S in soil in autumn 2002 from various S fertilizers applied at two rates in autumn and spring to canola near Tisdale in northeastern Saskatchewan Treatment y Amount of SO 4 -S (kg S ha 1 ) in soil depths (cm) Fertilizer z (kg ha 1 ) Time of application 0 15 15 30 30 60 0 60 Increase Fertilizer S source rate of S ES90 10 12.61 9.70 20.41 42.72 2.89 20 13.54 11.23 21.49 46.26 6.43 ES95 10 11.44 7.91 17.19 36.54 3.29 20 12.14 9.44 18.26 39.85 0.01 AP 10 12.38 9.70 19.87 41.95 2.11 20 15.41 13.53 22.02 50.96 11.12 AS 10 12.38 9.95 17.72 40.05 0.22 20 15.88 13.27 26.63 52.78 12.95 LSD 0.05 NS NS NS NS NS SEM 1.09NS 1.01NS 1.82NS 2.70NS 2.70NS Fertilizer S source time of application ES90 Autumn 14.01 9.96 21.49 45.45 5.62 Spring 12.14 10.98 20.41 43.53 3.69 ES95 Autumn 11.91 8.68 19.34 39.93 0.09 Spring 11.67 8.68 16.11 36.47 3.37 AP Autumn 13.31 9.96 23.63 46.90 7.06 Spring 14.48 13.27 18.26 46.01 6.18 AS Autumn 12.84 9.95 23.09 45.89 6.06 Spring 15.41 13.27 18.26 46.95 7.11 LSD 0.05 NS NS NS NS NS SEM 1.09NS 1.01NS 1.82NS 2.70NS 2.70NS time of application 10 Autumn 12.38 8.17 20.68 41.22 1.39 Spring 12.03 10.47 16.92 39.41 0.42 20 Autumn 13.66 11.10 23.09 47.86 8.02 Spring 14.83 12.63 19.61 47.07 7.23 LSD 0.05 NS NS NS NS NS SEM 0.77NS 0.71NS 1.29NS 1.91NS 1.91NS Fertilizer S source ES90 13.08 10.47 20.95 44.49 4.66 ES95 11.79 8.68 17.73 38.20 1.64 AP 13.89 11.61 20.95 46.45 6.62 AS 14.13 11.61 20.68 46.42 6.58 LSD 0.05 NS 2.03 NS 5.44 5.44 SEM 0.77NS 0.71 1.29NS 1.91* 1.91* 10 12.20 9.32 18.80 40.32 0.48 20 14.24 11.87 21.35 47.46 7.63 LSD 0.05 1.55 1.44 2.60 3.85 3.85 SEM 0.54* 0.51*** 0.91* 1.35*** 1.35*** Time of application Autumn 13.02 9.64 21.89 44.54 4.71 Spring 13.43 11.55 18.26 43.24 3.40 LSD 0.05 NS 1.44 2.60 3.85 NS SEM 0.54NS 0.51* 0.91** 1.35NS 1.35NS y In the zero-s control, amount of SO 4 -S was 10.74, 8.68, 20.41 and 39.83 kg S ha 1 in the 0 15, 15 30, 30 60 and 0 60 cm soil depths, respectively. *, **, *** and NS refer to significant treatment effects in ANOVA at P 0.05, P 0.01, P 0.001 and not significant, respectively. R and F T interaction effects were significant (Table 9). The percent recovery in plant was greater with sulphate-s fertilizers than with elemental S fertilizers. The recovery in plant tended to be lower at the 20 than at the 10 kg S ha 1 rate for sulphate- S fertilizers, but the opposite was true for ES-90. Also, the recovery in plant tended to be greater with spring application

MALHI FEASIBILITY OF ELEMENTAL S FERTILIZERS FOR CANOLA 789 than with autumn application of sulphate-s fertilizers, while it was greater with autumn application than with spring application of the elemental S fertilizers. The percent recovery as sulphate-s in the 0 60 cm soil was small, and only the main effects of S source and rate were significant (Table 9). The percent recovery in soil was greater with ammonium sulphate, Agrium Plus, and ES-90 than ES-95, was much greater at the 20 than at the 10 kg S ha 1 rate, and it tended to be greater with autumn application than with spring application. The percent recovery in plant + soil was significantly affected by the S source and F T interaction. It was considerably greater with sulphate-s fertilizers than with elemental S fertilizers, and it tended to be greater at the 20 than at the 10 kg S ha 1 rate. Also, it was much greater with autumn application than with spring application of elemental S fertilizers, but tended to be greater with spring application than autumn application of ammonium sulphate. DISCUSSION Yield and S Uptake Typical S deficiency symptoms (yellowing of new growth and cup-shaped leaves) on canola plants at early growth stages and exceptionally low seed and straw yields, as well as S uptake of canola in the zero-s plots indicated that soil was very deficient in plant-available S during the experimental period from 1999 to 2002. Because S is immobile in the plant, deficiency of S in soil in the growing season can cause a drastic reduction in seed yield without serious reduction in straw yield (Malhi and Gill 2002). Extremely low seed yields in the zero-s treatment were due to nutrient imbalance of N:S, because only N was applied to a S-deficient soil (Janzen and Bettany 1984a). But, relatively lower seed yields in the sulphate-s fertilizer treatments, particularly at 20 kg S ha 1 rate, could not be due to N:S imbalance. The relatively lower seed yields in the sulphate-s fertilizer treatments were most likely due to abnormal weather conditions (such as dry soil moisture condition/drought, cool temperature, hot temperature or even frost) during these years, which occurred during early spring, early summer or seed filling (or their combinations), and also due to coarse texture (loamy sand) of soil at this site. In addition, above-average precipitation in the early growing season in 1999 and 2000 may have caused leaching of some nutrients below the root zone in this sandy textured soil, resulting in reduced yield potential of canola. Compared with zero-s plots, across the S rates and years, average seed yield of canola in plots treated with ammonium sulphate at 20 kg S ha 1 was 5.1 times greater (range of 2.6 to 29.9 times), while straw yield increased 1.9 times (range of 1.4 to 2.9 times). The substantial increase in yield from ammonium sulphate suggests that this fertilizer provided S in the form that plants can absorb (Follett et al. 1981), and S deficiencies in crops can be prevented or eliminated by applying sulphate-s (Nyborg 1968). The 20 kg S ha 1 rate produced or tended to produce more seed yield than 10 kg S ha 1. These results were similar to those observed by Janzen and Bettany (1984a), who obtained a positive response of canola seed and straw yield to increasing S rate when adequate N was also applied. Sulphur in elemental S fertilizers must be converted to sulphate before it can be utilized by a crop (Bettany and Janzen 1984). In the present study, there was little or no increase in seed yield from the elemental S fertilizers compared with zero-s control in the first year (1999), especially with spring application. Presumably there was not sufficient available S from the elemental S fertilizers to enhance canola yield, as also evidenced by low amounts of sulphate- S in soil at spring sampling in plots that received S in autumn. This suggests that, under the conditions of this study, physical dispersion of the elemental S granules and oxidation of elemental S to sulphate-s was not rapid enough to supply a sufficient amount of available S in the first year to enhance canola seed yield and S uptake at this site. In earlier studies, availability of S from elemental S fertilizers was considered minimal in the year of application (Noellemeyer et al. 1981) and elemental S fertilizers have been found inferior to sulphate-s fertilizers for cereal and oilseed crops in the year of application (Ukrainetz 1982; Solberg 1986; Karamanos and Janzen 1991; Grant et al. 2001). The amount of plant-available S from elemental S fertilizers was observed to increase with time (Bettany and Janzen 1984). Autumn application of elemental S fertilizers for several years may thus produce accumulation of plantavailable S in soil and provide seed yield benefit. Cumulative effect, therefore, was assessed in the present study with annual applications of elemental S fertilizers for 4 yr on the same plots. In the second year of S application (2000), elemental S fertilizers significantly increased seed yield and S uptake over the zero-s control. This indicated the beneficial effect of further dispersion and increased time for oxidation of the elemental S fertilizer granules to make better contacts for S particles with soil microorganisms. However, seed yield and S uptake of canola with elemental S sources were much less than ammonium sulphate in the second year in most cases. Even after four annual applications, seed yield and S uptake of canola were less with elemental S fertilizers than with ammonium sulphate in some cases. This indicated that elemental S fertilizers did not consistently supply sufficient amounts of sulphate-s to canola plants in the growing season for optimum growth and seed yield. The conversion of elemental S in granular fertilizers to sulphate can be improved by increasing the contact area between elemental S particles and the soil by allowing granules to disintegrate on the soil surface prior to their incorporation at seeding (Solberg et al. 2003). Leaving granules of elemental S fertilizers exposed to frost or rain on the surface of soil speeds up the physical breakdown of the granules into fine particles, allowing faster oxidation to sulphate. In order to get enhanced conversion of elemental S to sulphate- S, granulated elemental S fertilizers broadcast the previous autumn were left on the soil surface until the following spring (just prior to seeding). Autumn-applied elemental S fertilizers were more effective than spring-applied elemental S fertilizers in correcting S deficiency and improving seed yield of canola. This may reflect a greater conversion