Yield and quality of canola seed as affected by stage of maturity at swathing

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1 Yield and quality of canola seed as affected by stage of maturity at swathing C. L. Vera 1, R. K. Downey 2, S. M. Woods 3, J. P. Raney 2, D. I. McGregor 2, R. H. Elliott 2, and E. N. Johnson 4 1 Agriculture and Agri-Food Canada, Melfort Research Farm, P.O. Box 124, Melfort, Saskatchewan, Canada SE 1A ( verac@agr.gc.ca); 2 Agriculture and Agri-Food Canada, Saskatoon Research Centre, 17 Science Place, Saskatoon, Saskatchewan, Canada S7N X2; 3 Agriculture and Agri-Food Canada, Cereal Research Centre, 195 Dafoe Road, Winnipeg, Manitoba, Canada R3T 2M9; 4 Agriculture and Agri-Food Canada, Scott Research Farm, P.O. Box 1, Scott, Saskatchewan, Canada SK 4A. Received 2 April 25, accepted 17 July 26. Vera, C. L., Downey, R. K., Woods, S. M., Raney, J. P., McGregor, D. I., Elliott, R. H. and Johnson, E. N. 27. Yield and quality of canola seed as affected by stage of maturity at swathing. Can. J. Plant Sci. 87: Swathing is an important canola (Brassica napus L.) harvest operation in western Canada. The determination of the optimum timing for this operation is worth considering, as premature swathing may lead to reduced seed yield and quality. Seed yield and quality of three canola cultivars (44A89, AC Excel and Ebony), as affected by two seeding dates and several harvest times (six or eight swathing times and one direct combined treatment) was investigated on a Black Chernozem silty loam soil at Melfort, Saskatchewan, Canada, during, 2 and 21. Seed yield, weight, protein content (oil-free meal basis) and oil content generally increased with seed development and swathing time. Early seeding was more conducive to achieving higher seed yield, especially in good growing conditions, and resulted in heavier mature seeds with higher oil content. Seed oil composition also changed during seed development. The proportion of oleic (C18:1) and linolenic (C18:3) acids increased, while that of myristic (C14:), palmitic (C16:), palmitoleic (C16:1), stearic (C18:), linoleic (C18:2) and arachidic (C2:) acids decreased. The levels of the long chain fatty acids eicosenoic (C2:1) and erucic (C22:1) acids were unaffected. However, the overall amount of fatty acids synthesized (mg 1 seeds 1 ) increased as seeds matured. Swathing was advantageous over direct combining in preventing weather-induced shattering. Key words: Brassica napus, canola, fatty acid, oil, protein, seed development, seed quality, shattering, direct combining, swathing Vera, C. L., Downey, R. K., Woods, S. M., Raney, J. P., McGregor, D. I., Elliott, R. H. et Johnson, E. N. 27. Variation du rendement grainier et de la qualité des graines du canola en fonction du stade de maturité à l andainage. Can. J. Plant Sci. 87: Dans l Ouest canadien, l andainage est une importante opération de la récolte du canola (Brassica napus L.). Il est essentiel d établir le moment optimal où l effectuer, car un andainage prématuré peut réduire le rendement grainier et la qualité du produit. Les auteurs se sont penchés sur le rendement grainier et la qualité de trois cultivars de canola (44A89, AC Excel et Ebony) et la manière dont ces paramètres varient en fonction de deux dates de semis et de plusieurs dates de récolte (six ou huit d andainage et une de récolte directe). Les essais se sont déroulés en, 2 et 21 sur un tchernoziom noir de la texture d un loam limoneux, à Melfort, en Saskatchewan (Canada). En général, le rendement grainier, le poids, la teneur en protéines (tourteau délipidé) et celle en huile s améliorent avec le degré de maturité de la graine et le moment où a lieu l andainage. Des semis hâtifs favorisent un meilleur rendement grainier, surtout quand les conditions de croissance sont propices à cette culture, et donnent des graines plus lourdes et plus riches en huile à maturité. La composition de l huile évolue également avec le développement de la graine. Ainsi, la proportion des acides oléique (C18:1) et linolénique (C18:3) augmente tandis que celle des acides myristique (C14:), palmitique (C16:), palmitoléique (C16:1), stéarique (C18:), linoléique (C18:2) et arachidique (C2:) diminue. La concentration des acides gras à chaîne longue comme les acides éicosénoïques (C2:1) et érucique (C22:1) n est cependant pas affectée. La quantité globale d acides gras synthétisés (mg par centaine de semences) augmente néanmoins avec la maturité des graines. L andainage s avère plus utile que la récolte directe pour prévenir l égrenage prématuré attribuable aux intempéries. Mots clés: Brassica napus, canola, acides gras, huile, protéines, développement des graines, qualité des graines, récolte Canola (Brassica napus L.) is an oilseed crop that developed in western Canada from a humble beginning in the mid 194s to almost 5 million seeded hectares per year by the end of the century (Statistics Canada 1999), rivaling wheat in its economic value. Swathing, also known as windrowing, is a preferred harvest operation in western Canada for canola and many other crops. Swathing can hasten maturity and reduce the effect of uneven seed ripening and thus minimizes seed loss due to 13 premature pod shelling (Anonymous 1987; Thomas 23). It can also protect the maturing crop from untimely frost and hail (Bowren and Kirkland 1975) and reduce problems caused by green weed undergrowth or crop re-growth (Anonymous 1987). Swathing has also been reported to reduce the effects of alternaria black spot, caused by Alternaria brassicae (Berk.), in canola (Duczek et al. 1999). The stage of maturity at which a crop is swathed can impact both seed yield and quality. Premature swathing of

2 14 CANADIAN JOURNAL OF PLANT SCIENCE canola has been reported to reduce yield (Bowren and Kirkland 1975; Brown et al. 1999; Ogilvy 1989), weight (Ogilvy 1989), protein content (Bowren and Kirkland 1975) and oil content (Bowren and Kirkland 1975; Ogilvy 1989) of the seed. It has also been found to influence the fatty acid composition and synthesis (Fowler and Downey 197) of canola seed oil. Early swathing can also result in chlorophyll retention in the embryo (Cenkowski et al. 1989a, b; Daun et al. 1983), which is associated with loss in seed grade (Daun 1987) and increased oil processing costs for chlorophyll removal (Daun 1982). It has also been associated with reductions in seed germination and seedling weight, both in laboratory and field conditions (Johnson et al. 25). Many previous publications on this subject have focused on the effect of premature swathing on a few or only isolated parameters, and near the end of seed development. The present experiment was designed to study and assess the changes that occur as canola seeds develop, in relation to swathing timing, not only in terms of dry matter increase, but also to determine how different seed quality parameters are affected. MATERIALS AND METHODS Site and Experimental Description The study was conducted at Melfort, Saskatchewan, in, 2 and 21. The trial was also planted in 1999, but the crop was damaged by herbicide. The soil was a Black Chernozem (Udic Haploborolls), with a silty clay texture, containing 82 g kg 1 organic matter. The long-term annual precipitation for the area is 413 mm, of which 6% occurs in the May to August growing season. On average the area has 93 frost-free days and 1517 annual growing degree days (GDD) (>5ºC). Precipitation (mm) and GDD for the May- September period, during the 3 yr of experimentation, along with long-term averages, are given in Table 1. The experimental design was a four-replicate split-split plot, with seeding dates (early and late) as main plots, three cultivars (44A89, AC Excel and Ebony rated as early, medium and late maturing, respectively) as subplots and swathing times as sub-subplots. There were six swathing times in and eight in 2 and 21. The first swathing treatment in each year commenced when the seed moisture of AC Excel approached 7 g kg 1 (see Fig. 1). Swathing times were at 4-d intervals. In addition, a standing crop treatment was direct combined; usually at the same time as the last swathing treatment was combined. When direct combined, most pods (95 1%) were dry, and seed moisture content of the early and medium maturing cultivars was 1 g kg 1. To determine seed moisture at time of swathing, seed samples were drawn from border plots of the same cultivar, which were sown on both ends of each subplot. Canola was sown into cultivated land with a double-disc plot seeder, at a seeding rate of 8 kg ha 1 and depth of 1 2 cm. Each sub-subplot consisted of 1 rows with the center six rows sown to canola and the two outside rows on each side sown to barley. The purpose for the barley rows was to protect the canola plants from wind damage after swathing. Rows were 18 cm apart and 4.2 m long, after plot ends were trimmed. The swaths were laid with a plot swather (1.42 m cutter bar) and left to dry in the field. Plots were fertilized to recommended rates, according to soil tests in each year. Measurements Seed moisture was determined at each swathing time by collecting five plants of each cultivar at random from border plots in each replicate. Five basal pods on the main raceme were shelled by hand and seed weight was recorded before and after drying at 6ºC for 24 h. Seed moisture when the standing crop was direct combined was also determined in 2 and 21. The rate of seed moisture loss was derived from linear regression equations for each seeding date and year. Seed weight, oil, protein and chlorophyll content and the fatty acid composition of the extracted seed oil were determined each year. Seed weight was determined by weighing a sample of 5 dried (4 C, 48 h) seeds from each plot. Seed oil content (dry matter basis) was measured using samples of 25 g of dry whole seed per sub-subplot, using an Oxford continuous-wave, low resolution nuclear magnetic resonance (NMR) instrument (Anonymous b). Seed protein content was calculated from nitrogen determinations, using samples of.5 g of dry whole seed per sub-subplot, combustion analysis (LECO FP-528) and nitrogen to protein conversion factor of Seed protein content was expressed on an oil-free basis, using the formula: protein content of the whole seed/(1 oil content of the whole seed/1). For fatty acid determinations, seed oil was extracted by shaking 2 g of seed in 5 ml of hexane for 1 h in an Eberbach shaker in plastic grinders containing steel rods (Raney et al. 1987), and transmethylated at room temperature with sodium methoxide. The fatty acid composition of the methyl esters was then determined by capillary gas chromatography (Anonymous c). Table 1. Monthly precipitation and growing degree-days for the growing seasons through 21, compared with the long-term average, at Melfort, Saskatchewan Precipitation (mm) Growing degree-days ( C) z Year May Jun Jul Aug Sep Total May Jun Jul Aug Sep Total Normal y z Base temperature = 5 C y Long-term average (1971 2)

3 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED 15 Precipitation (mm) Precipitation (mm) Precipitation (mm) Early seeding date 2 Early seeding date 21 Early seeding date Late seeding date Late seeding date Late seeding date First swathing (early seeding) First swathing First (late seeding) swathing (early seeding) First swathing (early seeding) First swathing (late seeding) Direct combining (early seeding) First swathing (late seeding) Direct combining (late seeding) Direct combining (early seeding) Direct combining (early seeding) Direct combining (late seeding) Direct combining (late seeding) May Jun Jul Aug Sep Day of year Fig. 1. Daily and cumulative precipitation during the growing seasons of, 2 and 21. Arrows indicate dates of seeding, first swathing and direct combining, for early and late seeding dates Cumulative precipitation (mm) Cumulative precipitation (mm) Cumulative precipitation (mm) Statistical Analysis A split-split-plot analysis was conducted on each year s data using the SAS procedure Mixed (SAS Institute, Inc. 24). Fixed effects in the model were seeding date (SD), cultivar (CV), swathing time (ST) and their interactions. Random effects were replicate (Rep) and the main- and sub-plot errors: Rep SD and Rep SD CV. The models were fitted using restricted maximum likelihood (REML), and F tests were carried out on the fixed effects. Slopes of moisture content versus days since first swathing date were compared among years and seeding dates using the SAS procedure GLM (SAS Institute, Inc. 24). The straight combined treatment was omitted from this comparison. To illustrate the trends in yield, seed weight, oil and protein versus moisture content at swathing, separate sigmoidal curves were fitted to the data for each year and seeding date. The equation of the curve is y = y + a/(1 + exp( (MC x )/b)), where MC is moisture content, exp is the exponential function exp(x) = e x, y and a are location and scale parameters

4 16 CANADIAN JOURNAL OF PLANT SCIENCE Table 2. Dates of seeding, flowering, first swathing and direct combining of three canola cultivars grown at Melfort, Saskatchewan, in, 2 and 21 First Direct Year Cultivar Seeding Flowering swathing combining 44A89 May 7 (127) z Jun. 26 (177) Jul. 21 (22) Aug. 2 (232) AC Excel Jun. 27 (178) Ebony Jun. 29 (18) 44A89 May 29 (149) Jul. 7 (188) Aug. 6 (218) Sep. 4 (247) AC Excel Jul. 8 (189) Ebony Jul. 1 (191) 2 44A89 May 5 (126) Jul. 5 (187) Jul. 31 (213) Sep. 12 (256) AC Excel Jul. 6 (188) Ebony Jul. 8 (19) 44A89 Jun. 5 (157) Jul. 2 (22) Aug. 14 (227) Oct. 6 (28) AC Excel Jul. 21 (23) Ebony Jul. 23 (25) 21 44A89 May 16 (136) Jul. 4 (185) Jul. 26 (27) Sep. 1 (244) AC Excel Jul. 5 (186) Ebony Jul. 7 (188) 44A89 Jun. 15 (166) Jul. 24 (25) Aug. 2 (232) Sep. 27 (27) AC Excel Jul. 26 (27) Ebony Jul. 3 (211) z Numbers in parentheses represent dates expressed as day of year. for y, and x and b are location and scale parameters for MC. All values of y are between y and y + a, and the steepest slope, a/4b, occurs when MC = x and y = y + a/2. The straight combined treatment was omitted from these computations. Polynomial equations were fitted to the data for fatty acids versus moisture content, averaged across years, seeding dates and cultivars. Because moisture content could not be precisely controlled, but was measured with error, the equations should not be used for prediction. RESULTS AND DISCUSSION Seeding Date and Plant Development An early and a late seeding date were included in this study to provide a wider range of crop conditions on which the effects of swathing time could be studied. The period between seeding and flower initiation was longer for the early seeding date in all years (Table 2), with averages of 51, 62 and 5 d, for the early seeding date, as opposed to the corresponding 4, 46 and 42 d in the late seeding date, for each of the 3 yr of the study, respectively. Cooler than normal spring temperatures contributed to the larger difference between the two seeding dates in 2 (16 d), compared with (11 d) and 21 (8 d). Although spring temperature was also below normal in 21 (only June), the length of the early development period may have been shortened as both seeding dates were about 1 d later than in the previous years. The period between flower initiation and first swathing time (near 7% seed moisture) showed less effect of seeding date, with differences of 5, 1 and 3 d in the 3 yr. The rate of seed moisture loss was affected by year, being higher in the drier and warmer years (21.4 and 18. g kg 1 d 1, for the early and late seeding dates, respectively, in, and 19.1 and 17.2 g kg 1 d 1, for the early and late seeding dates, respectively, in 21) and lower in the wetter and cooler year (14.6 and 12.5 g kg 1 d 1, for the early and late seeding dates, respectively, in 2) (Fig. 2). The rate of seed moisture loss seemed to have also been affected, but to a lesser degree, by date of seeding, being slightly higher for early seeding (18.4 g kg 1 d 1 ), as compared with late seeding (15.9 g kg 1 d 1 ). Ward et al. (1995), in a similar experiment, did not find differences in rates of seed moisture loss among seeding dates or years. Nevertheless, they did not discard the possibility that seed moisture loss may be affected under more extreme weather conditions, such as occurred in the present study. As seeds matured, changes in seed color were recorded in 2 and 21. In 2, seeds of all three cultivars started to turn (from green to brown) when seed moisture content was 4 45 g kg 1 (data not shown). But in the dry year of 21, seeds started to turn earlier, when seed moisture content was 45 5 g kg 1. Seed Yield Seed yield was significantly affected by all factors studied and many of their interactions (Table 3). Seed yield increased in a sigmoidal fashion as seeds developed, with a small increase early in the development, followed by a rapid and almost linear increase rate, to level off at physiological maturity (Fig. 3). Early seeding resulted in higher yield throughout the entire seed development in 2, and in the mid late seed development in 21. In, however, the difference between early and late seeding was small, and not significant near maturity. In, seed yield was mainly limited by precipitation (64% of normal), as GDD was adequate (11% of normal) throughout most of the growing season. Maximum seed

5 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED Early seeding y = x R 2 =.99** Late seeding y = - 18.x R 2 =.98** Early 44A89 Early AC Excel Early Ebony Late 44A89 Late AC Excel Late Ebony Early Late Early seeding Early seeding y = x R 2 =.99** y = x R 2 =.99** yield, for all cultivars and both seeding dates, was obtained when seed moisture was near 4 g kg 1. The average rate of yield increase during the period of rapid growth (maximum slope) was 4.6 and 7.8 kg ha 1 per g kg 1 of seed moisture loss, for the early and late-seeding dates, respectively. It is possible that in some shattering took place in the standing crop, as a slight decline in seed yield was detected when standing plants of AC Excel and Ebony were direct combined. In 2, a year with adequate precipitation throughout the growing season (115% of normal), seed yield of all three cultivars, as in, reached maximum near 3 g kg 1. The average rate of yield increase during the period of rapid growth (maximum slope) was 9.2 and 8.5 kg ha 1 per g kg 1 Day of year Late seeding y = - 13.x R 2 =.98** Late seeding 2 21 y = x R 2 =.98** Fig. 2. Seed moisture content at six () and eight (2 and 21) swathing times of three canola cultivars planted at two seeding dates each year. Linear regression equations correspond to mean values (solid lines). of seed moisture loss, for the early and late-seeding dates, respectively. Evidence of seed loss due to shattering was also noticed this year on the early seeded AC Excel and Ebony, as yield obtained from standing plants was substantially lower than that of the last swathing time. Strong winds at harvest may have caused mature pods on the standing crop to shatter, drastically reducing seed yield, without affecting swathed plants. The year 21 was extremely dry (36% of normal growing season precipitation), with small yield increases during seed development, especially when the crop was late seeded. Maximum seed yield values were reached near 3 g kg 1 seed moisture for both seeding dates. The average rate of yield increase during the period of rapid growth (maxi-

6 18 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. F values and error mean squares from analysis of variance of seeding date and swathing time effects on seed yield, seed weight, seed protein content and seed oil content of three canola cultivars grown at Melfort, Saskatchewan, in, 2 and 21 Seed yield Seed weight Seed protein Seed oil Source of variation df (kg ha 1 ) (mg) (%) (%) Seeding date (SD) ** * 3.3 Cultivar (CV) ** 41.7** 8.5** 8.3** SD CV ** 12.7**. 6.2* Swathing time (ST) ** 344.5** 115.2** 198.5** SD ST 6 2.6* 6.6** 6.2** 3.** CV ST SD CV ST Error mean square Seeding date (SD) * 62.2** 8.* 6.4 Cultivar (CV) 2 6.8** 55.2** 52.3** 29.1** SD CV **.9 8.6** Swathing time (ST) ** 563.9** 121.4** 554.** SD ST 8 6.6** 6.3** 3.3** 19.7** CV ST ** 3.3** 2.5** 3.8** SD CV ST ** 2.5** 1. 2.* Error mean square Seeding date (SD) * 38.8** ** Cultivar (CV) ** 22.6** 192.7** SD CV * ** Swathing time (ST) ** 138.7** 19.6** 483.** SD ST ** 3.1** 16.6** 4.4** CV x ST * 23.** 5.6** 15.4** SD CV ST * 2.7** Error mean square *,** F value significant at P.5 and P.1, respectively. mum slope) was 8.1 and 2.1 kg ha 1 per g kg 1 of seed moisture loss, for the early and late seeding dates, respectively. The larger rate of seed yield increase of the early seeded canola determined seed yield values at maturity almost twice as large as those of the late-seeded crop. Drought during May, June and most of July in 21 certainly had a detrimental effect on seedling development of both early- and late-seeded canola. However, the only substantial amount of precipitation (24 mm) that occurred this growing season, which took place in late July (3 wk after the early-seeded crop started to flower and at flower initiation of the lateseeded crop), appeared to have benefited seed development of the early-seeded more than the late-seeded canola. In addition, prolonged drier and warmer than normal weather, which continued through August and September, seems to have limited the development of the late-seeded crop. Unlike 2, winds were calm during the 21 harvest period and little or no seed shattering was detected this year. Thomas (23) and Gan et al. (24) have indicated that adequate moisture and temperature during and following flowering are important in inducing maximum seed yield. Thomas (23), summarizing numerous Western Canadian seeding date studies on B. napus, concluded that early and mid seeding provided the highest yields in 85% of the trials studied, while late seeding resulted in highest yields in only 5% of the trials. This suggests that, in most years, early seeding is favored by the growing conditions that normally occur in the geographical area where canola is usually produced in western Canada. In our study, highest seed yield at maturity was obtained when the crop was seeded early in 2, a year with adequate temperature and precipitation. Early seeding was also favored in the dry year of 21, apparently due to timely precipitation. Seed moisture and associated seed color change are widely used in the determination of optimal swathing time. Bowren and Kirkland (1975) indicated that best seed yields of Argentine canola (B. napus L.) were obtained when seed moisture content at swathing was approximately 4% (4 g kg 1 ), at which time the majority of the seeds were in the firm dough stage, starting to turn from green to brown color. This statement is in agreement with the present study, except for the early seeding date in 21, when maximum seed yield occurred at around 3 g kg 1 seed moisture. In recent studies, conducted by the Canola Council of Canada (Anonymous 21, 22), using hybrid cultivars, seed yield gains were recorded when swathing was delayed as late as 6 7% seed-color change. Brown et al. (1999), comparing swathing with direct combining of standing canola plants, concluded that swathing resulted in reduced seed yield in 2 out of 3 yr. In our study, it was observed that natural seed losses by shattering could be more prevalent on a standing crop, as strong winds may cause plant branches to collide, causing mature pods to open and discharge their seed. Studies done by the Canola Council of Canada (Anonymous 21, 22) also concluded that direct combining canola can result in reduced seed yield due to shattering. However, harvest equipment has also been indicated as a factor in the loss of canola seed at maturity (Thomas et al. 1991).

7 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED 19 Seed yield (kg ha -1 ) Seed yield (kg ha -1 ) Seed yield (kg ha -1 ) Early y = /(1+exp((x-581)/69.2)) R 2 =.9** Late y = /(1+exp((x-557)/39.7)) R 2 =.82** Early y = /(1+exp((x-592)/75.9)) R 2 =.86** Late y = /(1+exp((x-555)/65.3)) R 2 =.91** 2 Early y = /(1+exp((x-442)/34.3)) R 2 =.9** Late y = /(1+exp((x-635)/113.1)) R 2 =.92** Early 44A89 Early AC Excel Early Ebony Late 44A89 Late AC Excel Late Ebony Early Late Fig. 3. The effect of seeding date and seed moisture content at swathing on seed yield of three canola cultivars in, 2 and 21, at Melfort, Saskatchewan. Seed weight (mg seed -1 ) Seed weight (mg seed -1 ) Seed weight (mg seed -1 ) Early y = /(1+exp((x-564)/84.2)) R 2 =.91** Late y = /(1+exp((x-563)/43.1)) R 2 =.94** 2 Early y = /(1+exp((x-552)/64.3)) R 2 =.95** Late y = /(1+exp((x-533)/64.)) R 2 =.95** 21 Early y = /(1+exp((x-492)/6.)) R 2 =.96** Late y = /(1+exp((x-518)/53.8)) R 2 =.94** Early 44A89 Early AC Excel Early Ebony Late 44A89 Late AC Excel Late Ebony Early Late Fig. 4. The effect of seeding date and seed moisture content at swathing on the seed weight of three canola cultivars in, 2 and 21, at Melfort, Saskatchewan. Seed Weight Seed weight was influenced by most factors studied and by their interactions in all years (Table 3). Early seeding resulted in heavier seeds throughout seed development in 2, and in late development in and 21 (Fig. 4). Like seed yield, seed weight increased in a sigmoidal fashion, ranging from an average of 1.5 mg seed 1, near 7 g kg 1 seed moisture, and a maximum of about mg seed 1, near 3 g kg 1 seed moisture in most years. The rate of seed weight increase in the period of rapid growth was very similar for all years, seeding dates and cultivars (maximum slopes was mg seed 1 per g kg 1 seed moisture loss). A similar pattern of seed weight development has also been observed in other studies (Fowler and Downey 197; Rakow and McGregor 1975; Ogilvy 1989; Anonymous 21, 22). Seed Protein Seed protein content (oil-free meal basis) was affected by all factors studied and most interactions, but was most visibly affected by year (Table 3). In general, protein content of all cultivars increased in a sigmoidal fashion as seeds developed (Fig. 5), being favored by late seeding throughout most of the seed development in and 21. Maximum val-

8 2 CANADIAN JOURNAL OF PLANT SCIENCE Seed protein (%) Seed protein (%) Seed protein (%) Early y = /(1+exp((x-451)/54.7)) R 2 =.85** Late y = /(1+exp((x-468)/83.1)) R 2 =.83** 2 Early y = /(1+exp((x-446)/92.1)) R 2 =.76** Late y = /(1+exp((x-473)/52.5)) R 2 =.89** Early y = /(1+exp((x-418)/45.2)) R 2 =.66** Late y = /(1+exp((x-563)/89.9)) R 2 =.92** Early 44A89 Early AC Excel Early Ebony Late 44A89 Late AC Excel Late Ebony Early Late Fig. 5. The effect of seeding date and seed moisture content at swathing on the seed protein content (oil-free meal) of three canola cultivars in, 2 and 21, at Melfort, Saskatchewan. ues were obtained near 3 g kg 1 seed moisture in all years. Bowren and Kirkland (1975) also reported lower than maximum seed protein values when canola was swathed before physiological maturity (4 g kg 1 seed moisture). The dry year of 21 resulted in lower seed protein content than the other 2 yr. This seems to be in disagreement with the findings of Henry and MacDonald (1977), who reported lower seed protein content of rape (B. napus L.) when grown under irrigation. In addition, in the present study, drastic protein decline was also observed in seeds harvested from standing plants in, especially in the late-seeded crop, but this phenomenon was not observed in the other 2 yr. Seed oil content (%) Seed oil content (%) Seed oil content (%) Early y = /(1+exp((x-659)/112.4)) R 2 =.94** Late y = /(1+exp((x-555)/44.5)) R 2 =.87** Early y = /(1+exp((x-595)/55.6)) R 2 =.97** Late y = /(1+exp((x-682)/112.2)) R 2 =.95** 2 Early y = /(1+exp((x-594)/78.9)) R 2 =.9** Late y = /(1+exp((x-667)/89.7)) R 2 =.91** 21 Early 44A89 Early AC Excel Early Ebony Late 44A89 Late AC Excel Late Ebony Early Late Fig. 6. The effect of seeding date and seed moisture content at swathing on the seed oil content of three canola cultivars in, 2 and 21, at Melfort, Saskatchewan. Seed Oil Seed oil content was affected by most factors studied and their interactions, in all years (Table 3). In general, seed oil content progressively increased as seeds developed, in a pattern (sigmoidal) that was very similar in all years and cultivars (Fig. 6). Maximum values were obtained near 3 g kg 1 seed moisture, and stabilized as seeds matured. Bowren and Kirkland (1975) and the Canola Council of Canada (Anonymous 21, 22) reported seed oil losses when canola was swathed prematurely (before 4 g kg 1 seed moisture). Their findings agree with those of this study, as seed oil content declined sharply before this

9 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED Myristic (C14:) y = 1E-7x 2-5E-5x +.54 R 2 =.99** Palmitic (C16:) y = 6E-6x 2-27E-4x R 2 =.99** Palmitoleic (C16:1) y = 1E-6x 2-4E-4x R 2 =.99** Seed oil fatty acid composition (%) Stearic (C18:) Oleic (C18:1) Linoleic (C18:2) y = 4E-6x 2-19E-4x R 2 =.99** Linolenic (C18:3) y = - 6E-6x 2-32E-4x R 2 =.99** Behenic (C22:) y = - 7E-7x 2-3E-4x +.35 R 2 =.99** y = - 3E-5x 2.11x R 2 =.99** Arachidic (C2:) y = 2E-6x 2-6E-4x +.68 R 2 =.99** Erucic (C22:1) y = 5E-7x 2-4E-4x +.37 R 2 =.84* Eicosenoic (C2:1) 6 y = - 2E-5x 2-64E-4x R 2 =.99** Mean y = - 1E-4x R 2 =.91** Fig. 7. The effect of seed moisture content at swathing on fatty acid composition of canola seed oil in, 2 and 21 (combined data of two seeding dates and three cultivars). 2 seed moisture threshold. In addition, in the present study, early seeding resulted in higher seed oil content in and 21, and highest seed oil content values was observed in the dry year of 21. The occurrence of higher seed oil content in drought condition seems to contradict the observations of Henry and MacDonald (1977), who indicated that seed oil content of rape (B. napus L.) was higher under irrigation. Fatty Acid Composition and Synthesis The time at which canola plants were swathed affected not only the amount of oil that accumulated in the seed, but also its fatty acid composition (Table 4, Fig. 7). The proportion of oleic acid, and to a lesser degree linolenic acid, increased as seeds developed. With the exception of eicosenoic and erucic acids, which were not affected by swathing time, the proportion of all other fatty acids decreased as seeds devel-

10 22 CANADIAN JOURNAL OF PLANT SCIENCE Table 4. F values and error mean squares from analysis of variance of seeding date and swathing time effects on seed oil fatty acid composition (%) of three canola cultivars grown at Melfort, Saskatchewan, in, 2 and 21. Source of Myristic Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Arachidic Eicosenoic Behenic Erucic variation df C14: C16: C16:1 C18: C18:1 C18:2 C18:3 C2: C2:1 C22: C22:1 Seeding date (SD) ** * Cultivar (CV) 2 79.** 29.1** 6.8** 24.** 96.7** 14.3** 28.8** 96.1** 196.2** 422.6** 137.5** SD CV 2 5.3* 6.* 12.6** 16.5** * 8.6** 2.4** **. Swathing time (ST) ** 566.4** 789.5** 79.6** 199.5** 69.6** 147.9** 926.8** 3.9* 788.9**.9 SD ST 6 14.** 4.7** 14.8** 25.3** 27.** 21.1** 37.7** 16.4** *.8 CV ST ** 2.7* * ** 1.1 SD CV ST ** 3.9** 4.2** Error mean square E-6 z E E E Seeding date (SD) ** 18.2* ** 55.6** 24.3* 136.6** 35.** Cultivar (CV) ** 63.5** 59.6** 45.9** 23.2** 12.4** 79.6** 18.9** 89.4** 49.2** 64.3** SD CV ** 3.5* 26.5** 12.3** 1.4* 6.* 1.5** 5.3* Swathing time (ST) ** ** ** 864.** 74.8** 732.8** 147.7** 761.9** ** 2.4 SD ST ** * 27.6** 16.8** 7.4** 52.3** 13.8**.2 2.6*.4 CV ST ** 1.1** 1.4** 6.8** * 9.9** 3.1** * 1.2 SD CV ST ** 5.**.9 2.6* 6.1** 5.7** 2.6* 3.7**.1 4.3**.6 Error mean square E E-6 422E E E Seeding date (SD) 1 15.** ** 36.2** 74.3** 21.2** 156.7** 13.2* 14.9** 12.* 7.6 Cultivar (CV) 2 5.7** 32.8** 21.8** 435.5** 46.3** 24.2** 312.7** 88.4** 49.3** 22.3**.3 SD CV ** ** 4.8* 4.* 16.7**.7 Swathing time (ST) ** ** ** 828.2** 573.3** 813.3** 12.7** ** 2.8* ** 2.4 SD ST ** 3.5* 1.7** 5.1** 7.1** 26.2** 51.6** 13.4** 3.7** 28.3** 1.7 CV ST ** 37.6** 3.2** 29.6** 4.8** 9.4** 25.9** 19.2** 3.1** 13.6**.3 SD CV ST * 8.9** ** 6.3** 4.3**.6 2.4*.3 Error mean square E E-6 32E E E z E-6, E-5: multiplied by 1 6 or 1 5, respectively. *,** F value significant at P.5 and P.1, respectively.

11 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED 23 Table 5. F values and error mean squares from analysis of variance of seeding date and swathing time effects on seed oil fatty acid content (mg 1 seeds 1 ) of three canola cultivars grown at Melfort, Saskatchewan, in, 2 and 21. Source of Myristic Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Arachidic Eicosenoic Behenic Erucic variation df C14: C16: C16:1 C18: C18:1 C18:2 C18:3 C2: C2:1 C22: C22:1 2 Seeding date (SD) 1 4.6* * ** **.1 Cultivar (CV) ** 14.8** * 15.7** 12.2** 37.** 65.** 8.1** 91.** SD CV 2 28.** 16.6** 7.5** 7.2** 11.8** 17.3** 11.9** 6.7** **. Swathing time (ST) ** 355.4** 184.3** 176.1** 32.5** 48.7** 225.3** 199.9** 132.4** 28.7** 7.7** SD ST ** 9.3** 9.** 6.5** 7.4** 11.2** ** 3.1* 9.5**.9 CV ST ** ** ** 2.6* 6.2** SD CV ST * Error mean square E-6 z E E E Seeding date (SD) ** 45.7** 114.6** 139.6** 61.7** 35.6**. 52.7** 9.4** 11.9** 2.2 Cultivar (CV) ** 61.4** 15.** ** 44.6** 49.** 47.5** 88.2** 111.6** 63.6** SD CV 2 4.1* 12.6** * 22.5** 9.8** * 4.3* 2. Swathing time (ST) ** 622.9** 263.2** 384.6** 91.3** 67.9** 685.1** 329.7** 24.** 275.7** 12.9**** SD ST 8 5.9** 9.9** 9.5** 7.5** 13.** 9.** 9.5** 5.3** 3.* 4.3**.3 CV ST 16 3.** 2.4* ** 3.4** 4.9** **.6 1.** SD CV ST * 2.3* 7.8** * ** Error mean square E E E E Seeding date (SD) 1 5.9** 17.4** ** 14.4** 41.** ** ** 8.1 Cultivar (CV) ** 16.4** 14.7** 36.** 6.** 77.2** 86.9** 79.4** 64.7** 157.3**.5 SD CV ** 4.8* ** 5.6* 7.1** 9.5** 2.2 Swathing time (ST) ** 186.** 354.6** 981.3** ** ** ** 785.** 922.5** 718.** 4.3** SD ST 8 3.9** 7.2** ** 16.8** 14.** 3.* * CV ST ** 21.3** 8.1** 27.** 4.5** 35.9** 35.5** 18.** 2.2** 15.2**.5 SD CV ST ** * Error mean square 72 16E E E E z E -6, E -5 : multiplied by 1 6 or 1 5, respectively. *,** F value significant at P.5 and P.1, respectively.

12 24 CANADIAN JOURNAL OF PLANT SCIENCE Myristic (C14:) Palmitic (C16:) Palmitoleic (C16:1) Seed oil fatty acid synthesis (mg 1 seeds) y = -1E-7x 2 + 5E-5x +.67 R 2 =.99** Stearic (C18:) y = -4E-6x E-4x R 2 =.99** Linolenic (C18:3) y = - 3E-5x E-4x R 2 =.99** Behenic (C22:) y = - 8E-7x 2 + 3E-4x +.44 R 2 =.99** y = -1E-5x E-4x R 2 =.99** Oleic (C18:1) y = - 2E-x 2 +.5x R 2 =.99** Arachidic (C2:) y = -1E-6x 2 + 5E-4x +.85 R 2 =.99** Erucic (C22:1) 4 y = -5E-4x +.51 R 2 =.96** y = -6E-7x 2 + 2E-4x +.37 R 2 =.99** Linoleic (C18:2) y = - 5E-5x x R 2 =.99** Eicosenoic (C2:1) y = - 4E-6x 2 +1E-3x+ 2.2 R 2 =.98** Fig. 8. The effect of seed moisture content at swathing on canola seed oil fatty acid synthesis in, 2 and 21 (combined data of two seeding dates and three cultivars) Mean 2 oped. In most cases, the fatty acid composition of the canola seed oil stabilized near 3 g kg 1 seed moisture. The proportional decline observed in most fatty acids was offset by the progressive increase of seed weight (Fig. 4) and oil content (Fig. 6), rendering an overall increased amount (mg 1 seeds 1 ) of synthesized fatty acids as seeds developed (Table 5, Fig. 8). As with oil, the dry year of 21 resulted in the highest production for most fatty acids, while had the lowest values. High temperatures during seed development are known to favor a higher content of saturated and monounsaturated fatty acids (Deng and Scarth ). This was evident in the 21 values of C14:, C16:, C18: and C2:, but also of C16:1 and C18:1. Erucic acid (C22:1) showed the largest yearly variability. Norton and Harris (1983), in a high-erucic acid (ca. 5 %) oilseed rape (B. napus L.) cultivar, observed an increasing proportion of erucic and eicosenoic acids, while the proportion of other less abundant fatty acids decreased during seed

13 VERA ET AL. EFFECT OF SWATHING ON CANOLA SEED 25 development. This finding agrees with our study in that the proportion of the most abundant fatty acid (oleic) in the cultivars studied tended to increase, while that of most other fatty acids tended to decrease with seed development. This pattern was also observed by Rakow and McGregor (1975), in that the proportion of linolenic acid increased in a high (2%) linolenic acid rapeseed (B. napus L.) line, but decreased in a low (5%) linolenic acid line, as seeds developed. Results similar to the present study were also found by Fowler and Downey (197) when studying changes in fatty acid composition and total fatty acid synthesis in a zero-erucic acid line and a medium-erucic acid (3%) cultivar of summer rapeseed (B. napus L.), although they started taking measurements 7 d after pollination, while in the present study the first swathing time took place approximately 3 to 4 wk after flowering, depending on the cultivar and year. CONCLUSIONS This study confirms present recommendations that the best seed yield potential for canola is achieved by seeding early and swathing near physiological maturity, when seed moisture approached 4 g kg 1. Early seeding was more conducive to achieving higher seed yield, especially in good growing conditions, and resulted in heavier mature seeds with higher oil content. Premature swathing, especially in a year with good growing conditions such as 2, led to seed yield and seed weight reduction rates of up to 7 kg ha 1 and.48 mg seed 1 per g kg 1 seed moisture, respectively. It also compromised seed quality. Similarly, reductions in seed protein and seed oil were observed when swathing took place before 2 and 3 g kg 1 seed moisture, respectively. Seed oil fatty acids also tended to stabilize near the end of seed development (3 g kg 1 seed moisture), strengthening the argument in favor of delaying swathing to near complete seed maturity. Finally, when the maturing canola crop was left standing and direct combined it occasionally suffered substantial yield losses due to shattering, especially when windy weather conditions occurred near harvest. However, when planning the harvest of large seeded areas or when facing unfavorable weather forecasts, canola growers may need to make some compromises, as they decide on an optimum swathing time for their particular conditions, in order to secure near maximum seed yield and quality. ACKNOWLEDGMENTS We gratefully acknowledge Glenn Moskal, Colleen Nielsen, Ken McJuray, Sheldon Stobbs, Dawnne Campbell and Gerald Serblowski for technical support. We also recognize Ralph Underwood for final preparation of graphs, and Drs. Randy Kutcher and Kabal Gill for internal review of the manuscript. Anonymous Guide to farm practice in Saskatchewan. The University of Saskatchewan Division of Extension and Community Relations,. Saskatoon, SK. pp. 54. Anonymous. b. Oil content of oilseeds by nuclear magnetic resonance (method revised in 2). In D. Firestone, ed. Official methods and recommended practices of the AOCS. 5th ed. American Oil Chemists Society, Champaign, IL. Anonymous. c. Determination of fatty acids in edible oils and fat by capillary GLC (method revised in 21). In D. Firestone, ed. Official methods and recommended practices of the AOCS. 5th ed. American Oil Chemists Society, Champaign, IL. Anonymous. 21. Time of swathing trial. Canola Production Centre. Annual Report. Canola Council of Canada, Winnipeg, MB. pp Anonymous. 22. Time of swathing trial. Canola Production Centre. Annual Report. Canola Council of Canada, Winnipeg, MB. pp Bowren, K. E. and Kirkland, K. J Rapeseed, when to swath? Research communication pamphlet. Prepared for the Saskatchewan Rapeseed Growers Association. 2 pp. Brown, J., Davis, J. B., Erickson, D. A. and Brown, A. P Effects of swathing on yield and quality of canola in northern Idaho. J. Prod. 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14 26 CANADIAN JOURNAL OF PLANT SCIENCE SAS Institute, Inc. 24. SAS OnlineDoc, Version 8, SAS Institute Inc., Cary, NC. [Online] Available: com/documentation/ [26 Mar.17]. Statistics Canada November estimate of the 1999 production of principal field crops, Canada. Field Crop Reporting Series (8): 8. Thomas, P. 23. Canola growers manual. Canola Council of Canada. Winnipeg, MB. Thomas, D. L., Breve, M. A., Raymer, P. L Influence of timing and method of harvest on rapeseed yield. J. Prod. Agric. 4: Ward, K., Scarth, R., Daun, J. and Vessey, J. K Chlorophyll degradation in summer oilseed rape and summer turnip rape during seed ripening. Can. J. Plant Sci. 75: