Response of mustard to fertilization, seeding date, and seeding rate in southern Alberta

Transcription

1 Response of mustard to fertilization, seeding date, and seeding rate in southern Alberta R. H. McKenzie 1, A. B. Middleton 1, and E. Bremer 2 1 Crop Diversification Division, Alberta Agriculture, Food and Rural Development, Lethbridge, Alberta, Canada T1J 4V6 (ross.mckenzie@gov.ab.ca); and 2 Symbio Ag Consulting, Lethbridge, Alberta, Canada T1K 2B5. Received 22 October 2004, accepted 19 October McKenzie, R. H., Middleton, A. B. and Bremer, E Response of mustard to fertilization, seeding date, and seeding rate in southern Alberta. Can. J. Plant Sci. 86: Yellow mustard (Sinapsis alba L.), brown mustard (Brassica juncea L.), and oriental mustard (B. juncea) have been grown in Alberta since the 1950s, but limited agronomic information specific for this crop is available. The objective of this study was to determine the response of mustard to fertilization, seeding date and seeding rate in southern Alberta. Field experiments were conducted at 20 field sites over a 4-yr period ( ) under irrigated and dryland (fallow and stubble) conditions. Five experiments were conducted with the following treatments: (1) N fertilizer rate (0, 30, 60, 90 and 120 kg N ha 1 ), (2) urea placement (seed-placed and side-banded urea at rates of 0 to 120 kg N ha 1 ), (3) P fertilizer rate (0, 6.5, and 13.1 kg P ha 1 ), (4) S fertilizer rate (0, 10 and 20 kg S ha 1 ), and (5) seeding date (three dates at approximately 10-d intervals) and seeding rate (target plant densities of 75, 125, 175, 225, and 300 plants m 2 ). Experiment 1 was conducted with yellow mustard (AC Pennant), oriental mustard (Forge), brown mustard (Commercial Brown) and canola (Q2) (Brassica napus L.), while the remaining experiments were only conducted with yellow mustard. For maximum seed yield, mustard required 95 kg of available N Mg 1 of potential seed yield. Potential yields were closely related to available moisture, increasing 7 to 8 kg ha 1 for every mm increase in available moisture above a minimum moisture requirement of 90 mm. Seed-placed urea reduced plant stand at rates as low as 30 kg N ha 1 and reduced seed yield at rates of 60 to 120 kg N ha 1. Fourteen of 20 sites had a greater than 3% positive yield benefit due to P fertilizer. Mustard did not benefit from S fertilizer application. Delay in seeding by 3 4 wk, compared with seeding in late April to mid-may, reduced seed yield of yellow mustard by an average of 37%. Seed yield increased with seeding rate, but the maximum gain in seed yield due to high seeding rates was only 200 kg ha 1, with significant increases obtained only under very dry conditions. Early seeding and adequate N fertility were the most important agronomic practices for achieving high yields of mustard in southern Alberta. Key words: Sinapsis alba, Brassica juncea, yield, oil, nitrogen, phosphorus, sulfur, water-use efficiency McKenzie, R. H., Middleton, A. B. et Bremer, E Réaction de la moutarde à la fertilisation, à la date des semis et à la densité du semis dans le sud de l Alberta. Can. J. Plant Sci. 86: Bien qu on cultive la moutarde jaune (Sinapsis alba L.), la moutarde brune (Brassica juncea L.) et la moutarde chinoise (B. juncea) depuis les années 1950 en Alberta, on manque de données agronomiques sur cette culture. La présente étude devait établir la réaction de la moutarde à la fertilisation, à la date des semis et à la densité du semis dans le sud de l Alberta. Les expériences se sont déroulées à 20 endroits au cours d une période de quatre ans (de 1999 à 2002), sur des terrains irrigués ou pas (sur jachère et sur chaume). Les auteurs ont procédé aux cinq expériences que voici : 1) amendement azoté (0, 30, 60, 90 et 120 kg de N par hectare), 2) placement d urée (avec la semence et en bande latérale, à raison de 0 à 120 kg de N par hectare), 3) amendement phosphaté (0, 6,5 et 13,1 kg de P par hectare), 4) amendement soufré (0, 10 et 20 kg de S par hectare) et 5) date des semis (3 dates à 10 jours d intervalle environ) et densité du semis (densité ciblée de 75, 125, 175, 225 et 300 plants par m 2 ). La première expérience portait sur la moutarde jaune (AC Pennant), la moutarde chinoise (Forge), la moutarde brune (brune commerciale) et le canola (Q2) (Brassica napus L.). Les autres ne portaient que sur la moutarde jaune. Pour donner un rendement grainier optimal, la moutarde a besoin de 95 kg de N disponible par Mg de rendement potentiel. Le rendement potentiel présente une étroite corrélation avec la quantité d eau disponible et progresse de 7 ou 8 kg par hectare pour chaque millimètre supplémentaire d eau disponible au-dessus du minimum requis (90 mm). Le placement d urée avec la semence diminue la densité de peuplement même à un taux aussi faible que 30 kg de N par hectare; il réduit le rendement grainier dès le taux de 60 à 120 kg de N par hectare. L addition d engrais P a augmenté le rendement de plus de 3 % à 14 endroits sur vingt. L engrais soufré n a aucun effet sur la moutarde. Quand les semis sont retardés de trois ou quatre semaines plutôt que d avoir lieu à la fin d avril ou à la mi-mai, le rendement grainier de la moutarde jaune baisse d en moyenne 37 %. Le rendement grainier augmente avec la densité du semis, mais le gain attribuable à ce facteur ne dépasse pas 200 kg par hectare et les hausses ne s observent que par temps très sec. Des semis hâtifs et un amendement azoté suffisant sont les pratiques agricoles les plus importantes dans le sud de l Alberta pour garantir un rendement élevé de la moutarde. Mots clés: Sinapsis alba, Brassica juncea, rendement, huile, azote, phosphore, soufre, efficacité d utilisation de l eau Three types of mustard have been grown in Alberta since the 1950s: yellow, brown, and oriental. Most production is processed into condiments and mustard flour. Since 2002, 353 varieties of B. juncea that produce canola-quality oil have also been available, and considerable expansion of this crop is expected. Currently in Alberta, to ha of

2 354 CANADIAN JOURNAL OF PLANT SCIENCE mustard are grown each year, with average yields ranging from 400 to 1400 kg ha 1 (Alberta Agriculture Food and Rural Development 2004). Very little agronomic research specific for mustard production has been conducted in western Canada. Recommended seeding and fertilization practices are frequently based on research conducted on the two established canola species, B. napus L. and B. rapa L. Agronomic research specific for mustard production is desirable because differences among species may be significant, and mustard is typically grown in warmer drier regions than canola (Brandt 1992). Grant and Bailey (1993) provide an extensive review of fertility management for canola. Up to 200 kg N ha 1 may be required for maximum yields under favorable growing conditions with low levels of available soil N, although moisture generally limits yield and N requirements under dryland conditions. Canola is very sensitive to seed-placed N, particularly ammonium forms. Compared with cereals, canola requires relatively large amounts of P for growth (11 kg P Mg 1 ), but often attains maximum yield at low rates of P fertilizer addition because it is extremely efficient at acquiring P from soil and applied fertilizer. Responses of canola to K fertilizer are rare in western Canada due to efficient uptake, mobility of K within the plant, and high levels of exchangeable K in most soils. Canola has a much higher S requirement than cereals (15 kg S Mg 1 ), and frequently responds to S addition on sites where no S response occurs for cereals. Fertilizer requirements are generally assumed to be similar for mustard and canola. Previous agronomic research has shown that mustard should be seeded early for high yields. In a study conducted on a Dark Brown Chernozem in Saskatchewan, seeding of yellow mustard between May 01 and May 26 had only a small impact on yields in most years, but further delays decreased yields substantially (Brandt 1992). In a 4-yr study conducted on an Orthic Brown Chernozem at Swift Current, SK, seed yields of canola and mustard were highest or close to highest when seeded in late April, compared with seeding in fall or late May (Angadi et al. 2004). Yield benefits of early seeding are primarily due to reduced heat stress during flowering (Morrison and Stewart 2002; Angadi et al. 2004). A seeding rate of 4 kg ha 1 reduced yellow mustard yield compared with seeding rates of 8, 12 or 16 kg ha 1 (Brandt 1992). Seedling emergence varied considerably from year to year due to the requirement for shallow seeding and the corresponding sensitivity to environmental and soil conditions. Variable results have been observed for optimum seeding rate of canola. For example, Morrison et al. (1990) achieved maximum yields with 1.5 and 3.0 kg ha 1 seeding rate, while Clarke and Simpson (1978) achieved maximum yield with a seeding rate of 20 kg ha 1 under dryland conditions and 5 to 10 kg ha 1 under irrigated conditions. In a study with canola conducted at Swift Current, SK, yield levels were similar across a wide range of plant densities (20 to 80 plants m 2 ) in a year with slightly above-normal growing season precipitation, but declined as plant densities dropped below 40 plants m 2 in a year with well below normal precipitation (Angadi et al. 2003). Sufficient available water may be required for compensation of low plant densities by increased plant growth (Morrison et al. 1990). To optimize mustard production practices, growers require reliable information on the probability and magnitude of the response of mustard to agronomic practices. The objective of this study was to determine the relationship of mustard yield and oil content to fertilization, seeding date and seeding rate in southern Alberta. MATERIALS AND METHODS Field experiments were completed at 20 sites on Brown and Dark Brown Chernozemic soils in southern Alberta from 1999 to 2002 (Table 1). Experiments were also completed at 2 other sites, but these were excluded from the results because of poor crop growth caused by herbicides that persisted through 2 previous years of drought. One irrigated site was included each year, with the remainder under dryland conditions on cereal stubble or summerfallow. The dryland sites at Lethbridge in 2001 and 2002 were irrigated in the fall to ensure adequate moisture reserves for crop growth, but were not irrigated during crop growth. Except in 1999, most sites had been under minimum tillage for at least 5 yr and had not been tilled during the summerfallow period (chem fallow). Five experiments were conducted in this study. Experiments 1, 3 and 4 were conducted at all sites, exp. 2 was conducted at all sites in 2000 and 2001 and three sites in 2002, and exp. 5 was conducted at three sites in 2000 and all sites in 2002 and Experiment 1 The effect of N fertilizer rate was determined for one cultivar of each mustard type grown in southern Alberta: AC Pennant (yellow mustard), Forge (oriental mustard) and Commercial Brown (brown mustard). A canola cultivar, Q2, was also included in these trials. Urea (46-0-0) was banded at rates of 0, 30, 60, 90, and 120 kg N ha 1. At most sites, urea was applied in the fall. Triple superphosphate (0-45-0) was seed-placed in all plots at 13.1 kg P ha 1. Plots were arranged in a split-plot design with three replicates, mustard type as main plot treatment arranged in a randomized complete block design, and N rate as subplot treatment. However, due to seeding logistics, main plot treatments were not randomized between blocks 2 and 3. Experiment 2 The effect of urea placement was determined for AC Pennant. Urea was seed-placed and side-banded at the time of seeding at rates of 0, 30, 60, 90 and 120 kg N ha 1. An air seeder equipped with stealth (hoe type) openers was used to seed this experiment. The fertilizer band was placed 40 mm beside and 40 mm below the seed. Triple superphosphate (0-45-0) was seed-placed in all plots at 13.1 kg P ha 1. Plots were arranged in a split-plot design with three replicates, urea placement as main plot treatment arranged in a randomized complete block design, and N rate as subplot treatment. Main plot treatments were not randomized between blocks 2 and 3. Experiment 3 The effect of P fertilizer rate was determined for AC Pennant. Monoammonium phosphate ( ) was applied with the seed at rates of 0, 6.5, and 13.1 kg P ha 1. All plots

3 MCKENZIE ET AL. MUSTARD AGRONOMY 355 Table 1. Site characteristics Extractable soil nutrients (kg ha 1 ) v Precipitation Site Site history Seeding & irrigation 0 to 0.15 m 0 to 0.6 m no. Year Location Management Soil Irrigation Tillage y Fallow date x mm (% w ) ph N P K S N S Bow Island Irrigated Chin L z Yes Conv. None 14-Jun 260(NA) Bow Island Fallow Chin L No Min. 50% 14-Jun 187(99) Milk River Fallow Masinasin L No Conv. 50% 14-Jun 152(72) Milk River Stubble Masinasin L No Conv. 50% 14-Jun 152(72) Stirling Stubble Lethbridge CL No Conv. None 15-Jun 226(108) Bow Island Fallow Chin L No Min. 50% 28-Apr 79(42) Lethbridge Stubble Lethbridge CL Yes Min. None 27-Apr 185(87) Lethbridge Irrigated Lethbridge CL Yes Min. None 27-Apr 347(NA) Milk River Stubble Masinasin L No Conv. 50% 28-Apr 86(41) Carmangay Fallow Lethbridge CL No Min. 50% 2-May 67(29) Carmangay Stubble Lethbridge CL No Min. 50% 2-May 67(29) Lethbridge Stubble Lethbridge CL Yes Min. None 26-Apr 60(28) Lethbridge Irrigated Lethbridge CL Yes Min. None 26-Apr 347(NA) Warner Fallow Masinasin L No Min. 50% 28-Apr 93(44) Warner Stubble Masinasin L No Min. 50% 28-Apr 93(44) Carmangay Fallow Lethbridge CL No Min. 50% 14-May 331(140) Carmangay Stubble Lethbridge CL No Min. 50% 14-May 331(140) Lethbridge Stubble Lethbridge CL Yes Min. None 12-May 386(181) Lethbridge Irrigated Lethbridge CL Yes Min. None 12-May 397(NA) Warner Fallow Masinasin/Cranford L No Min. 50% 12-May 378(180) z L = loam, CL = clay loam. y Conv. = conventional tillage, Min. = minimum tillage x Seeding date for experiments 1, 3 and 4 and first seeding date for experiment 5. w Percent of long-term precipitation (May 01 Aug. 31) normals obtained from the nearest Environment Canada meteorological station. v Assumed bulk density of 1333 kg m 3 (i.e., 2 million kg per 0.15 m depth); N = NO3 -N, S = SO 4 -S.

4 356 CANADIAN JOURNAL OF PLANT SCIENCE were fertilized with urea at the recommended rate of N for each site, which ranged from 30 to 80 kg N ha 1. Plots were arranged in a randomized complete block design with five replicates. Experiment 4 The effect of S fertilizer rate was determined for AC Pennant. Ammonium sulfate ( ) was banded in the fall at rates of 0, 10 and 20 kg S ha 1. All plots were fertilized with the recommended rate of N and 13.1 kg P ha 1. Plots were arranged in a randomized complete block design with five replicates. Experiment 5 The effects of three seeding dates and five seeding rates were determined for AC Pennant. The first seeding date was the same as previous experiments and was completed in the period from late April to mid-may (Table 1). Second and third seeding dates were approximately 10 and 20 d after the first date, depending on weather conditions. At each date, AC Pennant was seeded at rates to provide target plant densities of 75, 125, 175, 225, and 275 plants m 2. All plots were fertilized with the recommended rate of N and 13.1 kg P ha 1. Plots were arranged in a split-plot design with three replicates, seeding date as main plot treatment arranged in a randomized complete block design, and seeding rate as subplot treatment. Main plot treatments were not randomized between blocks 2 and 3. Soil samples were obtained in late fall at all sites except site 2, which was sampled in early April. Five soil cores (50 mm) were obtained at each site and combined for sample depths of 0 to 0.15 m, 0.15 to 0.3 m, 0.3 to 0.6 m, and 0.6 to 0.9 m. Samples were air-dried and ground to pass a 2-mm sieve. Surface (0 to 0.15 m) samples were analyzed for soil ph (water) (Hendershot et al. 1993) and available P and K (modified Kelowna method, 0.15 M NH4F 0.25 M CH3COONH M CH3COOH) (Ashworth and Mrazek 1995). All soil samples were analyzed for nitrate and sulfate (0.01 M CaCl2) (Bettany and Halstead 1972). Precipitation from seeding till harvest was obtained using automated rain gauges (Tipping Bucket, Davis, CA) at each location. Soil moisture depletion over the growing season was determined gravimetrically to a depth of 0.9 m in four replicate plots of AC Pennant fertilized with 120 kg N ha 1 and 13 kg P ha 1. To avoid serious weed problems, Edge (ethalfluralin) was broadcast in the fall at recommended rates and, in 1999 only, incorporated with two passes of a cultivator and harrow. If required during the growing season, Poast (sethoxydim) was applied to control grassy weeds and Decis (deltamethrin) was applied to control flea beetle and cabbage seedpod weevil infestations. Mustard seed was obtained from the same commercial source for all sites each year and seeded at a target plant density of 175 seeds m 2, based on seed size, pre-seed germination and estimated field emergence rate of 95%. Each plot contained 10 rows, with the two outer rows planted to winter wheat. Row spacing was 178 mm and plot length was 7 m. A small plot seeder equipped with hoe openers was used for seeding in Due to poor soil to seed contact, crop emergence was very poor after the first seeding, thus all plots were reseeded in mid-june. The small plot seeder was equipped with no-till disc openers in subsequent years. After crop emergence, plant stand was determined by counting all plants in two 1 m 2 row areas in each plot. At maturity, whole plots were harvested with a small plot combine. Seed protein contents were determined by near infrared spectroscopy (Marten et al. 1989). The ratio of protein to N was assumed to be Seed P contents were determined by Technicon Industrial Method A. Seed S and oil contents were determined with methods published by the Association of Official Analytical Chemists (Helrich 1990). All yields and contents are reported on a dry weight basis. Data from all experiments at each site were analyzed with the Proc Mixed procedure of SAS (Release 8.01, SAS Institute, Inc., Cary, NC), with blocks as a random effect and treatments as fixed effects. The single constraint on randomization in exps. 1, 2 and 5 (main plots not randomized between blocks 2 and 3) was not modeled because no confounding trends in measured parameters across these blocks were evident. Determination of the N fertilizer response for all sites was conducted as follows: (1) Potential seed yield (Y pot ) at each site for all crop types was determined by averaging all N rate means that were not significantly less than the maximum. A weak test (P = 0.20, Dunnett s procedure) was used to ensure that means used to estimate Y pot were not less than potential yield. (2) Available soil N at each site was determined by dividing seed NY 0 (seed N yield at 0 kg N ha 1 ) (average of all crop types) by 0.58 (based on efficiency of conversion of fertilizer N to seed N determined at nine N-deficient sites). This method may underestimate available soil N at sites with low N deficiency because the efficiency of conversion of available N to seed N may be lower than (3) The amount of N available per unit of potential yield (available N ratio, or ANR), was calculated for all N rates and crop types at each site: ANR = (available soil N + fertilizer N)/Ypot (4) The relationship of relative yield (RY) to ANR was determined over all sites for each cultivar separately and for all cultivars combined using Proc NLIN (Release 8.01, SAS Institute, Inc., Cary, NC): RY = ANR / (a ANR + b) [ANR ANR max ] RY = 100 [ANR > ANR max ] ANR max = b/(a 0.01) Regression coefficients were compared among crop types using approximate confidence limits calculated by Proc NLIN. For exps. 2 and 5, a combined analysis was performed for very dry (average seed yield < 500 kg ha 1 ), dry (average seed yield between 500 and 1500 kg ha 1 ) and wet sites (average seed yield > 1500 kg ha 1 ). Data were transformed

5 MCKENZIE ET AL. MUSTARD AGRONOMY 357 Fig. 1. Seed yield of fertilized yellow mustard as a function of water use (sum of precipitation + soil water depletion to a depth of 0.9 m). Values are the mean from each site. Table 2. Proportion of sites with significant (P < 0.05) treatment effects Plant Seed Oil Protein Expt. Treatment stand yield content content Percent of sites 1 Crop type N rate Crop N Placement N rate Place N P rate ND z S rate ND Seeding date Seeding rate Date Rate z ND, not determined. if required to ensure homogeneity of variances. Treatment means were compared with contrasts or Tukey-Kramer tests. Treatment effects were considered statistically significant at P RESULTS AND DISCUSSION Growing Season Precipitation and Water Use Growing season precipitation ranged widely from year to year in this study (Table 1). Growing season precipitation was near normal in 1999, less than 50% of normal rates at all dryland sites in 2000 and 2001 except one site (7) that received a low rate of supplemental irrigation, and well above normal in Seed yield of fertilized AC Pennant was closely related to water use (Fig. 1). Above a minimum of 91 mm of water, seed yield increased by 8.1 kg ha 1 mm 1. The minimum amount of water to establish seed yield was less than that reported for canola or B. juncea in Saskatchewan (121 to 161 mm), while water use efficiency above this minimum was slightly higher than values reported in Saskatchewan (6.9 to 7.6 kg ha 1 mm 1 ) (Johnston et al. 2002). Nitrogen Fertilizer Response Nitrogen fertilizer had a significant effect on seed yield at 70% of the sites tested in exp. 1 (Table 2). The increase in seed yield due to N fertilizer application ranged from 10 to 367% among sites, while the amount of N fertilizer required to achieve potential yield ranged from 0 to 160 kg N ha 1 (data not presented). In general, seed yields were not significantly different among the highest rates of N fertilizer; negative effects of high rates of N fertilizer were only observed at one site (data not presented). The wide range in N fertilizer response among sites was due to large differences in yield potential and available soil N. Potential yields ranged from 100 to 600 kg ha 1 at sites with less than 160 mm of available moisture to 2100 to 4100 kg ha 1 at sites with more than 380 mm of available moisture (excluding brown mustard at two wet sites with low Y pot ) (Fig. 2). Canola Y pot was frequently less than that of mustard, particularly at sites with intermediate levels of available moisture (Fig. 2; statistics not presented). Mustard is generally considered to be more drought and heat tolerant than canola (Woods et al. 1991). Low canola yields were also partly due to the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull), which caused extensive damage despite one or two applications of insecticide. In comparison, yellow mustard is resistant and brown and oriental mustard are tolerant to the cabbage seedpod weevil (Brown et al. 1999). Estimates of available soil N based on unfertilized crop N yields ranged from 17 to 231 kg N ha 1 in this study. Values were not correlated with soil test NO 3 -N (Fig. 3). Mineralization of soil N or uptake of available soil N from below the depth of soil test NO 3 -N measurement was appreciable at most sites, as indicated by the difference between crop-determined estimates of available soil N and soil test

6 358 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 2. Potential seed yield of mustard and canola varieties as affected by available moisture. Values are means from each site. Available moisture for all varieties was assumed equal to water use of fertilized yellow mustard (see Fig. 1). NO 3 -N. For example, crop-determined estimates of available soil N were 74 to 202 kg N ha 1 greater than soil test NO 3 -N at Lethbridge sites (Fig. 3). Less than 10 kg soil test NO 3 -N ha 1 was present in the 0.6 to 0.9 m depth at these sites (data not presented), indicating that most of the difference was likely due to N mineralization. Deviations of crop-determined estimates of available soil N from soil test NO 3 -N may also occur due to incomplete uptake of available N (particularly under drought conditions), losses of available N due to volatilization, denitrification or leaching, or the presence of high levels of ammonium N. Inconsistency in the predictive value of soil test NO 3 -N may be largely due to variations in weather: studies conducted in or after years of extremely low or high growing season precipitation (this study; McKenzie et al. 2005) had a much poorer correlation between unfertilized N uptake and soil test NO 3 -N than studies conducted in or after years of normal growing season precipitation (McKenzie et al. 2004a, b). The response of three types of mustard and one variety of canola to N fertilizer was adequately described (R 2 = 0.69) when relative yields were expressed as a function of the amount of N available per Mg of potential yield (ANR) (Fig. 4a). Potential yields of mustard and canola varieties were achieved when ANR exceeded 95 kg Mg 1 (range 60 to 120 kg N Mg 1 ). Differences among crop types were not significant. Oil content decreased linearly with increasing ANR (Fig. 4b). Oil content was highest for canola and least for yellow mustard. The relationship between relative yield and ANR can be used to predict optimum N fertilizer rate if potential yield and available soil N can be predicted. The best predictor of potential yield is available moisture, which may be estimated from measurement of available spring soil moisture and historical records of growing season precipitation. The best predictor of available soil N likely remains soil test NO3-N, but mineralization of soil N must be included as a source of available N. Optimization of N fertilizer rates will require an assessment of the impact of uncertainty in predictions of potential yield and available soil N. Placement of urea with the seed rather than to the side significantly reduced yield at 60, 90, and 120 kg N ha 1 at very dry sites, 90 kg N ha 1 at dry sites and 120 kg N ha 1 at wet sites (Fig. 5). Application of as little as 30 kg N ha 1 with the seed significantly reduced plant stand at several sites (data not presented). As with canola, seed-placed N for mustard should be restricted to the N applied with ammonium phosphate fertilizer (Grant and Bailey 1993). Phosphorus and Sulfur Fertilization Phosphorus fertilizer significantly increased seed yield of yellow mustard at 2 of 20 sites (Table 2). The median increase in seed yield at all sites was 5% (data not presented), with 14 of 20 sites having a greater than 3% positive yield benefit due to P fertilizer. Oil and protein concentrations were unaffected by P fertilizer addition. Seed P concentrations ranged from 5.2 to 8.8 mg g 1 (mean = 7.1) and were only significantly increased by P fertilizer application at one site. Soil test P (modified Kelowna method, 0 to 0.15 m) ranged from 11 to 189 kg ha 1 (Table 1), but was not correlated with yield response. The small yield benefit of P fertilizer for yellow mustard was consistent with previous studies. In studies conducted in the Brown and Dark Brown soil zones in the early 1990s, P fertilizer significantly increased canola yields at 39% of sites tested, and provided an average yield benefit of 8% (McKenzie et al. 2003). The slightly smaller benefit of P fertilizer in the present study was attributed to the poor moisture conditions at many of the sites in this study.

7 MCKENZIE ET AL. MUSTARD AGRONOMY 359 Fig. 3. Relationship of crop-determined estimates of available soil N (NY 0 /0.58) with fall-determined soil NO 3 -N. Sites labelled with an L were located at Lethbridge. Fig. 4. Effect of available N ratio (ANR) on (a) relative yield and (b) oil content. Values are means from each cultivar at each site. Means with a coefficient of variation > 20% were excluded.

8 360 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 5. Effect of rate and placement of urea on yellow mustard yield at very dry, dry and wet sites. Values marked with an asterisk are significantly higher than seed-placed value at the same rate of urea application. Fig. 6. Effect of seeding date on relative seed yield of yellow mustard. Values are means from each site, averaged across seeding rates. Values marked with an asterisk are significantly (P < 0.05) less than value from first seeding date. Addition of S fertilizer did not affect oil or protein contents, and only affected seed yield at one site (Table 2). At the one site with a significant response to S fertilizer, seed yield was reduced at the high rate of S addition. Sulfur fertilizer rarely increases crop yields in southern Alberta, even though soil SO 4 -S is occasionally quite low in the surface 0.15 m (<10 kg S ha 1 ) (McKenzie et al. 2004a, b, 2005). Sufficient SO 4 -S is generally available from lower depths or mineralization of soil organic matter (Bole and Pittman 1984). Seeding Date and Rate Delayed seeding reduced seed yield, often substantially (Fig. 6). Seed yields were reduced when seeding dates were delayed by as little as 7 to 10 d, although the yield penalty varied from year to year, depending on weather conditions. In 2000, yield reductions due to delayed seeding were significant at all sites at the third seeding date, but were not significant at the second seeding date. In 2001, yield reductions were significant at both the second and third seeding dates at most sites. On average, yields were reduced 40% at the third seeding date compared with the first seeding date in 2000 and In 2002, yields at the third seeding date were reduced by 18% at three sites, but were reduced by 64% at the fourth site. The yield benefits of early seeding in this study were similar to those obtained for canola and mustard in southwestern Saskatchewan ( ) (Angadi et al. 2004). This study supports the conclusion of Angadi et al. (2004) that mustard should be seeded as early as practical in this region. High seeding rates increased plant stand (Table 3). On average, 40% of the seeds planted produced a plant. The maximum yield difference among seeding rates was 176 kg ha 1, with a significantly lower yield at the lowest seeding

9 MCKENZIE ET AL. MUSTARD AGRONOMY 361 Table 3. Effect of seeding rate on plant stand and seed yield of yellow mustard at very dry, dry and wet sites Actual density (plants m 2 ) Seed yield (kg ha 1 ) Target density Very dry Dry sites Wet sites Very dry Dry sites Wet sites (plants m 2 ) sites (n = 4) (n = 3) (n = 4) sites (n = 4) (n = 3) (n = 4) 75 28a 32b 39d 475b 1165a 2510a a 50b 57cd 544ab 1246a 2686a b 75ab 78bc 570ab 1255a 2680a b 96a 104ab 587a 1314a 2649a b 110a 113a 597a 1388a 2672a a d Values within a column followed by the same letter are not significantly different (P 0.05, Tukey-Kramer test). rate at very dry sites (Table 3). Differences among all other seeding rates were not significant. The sufficiency of 125 seeds m 2 in this study (approximately 8 kg ha 1 ) for maximum yield in this study was similar to that reported by Brandt (1992). Seeding date affected oil and protein contents at more than half of the sites tested (Table 2). On average, delayed seeding reduced oil content by 15 mg g 1 and increased protein content by 12 mg g 1. Seeding rate did not affect oil or protein content. CONCLUSIONS Fertilizer responses of mustard were similar to those of canola, but reflected the soil types and environmental conditions in southern Alberta, compared with more northerly areas where canola is typically grown. Potential yields were closely related to available moisture, increasing 7 to 8 kg ha 1 for every mm increase in available moisture above a minimum moisture requirement of 90 mm. To achieve potential yield, mustard required 95 kg of available N per Mg 1 of potential seed yield. Fourteen of 20 sites had a greater than 3% positive yield benefit due to P fertilizer, while S fertilizer did not affect yield. The other important practice affecting mustard yields was seeding date. Seed yields of yellow mustard were reduced by an average of 37%, when seeding was delayed by 3 4 wk, compared with seeding in late April to mid-may. ACKNOWLEDGMENTS The authors gratefully acknowledge the co-operators who kindly provided the land used in these trials and the Lethbridge field staff of Alberta Agriculture, Food and Rural Development for assistance in conducting the field trials. We would also like to thank the Agri-Food Laboratory Branch, Alberta Agriculture, Food and Rural Development, for soil analyses. Finally, we would like to thank the following organizations for funding this project: Alberta Agriculture Research Institute, Mustard Association, Agricore United, Agrium and Westco. Alberta Agriculture Food and Rural Development Alberta special crops Area, yield, production and price, [Online] Available: www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/sdd5291/$file/table95.pdf. Angadi, S. V., Cutforth, H. W., McConkey, B. 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