Published in Crop Sci. 44:2116-2122 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
CROP PHYSIOLOGY & METABOLISM
Yield Physiology of a Semidwarf and Tall Oat Cultivar
Pamela J. de Rocquignya,
Martin H. Entzb,*,
Roberta M. Gentileb and
Scott D. Duguidc
a Manitoba Agriculture, Food and Rural Initiatives, Soils and Crops Branch, Carman, MB, Canada R0G 0J0
b Dep. of Plant Science, Univ. of Manitoba, Winnipeg, MB, Canada R3T 2N2
c Agriculture and Agri-Food Canada, Morden Research Station, Morden, MB, Canada R6M 1Y5
* Corresponding author (m_entz{at}umanitoba.ca)
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ABSTRACT
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Oat (Avena sativa L.) production has increased dramatically in the eastern Canadian prairies. The introduction of semidwarf oat cultivars to this region has resulted in the need for research regarding how a semidwarf oat performs relative to conventional tall oat cultivars. Split-split plot experiments were conducted at three site–years during 1999 and 2000 in Manitoba to examine cultivar responses of ‘AC Ronald’, a short-stature oat, and ‘Triple Crown’, a tall oat, under different crop rotations (grain legume or oilseed as a previous crop) and N fertilizer rates. Triple Crown had greater (P < 0.05) dry matter production than AC Ronald at anthesis (two of three sites) and maturity (one of three sites). At two of three sites, Triple Crown also displayed higher (P < 0.05) early season plant N uptake than AC Ronald, and Triple Crown always had higher (P < 0.05) kernel weight. However, averaged across sites, AC Ronald yielded 433 kg ha–1 greater (P < 0.05) than Triple Crown. Higher yield for the short-statured cultivar was attributed to greater (P < 0.05) panicle and kernel densities, and better assimilate partitioning (i.e., higher harvest index). Both cultivars were susceptible to lodging; however, Ha significant cultivar x site interaction indicated that under some conditions, AC Ronald experienced less lodging than Triple Crown. No significant cultivar effect was observed for evapotranspiration (ET) or water use efficiency (WUE). Both oat cultivars responded similarly to crop rotation and N fertilizer rate. While the grain yield advantage of AC Ronald appeared stable across treatment environments tested here, some differential cultivar responses for kernels per panicle and lodging resistance across sites were observed. This research supports an expansion of semidwarf oat production in the eastern Canadian prairies.
Abbreviations: ET, evapotranspiration • WUE, water use efficiency
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INTRODUCTION
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OAT PRODUCTION has increased dramatically in the eastern Canadian prairies in recent years. Production for this region in 2002 was 2.07 million tonnes of oat grown on 1.01 million hectares of land (Manitoba Agriculture, Food and Rural Initiatives, 2002; Saskatchewan Agriculture, Food and Rural Revitalization, 2003). Several production issues face oat producers in this region, such as excess straw production and lodging, which may decrease grain yield and cause difficulties during harvest. Lodging is influenced by a variety of factors, including plant characteristics such as height, straw strength, and root anchorage, and environmental factors like N supply, soil moisture conditions, wind, and rainfall events (Pinthus, 1973).
Until recently, all oat cultivars available to Canadian oat producers were tall types. However, breeding efforts have resulted in AC Ronald, which is western Canada's first registered semidwarf oat cultivar. The pedigree for AC Ronald includes Dumont 68, Robert, and OT207. Brown et al. (1980) developed the semidwarf oat OT207 by selecting it from OT184 irradiated with fast neutrons. Dwarfing in OT207 is controlled by a single dominant gene designated Dw6, which results in shorter internodes. The semidwarf character in cereals is associated with increased yield through increased panicle production (Brinkman and Rho, 1984; Hamill, 2002), kernel production (Anderson and McLean, 1989; Hamill, 2002), harvest index (Pearman et al., 1978), and lodging resistance (Brown et al., 1980).
Soil water availability is a major factor limiting cereal grain production in western Canada (DeJong and Steppuhn, 1983). There has been no previous research comparing the ET and WUE of semidwarf and tall oat cultivars. In studies with wheat, Richards (1992) found no differences in consumptive water use between tall and dwarf cultivars, though Ehdaie and Waines (1996) observed tall wheat lines used an average of 7% more water than short lines. In examining the root growth of oat cultivars, MacKey (1988) found short-stature oat had shorter root lengths and a much lower proportion of root mass at deeper soil depths than a conventional-height cultivar. If the semidwarf character in oat has the potential to reduce root length and depth penetration, it may affect the water uptake and consumption of short cultivars.
Nitrogen management is important in oat production for yield optimization and lodging control (Brinkman and Rho, 1984; Marshall et al., 1987). Nitrogen directly influences yield by affecting the various yield components, such as panicle density and kernel number, as well as dry matter production and harvest index. The relative contribution of each yield component in response to increased N level will vary depending on the levels of N used and environmental conditions (Brinkman and Rho, 1984; Marshall et al., 1987; Anderson and McLean, 1989; Hamill, 2002). Hamill (2002) determined that a total N supply of 115 kg N ha–1 was optimum for maximum yield of oats in Manitoba and optimum N supply may differ between oat cultivars. While oat yield response to N fertilizer is well documented, there is limited information on the influence of organic N sources, such as rotational legume crops. The inclusion of a green manure legume in crop rotations can increase residual soil N levels and increase seasonal N availability to following crops (Badaruddin and Meyer, 1990; Stevenson and van Kessel, 1996).
The development of AC Ronald necessitates new research to investigate how the semidwarf cultivar performs relative to conventional oat cultivars, and how it responds to N fertilizer from both inorganic and organic sources. Therefore, the objective of this study was to compare the yield physiology of a semidwarf and tall oat cultivar under different N supply conditions. The main focus was to test cultivar effects and the stability of these effects across treatment environments. Triple Crown was selected for this study as a reference for yield performance of a typical conventional-height oat cultivar. In a previous comparison of oat cultivar performance across seven site–years in Manitoba, Triple Crown was shown to perform equivalent to conventional cultivars AC Assiniboia, AC Medallion, and CDC Boyer in terms of yield, yield components, and incidence of lodging (Hamill, 2002).
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MATERIALS AND METHODS
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Field experiments were conducted at the University of Manitoba field research stations at Carman, MB, in 1999 and 2000, and Winnipeg, MB, in 2000. The soil types for the three field sites were a Hochfeld fine sandy loam (coarse, loamy, mixed Udic Haplocryoll) at Carman in 1999, a Denham loam (fine, loamy/fine, mixed Udic Haplocryoll) at Carman in 2000, and a Riverdale silty clay (fine, silty clay, frigid Mollic Udifluvent) at Winnipeg in 2000. The experimental design was a split-split plot with previous crop as the main plot, oat cultivar as the subplot, and N fertilizer rate as the sub-subplot. Four replicates were used at all sites. The previous crop treatments included flax (Linum usitatissimum L. ‘NorLin’) and pea (Pisum sativum L. ‘Grande’). The two oat cultivars used were AC Ronald, a semidwarf cultivar, and Triple Crown, a tall cultivar. Nitrogen fertilizer treatments consisted of three N rates (0, 40, and 80 kg N ha–1) in 1999, and four N rates (0, 40, 80, and 120 kg N ha–1) in 2000. Sub-subplot sizes were 2 x 8 m at Carman and 2 x 6 m at Winnipeg.
Before flax and pea seeding, N fertilizer was broadcasted and incorporated at rates based on soil tests for each site and crop. Flax was seeded at a rate of 45 kg ha–1, and pea was seeded at a rate of 106 kg ha–1. Cell-Tech C liquid pea inoculant (Nitragin, Inc., Milwaukee, WI) was applied to the pea seed before seeding at a rate of 75 mL per 27 kg of seed. In-crop weed control in the flax and pea treatments was performed with 2.7 kg ha–1 bentazon [3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide]. The pea crop was soil incorporated at flowering by discing 2 to 3 times. Pea dry matter yield at soil incorporation was 6095 kg ha–1 at Carman in 1998, and pea yields for 1999 appeared comparable based on visual assessment. The flax crop was harvested for seed and yielded 1406 kg ha–1 at Carman in 1998, 1768 kg ha–1 at Carman in 1999, and 1611 kg ha–1 at Winnipeg in 1999.
The year following the pea and flax crops, the two oat cultivars were established in all experiments. Four soil samples were taken from each replicate in the spring 2 to 3 wk before oat seeding for nutrient analysis. Before seeding, sites were cultivated and harrowed to ensure an even seedbed. Trials were seeded with a Fabro no-till offset disc press drill (Swift Machinery Co., Swift Current, SK) with a cone seed distributor at a rate of 300 viable seeds m–2. Row spacing was 15 cm and seeding depth 5 cm. Phosphate fertilizer was banded with the seed at a rate of 13 kg P ha–1. Seeding dates were 17 May 1999 and 4 May 2000 at Carman, and 1 May 2000 at Winnipeg. One aluminum access tube was placed in the center of each sub-subplot receiving the 0 and 80 kg N ha–1 N fertilizer treatments immediately after seeding to allow for soil water measurements with a neutron moisture gauge.
The fertilizer treatments were applied at selected rates with ammonium nitrate topdressed immediately after crop emergence on 31 May 1999 and 24 May 2000 at Carman, and 25 May 2000 at Winnipeg. Weed control in the oat crop was performed with a mixture of 19.4 kg ha–1 propanil [N-(3,4-dichloro-phenyl)-propanamide], 0.2 g ha–1 thifensulfuron {methyl 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2-thiophenecarboxylate}, and 0.1 g ha–1 tribenuron methyl {methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl),ethylamino]carbonyl]amino]sulfonyl]benzoate}. At Carman in 1999, tebuconazole [
-[2-(4-chlorophenyl)ethyl]--(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol] was applied at a rate of 126 mL ha–1 to control leaf diseases. No leaf diseases were observed at the other two sites. Total precipitation and mean temperature were monitored by meteorological stations within 500 m of the experimental sites at each field research station.
Measurements conducted on the oat cultivars included grain yield, panicle density, number of kernels per panicle, kernel density, kernel weight, dry matter production, N accumulation, plant height, degree of lodging, ET, and grain WUE. Total aboveground dry matter accumulation of the oat cultivars was determined at stem elongation, anthesis, and maturity by harvesting two 1-m sections of row within each sub-subplot. Samples were oven dried at 65°C for at least 72 h and weighed. The dry matter samples were then ground using a Wiley Mill with a 2-mm mesh screen. Nitrogen concentration of the ground plant material was measured by dry combustion with a Leco N analyzer (model FP-428; Leco Corp., Mississauga, ON). Plant height, from soil surface to the tip of the panicle, was measured 1 wk to 1 d before grain harvest. Lodging was assessed before harvest on 20 Aug. 1999 and 15 Aug. 2000 at Carman, and 18 Aug. 2000 at Winnipeg. Lodging scores were assigned to each sub-subplot using a scale of 1 to 9. A rating of 1 indicated no lodging and a rating of 9 indicated 100% of the plot was lodged. Values between 1 and 9 were visually determined on the basis of degree and percentage of the plot area affected (Marshall et al., 1987).
Oat yield and yield components were measured or calculated for each treatment. Panicle density was determined by counting the number of panicles in two 1-m sections of row on 20 Aug. 1999 and 17 Aug. 2000 at Carman, and 23 Aug. 2000 at Winnipeg. The oats were combine harvested for grain on 15 Sept. 1999 and 24 Aug. 2000 at Carman, and 24 Aug. 2000 at Winnipeg. The sub-subplot area sampled for grain yield ranged from 1.9 to 5.2 m–2, depending upon location and year. Kernel weight was measured by counting the number of kernels in a 10-g sample. Bosom (double kernels) and dehulled kernels were removed before determining kernel weight. Kernel density was calculated by dividing grain yield by kernel weight. The number of kernels per panicle was determined by dividing kernel density by panicle density. Harvest index was calculated by dividing grain yield by total aboveground dry matter accumulation at harvest.
Soil water content for the 0- to 130-cm soil profile was measured at seeding and maturity for each 0 and 80 kg N ha–1 sub-subplot treatment. Volumetric soil water content was determined for the 10- to 130-cm depth in 20-cm increments using a field-calibrated neutron moisture gauge (Troxler Model 4330, Research Triangle Park, NC) and for the 0- to 10-cm depth using the neutron moisture gauge with a surface shield. Evapotranspiration was calculated as the sum of the difference in soil water contents of the 0- to 130-cm profile from seeding to maturity, and the amount of precipitation received during that interval. Water losses due to surface runoff and deep percolation below 130 cm were assumed to be negligible. Grain WUE was calculated by dividing grain yield by ET. Because of extremely wet soil conditions at Winnipeg in 2000, runoff and deep percolation losses could not be assumed to be negligible; therefore, ET and grain WUE were not calculated for this site–year.
Analyses of variance were performed on all measured variables using Proc GLM in the SAS statistical software (SAS Institute, 1999). The variables were analyzed in a split-split plot design with previous crop as the main plot effect, oat cultivars the subplot effect, and N fertilizer rate as the sub-subplot effect. A Bartlett's test was used to assess the homogeneity of error variances between the three site–years. Variables for which error variances were homogeneous at all site–years were analyzed across all site–years. For the combined site analysis, site and replicate were considered random effects, while cultivar, N rate, and previous crop were considered fixed effects. The random statement in Proc GLM was used to determine appropriate error terms and to accommodate fixed and random effects. When error variances were heterogeneous among the site–years, variables were analyzed separately for each of the three site–years. For individual site analysis, only replicate was considered random; all other effects were considered fixed. For both combined and individual site analysis, nonsignificant interactions were dropped from the analysis. Variables analyzed in a combined analysis were yield, kernels per panicle, kernel density, harvest index, lodging score ET, and grain WUE. Variables analyzed by site–year were panicle density, kernel weight, plant height, dry matter accumulation, and N accumulation. Treatment means were compared using a Fisher's protected LSD test at the P < 0.05 level.
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RESULTS AND DISCUSSION
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Environmental and Soil Conditions
Mean temperatures from May to August were 15.9°C at the two Carman site–years and 17.4°C at Winnipeg in 2000. Long-term average temperatures for these two locations are 16.7°C for Carman and 16.5°C for Winnipeg. Total precipitation received during the growing season at Carman was 340 mm in 1999 and 281 mm in 2000. These years were slightly above the long-term average precipitation of 260 mm. Precipitation conditions at Winnipeg were well above the long-term average of 283 mm, with 529 mm of precipitation received during the 2000 growing season.
Spring soil nutrient tests were taken before oat seeding to determine the N benefits contributed by the previous pea crop. Total nitrate-N levels (0–120 cm) following flax were 127 kg ha–1 at Carman in 1999, 83 kg ha–1 at Carman in 2000, and 83 kg ha–1 at Winnipeg in 2000. The pea plots had nitrate-N levels of 193 kg ha–1 at Carman in 1999, 174 kg ha–1 at Carman in 2000, and 167 kg ha–1 at Winnipeg in 2000. The average boost in soil nitrate-N from the pea green manure compared with the flax was 80 kg ha–1 across the three site–years.
Yield
AC Ronald yielded 433 kg ha–1 greater than Triple Crown, which was equivalent to a 10% yield advantage (Table 1). As expected, N rate also affected yield, with N application increasing grain yield. No site–year x cultivar interaction for yield was observed, nor were interactions between cultivar and previous crop or N rate observed for grain yields. These observations suggest that the cultivar yield difference was stable across the environments tested in this study.
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Table 1. Oat yield, kernels per panicle, kernel density, harvest index, lodging evapotranspiration (ET), and grain water use efficiency (WUE) response to site–year, previous crop, cultivar, and N fertilizer rate treatment effects.
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Yield Components
Among the yield components measured, panicle density and resulting kernel density were the most important contributors to the greater yield of AC Ronald. Panicle density was greater at all three site–years by an average of 67 panicles m–2 (Table 2). A significant cultivar x previous crop x N interaction for panicle density was observed at one of the three site–years (Winnipeg). This interaction was attributed to a difference in the way AC Ronald and Triple Crown responded to N in the different crop rotations. For example, following flax, both cultivars displayed an incremental response to N; however, the response by AC Ronald was stronger than for Triple Crown, with a higher panicle density at the highest N rate (348 panicles m–2 for AC Ronald vs. 300 panicles m–2 for Triple Crown). Following pea, however, AC Ronald had achieved maximum panicle density at the 0 N rate (300 panicles m–2 for AC Ronald vs. 210 panicles m–2 for Triple Crown). These observations suggest a possible stronger panicle density response to N for the short-statured cultivar at this site. Tiller production response to N was observed to be stronger for semidwarf compared with tall-statured wheat cultivars (Entz and Fowler, 1989). As the number of kernels per panicle was not affected by cultivar, increased panicle density with AC Ronald resulted in a 2484 m–2 greater kernel density for the short cultivar (Table 1). This greater kernel density contributed to increased yields despite the fact that AC Ronald consistently had lower kernel weight than Triple Crown at all site–years (Table 2). A number of interactions for kernels per panicle were observed (Table 2), but no clear pattern was established.
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Table 2. Oat panicle density, kernel weight, and height response to previous crop, cultivar, and N fertilizer rate treatment effects at three site–years.
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Kernel weight for AC Ronald averaged 2.5 mg less than Triple Crown. A significant cultivar interaction for kernel weight was observed at one of the three sites (Table 2). At Winnipeg, kernel weight for Triple Crown increased slightly under increased N rates, while kernel weight for AC Ronald decreased (data not shown). In general, lower kernel weight for AC Ronald in the present study did not translate into decreased seed yield. Similar results have been reported by others (e.g., Shanahan et al., 1984; Hamill, 2002). It has been suggested that seed yield in cereals is limited more by kernel density than kernel weight and so breeding efforts for yield at the expense of kernel weight may be acceptable (Fischer, 1979; Entz and Fowler, 1989). However, lower kernel weights in oat may lead to a reduction in milling quality, as kernel size and shape will be affected. Future research on the grain quality implications of yield increases due to increased kernel number at the expense of kernel weight is required. In general, oat yield component response to increased N through either crop rotation or fertilizer was an increase in panicle and kernel densities, and decrease in kernel weight (Tables 1– 2).
Dry Matter Accumulation and Harvest Index
There was some evidence for greater aboveground dry matter accumulation for Triple Crown compared with AC Ronald. For example, greater (P < 0.05) dry matter production for Triple Crown compared with AC Ronald was observed at stem elongation (Carman 1999), anthesis (Carman 1999 and 2000), and at maturity (Winnipeg) (Table 3). Final grain yield is a function of total dry matter accumulation and the percentage of dry matter partitioned to the seed (Fischer, 1979). AC Ronald had a 16% greater (P < 0.05) harvest index than Triple Crown (Table 1), indicating that the short-statured cultivar had more efficient assimilate partitioning. A positive correlation between harvest index and grain yield in oat was reported by Salman and Brinkman (1992). McMullan et al. (1988) found no correlation between oat plant dry matter at maturity and grain yield of different cultivars. In the present study, the improved harvest index of AC Ronald enabled it to yield higher than Triple Crown without greater dry matter production.
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Table 3. Oat dry matter response at stem elongation, anthesis, and maturity to previous crop, cultivar, and N fertilizer rate treatment effects at three site–years.
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Dry matter accumulation increased with N inputs from the pea rotation (eight of nine observations) and N fertilizer (eight of nine observations) (Table 3). However, N inputs from pea rotation or N fertilizer did not affect harvest index (Table 1). The cultivar effects for harvest index appear to be stable across all treatment environments, as there were no significant interactions among cultivar and site–year, previous crop, or N rate for harvest index.
Plant Height and Lodging
AC Ronald was shorter than Triple Crown at all three site–years, with an average height difference of 22 cm (Table 2). Lodging resistance is often cited as a reason for increased yield of semidwarf cultivars because of their shorter stature (McNeal et al., 1972; Brown et al., 1980; Marshall et al., 1987). In the present study, no difference in lodging resistance was observed between AC Ronald and Triple Crown when data was averaged across sites (Table 1). However, a significant site–year x cultivar interaction (Table 1) was attributed to different lodging responses across sites. At Carman in 1999, a higher lodging score was observed for Triple Crown compared with AC Ronald (6.2 for Triple Crown vs. 3.1 for AC Ronald), while no cultivar differences were observed at Carman and Winnipeg in 2000, where average lodging scores were 7.5 and 2.4, respectively. Lodging score differences were not related to plant height, as plants at Carman in 1999 were shorter, on average, than at the other two sites (Table 2). The lack of a clear relationship for this interaction suggests that the degree of lodging is the result of several plant characteristics and environmental factors, and not simply plant height (Pinthus, 1973). The high lodging score for both cultivars at Carman in 2000 (7.5) indicates that both cultivars are susceptible to lodging under certain conditions.
Plant heights and lodging scores were higher in the pea rotation and increased with increasing N rate. However, there were no interactions of cultivar with previous crop or N rate for these variables, indicating that the cultivars had similar responses to the N treatments.
Evapotranspiration and Grain Water Use Efficiency
Evapotranspiration and grain WUE of semidwarf and tall oat cultivars have not been previously compared. There was no difference in ET for AC Ronald and Triple Crown, which averaged 289 mm (Table 1). Entz et al. (1992) found no differences in ET or root growth of tall and semidwarf spring and winter wheat cultivars grown in Saskatchewan. There was also no difference in WUE for AC Ronald and Triple Crown in the present study (Table 1). Entz and Fowler (1989) found greater grain WUE of a semidwarf wheat, as compared with a tall cultivar, contributed to higher yields of the semidwarf. Previous crop and N rate did not have an effect on ET or grain WUE. Additionally, there were no significant cultivar interactions with site–year, N rate, or previous crop observed for ET or grain WUE.
Total Nitrogen Accumulation
Oat cultivar did not alter N accumulation, except during stem elongation at one site–year, when Triple Crown had greater N uptake than AC Ronald (Table 4). As expected, N fertilizer rate increased N accumulation at all sampling times and all site–years. Previous crop only affected N uptake at Carman in 2000, where oat following pea had greater N accumulation at all sampling times than oat following flax. No interactions between cultivar and previous crop or N rate were observed for N accumulation.
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Table 4. Oat total N accumulation response at stem elongation, anthesis, and maturity to previous crop, cultivar, and N fertilizer rate treatment effects at three site–years.
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The ability to detect variations in cultivar response to different N environments may be restricted by the relatively high soil N levels at these sites. Only two of three sites had soil N levels in the control treatment (0 kg N ha–1 in flax stubble) below the critical level of 115 kg ha–1 at maturity (Hamill, 2002), and even these soil nitrate levels are approximately 30 kg ha–1 above levels found in typical Manitoba fields. Therefore, conditions for testing the relative response of oat cultivars to N fertilizer application were not optimum. Inferences on the effect of a low and high N supplying rotation are likewise limited as oat production was not limited by N levels in the pea rotation. Further research on cultivar response to N under low fertility conditions may yield more variation in semidwarf and tall oat performance. However, since both cultivars had similar N uptake in all treatments, the higher yields of the semidwarf AC Ronald compared with Triple Crown were due to factors other than cultivar differences in response to N.
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CONCLUSIONS
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The development of AC Ronald prompted new research into the yield physiology of semidwarfs in comparison with conventional-height cultivars. In the present study, AC Ronald had a greater yield potential than Triple Crown, a representative tall-stature cultivar (Hamill, 2002). This yield advantage was attributed mainly to greater panicle density, kernel density, and harvest index. Therefore, the yield advantage of AC Ronald was associated with (i) greater preanthesis sink size (Shanahan et al., 1984) (i.e., kernel density); and (ii) improved assimilate partitioning (i.e., harvest index). Similar reasons have been given for yield increases of semidwarf wheat cultivars (Fischer, 1979). Triple Crown did produce more aboveground dry matter than AC Ronald in some instances, and showed some evidence of greater plant N assimilation during the preanthesis development period; however, total N uptake was similar between cultivars. Evapotranspiration and WUE were also similar between cultivars. Lodging was found to be independent of oat cultivar height and both cultivars were found to be susceptible to severe lodging under certain conditions. At one site, lodging score was lower for AC Ronald compared with Triple Crown. The grain yield advantage of AC Ronald over Triple Crown appeared stable across the treatment and site environments tested here; however, the presence of cultivar x environment interactions for kernels per panicle suggests some differential response of these cultivars to environment.
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ACKNOWLEDGMENTS
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We thank Dr. Jennifer Mitchell-Fetch of Agriculture and Agri-Food Canada's Cereal Research Centre for providing the AC Ronald cultivar, and Keith Bamford for his expert technical assistance. Funding for this research was provided by the Canadian Fertilizer Institute, Cargill Ltd., Quaker Oats, and the Manitoba Government.
Received for publication January 21, 2004.
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REFERENCES
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ABSTRACT
INTRODUCTION
