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Seeding Rate and Nitrogen Management on Milling and Baking Quality of Hard Red Spring Wheat Genotypes

Dep. of Plant Sciences, North Dakota State Univ., Fargo, ND, 58105

^* Corresponding author (Mohamed.Mergoum{at}ndsu.edu).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The end-use value of hard red spring wheat (HRSW) (Triticum aestivum L.) is determined by many factors including grain protein content (GPC), grain volume weight (GVW), thousand-kernel weight (TKW), and milling and baking characteristics. These quality traits can be affected by environment, genotype, seeding rate, and nitrogen management. Experiments were conducted under dryland (Casselton, ND) and irrigated (Carrington, ND) conditions in 2003 to 2005 to determine the influence of seeding rate and N management on spring wheat quality in selected genotypes. Treatments consisted of a factorial combination of HRSW genotypes (‘Alsen’, ‘Briggs’, ‘Granite’, and ND 740), seeding rates (2.9 and 4.2 million seeds ha^–1), N rate (140 and 224 kg ha^–1 for the non-irrigated site, 168 and 280 kg ha^–1 for the irrigated site), and timing of N application (pre-plant, 2-split applications, and 3-split applications). Genotype was the only factor that consistently affected the various quality traits measured. There were few interactions between factors and all involved genotype. GPC and GVW of Granite were 0.5 g kg^–1 and 14 kg m^–3 greater, respectively, than any of the other genotypes. Over all treatments, increasing the N rate increased the grain protein content by 8 g kg^–1. GPC was correlated with loaf volume but negatively correlated with flour extraction. Applying N in three splits when compared to applying it all preplant increased baking absorption by 0.8%, increased the mixograph score by 0.4 units, and decreased mixing time by 0.2 min. Seeding rate did not result in a significant change in grain quality or milling and baking quality in this study. Overall, genotype was the most important factor in determining grain quality and milling and baking performance. To a lesser extent, N timing influenced grain quality, particularly in its mixing characteristics.

Abbreviations: AACCI, American Association of Cereal Chemists International • CBCL, Crumb color • DO, dough handling characteristics • GPC, grain protein content • GVW, grain volume weight • FHB, Fusarium head blight • HRSW, hard red spring wheat • ND, North Dakota • NDSU, North Dakota State University • NUE nitrogen use efficiency • RCBD, randomized complete block design • SR, seeding rate • TKW, 1000 kernel weight • T, N timing • UAN, urea ammonium nitrate

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
HARD RED SPRING WHEAT (HRSW) produced in the U.S. Northern Great Plains is valued for its high protein and bread-baking quality. The relatively short growing season for HRSW in North Dakota allows for the production of high grain protein content (GPC) with very good milling and baking qualities. However, environmental conditions that impact grain quality vary from year to year. As an example, excessive rainfall coupled with cool conditions can favor the development of Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe, which seriously reduces grain quality. GPC concentration is a primary component in determining HRSW end-use quality, and is dependent on several factors including environment, fertilizer N rate, N application timing, genotype, and the interaction of these factors (Terman, 1979; Rao et al., 1993; Garrido-Lestache et al., 2004; Souza et al., 2004). Sufficient N is critical in the production of high protein HRSW. Staggenborg et al. (2003) and Boehm et al. (2004) found GPC to increase with higher rates of applied N. Others report that in addition to N availability, the amount of precipitation during the growing season can dramatically influence GPC (Fowler et al., 1990; Garrido-Lestache et al., 2004; Souza et al., 2004).

Foliar N applications have often been used as a way to increase GPC in wheat. Bly and Woodard (2003) found that post-pollination foliar N applications increased GPC, especially when the planned yield goal was exceeded. Woolfolk et al. (2002) reported a significant linear increase in total grain N with increasing N rates for post-flowering N applications. Similarly, Schatz et al. (1991) showed that postanthesis application of N increased grain protein by 0.95%. Nitrogen fertilizer is a key factor in determining bread-baking quality (Lopez-Bellido et al., 2001). Ayoub et al. (1994) indicate that delayed N applications can influence the bread-baking quality of the flour.

In North Dakota, most, if not all, of the N fertilizer is applied late in the fall or in the spring before planting. The relatively short growing season makes it difficult for wheat producers to apply N post-emergence in a timely manner. According to Garrido-Lestache et al. (2004), N application timing is less critical in spring wheat since crop development is much more rapid and generally occurs over a much shorter time period compared to winter wheat. Previous research on the effect of N application timing on grain protein in North Dakota is limited.

Seeding rate can also influence quality traits associated with the milling and baking properties of HRSW. Geleta et al. (2002) found that grain volume weight (GVW) was lowest at the 16 kg ha^–1 seeding rate but increased as seeding rate was increased to 65 and 130 kg ha^–1. The same study reported flour yield increased with increased seeding rates up to 65 kg ha^–1. Samuel (1990) also found GVW increased as seeding rates increased from 90 to 270 kg ha^–1, although the effects were minimal.

In recent years, intensive wheat management strategies including N management and seeding rates have been promoted in an effort to increase HRSW grain yield and quality. However, limited information regarding the effects of intensive wheat management on spring wheat quality has been published in North Dakota. This study was conducted to determine the effects of seeding rate, N rate, and timing of N application and their interactions on the quality traits that influence milling and baking properties of four HRSW genotypes under North Dakota growing conditions.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Experiments were conducted under dryland conditions at Casselton, ND, in 2003, 2004, and 2005, and under irrigation in 2003 and 2004 at Carrington, ND. Casselton is located at longitude 97° 7', latitude 47° 0', and an elevation of 284 masl in east central ND and has a Perella-Bearden silty clay loam (fine-silty, mixed, frigid Typic Haplaquolls, fine-silty, frigid Aerie Calciaquolls) soil type. Carrington is located at longitude 99° 1', latitude 47° 5', and an elevation of 483 masl in the central region of ND where the soil is a complex of Heimdahl loam (coarse-loamy, mixed, superactive, frigid calcic hapludolls) and Embrick loam (coarse-loamy, mixed, superactive, frigid pachic hapludolls). In 2003, experiments were planted on 29 April at Casselton and 24 April at Carrington. In 2004, they were planted on 17 and 27 April at Casselton and Carrington, respectively. In 2005, the experiment at Casselton was planted on 28 April. The previous crops were sugarbeet (Beta vulgaris L.) at Casselton in 2003 and soybean [Glycine max (L.) Merr.] in all other experiments. Sites were selected based on low residual soil N availability as determined from nitrate levels in the top 60 cm. Each site was sampled for residual soil N at the 0 to 15 and 15 to 60 cm soil depths. Before planting, a field cultivator was used to prepare the seedbed and to incorporate the dry granular urea (46-0-0) fertilizer applied preplant.

In the five environments previously described, a factorial field experiment with a split-split plot arrangement with main plots in a randomized complete block design was implemented. N levels served as the main plot, N application timing as the sub-plot, and genotypes by seeding rate as the sub-sub plot. Each experimental unit consisted of 7-rows with a 10 cm spacing 2.4 m long. Plots of equal size were planted on the edges of blocks to minimize any border effect. Grain harvested from each treatment was combined across replicates within a location to reduce the number of milling and baking sample tests, which are expensive and time consuming to conduct. Effectively, this composite grain sample served as an experimental unit, with environments representing blocks in the overall statistical analysis.

Four genotypes were used in this study ‘Alsen’ (Frohberg et al., 2006), ‘Briggs’ (PI 632970), ‘Granite,’ and ND 740. Briggs, released by South Dakota State University (SDSU) in 2002, has high grain yield and protein content, mellow gluten strength, medium early maturity, and medium straw strength. Alsen, released by North Dakota State University (NDSU) in 2000, has average grain yield, high grain protein content, traditional strong gluten strength, medium early maturity, and strong straw. Alsen is the most widely-grown cultivar in ND because of its resistance to FHB. Granite, released by WestBred, LLC. (Bozeman, Montana) in 2002, exhibits high grain yield, high grain protein content, traditional strong gluten strength, very strong straw, and medium late maturity. ND 740, an experimental line developed by the NDSU HRSW breeding program, has shown high grain yield potential, medium straw strength, medium strong to mellow gluten strength, and average GPC. Except for Alsen, all other genotypes are susceptible to FHB.

Two seeding rates, 2.9 million (low seeding rate) and 4.2 million (high seeding rate) seeds ha^–1 were used in this experiment. The low seeding rate is based on the current NDSU recommended seeding rate for spring wheat while the high seeding rate is recommended by intensive wheat management groups.

Two N levels included in the study were determined based on the N requirement of an average and highest likely attainable yield for each location. At Casselton, N rates (including the amount of nitrate N found in the top 60 cm of the soil before planting) were 140 and 224 kg ha^–1, targeting yields of 3362 and 5380 kg ha^–1, respectively. At the irrigated site in Carrington, 168 and 280 kg ha^–1 N were applied targeting yields of 4034 and 6725 kg ha^–1, respectively. The amount of N applied as fertilizer applied preplant was adjusted downward depending on the amount of nitrate N found in the soil. Nitrate-N levels were fairly similar across the environments, varying from 56 to 79 kg ha^–1.

Three N timings were used in the study, preplant, two-way split, and three-way split. For the preplant N treatment, all N was applied as dry granular urea fertilizer and incorporated into the soil before planting. In the two-way split, half the targeted N amount (minus the residue nitrate N in the soil) was applied preplant and half at the five leaf stage (Zadoks 15 stage) (Zadoks et al., 1974). In the three-way split, a third of the N, minus the soil nitrate N, was applied at preplant, a third at the five-leaf stage (Zadoks 15 stage), and a third postanthesis (Zadoks 69 stage). Post-planting N applications were made with urea ammonium nitrate solution (UAN) (280 g N kg^–1) and applied as a foliar solution with H₂O at a 1:1 mixture as late in the day as possible to minimize leaf burn. Nitrogen streamer bars were used at the Zaddock 15 stage to minimize leaf burn. A flat-fan nozzle was used for the Zadoks 69 stage application to ensure adequate spike and flag leaf coverage for maximum absorption.

Weeds were initially controlled with an application of 0.28 kg a.i. ha-1 bromoxynil octanoate ester (3,5-dibromo-4-hydrozybenzonitrile) and 0.28 kg a.i. ha-1 MCPA isooctyl ester (4-chloro-2-methylphenoxy) and fenoxaprop-p ethyl ester {2-[4-[(6-chloro-2-benzoxazoly) oxy] phenoxy]} propanoate plus mefenpyr –diethyl [1-(2,4 dichlorophenyl)-4,5 dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid] at 0.067 kg a.i. ha-1 at Zadoks 15 growth stage. Hand weeding at later stages was used as needed. Fungicide to control leaf spotting diseases was applied at Zadoks 39 stage using 0.126 kg a.i. ha^–1 propiconazole {1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl] methyl]-1H-1,2,4-triazole}. A split application (0.063 kg a.i. ha^–1) of tebuconazole -[2-(4-chlorophenyl)ethyl]--(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) to control FHB was made at the beginning of flowering (Zadoks 61 stage) and 7 d later.

The following analyses were performed on a 150 gm subsample of the composite sample previously described in each experiment. Moisture content was determined using a Motomco moisture meter (Motomco Inc., Paterson, NJ) according to Approved Method 44-11 (AACCI 2000). Samples were pretempered to a moisture basis of 125 g kg^–1 grain and tempered to moisture basis of 160 g kg^–1 grain for 18 to 20 h before milling according to Approved Method 26-10A (AACCI 2000). Grain was milled using a Quadrumat Jr. (Quadruplex) mill (C.W. Brabender Instruments Inc., Hackensack, NJ) to determine flour extraction (%). Flour extraction is the amount of flour obtained using the Quadrumat Jr. flour mill using 150 g of wheat at a 160 g kg^–1 flour-moisture basis.

Data were collected on GPC, GVW, flour extraction, baking absorption, dough handling characteristics (DO), mixograph score, mix time, loaf volume, crumb color, and crust color. Grain samples were cleaned on a Clipper grain cleaner (Clipper Separation Technologies, Bluffton, IN) and a Carter Dockage machine (Carter-Day Co., Minneapolis, MN) following harvest. Grain volume weight was determined according to Approved method 55-10 (AACCI, 2000). Thousand kernel weight (g) was determined based on the weight of 250 seeds counted on an electric seed counter (Seedburo Equipment Co., Chicago, IL). GPC (g kg^–1) was determined for each plot sample on a whole grain basis at 12.0% moisture content using Tecator Infratec 1226 Grain Analyzer (Foss, Eden Prairie, MN) according to Approved Method 39-25 (AACCI 2000).

Baking tests (25 g) were done according to Approved Method 10-10B (Experimental Bread Baking Long Fermentation) (AACCI 2000) to determine flour water absorption (%), DO (1–10), loaf volume (cc), crumb color (1–10), and crust color (1–10). Baking absorption is the amount of water required to hydrate flour components into an optimally developed dough mass with specific consistency. Baking absorption was expressed as a percent of flour with a high percentage being desirable. The higher the baking absorption, the greater the dough and bread yield. Dough character refers to the handling properties at the punching and panning stages and was expressed on a score from 1 to 10 with the higher score being the most desirable. The loaf volume refers to the volume, expressed in cubic centimeters (cc), of the experimental 25 g loaf. A high loaf volume is considered desirable. Crumb color of the internal loaf of bread was subjectively measured against a standard, and was expressed as a score from 1 to 10 with the highest score most desirable. Crust color of the external loaf of bread was subjectively measured against a standard and was expressed on a score from 1 to 10 with the highest score being the most desirable.

Finally, mixograph tests were conducted to determine an overall appraisal of the dough mixing characteristics of a sample. A 10 g flour sample was used in a mixograph machine (National Mfg. Co.) according to Approved Method 54-40A (AACCI 2000). Graphs for each sample were scored from 1 to 10 (1–2 = very poor; 3–4 = poor; 5–6 = average; 7–8 = good; and 9–10 = very good) according to the NDSU Cereal Science standardized mixogram chart.

Data was subjected to an analysis of variance (ANOVA) using SAS (SAS Institute, 2004) with the composite sample from each environment serving as blocks. Genotype, seeding rate, N level, and N timing were fixed effects and environment (block) was a random effect. F-tests were conducted using the appropriate denominator for the error term to determine significant differences among main effects and interactions. Mean separation tests were conducted using an F-protected LSD (P = 0.05) as described by Steel and Torrie (1997). Simple linear correlation coefficients were calculated between wheat quality characteristics and milling and baking traits.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Monthly precipitation for Casselton and Carrington are summarized in Table 1 . In 2003 and 2004, both Casselton and Carrington received below normal precipitation in April and above normal precipitation in May. June precipitation was above average in 2003 and in 2005 at Casselton, but below average in 2004. Rainfall at Carrington was below average in June and July in both 2003 and 2004. Growing degree days were above normal in April, below normal in May, and near normal in June and July at all environments. Accordingly, growing conditions for wheat in North Dakota were very favorable in both 2003 and 2004 with above normal rainfall, cool temperatures, and low disease pressure resulting in very good grain quality. In 2005, excessive precipitation in May and June contributed to reduced grain quality due to much higher disease pressure, including FHB.

Grain volume weight was significantly influenced by genotype (Table 2). Among genotypes, Granite produced the highest GVW with 818 kg m^–3, while ND 740, Alsen, and Briggs produced 804, 803, and 795 kg m^–3, respectively (Table 3). Other studies (Geleta et al., 2002; Souza et al., 2004) have shown that GVW can be strongly influenced by genotype. Seeding rate did not alter GVW. Other researchers reported increases in GVW with increasing seeding rate in some environments (Carr et al., 2003). Higher seeding rates tend to reduce spike size and the number of harvestable tiller spikes, which can favor the development of kernels with higher test weight. This was not the case in our study, possibly because water and nitrogen were adequate, so differences in kernel development within the different seeding rate treatments were not expressed.

Milling and Baking Qualities
Genotype had a significant effect on flour extraction, while seeding rate (SR), N level, and N timing (T) failed to influence flour extraction (Table 2). ND 740 had the highest flour extraction of 67.5% among the four genotypes. Alsen, Briggs, and Granite each had a flour extraction of 66.6, 65.3, and 62.3%, respectively (Table 3). Significant negative correlations were observed between flour extraction and GVW (r = –0.52**) and GPC (r = –0.44**) (Table 4 ). This negative correlation is contrary to what is normally expected, as GVW is generally considered a good predictor of flour extraction (Finney et al., 1987; Guttieri et al., 2001). Flour extraction, however, can be cultivar specific (Finney et al., 1987) and so the negative correlation between GVW and flour extraction in this study may have been related to the fact that the cultivar with the highest GVW, Granite, typically has lower flour extraction than the other cultivars included.

Loaf volume was significantly influenced by a G x T interaction and genotype main effect (Table 2). This interaction was due to Alsen, which had the greatest loaf volume with the preplant and 2-split N timing treatment, declining in loaf volume when N was split three times, while the loaf volume of the other genotypes was unaffected by N timing (Table 6 ). Averaged across all treatments, Alsen produced the greatest loaf volume, followed by Granite, ND 740, and Briggs (Table 3). Other researchers have reported genotypic differences in loaf volume (Amiour et al., 2002; Chung et al., 2003). Loaf volume was correlated with GVW (r = 0.28*) and grain protein (r = 0.46**) (Table 4). Loaf volume is one of the most important milling and baking traits used to screen genotypes since bakers are primarily interested in producing an adequate loaf of bread. The lack of significant response in loaf volume to the higher N treatment, even though GPC increased significantly, was probably due to the relatively small increase in GPC from the additional N. Genotype, as a factor, had a much larger range in GPC than did N level.

Mixograph scores were significantly influenced by the main effects of N timing and genotype (Table 2). Among N timings, the 3-split treatment produced a slightly greater mixograph score of 6.0 compared to the preplant and 2-split treatment scores of 5.6 and 5.7, respectively (Table 3). Across seeding rate, N level, and N timing treatments, Alsen, Granite, and ND 740 produced the highest mixograph scores of 6.1, 6.0, and 5.8, respectively, while Briggs was noticeably lower with a mixograph score of 5.1 (Table 3). Luo et al. (2000) and Souza et al. (2004) also found differences in mixograph scores between genotypes.

Mix time was significantly influenced by N timing and genotype main effects (Table 2). Among N timings, the preplant treatment produced a slightly larger mix time of 3.3 min compared the split-N treatments (Table 3). Among genotypes, Alsen had the longest mix time of 3.4 min compared to Briggs with 2.8 min (Table 3).

In summary, of the factors included in this study, genotype was consistently found to be an important factor in determining grain quality and milling and baking properties. Seeding rate failed to impact any of the measured traits in this study. Nitrogen level influenced GPC and GVW, but did not impact significantly any of the milling and baking properties in this study. Nitrogen timing rarely influenced traits in this study; baking absorption and the mixograph score increased slightly and the mix time decreased slightly with the 3-split N application timing treatment. These data indicate, at least within the scope of the levels of the management factors included in this work, that genotype selection is the most important determinant of end-use quality in spring wheat. When managing for wheat quality, growers should first consider the genotype grown, as there are limitations on other crop management practices in improving the end-use quality of wheat genotypes that may be deficient in one or more quality traits.

	ACKNOWLEDGMENTS

 
The authors would like to thank Truman Olson and Kelly McMonagle of the NDSU Plant Sciences Department for their assistance in the milling and baking lab. Many thanks go to Dr. Dwain Meyer and other reviewers at the Plant Sciences Department for their valuable suggestions.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
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Received for publication August 22, 2007.

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