Managing nitrogen fertility of irrigated soft white spring wheats for optimum quality

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1 SHORT COMMUNICATION Managing nitrogen fertility of irrigated soft white spring wheats for optimum quality Mary J. Guttieri, Katherine O Brien, Cecile Becker, Jeffrey C. Stark, Juliet Windes, and Edward Souza 1 University of Idaho Research and Extension Center, P.O. Box 870, Aberdeen, ID 83210, USA. Received 11 February 2005, accepted 13 November Guttieri, M. J., O Brien, K., Becker, C., Stark, J. C., Windes, J. and Souza, E Managing nitrogen fertility of irrigated soft white spring wheats for optimum quality. Can. J. Plant Sci. 86: Irrigated wheat growers often choose to apply only part of the crop s nitrogen fertilizer requirement at planting to avoid over-fertilizing the crop at early stages of growth. Later in the growing season, producers will apply additional nitrogen fertilizer as needed to optimize production. This study evaluated effects of top-dress nitrogen fertilizer application timing and rate on the milling and baking quality of two soft white spring wheat cultivars produced in an irrigated environment when the pre-plant fertility rates were insufficient for optimal crop yield. Top-dress N increased lactic acid solvent retention capacity (SRC), a measure of gluten strength, of the resulting flour by increasing flour protein concentration. Although lactic acid SRC response and the grain yield response to top-dress fertilizer were unaffected by application timing, other quality parameters, including break flour yield, flour ash, and, in the case of the cultivar Alturas, sugar snap cookie diameter, were affected by application timing. Earlier timing of top-dress fertilization minimized the detrimental effects of the fertilizer application on break flour yield and flour ash concentration. Key words: Soft wheat, nitrogen, gluten, flour ash Guttieri, M. J., O Brien, K., Becker, C., Stark, J. C., Windes, J. et Souza, E Gestion des amendements azotés sur les cultures irriguées de blé tendre blanc de printemps en vue d une qualité optimale. Can. J. Plant Sci. 86: Les agriculteurs qui irriguent leurs champs de blé n appliquent souvent qu une partie de l engrais azoté que requiert la plante pour éviter une fertilisation excessive durant les premiers stades de la croissance. Par la suite, ils fertilisent au besoin afin d optimiser le rendement. Les auteurs ont évalué les conséquences du moment où l engrais est appliqué en surface et de la quantité d engrais sur la qualité meunière et boulangère de deux variétés de blé tendre blanc de printemps cultivées sous irrigation quand le taux de fertilisation avant semis était insuffisant pour que la culture atteigne son rendement optimal. L application de N en surface augmente la capacité de rétention du solvant (CRS) de l acide lactique (un paramètre employé pour établir la fermeté du gluten) de la farine en accroissant la concentration de protéines dans cette dernière. Bien que la réaction à la CRS de l acide lactique et celle du rendement grainier à l application de l engrais en surface ne soient pas affectées par le moment de l application, d autres paramètres le sont, notamment le rendement en farine de broyage, la teneur en cendres de la farine et le diamètre des biscuits au sucre, pour le cultivar Alturas. En appliquant l engrais en surface plus tôt, on minimise les effets nuisibles de la fertilisation sur le rendement en farine de broyage et sur la teneur en cendres de la farine. Soft white spring wheat from the Pacific Northwest of the United States is traditionally used for confectionary products such as cookies, crackers, and cakes. Key quality characteristics for soft spring wheat include flour extraction (milling yield and break flour yield), flour protein concentration and composition, and water retention characteristics. The Solvent Retention Capacity Test [SRC; American Association of Cereal Chemists (AACC) method 56-11] is a relatively new test for profiling the water retention characteristics of soft wheat flours based on starch damage, pentosan content, and gluten. Some domestic and international users of Pacific Northwest soft white spring wheat have expressed interest in purchasing wheat with moderate gluten strength. One measure of gluten strength in soft wheat is the lactic acid Mots clés: Blé tendre, azote, gluten, cendres de la farine solvent retention capacity (Gaines 2000). Within a wheat cultivar, flour protein concentration is often correlated with lactic acid SRC (Guttieri et al. 2002). Therefore, management practices that increase flour protein concentration may increase flour lactic acid SRC. Nitrogen fertilization strongly influences the quantity of protein in hard wheat flour (Dubetz et al. 1979; Gauer et al. 1992). Numerous studies in hard wheat have demonstrated the importance of N application timing for optimal wheat yield, increased grain protein concentration, and reductions in N loss from the soil plant system (Hucklesby et al. 1971; Miezan et al. 1977; Altman et al. 1983; Fowler et al. 1989). Nitrogen applications later in the season, near anthesis, have been more efficient at increasing grain protein in hard wheat than earlier applications (Strong 1982; Wuest and Cassman 1 Current address: USDA ARS Soft Wheat Quality Laboratory, 1680 Madison Ave., Wooster, OH 44691, USA. 459 Abbreviations: NIR, near-infrared; SRC, solvent retention capacity

2 460 CANADIAN JOURNAL OF PLANT SCIENCE 1992), provided that irrigation or precipitation occurs after the nitrogen application. Modern hard wheat cultivars have been selected for flour properties that optimize manufacture of bread products. The primary quality considerations for hard wheat have been protein concentration (more is better) and protein quality (stronger gluten is preferred). In contrast, modern soft wheat cultivars have been selected for flour properties that optimize manufacture of pastry products. The primary quality considerations for soft wheat have been related to water absorption (less is better), a function of grain carbohydrate composition, and protein concentration (less is better). Therefore, management practices developed to optimize quality of hard wheats may not necessarily result in optimal soft wheats quality. In contrast to the body of literature on fertility management of hard wheat, relatively few studies have evaluated the effect of fertility practices on soft wheat yield and grain protein (Glenn et al. 1985; Bole and Dubetz 1986; Bruckner and Morey 1988; Gravelle et al. 1988; Carefoot et al. 1989, 1993; Fiez et al. 1994; Fowler 2003). These studies have demonstrated advantages to split applications of N in terms of improved crop yield and nitrogen use efficiency. However, these studies did not find the strong responses of flour protein to split N applications observed in studies with hard wheat. Moreover, among the soft wheat studies, only Bruckner and Morey (1988) evaluated the effect of fertility practices on the end use quality parameters of soft wheat, beyond protein concentration. However, this study evaluated milling and baking properties of only a composite sample of each treatment in only 1 yr of the study, limiting utility of the study. Studies that evaluate the effects of fertility practices on the end use quality of soft white wheat produced in irrigated environments are fewer still. In a previous study (Guttieri et al. 2002) under irrigated conditions, a 44 kg ha 1 topdress fertilizer application at anthesis did not increase flour protein concentration or lactic acid SRC, a measure of gluten strength. However, the rate of preplant fertilizer applied in this previous study (0.03 kg of N/ha (residual + applied) per kg ha 1 target yield) may have limited our ability to detect effects of additional fertility on quality. Response of soft wheat protein concentration to split application of N is variable. Split applications of N to soft red winter wheat increased grain nitrogen percent relative to an equivalent pre-plant N application in only 1 of 2 yr (Gravelle et al. 1988). Similarly, in a study of irrigated soft white spring wheat (Carefoot et al. 1993), split application of N at tillering, stem extension, and early heading significantly increased grain N concentration relative to an equivalent pre-plant N application in only 1 of 2 yr. As the SRC test is a relatively new tool for creating profiles of soft wheat flour quality, studies characterizing the effects of fertility management on SRC parameters are particularly limited (Guttieri et al. 2002). Our experience is that growers of irrigated soft white spring wheat in the western United States infrequently apply the recommended optimal rates of fertility, but rather underfertilize their wheat crop. This under-fertilization is due, in part, to economics of fertilizer application and, in part, to the availability of the option to add N later in the season. Some growers of irrigated soft white spring wheat with sandy soil, seeking to prevent leaching of N out of the root zone, routinely apply only part of the total fertilizer prior to planting. The objective of this study was to evaluate the effect of topdress nitrogen fertilizer application timing and rate on the milling and baking quality of soft white spring wheat cultivars produced in an irrigated environment when the preplant fertility rates are insufficient for optimal crop yield. Grain Production Field studies were conducted at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID, in 2002 and 2003 in a Declo sandy loam soil (coarseloamy, mixed, superactive, mesic Xeric Haplocalcids). Prior to planting, soil samples from the 0- to 0.6-m depth were analyzed for KCl-extractable nitrate-n, ammonium-n, NaHCO 3 -extractable phosphorus (P) and potassium (K), organic matter and ph. Residual soil nitrogen in 2002 and 2003 at the 0- to 0.6-m depth was 75 kg ha 1 and 113 kg ha 1 respectively. Soil tests indicated that P and K levels were adequate for maximum yield (Brown et al. 2001). Ammonium nitrate fertilizer (34-0-0) was broadcast and incorporated with a disk and light culti-packer operation prior to planting. In 2002, 45 kg ha 1 nitrogen was applied pre-plant on Apr. 12; and in 2003, 56 kg ha 1 nitrogen was applied pre-plant on Apr. 10. In 2002, an additional 22 kg ha 1 N was injected through the irrigation water as urea ammonium nitrate on May 23. Thus, total base N fertility rates on the trials in 2002 and 2003 were 142 and 169 kg ha 1, respectively. University of Idaho recommendations (Brown et al. 2001) call for 0.03 kg of N ha 1 (residual + applied) per kg ha 1 target yield. Assuming a target grain yield of 7200 kg ha 1, based on long-term performance of the test cultivars, Alturas (Souza et al. 2004) and Jubilee (Souza et al. 2003), in University of Idaho yield trials, the recommended base fertility was 216 kg ha 1. Therefore, the base fertility rates in 2002 and 2003 were 66% and 78% of recommended levels, respectively. Maximum total (base + top-dress) rates in 2002 and 2003 were 92% and 104% of recommended levels, respectively. Wheat was planted 2002 Apr. 25 and 2003 Apr. 11. Wheat was seeded at 270 seeds m 1 with a double disk drill set at 18-cm row spacing. Broadleaf weeds were controlled with application of bromoxynil + MCPA herbicides. The experimental design was a randomized arrangement of a split plot design with sic replications. Main plots (12.1 m 18.3 m) were cultivars (2): Alturas or Jubilee. Subplots (2.4 m 6.1 m) were factorial combinations of top-dress fertilizer application timing (three levels) and fertilizer application rate (three levels). The three timing treatments were: tillering (Zadoks 23), boot (Zadoks 47), and flowering (Zadoks 65). The three rate treatments were 0, 28, and 56 kg N ha 1, respectively, applied as ammonium nitrate (34-0-0). Topdressed N was immediately incorporated with 2.5 cm of irrigation water. Overhead sprinkler irrigation was used to irrigate the experimental area. Plots were irrigated weekly to replace

3 GUTTIERI ET AL. NITROGEN FERTILITY OF IRRIGATED SOFT WHITE SPRING WHEATS % estimated crop evapotranspiration (modified Penman method). Crop evapotranspiration estimates were obtained from the United States Bureau of Reclamation Pacific Northwest Region Agrimet System, which maintains a weather station at the University of Idaho Aberdeen Research and Extension Center. Plots measuring 1.5 m 4.6 m were harvested 202 Aug. 28 and 2003 Aug. 25 with a Wintersteiger small plot combine equipped with an onboard Harvestmaster (Juniper Systems, Logan, UT) weigh system. A sample was saved from each subplot for quality analyses. Quality Analyses Flour quality analyses were conducted at the University of Idaho, Aberdeen wheat quality laboratory at Aberdeen, ID. Milling, baking, and SRC analyses were conducted on one sample per subplot in each of three replications of the experiment in each year. Methods for tempering, near-infrared (NIR) hardness measurement, milling, measuring flour extraction, sugar snap cookie bake, and SRC analyses were as Guttieri et al. (2001) described and were in accordance with those described by the AACC (2000). Statistical Analysis Data were subjected to analysis of variance using PROC MIXED (SAS Institute Inc., Cary, NC, 1999). Initial analyses of variance testing year interactions with treatment factors indicated that treatment responses were similar in both years of the study; therefore, data were combined over years for analysis. Year, replication within year, and cultivar replication within year were treated as random effects. Cultivar, timing, and N rate were treated as fixed effects. Cultivar replication within year was used as the error term to test the significance of cultivar. Linearity of response to fertilizer rate and the interactions between fertilizer rate and application timing were evaluated using orthogonal contrasts. Results and Discussion Grain yield of Jubilee was significantly greater than grain yield of Alturas, averaging 8% greater yield (Table 1). Topdress fertilizer significantly improved grain yield of both cultivars, and the cultivars responded similarly to top-dress fertilizer application. Timing of top-dress application had no effect on grain yield or on response of grain yield to fertilizer rate. The 28 kg ha 1 and 56 kg ha 1 top dress fertilizer applications produced similar grain yield, which, on average, was 14% greater than yield without top-dress application (Table 2). Therefore, the base fertilizer application rate was, in fact, insufficient for optimum grain yield. Cultivar, top-dress fertilizer rate, and top-dress fertilizer timing all significantly affected break flour yield, but did not affect total flour extraction. The 28 and 56 kg ha 1 applications of fertilizer decreased break flour yield an average of 24 g kg 1 (Table 2). Flour ash was affected by top-dress fertilizer rate (Table 2) and timing (Table 3). The response of flour ash to topdress fertilizer rate was linear (linear contrast F = 39.7***; quadratic contrast F = 1.5, NS). And flour ash was lower when applied top-dress fertilizer was applied at tillering than at boot and flowering (contrast F = 4.6*). Flour ash was not significantly different when fertilizer was applied at boot versus at flowering (contrast F = 1.6, NS). The interaction of the linear response to fertilizer rate and the tillering versus boot and flowering applications was significant (contrast F = 5.9*). This interaction is illustrated in Fig. 1: the detrimental effect (increased flour ash) of top-dress N was most pronounced at the later application timings. Jubilee grain had significantly greater NIR hardness than Alturas grain (Table 1). Increasing N top-dress rates significantly increased NIR hardness, but the differences among N rates were substantially less than the differences between cultivars (Table 2). NIR hardness of Alturas and Jubilee responded similarly to N top-dress rate, and top-dress timing did not affect NIR hardness. Increased rates of top-dress N led to increased flour protein concentration (Table 2). The response of flour protein concentration to fertilizer rate was linear (contrast F = 79.7***, quadratic contrast F = 0.1, NS): flour protein concentration increased an average of 5.5 g kg 1 with each 28 kg ha 1 top-dress N. The effect of application timing on the response of flour protein to increasing top-dress N appears to be a consequence of a more pronounced response to N at later application timings, as illustrated in Fig. 2. Flour protein concentration was significantly lower when fertilizer was applied at tillering versus at boot and flowering (contrast F = 8.1**); however, flour protein concentration was not significantly different from applications at boot versus applications at flowering (contrast F = 0.9, NS). The interaction between linear response to fertilizer rate and the boot versus flowering application timing also was significant (contrast F = 5.1*). However, the interaction between the linear response to fertilizer rate and the tillering versus boot and flowering applications was non-significant (contrast F = 3.0). The response to of flour protein to top-dress N in this study are in contrast to results of our previous study (Guttieri et al. 2002). In our previous study (Guttieri et al. 2002), pre-plant fertilizer rate was sufficient to maximize yield and grain protein concentration; in the present study, pre-plant fertilizer rate was not sufficient to maximize yield and grain protein concentration. Water, sodium carbonate, and sucrose solvent retention capacities were significantly lower for Jubilee flours than for Alturas flours (Table 2). However, top-dressed N rate had no effect on water, sodium carbonate, or sucrose SRC of Jubilee and Alturas flours. Therefore, the increases in flour protein observed with increasing N did not lead to detrimental effects on these SRCs. Application timing significantly affected water SRC; mean water SRC for the boot, tillering, and flowering application timings were 485, 480, and 481 g kg 1, respectively. However, this small difference in water SRC is unlikely to meaningfully affect manufacturing applications. Lactic acid SRC was significantly greater for Alturas than for Jubilee flours (Table 1), and lactic acid SRC increased in flours of both cultivars with increased rates of top-dressed N (Table 2; linear contrast F = 30.9***, quadratic contrast F = 0.1, NS). Lactic acid SRC increased an average of 25 g kg 1 with each 28 kg ha 1 of top-dress N (Table 2). However,

4 462 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Effect of cultivar on break flour yield, solvent retention capacity, and sugar snap cookie diameter Solvent retention capacity Break Sodium Lactic Cookie Grain yield NIR flour yield Water carbonate Sucrose acid diameter Cultivar (t ha 1 ) hardness (g kg 1 ) (cm) Alturas 6.51a 2.1a 370a 489a 606a 890a 1068a 8.6a Jubilee 7.06b 13.6b 401b 475b 594b 819b 985b 8.8b a, b Means followed by the same letter are not significantly different according to a t-test at P < Table 2. Effect of top-dress fertilizer rate on grain yield, NIR hardness, break flour yield, flour ash and flour protein concentration, lactic acid SRC, and sugar snap cookie diameter Break Flour Lactic Cookie Fertilizer rate Grain yield NIR flour yield Flour ash protein acid SRC diameter (kg ha 1 ) (t ha 1 ) hardness (g kg 1 ) (cm) a 6.0a 401a 3.58a 84a 1002a 8.8a b 8.5b 378b 3.65b 90b 1025b 8.7b b 9.0b 376b 3.68b 95c 1052c 8.6b a, b Means followed by the same letter are not significantly different according to a Tukey s Studentized Range test at α = Table 3. Effect of top-dress fertilizer application timing on break flour yield, flour ash, and flour protein concentration Break Flour Flour Fertilizer flour yield ash protein timing (g kg 1 ) Tiller 389a 3.62a 88a Boot 391a 3.63ab 90ab Flowering 377b 3.65b 91b a, b Means followed by the same letter are not significantly different according to a Tukey s Studentized Range test at α = application timing did not affect lactic acid SRC or the response of lactic acid SRC to fertilizer rate. Lactic acid SRC is an indirect measure of glutenin content of flour (Gaines 2000). Therefore, lactic acid SRC is a function of both protein quantity and protein composition. Lactic acid SRC was correlated with flour protein concentration (r = 0.60***); lactic acid SRC increased 4.9 g kg 1 for each 1 g kg 1 increase in flour protein concentration. Application timing did not affect the response of lactic acid SRC to increasing flour protein concentration based on a test for heterogeneity of slope (F = 1.33, P = 0.26). This suggests that there was not a significant effect of application timing on protein composition, as measured by lactic acid SRC response to flour protein concentration. The diameter of sugar snap cookies produced from Jubilee flour was 0.2 cm greater than the diameter of cookies produced from Alturas flour (Table 1). Sugar snap cookie diameter decreased 0.1 cm with each 28 kg ha 1 increase in top-dress fertilizer (Table 2). The three-way interaction involving cultivar, N rate, and N timing sugar snap cookie diameter was significant. Therefore, the response of the two cultivars was reanalyzed separately. Cookie diameter from Jubilee flour responded only to N rate, averaging 9.0, 8.8 and 8.7 cm at the 0, 28, and 56 kg ha 1 rates, respectively (linear contrast F = 10.1**, quadratic contrast F = 0.2, NS). Contrasts to test the interaction of linear rate response and timing were non-significant. Cookie diameter from Alturas flour was also affected by N rate (linear contrast F = 10.6**, quadratic contrast F = 0.2, NS). The interaction between the linear response of Alturas cookie diameter to N rate and the tillering versus the boot and flowering application timings was significant (contrast F = 9.0**); however, the interaction between the response to N rate and the boot versus flowering application timing was non-significant (contrast F = 1.0, NS). The diameter of cookies produced from Alturas produced without additional top-dress fertilizer averaged 8.7 cm, and the diameter of cookies produced from Alturas flour with either 28 or 56 kg ha 1 top-dress fertilizer applied at flowering was 8.4 cm. In contrast, the diameter of cookies prepared from Alturas flour with 28 or 56 kg ha 1 applied at tillering averaged 8.6 cm. The negative relationship between flour protein concentration and cookie diameter is well documented. The response of Jubilee cookie diameter to fertilizer rate may simply be an effect of flour protein concentration. Inclusion of flour protein as a covariate in the analysis of variance of Jubilee cookie diameter eliminated the significance of all treatment effects. However, the response of Alturas cookie diameter to fertilizer rate is more complex than an effect of flour protein concentration alone. When flour protein was included as a covariate in the analysis of Alturas cookie diameter, the interaction between the linear response to rate and the tillering versus boot and flowering application timing was significant (contrast F = 6.0*). In the event that an irrigated soft white spring wheat crop is insufficiently fertilized at planting to achieve optimum grain yield, top-dress fertilizer application can increase grain yield, even when applied as late as flowering. Additional top-dress N can increase lactic acid SRC of the resulting flour by increasing flour protein concentration. Although lactic acid SRC and grain yield response to topdress fertilizer were not affected by application timing, other quality parameters, such as break flour yield, flour ash, and,

5 GUTTIERI ET AL. NITROGEN FERTILITY OF IRRIGATED SOFT WHITE SPRING WHEATS 463 Fig. 1. Response of flour ash concentration of two soft white spring wheat cultivars to top-dressed N application timing and rate. Fig. 2. Response of flour protein concentration of two soft white spring wheat cultivars to top-dressed N application timing and rate. in the case of Alturas, cookie diameter, were adversely affected by application after tillering. Earlier timing of N top-dress minimized the detrimental effects of the fertilizer application. Therefore, producers of irrigated soft white

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