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Published in Agron. J. 96:516-524 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

PRODUCTION PAPER

Basal Stem Nitrate Tests for Irrigated Malting Barley

Thomas L. Thompson*,a, Michael J. Ottmanb and Emily Riley-Saxtona

a Dep. of Soil, Water, and Environ. Sci., Univ. of Arizona, Tucson, AZ 85721
b Dep. of Plant Sci., Univ. of Arizona, Tucson, AZ 85721

* Corresponding author (thompson{at}ag.arizona.edu).

Received for publication July 17, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Nitrogen fertilizer use is essential for optimizing yield of irrigated malting barley (Hordeum vulgare L.) but must be managed carefully to achieve optimum grain protein concentrations demanded by the malting industry. Development of tissue tests, applicable for growing conditions in the desert Southwest, would be of benefit to growers for optimizing yield and grain protein of irrigated malting barley. Field experiments were conducted with two cultivars of malting barley [Morex (six row) and Crystal (two row)] under irrigated conditions in southern Arizona. The objectives were to (i) determine yield and grain protein response to N applications, (ii) determine the relationship between lower-stem tissue and sap NO3–N, and (iii) develop lower-stem and sap NO3 test guidelines for N management in malting barley. Yields ≥90% of maximum relative yield and grain protein concentrations acceptable for malting were achieved at N rates (kg ha–1) of 242 to 269 (1997–1998) and 205 to 269 (1998–1999) for Morex and 162 to 178 (1997–1998) and 166 to 181 (1998–1999) for Crystal. Stem and sap NO3–N were significantly correlated in both cultivars, with r2 values of 0.72 in Morex and 0.82 in Crystal. We propose that, to achieve acceptable grain yield and protein, lower-stem sap NO3–N in malting barley should be no less than 300, 180, and 120 mg L–1 and dry stem tissue NO3–N should be no less than 3000, 1000, and 800 mg kg–1 at Feekes growth stages 3, 7, and 10, respectively.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
ADDITIONS OF N FERTILIZER are essential for producing optimum yields of malting barley in the desert southwest U.S. However, in addition to increasing yield, N fertilizer additions may cause lodging and increase grain protein above desirable levels. Malting barley grain protein should be 115 to 130 g kg–1 for optimum malting quality of two-row malting barley varieties and 115 to 135 g kg–1 for six-row varieties, based upon 120 g kg–1 grain moisture content (American Malting Barley Association, 2002). Therefore, amounts of N fertilizer added must achieve a balance between optimum yield and grain protein.

Nitrogen applied to malting barley can also affect other properties of importance for the brewing process, including kernel plumpness, enzyme activities, extractable malt, and diastatic power (Lauer and Partridge, 1990; Clancy et al., 1991; Therrien et al., 1994). In general, as with yield and grain protein, additions of N fertilizer improve grain quality up to a point, beyond which further additions will decrease grain quality with respect to these properties. Therrien et al. (1994) concluded, after a series of experiments under dryland conditions in Manitoba, that environmental and genotype factors generally affect malting barley grain quality more than soil fertility does. Available N, however, was the most influential soil fertility property affecting grain quality.

Several researchers have investigated the relationship between cultural practices, particularly N fertilizer management, and malting barley grain protein. Most of these experiments have been conducted under dryland conditions. For example, Varvel and Severson (1987) found that malting barley grain protein never exceeded 130 g kg–1 under dryland conditions in Minnesota, with up to 168 kg N ha–1 applied. Birch and Long (1990) found that protein concentrations were <130 g kg–1 with up to 200 kg N ha–1 applied under dryland conditions in Queensland. However, Weston et al. (1993) found that standard malting barley cultivars had grain protein higher than acceptable levels, even when <150 kg N ha–1 was applied under dryland conditions in North Dakota.

Few researchers have reported the effects of N management practices on malting barley grain quality under irrigated conditions. Stark and Brown (1987) reported that malting barley grain protein was unacceptably high (>120 g kg–1) when soil plus fertilizer N was >210 kg ha–1 under irrigated conditions in Idaho. Lauer and Partridge (1990) found that grain protein occasionally exceeded 130 g kg–1 when 202 kg N ha–1 was applied to irrigated malting barley in Wyoming but that protein was always <130 g kg–1 with 134 kg N ha–1 applied.

Production of malting barley under irrigated conditions provides opportunities for optimum N management through fertigation. However, diagnostic tools are needed to predict the need for N fertilizer. Few reports exist in the literature illustrating diagnostic soil or tissue tests for malting barley. Stark and Brown (1987) reported that when soil (0–0.6 m) NO3–N plus fertilizer N applied was <210 kg ha–1, yield and protein were optimized under irrigated conditions in Idaho. They also reported N sufficiency levels in the lower-stem tissue for several growth stages of one malting barley cultivar. Weinhold and Krupinsky (1999) proposed a N sufficiency test for malting barley using a chlorophyll meter on leaves, comparing values obtained to those of a well-fertilized reference strip in the field. We chose not to employ a chlorophyll meter because tissue tests are already used in University of Arizona small-grain nutrient recommendations (Doerge et al., 1991) and growers should be accustomed to using them. To date, a tissue test specifically for malting barley has not been developed for irrigated conditions in the southwest USA. Development of a lower-stem nitrate test, applicable for growing conditions in the desert Southwest, would be of benefit to growers for optimizing yield and grain protein content of irrigated malting barley. A tissue sap test would also provide growers with a management tool allowing N management decisions to be made quickly.

The objectives of this experiment were to (i) determine the yield and grain protein response of two malting barley cultivars to N applications under irrigated conditions in the desert Southwest, (ii) determine the relationship between basal stem tissue and sap NO3–N, and (iii) develop basal stem tissue and sap NO3 test guidelines for N management of irrigated malting barley.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Experiments were conducted during the 1997–1998 and 1998–1999 growing seasons at the University of Arizona Maricopa Agricultural Center near Casa Grande, AZ, in a field mapped as a Casa Grande sandy loam (reclaimed fine-loamy, mixed, superactive, hyperthermic, Typic Natriargid). A six-row malting barley cultivar (Morex) and a two-row cultivar (Crystal) were planted in separate experiments during the two growing seasons. Cultivars were planted in separate blocks to facilitate planting using a grain drill. Each experiment was a randomized complete block design with five N rates (0, 67, 134, 202, and 269 kg N ha–1) and three replications. Sudangrass [Sorghum sudanenses (Piper) Stapf] was planted during the summer before each cropping season, irrigated, and cut several times to remove available soil N and reduce soil nutrient variability. Soil samples (0–0.3 m depth) collected before planting contained <10 mg NH4–N plus NO3–N kg–1 and 9 mg bicarbonate-extractable P kg–1.

Before planting each season, P (56 kg ha–1) was broadcast as triple-superphosphate (0–45–0) and incorporated. Malting barley cultivars were planted in level basins (18.3 by 122 m) using a grain drill with rows 0.15 m apart, and the seeding rate was 112 kg ha–1. After emergence, plot boundaries were established by using a tractor-mounted roto-tiller. Final plot size was 4.0 by 6.1 m. Planting dates were 21 Nov. 1997 and 19 Nov. 1998.

Irrigation was applied by flooding the level basins. There were five irrigation dates per season, and approximately 10 cm of water was applied at each irrigation event. Rainfall amounts between planting and harvest were 14.6 and 3.7 cm during the 1997–1998 and 1998–1999 seasons, respectively. Nitrogen was hand-applied as urea (46–0–0) in four split applications. Within each treatment, 40% of N was applied preplant, and the remaining 60% was applied in equal increments at Feekes growth stages 4, 7, and 10 (Large, 1954). Plots were irrigated immediately after each fertilizer application. We assumed that little or no lateral movement of fertilizer occurred. We based this assumption on the consistent appearance of unfertilized plots, regardless of the N rates applied to adjacent plots.

Basal stem tissue consisting of the lower 5 to 7 cm of stem tissue, excluding crowns, was collected from each plot at Feekes growth stages 3, 7, and 10 during each season. The first tissue sampling occurred at Feekes 3 because this growth stage typically occurs shortly before the first postemergence irrigation. Therefore, sampling at Feekes 3 gives current information regarding crop N status shortly before the first postplant opportunity to apply N. The sampling dates were 6 Jan., 11 Feb., and 4 Mar. 1998 and 5 Jan., 3 Feb., and 24 Feb. 1999. Thirty to 50 stems were collected in each plot between 0800 and 1200 h on each sampling date. The samples were immediately placed in plastic bags and stored on ice. Within 24 h of sampling, one-half of each sample was placed in an oven at 65°C, and the other half was used for sap extraction.

Sap was extracted by compressing cut stems with an arbor press. Nitrate concentration was determined by placing a few drops of sap on the sensing module of a Cardy compact NO3 meter (Horiba Ltd., Kyoto, Japan). The Cardy meter was calibrated after every 10th sample. Oven-dried samples were reweighed to determine moisture content and ground to <0.425 mm. Basal stem NO3 was determined by extraction with 0.015 M Al2(SO4)3, and NO3 concentrations were determined using a NO3–specific electrode (Baker and Thompson, 1992).

Plots containing Morex were harvested on 29 Apr. 1998 and 21 Apr. 1999, and those containing Crystal were harvested on 13 May 1998 and 28 Apr. 1999. Grain was harvested using a small-plot combine from an area of 1.5 by 4.3 m, and yield was calculated. Plant height and lodging were noted at harvest, and grain was sampled for determination of test weight and kernel weight. Grain N concentration was determined by using a micro-Kjeldahl method modified to recover NO3 (Bremner and Mulvaney, 1982). Grain N was converted to grain protein by multiplying N concentrations by 6.25. Grain yield and grain protein were corrected to a moisture content of 120 g kg –1. Analysis of variance and linear regression procedures were performed using SAS (SAS Inst., 1988).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Response to Nitrogen
Grain yield for Crystal malting barley showed a typical quadratic response to N, and maximum yields were achieved at N rates of approximately 180 kg ha–1 during each season (Fig. 1) . In contrast, yields of Morex apparently were not maximized within the range of the N rates used. Lauer and Partridge (1990) also found that malting barley yields were not maximized at N rates up to 202 kg ha–1 under irrigated conditions in Wyoming. Stark and Brown (1987) reported that yield of irrigated malting barley was maximized with >110 kg ha–1 of soil plus applied N. The reasons for the contrasting nature of the response curves for Morex and Crystal are not known but may be due to the higher lodging observed in Morex, particularly during the second season. The variance of yield data between seasons was not different at P = 0.05.



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  		Fig. 1. Mean grain yield and quadratic response equations for Morex and Crystal, 1997–1999.

 
The grain yields for Morex and Crystal were lower than the state average of 6000 kg ha–1 for 1998 and 1999 (Arizona Agric. Stat. Serv., 2002). Most of the barley grown in the state is semidwarf barley grown for feed. No separate statistics for Arizona exist for malting barley. Morex and Crystal are standard-height malting barley cultivars (taller than semidwarfs) that are not adapted to our area and are susceptible to lodging. Brewers typically offer contracts for growing malting barley cultivars with specific characteristics, yet these cultivars are not necessarily the best adapted to a particular area.

Grain protein responded in a linear fashion to increasing rates of applied N (Fig. 2) . With no N applied, grain protein was 50 to 90 mg g–1, well below the acceptable minimum value for malting (American Malting Barley Association, 2002). Each additional kilogram per hectare of N fertilizer increased grain protein by 0.12 mg g–1 (Morex in 1997) to 0.32 mg g–1 (Crystal in 1997). Stark and Brown (1987) reported that each additional kilogram per hectare of soil + applied N increased grain protein of three malting barley cultivars by 0.16 mg g–1 under irrigated conditions in Idaho. Two-row malting barley cultivars, such as Crystal, should have protein of 115 to 130 mg g–1 for optimum malting quality. This range of protein was achieved at N rates of 162 to 208 kg ha–1 during 1997–1998 and 166 to 240 kg ha–1 during 1998–1999. During each season, the highest N rate applied to Crystal resulted in excessively high grain protein. Six-row cultivars, such as Morex, should have protein of 115 to 135 mg g–1 for optimum malting quality. This range of protein was achieved in Morex at N rates of 235 to 269 kg ha–1 during 1997–1998 and 205 to 269 kg ha–1 during 1998–1999. Excessive grain protein concentrations were not observed in Morex. Several researchers have determined grain protein response to N application. Varvel and Severson (1987) found that grain protein in Morex did not exceed malting industry standards with up to 160 kg N ha–1 applied under dryland conditions. Weston et al. (1993) found that two standard malting barley cultivars achieved grain protein above acceptable concentrations when N applied was ≥150 kg ha–1 under dryland conditions. Stark and Brown (1987) found that irrigated malting barley grain protein exceeded standards (>120 mg g–1) when soil plus applied N was >210 kg ha–1. Lauer and Partridge (1990) found that irrigated malting barley grain protein exceeded acceptable concentrations when N applied was >150 kg ha–1.



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  		Fig. 2. Mean grain protein and linear response equations for Morex and Crystal, 1997–1999.

 
To evaluate effects of the various treatments, it is useful to denote zones of acceptable response. We define acceptable response as ≥90% of predicted yield (Fig. 1) and grain protein concentrations of 115 to 130 mg g–1 for Crystal and 115 to 135 mg g–1 for Morex (Fig. 2). According to these criteria, acceptable yield and grain protein were achieved at N rates (kg ha–1) of 242 to 269 (1997–1998) and 205 to 269 (1998–1999) for Morex and 162 to 178 (1997–1998) and 166 to 181 (1998–1999) for Crystal. Although response differed between the two cultivars, yield- and protein-optimizing N rates were similar within cultivars during the two seasons. These high yield-optimizing rates for Morex are atypical and are likely due to the unusual nature of the response curves, resulting from the high rate of plant lodging with this cultivar.

Test weight of Morex was significantly affected by N rate and season, but the effect differed between the two seasons, hence the significant season x N rate interaction (Table 1). During 1997–1998, test weight decreased with increasing N rate, whereas it increased with N applications up to 134 kg ha–1 during 1998–1999. Nitrogen rates of up to 134 to 202 kg ha–1 increased kernel weight of Morex during each season, but the highest N rate resulted in decreased test weight. Plant height and lodging of Morex were significantly affected by both season and N rate. The cooler, wetter conditions during 1997–1998 resulted in taller plants and a correspondingly higher lodging. These results further illustrate the benefits of avoiding excessive N applications to Morex malting barley. Test weight of Crystal was not significantly affected by N rate during 1997–1998 but was affected by N rate during the second season, hence the significant season x N rate interaction. Kernel weight of Crystal was not affected by N rate but was higher during the second season. Similar to Morex, both plant height and lodging of Crystal were higher during 1997–1998 than during 1998–1999, probably due to the cooler, wetter conditions that prevailed during that growing season.


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  		Table 1. Test weight, 1000-kernel weight, plant height, and percentage lodging of Morex and Crystal malting barley.

 
Development of Tissue Guidelines
There was a significant linear relationship between basal stem tissue NO3–N and basal stem sap NO3–N in both cultivars (Fig. 3) . Linear regression equations were determined for each cultivar at each of the three growth stages. We then used a t test, as described by Gomez and Gomez (1984), to determine homogeneity of regression coefficients. There were no significant differences between regression coefficients among growth stages or years within each cultivar. However, there was a significant difference between the regression equation slopes for Morex and Crystal. The r2 values of 0.72 for Morex and 0.82 for Crystal compare favorably to similar relationships presented for other crops. For example, Kubota et al. (1996) found an r2 of 0.77 between sap and petiole NO3–N in cauliflower (Brassica oleracea L. Botrytis Group), and Kubota et al. (1997) reported an r2 of 0.8 between sap and petiole NO3–N in broccoli (Brassica oleracea L. Italica Group). The x intercepts of the regression equations presented in Fig. 3 are approximately 60 mg NO3–N L–1, which suggests that the sap test may have overestimated sap NO3–N at low concentrations. This has been reported by other researchers (Westcott et al., 1993; Kubota et al., 1997). Kubota et al. (1997) suggest that this effect is most likely due to the effect of chemical interferences (i.e., Cl–) at low NO3 concentrations. However, this should have minimal effect on the practical use of sap NO3 values because the critical sap NO3 concentrations proposed below are >120 mg L–1, which is above the concentration at which interferences are of most concern.



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  		Fig. 3. Relationship between basal stem dry tissue NO3–N and basal stem sap NO3–N for Morex and Crystal, 1997–1999. ** Significant at P = 0.01.

 
We converted sap NO3–N concentrations to a dry matter basis and compared the resulting value with stem NO3–N (Fig. 4) . The resulting linear regression line had a slope of 0.93. This is not significantly different from the 1:1 line, indicating that the stem NO3 and sap NO3 tests measure essentially the same pool of NO3 in the plant. Therefore, sap NO3–N concentrations determined using the Cardy meter can be used directly or converted to stem NO3–N concentrations by using Eq. [1] for Morex and Eq. [2] for Crystal:

[1]

[2]
where Y = stem dry tissue NO3–N (mg kg–1) and x = sap NO3–N (mg L–1).



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  		Fig. 4. Relationship between basal stem dry tissue NO3–N and basal stem sap NO3–N, where sap NO3–N is expressed on a dry matter basis for Morex and Crystal, 1997–1999. The solid line represents the linear regression equation, and the dashed line represents a 1:1 relationship. ** Significant at P = 0.01.

 
Relative grain yields were calculated by dividing the individual plot yields by the highest plot yield for that season and cultivar. Relative yields were then plotted against stem NO3–N concentrations (Fig. 5) . The Cate–Nelson graphical method (Cate and Nelson, 1971) was used to estimate critical stem NO3–N concentrations associated with >90% relative yield. In the graphs shown in Fig. 5, 82% of the data points for Morex and 70% of those for Crystal fell within the lower-left and upper-right positive quadrants using the Cate–Nelson approach. The resulting critical concentrations were 5000, 2000, and 1200 mg kg–1 for Morex at Feekes 3, 7, and 10, respectively. The critical concentrations for Crystal were 4000, 1800, and 1000 mg kg–1 at Feekes 3, 7, and 10. In some cases, high stem NO3 was associated with low (<80%) relative yield. Most of these data represent plots where percentage lodging was high, a situation that usually lowered grain yield.



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  		Fig. 5. Relative grain yield and basal stem dry tissue NO3–N at Feekes growth stages 3, 7, and 10 for Morex and Crystal, 1997–1999. Dashed lines represent Cate–Nelson quadrants based upon 90% of maximum relative yield.

 
Knowles et al. (1991) proposed that basal stem NO3–N concentrations should be 3000 to 4000, 1000 to 1500, and 800 to 1200 mg kg–1 for irrigated durum wheat at Feekes 3, 7, and 10, respectively. Stark and Brown (1987) proposed sufficiency levels of 6000 and 1000 mg NO3–N kg–1 for irrigated malting barley at Feekes growth stages 2 and 9, respectively. Therefore, the critical concentrations determined in our experiment, based upon relative yield, are similar to those derived for similar crops and conditions.

Relative yield was plotted against sap NO3–N to determine if a rapid sap NO3 test would provide an index of N sufficiency as it relates to yield (Fig. 6) . Again, the critical values for basal stem sap NO3 were estimated by using the Cate–Nelson graphical method (Cate and Nelson, 1971) and a criterion of >90% relative yield. The resultant estimated critical values are shown in Fig. 6: 400, 200, and 130 mg NO3–N L–1 for both cultivars at Feekes 3, 7, and 10, respectively. In the graphs shown in Fig. 6, 84 and 74% of the data points for Morex and Crystal, respectively, fell within the positive Cate–Nelson quadrants.



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  		Fig. 6. Relative grain yield and basal stem sap NO3–N at Feekes growth stages 3, 7, and 10 for Morex and Crystal, 1997–1999. Dashed lines represent Cate–Nelson quadrants based upon 90% of maximum relative yield.

 
Grain protein is an important factor for evaluating outcomes of malting barley production; therefore, to be most effective, tissue NO3 tests should have predictive power related to grain protein. Therefore, a Cate-Nelson approach was again used to divide basal stem tissue NO3 (Fig. 7) and sap NO3 (Fig. 8) values into those with adequate and inadequate protein. The resulting stem tissue critical values were 3000, 1000, and 800 mg NO3–N kg–1 for Morex and 2100, 800, and 800 mg NO3–N kg–1 for Crystal, at Feekes stages 3, 7, and 10, respectively (Fig. 7). It appears, from an examination of Fig. 5, that utilizing the lower protein-based critical concentrations could have a more negative effect on yield of Morex than of Crystal.



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  		Fig. 7. Grain protein and basal stem dry tissue NO3–N at Feekes growth stages 3, 7, and 10 for Morex and Crystal, 1997–1999. Shaded areas represent zones of acceptable grain protein concentration. Dashed lines represent Cate–Nelson quadrants based upon 90% of maximum relative yield.

 


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  		Fig. 8. Grain protein and basal stem sap NO3–N at Feekes growth stages 3, 7, and 10 for Morex and Crystal, 1997–1999. Shaded areas represent zones of acceptable grain protein concentration. Dashed lines represent Cate–Nelson quadrants based upon 90% of maximum relative yield.

 
The sap NO3–N critical values associated with adequate grain protein were 300, 180, and 120 mg L–1 at Feekes growth stages 3, 7, and 10 for Morex. For Crystal, the critical sap NO3–N values were 280, 180, and 120 mg L–1 at Feekes 3, 7, and 10, respectively (Fig. 8). In general, both the tissue and sap tests were more effective at predicting protein response than yield response. For Morex, 83% of the stem NO3–N data points (Fig. 7) and 88% of the sap NO3–N data points (Fig. 8) were in positive quadrants according to the Cate–Nelson test. The corresponding values for Crystal were 92% for the stem test (Fig. 7) and 89% for the sap test (Fig. 8). Both tests were effective at detecting N deficiencies related to inadequate grain protein but unfortunately were not sufficiently sensitive at detecting excess N leading to excessive grain protein in Crystal. The critical values presented here should be considered minimum values for achieving adequate grain protein. Maintaining sap NO3–N concentrations near, but above, these concentrations should create conditions for achieving adequate, but not excessive, grain protein.

It is instructive to compare the critical stem tissue NO3 and sap NO3 values associated with minimum acceptable grain protein with those presented above, based upon 90% of maximum relative yield (Table 2). It is important to note that the critical stem and sap concentrations based upon 90% relative yield are higher than those based upon grain protein. Because protein concentration is important for malting barley quality and overfertilization can reduce yield and increase protein to undesirable concentrations, it is most appropriate to use the lower critical concentrations.


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  		Table 2. Critical stem tissue NO3–N and sap NO3–N concentrations for Morex and Crystal malting barley, based upon relative yield and grain protein.

 
The similarity in critical concentrations between these two cultivars suggests that these concentrations may be applicable across two- and six-row malting barley cultivars. Therefore, we propose that sap NO3–N in malting barley should be no less than 300, 180, and 120 mg L–1 at Feekes 3, 7, and 10, respectively. The critical stem NO3–N concentrations for these three growth stages are 3000, 1000, and 800 mg kg–1. Maintaining irrigated malting barley tissue concentrations above these values should result in adequate grain yield and grain protein.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 




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