Irrigation and Nitrogen Fertilization Affect End-Use Quality of Spring Wheat of Three Market Classes

N fertilizer is a principal and costly nutrient input, but its use efficiency is only about 40%–50% in most U.S. agricultural operations. Low N use efficiency (pounds of N applied per bushel of crop produced) results from a loss of applied N to the soil-plant system via various pathways (e.g., gaseous plant emission, denitrification, leaching, surface runoff, and volatilization). Improving N use efficiency in cereal crops is thus a challenging task. It requires an ability to coordinate an accurate estimate of crops’ need for N with the development of nutrient management practices that provides the best return from N fertilizer application.

Wheat is an integral crop in Idaho, where it is grown as a main cash crop or as a vital rotational crop with others such as vegetables, potatoes, sugar beet, pulses, and oil seeds. In order to maximize wheat grain yields and enhance grain quality, wheat producers urgently need to develop more efficient water and nutrient management strategies. But it’s a complex pursuit. The uptake of water and N for crop growth and production is fundamentally interactive. Soil moisture significantly affects both nutrient release from applied fertilizers and mineralization reactions within the soil ecosystem. Thus, when developing N guidelines for irrigated crops, it is necessary to address the efficiency of water and N applications at the same time.

Water and N management for wheat grain yield improvement have been well documented, whereas there is a lack of evaluations of grain quality in response to these management practices. Many of the parameters that are indicative of wheat grain quality deserve more discussion or attention, starting with the utility of test weight as a measure of grain bulk density and quality. Indeed, a high test weight generally represents good grain quality and a great economic value. Falling number is another one that indicates α-amylase activity and the degree of sprout damage. Generally speaking, a wheat grain sample with a greater falling number (e.g., > 350 sec) denotes lower enzyme activity and better quality. Protein content is probably the single most important grain quality trait, since it directly relates to many important processing properties such as water absorption, gluten strength, texture, and appearance. Higher-protein dough usually absorbs more water and takes longer to mix, qualities usually regarded as undesirable in baking. The solvent retention capacity (SRC) test is a more recently developed method and provides useful information such as gluten strength and starch damage during the milling process. Flour yield represents the portion of the wheat kernel that can be milled into flour and is an important indicator of milling profitability. Lastly, ash content indicates how well flour separates from the bran. Since ash content can affect flour color, a low ash content is often a high priority among millers for white flours.

To date, most recommendations for irrigation and N fertilization are calibrated for optimal grain yield, but few studies have investigated their effects on grain quality. Therefore, the objective of this study is to determine N and water requirements for optimal wheat grain quality.

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Field Experiments

Three field experiments were performed in 2016 and 2017 at three locations, including the University of Idaho Aberdeen Research and Extension Center; the University of Idaho Parma Research and Extension Center; and the Montana State University Northwestern Agricultural Research Center at Kalispell. Characterization of the top-foot soil at each location and in each year is listed in Table 1. Experimental locations in 2016 and 2017 at each location were adjacent to each other to minimize soil heterogeneity and carryover effects from different experimental treatments from previous seasons. Experimental plot size was 10 × 20 ft (i.e., 200 ft²) with 7-in row spacing, and the seeding rate was 1,000,000 seeds/ac at each location. Hard white spring wheat (‘Dayn’), soft white spring wheat (‘Alturas’), and hard red spring wheat (‘Egan’) were planted at Aberdeen, Parma, and Kalispell, respectively (Table 2).

At each location, the experiment was established with two factors and four replications for each year. The first factor was irrigation treatment, including 0% (dryland control), 50%, 75%, and 100% crop evapotranspiration (ET_c) replenishment. Daily ET_c was calculated by daily atmospheric grass-referenced evapotranspiration (ET_o) multiplied by crop coefficient (K_c). Daily ET_o was retrieved from AgriMet Cooperative Agricultural Weather Network weather stations located within 1 mi of each experimental location. The K_c for key growth stages of wheat was obtained from Allen et al. (1998). Irrigation was applied via dripping systems and was triggered when 35% of the plant-available water in the soil was depleted and terminated at stages between late milking and early soft dough. Rainfall and irrigation for the 100% ET_c treatment during each growing season are listed in Table 2.

N fertilization was the second factor. Target soil N levels included 150-, 200-, and 250-lb N ac-1, which were denoted by low, medium, and high N rates, respectively. Actual N application rate was calculated by subtracting soil residual N (Table 1) from the target N level. N as urea (46–0–0) was incorporated prior to planting. A control treatment with no N addition (i.e., zero N rate) was also included. Phosphorus (P) and potassium (K) were supplied as monoammonium phosphate (11–52–0) and potassium chloride (0–0–60), according to soil test results for each location and year, following the guidelines of the University of Idaho and Montana State University for crop fertilization under irrigated conditions. Herbicides, fungicides, and insecticides were applied as needed at each location.

Plots were harvested at maturity using a small-plot combine. The University of Idaho’s Wheat Quality Laboratory at Aberdeen analyzed all end-use quality attributes. Evaluated end-use quality traits and their implications are listed in Table 3.

Hard White Spring Wheat at the Aberdeen Research and Extension Center

‘Dayn’ is a hard white spring wheat cultivar that the Washington State University Agricultural Research Center and the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) released in 2012. It produced the highest grain yield in variety trials conducted in 2016 and 2017 in southern Idaho. In the Aberdeen experiment, irrigation significantly improved test weight and flour yield; however, flour ash content, flour protein content, dough optimal mixing time (mixograph peak time), dough/gluten strength (mixograph height and lactic acid-retention capacity), and baking loaf volume decreased following irrigation (Table 4). There was no significant difference in any evaluated grain quality traits between the 75% and 100% ET_c irrigation treatments. Falling number was not affected by irrigation treatment nor N rate.

N fertilization slightly decreased test weight, but increased flour ash content, flour protein content, mixograph height, and baking loaf volume. No significant difference was observed in any evaluated end-use quality attribute among the low, medium, and high N rates.

Hard Red Spring Wheat at the Northwestern Agricultural Research Center

‘Egan’ is a recently released hard red spring wheat cultivar by Montana State University and is known for its high yield potential, high protein content, and resistance to orange wheat blossom midge. In the experiment conducted at Kalispell, the 75% and 100% ETc irrigation treatments produced similar grain quality (Table 5). ‘Egan’ was able to maintain high and consistent flour protein content (>15%) under different irrigation treatments, which surpasses the premium market quality of grain protein content for hard red spring wheat (14%). This cultivar also showed improved dough/gluten strength (mixograph height and lactic acid-retention capacity) and baking loaf volume with irrigation.

Although N application decreased the falling number, it is not a primary concern since the falling numbers were all above 350 sec (Table 5). Minimal differences were observed between the medium and high N rates in most evaluated end-use quality attributes.

Soft White Spring Wheat at the Parma Research and Extension Center

‘Alturas’ is a soft white spring wheat cultivar released by the Idaho Agricultural Experiment Station and USDA-ARS in 2002 that has been planted throughout southern Idaho. In the experiment conducted in Parma, flour protein content of ‘Alturas’ increased with N rate, but flour yield, flour ash content, and cookie diameter were not affected by N fertilization (Table 6). Flour yield, flour protein content, flour ash content, and cookie diameter responded minimally to irrigation treatments.

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Conclusion and Recommendations

• The results from experiments conducted at multiple locations in multiple years provide helpful data on water and N management to achieve optimal grain quality in spring wheat of different market classes.
• No difference was observed in any end-use quality attributes under a 25% reduction in irrigation (i.e., 75% ET_c) compared to the full irrigation treatment (i.e., 100% ET_c) in spring wheat of any class, suggesting minimal effects on end-use quality from the irrigation reduction.
• End-use quality attributes did not differ between the high (250 lb/ac) and medium N rate (200 lb/ac equals soil residue N plus applied N fertilizer) in any tested spring wheat cultivar, suggesting that 200 lb/ac might be adequate to achieve optimal end-use quality.

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References

Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements. FAO Irrigation and Drainage Paper 56. Rome: Food and Agriculture Organization of the United Nations. 300 (9): D05109.

Blake, N.K., R.N. Stougaard, B. Bohannon, D.K. Weaver, H.-Y. Heo, P.F. Lamb, D. Nash, D.M. Wichman, K.D. Kephart, J.H. Millerm, G.V.P. Reddy, J.L. Eckhoff, W.E. Grey, S.P. Lanning, J.D. Sherman, and L.E. Talbert. 2014. “Registration of ‘Egan’ Wheat with Resistance to Orange Wheat Blossom Midge.” Journal of Plant Registrations 8, no. 3: 298–302.

Marshall, J., C. Jackson, T. Shelman, L. Jones, S. Arcibal, and K. O’Brien. 2017. 2016 Small Grains Report: Southcentral and Southeastern Idaho Cereals Research and Extension Program. Idaho Agricultural Experiment Station, Research Bulletin 191. 148 p.

Marshall, J., C. Jackson, T. Shelman, L. Jones, S. Arcibal, and K. O’Brien. 2018. 2017 Small Grains Report: Southcentral and Southeast Idaho Cereals Research and Extension Program. Idaho Agricultural Experiment Station, Research Bulletin 193. 150 p.

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About the Authors

Rui Yang—Postdoctoral Fellow, University of Idaho, Aberdeen Research and Extension Center

Xi Liang—Cropping Systems Agronomist, University of Idaho, Aberdeen Research and Extension Center

Olga S. Walsh—Cropping Systems Agronomist, University of Idaho, Parma Research and Extension Center

Jessica A. Torrion—Crop Physiologist, Montana State University, Northwest Agricultural Research Center

Kathrine O’Brien—Lab Manager, University of Idaho, Wheat Quality Lab

Sanaz Shafia—Postdoctoral Fellow, University of Idaho, Parma Research and Extension Center

Acknowledgment

This publication is funded by a grant from the USDA-Western Sustainable Agriculture Research and Education program (grant no. SW16-031).

BUL 957 | Published December 2019 | © 2022 by the University of Idaho

Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Barbara Petty, Director of University of Idaho Extension, University of Idaho, Moscow, Idaho 83844. The University of Idaho has a policy of nondiscrimination on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity/expression, age, disability or status as a Vietnam-era veteran.