Sugar beets must be properly irrigated and fertilized to maximize sugar
production. Both yield and sugar content can be materially altered by water
or fertilizer deficiency or excesses (4, 5). Farm operators must carefully
manage fertilization and irrigation to obtain the greatest net return from
sugar beets

Carter, J.N.

Jensen, M.E.

Northwest Irrigation & Soils Research Laboratory Publications

Changes in Nitrate-Nitrogen Concentration in Sugar Beet Petioles as Influenced by Irrigation and Fertilizer Practices

USDA - ARS - NWISRL

gr4Purchased by fhe O. S. Departmenf of Agriceltuf$For Official Use131CHANGES IN NITRATE-NITROGEN CONCENTRATIONIN SUGAR BEET PETIOLES AS INFLUENCED BYIRRIGATION AND FERTILIZER PRACTICES liJ. N. Carter and M. E. Jensen3INTRODUCTIONSugar beets must be properly irrigated and fertilized to maximize sugarproduction. Both yield and sugar content can be materially altered by wateror fertilizer deficiency or excesses (4, 5). Farm operators must carefullymanage fertilization and irrigation to obtain the greatest net return fromsugar beets.Of the common fertilizer elements, nitrogen has the greatest effect onsugar beet yield and sugar content (1, 2). Inadequate nitrogen, either residualor applied, limits root yield. On the other hand, excess nitrogen stimulatestop growth and reduces root sugar percentage. An adequate soil or tissue testis needed to properly manage nitrogen fertilization of sugar beets. The pur-pose of this study was to evaluate procedures for determining the NO3-N con-tent of sugar beet petioles at all plant growth stages and to relate valuesobtained to irrigation practices and nitrogen fertilizer requirements.MATERIALS AND METHODSA field experiment was conducted in 1966 on a Portneuf silt loam nearTwin Falls, Idaho. Four replications of randomized soil moisture plots,split for nitrogen rates, were used. Each replication contained 8 plots.Two soil moisture or irrigation treatments were used. The M 1 treat-ment was irrigated 12 hours per set when the soil moisture tension at the18-inch depth approached 0.65 atm, except for the first and second irrigation.The first irrigation of 6 hours was made when the tension reached 0.45 atmand the second of 8 hours at 0.55 atm tension. The M2 treatment was irriga-ted at the same time as the M 1 except the duration of the first irrigation was12 hours and that of all others was 24 hours.Four rates of nitrogen that were some fraction or multiple of an opti-mum rate, Fo, were used. The rates were 0. 5 Fo, Fo, 1.5 Fo, and 2 Fo .The optimum nitrogen fertilization rate was determined by the differencebetween the estimated amount needed for a 30-ton root yield (280 lbs of N/A)and the residual nitrogen that would be available for plant growth. The resi-dual soil nitrog en that would become available for plant growth during the1 Proceedings. Eighteenth Annual Fertilizer Conference of the PacificNorthwest, Twin Falls, Idaho. July 11-13, 19672Contribution from the Northwest Branch, Soil and Water ConservationResearch Division, Agricultural Research Service, USDA; IdahoAgricultural Experiment Station cooperating.3 Research Soil Scientist and Research Agricultural Engineer, respec-tively, Snake River Conservation Research Center, Kimberly, Idaho.132growing season was estimated by determining the water-extractable NO3-Ncontent of the soil after 3 weeks' incubation at 30° C.Phosphorus was uniformly applied March 23 at a rate of 55 pounds ofP per acre. The experimental area was then disked, plowed to a depth of 8inches and a seedbed prepared. The sugar beets were first planted March 30,but froze April 18. They were replanted April 23 and thinned to approximatelya 9-inch spacing early in June. Ammonium nitrate was applied June 17 as aside dressing just below and to the side of the irrigation furrow to minimizeleaching. All plots were irrigated June 28, using every furrow.Beet petiole samples were taken from each plot at regular intervalsthroughout the season for NO 3 -N analysis. Forty petioles were taken atrandom from each plot by selecting a young, fully mature leaf from eachplant sampled. Samples were taken during the late morning hours at eachsampling date. The petioles were brought into the laboratory and cut in half.Twenty leaf ends and twenty beet ends of these petioles, selected at random,were used for a quick-test for NO3-N content using fresh tissue. The re-maining halves were cut into 1/8-inch sections and mixed. Then, one-halfof this sample was oven-dried at 50 0 C and the other half was freeze-dried.The dried samples were ground to a 40-mesh size and subsampled forNO3 -N analysis.The NO3-N content of sugar beet petioles was determined by two differ-ent methods. The quick-test on the fresh tissue reported in this experimentwas made by a commercial fertilizer company using methods normally usedin their tissue testing program. The nitrate concentrations of the oven-and freeze-dried samples were determined by the phenoldisulfonic acidmethod (3) using a water extract of the beet petioles.RESULTS AND DISCUSSIONA comparison of the NO 3 -N level as indicated by the quick-test on thefresh petioles and the laboratory analysis on the ground tissue on individualsampling dates showed a greater variation on July 8 and July 22 (Figure 1).The standard error of the quick-test measurement was 16.6 on July 8 and23. 0 on July 22, as compared with 5. 8 on August 5, 4.4 on August 19, and6.9 on September 2. Variations occurred in the slope and intercept of theregression line on the different dates of sampling. This variation couldhave been caused by the differences in the petiole tissue or in the samplingtechniques used by the quick-test on the different dates sampled. If the threehigh F points on July 22 are not used, the regression equation is Y = 1, 7 ÷0. 00574 N. The quick-test method as used appears to be suitable forroughly determining if a field of beets had low, medium, or high levels ofnitrogen available for plant growth. A nonrepresentative fresh tissue sampleis the most probable cause of the variability encountered in the quick-test.Additional subsampling may reduce this variability. A composite graph ofall quick-test and laboratory data is presented in Figure 2. A technique thathas the speed of the quick-test and the accuracy of the detailed laboratoryanalysis is needed for determining the NO3-N level.Small variations in the NO3-N concentration in the petioles occurredbetween oven-dried and freeze-dried samples (Table 1). In general, theNO3-N values for the oven-dried samples were higher than for the freeze-dried133samples. This difference could have been due to the lower level of moisturein the oven-dried samples. From the results of this work, it can be con-cluded that no significant loss of NO 3 -N, or carbonaceous material, can beexpected in the oven-drying process if the oven temperature is kept near50A° C.The NO3-N level of the sugar beet petioles varied with stage of plantgrowth, level of applied nitrogen fertilizer, and to a limited extent with themoisture level as shown in Figures 3 and 4. The NO3-N concentration inthe petioles increased during the early plant growth stages at all nitrogenapplication levels and declined rapidly after about July 8 as the plant growthincreased. The NO3-N concentration at any selected plant growth stage wasdirectly related to the applied nitrogen level. 'Excessive irrigation caused amore rapid decrease in the NO3-N in the petioles on the 0.5 Fo and Fonitrogen treatments. There was very little difference in NO3-N content be-tween irrigation levels on the 1.5 F o and 2. F o nitrogen treatments.The generally accepted critical low range for NO 3 -N, based on water-extractable nitrates from mature petioles, is between 1000 and 2000 ppm.Also, if the NO3-N concentration drops below 1000 ppm for any appreciabletime before midseason, root and sugar yield will be reduced. The availablenitrogen supply of the soil should be depleted about 4 to 6 weeks before harvestor about August 20 in this area. The data in Figures 3 and 4 show that theNO3-N concentration on the 0.5 Fo treatment dropped below 1000 ppm early inAugust; hence, a reduction in yield would have been expected according toprevious studies. The root yield on the 0.5 Fo treatment was about 2 tons peracre less than on the 1.5 Fo and 2 Fo. Therefore, maintaining the NO3-Nlevel above 1000 ppm until the latter part of August would appear to eliminatenitrogen as a limiting factor in sugar beet yields, as was evidenced by thenitrogen level on the 1.5 Fo and 2 Fo treatments.There was a slight depression in the percentage of sugar in the roots atthe highest level of applied nitrogen (Table 2). However, this lower sugarcontent was offset by an increase in yield (Table 3), so that sugar productionwas about the same on all but the low nitrogen treatment (Table 4).Predicting the nitrogen level in the petioles during the latter part ofAugust from petiole analyses early in the season would be the goal of a tissuetesting program. This would enable the producer to apply additional nitrogenfertilizer, if needed, for maximum production of a high-quality beet root.Preliminary analysis of the data indicates that after the nitrate-nitrogen had reached a peak on all treatments, the decline in NO 3 -N followeda definite functional relationship. The rate of decrease in NO3-N in thepetioles was proportional to the concentration in the petioles as indicated byequation 1:dNdt —C , N 1where N is the NO3-Nconcentration in the petioles, t is time, and CI is aconstant for a given treatment. Integration of equation 1 with the peak con-centration of nitrogen at t = 0 used as the integration constant results in thefollowing equation:No exp (—Ci t)	 2134where No is the peak concentration of NO3-N, t is the time after the peak(to) occurs, and C1 is a constant which can be evaluated by determining theNO3-N content at two dates any time after the peak occurs.Equation 2 is evaluated in Figures 3 and 4. The solid lines after July 8represent equation 2 where No is the NO3-N on July 8, and C l was deter-mined by the change in NO 3 -N between July 8 and July 22. The solid linesprior to July 8 were merely fitted to the points. The dashed lines representthe estimated increase in NO3-N from July 1 to July 8. The data presentedin Figures 3 and 4 indicate that equation 2 adequately predicts the NO 3 -Nin the sugar beet petiole for all practical purposes. Therefore, if NO3-Ncontent of the petioles can be determined on two dates after the peak has beenreached, the NO3-N concentration during the remainder of the season can bepredicted to determine the adequacy or inadequacy of available nitrogen.A functional relationship between NO3-N early in the season and its rateof change with time is needed to determine the need for adding additional nitro-gen. Other factors will also probably need to be considered. For example,if the beets had already been sidedressed, as was done in this study, and theroot system was not utilizing this nitrogen, the nitrate content of the petiolesmight not reflect the available soil nitrogen. If nitrogen had been mixed inthe upper layers of the soil earlier in the season, then a functional relation-ship based on the NO3-N concentration of the petioles early in the seasonmight permit predicting the adequacy of nitrogen during the remainder of theseason for optimum sugar production. The NO 3 -N content at two dates withan interval of one or two weeks between sampling dates would probably beneeded for this purpose.SUMMARY AND CONCLUSIONSThe results of this experiment indicate that the level of nitrogen to beapplied for maximum sugar production can be estimated from a reliable soilor tissue test. The soil test, performed early in the growing season, wouldbe preferred to the tissue test so that nitrogen could be applied before plant-ing. Tissue testing of the beet petioles can be used to supplement a soil testin predicting the adequacy of nitrogen during the growing season. By the useof an adequate soil nitrogen test and the mathematical approach discussedin this paper for predicting the change in NO3-N in the petiole, maximum pro-duction of a high-quality beet root can be achieved.135Table 1. Effect of drying methods on the NO3-N concentration in sugarbeet petioles.Fertilizer	 ppm NO 3 -N in petiolestreatment	 24 June	 2 September0.5 FoFoFreeze-dry*76209670Oven-dry**755010350Freeze-dry*40200Oven-dry**220360M 1 1.5 F 8490 9330 1830 13102 Fo 10150 10800 2140 1620Avg 8980 9510 1050 8800.5 F o 8960 9550 110 240F 9540 10460 310 340M 2 1.5 Fo 9780 9810 680 7502 F 11030 10640 2010 2050Avg 9830 10110 780 850*Dried until the samples reached room temperature.**Dried at a temperature of 50° C.Table 2. Effect of nitrogen and moisture level on the sugar content ofbeet roots.Fertilizer	 Sugar content at moisture levelstreatment	 M 1	 M2	 Average0.5 Fo 17.3 17.3 17. 3Fo 17.4 17.2 17.31.5 Fo 17.3 17.0 17.22 Fo 16.9 16.6 16. 8Average 17.2 17.0 17.1136Table 3. Effect of nitrogen and moisture level on the yield of sugar beet roots.Fertilizer	 Yields at Moisture Levels Average   treatment M 2tons/acre	 tons/acre	 tons/acre0.5 Fo 22.5 24.3 23.4F 0 22.5 24.2 24.91.5 F0 24.6 25.7 25.221- 0 24.9 26.6 25.8Average 24.4 25.2 24.8Table 4. Effect of nitrogen and moisture level on the yield of sugar.Fertilizer	 Sugar yields at moisture levelstreatment m i M2tons/acre tons/acre tons/acre0.5 F0 3.88 4.21 4.05F o 4.43 4.17 4.301.5 Fo 4.24 4.37 4.312 Fo 4.22 4.40 4.31Average 4.19 4.29 4.24Average137LITERATURE CITED1. Haddock, Jay L. 1952. The nitrogen requirements of sugar beets.J. Amer. Soc. of Sugar Beet Technologists 7:161-165.2. James, D. W. 1966. Growing sugar beets for maximum sugar production.Wash. Agr. Exp. Sta. Cir. 464.3. Johnson, C. M. and A. Ulrich. 1959. Analytical methods for use inplant analysis. California Agr. Exp. Sta. Bul. 766.4. Robins, J. S. , C. E. Nelson, and C. E. Domingo. 1956. Some effectsof excess water application on utilization of applied nitrogen by sugarbeets. J. Amer. Soc. of Sugar Beet Technologists 9:180-188.5. Ulrich, A. D. Ririe, F. J. Hills, A. G. George, and. M. D. Morse.1959. Plant analysis, a guide for sugar beet fertilization. CaliforniaAgr, Exp. Sta. Bul, 766.138LIST OF FIGURES AND TABLESTable 1	 Effect of drying methods on the NO 3 -N concentration in sugarbeet petioles.Table 2.	 Effect of nitrogen and moisture level on the sugar content of beetroots.Table 3.	 Effect of nitrogen and moisture level on the yield of sugar beetroots.Table 4.	 Effect of nitrogen and moisture level on the yield of sugar.Figure 1.Figure Z.Comparison between a quick-test on the fresh tissue (F) and alaboratory analysis on the dried, ground petioles for NO 3 -N (N)concentration in sugar beet petioles at various sampling dates.Comparison between a quick-test on the fresh tissue (F) and alaboratory analysis on the dried, ground petioles for NO 3 -N (N)concentration in sugar beet petioles.Figure 3. Effect of sampling time and nitrogen fertilizer addition on theNO3-N concentration in the beet petioles on the Mi moisture level.Figure 4. 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Changes in Nitrate-Nitrogen Concentration in Sugar Beet Petioles as Influenced by Irrigation and Fertilizer Practices

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