Sucrose Production by Sugarbeets
1 J . N . C A R T E R , C . H . P A I R , a n d D . T . W E S T E R M A N N2Received for publication September 8, 1975
For m a x i m u m sucrose p r o d u c t i o n by sugarbeets (Beta vulgaris L.) in s o u t h e r n I d a h o , the available soil nitrogen (N) level should be highest d u r i n g early July, w h e n t h e p l a n t N u p t a k e (Nup) r a t e is high- est, a n d lowest by t h e latter part of A u g u s t (1, 12)3. I n a d e q u a t e N d u r i n g the early growth stages limits r o o t a n d sucrose yield, whereas excess N stimulates t o p growth, increases root impurities, a n d de- creases sucrose p e r c e n t a g e a n d extractable sucrose (7). I n a d e q u a t e irrigation limits root a n d sucrose yields, whereas overirrigation leaches N a n d may affect t h e sugarbeet response to N application (2, 6, 9, 11).
Maintaining o p t i m u m levels of available N for plant growth d e - p e n d s u p o n p r o p e r N-fertilizer application, either as a p r e p l a n t or side-dress application, in relation to the N available from soil sources ( 1 , 3). However, overfertilization with N may occur even with an ade- q u a t e testing p r o g r a m d u e to overestimation of t h e yield potential or yield reductions d u e to p o o r stands, insect d a m a g e , disease, o t h e r n u t r i e n t deficiencies, or adverse climatic factors. If the available N supply in t h e soil is too high for the expected yield d u r i n g the season, mid- to late- season removal of p a r t or all of t h e excess N may i m p r o v e beet quality and sucrose p r o d u c t i o n .
N i t r a t e - n i t r o g e n (NO3-N) a c c u m u l a t e s o n o r n e a r t h e r i d g e surface in furrow-irrigated sugarbeets. T h i s concentration increases as the season progresses, d u e to water a n d N O3- N m o v e m e n t towards the d r y i n g surface. T h e NO3-N below and n e a r t h e irrigation furrow decreases at each irrigation because of N leaching below the furrow, m o v e m e n t of NO3-N towards the d r y i n g surface, a n d Nu p by the plants. Rainfall sufficient to move the accumulated NO3-N into the r o o t zone may have beneficial effects on plant growth early in the season. However, if sufficient NO3-N is washed into t h e root zone late in t h e season, it may stimulate vegetative growth a n d have d e t r i m e n t a l effects on both sucrose p e r c e n t a g e and sucrose yield. Sprinkler irriga- tion r a t h e r t h a n furrow irrigation p r e s u m a b l y p r e v e n t s the N O3- N accumulation on t h e soil surface. As a result, sucrose p e r c e n t a g e a n d
1Contribution from the Western Region, Agricultural Research Service, USDA.
2Soil Scientist, Agricultural Engineer (retired), a n d Soil Scientist, respectively, Snake River Con- servation Research Center, Kimberly, I d a h o 8 3 3 4 1 .
3N u m b e r s in parentheses refer to literature cited.
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sucrose yield may be greater under sprinkler than furrow irrigation, especially in irrigated areas where rainfall is concentrated in the late summer or early fall.
This paper summarizes studies on the effects of irrigation method and the reduction in NO
3-N late in the season, at different N levels, on sucrose production by sugarbeets.
Materials and Methods
Three field experiments were conducted on a Portneuf silt loam soil (Xerollic Calciorthid; coarse-silty, mixed, mesic) near Twin Falls, Idaho. This soil has a weakly cemented hardpan at the 16- to 20-in depth that has little effect on water movement when saturated, but may restrict root penetration. Adequate phosphorus (P) fertilizer (44 lb P/A) was broadcast on all experimental areas before seedbed prepara- tion. Adequate potassium was present from soil and irrigation water sources.
Experiment 1 plot area had been cropped to barley without fertilizer the previous year, and a soil test predicted 100 lb of fertilizer N/A was needed for maximum sucrose yield. Two irrigation methods (furrow and sprinkler) and two irrigation treatments (nonleached and leached) were used as main plots with four N-fertilization rates (50, 100, 150, and 200 lb N/A) as subplots; all were replicated four times.
Experiment 2 plot area had been cropped to barley (straw burned) without fertilizer the previous year, and a soil test predicted 296 lb of fertilizer N/A was needed for maximum sucrose yield. Two furrow irrigation treatments (nonleached and leached) were used as main plots with three N rates (0, 100, and 200 lb N/A) as subplots; all were replicated two times.
Experiment 3 plot area had been cropped to sugarbeets without fertilizer the previous year and a soil test predicted sufficient available residual N for maximum sucrose yield. Two cropping treatments (no sudangrass and sudangrass) and two N rates (100 and 200 lb N/A) were used; all were furrow-irrigated and replicated four times in a randomized block.
Sugarbeets (Beta vulgaris L.) were planted in 24-in rows on April 15 and replanted May 12 because of poor stand in Experiment 1, on April 14 in Experiment 2, and April 21 in Experiment 3. In early June, plants were thinned to a within-row spacing of approximately 12 in. Piper sudangrass (Sorghum sudanense) was planted in Experiment 3 plots by a broadcast application on July 9 just before the last cultivation at the rate of 100 lb/A.
Nitrogen fertilizer (NH
4NO
3) was applied below and to the side of
the irrigation furrow as a side-dressing in early June in Experiments 1
and 3, and broadcast preplant (Ca(NO
3)
2) in Experiment 2.
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All plots were irrigated when their soil moisture reached pre- scribed levels based on estimated evapotranspiration (8), except w h e n the plots were intentionally leached (Fig. 1).
Figure 1.—Irrigation water applied and rainfall. (Total irrigation water applied from 6/1 to 9/30, based on estimated evapotranspiration, was 28, 30, and 33 in, while the leaching fraction was 18, 24, and 0 in in Experiments 1, 2, and 3, respectively. Irrigations previous to 6/1 are not shown.)
Irrigation Water in E x p e r i m e n t 1 was applied to alternate furrows (every o t h e r furrow, alternating furrows at each irrigation) d u r i n g t h e first two irrigations. After t h e side-dressed fertilizer application, t h e third irrigation (June 22) was applied to all furrows. B e g i n n i n g with t h e fourth irrigation (July 11), a n d for t h e r e m a i n d e r of t h e season, half of each replication was furrow-irrigated using alternate furrows, and the o t h e r half sprinkler-irrigated. Half of t h e sprinkler- a n d furrow-irrigated areas was leached with about 18 in of water in late August and early S e p t e m b e r (Fig. 1A, B).
E x p e r i m e n t 2 had irrigation water applied to alternate furrows on all plots the first five irrigations. B e g i n n i n g with the sixth irrigation (July 22), half the plots were irrigated using alternate furrows a n d half
VOL. 18, No. 4, OCTOBER 1975 335
using every furrow. Areas with every furrow irrigated received 14.2 in of extra irrigation water on the seventh irrigation (Aug. 2). The time and duration of the alternate and every-furrow irrigation treatments were the same, except for the seventh irrigation (Fig. 1C).
Experiment 3 was irrigated using alternate furrows at pres- cribed levels based on evapotranspiration for the entire season (Fig.
1D).
Weekly petiole samples consisting of 24 of the youngest, fully mature leaves were taken at random from each plot at each sampling date. The petioles were cut into 0.25-in sections, dried at 65°C, ground to pass through a 40-mesh sieve, subsampled, and analyzed for NO
3-N.
Petiole NO
3-N concentration was determined by the phenoldisulfonic acid method using a water extract of the petioles for Experiments 1 and 3 (12), and using a nitrate specific ion electrode for Experiment 2 (10).
In late October, the beet roots were harvested for Experiments 1 and 3 by taking eight 30-ft rows, and in Experiment 2 by taking six uniform 10-ft row sections. Sucrose content was determined on two samples (30 lb each) of randomly selected roots from each plot by a sugar company using their standard procedures.
Results and Discussion Experiment 1
The overall effect of N fertilizer was to significantly increase beet root yield at the two higher N levels as compared with the 50-lb/A rate (Fig. 2A). However, because the sucrose percentage decreased as each applied-N level increased, there was no significant change in sucrose production at different N rates. Although there was no significant change in sucrose production, there was a steady decline in sucrose yield with each N addition above the 50-lb/A rate.
The soil test for available N (1) indicated that approximately 100 lb of applied N/A would be required for the expected root yield of 27 T/A.
However, the 50-lb/A rate was adequate at the relatively low produc- tion level attained because of replanting. Petiole analysis confirmed that sufficient or excess N (2, 12) was available for maximum produc- tion on all N treatments (Fig. 3).
Sprinkler-irrigated sugarbeets consistently produced slightly greater root and sucrose yields at the three lower N levels as compared with those furrow-irrigated (Fig. 2B); yet the differences were signifi- cant only at the 100-lb/A N rate. The sucrose percentage decreased as N rate increased for both irrigation methods. However, there were no significant differences in sucrose percentage between the two irriga- tion methods. Nevertheless, sprinkler-irrigated sugarbeets produced an average of 5% more sucrose than did furrow-irrigated sugarbeets at the three lower N levels.
There was no rainfall from July 7 to September 10, which favored
the accumulation of NO
3-N in the ridges of the furrow-irrigated
Figure 2.—Effect of N, irrigation method, and leaching on root yield, sucrose yield, and sucrose percentage of sugarbeets in Experiment 1.
(Means within a method of irrigation followed by the same letters are not significantly different at the 5% level according to Duncan's Multiple Range Test. ‡ Tukey's value (w). Means with differences larger than w are signifi- cantly different at the 5% level.)
sugarbeets. Rainfall on September 10 (0.63 in) and 20 (0.19 in) was sufficient to move p a r t or all the NO3-N accumulated in the ridges into the root zone. C o n t r a r y to expectations, t h e NO3-N concentrations in the petioles of the sprinkler-irrigated beets generally were h i g h e r than those in furrow-irrigated beets (Fig. 4A, B) d u r i n g t h e latter part of the season (average furrow-irrigated, petiole NO3-N (Y) = In 3164 — 0.026 X sampling d a t e (x), r = 0.99; average sprinkler-irrigated, peti- ole NO3-N (Y) = In 3752 - 0.019 x sampling d a t e (x), r = 0.88). T h e sucrose p e r c e n t a g e with the two forms of irrigation, however, was c o m p a r a b l e (Fig. 2B).
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Figure 3.—Nitrate-nitrogen concentration in sugarbeet petioles at various sampling dates using two methods of irrigation and four N rates in Experiment 1.
methods resulted mainly from differences in root production. Petiole analysis indicated the N nutrition was not a contributing factor in these differences on three of the N treatments (Fig. 3). However, furrow- irrigated beets receiving 100 lb N/A had a substantial reduction in petiole N0
3-N from midseason as compared with sprinkler-irrigated beets at the same N treatment. This indicated a growth factor or N difference on this treatment that we could not account for, but may have been the contributing factor in the significant difference in root and sucrose yields at this N treatment. If differences do exist between furrow- and sprinkler-irrigated beets, the cause may be due to growth characteristics of the plant under the two forms of irrigation. Haddock (6) showed that sugarbeets grown under sprinkler irrigation had a higher top:root ratio and a greater top yield. In our work, sugarbeets grown under sprinklers seemed to have a higher leaf area index and a more erect growth enabling a possible greater efficiency in use of the radiant energy.
Increased irrigation water application to leach N0
3-N from the
root zone late in the season reduced beet root yield as compared with
nonleached areas at the three lower levels of applied N (Fig. 2C). How-
ever, leaching increased sucrose percentage from 0.3 to 0.75% and
averaged 0.52%. As a result of the root decrease and sucrose percen-
tage increase with leaching, no significant effect was found on sucrose
production.
338 JOURNAL OF THE A. S. S. B.T.
T h e lower r o o t yield on leached plots may have b e e n caused by adverse conditions d u r i n g a n d immediately after the leaching period.
D u r i n g this period, sugarbeet plants wilted a n d sprinkler-irrigated p l a n t leaves had a white a p p e a r a n c e . T h i s wilting could have b e e n d u e to partial anaerobic conditions in the root zone d u r i n g leaching (13).
However, we did n o t d e t e r m i n e the cause of t h e white a p p e a r a n c e of the beet leaves, b u t this was probably d u e to d r i e d salts from water of guttation or irrigation water. Either or b o t h factors may have con- tributed to the r e d u c e d root yield.
Petiole analysis indicated that available N supply d e c r e a s e d after the period of heavy water application u n d e r b o t h irrigation m e t h o d s (Fig. 4A, B). Sufficient N was still available to keep the plants at a high NO3-N level, particularly on the h i g h e r levels of applied N. Earlier
Figure 4.—The effect of late season removal of N 03- N from the root zone on petiole NO3-N concentration of sugarbeets in Experiments 1, 2, and 3.
VOL. 18, No. 4, OCTOBER 1975 3 3 9 leaching of N m i g h t have caused a m o r e desirable available soil-N de- crease a n d a sufficient sucrose p e r c e n t a g e increase to m a k e leaching a potentially feasible practice. Also, t h e p l a n t N Os- N level c o u l d be m o r e easily controlled on a sandy, low mineralization capacity soil t h a n on the silt loam used in this e x p e r i m e n t . However, t h e intentional leach- ing will increase t h e possibility of c o n t a m i n a t i n g g r o u n d w a t e r with N O3- N .
Experiment 2
As N-fertilizer rates increase, root a n d sucrose yields significantly increased, b u t p e r c e n t a g e sucrose at both levels of irrigation water was not affected (Fig. 5A). H o w e v e r , t h e r e was no significant or noticeable difference between these yield factors a n d the level of irrigation.
Petiole analysis indicated that p a r t of t h e N 03- N was leached below t h e root zone, denitrified, or r e d u c e d in availability to t h e p l a n t on t h e plots receiving N fertilizer (Fig. 4C). For the no-N t r e a t m e n t , N O3- N in t h e petioles increased t h r o u g h o u t t h e season a n d was consistently h i g h e r at the h i g h e r irrigation level. A p p a r e n t l y , at these low-to-adequate levels of N, only small a m o u n t s of the potentially available N was
Figure 5.—Effect of N, leaching, and growth of sudangrass on root yield, sucrose yield, and sucrose percentage of sugarbeets in Experiments 2 and 3. not used in statistical analysis. Means within a method of irriga- tion or cropping treatment followed by the same letters are not significantly different at the 5% level according to Duncan's Multiple Range Test.)
340 JOURNAL OF THE A. S. S. B.T.
p r e s e n t in N 03- N form a n d available for leaching. N i t r o g e n that did become available was primarily from mineralizable sources and was rapidly taken up by the plant. W h e n every row was irrigated at the higher irrigation level, m o r e soil was kept at o p t i m u m moisture levels for releasing mineralizable N, as was d e m o n s t r a t e d on the no-N treat- m e n t by g r e a t e r concentration of N 03- N in the petioles t h r o u g h o u t the season at the higher irrigation t r e a t m e n t . T h e r e f o r e , on soils with a high mineralization capacity, leaching of N 03- N may be a d v a n t a - geous w h e n excess N 03- N is p r e s e n t in the soil a n d the total available N is too high for m a x i m u m sucrose yield.
Experiment 3
In E x p e r i m e n t 3, a d d i n g N fertilizer h a d no effect on root yield, decreased sucrose percentage, and r e d u c e d sucrose yield above 100 lb N/A on both c r o p p i n g t r e a t m e n t s (Fig. 5B). T h e r e was no significant or noticeable difference between these yield factors and the c r o p p i n g t r e a t m e n t . T h e r e was no indication that growth of sudangrass h a d any significant effect on the N supply of the sugarbeets (Fig. 4D). T h e d e v e l o p m e n t of a heavy sugarbeet canopy in mid-July caused inade- q u a t e sudangrass growth a n d N Sudangrass growth was n o r m a l w h e r e t h e r e w e r e o p e n i n g s in t h e c a n o p y , which was p r i m a r i l y caused by skips in the beet plants. Earlier s u d a n g r a s s plantings may have alleviated this problem, but would have interfered with weed control.
O u r results indicate that in this soil when a d e q u a t e water is applied as n e e d e d , except for o n e anomaly, t h e type of irrigation used has little effect on the N nutrition or sucrose p r o d u c t i o n by sugarbeets. T h e s e e x p e r i m e n t s also indicated that the N 03- N reduction in the soil d u r i n g the latter p a r t of the season h a d little effect on sucrose p r o d u c t i o n . T r e a t m e n t s that r e d u c e d t h e N 03- N level in the soil a n d its availability to the plant may have increased sucrose p e r c e n t a g e , but caused ad- verse plant growth conditions, t h u s lowering the r o o t yield. Conse- quently, sucrose yield benefits could not be d e m o n s t r a t e d by using these practices on this soil. T h i s may also apply to t h e practices of r e d u c i n g the irrigation level late in the season to increase sucrose percentage. Reduction in water at this stage may increase sucrose percentage, but may also r e d u c e plant growth a n d root p r o d u c t i o n (4, 5).
T h e s e d a t a s u p p o r t t h e hypothesis that sucrose concentration in the sugarbeet may be influenced m o r e by the N supply a n d r a t e of N early in the season t h a n by N available later in the season (2, 3, 11).
If the sucrose concentration is basically d e t e r m i n e d early in t h e season by the r a t e of N t h e N nutrition of the plant m u s t be controlled by p r o p e r l y a d d i n g N fertilizer, either as a p r e p l a n t or side-dressed application, based on an a d e q u a t e soil test (1). T h e side-dressed N application after t h i n n i n g a n d j u s t before the period of increased N
VOL. 18, No. 4, OCTOBER 1975 3 4 1 would be p r e f e r r e d , n o t only for efficient N use (1), b u t N a d d i t i o n s could be m a d e u s i n g a revised e x p e c t e d yield based on stand, disease, p l a n t i n g d a t e , p l a n t e m e r g e n c e , a n d climatic factors. T h e application of o p t i m u m N levels early in t h e season with a d e q u a t e water f r o m e i t h e r f u r r o w o r s p r i n k l e r i r r i g a t i o n s h o u l d p r o m o t e m a x i m u m sucrose p r o d u c t i o n w i t h o u t f u r t h e r m a n i p u l a t i n g t h e N level in t h e soil or plant.
Summary
Field e x p e r i m e n t s w e r e c o n d u c t e d to study t h e effect of irrigation m e t h o d a n d t h e r e d u c t i o n o f soil a n d plant N O3N late i n t h e season, at different N levels, on sucrose p r o d u c t i o n by sugarbeets. O u r results indicated t h a t on this soil t h e type of irrigation used has little effect on t h e N n u t r i t i o n or sucrose p r o d u c t i o n on sugarbeets w h e n a d e q u a t e water was applied as n e e d e d . T r e a t m e n t s that r e d u c e d t h e N 03- N level in the soil a n d its availability to t h e p l a n t may have increased sucrose p e r c e n t a g e , b u t c a u s e d a d v e r s e conditions for p l a n t g r o w t h a n d root p r o d u c t i o n . C o n s e q u e n t l y , we could not show sucrose yield benefits from using these practices. For m a x i m u m sucrose yield, o p t i m u m a m o u n t s of N fertilizer, based on an a d e q u a t e soil test, s h o u l d be ap- plied p r e p l a n t or as a side-dress application. T h e side-dressing of N fertilizer after t h i n n i n g a n d j u s t before the period of increased N up- take would be p r e f e r r e d so t h a t N could be a d d e d relative to a revised e x p e c t e d yield, based on climatic a n d plant conditions up to t h e time of N fertilizer application.
Literature Cited
(1) CARTER, J. N., M. E.JENSEN, and S. M. BOSMA. 1974. Determining nitro- gen fertilizer needs for sugarbeets from residual soil nitrate and mineralizable nitrogen. Agron. J. 66:319-323.
(2) CARTER, J. N., M. E. JENSEN, B. J. RUFFING, S. M. BOSMA, and A. W.
RICHARDS. 1972. Effect of nitrogen and irrigation on sugarbeet pro- duction in southern Idaho. J. Am. Soc. Sugar Beet Technol. 17:5-14.
(3) CARTER, J . N . , D.T. WESTERMANN, and M. E . J E N S E N . 1976. Sugarbeet yield and quality as affected by nitrogen level. Agron. J. 68: Jan.-Feb.
(4) ERIE, L. J., and O. F. FRENCH. 1968. Water management of fall-planted sugarbeets in Salt River Valley of Arizona. Trans. ASAE 11:792-795.
(5) FERRY, G. V., F . J . HILLS, and R. S. LOOMIS. 1965. Preharvest water stress for Valley sugar beets. Calif. Agr. 19(6): 13-14.
(6) HADDOCK, JAY L. 1958. Yield, quality, and nutrient content of sugar beets as affected by irrigation regime and fertilizers. J. Am. Soc. Sugar Beet Technol. 10:344-355.
(7) HILLS, F. JACKSON, and ALBERT ULRICH. 1971. Nitrogen nutrition.
p. 112-135. In: R. T.Johnson, J. T. Alexander, G. E. Rush, and G. R.
Hawkes (eds.), Advances in Sugarbeet Production: Principles and Practices. T h e Iowa State Univ. Press, Ames.
342 JOURNAL OF THE A. S. S. B.T.
(8) JENSEN, M. E. 1969. Scheduling irrigations using computers. J. Soil Water Conserv. 24:193-195.
(9) JENSEN, M. K., and L.J. ERIE. 1971. Irrigation and water management.
p. 189-222. In: R. T.Johnson, J. T. Alexander, G. E. Rush, and G. R.
Havvkes (eds.), Advances in Sugarbeet Production: Principles and Practices. The Iowa State Univ. Press, Ames.
(10) MILHAM, P. J., A. S. Aw AD, R. E. PAXIL, and J. H. BULL. 1970. Analysis of plant, soils and waters for nitrate by using an ion-selective electrode.
Analyst 95:751-757.
(11) ROBINS, J. S., C. E. NELSON, and C. E. DOMINGO. 1956. Some effects of excess water application on utilization of applied nitrogen by sugar beets. J. Am. Soc. Sugar Beet Technol. 9:180-188.
(12) ULRICH, ALBERT, D. RIRIE, F. J. HILLS, A. G. GEORGE, M. D. MOORE, and C. M. JOHNSON. 1959. I. Plant analysis, a guide for sugar beet fertiliza- tion; II. Analytical methods for use in plant analysis. Calif. Agr. Expt.
Sta. Bull. 766.
(13) WILLEY, C. R. 1970. Effect of short periods of anaerobic and near-an- aerobic conditions on water uptake by tobacco roots. Agron. ]. 62:224- 229.