Interrelationships of Applied Nitrogen,
VOL. 17, No. 4, OCTOBER 1973 359
eastern New Mexico is border-line with regard to available levels of zinc, and crops such as corn respond considerably to application of zinc.
Materials and Methods
The 1971 experiment was established on a Pullman silty clay loam soil in east-central New Mexico using a rotatable central-composite design (1) involving applied nitrogen, applied zinc, plant population, and irrigation frequency as variables. The study involved several other crops, and it was necessary to keep the total number of main plots small in order to have irrigation frequency as a variable. Thus, it was neces- sary to restrict the study to only one replication of the main treatments with the central treatment replicated seven times to allow estimation of experimental error. The 25 treatments involving 31 plots are shown in Table 1 along with the five levels used for each of the four variables.
The regression equations used to evaluate results are based on coded levels ( - 2 , - 1, 0, + 1 , +2) for the variables. In 1972, the beets were grown on the plots that had been in grain sorghum in 1971. Nitrogen was reapplied at the same rate as in 1971, but zinc was applied only in 1971. As zinc sulfate, it was broadcast on the surface of the beds with a calibrated fertilizer spreader just before planting. The nitrogen was applied as ammonium nitrate with a fertilizer grain drill which worked both zinc and nitrogen into the surface of the beds.
Holly HH10 pelleted seed was planted on 40-inch beds with two rows ten inches apart on each bed. The seed was machine-planted at about double the intended final stand. After complete emergence, beets were hand-thinned to final stands. Inadequate emergence in 1971 resulted in somewhat lower stands than had originally been intended.
Each plot consisted of four beds 30 feet long. Water was run in the center three furrows of each plot for 10 to 24 hours, depending on the treatment, with the purpose of filling the soil profile. A relatively tight caliche layer at a depth of five or six feet prevented excessive internal drainage or leaching of nutrients. Irrigation intervals were based on the amount of accumulated evaporation (corrected for rain- fall) from a Class A weather pan.
Curly top disease was controlled by a preplant application of
Thimet below the center of the beds, and Cercospora leaf spot was con-
trolled by periodic application of Benlate during July, August, and
September. Beets were harvested from the center two rows of each
plot. Samples were sent for sugar analysis to the Holly Sugar Corp.,
Hereford, Texas, in 1971 and for sugar and purity to the Great
Western Sugar Co., Longmont, Colorado, in 1972. Extractable sugar
content, based on the sucrose percentage of the beets, was derived
from a table supplied by the Holly Sugar Corp. Purity was determined
360 JOURNAL, OF THE A. S. S. B. T.
in t h e 1972 beets by t h e G r e a t W e s t e r n S u g a r C o . with a m e t h o d based on t h e difference between s u g a r c o n c e n t r a t i o n s as d e t e r m i n e d by p o l a r i m e t r y a n d by r e f r a c t o m e t r y .
Leaf samples (youngest m a t u r e leaves f r o m 10 plants) w e r e taken a t four times d u r i n g each g r o w i n g season. Petioles a n d blades w e r e s e p a r a t e d immediately, d r i e d at 70° C, g r o u n d in a m i c r o Wiley mill, a n d analyzed. N i t r a t e - N was d e t e r m i n e d on t h e petioles, with a l u m i - n u m sulfate as t h e e x t r a c t a n t a n d a n i t r a t e e l e c t r o d e for n i t r a t e d e t e r - m i n a t i o n . A 2% acetic acid e x t r a c t was m a d e a n d p h o s p h a t e d e t e r - m i n e d on t h e petioles by t h e v a n a d a t e c o l o r i m e t r i c m e t h o d . Zinc, m a n g a n e s e , c o p p e r , a n d iron w e r e d e t e r m i n e d o n 2 % acetic acid extracts of t h e leaf blades by a t o m i c a b s o r p t i o n . I r o n was also e x t r a c t e d from most of t h e 1972 samples by d r y a s h i n g .
Available zinc in t h e soil was d e t e r m i n e d from soil samples t a k e n i n F e b r u a r y following harvest o f t h e 1972 s u g a r b e e t c r o p . T h e D T P A m e t h o d o f Lindsay a n d Norvell (1969 A g r o n o m y Abstracts, p p . 84) was used.
Results and D i s c u s s i o n
Yields r a n g e d up to almost 50 t o n s p e r acre b o t h years (Tables 1 a n d 2), indicating high p o t e n t i a l for s u g a r b e e t s as a c r o p in t h e a r e a . T h e solution of t h e regression e q u a t i o n for t h e c o m b i n a t i o n of vari- ables r e s u l t i n g in m a x i m u m yield of b o t h beets a n d e x t r a c t a b l e s u g a r indicated t h a t h i g h levels of all f o u r variables w e r e n e e d e d in 1 9 7 1 . H o w e v e r , in 1972, with plant p o p u l a t i o n at a s o m e w h a t g r e a t e r r a n g e of levels, m a x i m u m yields w e r e o b t a i n e d with n i t r o g e n a n d p o p u l a t i o n at low levels a n d zinc a n d irrigation at h i g h levels. T h e c u r v e s s h o w n in t h e figures w e r e calculated from t h e regression e q u a t i o n s b a s e d on t h e c o m b i n a t i o n s a p p r o a c h i n g t h e o p t i m u m . R e s p o n s e t o n i t r o g e n applications indicated their e c o n o m i c feasibility b o t h years u p t o a b o u t t h e 2 4 0 p o u n d s p e r acre level w h e n zinc, p o p u l a t i o n , a n d irrigation w e r e k e p t h i g h (Figure l a ) . At lower p l a n t p o p u l a t i o n levels ( F i g u r e l h ) , however, t h e yield r e s p o n s e to n i t r o g e n d r o p p e d off drastically.
T h e s o m e w h a t g r e a t e r r e s p o n s e i n 1972 was d u e t o m o r e c o m p l e t e r e m o v a l of n i t r o g e n from t h e soil profile by t h e 1971 s o r g h u m c r o p . Severe n i t r o g e n deficiency s y m p t o m s o c c u r r e d at t h e 0 a n d 80 p o u n d s a p p l i c a t i o n levels i n 1972. I n c r e a s i n g n i t r o g e n r e d u c e d s u c r o s e p e r c e n t a g e a n d purity (Figure 3a) b o t h years, b u t this was m o r e t h a n c o m p e n s a t e d by i n c r e a s e d yield of e x t r a c t a b l e s u g a r ( F i g u r e l a ) . N i t r o g e n was r e q u i r e d m u c h m o r e for yield of beets t h a n for yield of e x t r a c t a b l e s u g a r (Table 3, linear r e g r e s s i o n coefficients for n i t r o g e n ) .
T h e a p p a r e n t o p t i m u m plant p o p u l a t i o n ( F i g u r e 1 c ) varied f r o m a b o u t 2 5 , 0 0 0 plants p e r acre, with heavy n i t r o g e n applications, to less t h a n 18,000 a t 8 0 p o u n d s o f n i t r o g e n p e r a c r e . A t t h a t n i t r o g e n r a t e , i n c r e a s i n g p o p u l a t i o n was very d e p r e s s i n g to yield of beets ( F i g u r e 2f)
Table 1.—Effect of nitrogen, zinc, plant population, and irrigation frequency on yield of sugarbeets and extractable sugar, and concentra- tion of sucrose for 1971.
Table 1.—Continued.
Table 2.—Effect of nitrogen, zinc, plant population, and irrigation frequency on yield of sugarbeets and extractable sugar, concentration of sucrose, and degree of purity for 1972.
Table 2.—Continued.
Figure 1.—Effect of applied nitrogen, applied zinc, plant population, and irrigation frequency (based on open pan evaporation less rainfall) on yield of extractable sugar of sugarbeets (from regression equation).
VOL. 17, No. 4, OCTOBER 1973 365
Table 3.—Regression equations (based on coded levels) for effect of nitrogen (1), zinc (2), plant population (3), and irrigation frequency (4) on yield of sugarbeets and extractable sugar, concentration of sucrose, and degree of purity for 1971 and 1972.
** Statistically significant at 1% level.
* Statistically significant at 5% level.
Figure 2.—Effect of applied nitrogen, applied zinc, plant population, and irrigation frequency (based on open pan evaporation less rainfall) on yield of sugarbeets (from regression equation).
VOL. 17, No. 4, OCTOBER 1973 367
368 JOURNAL OF THE A. S. S. B. T.
d u r i n g b o t h years. At low n i t r o g e n , i n c r e a s i n g p o p u l a t i o n ( F i g u r e 3f) r e s u l t e d i n greatly i n c r e a s e d p u r i t y a n d s u c r o s e p e r c e n t a g e s b u t differences w e r e small at a h i g h n i t r o g e n level ( F i g u r e 3c).
T h e r e was definite r e s p o n s e t o zinc a p p l i c a t i o n ( F i g u r e l b ) a t h i g h levels of n i t r o g e n , p o p u l a t i o n , a n d water. H o w e v e r , at low n i t r o g e n a p p l i c a t i o n r a t e s , t h e r e s p o n s e d i s a p p e a r e d o r b e c a m e n e g a t i v e ( F i g u r e 1e). With h i g h plant p o p u l a t i o n s , zinc i n c r e a s e d b o t h s u g a r a n d p u r i t y ( F i g u r e s 3b, 3e). In 1972, t h e r e was c o n s i d e r a b l e r e s p o n s e to zinc at low n i t r o g e n a n d p o p u l a t i o n levels ( F i g u r e l m ) , b u t t h e r e s p o n s e to zinc in 1971 was negative. T h e 1972 second level of p o p u l a - tion, h o w e v e r , was as h i g h as t h e f o u r t h level in 1 9 7 1 . T h i s p r o b a b l y e x p l a i n s t h e less positive zinc r e s p o n s e in 1971 at t h e low n i t r o g e n r a t e .
T h e r e s p o n s e to irrigation frequency was similar in b o t h years, a l t h o u g h 1972 h a d considerably m o r e r a i n s o t h a t t h e r e s p o n s e was less to t h e highest levels. In g e n e r a l , c o m b i n a t i o n s of n i t r o g e n a n d p o p u l a t i o n t h a t r e s u l t e d in t h e h i g h e s t yield levels ( F i g u r e s 1d, 1n) r e s p o n d e d most to increased irrigation f r e q u e n c y . If e i t h e r n i t r o g e n or p o p u l a t i o n was low in relation to t h e o t h e r , irrigation f r e q u e n c y m a d e little difference (Figures 1g, 1k).
T h e m e a n n i t r a t e - N c o n t e n t of leaf petioles ( T a b l e 4) varied considerably, t e n d i n g to be h i g h e s t early in t h e g r o w i n g season. D u r i n g p e r i o d s o f d r o u g h t , soil n i t r a t e t e n d e d t o a c c u m u l a t e a t t h e tops o f t h e r i d g e s , r e s u l t i n g in lower n i t r a t e levels in t h e petioles. T h e n w h e n suf- ficient r a i n fell, t h e n i t r a t e was w a s h e d d o w n into the r o o t u p t a k e z o n e a n d t h e levels b e c a m e h i g h e r i n t h e petioles. T h u s , e v e n n e a r t h e e n d of t h e g r o w i n g season, m e a n n i t r a t e levels w e r e c o n s i d e r a b l y above Ulrich's critical level (9) of 1000 p p m in t h e petioles for yields of 9 0 % o f m a x i m u m . T h e v a r y i n g levels o f n i t r a t e i n t h e leaves d u r i n g t h e season, a l o n g with t h e g r e a t d e p e n d e n c e o f n i t r o g e n r e s p o n s e o n p l a n t p o p u l a t i o n level, p r e v e n t e d d e t e r m i n a t i o n of definite critical levels u n d e r f i e l d c o n d i t i o n s . Plant p o p u l a t i o n a n d zinc h a d little influence on n i t r a t e levels in petioles; i n c r e a s e d f r e q u e n c y of irrigation t e n d e d to d e c r e a s e t h e levels. A p p l i e d n i t r o g e n greatly i n c r e a s e d petiole n i t r a t e levels t h r o u g h o u t b o t h seasons, e x c e p t for t h e O c t o b e r 20, 1972, s a m p l i n g .
T h e m e a n p h o s p h a t e - P levels of leaf b l a d e s ( T a b l e 4) was far above Ulrich's critical level (9) of 7 5 0 p p m for petioles t h r o u g h o u t t h e season.
F u e h r i n g a n d H a s h i m i (2) r e p o r t e d an a p p r o x i m a t e critical level of 1500 p p m in petioles for h i g h - y i e l d i n g s u g a r b e e t s in L e b a n o n . In g e n e r a l , i n c r e a s i n g n i t r o g e n application t e n d e d t o d e c r e a s e p h o s p h a t e in t h e leaf blades, while t h e effects of zinc, p l a n t p o p u l a t i o n , a n d i r r i g a t i o n f r e q u e n c y w e r e generally small a n d variable.
T h e m e a n zinc levels o f leaf blades d e c l i n e d d u r i n g b o t h g r o w i n g seasons ( T a b l e 4). B o t h n i t r o g e n a n d zinc application i n c r e a s e d zinc in t h e leaf blades, with n i t r o g e n h a v i n g c o n s i d e r a b l y m o r e effect t h a n
Figure 3.—Effect of applied nitrogen, applied zinc, plant population, and irrigation frequency (based on open pan evaporation less rainfall) on level of sucrose and purity of sugarbeets (from regression equation).
V O L . 17, No. 4, OCTOBER 1973 3 6 9
Table 4.—Linear effects (regression coefficients based on coded levels) of nitrogen, zinc, plant population (Pop), and irrigation frequency (water) on seasonal leaf composition of sugarbeets during 1971 and 1972.
Table 4.—Continued.
** Statistically significant at 1% level.
* Statistically significant at 5% level.
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zinc i n several s a m p l e s . H i g h n i t r o g e n , p l a n t p o p u l a t i o n , a n d i r r i g a t i o n levels r e s u l t e d in c o n s i d e r a b l e r e s p o n s e to zinc a p p l i c a t i o n d u r i n g b o t h seasons, s u g g e s t i n g t h a t a level of a r o u n d 20 p p m in t h e blades was necessary for n e a r m a x i m u m yields o f e x t r a c t a b l e s u g a r u n d e r t h e s e c o n d i t i o n s . T h i s c o m p a r e s to a critical level of 9 p p m as given by Rosell a n d Ulrich (7) for 9 0 % of m a x i m u m .
T h e level of D T P A e x t r a c t a b l e zinc in t h e soil was m e a s u r e d two years after zinc was a p p l i e d a n d c r o p s o f g r a i n s o r g h u m (1971) a n d s u g a r b e e t s (1972) h a d b e e n g r o w n . Soil levels of zinc ( T a b l e 5) w e r e materially affected by all levels of a p p l i e d zinc. T h e a v e r a g e level in t h e t h r e e checks o f 0.72 p p m was s o m e w h a t h i g h e r t h a n n o r m a l (0.4 t o 0.8 p p m ) for t h e a r e a . Levels o f 0.5 t o 0.8 p p m o f D T P A e x t r a c t a b l e zinc have b e e n indicated as a b o u t t h e critical level for c o r n . It a p p e a r s t h a t a level of at least 1.0 p p m in t h e soil was r e q u i r e d for n e a r maxi- m u m yields o f extract able s u g a r u n d e r t h e c o n d i t i o n s o f t h e s t u d y r e p o r t e d h e r e . A n application o f f o u r t o eight p o u n d s o f zinc was e n o u g h to raise t h e soil level above 1.0 p p m for two years a n d p r o b a b l y l o n g e r a t t h e h i g h e r r a t e .
Table 5.—Levels of DTPA extractable zinc in soil two years after application and following successive crops of grain sorghum and sugarbeets.
T h e m e a n m a n g a n e s e level o f leaf b l a d e s t e n d e d t o d e c r e a s e d u r i n g b o t h seasons (Table 4). N i t r o g e n a p p l i c a t i o n h a d a s t r o n g in- c r e a s i n g effect on leaf m a n g a n e s e levels in 1971 (following w h e a t in
1970) a n d a s t r o n g d e c r e a s i n g effect in 1972 (following g r a i n s o r g h u m in 1971). T h e r e a s o n for this striking d i f f e r e n c e is n o t a p p a r e n t . Soil levels of available m a n g a n e s e in t h e P u l l m a n soil a r e h i g h , a c c o r d i n g to t h e D T P A e x t r a c t i o n soil test. Ulrich (9) r e p o r t s a critical level of 10 p p m for m a n g a n e s e in leaf blades, so t h e levels f o u n d h e r e a r e possibly excessive. Zinc a n d p l a n t p o p u l a t i o n h a d relatively little effect on leaf m a n g a n e s e levels. I n c r e a s i n g f r e q u e n c y o f irrigation d u r i n g relatively wet 1972 r e s u l t e d in significant d e c r e a s e s in leaf m a n g a n e s e levels as t h e season p r o g r e s s e d .
I r o n levels in leaf blades varied c o n s i d e r a b l y t h r o u g h o u t t h e season ( T a b l e 4). It was f o u n d t h a t 2% acetic acid was e x t r a c t i n g only a b o u t o n e - f o u r t h o f t h e total i r o n (probably d u e t o i n t e r f e r e n c e f r o m
VOL. 17, No. 4, OCTOBER 1973 373
oxalate), and dry ashing was used during most of 1972. The mean amount of iron extracted by dry ashing was considerably above the 55 ppm critical level cited by Ulrich (9). No iron deficiency chlorosis was noted. Nitrogen application resulted in decreased iron levels during both years. There was a tendency for increased irrigation frequency to cause decreased iron levels in leaf blades. Neither zinc nor plant population had much effect on iron levels.
The mean copper levels in sugarbeet leaf blades varied consider- ably during 1972 although there was a seasonal decline during 1971 (Table 4). Soil test levels (DTPA extract) of available copper are four to six times the critical level (0.2 ppm), so it is probable that these levels are more than adequate. Nitrogen tended to have a decreasing effect on leaf copper levels early in the season, but this effect disappeared late in the season. Increasing plant population and irrigation fre- quency tended to result in decreased copper in leaf blades while zinc had little effect.
The yield response to zinc found here may be due to the excessive levels of manganese and possibly iron and copper, resulting in an imbalance of the micronutrient cations. High phosphate levels in the leaves may also be a contributing factor.
Summary and Conclusions
It appears that obtaining maximum yields of extractable sugar
involves balancing the supply of nitrogen with the plant population
level. With adequate but not excessive nitrogen, a plant population
between 20 and 25 thousand plants per acre is desirable. The amount
of applied nitrogen needed depends on the amount present in the soil
as well as the likelihood of leaching. Plots receiving 80 pounds of nitro-
gen per acre in both 1971 and 1972 yielded 20 tons (34 vs. 14) per acre
more in 1972 than those receiving no nitrogen either year. Each addi-
tional increment of 80 pounds increased yield about two to four tons
per acre on the average, but with decreased purity and sugar percent-
age. Thus, the first 80 pounds per acre increment increased yield by
about a ton of beets for each four pounds of nitrogen applied. About
200 pounds total nitrogen (residual plus applied) per acre is adequate
to supply all the nitrogen needed for a full set of leaves, which is
enough to produce 40 or 50 tons of beets per acre provided the leaves
survive for the entire season. Under conditions of borderline avail-
able soil zinc levels and adequate nitrogen, population, and irrigation
levels, application of four to eight pounds per acre of zinc as zinc sul-
fate will increase yields of extractable sugar by 30 to 50 percent. Where
nitrogen, zinc, and plant population were adequate, beets responded
to more frequent irrigation. At lower yield levels, where other factors
were out of balance, increasing moisture stress by longer intervals
between irrigations had little effect on yield. Percentage purity was
374 JOURNAL OF THE A. S. S. B. T.
usually c o r r e l a t e d with p e r c e n t a g e s u c r o s e e x c e p t at low p o p u l a t i o n levels a n d h i g h n i t r o g e n levels.
M e a n levels o f n i t r a t e - N , zinc, p h o s p h o r u s , i r o n , a n d c o p p e r i n t h e leaves w e r e h i g h , with m a n g a n e s e possibly b e i n g at excessive levels.
I t was p o s t u l a t e d t h a t t h e yield r e s p o n s e t o zinc u n d e r s o m e c o n d i t i o n s in this study m a y be d u e to t h e i m b a l a n c e of zinc with excessive m a n g a n e s e a n d c o p p e r a n d possibly i r o n a n d p h o s p h o r u s .
It was c o n c l u d e d t h a t i n t e r a c t i o n effects w e r e very i m p o r t a n t a n d t h a t o p t i m u m levels o f each variable c h a n g e d greatly d e p e n d i n g on t h e levels of t h e o t h e r variables. F u r t h e r w o r k is n e e d e d to establish t h e c o n d i t i o n s r e g u l a t i n g r e s p o n s e t o a p p l i e d zinc a n d t o p l a n t p o p u l a t i o n levels.
Literature Cited
(1) COCHRAN, W. G. and G. M. Cox. 1957. Experimental designs, 2nd Ed.
John Wiley and Sons, Inc., New York.
(2) FUEHRING, H. D. and M. A. HASHIMI. 1967. Foliar analysis in the nutri- tion of sugarbeets. Proc. Centennial Symposium, Faculty of Agricul- tural Sciences, American University of Beirut.
(3) FUEHRING, H. D., M. A. HASHIMI, K. S. HADDAD, K. K. HUSSIENI, and M. U. MAKHDOOM. 1969. Nutrient interaction effects on sucrose yield of sugarbeets. Soil Sci. Soc. Amer. Proc. 33:718-721.
(4) FUEHRING, H. D., A. MAZAHERI, M. BYBORDI, and A. K. S. KHAN. 1966.
Effect of soil moisture depletion on crop yield and stomatal infiltra- tion. Agron. J. 58:195-198.
(5) HERRON, G. M., D. W. GRIMES, and R. E. FINKNER. 1964. Effect of plant spacing and fertilizer on yield, purity, chemical constituents and evapotranspiration of sugarbeets in Kansas. I. Yield of roots, purity, percent sucrose, and evapotranspiration. J. Am. Soc. Sugar Beet Technol. 12:686-698.
(6) ROBINSON, F. E. and G. F. WORKER, J R . 1969. Plant density and yield of sugarbeets in an arid environment. Agron. J. 61:441-443.
(7) ROSELL, R. A. and A. ULRICH. 1964. Critical zinc concentrations and leaf minerals of sugarbeet plants. Soil Sci. 97:152-167.
(8) SCHMEHL, W. R., R. FINKNER, and J. SWINK. 1963. Effect of nitrogen fertilization on yield and quality of sugarbeets. J. Am. Soc. Sugar Beet Technol. 12:538-544.
(9) ULRICH, ALBERT and F.J. HILLS. 1967. Principles and practices of plant analyses. In Soil testing and plant analysis, Part II. SSSA special publi- cation 2:11-24.
(10) WORZELLA, W. W., H. D. FUEHRING, A. SAAD, A. R. SAGHIR, and D. W.
BRAY. 1968. Sugarbeet production studies in the Beqa'a Plain, Leba- non. American University of Beirut, Faculty of Agricultural Sciences Publication No. 30.