www.elsevier.com/locate/eja
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ff
ect of plant density and nitrogen rates upon the leaf area of
seed sugar beet on seed yield and quality
M. Pospisˇil
a,
*, A. Pospisˇil
a
, M. Rastija
b
aFaculty of Agriculture, University of Zagreb, Department of Field Crops, Svetosˇimunska 25, 10000 Zagreb, Croatia bFaculty of Agriculture, University of J. J. Strossmayer, Trg sv. Trojstva 3, 31000 Osijek, Croatia
Accepted 14 September 1999
Abstract
Three-year field trials were set up on eutric brown soil in northwestern Croatia ( Zagreb) with the objective to determine the effect of plant density and nitrogen rates on the formation and size of leaf area of seed sugar beet, and on the yield and seed quality in seed production without transplanting. Investigations should also reveal how much the yield and quality of sugar beet seed depend on the leaf area index (LAI ). Four plant densities of seed sugar beet were investigated after crop wintering (40 000, 80 000, 120 000, and 160 000 plants/ha) as well as three nitrogen rates (60, 120, and 180 kg/ha) applied in two identical topdressings: at the beginning of the spring growing period and immediately before shooting of inflorescence stalks. Leaf area formation was strongly influenced by weather conditions. An increase of plant density from 40 000 to 160 000 plants/ha led to a decrease of leaf area per plant. Raised nitrogen rates in topdressing caused an increase of leaf area, depending on the precipitation and soil fertility. Maximum LAI, achieved in the flowering stage, grew almost linearly with increasing plant density (LAI: 1.77–4.85 m2/m2), but was statistically significant only up to 120 000 plants/ha. Raised nitrogen rates in topdressing led to a significant increase of the LAI in the stage of inflorescence stalk shooting, though not in full flowering. On the basis of this research, seed yield and germination of seed sugar beet could not be predicted regarding LAI in the flowering stage. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:LAI; Leaf area per plant; Nitrogen rates; Plant density; Seed sugar beet
1. Introduction per unit area, as well as appropriate fertilization,
particularly with nitrogen, are central problems in the technological production process of all field Research on the extent to which the plant
crops and specially in sugar beet seed production. density and nitrogen rates influence the growth
A survey of the research results, available to us, and formation of leaf area in particular
develop-on this problem in the world and in this country ment stages, especially those decisive for the yield
did not reveal any published results on the effect
and quality of sugar beet seed, has major scientific
of leaf area, or leaf area index (LAI ) upon the and production importance since it contributes to
yield and quality of sugar beet. Various methods a better seed utilization in final processing. It is
have been applied to determine leaf area in sugar thought that number and distribution of plants
beet (Campbell and Viets, 1967; Barbieri, 1983; Fo¨rkel, 1985; Milford et al. 1985; Rover and
* Corresponding author. Tel.:+385-1-239-3775;
Koch, 1995).
fax:+385-1-239-3703.
E-mail address:mpospisil@agr.hr (M. Pospisˇil ) Areas under seed sugar beet are small in
70 M. Pospisˇil et al./European Journal of Agronomy 12 (2000) 69–78
parison with areas under other field crops. This is split-plot method in five replications. Cultivar
OS-Nada, its mother (2n=18) and father (4n=
the main reason why there are very few
profes-sional or scientific studies from this area. 36) lines, were used as test crops. The ratio of
mother and father components at sowing was Researchers from North America (Campbell,
1968), the UK and Denmark (Scott, 1968; 6:0:2. Basic fertilization for seed sugar beet was
carried out with 50 kg/ha of N, 150 kg/ha of
Longden and Scott, 1973; Longden, 1974)
con-ducted research with twice as many plants P
2O5, and 300 kg /ha of K2O. Sugar beet was
sown at the end of August at a between-row
(>300 000 plants/ha at harvest) as commonly
recommended in other production regions. spacing of 50 cm and within-row spacings of 11.4,
8.6, 7.1, and 5.7 cm. In spring, a density correction Trogisch (1985) maintains that a plant density of
150 000–250 000 plants/ha at harvest is desirable was made according to the test treatments.
Leaf area per plant and the LAI were deter-for seed sugar beet grown under European
condi-tions. Under the conditions prevailing in mined in characteristic pheno-stages of seed sugar
beet (at the start of vegetation in spring, in the Vojvodina (FR Yugoslavia), the highest yield and
best seed quality of sugar beet were obtained with stage of inflorescence stalk appearance and in full
flowering) using the punch method (Campbell and
plant densities of 130 000 to 150 000 plants/ha after
wintering (Stefanovic´, 1987). Based on the trial Viets, 1967). In the said stages, measurements were
made on ten plants from each treatment and results achieved in eastern Slavonija (Croatia),
Kristek and Matic´ (1984) concluded that good involved the number of leaves, the leaf weight per
plant and their dry matter. Leaves with blades yields might be obtained with 65 000–80 000
plants/ha at harvest. According to the authors, longer than 2 cm were counted. All observations
and measurements in the trial were carried out on nitrogen rates applied with topdressing to
direct-drilled seed sugar beet vary, depending on the soil, mother plants. Seed sugar beet was harvested at
the end of July. Seed yield and quality were
from 150 to 250 kg/ha (Longden and Johnson,
1977; Zarisˇnajak and Sˇijan, 1991; Rastija, 1993). determined after the harvest. The data obtained
were processed by up-to-date statistical methods The objective of this research is to determine
the effect of plant density and nitrogen application (analysis of variance, correlation) applying
com-puter programs (Microsoft Excel 5.0 and Mstat). upon the formation and size of leaf area, LAI,
yield and quality of sugar beet seed. Investigations Analyses of weather conditions during three
growing seasons showed considerable variation in should also reveal how much the yield and quality
of sugar beet seed depend on the LAI. precipitation distribution from year to year
(Fig. 1). Particularly unfavourable precipitation distribution was recorded in 1991–92. Water balance after Thornhwaite’s method indicates a 2. Material and method
balance between potential and actual evapotrans-piration all the way to June, when water deficiency Investigations were carried out through field
trials set up on the experimental field of the Faculty appeared in soil. Water deficiency in June and July
was unfavourable because seed sugar beet has the of Agriculture, Zagreb, during 1991–92, 1993–94
and 1994–95. The trial comprised four plant densi- biggest needs for water in those months. Very
favourable conditions for the growth and develop-ties of seed sugar beet (Beta vulgaris var. altissima
D. C.), after crop wintering (40 000, 80 000, ment of seed sugar beet prevailed throughout
1993–1994. Precipitation distribution in 1994–1995
120 000, and 160 000 plants/ha) and three nitrogen
rates (60, 120, and 180 kg/ha) applied in two was slightly less favourable for seed sugar beet.
There was less precipitation, accompanied by topdressings. The first topdressing (with half of
the foreseen N fertilizer quantity) was done at the slightly higher temperatures, in April, at the time
when inflorescence shoots were formed, which beginning of the spring growing period and the
second immediately prior to the shooting of inflo- accelerated the development of seed sugar beet.
Rainfall was sufficient throughout the growing
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72 M. Pospisˇil et al./European Journal of Agronomy 12 (2000) 69–78
Table 1
Chemical properties of the plough layer, soil depth 0–30 cm, Zagreb–Maksimir
Year pH Humus (%) Total N (%) AL-method (mg/100 g soil ) H
2O 1M KCl P2O5 K2O
1991–92 7.7 7.2 2.2 0.14 35.7 17.5
1993–94 7.2 6.6 2.1 0.13 20.3 18.6
1994–95 5.3 4.7 2.1 0.12 10.1 12.6
period, from May to July. Lower temperatures in plants develop a relatively higher leaf weight if
springs are colder. Leaf area is mainly formed in
May and June, along with sufficient humidity in
this period, disturbed the balance between vegeta- the stage of intensive growth, which lasts from
stem appearance to the beginning of flowering, the tive and generative growth, which was negatively
reflected in seed quality. Water deficiency in soil proceeding of the stage being strongly influenced
by weather conditions, notably precipitation and was recorded in July, i.e. at the time of seed
formation and maturing. temperature. In 1991–1992 and 1993–1994, most
of the leaf area, about 2/3, was formed in the
Soil of the experimental field Zagreb–Maksimir
is anthropogenized eutric brown, on slightly luvic period from the beginning of May to mid June. In
1994–1995, the weather conditions throughout loam ( Vidacˇek et al., 1994). Chemical soil
proper-ties are shown in Table 1. April and May favoured intensive development,
and sugar beet seeds grew in June and July. Thus, the major part of leaf area was formed in the second part of spring vegetation (during June). 3. Results and discussion
Consequently, interference of weather conditions might sometimes disturb the balance between the The results obtained in the 3 year investigations
indicate that hydrothermal characteristics of the vegetative and reproductive growth, which has an
adverse effect, especially on seed quality. Leaf area
climate and soil fertility had the dominant effect
on the growth and development of sugar beet per plant and LAI are not very important, as such;
however, they may have considerable bearing on
seeds. As a result of the differences in dry matter
accumulation, productivity of photosynthesis and the yield and quality of seed, since enhanced leaf
growth due to higher nitrogen rates may favour
nitrogen uptake, differences were also recorded in
leaf area per plant, as well as in LAI, depending vegetative growth on account of seed development
(competition for assimilates between seed and on plant density and nitrogen rates. At the start
of vegetation in spring, in all three of the experi- leaves). Scott and Longden (1973) maintain that
too lush plant growth is not desirable since it
mental years, plant density had no significant effect
upon leaf area per plant, so these results are not deteriorates the quality traits of sugar beet seed.
At a low plant density, plant growth is more presented. In 1994–1995, at the beginning of plant
growth in spring up to stem appearance, plants intensive, flowering is delayed, and the late-formed
fruits cannot mature before the harvest, thus had well-developed leaf rosettes. As the plant grew,
part of the leaf rosette started to degenerate and decreasing the quality of harvested seed. Matic´
et al. (1983) report that abundant rainfall in the a relatively small leaf weight was determined in
the flowering stage. A more pronounced effect of flowering period may influence a decrease in the
germination of sugar beet seed, particularly on plant density and nitrogen rates on leaf area per
plant was determined in the stage from stem soils rich in nitrogen. In such cases, luxury nitrogen
uptake occurs and causes a disproportion in the appearance up to full flowering ( Table 2). The
intensity of leaf area formation varied per trial development of vegetative and generative plant
Table 2
Influence of plant density and nitrogen rate in spring topdressing on seed sugar beet leaf area per plant
Factor Seed sugar beet leaf area per plant (cm2)
Stage of inflorescence stalk appearance In full flowering
1991–1992 1993–1994 1994–1995 1991–1992 1993–1994 1994–1995
Plant density (plants/ha) 40 000 1480 1777 1735 5820 5698 1762
80 000 1400 1594 1680 3988 4468 1881
120 000 1457 1514 1398 3952 3843 1943
160 000 1280 1581 1492 4401 3096 1594
LSD 5% NS NS NS 1184 1136 NS
1% NS NS NS – 1593 NS
Nitrogen topdressing (kg/ha) 60 1125 1564 1430 4044 3520 1548
120 1478 1719 1621 4698 4537 1915
180 1610 1566 1678 4880 4764 1922
LSD 5% 313 NS NS NS 698 278
1% – NS NS NS 1016 –
Large differences in leaf area per plant were (1993) recorded marked differences between plants
to which nitrogen topdressing was applied
recorded between particular years and growth and
development stages in the 3 year trial period. In (150 kg/ha towards the end of March) and those
grown without topdressing. The former were of the stage of inflorescence stalk appearance, plant
density had no statistically significant influence on dark green colour and had a more rapid initial
growth and a lusher habit. leaf area per plant in any of the trial years. In this
stage, leaf area was significantly influenced by LAI also depended on the extent of plant
devel-opment, i.e. growth stage. When vegetation started nitrogen applied in early spring topdressing (half
of the foreseen N fertilizer rate) and interaction of in spring of all three experimental years, the
sig-nificantly highest LAI was achieved with a plant higher nitrogen rates in topdressing (120 and
180 kg/ha) as well as lower plant densities, though density of 160 000 plants/ha. In the stage of
inflo-rescence stalk appearance, the LAI grew signifi-only in 1991–1992.
More-pronounced differences in the values of cantly with increasing plant density to 160 000
plants/ha ( Table 3). An increase of topdressing
leaf area per plant, as caused by plant density,
occurred during full flowering. Significantly largest nitrogen rate from 60 to 180 kg/ha increased the
LAI as well. The highest, and statistically signifi-leaf area per plant was obtained with the plant
density of 40 000 plants/ha, whereas further cant, increase of LAI (1991–92 and 1994–1995)
was that between topdressing with 60 and increasing of plant density resulted in a significant
leaf area reduction (in 1991–1992 and 1993–1994), 180 kg/ha of N. In the full flowering stage, LAI
rose significantly with increasing plant density to except in 1994–1995 when intensive growth was
still going on. In 1993–1994 and 1994–1995, in the 120 000 plants/ha (1993–1994 and 1994–1995).
Further increase of plant density to 160 000 stage of full flowering, application of 120 and
180 kg/ha of N significantly increased the leaf area plants/ha reduced the ability of biological
self-regulation of plant leaf area, which led to a further
values in comparison with 60 kg/ha of N. In 1991–
1992, increased nitrogen rates in topdressing led linear increase of the LAI. The analysis of variance
for topdressing nitrogen rates shows that topdress-to an increase in leaf area, which was not
statistic-ally significant due to water deficiency that ing did not significantly increase the LAI during
full flowering in any experimental year. occurred in soil at that time. In trials conducted
74 M. Pospisˇil et al./European Journal of Agronomy 12 (2000) 69–78
Table 3
Influence of plant density and nitrogen rate in spring topdressing on seed sugar beet LAI
Factor Seed sugar beet LAI (m2/m2)
Stage of inflorescence stalk appearance In full flowering
1991–1992 1993–1994 1994–1995 1991–1992 1993–1994 1994–1995
Plant density (plants/ha) 40 000 0.59 0.71 0.69 2.33 2.28 0.70
80 000 1.12 1.28 1.34 3.19 3.57 1.50
120 000 1.75 1.82 1.68 4.74 4.60 2.33
160 000 2.05 2.53 2.39 7.04 4.95 2.55
LSD 5% 0.24 0.39 0.42 1.63 1.36 0.52
1% 0.34 0.60 0.59 2.34 1.95 0.73
Nitrogen topdressing (kg/ha) 60 1.09 1.52 1.37 3.74 3.29 1.51
120 1.41 1.70 1.56 4.61 3.95 1.89
180 1.63 1.54 1.65 4.62 4.33 1.91
LSD 5% 0.34 NS 0.21 NS NS NS
1% – NS – NS NS NS
plant, and LAI, mention should be made of its further raising of nitrogen to 180 kg/ha the seed
yield continued to increase, though not in a statis-duration at the plant densities studied and the
nitrogen rates in the period of seed formation and tically significant manner (except for 1994–1995).
These results are in accord with those obtained by accumulation of dry matter in seed. From such
long measuring intervals, it is impossible to deter- Zarisˇnajak and Sˇijan (1991), who also achieved
the highest seed yield with topdressing involving mine the leaf area duration (LAD); however,
certain changes were observed on the crop due to 120 kg N/ha. Based on soil analyses, Bornscheuer
et al. (1993) recommend an almost identical nitro-the influence of environmental factors. At nitro-the end
of the period of dry matter accumulation in seed, gen rate for topdressing. In the research done by
Longden and Johnson (1977), Montanari et al. lower and middle leaves were dry at higher plant
densities, whereas only lower leaves were dry at (1982), Rastija (1993), seed yield did not depend
on topdressing nitrogen rates. An increased lower densities, especially in treatments with lower
nitrogen rates. Higher leaf dehydration in dry number of plants per unit area decreased the
production (yield ) of seed per plant ( Table 5). At
years (1991–1992) might have had a negative effect
on the activity of the photosynthetic apparatus larger area per plant, seed sugar beet produced
three to four times higher seed production per during seed formation, as well as on translocation
of assimilates into seed. In 1993–1994, the crop plant than plants grown at high density. The limit
for this kind of compensation was 120 000
was infested by plant diseasesCercospora beticola
Sacc. andPhoma betae Frank, especially the treat- plants/ha. Increase of the nitrogen rate in
topdress-ing from 60 to 120 kg/ha led to a significant
ments involving higher nitrogen rates and higher
plant densities, so plants had fewer photosyntheti- increase in seed production per plant. Interactions
were also recorded between the lowest plant den-cally active leaves at harvest.
Yield of primarily processed seed (filled fruits sity and the highest topdressing nitrogen rate. The
influence of the investigated factors on seed germi-of 3.5–5.5 mm) increased significantly up to a
density of 80 000 plants/ha in 1991–1992 and 1993– nation was less expressed than that of experimental
years ( Table 6). The best seed germination (seed
1994, and to 120 000 plants/ha in 1994–1995
( Table 4). Topdressing nitrogen rate of 120 kg/ha fraction: 3.5–5.5 mm) was achieved in the year
with a warmer July with less precipitation. In the led to a significant yield increase of primarily
Table 4
Influence of plant density and nitrogen rate in spring topdressing on sugar beet primarily processed seed yield
Factor Primarily processed seed (kg/ha)
1991–1992 1993–1994 1994–1995
Plant density (plants/ha) 40 000 767 999 565
80 000 843 1086 601
120 000 778 1147 665
160 000 838 1141 681
LSD 5% 49 99 56
1% 68 – 78
Nitrogen topdressing (kg/ha) 60 710 996 592
120 872 1117 612
180 838 1166 680
LSD 5% 47 87 32
1% 69 127 47
60 to 180 kg/ha showed a downward trend in weather conditions prevailing in Croatia in the
period of flowering, seed setting and maturing germination (higher percent of empty fruits). The
number of plants per unit area and nitrogen rates constrain the growth and favour maturing
pro-cesses, so that the differences in LAI due to
of topdressing had no significant effect upon the
1000 seed weight and production of single-germ different areas/plant are not manifested. Hence, it
is unlikely that any treatment, within normal seeds.
Differences in the size and shape of the area per limits, would speed up or slow down maturing to
such an extent as to be reflected in the seed quality plant were not so pronounced in our trials as to
have a considerable effect upon the growth and traits. For the time being, no irrigation is applied
in the Republic of Croatia during flowering and habit of plants. As the densities studied involved
uniformly spaced plants, the growth of plants was fruit maturing, and precipitation cannot provide
the necessary moisture in some years. This is rather restricted by their mutual competition even
at the lowest density. On the other hand, the especially pronounced in the case of denser plant
Table 5
Influence of plant density and nitrogen rate in spring topdressing on sugar beet seed production per plant
Factor Seed production per plant (g/plant)
1991–1992 1993–1994 1994–1995
Plant density (plants/ha) 40 000 50.7 54.7 46.2
80 000 29.4 29.3 26.3
120 000 18.8 21.7 17.8
160 000 16.2 17.1 14.6
LSD 5% 2.8 2.1 3.1
1% 3.9 2.9 4.4
Nitrogen topdressing (kg/ha) 60 24.9 27.6 24.4
120 30.3 31.7 26.0
180 31.1 32.8 28.3
LSD 5% 2.1 3.0 1.6
76 M. Pospisˇil et al./European Journal of Agronomy 12 (2000) 69–78
Table 6
Influence of plant density and nitrogen rate in spring topdressing on seed germination
Factor Germination (%)
1991–1992 1993–1994 1994–1995
Plant density (plants/ha) 40 000 96.3 96.6 89.8
80 000 96.3 96.5 90.2
120 000 96.7 97.5 93.6
160 000 96.7 97.2 91.8
LSD 5% NS NS 2.6
1% NS NS –
Nitrogen topdressing (kg/ha) 60 97.1 96.4 91.2
120 96.6 97.0 91.8
180 95.8 97.4 91.1
LSD 5% NS NS NS
1% NS NS NS
populations with very high total water consump- 1969) point to the conclusion that it is only in
cases of quite low or too high plant densities that tion. Plants grown at high density have a delayed
growth, which has a detrimental effect on seed differences may be expected in the maturing rate
and germination of harvested seed. In regions for quality (Bornscheuer, 1969). Under the conditions
of uninterrupted growing throughout winter, even which the recommended plant density is over
300 000 plants/ha at harvest, the growing period
a smaller number of plants per unit area (65 000–
80 000 plants/ha at harvest) revealed a higher lasts for 13–14 months, which is much longer than
in the conditions prevailing in the Republic of yielding potential, thus levelling up seed yields
( Kristek and Matic´, 1984). Literature data (Scott, Croatia or southern European countries. This
Fig. 3. Correlation between LAI and seed germination.
means that plants remain active for a considerably thetic potential. However, the considerable effect
of the prevailing agroecological conditions should longer period of time, which allows their adequate
development even in higher populations. Another be pointed out as well.
The highest LAI at full flowering was achieved important factor under these conditions is water
availability to plants. Radisˇic´ (1977) and in the year in which the vegetative stage of seed
sugar beet growth was very intensive (sufficient
Stefanovic´ (1987) reported that, at a uniform
planting spacing, plant density also had little effect precipitation and moderate air temperatures at the
onset of vegetation in spring), whereas the lowest on seed germination.
In the 3 year research period, the most reliable index was recorded in the year with expressly early
and rapid development of generative plant parts estimation of connection between yield of
primar-ily processed seed and LAI (R2=0.23), as well as ( less precipitation and higher temperatures in
April ).
between seed germination and LAI (R2=0.35),
was defined with logarithmic function ( Figs. 2 and A population increase to 120 000 plants/ha had
a positive effect on LAI as well as on seed yield
3). These coefficients of determinations are fairly
low. This kind of functional connection is partly and quality.
The efficiency of nitrogen rates in topdressing
the result of their low correlation in every year
(Figs. 2 and 3), which was more expressive in was predominantly influenced by precipitation and
soil fertility. In the year with abundant precipita-1994–1995.
tion throughout spring and summer as well as on
poorly fertile soil (<2 mg N-min/100 g soil, at a
depth of 0–60 cm), the leaf area per plant increased 4. Conclusions
significantly up to the application of 120 kg/ha of
N in topdressing. This research points to the fact that the increase
of plant density and nitrogen nutrition up to a The yield and quality of seed also depended
considerably on the weather conditions prevailing certain limit promoted the formation of leaf
78 M. Pospisˇil et al./European Journal of Agronomy 12 (2000) 69–78
Milford, G.F.J., Thorne, H.G., 1972. Effects of temperature
On a soil with good nitrogen availability in
and radiation at different stages of sugar beet, Report of
spring (>5 mg N-min/100 g soil, at 0–60 cm depth)
the Rothamsted Experimental Station for 1971, Part I,
the nitrogen rate of 120 kg/ha in topdressing gave 101–102.
a high yield and satisfactory quality of seed at a Milford, G.F.J., Pocock, T.O., Jaggard, K.W., Biscoe, P.V.,
Armstrong, M.J., Last, P.J., Goodman, P.J., 1985. An
plant density of 80 000 to 120 000 plants/ha.
analysis of leaf growth in sugar beet. IV. The expansion of
On less fertile soil (<2 mg N-min/100 g soil, at
the leaf canopy in relation to temperature and nitrogen.
0–60 cm depth), seed yield showed a steady
sig-Ann. Appl. Biol. 107 (2), 335–347.
nificant increase up to the application of 180 kg/ha Montanari, M., Lovato, A., Cazzola, V., 1982. Influence of
of N, with a slight decrease of quality. plant density nitrogen fertilizer and topping on seed yields
in sugar beet. Rivista di Agronomia 16 (2), 111–116. Radisˇic´, V., 1977. Proucˇavanje problema u vezi sa
proizvodn-jom pojedinih kategorija semena sˇec´erne repe. a) Vegetacioni
References
prostor biljaka semenjacˇe i vreme uspostavljanja istog kao faktori prinosa i kvaliteta semena kod tetraploidnog selekci-onog materijala. Godisˇnji izvesˇtaj, Institut za ratarstvo i Barbieri, G., 1983. Determinazione dell area fogliare in
barba-bietola da zucchero (Beta vulgaris L. saccharifera). Rivista povrtarstvo,, Novi Sad.
Rastija, M., 1993. Prinos i kvaliteta sjemena sˇec´erne repe u de Agronomia 17 (2), 342–348.
Bornscheuer, E., 1969. Saatgutfibel-Zuckerru¨be, KWS Klein- zavisnosti od gnojidbe i uvjeta proizvodnje. Magistarski rad. Sveucˇilisˇte Josipa Jurja Strossmayera u Osijeku. Poljo-wanzlebener Saatzucht ag. 25.
Bornscheuer, E., Meyerholz, K., Wunderlich, K.H., 1993. Seed privredni fakultet Osijek.
Rover, A., Koch, H.J., 1995. Indirect determination of leaf area production and quality. In: Cooke, D.A., Scott, R.K.
( Eds.), The Sugar Beet Crop: Science into Practice. Chap- index of sugar beet canopies in comparison to direct meas-urement. J. Agron. Crop Sci. 174 (3), 189–195.
man & Hall, London, pp. 121–155.
Campbell, R.E., Viets, F.G., 1967. Yield and sugar production Scott, R.K., 1968. Sugar beet seed growing in Europe and North America. J. Int. Inst. Sugar Beet Res. 3, 53–84.
by sugar beets as affected by leaf area variations induced by
stand density and nitrogen fertilization. Agron. J. 59, Scott, R.K., 1969. The effect of sowing and harvesting dates, plant population and fertilizers on seed yield and quality of 349–354.
Campbell, S.C., 1968. Sugar beet seed production in Oregon, direct-drilled sugar beet seed crops. J. Agric. Sci. Cambridge 73, 373–385.
USA, Report of the 31st Winter Congress of the
Interna-tional Institute for Sugar Beet Research, 165–174. Scott, R.K., Longden, P.C., 1973. The production of high qual-ity seeds. In: Heydecker, W. (Ed.), Seed Ecology. Butter-Fo¨rkel, H., 1985. Beziehungen zwischen Blattmasse und
Blatt-fla¨che bei Zuckerru¨ben. Archiv fu¨r Acker und Pflanzenbau worth, London, pp. 811–895.
Stefanovic´, D., 1987. Prinos i poljoprivredna vrednost semena und Bodenkunde 29 (7), 465–469.
Kristek, A., Matic´, I., 1984. Utjecaj gustoc´e usjeva i termina sˇec´erne repe u zavisnosti od sklopa useva, roka zˇetve i desi-kacije. Disertacija, Univerzitet u Novom Sadu, Poljo-zˇetve na prinos i kvalitet sjemena sˇec´erne repe. Agronomski
Glasnik 46, 3–4, 259–269. privredni fakultet Novi Sad.
Trogisch, C., 1985. Techniques of Modern Sugar Beet Seed Longden, P.C., 1974. Harvesting sugar beet seed. J. Agric. Sci.
Cambridge 83, 435–442. Multiplication. KWS Eigenverlag.
Vidacˇek, Zˇ ., Sraka, M., Husnjak, S., Pospisˇil, M., 1994. Lizime-Longden, P.C., Johnson, M.G., 1977. Effects of single or split
aplications of nitrogen fertilizer to in situ sugar-beet seed trijsko mjerenje otjecanja vode iz tla u uvjetima agroeko-losˇke postaje Zagreb–Maksimir, Znanstveni skup plants in the spring of their second years growth. J. Agric.
Sci. 89 (3), 609–620. ‘‘Poljoprivreda i gospodarenje vodama’’, Bizovacˇke toplice, 17.–19. studenog 1994. god., Priopc´enja, 223–232. Longden, P.C., Scott, R.K., 1973. Growing Sugarbeet for Seed
in England. ADAS Quart. Rev. no. 9. Zarisˇnajak, A.S., Sˇijan, P.N., 1991. Vlijanie udobrenij na inten-sivnosc´ rosta, postuplenie pitateljnjih vesˇestv, urozˇajnosc´ i Matic´, I., Dłurdłevic´, M., Kristek, A., 1983. Osvrt na
proiz-vodnju sjemena sˇecerne repe. Agronomski Glasnik 45, kacˇestvo semjan bezvisadocˇnjih semennikov saharnoj svekli. Agrohimija (5), 71–78.
