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 mg100 g soil H
2 O
1M KCl P
2 O
5 K
2 O
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 23, 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 parts at the expense of seed quality.
years. Milford and Thorne 1972 established that
73 M. Pospisˇil et al. European Journal of Agronomy 12 2000 69–78
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 cm
2 Stage of inflorescence stalk appearance
In full flowering 1991–1992
1993–1994 1994–1995
1991–1992 1993–1994
1994–1995 Plant density plantsha
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 kgha
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 kgha 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 kgha as well as lower plant densities, though
density of 160 000 plantsha. 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 plantsha 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 kgha increased the LAI as well. The highest, and statistically signifi-
leaf area per plant was obtained with the plant density of 40 000 plantsha, 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 kgha 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 plantsha 1993–1994 and 1994–1995. Further increase of plant density to 160 000
stage of full flowering, application of 120 and 180 kgha of N significantly increased the leaf area
plantsha reduced the ability of biological self- regulation of plant leaf area, which led to a further
values in comparison with 60 kgha 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 during the growing season, notably in May, Rastija
Besides the maximally achieved leaf area per
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 m
2m2 Stage of inflorescence stalk appearance
In full flowering 1991–1992
1993–1994 1994–1995
1991–1992 1993–1994
1994–1995 Plant density plantsha
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 kgha
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 kgha 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 Nha. Based on soil analyses, Bornscheuer
et al. 1993 recommend an almost identical nitro- the influence of environmental factors. At 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 diseases Cercospora beticola
Sacc. and Phoma betae Frank, especially the treat- plantsha. Increase of the nitrogen rate in topdress-
ing from 60 to 120 kgha 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 plantsha 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 plantsha in 1994–1995
Table 4. Topdressing nitrogen rate of 120 kgha 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
processed seed compared with 60 kgha. Upon dry 1991–1992, the increase of nitrogen rate from
75 M. Pospisˇil et al. European Journal of Agronomy 12 2000 69–78
Table 4 Influence of plant density and nitrogen rate in spring topdressing on sugar beet primarily processed seed yield
Factor Primarily processed seed kgha
1991–1992 1993–1994
1994–1995 Plant density plantsha
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 kgha
60 710
996 592
120 872
1117 612
180 838
1166 680
LSD 5
47 87
32 1
69 127
47
60 to 180 kgha 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 areasplant 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 gplant
1991–1992 1993–1994
1994–1995 Plant density plantsha
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 kgha
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 1
3.0 4.4
2.3
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 plantsha
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 kgha
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 plantsha at harvest, the growing period a smaller number of plants per unit area 65 000–
80 000 plantsha 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. 2. Correlation between LAI and yield of primarily processed seed.
77 M. Pospisˇil et al. European Journal of Agronomy 12 2000 69–78
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 R
2=0.23, as well as less precipitation and higher temperatures in
April . between seed germination and LAI R
2=0.35, was defined with logarithmic function Figs. 2 and
A population increase to 120 000 plantsha 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-min100 g soil, at a depth of 0–60 cm, the leaf area per plant increased
4. Conclusions
