germination while heavier compaction generally reduced yields even in insensitive crops like bar-
ley. Soane et al. 1982 indicated that cereal plants’ growth and yield are likely to show opti-
mum response to certain soil compaction level. This optimum is related to soil type, crop growth
stage and climatic conditions. They referred to data by Jaggart 1972 showing that compaction
at 0 – 160 mm depth causing an increase of dry bulk density from 1.3 to 1.6 Mgm
3
affected beets and reduced sugar yield by 0.9 Mgha. Soane et
al. 1982 mentioned data reported by Cooke and Jaggart 1974 which indicated that compaction
reduced sugar yield by 1.9 Mgha and tops yield by 7 Mgha. Hebblethwaite and McGowan 1980
showed that compaction affects inversely sugar beet population and yields. Gemtos and Lellis
1997 showed that sugar beets growing in pots in a glasshouse are sensitive to compaction in the
initial stages of growth and only very light com- paction around 100 kPa was beneficial to the
crop. Compaction is considered as a factor adversely
affecting crop growth and yields although that contradicting results have been reported Soane et
al., 1982. Differences in rainfall over the years along with soil type are the two factors probably
explaining the contradicting results. Genotypic ef- fects could be considered as well but to our
knowledge data have not been reported. Modern varieties were developed under optimum soil con-
ditions resulting from continuous soil tillage mainly by ploughing. It is then reasonable to be
expected that they are adapted to conditions of minimum soil compaction. Taking into account
the variety of existing agronomic factors, and the complex
genotype × environment interactions,
genotypic differences for adaptation to soil condi- tions and especially response to soil compaction
stress could not be ruled out. The aim of this research was a preliminary attempt to study the
response of 11 sugar beet genotypes to stresses imposed by soil compaction.
2. Material and methods
Eleven sugar beet genotypes representing differ- ent ploidy, inbreeding levels and seed morphology
were used Table 1. There were five lines, propri- etary of Hellenic Sugar Industry and three experi-
mental varieties using these lines in some hybrid combinations. Lines 031 and 009 are diploid,
monogerm, broad based inbreds whereas line 002 is diploid, monogerm, nearly inbred. Lines 782
and 795 are tetraploid, multigerm, narrow based synthetics. Genotype P104 is a diploid, monogerm
single cross hybrid 002 × 009, genotype S562 is triploid, monogerm, single top cross hybrid
031 × 765, whereas genotype T1504 is a triploid, monogerm, three way top cross hybrid P104 ×
782. RIZOR and VERGINA are commercial monogerm triploid hybrid varieties largely grown
in Greece whereas genotype A1991 represents seed lot of a monogerm commercial hybrid vari-
ety produced in 1991.
The soil compaction effects were studied in pots as follows. Plastic bags placed in a metal tube of
80 mm diameter and 120 mm height were filled with soil up to 3 cm under the cylinder top. Three
Table 1 Description of genotypes used in the soil compaction effect
study Entry
Description Identification
031 1
Monogerm, inbred S
3
,diploid male sterile
002 Monogerm, inbred line, diploid
2 male sterile
3 009
Monogerm, inbred S
3
, diploid 4
P104 002×009, monogerm, single cross,
diploid hybrid S-562
Triploid, monogerm, single cross 5
031×765, experimental hybrid variety
782 6
Multigerm, OP line, tetraploid 7
Commercial monogerm triploid VERGINA
hybrid variety RIZOR
8 Commercial monogerm triploid
hybrid variety 765
9 Multigerm, OP line tetraploid
T1594 10
Triploid, monogerm, three way top cross experimental hybrid
variety P104×782 A1991
11 Seed lot of a commercial
monogerm triploid hybrid variety
sugar beet seeds were placed on the top of the soil. Then 3 cm of soil were added on the top of
the seed to fill up the tube in such a way to secure that initial soil volume was equal to that of the
tube. Soil bags were compacted using the equip- ment and the procedure described by Gemtos and
Lellis 1997 at pressures varying from minimum compaction it is considered as compaction of 1
kPa up to 400 kPa. The equipment consisted of a metal frame and a hydraulic jack. The metal tube
with the soil was secured in the frame and the jack applied the pressure. A pressure gauge measured
the hydraulic fluid pressure in the jack. The pres- sure gauge was calibrated with known weights for
each applied force, and later was divided by the soil core surface area to give compaction pressure.
Seven pressure levels were applied. In the lower level 1 kPa, the soil was just levelled by hand
causing a minimum pressure. The other six pres- sures levels were equivalent to 50, 125, 200, 280,
340 and 400 kPa. After compaction the sinking of the soil surface was measured and the final vol-
ume was calculated. The soil was weighted just after compaction and before watering and the
specific weight of the compacted soil was calcu- lated. The procedure followed allowed for a wide
range of compaction pressures to be tested. The lower pressures corresponded to those applied by
drilling machines or cylinders used after drilling. Tractors’ compacting pressures depend on their
weight and tyre size, which usually range between 100 and 200 kPa. Heavy harvesting machinery,
heavy compaction cylinders, spraying tankers or other similar machinery, cause higher compaction
pressures Gemtos et al., 1999. Compaction is applied to the whole soil mass permitting the
studying of the effects of the compacted surface layer affecting emergence and of the deeper lay-
ers affecting root growth. The procedure was used in many experiments and no damage to the
seeds was observed even in larger seeds such as cotton. Two soil types, a sandy loam sand 72.6,
clay 12.9, silt 14.5 and organic matter content 1.2 and a clay loam sand 37.3, clay 27.0,
silt 35.7 and organic matter content 0.98, were used, at two initial water contents each. The
water contents were 10 and 16 for the sandy loam, and 12 and 18 for the clay loam giving
dry and
wet initial
soil conditions.
Thus there were 7 × 2 × 2 × 11 compaction pressure ×
water content × soil type × genotypes treatments analysed as a factorial experimental design with
four replications. The single pot was the experi- mental unit. The pots, after soil compaction, were
placed in a glasshouse in order to avoid weather effects. Only one plant was left in each pot the
first to emerge. The pots were watered every other day up to the field capacity of the soil. The
experimental period was 30 days and the follow- ing observations were recorded:
1. Time to shoot emergence. Observations were taken twice every day.
2. Daily growth as measured by the height in- crease of the plant. Observations taken every
other day. 3. Above ground and root dry matter. At the end
of the experiment the aerial part was cut at ground level and oven dried at 72°C for 48 h.
The soil was washed out from the root by running water and then the wet root was oven
dried, in the same manner as for the aerial part.
4. In addition, before drying, root dimensions were recorded as follows: root diameter at the
soil surface and at the bottom of the pot along with the main root length.
Data were analysed using the conventional fac- torial analysis of variance. Main effects and all
interactions were estimated, using Statgrafics soft- ware. Then a modified analysis was performed.
The 11 genotypes were considered as main factor and the three conditions pressure, water content
and soil type as one ‘environment’. In this way all interactions could be pooled to a single geno-
type × environment giving the possibility to parti- tion the variance observed for genotypes in three
components: genotypic, environmental and geno- typic × environmental Hallauer, 1988. Although
three seeds were planted in each pot, pots having no emerged plants were recorded and will be
herein referred to as empty pots. The empty pots were analysed separately and their frequency was
estimated. Time to shoot emergence was analysed using observations only from pots with emerged
plants while for the other variables empty pots were considered as zero values. Simple phenotypic
correlations for growth data were estimated.
Fig. 1. Effect of compaction pressure on the soil dry bulk density.
rate was 72.6 meaning that in 362 out 1320 pots 27.4 were empty that is having no
emerged plants. The frequency of empty pots, averaged over genotypes for soil water content,
was 62 under high initial water content condi- tion and 38 for the low water content. The
corresponding frequencies for sandy loam and clay loam soil types were 42 and 58, respec-
tively. These frequency estimates indicated a wa- ter content and soil type effect on emergence. In
the same manner a compaction pressure effect Fig. 2 was indicating that compaction pressure
higher than 125 kPa resulted in 3 – 9 increase of empty pots.
Variable genotypes, empty pots, showed the expected response with the inbreeds being affected
more severely due to inbreeding depression Fig. 3. Besides this expected response some differ-
ences were evident within the group of outcrossed genotypes indicating possible genotypic differ-
ences. Main effects were highly significant for all variables and some interaction effects, as well
Table 2. In spite of some interaction effects and especially those for the root diameter being sig-
nificant, interaction effects generally contributed no more than 3.5 to the total variance for each
main effect. This means that the average main effects could be considered disregarding interac-
tions Table 3.
Time to shoot emergence was affected by the factors studied, as well Tables 2 and 3. Com-
Fig. 2. Frequency histogram of empty pots versus compaction pressure.
3. Results
