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LATE SEASON WATER AVAILABILITY AND DAMAGE AND MECHANICAL PROPERTIES IN SUGAR BEET ROOTS DISCUSSION

Abstract

Rates of harvest damage in various vegetable crops has been linked to soil water content at harvest and the resulting cell turgor. Casual observation in sugar beet suggests that rates of surface cracking at harvest are similarly linked to soil water content. The rates of damage during harvest and handling of sugar beet has also been linked to their mechanical properties. It is, however, unclear that the standard metrics used for quantifying sugar beet mechanical property will capture the dimensions on which cell turgor affects mechanical properties. A small exploratory study was undertaken in Sweden during 2021. Sugar beets were taken from a field grown under commercial conditions. Two treatments were applied in the field in four replicates during the six weeks prior to harvest and assessment; grown under a shelter, or irrigated twice. A third and separate treatment of dehydration through high airflow over the one week period prior to assessment was also applied. Untreated beets were taken as the control. Mechanical properties were assessed with the standard pseudo-static measures of puncture resistance and tissue firmness. Mechanical property assessment was extended to also include the apparent elastic modulus, plus a dynamic falling-ball test. Damage from the dynamic test was assessed as degree of surface abrasion and cracking. The results showed that the irrigated sugar beets had a lower puncture resistance compared to both those grown under a roof and the dehydrated beets. The falling-ball test showed that irrespective of dry or wet conditions immediately prior to harvest, the sugar beets cracked at the same incidence. The puncture resistance of the dehydrated sugar beets did not differ from the control, but rates of damage were greatly reduced. The dehydrated beets also returned lower tissue firmness and higher elastic behaviour than the other treatments, suggesting a link between damage during dynamic impacts and these traits.
LATE SEASON WATER AVAILABILITY
AND DAMAGE AND MECHANICAL
PROPERTIES IN SUGAR BEET ROOTS
DISCUSSION
The soil water available to sugar beet
in the weeks prior to harvest had little
effect on rates of damage to roots. This
suggests that extra damage at harvest
that is observed in the field following
rain events is a result of machine
operating conditions. This was a pilot
study.
CONCLUSION
Late season water availability
had little effect on damage rates.
Elasticity appears an important
parameter in predicting rates of
damage to sugar beet roots.
METHOD
Treatments (2021). Prior to testing:
1. Irrigated heavily 25 and 1 day prior
2. Grown under untreated conditions
3. Grown under roof 8 weeks
4. Harvested and ventilated one week
Testing (19 & 20 Sept 2021):
-4 replicates, 10 roots per replicate.
-Damage: Falling-ball test: Ø 70 mm
1.4 kg steel ball, 93 cm fall height.
Cracks and surface damage
assessed.
-Mechanical properties: Laboratory
testing. Ø 2 mm cylindrical plunger.
60 mm/min. 3 samples per root.
Puncture resistance, Tissue firmness,
Apparent Elastic Modulus.
RESULTS
ABOVE: The four treatments. (clockwise from top-left);
irrigated, untreated, ventilated drying, roof.
BELOW: Still images from the falling-ball test.
HELENE LARSSON JÖNSSON
Researcher
Department of Biosystems and
Technology
Swedish University of
Agricultural Sciences
helene.larsson.jonsson@slu.se
WILLIAM ENGLISH
Doctoral student
Department of Biosystems and
Technology
Swedish University of
Agricultural Sciences
william.english@slu.se
www.slu.se
Soil moisture profiles (to 45 cm) for
treatments 1, 2 and 3 ranged from
saturated (irrigated), to completely
dry (roof). These variations in soil
moisture at harvest resulted in minor
variation in textural properties, and
resulted in no differences in rates of
damage. The beets that were
subjected to post-harvest ventilated
drying displayed more elastic
behaviour and experienced less
damage on all metrics.
TREATMENT PUNCTURE
RESISTANCE
[MPa]
TISSUE
FIRMNESS
[MPa]
DISTANCE TO
PUNCTURE
[mm]
ELASTIC
MODULUS
IRRIGATED 5.83a5.12a1.51b3.93b
UNTREATED 6.07ab 5.35a1.43ab 4.27a
ROOF 6.17b5.31a1.39a4.47a
VENTILATED 6.14b4.81b1.76c3.51c
TREATMENT CONTACT POINT
DAMAGE
[Grade 1-5]
CRACKS:
NUMBER
CRACKS:
LENGTH
[cm]
IRRIGATED 1.50a1.25a8.64a
UNTREATED 1.25a1.18a5.61a
ROOF 1.49a1.08a6.90a
VENTILATED 0.80b0.03b0.13b
TABLE 1: Mechanical properties of sugar beet roots, using standard laboratory testing, by treatment.
2021. Letters indicate significant groups from Post-Hoc Tukey test. N = 40.
TABLE 2: Damage assessment of sugar beet roots subject to a falling-ball test, by
treatment. 2021. Letters indicate significant groups from Post-Hoc Tukey test. N = 40.
FIGURE 1: Treatment average distance -pressure curves for sugar beet roots from laboratory
testing. 2021. Puncture resistance = curve peak. Tissue firmness = average of curve tail. Distance to
puncture indicated by dotted vertical lines. Elastic modulus = average curve slope to puncture.
FIGURE 2: High damage
on an untreated sugar beet.
Untr
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