Cover: The Nabla Beet was adopted as the logo of the study that resulted in Paper IV of this thesis. The Nabla (∇) is mathematical notation applied widely in the science of fluid dynamics and heat transfer to represent vector differential operators; primarily the gradient and divergence. It encompasses multi-dimensional change. The leaves of The Nabla Beet are taken from the logo of Nordic Beet Research foundation. It is proudly displayed on the cover of this thesis, symbolising the context of multi-dimensional change in which this research project existed, and as a (not so) subtle nod to NBR.
ISBN (print version) 978-91-8046-124-5
ISBN (electronic version) 978-91-8046-125-2
© 2023 William English, https://orcid.org/0000-0001-5197-2342
Swedish University of Agricultural Sciences, Department of Biosystems and Technology, Alnarp, Sweden
The summary chapter of this thesis is licensed under CC BY 4.0, other licences or copyright may apply to illustrations and attached articles.
Print: SLU Service/Repro, Alnarp 2023
Long-term post-harvest field storage of sugar beet (Beta vulgaris subsp. vulgaris)
The post-harvest storage of the sugar beet crop in Sweden occurs in the field. The harvest of roots generally ends along with the month of November, but the processing campaign can continue into February. The loss of quality of the stored roots during this period is economically important. This thesis groups the main mechanisms that results in loss of quality during post-harvest storage in two categories: plant health, and the storage environment. It focuses on the plant health dimension of mechanical properties, and the storage environment dimensions of moisture and temperature.
The relationship between key agronomic inputs and mechanical properties and storability of sugar beet roots was investigated. Growing season available nitrogen and water were found to have little impact on mechanical properties. The storability of roots was found to decrease significantly when irrigation gave an optimal soil water availability throughout the season. This is likely a result of an interaction with an unspecified dimension of plant health. The quantification of sugar beet root mechanical properties with a traditional handheld penetrometer applied in-field was found to be reliable. It was also found that the methods used in the analysis of mechanical properties could be expanded to include the apparent modulus of elasticity and that fall-tests can be used to assess dynamic impacts.
The use of a short, intense period of forced ventilation of a sugar beet bulk was found to lead to dehydration of sugar beet roots in a predictable manner. This resulted in increases to sucrose concentrations that would lead to greater gross income. Computational Fluid Dynamics modelling of the temperature within a clamp proved to be possible and insightful. The fluid dynamics within the clamp are
important to include in such modelling.
Keywords: clamp, quality, mechanical properties, handheld penetrometer, forced ventilation, computational fluid dynamics, mass transfer, heat transfer.
To the sugar beet growers of Sweden, and the rest of the world.
List of publications
This thesis is based on the work contained in the following papers, referred to by Roman numerals in the text:
I. Hoffmann, C. M., Kleuker, G., Wauters, A., English, W., and Leijdekkers, M. (2022). Root tissue strength and storage losses of sugar beet varieties as affected by N application and irrigation. Sugar Industry, 147(1):34–41.
II. English, W., Ekelöf, J., Vancutsem, F., Leijdekkers, M., Kleuker, G., and Hoffmann, C. M. (2022). Method for in-field texture analysis of sugar beet roots using a handheld penetrometer. Acta Agriculturae Scandinavica, Section B — Soil & Plant Science, 72(1):623–634
III. English, W. and Larsson Jönsson, H. (2023). Quality and mass transport properties of sugar beet roots under short duration, high airflow post-harvest storage. Manuscript
IV. English, W. and Mousavi, S. M. (2023). A Computational Fluid Dynamics Model of Airflow and Temperature in a Sugar Beet Clamp. Submitted to: Biosystems Engineering
Paper I is reproduced with the permission of the publishers. Paper II is reproduced under the terms of the Creative Commons CC BY license. Two additional unpublished exploratory supplementary studies are discussed in this thesis. They are summarised in the conference posters (not reproduced):
SS1. Nilsson, M., English, W., and Telezhenko, E. (2020). Pressure Mapping Sugar Beets. In 77th Congress of the International Institute for Sugar Beet Research, Brussels, Belgium. International Institute of Sugar Beet Research (IIRB)
SS2. Larsson Jönsson, H. and English, W. (2022). Late season water availability and damage and mechanical properties in sugar beet roots. In 78th Congress of the International Institute for Sugar Beet Research, Mons, Belgium. International Institute of Sugar Beet Research (IIRB)
The contribution of William English to the papers included in this thesis was as follows:
I. Conducted fieldwork, with assistance from Hushållningssällskapet Skåne. Conducted laboratory analysis. Drafted manuscript.
II. Developed and formulated research question. Wrote application for funding. Conducted fieldwork, with assistance from Hushållningssällskapet Skåne. Coordinated international fieldwork. Evaluated data. Drafted manuscript.
III. Developed and formulated research question. Wrote application for funding. Designed and constructed experimental unit. Conducted fieldwork, with assistance from Hushållningssällskapet Skåne. Evaluated data. Drafted manuscript.
IV. Developed and formulated research question. Conducted model development. Evaluated data. Drafted manuscript.
SS1. Developed and formulated research question. Wrote application for funding. Conducted fieldwork. Evaluated data. Drafted manuscript.
SS2. Developed and formulated research question. Wrote application for funding. Conducted fieldwork. Evaluated data. Drafted manuscript.
Terms, Abbreviations, Symbols
Bulk – General term for a collection of sugar beet roots post-harvest, including in the clamp and pile storage systems, and in experimental systems.
Clamp – System of in-field post-harvest storage of a bulk of sugar beet roots, often employed in Europe.
In-situ storage – System of in-field storage of sugar beet roots in which roots are not harvested after the end of a season’s growth.
Industry – The purchaser and processor of sugar beet. Usually also a marketer of processed sugar. Currently Nordic Sugar in Sweden.
Pile – System of large, factory based post-harvest storage of sugar beet roots, often employed in North America.
AIR – Alcohol Insoluble Residues. Indicative of plant cell wall content.
CFD – Computational Fluid Dynamics. A mechanistic modelling approach commonly adopted in the study of fluid dynamics and heat transfer.
COBRI – Coordination Beet Research International. Research collaboration between the national sugar beet research organisations of SE, DE, NL, and BE.
ICUMSA – International Commission for Uniform Methods of Sugar Analysis.
IfZ – Institut für Zuckerrübenforschung [The Institute of Sugar Beet Research]. National sugar beet research organisation of Germany.
IIRB – International Institute for Sugar Beet Research. International academic knowledge sharing organisation for sugar beet research.
NBR – Nordic Beet Research foundation. National sugar beet research organisation of Sweden and Denmark. Co-sponsor of this project.
SBU – Sockernäringens BetodlingsUtveckling. The immediate predecessor to NBR in Sweden.
SSA – Svenska Sockerfabriksaktibolaget. The main company involved in the Swedish sugar industry between 1907 and 1992
°Cd – Degree-days. Cumulative temperature. Base temperature: 0 °C
∇ – Nabla operator. Represents vector differential operators; primarily the gradient and divergence
α – Effective diffusivity
Δ𝑐 – Water vapour pressure deficit
ε – Porosity
ρ – Density
τ – Convective stress tensor
Asf – Specific surface area
Cp – Specific heat
D – Darcy coefficient
Dab – Diffusivity of water
f – Fluid
F – Forchheimer coefficient, or, Force
hsf – Convective heat transfer coefficient
kc – Convective mass transfer coefficient
K – Thermal conductivity
L – Characteristic length
m – Mass
𝑚̇𝑤 – Mass flux of water
p – Pressure
Qr – Heat of respiration
Re – Reynolds number
s – Solid
S – Source term
Sc – Schmidt number
Sh – Sherwood number
t – Time
T – Temperature
U – Velocity
v – Velocity