This thesis addressed issues related to the long-term post-harvest field storage of sugar beet roots. It was guided by the context of Swedish agriculture and the applied research environment it was born in. Two principles of long-term post-harvest storage of sugar beet roots were proposed; healthy sugar beet roots store better than unhealthy roots, and sugar beet roots store better when held within an optimal environment. With respect to plant health pre-storage, this thesis has shown;
- Growing season available nitrogen does not have a significant impact on the mechanical properties of sugar beet roots, nor their storability.
- Growing season available water does not have large impacts on mechanical proprieties of sugar beet roots, nor rates of damage at harvest. It can have an impact on quality loss during storage, which seems to be through an interaction with an unspecified dimension of plant health.
- A traditional handheld penetrometer is a viable tool for assessing the mechanical properties of sugar beet roots. It has benefits and drawbacks that should be considered in its adoption.
- The assessment of mechanical properties outside of the current standard methodology, such as responses to dynamic impacts and the apparent modulus of elasticity, is valuable to consider.
In the context of rapid turn-over of varieties and high capacity mechanical harvesting, the assessment of mechanical properties will remain valuable. Assessment of mechanical properties is an efficient means of assessing likely rates of damage and the consequential loss of quality during post-harvest storage. As noted in Paper II, the method for the assessment of mechanical properties of sugar beet roots described in Kleuker and Hoffmann (2019) remains the gold standard. This thesis suggests that the metrics included in this method should not be taken as the only metrics to consider. This thesis has also reinforced that mechanical properties are not the only dimension of plant health that matters for post-harvest storage of sugar beet roots. There remained a high degree of variation in storability related to the growing site. The suggestion was made that NBR might need to get back to its roots (pun intended) and again have a major focus on soil assessment, including both physical properties and the biological aspects.
With respect to the optimum post-harvest storage environment aspect of successful long-term storage of sugar beet roots, this thesis has shown;
- The deliberate dehydration of sugar beet roots during post-harvest storage with short duration, high airflow ventilation can improve quality and lead to increased gross income. It can also have negative impacts on mechanical properties.
- The dehydration of roots within a sugar beet post-harvest storage system is predictable and could be modelled.
- The temperature of roots within a sugar beet post-harvest storage system is predictable and possible the model. The inclusion of airflow within the bulk of roots is important.
- Further development of the understanding of fluid flow and heat transfer within the post-harvest storage system through further field experimentation would improve the accuracy and applicability of the model developed in this research project.
In the context of the highly variable open field storage environment, a changing climate, and a large volume crop, being able to assess changes to the post-harvest system through modelling has great potential. Ideas can be examined more rapidly and with much lower risk. The development of models and choice of parameters to include needs careful consideration. Modelling will never replace applied field research, but it can be a valuable complement.