Breeding goals in sugarbeet - Yield

Root Yield

Sugar beet yield per unit area of land is dependent upon a variety of factors. It is determined by:

• Soil quality
• Climatic conditions
• Supply of nutrients and water
• Genetic potential that a breeder has the power to influence

An optimum beet stand of approx. 90,000 plants per hectare permits a harvest of 400 to 1000 decitonnes (dt) (100 kg) topped* beets per hectare depending upon location.

* When processing beets to sugar only the root of the beet plant can be used. Hence the beets are ‘topped’ during harvesting.

Sugar Content

Following years of breeding dedicated to sugar beet its sugar content has significantly increased and it currently makes up 15 – 20% of the beet’s raw weight. Sugar beet has a water content of approx. 75% and sugar makes up the bulk of the dry contents.

Sugar content and root yield are generally inversely correlated, i.e. varieties with high sugar content possess a lower root yield than varieties with lower sugar content.

Did you know how many cubes of sugar the first sugar beets contained? A maximum of 5 g sugar - the equivalent of 2 sugar cubes! Today the yield is 140 g sugar or 56 sugar cubes.

Sugar Yield

Sugar yield is measured in decitonnes per hectare and is calculated from the root yield per hectare multiplied by its sugar content. Since high sugar yield is the ultimate goal, financially speaking, the plant breeder’s task is to combine high sugar content and high root yield in one and the same variety.

Raw Sugar Quality

The harvested beets are delivered to the sugar factory where they are chopped and boiled. In a series of steps raw juice is purified by eliminating organic and inorganic non-sugar substances. The resulting clear or thin juice is later made concentrated through evaporation.

Components of molasses, mainly calcium, sodium and organic nitrogen compounds, bind parts of the sugar and so prevent their extraction from the juice. Whilst the sodium content in newer varieties has already been significantly reduced, breeders are still faced with the task of further reducing alpha-amino nitrogen content, which impacts negatively on sugar crystallisation. In recent years the increase in the quantity of exploitable sugar has also been made possible by cutting the nitrogen fertilisers used by half.

White Sugar Yield

In the final stage of refining sugar the syrup, that is the non-crystalline sugar component, is separated in centrifuges from the sugar crystals. The sugar crystals are then rinsed with steam and white sugar obtained. The yield per hectare of white sugar can be estimated from the calculated sugar yield minus the losses due to the molasses and technical reasons. In recent years loss calculations have been modified to take better account of the negative impact of alpha-amino nitrogen particularly during sugar extraction.