Complete: Varietal differences in crown size and greater recovery of crown material at harvest

Timescale: 2009 - 2011
Project Lead: E Burks, C Walters & G Milford
Project Sponsor: BBRO

Project Summary

The UK sugar-beet industry has largely achieved its objective of increasing national average yields to 70 t/ha. The opportunities offered by recovering and processing the whole of the crown material are being explored to improve yields even further. Crowns contain significant amounts of sugar, but at low concentration and accompanied by high concentrations of impurities which have, in the past, impaired the extraction and crystallisation of sugar. Improved factory technologies and new opportunities for by-products now make the recovery of crown sugar a more attractive proposition.

Main Objectives

Conventional harvesters generally operate a two-stage process for topping beet – using a forward-mounted flail to remove the bulk of the green top followed by scalper knife that removes the uppermost quarter to a third of the biological crown. This crown material is left in the field and does not contribute to recovered yield. Improved flail-only topping systems that remove only the leaves and petioles and so allow more of the crown material to be recovered are being tested on the continent and in the USA.

This project examined:

  • How much extra yield can be obtained by flail-only harvesting systems;
  • How far these yield gains are affected by varietal differences in crown size;
  • Whether flail-only systems allow more yield to be recovered from widely or irregularly spaced crops and whether they can cope with large, lush leaf canopies;
  • The effect of the extra crown material on the overall quality of the beet.


Outcomes / Key Message For Growers And Industry

The general conclusion from these initial experiments is that a flail-only harvesting approach has the potential to deliver 5-10% extra adjusted clean beet yield over that delivered by conventional harvesting systems. Moreover, these significant gains in yield are achieved at little cost to beet quality. How much extra yield is obtained is largely determined by the initial biological size of the crown - this primarily being a varietal characteristic that may be enhanced by factors that favour shoot growth, principally the nitrogen and moisture status of the soil during early growth.

The yield gains in the present UK experiments were somewhat larger than the 2 - 5% increases obtained in recent German commercial trials reported by Wollenweber et al. (2010)[1], Wulkow et al. (2010)[2] and Hoffmann & Wulkow (2010)[3] and calculated from the data of Jaggard et al. (1999)[4]. Wulkow & Hoffmann (2010)[5] reported potential theoretical gains of 8-9% from studies on hand-harvested beets that are closer to those observed in our study. The commercial differences can be partly attributed to the different criteria used for topping beet in the two countries. The Germans consider the level of the lowest living leaf to be the optimal point of topping whereas, in the UK, beet may be topped anywhere between this point and that of lowest leaf scar - the contractual point for factory crowning - depending on how much crown tare UK growers wish to deliver. More of the crown will therefore be delivered by conventional harvesting systems in Germany than in the UK, and the potential gains from the flail-only as opposed to conventional harvesting would, conversely, normally be greater in the UK than Germany.

As would be expected, biological crown size was the main factor that influenced the yield gains obtained through flail-only harvesting. Crown size is a varietal characteristic and the most recent update of the biological crown size of the 58 varieties introduced onto the BBRO Recommended Lists since the early 1990s, shows that crown size, which ranges from 6% of the contractually-crowned root in varieties such as Alota, Saracen and Trinita to over 18% in Wildcat and Priscilla (Fig. 3) has, on average, tended to be smaller in more-recently introduced varieties (Fig. 4). If flail-only harvesting were to become more widely practiced the introduction of large-crowned varieties with their inherent yield advantage, may well reverse this trend - especially if the flail-only approach was also used to harvest BBRO Recommended List variety trials.


[1]  Wollenweber D, Töppe D & Schäfer B (2010). Ertrag und Qualität von geköpften und entblätterten Zuckerrűben. Zuckerrűbe 1, 22-25 (2010).

[2] Wulkow A, Coenen H, Michiels-Corsten, Leipertz H, Windt A, Bűrcky & Hoffmann C (2010). Defoliated and topped sugar beet – comparison of the harvesting systems in yield and quality. Sugar beet Conference, Göttingen, 2010.

[3] Hoffmann C & Wulkow A (2010). Are there any differences in beet tops among varieties

[4] Jaggard KW, Clark CJA & Draycott AP (1999). The weight and processing quality of components of the storage roots of sugar beet (Beta vulgaris L). Journal of the Science of Food and Agriculture 79, 1389-1398.

[5] Wulkow A & Hoffmann C (2010). Yield and quality of topped and defoliated sugar beet: theoretical potential and practical importance. Sugar beet Conference, Göttingen, 2010.

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