11 December 1998

Beet faces a watershed

BETTER water use is the key to boosting sugar production from beet, according to a leading plant physiologist.

Plant populations may be worth re-investigating, canopy management might help, and herbicide-resistant crops could clearly have a role to play, says Keith Scott of Notts University*. But water supply to the crop is likely to be of over-riding importance, he suggests.

Warmer weather, improved varieties, earlier drilling, better establishment, and more robust weed and disease control have all helped lift UK national yields from 5.6t/ha (2.3t/acre) in the 1970s to 7.8t/ha (3.1t/acre) in the 1990s, says Prof Scott. But since the eighties water supply has become a brake.

Conserving winter rainfall for use in the summer will be increasingly important. "And everything we can do to clock up productivity per unit of water is going to be beneficial.

"Different varieties of wheat differ in their ability to mine water." Exploiting similar variations in beet will be a valuable step forward, he believes. IACR-Brooms Barn is already searching for more water-efficient wild beet relatives, especially those in drier parts of the world, for use in breeding programmes.

Nineties temperatures 0.5C (0.9F) above the long term average and a trend to drilling in late March rather than April, giving full canopy cover a week earlier, partly account for recent good results, says Prof Scott.

About 0.7t/ha (0.3t/acre) of the extra sugar achieved between the seventies and eighties was due to better plant populations, achieved through improved seed quality and crop protection, he estimates.

Progress in that area has slowed recently, the lift being only 0.1t/ha (0.04t/acre) between the eighties and nineties. By contrast lack of water to the crop over the same period is estimated to have trimmed output by 0.4t/ha (0.16t/acre).

Seventies trials with populations nearly twice the average 87,300 plants/ha (35,300 plants/acre) now regularly achieved found that more sunlight could be trapped, but there were no benefits to root yield. But since then breeders have steadily raised harvest indices, the relative proportion of sugar in leaves and roots, notes Prof Scott. "The new material might just show a response to increased plant population."

Canopy management through nitrogen manipulation, as with wheat, is also worth exploring. Compared with wheat, which has an optimum leaf area index of 5-6, sugar beets appears to be 3, at which point the crop contains about 120kg/ha of nitrogen. All the benefits from fertiliser N come from promoting leaf growth to achieve a leaf area index of three by early July, says Prof Scott. But more data is needed, for example on soil mineral N at sowing and at 85% establishment, to allow a system to be fined-tuned for beet. "The jury is still out but there is a measure of worth in following it up."

Herbicide tolerant beet, avoiding yield depressions caused even by more benign modern weed-killers, offers another route to improved performance, he adds.

* Prof Scotts views were relayed at the inaugural lecture in memory of Raymond Hull, first director of Brooms Barn who died in 1996.

Factors affecting changes in output from UK sugar beet

1970-79 1980-89 1990-98

Sugar yield (t/ha) 5.6 7.0 7.8**

Sowing date – +0.6

Plant population +0.7 +0.1

Water supply – -0.4

Breeding

(harvest index) +0.3 +0.3

Disease + pest

control +0.3 +0.1

Harvest, storage

& transport ? ?

Factors affecting UK sugar beet output (t sugar/ha)

1970-79 1980-89 1990-98

Sowing date – +0.6

Plant population +0.7 +0.1

Water supply – -0.4

Breeding (harvest index) +0.3 +0.3

Disease + pest control +0.3 +0.1

Harvest, storage& transport – –

Sugar yield (t/ha) 5.6 7.0 7.8 (est)

Pot of gold? Sugar yields rose almost 2% a year over the past 20 years. Water supply is now set to dictate future prospects, says Keith Scott.