8 March 1996

Tailored fertiliser – top beet

Better fertiliser practice produces higher yields of better quality sugar beet even in drought, according to a Cambs consultant. Robert Harris delves into the science and finds out how it works in practice

MANY sugar beet growers had a tough time last year. Poor establishment and early senescence caused by the unusually dry season pegged yields and sugars and raised impurities.

But Mark Law, managing director of Elsworth-based Law Fertilisers, believes growers can offset that by using more suitable fertilisers at the right time.

"The key is to integrate nutrition to speed establishment and maintain good growth through the season even when dry. To do that, growers should understand a bit more of the science behind it and be prepared to experiment."

Key areas are sodium, nitrogen and trace elements, says Mr Law. Sodium, well known as a yield improver and a potash replacer, is "greatly underrated" as a plant development promoter. "Recent research in Chile has shown that it increased sugars by 1% and yield by 6t/ha when applied at planting rather than 60 days after emergence."

Maximised leaf area

High leaf concentrations increase foliar bulk, maximising leaf area. Leaves are thicker and more succulent, thanks to the water-attracting properties of sodium. The plant is, therefore, not only bigger but more drought proof, he explains.

Mr Law reckons all soils, including fenland peats and silts, need sodium. "The belief that such soils have high levels is misguided. Beet needs at least 130 units/acre for maximum yield which has to come from the bag."

Plants assimilate most sodium in the first 60-80 days. About half should be applied as sodium chloride on top of ploughing in February or early March. "Sodium is very mobile, so some is lost if it is ploughed down. And we have never found any deleterious effects even when applying high rates in front of the drill."

The rest should be applied as chlorine-free sodium nitrate (16N:26Na) at five bags a hectare (2/acre) at the two-leaf stage.

That will supply enough nitrogen to start crops off. On most soils, the balance should be applied as urea – it releases nitrogen slowly, "drip feeding" the crop after the sodium nitrate portion has been used. "We are looking to regulate supplies to avoid irregular growth, which causes yield loss and high amino-N levels."

If drought strikes, a further half rate of sodium nitrate can be added in summer to reduce wilting and maintain growth – dews provide enough moisture to ensure uptake, Mr Law claims.

On sandy soils with high N demand, Nitrimix should be applied with the first trace element spray, says Mr Law. The liquid blend supplies 22.5kg/ha (18 units/acre) of ammoniacal nitrogen, which can be taken up directly by roots. "For maximum yields plants need a mix of nitrate nitrogen for vegetative growth and ammoniacal nitrogen for roots. Normally all N is taken up in the nitrate form and converting that is wasteful. Nitrimix can be used directly by the root, improving its development, raising sugar levels and yield and reducing stress, while allowing overall nitrogen levels to be reduced by at least 10%."

Similar savings can be made by tailoring micronutrient application to plant need, he explains. "Besides protein production, the plant uses nitrogen to make organic acids, which act as a sink to increase micronutrient uptake. By ensuring an adequate supply of those micronutrients, the plant reduces the sink, so less nitrogen is needed."

Tissue tests

Soil analyses coupled with crop demand provide a useful starting point. Applications can be fine-tuned using tissue tests in the growing crop.

Too much manganese is used, he warns. "It is cheap and often applied excessively. We consistently find toxic levels of manganese in tissue samples."

As a guide, growers should cut manganese doses by 30% and add copper and boron, he maintains. "I am a great believer in broad spectrum trace elements – dry conditions create manganese deficiency and also limit copper and boron uptake.

"But as with all nutrients, applications should be related to individual need and growth. There is no blueprint – each field is different. But growers should not give up in dry conditions. By being proactive they will find plants can respond, and yields and quality raised," he says.


Biggins Farms beet fertiliser – peat soils

ProductRate (kg/ha)Cost (£/ha)When applied

NPKNa

Old system

10:6:24 blend7545180-81.002-3 weeks

before drilling

New system

21K:19Na–15714256.00Feb – on

(Sylvinite)ploughing

16N:26Na40–6540.002-leaf stage

(Sodium nitrate)

16N:26Na10-20–16-3210-20As needed (Sodium nitrate)when dry

*Calcium prevents ammonium N transformation to nitrate.

Tighter water supply is one reason why farm partners David (centre) and Bryan Hawes (left) are following consultant Mark Laws plan to use more sodium on sugar beet crops at Biggins Farm, Manea, Cambs, this year.