8 January 1999

Irresponse gives growers the most up-to-date advice for making best use of irrigation water, says ADASs Roger Bailey.

Irrigation know-how

SPREAD limited irrigation water widely on potatoes and avoid holding supplies back as insurance against late drought. That is the early advice from a new ADAS computer model due to be commercialised in the next 12 months.

Outlining progress with the irresponse model, Roger Bailey of ADAS Gleadthorpe told a recent AAB meeting that it is being designed to help growers decide how best to make use of water, especially in dry years like 1976 when crop demand exceeds supply.

The 1976 drought was thought to have been a once in a century event. But irrigation needs were similar in 1989, 1991 and 1995 by which time over half the crop was being watered, notes Dr Bailey.

In the past 30 years average irrigation requirement at Gleadthorpe has been 125-150mm/yr. In 1995 it was 275mm.

"The frequency of dry years has increased. That has changed the questions growers are asking. Instead of asking how shall I irrigate to get maximum yield or best quality?, they now say I have only got so much water because of restrictions. Do I distribute it evenly between fields or in time, or should I be holding some back in case we get a late season drought?"

The new model, based on work by Mike Carr at Silsoe and backed by BPC and MAFF cash, aims to provide some answers using information such as soil type, weather patterns and variety.

Tests in 1994 and 1995, using Record, found good agreement with measured field values for yield and evapotranspiration, says Dr Bailey.

Where common scab control is important, concentrating irrigation on certain fields may be justified, he acknowledges. But where overall yield is the main concern the model clearly suggests otherwise.

Applying it to the three dry years of 89, 91 and 95 showed that in every case there would have been a yield advantage of about 5t/ha (2t/acre) from spreading the available water thinly over the whole crop area.

Neither would it have paid to delay applications of a theoretically limited 75mm, best output in all three years coming from three early 25mm doses.

, when the canopy is developing fastest, explains Dr Bailey. "There was no case where it was advisable to save water just in case of a drier period in August."

Irresponse model

&#8226 Irrigation management tool.

&#8226 Calculates daily water balance.

&#8226 Predicts yields.

&#8226 Proven in two dry years.

IRRESPONSEMODEL

&#8226 Irrigation management tool.

&#8226 Calculates daily water balance.

&#8226 Predicts yields.

&#8226 Proven in two dry years.

Get rolling rate right

GROWERS planning chemical applications to seed or ware potato tubers on roller tables should aim for a precise throughput of potatoes. Too many, or too few, will mean less chemical than intended hits the target, say Writtle College researchers.

"If farmers do one thing when using roller tables, it has to be to control the throughput of potatoes," says post harvest technologist, Chris Bishop.

Tuber size also needs taking into account. More surface area on smaller tubers means more chemical is needed per tonne to maintain dose per unit of skin area. Ungraded samples present particular problems, as tubers form a raft and do not rotate normally, resulting in uneven application.

TABLE

Target Throughput 7.5t/hr

Actual % chemical deposition

2.0 t/hr 58

7.5t/hr 100

15.0t/hr 70

Target throughput 7.5t/hr

Actual throughput % chem deposition

2.0 t/hr 58

7.5t/hr 100

15.0t/hr 70

PCNmapping

– ADAS warns

Research into root crop management was keenly debated at

a recent conference organised by the Association of

Applied Biologists in Cambridge. Andrew Blake and

Andrew Swallow report the highlights which are set to

help sugar beet and potato growers

POTATO growers need to be alert to the shortcomings of gps potato cyst nematode mapping, says ADAS. Long-term production is being put at risk, it believes.

"PCN is a very unforgiving pest. If you get control wrong, the consequences are very severe and long term," says Bill Parker, principal research consultant at ADAS Wolverhampton.

Many of the claims and uses of current gps pcn mapping systems are inappropriate. Growers and advisers are getting carried away with the technology, forgetting the biology of the pest, he warns.

Variable nematicide rate and population contour maps are the worst offenders, tempting growers to make short-term cuts in nematicide use. Assurance schemes and cash savings on the cost of inputs make ignoring the long-term consequences of such decisions easier.

"Contour maps are in the realms of fantasy accuracy. Unless growers are prepared to make a very big investment in intensive sampling then the industry should leave contour maps well alone," he says.

Typical gps sampling in hectare blocks may indicate whether potatoes should be grown or not, and possibly where soil fumigation is required. But it will not determine where to patch apply nematicides. The risk of missing low-level hot-spots is too great.

"Only at a sixteenth of a hectare do you start to see where the hot spots are," he stresses.

However, mapping may have a role in long-term control plans. Point maps can help growers and advisors get to know the exact behaviour of the enemy in each field, he suggests.

"PCN multiplication and decline rates vary considerably from site to site. GPS can be a useful way of going back year on year to exactly the same spot to see what is going on. Ideally a range of high and low infestation areas should be sampled and mapped."

Mapping, if used, must form part of an integrated nematicide control strategy, incorporating rotation, resistant varieties, nematicides and other possible cultural measures. It is not a panacea for pcn management and its limitations should be recognised.

BOX

PCN Mapping Applications

(tick) Point mapping for population monitoring

(tick) Yes or no decision for spuds

(tick) Fumigation blocking at high populations

(cross) Patch nematicide treatments

(cross) Variable rate nematicide treatments

ENDS 346 WORDs

PCNMapping Appplications

Point mapping for population monitoring 3

Yes or no decision for spuds 3

Fumigation blocking at high populations 3

Patch nematicide treatments 7

Variable rate nematicide treatments 7

Stopping sprout

growth

MODIFIED atmosphere potato storage could end the use of chemical sprout suppressants and improve seed management. Commercial trials supported by MAFFwith a leading supermarket show promise.

"At high carbon dioxide concentrations there is virtually no sprout growth," says Jeff Moorby, of Wye College. "This is potentially a very useful means of stopping sprout growth in long-term storage."

Conversely, in reduced oxygen conditions, many more sprouts are produced, which could be used as a seed treatment to influence sprouting and hence tuber size in the following crops, he suggests.

Trials for Sainsbury successfully stored large volumes of ware without sprout suppressants by raising store carbon dioxide concentrations up to 400 times ambient air levels.

When the resulting unsprouted tubers were sold in May, they passed all consumer acceptability and cooking trials normally done by the supermarket.

Normal storage tends to increase carbon dioxide naturally due to respiration in the tubers.

However, this natural increase alone is insufficient to suppress sprout growth, and may actually increase sprouting, says David Mortimer of Writtle College. Variety and temperature influence the sprouting response too, and further work is needed to establish reliable seed management techniques, he believes.

Prof Moorby is more confident of modified atmosphere applications to ware storage. "We think we have a system that works, but we need to know what is happening inside the potato."

Both trials used fruit stores, which could be a low cost way for growers to pioneer this method of storage, reckons Keith Mawson, scientific officer at Sutton Bridge Experimental Unit.

"With existing potato stores this technique is going to be expensive, but there are many dis-used apple stores which would not require any modification," he says.

One drawback could be inferior control of fungal skin disease, notes Prof Moorby, particularly at the highest carbon dioxide concentrations.

At high carbon dioxide concentrations such as those used in the Sainsbury trial, stores would not be safe to enter and breathing apparatus may be required on site for health and safety reasons, he adds.

&#8226 Work at Sutton Bridge using raised carbon dioxide and reduced oxygen aims to extend the availability of British soft skin potatoes. Up to 10 weeks storage is possible without any loss of sweetness. That could keep British second crop, fluffy skin potatoes on supermarket shelves in to the New Year.

SPUD STORAGE FACTS

&#8226 Chemical free sprout control.

&#8226 Small increases in CO2, more sprouts.

&#8226 Large increases in CO2, no sprouting.

&#8226 Ware and seed applications.

SPUDSTORAGEFACTS

&#8226 Chemical free sprout control.

&#8226 Small increases in CO2, more sprout growth.

&#8226 Large increases in CO2, no sprouting.

&#8226 Ware and seed applications.

GMbeet is a boon for all, say Dutch

HERBICIDE resistant sugar beet will have benefits for farmers, the sugar industry, and the environment, says Jan Wevers of IRS, the Dutch sugar beet research centre.

"The effectiveness of glyphosate is very clear. In all cases yields increased and there were no late weeds, which is very surprising as there is no residual effect. The only explanation is that the late weeds are not late emerging, but that they are escaping the early conventional treatments."

Tackling such late or difficult weeds with lenacil (Venzar), clopyralid (Dow Shield) or using graminicides, takes the environmental impact of conventional herbicide programmes beyond acceptable levels, he says.

Glyphosate slashes that environmental impact to zero, and takes care of volunteers such as potatoes and oilseed rape, he says. Typically glyphosate or glufosinate-ammonium based treatments increased yields by 5-6%.

over standard conventional herbicide programmes in the Dutch trials.

Careful clamp construction and regular checking to avoid overheating or freezing is vital to protect beet quality, warns BS.

Keep keen eye on clamps, warns BS

SUGAR beet clamps need careful monitoring to avoid costly overheating losses, says British Sugar.

Dirty beet from this winters campaign are particularly at risk, as soil can block gaps between beet, which are vital for ventilation.

"To avoid frost damage growers must cover clamps if temperatures go below -2C," says British Sugars Barry Houghton. "But covers stifle ventilation and the temperature in a covered clamp goes up by about 1C/day, so the message is get the covers off as soon as its not freezing to allow natural ventilation through the beet."

Clamps are best built in exposed areas, with bale walls placed on pallets, open end outwards, to allow air into the base of the stack. Later in the season these vents may need blocking in severe wind frosts, he notes.

Dirt should be removed as far as possible before clamping. But whether cleaning is worthwhile depends on the level of damage it does to the beet, he says.

Growers are advised to build at least one temperature probe into the middle of the clamp, and to keep clamp temperatures close to ambient air temperatures.

Within 5C of ambient air temperatures clamp conditions are controllable but losses increase with temperature and at 10C over outside temperatures the clamp is seriously overheating. Expert advice should be taken, he suggests. Even under good storage conditions, 7% of sugar yield is lost during eight weeks of storage, and amino-N tends to increase.

As temperatures increase buds at the crown of the root start to grow, blocking gaps between beet and exacerbating ventilation problems. "Once the gaps between the beet are blocked the centre of the clamp will go its own way, regardless of external temperatures," he warns.

Beet Clamp Advice

Keep clamp core at 0-5C

Bales on pallets for ventilation

Remove covers when not freezing

Avoid soil in stack.