Integrating agronomy to reduce energy

Rising energy prices mean growers must reduce costs to preserve margins, Richard Crowhurst reports.

Trojan band sprayer - image: VCS
Trojan band sprayer - image: VCS

With energy prices still on the rise, growers continue to have a strong focus on reducing costs through a variety of efficiency measures and alternative forms of energy generation, such as anaerobic digestion.

Another factor that underlies the increased attention on energy use is the growing interest in the carbon and energy footprint of agricultural and horticultural production. This is perfectly illustrated by a number of retailers that have announced projects to measure, manage or reduce the impact of their own-label food production.

Mark & Spencer's Plan A, for example, aims to have all of its fresh produce farms engaged in its Sustainable Agricultural Programme by 2012.

Fortunately, by adopting new integrated crop production methods throughout the agronomic process, from the soil preparation stage through to crop storage at the end of the growing process, growers can significantly reduce their energy demand.

Vegetable Consultancy Services (VCS) in Norwich has been developing such methods. Consultant agronomist Tom Will says: "At its core, this approach is about challenging some of the issues that are developing in the industry."

He adds: "As specialist agronomists, our role is to help devise equipment and systems to improve energy use efficiencies whilst maintaining/improving crop productivity and quality, so we're trying to come up with practical solutions to issues.

"It's all about maximising integrated management techniques, particularly in root crop production, while reducing pesticide use and saving energy. We hope to combine factors from good soil husbandry to reviewing operations and sequences to have a truly integrated way of growing things."

Fertiliser use, particularly when associated with the mining and transportation of large quantities of inorganic nutrients, is frequently implicated as a major source of greenhouse gases associated with crop production.

To improve the efficiency of phosphate application, starter fertiliser has been used for years in onions, with growers typically injecting it under the coulter at planting. However, this can cause the coulter to bulldoze and with 8:24:0 or 7:21:0 mixes it also requires volumes of around 300 litres/ha to give adequate supply.

VCS is therefore working with a Dutch company to develop a fertiliser that can be sprayed onto the seed and, by using just 30 litres/ha of product, reduces the amount required.

The seed gets all the benefits of a starter fertiliser, plus, because growers are spraying it onto the seed inside the coulter, there is no injection knife causing drag and coulter "bobbing". Such a modification to phosphate application makes a positive reduction to the overall energy footprint of the crop.

Other pressures on fertiliser use can also have positive effects on the overall crop production. The management changes stimulated by the nitrate vulnerable zones regulations have created additional benefits for soils and crops. VCS has worked with Ryton Organic Gardens, sponsored by the Horticultural Development Company (HDC), to study the use of green manures, in particular on sand lands and Breckland soils.

As well as trying to improve nutrient management in these areas by fixing nitrogen (N) with leguminous crops, or just capturing N with general green manures, the use of green manure crops has also been shown to have a major contribution to soil structure.

The roots from green manure crops hold the soil together and reduce wind erosion and blowing, which can help to prevent crop loss. The incorporated biomass was shown to significantly improve soils' moisture-holding capacity, which was perhaps the single biggest factor in increasing crop productivity on the Breckland sandy soils.

Increasing crop production

Irrigation efficiency is not only key to crop production on light soils but has huge scope to be refined, potentially improving crop productivity and quality with reduced energy use.

VCS is investigating the best way to optimise irrigation in onion crops in an HDC-sponsored trial based at Brooms Barn - the crop sciences experimental station based in Bury St Edmunds, Suffolk.

Will says: "By building up lots of small changes throughout the growing process it is possible to deliver real benefits to both growers and the environment." He adds that one example is in the use of band spraying.

"While there are already plenty of band sprayers available to growers, we couldn't find a machine that was fully adjustable and robust - suitable for broadacre vegetable production."

As a consequence the company developed the Trojan Bandsprayer, which was launched last year. The sturdy machine allows each of the spray units to slide to any position on the tool bar, meaning it can be used on any bed configuration while having adjustable hood widths and nozzle heights.

Each anti-drip nozzle is fitted with its own flow monitor. The machine is fitted with two tanks so growers can have a different spray in the wheeling to that applied to the crop, although solution transfer is also available to allow longer periods of operating with a single product. Because of its study construction, growers can confidently push it through dense crop canopies and the typical work rate is 25ha a day.

This equipment is increasingly being adopted by carrot, parsnip, leek and onion growers - allowing a reduction of overall pesticide use, improved control of difficult weeds and, in the case of onions, a clean wheeling that is so important to improve the efficiency of harvest, store loading and crop curing.

Another area where VCS has adapted old technology to meet new challenges is with the brush hoe. "Brush hoes have been around for 50 years but we've developed a Triple Brush Hoe for use in broadacre systems providing early mechanical weeding soon after crop emergence," says Will.

"Its use in combination with GPS means that you can accurately follow the drill or another machine allowing increased work rates and more efficient energy use."

This brush hoe also has the option of an incorporated band sprayer, allowing dual treatments in a single pass. Once the crop has been grown, there are still plenty of opportunities to save energy, particularly with crops that are stored for a significant period, such as onions.

Will explains: "Here you are potentially dealing with stores that have large fans that often switch on and off at regular intervals, governed by relative humidity sensors in the crop. This traditional approach to stage-two curing has a large energy requirement and may give poor air distribution in store."

From studying airflow dynamics in a number of onion stores, VCS discovered that in many cases the fans are actually working against themselves due to the high duct back pressure.

To reduce this inefficiency it has developed the Vegtec Controller, which runs the fans at the ideal speed to optimise air distribution and energy use. This patented system uses duct back pressure and crop air speed sensors to ensure that curing is even and efficient.

Electricity savings of up to 30 per cent have been recorded in some stores. The Vegtec Controller has the capacity to run up to 12 stores and has the additional advantage of modem access, graphing functions, point and total energy use meters and disease library - all designed according to store operator demands.

The Vegtec Controller can be retro-fitted and, when used with inverters on the fans, qualifies for the Carbon Trust energy efficiency loan scheme so theoretically the money it saves will pay back the loan. "There are already several units operating in the UK and there is growing interest abroad too," says Will.

These examples are just some of the developments that agronomists in the UK vegetable industry have introduced - developments that potentially, in combination, are progressing towards a truly integrated and sustainable approach to vegetable production.

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