David Hutchinson, ADAS Senior Nursery Stock Consultant, looks to the way growers are changing to meet the challenges of new environmental legislation and the withdrawal of pesticides. The origins and nature of 'compost tea' is explained along with how it can be made and applied. The experiences of some 50 growers, using compost tea in the UK , are summarised with helpful hints for getting started.

Why is there renewed attention and interest in organic applications like compost tea in growing crops?

If you read up on all the editorial columns of any of the leading horticultural publications across the EU you can quickly pick up on statements like "concern over the decreasing availability of chemical plant protection products" or the "withdrawal of another product which helped to control a certain root or foliage disease problem". In addition ground water regulations and nitrate vulnerable zones have been extended with increased regulation and control in prime production areas.

While a number of countries actively encourage their growers to use integrated crop management (ICM) programmes it is so often the innovation and vision of growers and their suppliers that leads to solutions. Growers understand these concerns and have been asking the question "is there another way" to grow crops with less reliance on pesticides and high cost inputs? Yes Compost Tea!

Needless to say growers have had to go 'back to basics', relying on well tried and trusted holistic techniques, which have served agriculture and horticulture in the past.

No, the use of organic solutions to provide nutrition and mitigate crop problems can be traced back through to the Roman occupation of these islands and to Biblical times when man started to irrigate and fertilise crops with vegetable and animal manures.

In recent times growers have re-cycled roof and catchment water, using techniques such as self-cleaning micro filters and slow sand filters. They have aerated water with iris and lava beds, all of which adds value to water (via more natural control of disease). Growers have added humic and green compost to growing media which suppress root and foliage disease and in addition, leading growers have moved to a more holistic approach by feeding the plants exactly according to their needs, with aerated growing media, via graded peat fractions, pine and other bark products.

Growers are now realising they must find a solution and are looking towards a more sustainable way of growing crops. Included in this approach is the use of ‘compost tea’ derived from green and humic compost processes with full traceability.

Compost Tea - What’s in the Compost?

In well managed and re-cycled compost there are millions of bacteria of some thousands of species. In addition there are many types of protozoa, beneficial fungi and friendly nematodes which help make up the modern day term the ‘soil food web’. It is the range and diversity of micro-organisms that make high quality compost.

This is achieved only by careful control in the composting process paying particular attention to selection of the original plant material, critical maintenance of temperature and time to develop the humus content essential for the micro-organisms to multiply and maintain populations.

Humic Compost

Humus is the dark brown colloidal / clay sized particle, high in humic acid, which maintains the rich diversity of microbes in a growing media and soil. It is also important for nutrient supply and improving the moisture content of soils.

The potential for Humic Compost to suppress root and soil borne disease is well documented world-wide and success has been achieved in container production systems.

Green Compost

Green compost, as the name suggests, is from fresh, green material from the prunings and trimming of urban gardens and managed landscape vegetation. During its composting process it is carefully sorted to exclude plastic and metal.

The compost tea ingredients are derived from the rich humic based compost or green compost blend. The recipes are well thought out with additions to supply food for the micro-organisms. Most of the products used to date are from the company of Van Iersel based in Biezenmortel, Holland and available in the UK through Fargro Limited (Tel: 01903 721591).

The ingredients are sold in two forms; bacteria or fungi dominant. These supply the food for the micro-organisms to multiply in the presence of oxygen supplied by a high capacity air pump. The choice of mix depends on the plant subject and type of disease to be countered.

What equipment is needed?

It is very important to have an efficient and reliable machine to make compost tea. It is equally important to use a machine of proven performance to provide essential oxygen to the compost tea brewing process.

. Any failure in the equipment to provide oxygen will produce poor quality compost tea.

How is compost tea made?

It is very important to use clean, preferably chlorine-free, water although it is possible to use treated mains water providing any residual chlorine is removed by running the compost tea machine for a period of two hours before brewing. The brewing process runs for a period of 18 to 24 hours which extracts and multiplies the bacteria, fungi and protozoa.

What is compost tea?

It is the brown watery extract of compost that contains the soluble nutrients and a rich diversity of microbes that has passed through a 400 mesh sieve. Once brewed it should be applied as soon as possible to growing crops.

What are the application rates of compost tea?

The standard rate for a micro feeding programme of compost tea is 50 litres per hectare or 5.0 ml/m2. To increase the presence of the micro-organisms on new emerging plant growth, micro feeding is repeated at 14 day intervals and a minimum of 70% of the foliage should be covered.

How to apply compost tea?

Most growers who are well organised and have planned their applications can easily apply compost tea at a rate hectare per hour through a dilutor and their overhead irrigation lines as part of the crop/plant water requirements. Dilution is usually 1:100 in summer, however, in winter, when crop water requirements are very low,
1:10 can be used. Alternatively compost tea can be applied through a conventional boom sprayer or knapsack. In intensive crops where there are no overhead spray lines, a dilutor and hand lance operation consistently gives excellent results.

When to apply compost tea to growing crops?

The brewed compost tea needs to be applied to crops as soon as possible after brewing, remembering that the half life of fresh tea is 12 hours. Compost tea needs to be applied at 14 day intervals to maintain the feeding programme. Micro feeding on protected crops should continue through the winter as part of the plant water requirement. However, last winter’s experience suggests that it is possible to cease applications for a period of six weeks as the crop plants are dormant in late December and then return back to the micro feeding programme of every two weeks.

A word of warning is very careful if you introduce untreated stock to a treated area and especially so if no provision is made to conventionally treat the crop. These introduced crops plants do not have any suppression of the key over wintering diseases of Botrytis and Rhizoctonia.

It stimulates plant growth, through the provision of micro-nutrients to the roots and foliage.

Compost tea can be applied as a Foliar applications to-:

• suppress disease pathogens that can invade infection sites
• provide nutrients (to stimulate growth, as a foliar feed does)

Compost tea can be applied as a Drenching growing media helps to: -

• Develop a biological barrier around the roots
• Maximise disease suppression
• Provide nutrients for the roots to take up and stimulate growth
• Improve the micro-organism life in the soil or growing media
• Improve the re-cycling, availability and retention of nutrients

Which diseases are specifically affected by compost tea?

Diseases mentioned in the literature and reported to be suppressed by high quality compost tea applications include: -

What are the costs od compost tea?

Thecompost tea ingredient cost per hectare is approximately £18.00 plus the machine cost of £1.25. Fifteen applications are in the region of £270.00 per hectare during the year.

Micro feeding -Using Compost Tea in Growing Crops.

Grower Experiences of compost tea in 2004

• Staff like the idea of micro-feeding as they do not have to handle noxious chemicals
• It’s a more natural and sustainable approach
• Works well with existing IPM Programmes
• Micro feeding fits in well with the new ADAS Nursery Integrated Crop Management System.
• After staff training the monitoring of crops is easier, and the staff more confident.
• No longer need to rely on the use chemicals and pesticides to grow quality crops.
• Input costs can be reduced with confidence.
• With the natural stimulation of shoot and root growth; high levels of CRF are not required and growers are able to reduce CRF rates by 15%.
• Less leaching and pollution of ground water.
• Reduced losses and down grading due to foliage and root pathogens.
• Significant reduction in Botrytis, Rhizoctonia and leaf disease infections.
• No need to apply routine fungicides.
• Field grown stocks are equally responsive.
• Treated woody stock such as roses, and top fruit stocks out performed standard treatments.
• Simplified spray programmes with cost savings from reduced fungicide costs.

Other Biological /Compatible Products to compost tea.

Growers are using other products i.e. sulphur, potassium hydrogen bi-carbonate and potassium phosphite to complement the micro feeding approach. These are being trialled by growers to suppress diseases such as Powdery Mildew, Downy Mildew and to supply micro nutrients.

Organic based products are being used to compliment routine compost tea applications. Biosept, a proprietary by-product produced from citrus, fits well with compost tea in suppressing and controlling disease in propagation environments. Garlic extracts have also been effective in controlling pests such as aphids, two spotted mite, slugs and snails.

Which crops have been successfully treated with compost tea?

World wide farmers, treating a range of arable crops, lead the field with applications to garden turf at the other end of the spectrum. The top and soft fruit industries, together with viticulture, are successfully using micro-feeding techniques. Vegetable farmers, and in particular salad growers, are finding numerous benefits, so too are producers of field and container grown ornamentals.

Crops successfully treated with compost tea in the UK

• Hardy Ornamental Nursery Stock - stock plants, cutting in propagation, weaning plugs, liners and finished plants.
• A wide range of container grown woody stock including ericaceous, deciduous and evergreens.
• Field grown ornamental and fruit trees, roses, shrubs and bamboo and herbaceous perennials.
• Protected crops of Perennial Patio Plants, Alpines , Flowering Bulbs, Ferns, Hebe, and Herbs
• Cut Flowers include Alstroemeria, Chrysanthemum and Lisanthus.
• Strawberry plug /pot plant production.

Crops successfully treated with compost tea in the NL

Includes all the above as well as Asparagus, Celery, Cucumber, Paprika, Peppers, Strawberry Fruiting Tables, Tomatoes and Lettuce.

Getting Started with Micro feeding using Compost Tea

Helpful Hints on compost tea.

• Remember that you are taking a holistic approach to the feeding and nutrition of your crops.
• Start with the new crops so as to inoculate and add the micro-organisms commencing when you propagate by preparing and inserting cuttings.
• Propagators find that using other organic based control measures are just as effective as other standard fungicides and fit with one or two week interval applications compost tea applications.
• Follow up by regular two week applications of compost tea at the standard rate of 5ml/m2 or 50 litres per hectare.
• Maintain and treat all weaning crops prior to potting.
• Treat all newly potted liners or final potted crops with Compost Tea.
• Maintain the programme and build up suppression through the growing season.
Continue through until the need for dormancy in crops in December to January.
• To avoid frost damage to water supplies over the period week 50 to week 4 growers have ceased compost tea applications and have found that disease suppression has continued.
• However after two years’ results I recommend crops are continually monitored weekly to see that no foliage diseases establish.
• When monitoring crops assess as you would monitor for IPM both thoroughly and carefully and especially in the lower foliage and stems.
• Use a weekly check sheet to record your pest /disease incidence as low, medium or high.
• Maintain weekly records of the compost brewing process and applications in a Nutritional Compost Tea /Fertiliser File

Before you start up your compost tea machine.

• Make sure that it is installed correctly to the manufacturer’s recommendations.
• Use a qualified electrician to wire up the equipment to IEE/UK standards.
• Choose to use collected roof water or water from a bore-hole which has not been treated with chlorine.
• If you have to use mains water, then run the compost tea machine for a period of two hours to aerate and drive off the chlorine residual gas.
• Check the irrigation/ dilutor or chosen application method before you brew so as to get the correct rate.
• Always ensure optimal application cleanliness, i.e. clean tank, pipe work, mixing vessels, filters, etc.
• Plan to time the CT applications when best conditions are practical i.e. early morning or early evening. Avoid the heat of the day in summer.

Making compost tea

• Plan the area you wish to treat so as not to rush the treatments.
• Measure up and carefully brew the correct amount.
• Calculate the start time to fit the convenience of when you need to apply the Compost Tea, i.e. Start Wednesday at 1700 the 18 hour brew period is completed at 1100 Thursday.
• Record all brewing time(s) and events in a Nutrition /Compost Tea file or book.
• Use sunflower oil to reduce ‘frothing ‘on the surface of the brewing process. 15ml /50.0litre.
• Only use reputable well prepared compost tea ingredients from reputable companies.

Applying Compost tea

• Remember that the half life of the fresh brewed compost tea is 12 hours.
• 70% leaf cover is necessary
• Applications through overhead irrigation works well but check pressures first.
• Spray pressure should not exceed 4 bars.
• Dilution Rates of up to 1 :10
• Consider applying CT with air assisted sprayer as this will ensure good cover on the underside of the leaf/foliage.

What Compost Tea does?

• Provide micro - nutrients for plant growth.
• Contains soluble nutrients and a diversity of micro-organisms.
• Increases the range of micro-organisms in the soil /growing media.
• Supports the system of natural processes.
• Compost Tea stimulates a biological barrier around the roots.
• Beneficial micro-organisms in compost tea consume any leaf exudates instead of the ‘disease pathogens’ invading the plant tissue.
• CT covers possible infection sites by the beneficial micro-organisms taking possession.

What Compost Tea is NOT

• It is Not a pesticide – compost tea only stimulates growth and suppresses pathogens and certain nematodes.
• Not just a product - it provides sustenance for the food web as part of a dynamic system.
• Not a wonder potion – compost tea only supports natural processes.

Useful web sites

www.vanierselcompost.com www.soilfoodweb.com
www.compara.nl www.trefgroup.com
www.xtractor.nl www.psd.gov.uk
www.attra.org/attra-pub/comptea.html www.biosept.com
www.fargro.co.uk www.garlic-farms.co.uk

Future R&D in the UK

The HDC Hardy Ornamentals Panel in November 2003 commissioned the project HNS 125 “Putting science into compost teas” and work is proceeding at SAC Aberdeen led by Dr Audrey Litterick. Grower trials commenced this autumn.

For further details on compost tea contact:-

David Hutchinson is a Senior Nursery Stock Consultant in ADAS Horticulture. He can be contacted on David.Hutchinson@adas.co.uk or Tel/Fax: 02380 251191.