Seabrook on...Benefits of Controlled-release fertilisers under threat

The vote to leave the EU looks to be the right decision when facing the difficulties of getting a score and more countries to agree on policy.

Take for example the new draft criteria for biodegradable polymers that, if brought in next year as proposed, will eliminate all the controlled-release fertiliser (CRF) products used in the UK and Europe.

It is too easy to take for granted the steady improvements science brings to our everyday lives and in the case of CRFs the remarkable developments over the past 50 years.

They are now fundamental to UK container, amenity and food crop care. Indeed, the much improved results obtained by home gardeners growing in containers is without doubt the result of slow-release plant feeding.

They are made by enclosing up to 12 different nutrients in a polymer resin with tiny pores that open with heat expansion to let in moisture and close when temperatures drop.

The higher the soil and compost temperatures, the more water moves in and the greater the release of plant foods by osmosis. Currently there are products available with release times of six weeks, three-to-four months, five-to-six months, 12-14 months and up to 18 months.

They allow nutrients to be added to composts at mixing to be metered out through the growing season, reducing the costs of repeated application. The new criteria require decomposition in two years and rapid break down would mean a surge in the release of fertilisers, damaging plant roots and increasing nitrate run-off.

Growers have to meet the requirements of the Water Framework Directive and the new directive would mitigate this by increased leaching into ground and surface water. If my information is correct the new draft regulations appear to have been translated from the use of polymers for other purposes and including mulching films.

While the industry accepts the need to be environmentally friendly with the products it supplies, in the case of CRFs it will take time to develop a casing that is both biodegradable and able to deliver plant foods in the right quantities for the climatic conditions over a period of months.

Several growers and retailers have provided detailed information about the use and benefits of CRFs in horticulture in support of an industry counter proposal being submitted to the European Commission. Let’s hope that this initiative, in conjunction with similar feedback from other European countries, has the desired effect in changing their minds.

Peter Seabrook is a gardening writer and broadcaster


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