Long-term effects of applying different forms of organic matter on soil quality

RHS project team
Dr Paul D Alexander
Start date
31/01/2007 13:08:44
End date
31/01/2017 13:08:53

Soil, organic matter, carbon, cultivation, RHS

The problem

In agriculture and horticulture organic matter has long been seen as a useful method of managing soil and plant fertility. Focus is increasingly on the role soil management can play in climate change mitigation (through carbon sequestration) and this project will examine the role individual gardeners can play through the use of different forms of organic matter. However, long-term repeated annual applications of the same form of organic matter may also have detrimental affects on soil quality and subsequently plant health.


A 10-year field experiment has been set up at our trials site at Deers Farm, Wisley. This is a randomised and replicated (10 replicates) experiment where different forms of organic matter are applied annually to the same 3x3m plots. The forms of organic matter are double-chop mushroom compost, horse manure, bark/wood chip, Wisley green compost (at two application rates) and composted bracken. One replicate is also left bare.

An annual ‘crop’ of plants are grown on the plots to reproduce the nutrient ‘sink’ effect of plants in garden borders and best replicates gardening practices.

On an annual basis, soil analysis, plant nutritional analysis and general plant health are assessed.


To assess the long-term effects of different forms of organic matter on soil quality in terms of biological and chemical factors.

To demonstrate how a standard gardening practice such as incorporating organic matter can potentially help mitigate climate change by locking-up carbon in the soil.

Benefits to gardeners

The project results will enable the gardener to make an informed decision on whether it is necessary to apply organic matter annually, how it will affect their soil and which type of organic matter will suit their needs best.

With the results from this experiment, gardeners will be also able to better appreciate how they can potentially help mitigate climate change.

There are the additional benefits of engaging current and future RHS members, informing policy and contributing to the scientific community worldwide.

Advisory information

Tips on mulches and mulching

Soil management in gardens

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.