The influence of organic farming on the vegetation composition of upland pasture OF0104

Summary

This work is a continuation of the investigation into the effects of the adoption of an organic farming regime in the uplands, on the dynamics of plant species and plant communities. The work comprises six vegetation trials: three investigating the differences between dynamics of organically and conventionally managed sub-units of each type of vegetation system on the unit (temporary ley, improved hill, semi-natural), two which investigated the effects of different UKROFS approved PK fertilisers on the composistion of improved hill and in-bye swards, and one which is investigating the effect of different sources of external nitrogen inputs on the composition of an in-bye sward.
The vegetation was monitored using 1m2 quadrats, surveyed either annually or beennially, depending on the dynamics of the system. The vegetation data were used to quantify diferences in species abundance over time, and as inputs for a community level model.
The model used the National Vegetation Classification (NVC) as a reference point for comparison with the vegetation communities identified at Redesdale were placed in ordination space along with fixed positions of the NVC communities which typify these. The temporaral movement in ordination space, of the Redesdale communities indicate the response of each management unit to the applied regime.
The NPK fertiliser trials finished in 1996 after 6 years, and the N trial is now in its third year. Although in all trials the sward exhibits a very dynamic response to the environmnet, there have been no differences between treatments.
On the less dynaic improved hill and semi-natural (native hill) communities, analysis at both the quadrat-scale and community-scale has shown that the behaviour or organically managed sites appears to be the same as the parallel conventionally managed system. This suggests that environmental and general management variables exert a greater influence on the dynamics of the system that differences between both management regiemes. As monitoring has only taken place over a six year period, it is too early to say whether there are any differences in the dynamics of the semi-natural vegetation. Of particular interest on the semi-natural vegetation trial is the increase (not significant) in cover of Calluna vulgaris on the heft where the stocking rate was reduced by 30%.
The organic management system adopted at ADAS Redesdale, has aimed to elevate and maintain a high cover of Trifolium repens on the improved and intensively managed leys. The quality of the organic in-bye swards has been consistently better in terms of raised Trifolium repens and reduced weed populations than in the conventional in-bye. However, the dynamics of these swards appear too respond more to site specific environmental forcing variables than to a particular variant of management regime.