4*. Mandatory – Some effect on hill, most impact on uplands and associated lowland *See Table 2 page 8
The use of mineral nitrogen fertilisers is prohibited by all organic standards. Conversion to organic farming can only begin after the last date of any application of N fertiliser, and cannot be completed until a minimum of 24 months has elapsed since the last application. One of the consequences of the cessation of N fertiliser use is that organic farmers need to maximise the benefit of their FYM, which requires efficient manure management practices. There is typically a reduction in stocking rates of between 10 and 50% as a result of cutting N fertilisers.
(Allen, 1995) notes that even modest applications of nitrogen can rapidly and fundamentally alter the composition of a species-rich meadow in favour of competitive and more productive grasses. The positive impacts on floral species will correlate with positive impacts on faunal species they support.
It should be noted that on organic farms inputs are restricted or prohibited over the whole holding whereas on the non-organic Tir Gofal farms this only occurs on parts of the farm where specific management agreements require it.
6.1.1 Biodiversity Impacts: Flora
The addition of N fertilisers is intended to promote lush growth of crop plants such that they out-compete less robust and scarcer species that cannot tolerate high nutrient levels (Gimingham, 1989). The UK Biodiversity Action Plan Steering Committee has identified a series of actions necessary to protect and conserve Biodiversity Action
Plan (BAP) habitats and species. The Agricultural and Rural Affairs Department of the National Assembly for Wales (now Department for Environment, Planning and the Countryside) committed itself as an actionee for 90 Species Action Plans (SAPs) and 16 Habitat Action Plans (HAPs). In many cases, BAP actions parallel organic standards, and this is particularly so where BAP actions call for limitations on fertiliser and biocide use. Some examples where control of fertiliser is specifically mentioned are:
BAP Actions BAP Habitats and Species
Reduce the risk posed by run-off of agricultural chemicals including nitrate and phosphate fertilisers
Violet Crystalwort, Riccia huebeneriana
Control drift and run-off of agricultural chemicals
Earth-Tongue, Microglossum olivaceum
Reduce the threat of adverse practices (including herbicide and fertiliser use)
Lesser Bearded Stonewort, Chara curta
Protect hedges from fertilisers and pesticides
Ancient and/or species-rich hedgerows
The use of soluble nitrogen fertilisers is prohibited by organic farming standards. On lowland organic farms crop rotations include legumes to provide sufficient nitrogen to maintain the level of productivity. In the uplands, however, maintaining high performance productive pasture is often associated with establishing ryegrass/clover swards, usually, but not necessarily, on in-bye land. The performance of these swards without N input decreases rapidly because the sward is dependent on the clover content which itself is adversely affected by the abiotic environment (Frame, 1996; Frame and Boyd, 1987; Newbould, 1982). This is a major problem for organic farming in the hills and uplands, and in northern latitudes (Dyrmundsson, 2000). This is also influenced by inputs of P, K and Ca, which will be used in appropriate forms by organic farmers, but may conflict with environmental objectives to avoid increasing fertility, or even to reduce fertility. This is one area of potential conflict between organic food production and environmental objectives, although organic farming still offers benefits compared to conventional farmers who are not restricted in their ability to import N and other nutrients.
The study by ADAS for the National Assembly for Wales concluded that organic farming methods are largely consistent with actions for BAP species and habitats, and that where one or more UKBAP species are present on a farm, the site would benefit from the adoption of organic farming methods (Frost, 2003). Non-farmed components of a farm such as field margins, hedgerows and woodland contain relatively higher levels of floral biodiversity. The removal of artificial N from the system can only be beneficial to the flora and its supported fauna in such areas. A number of species that are adapted to the semi-cultivated landscape common to LFAs cannot co-exist even with modern organic farming, because any inputs would leave the system too fertile for them (Hampicke, 1978). Therefore not all organic farms are benign to nature conservation; there may be cases of relatively highly stocked organic farms (most likely to be dairy) that also participate in Tir Gofal that bring less environmental benefit than a non-organic extensive farm only subscribing to Tir Gofal.
Peat-based ecosystems respond rapidly to enhanced N deposition. Emissions of N oxides result primarily from fossil fuel burning, and the main source of NH3 emission is from farm animals and from small, but significant, amounts of inorganic fertilisers (Kirkham, 1999). Reduced stocking rates encouraged by organic standards, combined with no N application will be beneficial relative to conventional farming. On acid moorlands the interaction between grazing pressure and atmospheric nitrogen deposition affects vegetation composition.
Large scale studies investigating the effect of annual applications of fertiliser (N, P and K) to grazed and ungrazed heather stands found that in grazed areas, N reduced C. vulgaris cover relative to grass species, mainly Nardus stricta. This effect was most pronounced in those areas where plants were already in poor condition due to grazing pressure (Kirkham, 1999).
6.1.2 Biodiversity Impacts: Fauna
The cessation of N applications is likely to have a number of consequences; the onset of sward growth is likely to be delayed, the structure of the vegetation will affect ground nesting birds and invertebrate populations. Larger invertebrate populations are associated with improved grassland but with lower species diversity and lower average body mass, which is detrimental to bird species feeding on them. (McCracken et al., 1995).
6.1.3 Soil Quality Impacts
Soil temperatures are slower to warm up in the uplands in spring, so natural bacterial activity releasing available N into soil occurs later in the season. For this reason, many upland farmers have been reluctant to convert to organic, claiming that successful early grass growth is dependent on application of inorganic N. Thus the cessation of N applications will reduce overall productivity, which may reduce soil organic content .
Soil flora and fauna are likely to be positively affected by the cessation of N applications. Little is as yet know about the mechanisms maintaining soil biodiversity, but applications of N are associated with negative impacts on mycorrhiza and soil fungi in general (Shannon et al., 2002).
6.1.4 Air Quality Impacts
Fertilised grassland is commonly responsible for the highest emissions of N20 and relatively low soil oxidation rates of atmospheric CH4. Grassland emissions from the ley phase of an organic rotation were low (Ball et al., 2002).
6.1.5 Water Quality Impacts
N leaching to water is governed by soil type and structure, rainfall patterns and the supply of easily leached N (Davies, 1974). The cessation of N addition will substantially reduce the problems of nitrite toxicity to aquatic life and eutrophication of water bodies in the uplands.
6.1.6 Resource Use Impacts
Impacts will depend on what N applications are replaced by; but the industrial N fixation process is hugely energy consuming so a significantly reduced energy use is likely.
6.1.7 Further Research
The Centre for Ecology and Hydrology in Bangor is leading a project to determine changes in nitrogen fluxes and critical chemical values in soils, vegetation and waters, which are indicative of changes in species performance. This work will assess the validity of current nitrogen critical load (CL) values in Wales.