Evaluating policies on nutrient management and water quality at the catchment scale
Plant nutrients such as nitrogen (N) and phosphorus (P) are essential for grassland and tillage production, and optimal use according to recommended guidelines in feed and fertiliser is essential to maximise farm outputs and profits. The implementation of the EU Nitrates Directive into Irish law (SI 101 of 2009) also regulates the management of these nutrients and is aimed at maintaining productivity whilst reducing the water quality risks associated with losses from soils and yards to water courses and groundwater. These water quality risks concerning nutrients are chiefly;
- Leaching of N as nitrate from the soil to groundwater which can result in unacceptably high nitrate levels in drinking water supplies
- Surface loss or runoff of soluble forms of N and P from soils or manure, or movement of P enriched soil to drainage channels, ditches or streams which can then cause the eutrophication of rivers, lakes and coastal waters
Eutrophication is the over-nourishment and subsequent growth of aquatic plants. It can be caused by excessive concentrations of N and P in water and lead to de-oxygenation of sensitive water-bodies, changes in ecological structure and decreases in amenity. Excessive N as nitrate in drinking water supplies can also be toxic above a maximum acceptable concentration.
The implementation of this legislation has created significant challenges for the farming sector whereby farmers must comply with SI 101 of 2009 in order to meet cross compliance requirements for single farm payments and is transposed into the Good Agricultural Practise (GAP) regulations. For example:
- An upper limit for livestock manure loading on a holding shall not exceed 170 kg/ha of organic N each year averaged over the farmed. Livestock farmers can apply each year for a derogation to farm up to 250 kg/ha N but this will be granted subject to stringent environmental conditions.
- The country is divided into management zones each with specific over winter manure storage requirements. Each of these zones has a specific period during which the land application of livestock manures and chemical fertilisers is prohibited (closed period).
- Nutrients supply (in particular N and P) should be matched to crop requirement, both in terms of quantity applied and the time of application relative to crop yield, soil and climatic conditions.
- Buffer zones must be respected when applying organic or chemical fertilisers in order to keep them on the field soils and minimise movement into water courses.
- Within each management zone the ploughing of land is prohibited during the closed period unless a crop is established with 6 weeks. Green cover must be established and maintained on all farmed areas during the closed period to utilise nutrients within the root zone.
These regulations are aimed at maximising the use of organic and inorganic fertilisers, pertinent in terms of farm economics, and minimising transfers from farms and soils.
The Agricultural Catchments Programme was initiated to provide a comprehensive scientific and socio-economic evaluation of the GAP regulations in Ireland. A catchment is an area of land that defines the water supply influence on a river, lake or estuary and is the scale at which all EU member states must manage water bodies. Small catchments have, therefore, been selected based on criteria that include farming intensity, soil type, and minimal influences from rural populations and forestry. Catchments have also been chosen to include representations of tillage agriculture in Ireland and medium to high stocking densities on grassland enterprises. As the use of N and P is a farm management and economic concern as well as a concern in the aquatic environment, four component programme tasks are being undertaken with original data collection and assessments. These are:
- SOCIO-ECONOMIC factors – assessing how management trends, habits and attitudes are affected by the GAP regulations and what the perceived implications are for farm incomes
- SOURCE factors – investigating how nutrients at the soil and farm scale are influenced in terms of supply/availability and potential mobilisation to water
- PATHWAY factors – defining the main pathways for mobilised nutrients in each farming catchment
- DELIVERY factors – identifying the load and concentration patterns of nutrients from the catchments, in each river
IMPACT factors – establishing the current ecological status of each catchment river network and the implications for water bodies downstream of the catchments
It is vital that farming stake-holders are fully aware and receptive to the management implications of the legislation and so these tasks are being supported by a Teagasc advisory team in each catchment.
The outcomes of the Agricultural Catchments Programme will be assessments and recommendations of how effective the GAP regulations are in terms of farm economics and the links between farm management, landscape and water quality.