Using a Parish Level Approach to continually inform Dynamic Nutrient Management

The implementation of the EU Nitrates Directive (91/676/EEC) in Scotland has led to the development of Nitrate Vulnerable Zones (NVZs) in catchments where freshwater is expected to exceed 50 mg NO3/l (Scottish Government, 2014). The success of the policy has been measured by benchmarking nitrate concentrations in surface water over time. It is often challenging to relate surface water nitrate concentrations directly to farm nutrient management practice. However, it is important for future policy making to understand what changes in farm management have led to observed changes in nitrate in surface waters. Here we take a new approach using existing data on land use and combining it with data collected on farm and from national statistics to address changes in nutrient management in agricultural catchments over time. In terms of water quality, most studies focus on nitrogen (N) and phosphorus (P) but we also include potassium (K) because of its relevance to productivity.
In this work, a nutrient budgeting approach which uses agricultural parish (municipality) level data has been developed. Data used to produce the parish nutrient budgets were drawn largely from government datasets at a range of scales for example, the June Agricultural Census (JAC), and the British Survey of Fertiliser Practice (BSFP) as well as, non-governmental but publicly available data. Farmers were also surveyed to provide farm data such as cropping patterns or livestock numbers and consequently these data were used to cross-reference findings gained through secondary data. The Ythan hydrological catchment is a typical example of an agricultural catchment in Eastern Scotland and is part of one of the first hydrological catchments to be designated as a NVZ in Scotland (Domburg et al., 1998; Raffaelli, 2000). We selected eleven agricultural parishes in the catchment covering cropping and grassland systems and calculated N, P and K budgets pre and post the introduction of the NVZ.
This work has shown that nutrient balances for N (kg N ha-1 yr-1) have largely decreased between the pre and post NVZ implementation periods, in response to a reduction in applications of inorganic N fertiliser. In addition, nutrient balances have shown that P and K deficits have been experienced in some agricultural parishes. It was also identified that better use of excreta in some agricultural parishes post-NVZ could support a further reduction of inorganic P and K use. Moreover, another outcome is the methodology structure itself – the parish level nutrient budget approach is key.
The work has shown that it provides an opportunity to transform agricultural practice and reduce the burden on policymakers and farmers, by linking agricultural management to nutrient surpluses and deficits. It is beneficial because the method re-uses data that is already collected by government. To conclude, the approach has the potential to be used beyond the research period, integrating farmer data and giving farmers a purpose in the process.
References:
Domburg, P., Edwards, A. C., Sinclair, A. H., Wright, G. G., Ferrier, R. C. (1998). Changes in fertilizer and manurial practices during 1960–1990: Implications for N and P inputs to the Ythan catchment, N.E. Scotland. Nutrient Cycling in Agroecosystems. https://doi.org/10.1023/A:1009787618943
Raffaelli, D. (2000). Interactions between macro-algal mats and invertebrates in the Ythan estuary, Aberdeenshire, Scotland. Helgoland Marine Research, 54(2–3), 71–79. https://doi.org/10.1007/s101520050004
Scottish Government (2014). The Nitrates Directive Review of Nitrate Vulnerable Zone Designated Areas in Scotland – 2013, Edinburgh.