Farm nitrogen balances in six European landscapes as an indicator for nitrogen losses and basis for improved management

[摘要] Improved management of nitrogen (N) in agriculture is necessary to achieve asustainable balance between the production of food and other biomass, andthe unwanted effects of N on water pollution, greenhouse gas emissions,biodiversity deterioration and human health. To analyse farm N-losses andthe complex interactions within farming systems, efficient methods foridentifying emissions hotspots and evaluating mitigation measures aretherefore needed. The present paper aims to fill this gap at the farm andlandscape scales. Six agricultural landscapes in Poland (PL), theNetherlands (NL), France (FR), Italy (IT), Scotland (UK) and Denmark (DK)were studied, and a common method was developed for undertaking farminventories and the derivation of farm N balances, N surpluses and forevaluating uncertainty for the 222 farms and 11 440 ha of farmland includedin the study.

In all landscapes, a large variation in the farm N surplus was found, andthereby a large potential for reductions. The highest average N surpluseswere found in the most livestock-intensive landscapes of IT, FR, and NL; onaverage 202 ± 28, 179 ± 63 and 178 ± 20 kg N ha⁻¹ yr⁻¹,respectively. All landscapes showed hotspots, especially from livestockfarms, including a special UK case with large-scale landless poultryfarming. Overall, the average N surplus from the land-based UK farmsdominated by extensive sheep and cattle grazing was only 31 ± 10 kg Nha⁻¹ yr⁻¹, but was similar to the N surplus of PL and DK (122 ± 20and 146 ± 55 kg N ha⁻¹ yr⁻¹, respectively) when landlesspoultry farming was included.

We found farm N balances to be a useful indicator for N losses and thepotential for improving N management. Significant correlations to N surpluswere found, both with ammonia air concentrations and nitrate concentrationsin soils and groundwater, measured during the period of N management datacollection in the landscapes from 2007–2009. This indicates that farm Nsurpluses may be used as an independent dataset for validation of measuredand modelled N emissions in agricultural landscapes. No significantcorrelation was found with N measured in surface waters, probably because ofspatial and temporal variations in groundwater buffering and biogeochemicalreactions affecting N flows from farm to surface waters.

A case study of the development in N surplus from the landscape in DK from1998–2008 showed a 22% reduction related to measures targeted at Nemissions from livestock farms. Based on the large differences in N surplus betweenaverage N management farms and the most modern and N-efficient farms, it wasconcluded that additional N-surplus reductions of 25–50%, as compared tothe present level, were realistic in all landscapes. The implementedN-surplus method was thus effective for comparing and synthesizing resultson farm N emissions and the potentials of mitigation options. It isrecommended for use in combination with other methods for the assessment oflandscape N emissions and farm N efficiency, including more detailed Nsource and N sink hotspot mapping, measurements and modelling.

[学科分类] 地球化学与岩石