Long-term monitoring of nitrogen in surface and subsurface runoff from small agricultural dominated catchments in Norway

• Long-term monitoring data from 13 sites were investigated.
• The field site N losses were dominated by subsurface drainage.
• Catchment with cereal production showed highest N concentrations during spring and autumn.
• N balances were highest and showed highest variation within catchment with manure applied.
• Mitigation methods should focus on improved manure management and reducing mineral N.

The use of nitrogen (N) is of high interest due to its importance for food production, climate change and water quality. A comparison of N loss from agricultural areas to water in the Nordic-Baltic countries showed that the highest losses occurred in Norway. The objective of this paper was to identify temporal and spatial patterns in N concentrations in agricultural streams and to quantify the effect of production systems and agricultural management on N loss. The study includes monitoring data obtained from ten agricultural catchments (65–2830 ha), two agricultural fields (4–6 ha) and one forested catchment (19 ha). All arable areas were artificially tile drained with 8–10 m spacing and at a depth of 80–100 cm. The results showed that for all production systems average N concentrations in subsurface drainage were 2–4 times higher than in surface runoff. The average N balances for the monitored catchments varied from −12 to 132 kg ha−1 yr−1, but six of the catchments showed average N balances below 65 kg ha−1 yr−1 at which level N leaching may not be affected by increased N balance. However, N balances from single fields within the catchments varied largely, especially for areas with manure application. Seasonal variation in TN concentrations was higher in the streams in areas dominated by cereal production compared to grassland areas with the highest concentrations in May–June and September–December. Based on this study it is suggested that a strategy to even out manure application within the catchments with high livestock density should be developed. For areas with cereals, mitigation method should focus on reducing soil mineral N in spring and autumn.