Long-term monitoring of nutrient losses from Norwegian micro-catchments

1. Long-term monitoring of nutrient losses from Norwegian micro-catchments Marit Hauken, Marianne Bechmann, Johannes Deelstra, Hans-Olav Eggestad and Lars-Erik Sørbotten Introduction Nutrient losses from agricultural catchments in Norway have been monitored since 1992 as part of the Norwegian Agricultural Environmental Monitoring Programme(JOVA). The catchments are at locations which are chosen to represent typical Norwegian agricultural systems such as the production of cereals, grass/livestock and vegetables. Losses are reported annually. Volbuis located in the middle of Southern Norway. Grass is the main production and the winter can be harsh. The Skuterud catchment is located in the South-Eastern part of Norway, in an area typically suited for cereals. Time is a catchment in the South-Western part of Norway, an area dominated by grass and livestock. Methods The monitoring covers 13 catchments, geographically distributed from Bodø in the North to Grimstad in the South. There are five locations in the Central/Eastern part of the country, and two in the Western part. Every location has a monitoring station equipped to measure water discharge, and to take discharge-proportional water samples automatically. Approximately 24 samples are taken every year from each location. Total annual runoff from each catchment is calculated, and the water samples are analysed for nitrogen (N), phosphorus (P), pH and suspended solids (SS). During the growing season, most of the samples (eight catchments) are also analysed for pesticides. Soil and nutrient losses during the agrohydrological year (May-April) are then calculated. Information on agricultural practices such as crop types, yields, tillage and fertilization is collected after the growing season from the farmers themselves (small catchments) or from Statistics Norway (large catchments). Results The monitoring produces a large amount of data which is widely used, e.g. in research projects and in calibration and validation of models for the simulation of nutrient and soil loss. The average soil loss for the catchments during the monitoring period ranges from 46 – 1630 kg/ha/year. The average loss of phosphorus (total-P) ranges from 0.2 – 5.1 kg P/ha/year, the highest being 18.9 kg P/ha/year, reported in 2000-2001 at the Grimstad location. This catchment is dominated by vegetable cultivation, and some of the crops demand high rates of phosphorus. The average yearly loss of nitrogen (total-N) ranges from 10 – 67 kg N/ha. In general, the data show a close correlation between runoff and loss of both soil and nutrients. Average nutrient application rates in the catchments are 130-330 kg/ha of nitrogen (N) and 17-52 kg/ha of phosphorus (P). Discussion and conclusion The results show a large variability in soil and nutrient losses between catchments, mainly due to differences in climatic and topographical conditions, as well as in soil properties and agricultural practice. There is also a large annual variation in losses for each catchment, mainly due to variations in precipitation and winter conditions. Soil and nutrient losses are results of complex processes that show great variation in time and space. Long-term monitoring combined with modelling may contribute to increased understanding of the effect of agricultural management on soil and nutrient losses, and hence increase the potential for minimizing these losses. The results from the JOVA programme may have wide uses in studies of the effects of climate change, and the programme may be an important contributor in such efforts.