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Nutrient leaching from clay soils can show extreme temporal and spatial variation. Using an optical sensor (hourly data storage), a Swedish field with vermiculite clay was monitored for water flow (Q expressed in mm), turbidity values (TURB), and nitrate-nitrogen concentrations (CNO3N, mg L-1) in four hydrological years representing different cropping/soil management regimes. Mean TURB-Q slope (1300) decreased in the order: ploughed soil > winter wheat > unfertilized fallow > winter wheat after drainage system renovation + structure-liming of topsoil and backfill, estimated in the initial phase from 16 selected autumn events. A similar ranking was found for variability in turbidity relative to that in discharge (CVT/CVQ) in the entire autumn. Mean CNO3N-Q slope (=2) was significantly lower under fallow than in the three cropping systems (7-32), confirming results from adjacent experimental plots. A spring-period had no snow cover or intensive rain, but in situ monitoring revealed that nutrient leaching was still substantial. Particulate- and dissolved reactive phosphorus, and nitrate-nitrogen leaching was estimated reasonably well (less than 8% difference) based on in situ high-frequency resolution measurements, compared with laboratory analysis of weekly composite samples. Accurate assessment of C-Q relationships in agricultural drainage water across temporal and spatial scales is therefore important.

Domestication of biennial Lepidium campestre L. offers possibilities for more varied crop rotations in cold regions, with increased crop cover during winter. In the first winter after sowing, L. campestre can reduce nitrogen (N) leaching before harvesting in the second year. In this system no soil tillage is needed during the first year, unlike in systems with annual crops. A three-year leaching study on loam soil in southern Sweden revealed significantly (p