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Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO4-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresponding concentrations in near-simultaneously sampled drain water. A similar connection was not observed for Na and Cl in the period before drain repair. Elevated concentrations of nitrate-nitrogen (NO3-N) were recorded both in shallow groundwater and in drainage water from 1998 to 2010, especially after incorporation of chicken manure into the soil in 1998. Based on simulated discharge (assuming a functioning measuring station throughout), estimated flow-weighted mean NO3-N concentration in drainage water increased from 5.6 mg L−1(1977–1998) to 15.7 mg L−1in the period 1998–2000. Simultaneously, mean NO3-N concentration in shallow groundwater increased from 0.2 to 4.0 mg L−1, and then to 4.8 mg L−1in the period 2000–2012. It was estimated that after drain repair, a greater proportion of infiltrated NO3-N entered the receiving stream directly via the outlet of the tile drainage system close to the field's monitoring station than was the case before repair. [ABSTRACT FROM PUBLISHER]