Leaching of nutrients and major ions from an arable field with an unfertilized fallow as infield buffer zone

Leaching of nutrients and major ions from a tile-drained arable field was evaluated over a 25-year period (1980-2005). The soil, classified as a Gleyic Cambisol, received moderate applications of fertilizers. During later years the soil was more frequently under ley, and since 2002, an area of ravine (29% of the total field) has been managed as a permanent fallow with annual cutting without removing the grass material. A decrease in the concentration of nitrate nitrogen (NO3 - N) in the drainwater was estimated in 1980-2005, based on non-parametric tests on concentrations flow-normalized with a robust fitting curve procedure. The average concentration of soluble reactive phosphorus after pre-filtration (RPf) of 0.030 mg 1(-1) corresponded to a calculated degree of phosphorus saturation (DPS) of 6% in acid extract of ammonium lactate from the topsoil. Between 1995 and 2005, concentrations of suspended solids (SS), RP and total organic carbon (TOC) decreased significantly in the drainage water from the entire field. Throughout the entire period, there was a negative net accumulation of the major ions to the soil. The order of decrease in relative terms was calcium (Ca2+) > magnesium (Mg2+) > sulphate (SO42-) > chloride (Cl-) > potassium (K+). In addition, the soil phosphorus (P) balance was negative. A significant reduction in ion concentrations in the drainwater, including sodium (Na+) and hydrogen carbonate HCO3 (-), was estimated. The order of reduction in relative terms was: SO42- > Mg2- > Ca2+ > HCO3- > Cl- > NO3- > Na+ > HPO4. Altogether these trends were equal to approximately 0.1 mmol(c) 1(-1) yr(-1) of positively and negatively charged ions. Based on measured concentrations, decreasing trends in SO4 (2-) and Ca2+ were also observed in the shallow groundwater (3.6 m below the soil surface), while K+, Na+ and HCO3- tended to increase. Trends of cations in deeper groundwater (5.8 m below the soil surface) were in some cases the opposite of the trends in the drainwater.