35-year trends of acidity and soluble nutrients in cultivated soils of Finland

Nutrient status of arable soils is linked to food production potential and environmental risks. The use of nutrients is affected by policy measures, which formulation calls for data on the long-term development of soil fertility. In Finland, the chemical status (pH 4.65 ammonium acetate-extractable nutrients and pHw) of cultivated topsoils has been surveyed at the same sites in 1974 (n = 1835), 1987, 1998 and 2009 (n = 524). The aims of this study were to determine the temporal trends in P, S, macro nutrient cations and pH utilizing the monitoring data, to find explanations for the trends, and to assess the current status of fertility in the Finnish cultivated soils. The mean soil P concentrations continuously increased with time in clay, fine-textured and mull soils, or first increased but later turned to a decrease in coarse mineral soils, and exhibited no trend in peat soils. Between 1998 and 2009, high P concentrations tended to decrease whereas low P increased, the magnitude of the change being dependent on cropping system (if > 80% of the time planted with annual crops, perennial crops, or under rotation of the two). The trends of the other nutrients mostly reflected the balances of the elements in agricultural soils. The trend for S was generally increasing between 1987 and 1998, but turned to a decline after 1998. The general trends in the mean Ca, Mg and pH were increasing, whereas the initial upward trend for K leveled off after 1987. Based on the 2009 sampling, the current soil fertility is sufficient, but attention is to be paid on S and K status, and the overall fertility of coarse mineral soils.