Vertical changes in soil solution chemistry in soil profiles under coniferous forest

Abstract

Soil solution samples from six layers in a brown forest soil were collected regularly over a four year period in a Cryptomeria japonica D. Don plantation, Shiga prefecture, Japan. Samples were analyzed for inorganic N, organic N, total P, Cl −, SO 2− 4, Ca 2+, Mg 2+ and Na +. Inorganic N mainly consisted of NO − 3 in the soil solutions. NO − 3, Ca 2+ and Mg 2+ were predominant in the soil solutions. over the study period. NO − 3, Ca 2+ and Mg 2+ concentrations and fluxes showed a clear seasonal pattern with peaks in late autumn to early winter in the Ah horizon throughout the study period. Nitrification potentials in the six soil layers were estimated. Nitrification occurred mainly in the Ah horizon. Nitrification in the Ah horizon accounted for about 90% of the total NO − 3 production in the soil. In the Ah horizon, the temporal variations in NO − 3 concentrations and fluxes were attributed to the seasonal nitrification processes. While in the Bw horizon, the patterns were variable, and were attributed to the percolation processes of NO − 3 produced in the Ah horizon. NO − 3 fluxes from the Bw horizon were estimated and ranged from 81 to 186 kg N ha −1 yr −1. The estimated high fluxes of NO − 3 reflected the fertile and nitrogen saturated soil conditions in the Cryptomeria plantation.