Leaching of soil organic carbon and nitrogen in sandy soils after cultivating grass-clover swards

Summary

Dissolved organic matter is the basis for many of the biogeochemical processes in the soil. Several studies have focused on the formation and losses of dissolved organic matter in forest systems, whereas a limited number have dealt with this aspect in agricultural soils. The purpose of this study was to estimate the leaching of dissolved organic carbon (DOC) and nitrogen (DON), with focus on the period after cultivating grass-clover swards. Grass-clovers were ploughed in the spring prior to sowing cereals followed by either catch crops or bare soil. The concentrations of DOC and DON decreased with soil depth and ranged at 90 cm soil depth between 7 and 21 mg C L-1, and between 1 and 3 mg N L-1, respectively in a sandy loam soil, and between 16 and 63 mg C L-1, and between 1 and 10 mg N L-1, respectively, in a coarse sandy soil. The highest concentrations of DOC were measured in treatments with catch crop, whereas the highest values of DON were from the bare soil treatments. The resulting DOC/DON ratios were in the range between 2 and 42 with higher values in the coarse sandy soil than in the sandy loam soil. The total percolation was 218 mm in the sandy loam soil and 596 - 645 mm in the coarse sandy soil, which resulted in an annual leaching of 22 - 40 kg DOC ha-1 year-1 and 3 - 4 kg DON ha-1 year-1 in the sandy loam soil, and 174 - 310 kg DOC ha-1 year-1 and from 10 - 31 kg DON ha-1 year-1 in the coarse sandy soil.