The performed studies dealt with of problem of peatland surface subsidence on the Wizna study area with a functioning prototype of an amelioration system consisting of collective ditches spaced at an interval of 500 m and a low-slope (i= 0.5 %о) drainage-irrigation network. The studies involved well irrigated wet (A) and semi-dry (C) potential soil-moisture complexes. The obtained results refer to the peatland close to the drains i.e. the area, which was deformed, artificially lowered and compacted due to melioration measures. Parts of the studied plots were used as highly productive meadows. Except for the modernization of the melioration system (replacing ditches with drains) and post-melioration management of complete cultivation (on plot B-16 this management was performed twice), systematic intensive measures using of heavy equipment were carried out on these areas. The studies showed that on a peatland meliorated between 1963 and 1964 the surface still slowly subsided. In the period 1975-1995, the peatland surface declined on average by 0.3 cm ∙y-1 on a wet complex (A) and twice that, i. e. by 0.6 cm∙ y-1 on a semi-dry complex (C).