Nitrogen mineralization in lime- and gypsum-amended substrates from ameliorated acid forest soils

In 1964 amelioration treatments were begun in an 87-yr-old stand of Scots pine (Pinus sylvestris L.) in northeast Bavaria to restore soil fertility lost through four centuries of litter raking and other human influences. This paper reports research to measure nitrogen mineralization differences in substrates from the degraded pine forest that had received contrasting amelioration treatments over a 19-yr period. Field plots with a “fertilizer” treatment received Ca, P, K, Mg, and repeated N fertilization; those with a “lupine” treatment were fertilized with Ca, P, K, and Mg, then tilled and underplanted with Lu-pinus polyphyllus L. Laboratory N mineralization was measured on organic (F + H horizons) and mineral soil (0− to 10-cm) substrates from control, fertilizer, and lupine field plots. The effect of lime and gypsum laboratory amendments on N mineralization was also studied. Substrates were incubated at 35°C and moisture content equivalent to 0.08 mPa for 10 wk. Samples were leached at 2, 4, 7, and 10 wk with 0.01 M KCI and analyzed for inorganic N. Total N mineralized (10 wk) was about 20-fold higher in organic layer substrates than in mineral soil substrates, and about 2-fold higher on both substrates from the lupine plots than from control or fertilizer plots. The substrates responded differentially to lime and gypsum treatments; these treatments had no effect on mineralization of the organic layer, but liming resulted in a 3-fold increase in N mineralization of the mineral soil. Gypsum had no effect on either substrate.