Changes in soil organic carbon storage under grassland as evidenced by changes in sulphur input-output budgets

Information about temporal changes in soil organic carbon (C) pools may be obtained indirectly from changes in input-output budgets of organically com bined nutrients such as sulphur (S). Sulphur budgets were therefore evaluat ed for Northern Ireland (NI) for the period 1940-1990, inclusive. These bud gets indicated that the land or soil had acted first as a sink but then as a source for S, and that reserves of soil S built up between 1940 and 1965 were totally depleted by the mid-1980s. Pooled data from six long-term soil -monitoring sites on undisturbed grassland suggested that negative S budget s from the late-1970s onwards had been due to the net mineralization of soi l organic matter and thus were indicative of net losses of organic C from s urface soil horizons. There was some evidence that the decline in rainfall and fertiliser S inputs from the mid-1960s may have precipitated the breakd own of soil organic matter. (C) 2000 Elsevier Science Ltd. All rights reser ved.