Land restoration management after topsoil mining and implications for restoration policy guidelines in New Zealand

A three-year field trial on an upland loessial soil (Belmont silt loam) in New Zealand investigated the effects of ripping, application of fertilizer N and grazing management on the recovery of some physical, chemical and bio chemical properties of soil and pasture productivity following removal (min ing) of topsoil. Removing the top 31 cm of soil by mining (all of the A hor izon and part of the AB horizon) also removed most of the soil's labile org anic matter fractions, and to a lesser extent its total organic matter. Aft er three years, the microbial C and mineralizable N in the 0-10 cm depth of mined soil had reached 65 and 62 per cent of the corresponding levels in u nmined soil. Ripping to a depth of 30 cm, application of fertilizer N and l enient grazing of the pasture failed to enhance the recovery of soil fertil ity. A soil sampling depth of 20 cm provided a reasonable basis to assess t he microbial biomass and potential fertility. Pasture productivity was, on average, 30 per cent lower on mined land than on unmined land over the firs t three years after mining. Application of N proved uneconomic in terms of farm production, although a good pasture response to N fertilizer was obtai ned. The results from this and related trials are summarized as a series of recommendations for the monitoring and regulation of topsoil mining. An in centive regime is also recommended to encourage land owners and/or topsoil miners to use successful restoration techniques on topsoil-mined land. Copy right (C) 1999 John Wiley & Sons, Ltd.