Use of nitrogen fertiliser in restoration of pasture productivity and soil fertility after topsoil mining

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Abstract
The response of a grass-clover pasture to fertiliser nitrogen (N) on land mined of its topsoil 6 years previously was measured over 2 years. The effect of fertiliser N on the soil microbial biomass and organic matter content was also measured. N (150 kg N/ha in three split dressings of urea) increased the annual pasture production of 4850 kg dry matter (DM)/haby 47% in the first year of application. In the second year, N (200 kg N/hain four split dressings) increased the annual pasture production of 9500 kg DM/ha by 34%. Grass responded to the addition of fertiliser N whereas clover was suppressed. The soil microbial biomass content of the surface 20 cm was 70% higher after 2 years of adding fertiliser N. The corresponding organic matter content was 10% higher after addition of fertiliser N. These results are discussed in relation to use of fertiliser N as a management tool in restoring plant productivity and soil fertility on land disturbed by topsoil mining.