MICROBIAL BIOMASS, N-MINERALIZATION, AND THE ACTIVITIES OF VARIOUS ENZYMES IN RELATION TO NITRATE LEACHING AND ROOT DISTRIBUTION IN A SLURRY-AMENDED GRASSLAND

High rates of cattle slurry application induce NO3- leaching from gras sland soils. Therefore, field and lysimeter trials were conducted at G umpenstein (Austria) to determine the residual effect of various rates of cattle slurry on microbial biomass, N mineralization, activities o f soil enzymes, root densities, and N leaching in a grassland soil pro file (Orthic Luvisol, sandy silt, pH 6.6). The cattle slurry applicati ons corresponded to rates of 0, 96, 240, and 480 kg N ha-1. N leaching was estimated in the lysimeter trial from 1981 to 1991. At a depth of 0.50 m, N leaching was elevated in the plot with the highest slurry a pplication. In October 1991, deeper soil layers (0-10, 10-20, 20-30, 3 0-40, and 40-50 cm) from control and slurry-amended plots (480 kg N ha -1) were investigated. Soil biological properties decreased with soil depth. N mineralization, nitrification, and enzymes involved in N cycl ing (protease, deaminase, and urease) were enhanced significantly (P<0 .05) at all soil depths of the slurry-amended grassland. High rates of cattle slurry application reduced the weight of root dry matter and c hanged the root distribution in the different soil layers. In the slur ry-amended plots the roots were mainly located in the topsoil (0-10 cm ). As a result of this study, ow root densities and high N mineralizat ion rates are held to be the main reasons for NO3- leaching after heav y slurry applications on grassland.