Influence of topsoil removal on soil fertility and barley growth

Greenhouse and incubation experiments were conducted on two central-Alberta Mollisols to determine the effect of topsoil removal on N-mineralization potentials, loss in crop productivity and productivity restoration using fertilization with Nor P. Soil samples, 15-cm (6 in) deep, were obtained after removing 0, 6, 12 and 18 cm (0, 2, 5, and 7 in) of topsoil from cereal-grain cropped fields mapped as Malmo clay (Pachic Udic Haploboroll) and Peace Hills silt loam (Udic Haploboroll). At both sites, artificially-eroded topsoil had reduced concentration of total C, N, and NO3-N. In both soils, N-mineralization potentials (No) varied five-fold with depth of topsoil removal. The decrease of N0 was linear with depth of topsoil removal. Barley yields decreased with removal of topsoil on the treatment without N but the yield loss was restored with the addition of fertilizer N. Up to 200 mg N/kg of soil were needed to obtain maximum yields. Without addition of P, topsoil removal reduced barley yield only in the Peace Hills soil. The rate of P necessary to eliminate the yield difference between eroded and non-eroded soil was about 10 mg/kg. On the Malmo soil, barley yields also increased with the addition of P but these increases were similar over all levels of topsoil removal and smaller than those obtained in Peace Hills soil. We conclude that 1) the productivity of the two Mollisols studied, as measured by plant yield and N-mineralization potentials, was substantially reduced by topsoil removal; and 2) additions of N or P fertilizers to eroded topsoils improved yields, but these could not reach those attained on non-eroded topsoils under the same fertilizer treatment.