Larney, F. J., Olson, A. F. and DeMaere, P. R. 2012. Residual effects of topsoil replacement depths and one-time application of organic amendments in natural gas wellsite reclamation. Can. J. Soil Sci. 92: 883-891. The success of reclamation on abandoned wellsites depends on their capacity to recover and sustain levels of soil quality similar to those existing prior to soil disturbance. A 1997-2000 study looked at four (0, 50, 100 and 150%) topsoil replacement depths (TRD) and five amendments [compost, manure, alfalfa (Medicagosativa L.) hay, wheat (Triticumaestivum L.) straw, check] in the reclamation of three natural gas wellsites in Alberta. In 2007 (10 yr after establishment) the wellsites were re-sampled to examine residual effects of reclamation treatments on soil properties. In 2007, there was no difference in SOC between the 50, 100 and 150% TRD treatments and all three were significantly higher than the 0% TRD by an average of 18%. Therefore adding half the amount of topsoil (50%) 10 yr previously caused long-term improvement in SOC (vs. 0% TRD), but adding more topsoil (100, 150%) did not produce further gains. Soil organic C (0- to 15-cm depth) on the compost and manure treatments (across all sites and TRD treatments) was significantly higher ( 8%) than straw, alfalfa and check treatments some 10 yr later. Results show that initial investment in organic amendments for wellsite reclamation can have residual effects on soil quality.