An artificial soil mix made out of industry wastes and sewage sludge has been created for the revegetation of an industrial site. Physico-chemical properties were measured over time to examine soil formation in a chronosequence of 11 gardens aged 3–11 years, and in a 3-year longitudinal study of 8 replicate experimental plots. In the field plots, available nutrient content was initially high but declined quickly in 3 months. Particle weathering occurred, with an increase in the finer soil fractions after 1 year. pH was initially 7.62 and declined to 6.85 by 3 years. Native tree growth was exceptionally good over the 2 years monitored, with average trunk diameter increases of 144 mm for Corymbia maculata, 94 mm for Acacia floribunda, and 39 mm for Callistemon salignus. In the chronosequence study, there was a build- up of nutrients (C, N, and P) in the soil mix over 6–10 years, with a slight decrease by 11 years. This study has shown that soil development has occurred in the short and longer terms, with rapid changes seen in the first 12 months. High levels of N and P remaining after 11 years, and abundant organic C for microbial decomposition, indicate the potential for nutrient cycling

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Many Hawaiian agricultural soils are acidic with low-nutrient retention; therefore, organic soil amendments are often used to improve soil properties and increase yields. Amendments can be incorporated for annual crops, but perennial orchards need surface application to avoid damaging surface roots. Pot trials compared responses to incorporated (IBC) or surface-applied (SBC) combination of hardwood biochar and chicken manure compost (4% v/v of each amendment) added to an Andisol and Oxisol. Soil pH was increased by 0.4–1.1 units in IBC and by 0.2–0.5 for SBC in the 0–10 cm soil layer. Both SBC and IBC increased soil total N, extractable P, Ca and Mg in the 0–10 cm soil layer. Soil pH, total C and extractable Ca were also higher in the 10–20 cm soil layer for IBC soil, indicating movement and/or leaching of amendments. Chinese cabbage biomass was 18–70% higher in the IBC and 14–47% higher in the SBC than that in the unamended soil, while papaya biomass was 23% and 19% higher in SBC and IBC, respectively. There was a greater response in the more acidic Andisol soil, with larger improvements in soil pH, plant nutrient uptake and root biomass than the Oxisol. Surface application was as effective in increasing plant growth as the incorporated amendment, providing evidence for farm scale assessment. Biochar and compost are recommended for use in tropical soils, and surface application may be beneficial to annual and perennial crops.

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Waste disposal has become a major concern for industries that create a large amount of by-products due to the cost of landfill and environmental responsibility. Beneficial re-use of these by-products which contain resources for other industries, will solve some of these problems. An artificial soil mix has been created out of ironmaking and sewage wastes, for use in a revegetation program to improve the BHP Steelworks site in Australia. Coal washery refuse, blast furnace slag and sewage sludge have been combined to form a topsoil which is placed on waste mounds and revegetated. Field trials were established to evaluate the soil forming characteristics of this artificial media. The fine fraction (<2mm) of the particle size distribution decreased from 71% to 64% in one year, showing evidence of weathering and particle breakdown. Bulk density remained the same (1.0 g/cm 3) in a two year comparison. The pH of the soil mix declined from 7.6 to 7.1 in one year. Native tree growth in the soil mix was very good, although comparisons could not be made with real soil. The long term viability of the soil mix in relation to nutrient cycling could not be extrapolated with only two years of data. The potential is promising for the use of this soil substitute in urban landscaping, land restoration and revegetation, and opportunities for further research are available.