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

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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