Amelioration of a saline-alkaline soil using biochar and compost: Impacts on plant growth, soil biological and chemical characteristics

Land degradation reduces productivity and biodiversity, and requires restoration of both soil condition and vegetation to re-establish ecosystem services. Organic amendments can improve soil biological and chemical properties, thereby enhancing revegetation success in severely degraded soil. This study investigated the use of compost and biochar to support revegetation and soil restoration. Soil was collected from a severely degraded creek bed in an agricultural farm in south-western Australia (UWA Farm Ridgefield) and amended with compost (2.5% and 5%) and biochar (5% and 10%), both alone and in all pairwise combinations. Saltbush (Atriplex nummularia) seedlings were grown for 10 weeks in glasshouse conditions. Following harvest, plant growth and soil chemical properties were analysed. DNA was extracted from rhizosphere soil for bacterial diversity profiling with subsequent putative functional genes relating to carbon, nitrogen and phosphorus cycling using an in-silico approach. Compost improved growth of root and shoot biomass. Both compost and biochar improved the alkaline soil by reducing pH and increasing nitrate, phosphorus and potassium levels. Compost addition also had a significant effect on rhizosphere bacterial community structure, decreasing alpha diversity and altering beta diversity indices. Amendment of soil also changed the relative abundance of putative nutrient cycling genes, with an increase in the potential for denitrification, carbon and phosphorus cycling and a decrease in ammonification potential. Application of this compost-biochar combination improved plant growth and soil condition by altering both chemical and biological characteristics of the soil, and therefore may provide an effective management strategy for supporting restoration in a degraded landscape.