Amelioration of different acidic soils in China using seafood shell biochars

Soil acidification limits crop and pasture production and leads to the degradation of agroecosystems. A substantial volume of seafood shells are discarded each year, which creates enormous environmental and social pressures. In this study, the anaerobic pyrolysis characteristics of four types of seafood shells (clam, scallop, oyster, and mussel) were evaluated. Then, outdoor pot experiments using canola (Brassica napus L.) were conducted and the soil solution was collected in situ to determine the pH, organic matter, nutrient content, and aluminum (Al) species in soil liquid and solid phase. Finally, the relationships between the growth of canola and the concentration of phytotoxic Al were investigated to evaluate the amelioration efficacy and mechanism of seafood shell biochars applied to three typical acidic soils in China. The results showed that seafood shell biochars pyrolyzed under 800 °C anaerobic conditions had characteristics of inorganic and organic amendments. The addition of 2 g kg^-1 four seafood shell biochars pyrolyzed at 800 °C could increase pH of three kinds of severely acidified soils and soil solutions to more than 5.0, and adding 4 g kg^-1 could increase they to more than 6.0. After adding 4 g kg^-1 four seafood shell biochars in Oxisol-GD, Ultisol-AH and Ultisol-JX, the Al concentration of soil solution decreased by more than 89%, 88% and 80%, respectively; the effects were similar to lime. The application of four seafood shell biochars promoted the transformation of water-soluble Al and exchangeable Al in acidic soils into organically bound Al, adsorbed hydroxyl Al, and more stable Al, thus greatly reducing the concentration of Al in soil solution; this improved the growth of canola and increased the yield.