Aluminum toxicity is one of the main factors limiting the growth of crops in southern acid soils.In this experiment,the differences and potential mechanisms of aluminum toxicity alleviation effects of different modifiers on acidaluminum enriched soils were studied by adding exogenous aluminum and planting crops in red soil.Pot experiment with acid red soil,adding exogenous aluminum,and applying anendment humic acid(HA),biochar(C) and quicklime(CaO),planting pakchoi,setting 8 treatments including CK,HA (0.3% HA),C (2% C),CaO(0.3% CaO),Al(1 mmol/kg Al3+),Al+HA (1 mmol/kg Al3++0.3% HA),Al+ C (1 mmol/kg Al3++2% C),Al+CaO (1 mmol/kg Al3++0.3% CaO) was conducted to analyze the effects of humic acid,biochar and quicklime on different forms of active aluminum and crop growth in aluminum rich red soil.The results showed that aluminum toxicity significantly decreased the emergence rate and fresh weight of pakchoi,and increase the aluminum content in pakchoi.The growth of pakchoi improved and the Al content reduced under amendment addition.Compared with Al treatment,the fresh weight of Al+HA,Al+C,Al+CaO treated pakchoi reduced by 86%,775% and 1 014%,respectively.The pH of Al treatment decreased by 0.17 compared with CK treatment,the content of active aluminum significant increased,the amount of active aluminum decreased after added the amendment.The exchangeable Al3+ of Al treatment increased by 11.17% compared with CK treatment,but the exchangeable Al3+ of Al+HA,Al+C and Al+CaO treatment decresed by 11.81%,59.63% and 87.82% compared with Al treatment.The content of dimer hydroxyl aluminum ion Al(OH)2+,Al(OH)+2 increased.The exogenous aluminum significantly reduced soil pH.The content of exchangeable Al3+ increased,inhibiting the growth of pakchoi.Humic acid,biochar and calcareousness reduced the exchangeable Al3+ content.Biochar and calcareousness effectively reduced the pH of red soil and improved the growth of pakchoi.It is indicated that anendment affects crop growth by combining soil pH,nutrient content and exchangeable Al3+ content.