Acidic soils are characterized by more ammonium and more available (and thus potential toxic) aluminium compared with neutral-to-calcareous soils, which have more nitrate and less available aluminium. Zhao et al. compare the responses of 30 varieties of rice (Oryza sativa, equally divided between japonica and indica cultivars) to aluminium and various ammonium/nitrate ratios under acidic conditions and find that indica is generally aluminium-sensitive and nitrate-preferring, while japonica is generally aluminium-tolerant and relatively ammonium-preferring. Further, the results suggest that aluminium tolerance in rice is antagonistic with nitrate preference and synergistic with ammonium preference under acidic solution conditions: aluminium enhances growth in ammonium-fed rice but inhibits growth in nitrate-fed rice.
