Medium-term soil pH and exchangeable aluminium response to liming at three high country locations

Acid soil conditions and associated aluminium (Al) toxicity pose a serious impediment to legume establishment, persistence and productivity in high country. However, data that report soil exchangeable Al concentrations in response to lime applications are scarce. Three historical (3-8-year-old) lime trial soils were sampled for soil pH and exchangeable aluminium (Al). Soil pH ranged from 4.8 to 7.5, with exchangeable Al concentrations (CaCl2 extraction) of 0.2 to 24 mg Al/ kg. Soil pH and exchangeable Al changed significantly when lime was applied, but the shape of the response differed between the three site locations. The soil pH changes (0-7.5 cm horizon) were 0.16, 0.10 and 0.20 pH units/t lime applied. Critical research needs to be conducted to investigate the key soil factors and mechanisms that result in Al toxicity in high country soils to enable development of mitigation strategies. On-farm decisions on lime rates and legume species suitability need to be based on soil pH and Al testing from individual farm blocks rather than using "rule of thumb" approaches. Keywords: soil pH, soil exchangeable aluminium, lime, pasture legumes