Liming and re-liming needs of acidic soils used for crop - pasture rotations

Summary. In a long-term liming experiment in north-eastern Victoria, we have re-applied lime and applied gypsum (1992 season) to assess wheat grain yield responses with on-going changes in soil pH and extractable aluminium. An acid-sensitive wheat (cv. Oxley) was grown in 2 seasons (1992–93), 12 years after initial applications of lime. Where lime (2.5 t/ha) was applied in 1992 to a previously unlimed soil, grain yield was increased by 19 and 46% respectively in the 2 seasons. However, the yield from these newly limed plots was well below the yields obtained from plots limed in 1980. Re-liming plots limed in 1980 resulted in further yield increases, with lime re-applied at 2.5 t/ha increasing yields by 12% in both seasons. Gypsum decreased grain yields on unlimed soil in the year of application but in the second year gave increases in yield. Whilst pH had changed little in the unlimed soil over the 12 years, the concentrations of extractable aluminium in the root zone increased substantially such that these concentrations far exceed levels which may affect acid-sensitive wheats. Liming at 2.5 t/ha did reduce the aluminium at 0–10 cm depth, but the concentrations at 10–20 cm depth (11.7 mg/kg) are likely to restrict grain yield. The data illustrate the progressive nature of soil acidification and the risk to wheat productivity through delaying treating this soil degradation problem.