LONGEVITY OF WHEAT YIELD RESPONSE TO LIME IN SOUTH-EASTERN AUSTRALIA

A long-term experiment in north-eastern Victoria has been regularly mo nitored for wheat yield responses to a range of lime and fertiliser tr eatments, and the soil sampled for acidity attributes. Substantial gra in yield increases have been consistently obtained over a period of 12 years with a single lime application. Lime applied at 2.5 t/ha in 198 0 was still providing yield increases of 24% with an acid-tolerant whe at (Matong, 1992 season) and 79% with an acid-sensitive wheat (Oxley, 1993 season) relative to no lime treatment. The 2 wheat cultivars resp onded differently to phosphorus fertiliser, with the acid-sensitive wh eat less responsive to phosphorus fertiliser in the absence of lime. T he use of a regular lime application applied as a fertiliser (125 kg l ime/ha) with the wheat seed gave only a small grain yield increase (8% Matong, 16% Oxley), despite 1 t/ha of lime applied over the 12-year p eriod. Liming the soil at a rate of 2.5 t/ha (1980) initially raised t he soil pH by about 1.0 unit and removed most soluble aluminium (0-10 cm). However, after 12 years of crop-pasture rotation after the initia l 2.5 t lime/ha treatment the soil pH had declined by 0.7 of a pH unit and exchangeable aluminium was substantially increased, almost to lev els prior to the initial application of lime. Given the continued yiel d responsiveness obtained following the initial application of lime, t his practice, rather than regular applications of small amounts of lim e, is recommended for wheat production on strongly acidic (pH(w)<5.5) soils in south-eastern Australia.