Aluminium tolerance and lime increase wheat yield on the acidic soils of central and southern New South Wales

Acidic soils constrain wheat yield in some parts of central and southern Ne w South Wales. This paper describes research designed to evaluate the usefu lness of aluminium (Al) tolerance, manganese (Mn) tolerance and the interac tion of lime use and Al tolerance in improving wheat yields. Closely related pairs of wheat lines with tolerance and sensitivity of Al a nd Mn were bred. Carazinho (a Brazilian wheat cultivar) was used as a sourc e of Al tolerance in a backcrossing, recurrent selection program to introdu ce tolerance into an Egret background (a locally adapted Australian cultiva r). Aluminium tolerance was determined using the haematoxylin root tip test and Mn tolerance was determined using a subirrigated gravel bed system. Ei ght pairs divergent in tolerance of Al were evaluated for their yield on 3 acidic soil types in 5 field experiments. Grain yield increased in Egret-de rived lines when Al tolerance from Carazinho was introduced. Yield from the Al-sensitive genotypes (averaged over the 8 pairs) compared with the Al-to lerant genotypes was 0.43 to 0.98 t/ha and 0.88 to 1.38 t/ha respectively o n an acid earthy sand in central western New South Wales (Binnaway) in 2 se asons, and 1.08 to 1.96 t/ha and 1.29 to 1.88 t/ha on an acid podsolic soil in southern New South Wales (Borambola). On a moderately acidic red earth site (pH(Ca) 4.8) at Wagga Wagga, no such advantage accrued to the Al-tolerant group with the average yield for the s ensitive and tolerant pairs being 5.00 and 4.78 t/ha, respectively. Mangane se tolerance was assessed in only 1 of these experiments (Borambola) using 6 pairs of lines tolerant of Al but with contrasting Mn tolerance. No advan tage of Mn tolerance was apparent at this site. At Binnaway the tolerant and sensitive lines responded to lime application with the tolerant lines yielding on average about 0.42 t/ha of grain more t han the sensitive lines even when 5 t/ha of lime was applied. At Borambola the tolerant lines yielded 0.59 t/ha of grain more than the sensitive lines when no lime was applied. With lime application this difference in perform ance disappeared and Al-tolerant and sensitive lines yielded equally. At th e Wagga Wagga site, the addition of lime did not affect the yield of the se nsitive lines, while the tolerant lines showed a yield depression of 0.32 t /ha of grain with lime application. Three different relationships between lime application and Al tolerance wer e observed. While 2 relationships fit with our previous understanding, grai n yield depression resulting from the combined use of Al tolerance and lime at our least acidic site remains poorly understood.