Subsurface acidity with high levels of toxic aluminium (Al) is a major limiting factor in cereal production in many parts of the world. While surface liming is a common practice to ameliorate topsoil acidity, growing Al-tolerant crops may provide an additional strategy to combat the subsurface acidity problem. The present study compared the growth, water use and yield of two near-isogenic wheat genotypes differing only in Al tolerance in response to subsurface acidity in the field.The trial was conducted on a sandy soil in the low-rainfall region of Western Australia, and received 130 mm rainfall during the growing season (May-October 2000). The soil had pH 4.4 (0.01 M CaCl2) and extractable Al 5.2 mg kg(-1) in the 0.1-0.4 in layer. The trial consisted of seven irrigation treatments and two wheat genotypes (Al-tolerant ET8 and Al-sensitive ES8). The water treatments were natural rain, weekly, fortnightly and monthly irrigation of 0.3 or 0.6 of the pan evaporation. Genotype ET8 produced more shoot biomass than ES8 from 34 days after sowing (DAS). At maturity, ET8 produced 51% higher yield than ES8 under natural rain. Under irrigation, ET8 produced up to 26% higher yield than ES8 but the yield difference was greater in monthly irrigation treatments. While both genotypes had similar root length density in the topsoil, root length density in the 10-40 cm layer was 20-50% higher in ET8 than in ES8. Soil water was depleted faster under ET8 than under ES8 in soil layers between 10 and 110 cm. Under irrigation, the decrease in water content was not evident below 70 cm for ES8 and below 110 cm for ET8, indicating that ET8 roots grew deeper than those of ES8.The results suggest that the higher yield of Al-tolerant wheat than Al-sensitive wheat grown with subsurface acidity results from the greater root proliferation and hence water use in the subsurface layers, and that growing M-tolerant wheat provides an additional strategy to liming to combat subsurface acidity. (C) 2002 Elsevier Science B.V. All rights reserved.