Responses of some crop plants to correction of subsoil acidity

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Abstract
The effects of subsoil acidity and lime incorporation on plant growth were examined for several crop species (wheat, rape, lucerne and phalaris) growing in reconstituted soil profiles. The pH levels of the profiles had been differentially lowered because they had been under improved subterranean clover pastures for various periods up to 55 years. Acidities in the upper layers differed by at least one pH unit and the depth of the acidified horizons reached 60 cm in the most severely affected soil. All species showed good root growth in soil from 'unimproved' native pasture. Root growth was much poorer in the more acid profiles, particularly between 10- and 40-cm depths, where CaCl2-extractable aluminium was high (> 6 ¦g g-1). Liming throughout the profile reduced exchangeable aluminium (to about 1 ¦gg-1) and increased root lengths in the most acid profile by about 60% (0-40 cm depth), so that root lengths then approached those in the 'unimproved' soil. Liming increased shoot yields of all crops except phalaris. The increase was greatest for lucerne (400%), with smaller increases for wheat (39%) and rape (26%). Liming the surface horizon (0- 10 cm) had little effect on most species, but substantially improved root length and shoot yield of lucerne (75 and 300% respectively). The agronomic implications of these findings in crop establishment and drought resistance on acidified soils are discussed.