AMELIORATION OF COARSE-TEXTURED ACIDIC SOILS USED FOR MACADAMIA PRODUCTION .2. EFFECTS OF SURFACE-APPLIED LIME ON SUBSOIL PROPERTIES

The chemical properties of the soil at depths of 0-5, 5-10, 10-20, 20- 30 and 30-50 cm at two field sites with established macadamia trees we re monitored for 5 years following the surface application of various rates of lime (0-1200 g/m(2)). The effects of annual applications of N and N plus lime were also studied at one site. Both sites received >1 700 mm annual rainfall and had strongly acidic, sandy soils. A residua l effect of increased pH in the surface soil (0-5 cm depth) was eviden t after 5 years for lime rates greater than or equal to 200 g/m(2). Di fferences in the nature of the residual effect at each site are discus sed in relation to soil acidification, lime dissolution and leaching. High lime rates (>300 g/m(2)) applied to the soil surface increased pH and reduced extractable Al in the 10-20 cm depth interval after 12 mo nths. Three years after application, the soil pH at depths of 20-30 an d 30-50 cm had been significantly (P < 0.05) increased by surface appl ications of 600 and 1200 g lime/m(2), respectively. The results of thi s study show that surface application of lime at economic rates (300 t o 600 g/m(2)) can reduce subsoil acidity in coarse-textured soils in h igh rainfall areas.