No abstract

In many highly weathered soils of the humid tropics, crop exploitation of the subsoil environment is limited through acid soil infertility. Since the use of mechanical pro®le modi®cation is often prohibitive, surface incorporation of soil amendments is often the only means available to rectify this problem. A ®eld trial was established with sugarcane on a strongly Acidic Dystrophic Brown Dermosol (Oxic Humitropept) in 1978 to evaluate the eects of surface incorporated lime additions on yield and performance of sugarcane. Eighteen years after the establishment of this trial, signi®cant responses in cane yield were still evident following a single application of 5 t lime ha 71 made in 1978, as well as repeated applications of 5 t ha 71 on three occasions over the past 18 years. Progressive reductions in exchangeable acidity were accompanied by increases in subsoil Ca 2+ and Mg 2+ . Soil pH increased signi®cantly to a depth of 100 cm, this being attributed to the formation of ion pairs with NO 3 7 in the surface soil, the subsequent leaching of these complexes and the dierential uptake of NO 3 7 at depth by roots. The results from this long-term study indicate that surface incorporation of lime is an economically viable approach to the remediation of subsoil acidity on soils such as those studied, namely, those with a low inherent cation exchange capacity and anion exchange capacity.