Abstract
The extent to which the base status of very acid subsoils can be improved by surface applications of limestone used in conjunction with residual-acid nitrogen fertilizers was studied in a typical red-yellow latosolic soil (Las Lomas sandy loam) in Trinidad. The use of residual-acid nitrogen fertilizers (ammonium sulphate, urea and calcium ammonium nitrate) resulted in an appreciable downward transfer of bases in the profile. Urea had the most ameliorating effect on the subsoil pH and the movement of bases (Ca and Mg) through the profile. Ammonium sulphate appeared to be the worst of the three carriers in this respect. The deleterious effect of adding ammonium sulphate only on soil pH and on the depletion of soil bases was quite evident from this study. The effect of the various lime and nitrogen applications on the yields of ten-year-old Valencia orange trees was also studied. Results showed that all treatments receiving lime plus nitrogen gave significantly higher yields than lime alone. There was no significant difference in yields between the various N carriers.
