COPING WITH SOIL VARIABILITY IN AN ACID, HIGH MANGANESE OXISOL

In order to stabilize yields in an Oxisol in Isabela, north coast of Puerto Rico, lime was applied yearly over a four-year period according to lime requirements determined by titration in CaCl,, to pH 6.0. Due to high soil variability, the land was divided into two-acre fields and analyses performed on composite samples from each. In some cases the variability was so high that these fields were further subdivided and the subdivisions analyzed separately for soil properties. While water pH values did not increase significantly in most areas, CaCl2 pH and yields did. In plots which showed particularly poor growth, numerous nodules high in manganese and iron were found. These plots corresponded to areas very high in Mehlich 3 extractable manganese and many were low in extractable zinc. Extractable manganese decreased steadily over the course of the study as yields increased. When problem areas were sidedressed with 560 kg ha- 1 lime, the corn and sunflowers recovered rapidly and gave good to reasonable yields