The researchers compared different types of fertilizers for growing pasture on sandy soils in high rainfall areas. They found that 'coastal superphosphate' was the most effective in annual applications, while all fertilizers were equally effective in one-time applications. The sandy soils have enough hydrogen ions to dissolve rock phosphate effectively, making it as good or better than single superphosphate. The presence of elemental sulfur in 'coastal superphosphate' helps enhance the dissolution of rock phosphate, leading to better pasture growth.