The Influence of Ammonium Sulfate Fertilization on the pH of Sugarcane Soils

Abstract

The continuous use of ammonium sulfate as a nitrogen source for sugarcane has caused a lowering of soil pH and changes in available nutrients on a Vega Alta clay loam as follows: 1. Increasing rates of ammonium sulfate fertilizers lowered soil pH values for all soil horizons from 0 to 6 to 12 to 18 inches. 2. Available calcium decreased with increasing amounts of ammonium sulfate in all soil horizons from 0 to 18 inches. 3. The loss of available magnesium in the soil was slight when compared to calcium, giving rise to narrow calcium:magnesium ratios in the surface 0 to 6 inches of soil. 4. With increasing acidity there were large increases in soluble manganese, iron, and aluminum in all soil horizons. 5. The quantity of soluble manganese was much higher than that of iron giving rise to iron:manganese ratios of less than 1. 6. The rapid decrease in soil pH with increasing rates of ammonium sulfate application was evident not only in an 18-year experiment but also in a 3 1/2-year experiment on the same soil. 7. A Vayas clay with a pH of about 8 failed to have its soil pH lowered to any marked degree by use of ammonium sulfate for 19 years. 8. The application of the ammonium sulfate in the cane row instead of between the cane rows has caused soil pH values to be lower in the cane row than between the rows.