Inhibiting Effect of Dicyandiamide on Soil Acidification Induced by Application of Urea or Ammonium Bicarbonate

Heavy applications of ammonium-based fertilizers greatly accelerated the acidification of agricultural soils in southern China. The effects of dicyandiamide on soil pH and contents of ammonium nitrogen (NH4+-N) and [nitrate (NO3-) + nitrite (NO2-)-N] were investigated with incubation experiments to evaluate the inhibiting effect of dicyandiamide on soil acidification induced by ammonium-based fertilizers. Results showed application of urea or ammonium bicarbonate increased the pH of an acidic soil at the beginning of incubation, whereas nitrification led to a decrease in soil pH in the later stages. Dicyandiamide elevated soil pH through inhibition of nitrification. At the end of an 85-day incubation, soil pH was 1.30 and 2.20 units greater than the unfertilized sample, and 0.66 and 1.56 units greater if dicyandiamide was added with either 14.29 or 28.57 mmol N kg(-1) of urea. Similar results occurred for ammonium bicarbonate. Therefore, application of urea or ammonium bicarbonate with dicyandiamide reduced the soil acidification caused by ammonium-based fertilizers.