Dicyandiamide effects on nitrification and total inorganic soil nitrogen in sandy soils

Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO3‐N) to ammonium‐nitrogen (NH4‐N). If the conditions for NO3‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH4‐N + NO3‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH4NO3) at 67, 134, and 202 kg N ha‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha‐1. Soil NH4‐N, NO3‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO3‐N/(NH4‐N + NO3‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH4‐N.