INFLUENCE OF TEMPERATURE ON MINERALIZATION KINETICS WITH A NITRIFICATION INHIBITOR (MIXTURE OF DICYANDIAMIDE AND AMMONIUM THIOSULFATE)

The influence of temperature on the action of a dicyandiamide nitrific ation inhibitor was studied during a laboratory incubation after the a ddition of ammonium sulphate labelled with N-15. In the control treatm ent, nitrification was only slightly affected by temperature and was r apid; on the 42nd day, two-thirds of the N-15 was incorporated into th e nitrate fraction while no further tracer was found in ammoniacal for m. With the addition of dicyandiamide, the process was slowed down con siderably when the temperature was maintained at 10-degrees-C, and onl y about 10% of the N-15 was nitrified in 6 months. After 1 month of in cubation at 10-degrees-C, a temperature increase to 15-degrees-C for 4 weeks modified the nitrification kinetics only slightly. However, as soon as the temperature reached 20-degrees-C, the beginning of dicyand iamide decomposition and an increase in the quantity of NO3--N was obs erved. The inhibition was measured by the nitrification index, which w as greater than 80% as long as the temperature did not exceed 15-degre es-C, and decreased to 10% after 6 months; this value was reached only after 1 year in soil maintained at 10-degrees-C. The half-life of the NH4+ was decreased by raising the temperature. In the experimental co nditions described, nitrification was inhibited by the dicyandiamide f or at least 6 months provided the temperature did not exceed 15-degree s-C.