Effects of 4-amino 1,2,4 triazole, dicyandiamide and encapsulated calcium carbide on nitrification inhibition in a subtropical soil under upland and flooded conditions

Nitrification inhibition of soil and applied fertilizer N is desirable as t he accumulation of nitrates in soils in excess of plant needs leads to enha nced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibito rs (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commo nly available and economical material, encapsulated calcium carbide (CaC2) (ECC) on the nitrification of soil and applied NH4+-N in a semiarid subtrop ical Tolewal sandy loam soil under upland [60% water-filled pore space (WFP S)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH4+-N kg(-1) soil under upland conditions was retarded most effectively ( 93%) by ECC for up to 10 days of incubation, whereas for longer periods, AT C was more effective. After 20 days, only 16% of applied NH4+-N was nitrifi ed with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soi l conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effec tiveness, namely, concentration of NH4+-N and NO3-N, percent nitrification inhibition, ratio of NH4+-N/NO3--N, and total mineral N, ECC showed the hig hest relative efficiency throughout the 20-day incubation under flooded soi l conditions. At the end of the 20-day incubation, 96%, 58% and 38% of appl ied NH4+-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results sugge st that for reducing the nitrification rate and resultant N losses in flood ed soil systems (e.g. rice lowlands), ECC is more effective than costly com mercial NIs.