Direct and indirect nitrous oxide emissions with application of nitrification inhibitor and plant growth regulator in a calcareous soil 

Numerous studies have shown that nitrification inhibitors (NIs) are an effective tool to reduce direct N2O emissions. However, some studies have showed the positive effect of NIs on ammonia volatilization and increase the indirect N2O emission from AV. This study aimed to investigate the effect of nitrapyrin (NP) as a NI and gibberellic acid (GA3) as a plant growth regulator (PGR) on direct and indirect N2O emissions. A randomized complete block design including three treatments and five replicates was used in this study. The treatments were: T1 (control treatment-without N fertilizer), T2 (Urea only), and T3 (Urea+NI+GA3). Urea was applied in three split applications. GA3 was foliar sprayed only at stem elongation stage. NP and GA3 were applied at a rate of 0.51% and 0.03% of the applied N (weight/weight), respectively. Ammonia volatilization was measured with semi-static chambers and direct N2O emission was measured with static chambers. Cumulative N2O was 1.45 ± 0.13 and 1.11 ± 0.10 (kg N2O-N ha-1) in urea alone and urea in combination of NP+GA3. The estimated values of indirect N2O-N produced from AV in urea and urea+NP + GA3  were 0.38 and 0.45 kg N ha− 1, respectively. The results showed that the indirect N2O emission from the ammonia path in this type of soil which has high pH cannot be ignored and should be included in the net emission. Also, the results showed that the increase in the indirect emission of N2O from ammonia path induced by NP is negligible.