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.