*2.3. Collection and Measurement of Emitted CO2 and N2O*

The rate of CO2 and N2O emissions was calculated by measuring the concentration of these gases from each pot at different times. The CO2 and N2O samples were collected once a day during the first week, once after two days during the second week, and once after three days during the rest of the incubation period. For sampling, the pots were closed first and then gas samples were collected at 0, 20, 40 and 60 min. A 10-mL syringe with a hypodermic needle was used to collect the gas samples. The gas samples were stored in pre-evacuated Chromacol glass vials with chloro-butyl rubber lids that prevent the leakage of gas samples. Each gas sampling was carried out between 09:00 and 11:00 am. Except for the times when gas samples were collected, the pots were left open.

The concentrations of CO2 and N2O in the gas samples were measured by gas chromatograph (Agilent 7890A GC, Agilent, CA, USA). The rate of CO2 and N2O emissions from each pot (ppm/min) during lid closure was calculated using headspace volume of the pot and a linear relation between CO2 and N2O concentrations and time [19]. The flux of CO2-C (μg h−<sup>1</sup> kg<sup>−</sup>1) and N2O-N (ng h−<sup>1</sup> kg<sup>−</sup>1) was calculated with the following equation:

$$\text{EN}\_2\text{O-N} = \frac{R \times 60 \times V\_{\text{gas}} \times AR}{W\_{\text{soil}} \times V\_{\text{m}}} \times 2 \times 1000 \tag{1}$$

$$\text{ECO}\_2\text{-C} = \frac{R \times 60 \times V\_{\text{gas}} \times AR}{W\_{\text{soil}} \times V\_{\text{m}}} \tag{2}$$

where ECO2/N2O is the flux of CO2-C (μg h−<sup>1</sup> kg−1) and N2O-N (ng h−<sup>1</sup> kg−1), *R* is the rate of CO2 and N2O emissions from each pot (ppm/min), *Vgas* is the gas volume in pot

(L), *Wsoil* is the weight of dry soil in pot (kg), *AR* is the relative atomic mass of C and N, i.e., 12 and 14, respectively, and Vm is the molar volume of gas which is 23.7 L/mol at 15 ◦C. Total CO2 and N2O emissions during the experimental period were calculated from the daily emissions of the gases. The relative lowering of total N2O emission (%) from NI-treated soils as compared to control was regarded as the efficiency of NIs.

#### *2.4. Analysis of NH4 <sup>+</sup> and NO3* − *in Soil*

Soil samples (0–20 cm depth) were collected from the pots on day 1, 15, 29, 43 and 57 of incubation for the measurement of NH4 <sup>+</sup> and NO3 − concentration. Each soil sample was divided into two subsamples; one was oven-dried at 105 ◦C for 8 h to calculate water content while the other was used for determination of NH4 <sup>+</sup> and NO3 −. For the analysis of soil mineral N, 10 g of fresh soil was mixed with 40 mL of 0.0125 *M* CaCl2 solution (1:4) and shaken for 1 h. After centrifugation for 10 min, the extracts were filtered through Whatman filter paper No. 40 and stored at 4 ◦C. The extracts were analyzed for NH4 <sup>+</sup> and NO3 <sup>−</sup> concentrations using a continuous flow analyzer (San++ Automated Wet Chemistry Analyzer—Continuous Flow Analyzer (CFA), Skalar, The Netherlands).
