Effects of soil type and nitrate concentration on denitrification products (N₂O and N₂) under flooded conditions in laboratory microcosms

Figures & data

Table 1 Selected properties of soils used.

Parameter	PV	MV	PJ
pH (1:5)	5.8	4.3	7.0
EC (mS m^−1)	5.9	77.0	7.1
Particle size distribution(%)
Clay	22	16	7
Silt	42	25	16
Sand	36	59	77
NO3^–-N (mg kg^−1)	n.d.	n.d.	n.d.
NH4^+-N (mg kg^−1)	30.1	12.3	1.4
DOC (mg kg^−1)	102.5	83.8	97.5
TC (g kg^−1)	10.4	6.3	7.9
TN (g kg^−1)	1.2	0.6	0.8
C:N ratio	8.9	9.9	10.4
CEC (cmolc kg^−1)	6.8	5.6	8.0
Density of denitrifying bacteria (MPN g^−1)	0.14 × 10^4	0.12 × 10^4	2.7 × 10^4

PV = paddy soil from Vietnam; MV = mangrove soil from Vietnam; PJ = paddy soil from Ushimado, Japan; n.d. = not detected. The density of denitrifying bacteria was measured by the most probable number method. EC, electrical conductivity; NH₄⁺-N, ammonium-nitrogen; NO₃^–-N, nitrate-nitrogen; DOC, dissolved organic carbon; TC, total carbon; TN, total nitrogen; CEC, cation exchange capacity.

Table 2 Change of NO₃^– (mg N kg⁻¹)^† after 7 d incubation with acetylene at 25°C.

NO3^–	PV			MV			PJ
mg N kg^–1	Day 0	Day 7	NO3^– removal	Day 0	Day 7	NO3^– removal	Day 0	Day 7	NO3^– removal
0.0	0.0	0.0 ± 0.0	0.0	0.0	0.0 ± 0.0	0.0	0.0	0.0 ± 0.0	0.0
63.4	65.9	7.7 ± 8.1	58.2	66.5	62.8 ± 0.9	3.7	66.1	7.3 ± 4.4	58.8
126.5	131.4	78.9 ± 14.4	52.5	135.1	127.6 ± 0.4	7.5	132.0	35.9 ± 12.3	96.1

Data are the mean ± standard deviation, n = 3. ^†NO₃^– concentrations (mg N L^–1) in solutions were converted to NO₃^– (mg N kg^–1). Nitrate removal, difference in NO₃^– concentrations in solution between days 0 and 7; PV, paddy soil from Vietnam; MV, mangrove soil from Vietnam; PJ, paddy soil from Japan.

Figure 1 Accumulated nitrous oxide (N₂O) emissions (mg N kg^–1) in (a) PV, (b) MV, and (c) PJ soils and nitrogen (N₂) emissions (mg N kg^–1) in (d) PV, (e) MV, and (f) PJ soils during 7 d incubation at 25°C. Bars indicate standard deviation, n = 3. Note: N₂O emission (mg N kg^–1) was measured in the incubation bottle without acetylene (C₂H₂). N₂ emission (mg N kg^–1) was calculated by the differences in N₂O emissions during 7 d incubation with and without C₂H₂. PV, paddy soil from Vietnam; MV, mangrove soil from Vietnam; PJ, paddy soil from Japan.

Figure 2 Relationship between nitrate (NO₃^–) removal (x-axis) and denitrification (y-axis) in MV soil (triangles), PV soil (squares) and PJ soil (circles) on day 7 at 25°C. Bars indicate standard deviation, n = 3.