Effects of water regimes on soil N2O, CH4 and CO2 emissions following addition of dicyandiamide and N fertilizer.

Water regimes strongly impact soil C and N cycling and the associated greenhouse gases (GHGs, i.e., CO2, CH4 and N2O). Therefore, a study was conducted to examine the impacts of flooding-drying of soil along with application of nitrogen (N) fertilizer and nitrification inhibitor dicyandiamide (DCD) on GHGs emissions. This study comprised four experimental treatments, including (i) control (CK), (ii) dicyandiamide, 20 mg kg-1 (DCD), (iii) nitrogen fertilizer, 300 mg kg-1 (N) and (iv) DCD + N. All experimental treatments were kept under flooded condition at the onset of the experiment, and then converted to 60% water filled pore space (WFPS). At flooding stage, N2O emissions were lower as compared to 60% WFPS. The highest cumulative N2O emission was 0.98 mg N2O-N kg-1 in N treated soil due to high substrates of mineral N contents, but lowest (0.009 mg N2O-N kg-1) in the DCD treatment. The highest cumulative CH4 emissions (80.54 mg CH4-C kg-1) were observed in the N treatment, while uptake of CH4 was observed in the DCD treatment. As flooded condition converted to 60% WFPS, CO2 emissions gradually increased in all experimental treatments, but the maximum cumulative CO2 emission was 477.44 mg kg-1 in the DCD + N treatment. The maximum dissolved organic carbon (DOC) contents were observed in N and DCD + N treatments with the values of 57.12 and 58.92 mg kg-1, respectively. Microbial biomass carbon (MBC) contents were higher at flooding while lower at transition phase, and increased at the initiation of 60% WFPS stage. However, MBC contents declined at the later stage of 60% WFPS. The maximum MBC contents were 202.12 and 192.41 mg kg-1 in N and DCD + N treatments, respectively. Results demonstrated that water regimes exerted a dramatic impact on C and N dynamics, subsequently GHGs, which were highly controlled by DCD at both flooding and 60% WFPS conditions.

Reduction in soil N2O emissions by pH manipulation and enhanced nosZ gene transcription under different water regimes.

Several studies have been carried out to examine nitrous oxide (N2O) emissions from agricultural soils in the past. However, the emissions of N2O particularly during amelioration of acidic soils have been rarely studied. We carried out the present study using a rice-rapeseed rotation soil (pH 5.44) that was amended with dolomite (0, 1 and 2 g kg-1 soil) under 60% water filled pore space (WFPS) and flooding. N2O emissions and several soil properties (pH, NH4+N, NO3--N, and nosZ gene transcripts) were measured throughout the study. The increase in soil pH with dolomite application triggered soil N transformation and transcripts of nosZ gene controlling N2O emissions under both water regimes (60% WFPS and flooding). The 60% WFPS produced higher soil N2O emissions than that of flooding, and dolomite largely reduced N2O emissions at higher pH under both water regimes through enhanced transcription of nosZ gene. The results suggest that ameliorating soil acidity with dolomite can substantially mitigate N2O emissions through promoting nosZ gene transcription.

Influence of ameliorating soil acidity with dolomite on the priming of soil C content and CO2 emission.

Lime or dolomite is commonly implemented to ameliorate soil acidity. However, the impact of dolomite on CO2 emissions from acidic soils is largely unknown. A 53-day laboratory study was carried out to investigate CO2 emissions by applying dolomite to an acidic Acrisol (rice-rapeseed rotation [RR soil]) and a Ferralsol (rice-fallow/flooded rotation [RF soil]). Dolomite was dosed at 0, 0.5, and 1.5 g 100 g-1 soil, herein referred to as CK, L, and H, respectively. The soil pH(H2O) increased from 5.25 to 7.03 and 7.62 in L and H treatments of the RR soil and from 5.52 to 7.27 and 7.77 in L and H treatments of the RF soil, respectively. Dolomite application significantly (p ≤ 0.001) increased CO2 emissions in both RR and RF soils, with higher emissions in H as compared to L dose of dolomite. The cumulative CO2 emissions with H dose of dolomite were greater 136% in the RR soil and 149% in the RF soil as compared to CK, respectively. Dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased and reached at 193 and 431 mg kg-1 in the RR soil and 244 and 481 mg kg-1 in the RF soil by H treatments. The NH4--N and NO3--N were also increased by dolomite application. The increase in C and N contents stimulated microbial activities and therefore higher respiration in dolomite-treated soil as compared to untreated. The results suggest that CO2 release in dolomite-treated soils was due to the priming of soil C content rather than chemical reactions.