Qi-an Peng

Nitrous oxide emission from two acidic soils as affected by dolomite application

The effect of dolomite (CaMg(CO3)2) application on nitrous oxide (N2O) emission was examined in a laboratory study with soil from a rice paddy–rapeseed rotation (PR soil, pH 5.25) and from a rice paddy–fallow–flooded rotation soil (PF soil, pH 5.52). The soils were treated with 0, 0.5 (L) and 1.5 (H) g dolomite 100 g–1 soil. Results showed that N2O emissions were higher in control treatments (untreated dolomite) in both soils. Application of dolomite decreased N2O emissions significantly (P ≤ 0.001) as soil pH increased in both soils. The H treatment was more effective than the L treatment for the reduction of N2O emissions. The H treatment decreased the cumulative N2O emissions by up to 73.77% in PR soil and 64.07% in PF soil compared with the control. The application of dolomite also affected concentrations of dissolved organic carbon, microbial biomass carbon, ammonium and nitrate in soils, which related to N2O emission. The results suggest that dolomite not only counteracts soil acidification but also has the potential to mitigate N2O emissions in acidic soils.

Effects of soluble organic carbon addition on CH4 and CO2 emissions from paddy soils regulated by iron reduction processes

An incubation experiment with the addition of glucose was conducted to evaluate the effects of carbon and iron (Fe(III)) reduction on methane (CH4) and carbon dioxide (CO2) emissions from paddy soils. Soils of a rice–rapeseed (Brassica napus) rotation and rice–fallow/flooded rotation were collected from Qianjiang (QR and QF, respectively) and Xianning (XR and XF). Incubation was conducted under flooding at 25°C ± 1°C with or without (CK) glucose over 40 days. With glucose addition, cumulative CH4-C emissions from QR, QF, XR and XF soils were 5.31, 35.26, 13.92 and 27.58 mg kg–1, respectively, and cumulative CO2-C emissions were 594.33, 620.49, 549.42 and 792.46 mg kg–1. Compared with CK, glucose addition significantly (P < 0.05) increased cumulative CH4 fluxes in QR and QF soils 11.07-fold and 1.39-fold, respectively, and cumulative CO2 fluxes 0.41-fold and 0.44-fold, whereas the effects of glucose addition on CH4 and CO2 fluxes in XR and XF soils were negligible. In addition, the soil Fe(II)/(Fe(II) + Fe(III)) fraction correlated positively with CH4 fluxes during the major emission period (P < 0.05), and the Fe(II) production rate was positively correlated with the CO2 flux during the whole incubation period. Furthermore, Fe(III) reduction strongly competed with CH4 emission, especially in XR and XF soils, which derived from quaternary red clay. The results suggest that Fe(III) reduction plays a key role in mediating the carbon cycle of paddy soils.

Changes in the soil N potential mineralization and nitrification in a rice paddy after 20 yr application of chemical fertilizers and organic matter

Abstract: The effect of long-term (20 yr) fertilizer application on soil nitrogen (N) transformation in paddy soils was studied at three sites (Xinhua, Ningxiang, and Taojiang) in Hunan province, China. Four fertilization practices were chosen: chemical fertilizers (NPK), chemical fertilizers plus a medium or high amount of pig manure (MM + NPK), chemical fertilizers plus a high amount of pig manure (HM + NPK), and chemical fertilizers plus straw incorporated (Str. + NPK). A treatment with no fertilization was included as a control (CK). Ten week aerobic incubations were conducted to determine N potential mineralization and nitrification. Application of organic plus chemical fertilizer increased soil organic carbon, total nitrogen, and microbial biomass carbon (Cmic) and nitrogen (Nmic), whereas the response of Cmic/Nmic ratio to fertilizer application varied among sites. Across all sites, the HM + NPK treatments had the highest potentially mineralizable N and maximal nitrification rate, and the CK had the lowest. The MM + NPK, Str. + NPK, and NPK treatments had lesser effects on mineralizable N and nitrification. Results indicated that chemical fertilizer along with a high rate of manure application is an effective method to improve available soil N by increasing the N mineralization rate. However, higher N nitrification was also induced by manure application, which may lead to increased N losses, and also should be considered in practical applications.

Reduction in soil N 2 O 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.