Xu Junzeng

Organic carbon content and its liable components in paddy soil under water-saving irrigation

Ma Y., Xu J.Z., Wei Q., Yang S.H., Liao L.X., Chen S.Y., Liao Q. (2017): Organic carbon content and its liable components in paddy soil under water-saving irrigation. Plant Soil Environ., 63: 125–130. Variation of soil organic carbon (SOC) and its liable fractions under non-flooding irrigation (NFI) were investigated. In NFI paddies, the soil microbial biomass carbon (SMBC) and water extractable organic carbon (SWEC) content in 0–40 cm soil increased by 1.73–21.74% and 1.44–30.63%, and SOC in NFI fields decreased by 0.90–18.14% than in flooding irrigation (FI) fields. As a result, the proportion of SMBC or SWEC to SOC increased remarkably. It is attributed to the different water and aeration conditions between FI and NFI irrigation. The non-flooding water-saving irrigation increased soil microbial activity and mineralization of SOC, which broke down more soil organic nutrients into soluble proportion and is beneficial for soil fertility, but might lead to more CO2 emission and degradation in carbon sequestration than FI paddies.

Influence mechanism of controlled irrigation on N 2 O emissions from paddy fields

In order to study the effects of controlled irrigation (CI) on seasonal variations of N 2 O emissions from paddy fields, N 2 O emissions from CI paddy fields were investigated by the method of static chamber/gas chromatography. Soil moisture, soil temperature and soil redox potential ( Eh ) were also measured. The quantitative relationships between N 2 O emissions and affecting factors were analysed. Soil drying incurred substantial N 2 O emissions, while no substantial N 2 O emission was observed after the soil was re-wetted following the drying phase. The peaks of N 2 O emissions from the CI paddy fields were all observed 8-10 days after soil drying with the WFPS ranging from 78.1% to 85.3%. However, no significant correlation was found between soil temperature and N 2 O emissions ( p > 0.05), indicating that soil temperature is not a critical factor in N 2 O emission. N 2 O peaks were observed at soil Eh values ranging from +207.5 to +275.2 mV in CI paddy fields. No significant N 2 O emission occurred at Eh values higher than +300 mV or lower than +120 mV. These results suggest that N 2 O emissions may be reduced obviously by keeping the WFPS higher than 83.5% after each fertilizer application.

Nitrogen Wet Deposition and Its Correlation with Ammonia Volatilization Losses from Rice Paddy during Crop Period: A Case Study in Taihu Lake Region

Atmospheric nitrogen deposition is one of the most important sources of nitrogen for surface water and eco-system. Ammonia volatilization is one of the most loss of nitrogen from rice paddy field and sources of atmospheric nitrogen. In order to quantify the nitrogen wet deposition and its correlation with ammonia volatilization losses from rice paddy during rice growth season, field experiments were carried out in high nitrogen input rice paddy in Taihu Lake region. Total wet deposition of total nitrogen, ammonia nitrogen and nitrate nitrogen are 16.04kg•hm-2, 7.40kg•hm-2 and 3.39kg•hm-2 in rice growth season. It equals to 37.7kg•hm-2 urea inputs to rice paddy and takes 3835t total nitrogen, 1730t ammonia and 793t nitrate into surface water of Taihu lake. Seasonal ammonia volatilization is estimated to be 95.21kg•hm-2, account for 23.6% of seasonal total nitrogen inputs. Urea applications leads to the sharply increase in ammonia volatilization, more than 90% ammonia volatilization emission occurs within one week after urea fertilization. Ammonia and total nitrogen contents in rainfall water are likely relevant to the fertilizer management, but ammonia and total nitrogen were determined both by the precipitation volumes and the nitrogen fertilizer management. Total nitrogen and ammonia nitrogen contents in rainfall water are confirmed high relative to synchronous three-day ammonia volatilization, but not nitrogen wet deposition. Controlled-release urea reduced seasonal ammonia volatilization to 28.97 kg•hm-2, it is reduced by 69.6% when compared with traditional urea. Widely application of controlled-release urea is efficient to cut off the ammonia volatilization and hence the nitrogen wet deposition.