Zucong Cai

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earths land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500–6000 Mt CO2-eq. yr−1, with economic potentials of approximately 1500–1600, 2500–2700 and 4000–4300 Mt CO2-eq. yr−1 at carbon prices of up to 20, up to 50 and up to 100 US

Methane and nitrous oxide emissions from rice paddy fields as affected by nitrogen fertilisers and water management

t CO2-eq.−1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO2-eq. yr−1 at 0–20, 0–50 and 0–100 US

Autotrophic growth of nitrifying community in an agricultural soil

t CO2-eq.−1, respectively.

Methane emission from rice fields in China: Measurements and influencing factors

Methane and N2O emissions affected by nitrogen fertilisers were measured simultaneously in rice paddy fields under intermittent irrigation in 1994. Ammonium sulphate and urea were applied at rates of 0 (control), 100 and 300 kg N ha-1. The results showed that CH4 emission, on the average, decreased by 42 and 60% in the ammonium sulphate treatments and 7 and 14% in the urea treatments at rates of 100 and 300 kg N ha-1, respectively, compared to the control. N2O emission increased significantly with the increase in the nitrogen application rate. N2O emission was higher from ammonium sulphate treatments than from the urea treatments at the same application rate. A trade-off effect between CH4 and N2O emission was clearly observed. The N2O flux was very small when the rice paddy plots were flooded, but peaked at the beginning of the disappearance of floodwater. In contrast, the CH4 flux peaked during flooding and was significantly depressed by mid-season aeration (MSA). The results suggest that it is important to evaluate the integrative effects of water management and fertiliser application for mitigating greenhouse gas emissions in order to attenuate the greenhouse effect contributed by rice paddy fields.

Effects of nitrogen fertiliser and wheat straw application on CH4 and N2O emissions from a paddy rice field

The two-step nitrification process is an integral part of the global nitrogen cycle, and it is accomplished by distinctly different nitrifiers. By combining DNA-based stable isotope probing (SIP) and high-throughput pyrosequencing, we present the molecular evidence for autotrophic growth of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB) in agricultural soil upon ammonium fertilization. Time-course incubation of SIP microcosms indicated that the amoA genes of AOB was increasingly labeled by 13CO2 after incubation for 3, 7 and 28 days during active nitrification, whereas labeling of the AOA amoA gene was detected to a much lesser extent only after a 28-day incubation. Phylogenetic analysis of the 13C-labeled amoA and 16S rRNA genes revealed that the Nitrosospira cluster 3-like sequences dominate the active AOB community and that active AOA is affiliated with the moderately thermophilic Nitrososphaera gargensis from a hot spring. The higher relative frequency of Nitrospira-like NOB in the 13C-labeled DNA suggests that it may be more actively involved in nitrite oxidation than Nitrobacter-like NOB. Furthermore, the acetylene inhibition technique showed that 13CO2 assimilation by AOB, AOA and NOB occurs only when ammonia oxidation is not blocked, which provides strong hints for the chemolithoautotrophy of nitrifying community in complex soil environments. These results show that the microbial community of AOB and NOB dominates the nitrification process in the agricultural soil tested.

Measurements of CH4 and N20 emissions from rice paddies in Fengqiu, China

Methane emissions from rice fields in China were measured at eight sites in five provinces under conditions representative of local practices for rice cultivation. Methane emission rates during the rice growth period varied greatly from site to site and with treatments at the same site, ranging from 0.3 to 205 g CH4/m2. Flooded or waterlogged rice fields in the nonrice growth season continuously emitted CH4 substantially. The average CH4 emission rate from a rice field in Chongqing was as high as 36.2 g CH4/m2 in the nonrice growing season. Furthermore, flooding in the nonrice growth season also significantly stimulated CH4 emission during the rice growth period in the next year. Increases in the rate of CH4 flux after rice transplanting were less when the number of consecutive upland crops grown before rice transplanting was greater. CH4 emissions from rice fields located on downslope was larger than from those on midslope and upslope in hilly areas due to poor drainage of the former. Application of rice straw in fall when winter wheat was sown did not increase CH4 emission significantly during the following rice growth period. CH4 emission was depressed by the application of ammonium sulfate but was, in general, not significantly affected by urea application.

Effects of nitrogen fertilization on CH4 emissions from rice fields

A 3-year field experiment was conducted to study the effects of nitrogen fertiliser and straw application on CH4 and N2O emissions from a paddy rice field in China from 2003 to 2005. Three rates of nitrogen fertiliser (0, 200, and 270 kg N/ha) and 2 levels of wheat straw (0 and 3.75 × 10 3 kg/ha) were adopted in this experiment. The effect of nitrogen fertiliser application on CH4 emission seemed to be affected by application rate. Nitrogen fertiliser decreased CH4 emission relative to the control when applied at a rate of 200 kg N/ha, but the effect lessened if the application rate was further increased to a rate of 270 kg N/ha. The depressive effect of nitrogen fertiliser application on CH4 emissions from rice fields became more pronounced when wheat straw was also incorporated with fertiliser, compared with nitrogen fertiliser application alone. Straw incorporation significantly enhanced CH4 emission by 3-11 times (P 0.05). More than 50% of seasonal total amount of N2O was emitted within 11 days after fertiliser application at panicle initiation. The global warming potential caused by both CH4 and N2O emissions was affected by nitrogen fertiliser application rate and significantly stimulated by wheat straw incorporation. The global warming potential was lowest when nitrogen fertiliser was applied at a rate of 200 kg N/ha. Additional keyword: GWP.

Key factors affecting spatial variation of methane emissions from freshwater marshes.

Abstract Methane emissions were measured by a closed chamber method in rice plots with sandy, loamy, and clayey soil, respectively, under a water regime consisting of a flooding and draining cycle in Fengqiu, Henan Province, China in 1993 and 1994. Nitrous oxide emissions were measured for every two measurements of CH4 flux in 1994. The results showed that CH4 emissions were low compared with those recorded in previous reports and the means of CH4 fluxes ranged from 0.16 to 1.86 mg CH4 m-2 h-1 in the growing season (108 d). The lowest mean flux of CH4 was observed in the clayey plot in both years. Statistically, soil temperature and soil Eh at 5 em depth significantly affected the fluctuations of the CH4 flux measured in the morning and afternoon, but they were not the main factors controlling the seasonal variation of the CH. flux. Flooding and draining cycle, as well as high rate of water percolation and low organic matter content of the soils resulted in low emissions of CH4. In contrast, the studied p...

Nitrification of archaeal ammonia oxidizers in acid soils is supported by hydrolysis of urea

Abstract Nitrogen fertilization is essential for achieving high rice yields and is widely practiced in rice cultivation. There is an ongoing discussion on the possible effects of N application on CH4 emission from rice fields. CH4 emission is a net consequence of CH4 production, oxidation and transport from the soil in which the CH4 is produced to the atmosphere, and the interactions among these processes. Nitrogen influences all the processes of CH4 emission from rice fields either directly or indirectly and the effects are either negative or positive at the ecosystem, microbial and biochemical level. Because of this complexity and counter-balance among the effects, it is difficult to assess the net N effect on CH4 emissions from rice fields on a national or global scale. Field measurements also show a contradiction in that positive, negative and no effects of N application on CH4 emissions have been observed. Nevertheless, it is clear that the effect of N application on CH4 emission is N-form dependent. Nitrate-based fertilizers are able to mitigate CH4 emission, but they are rarely applied to rice fields and generally not practicable to mitigate CH4 emission because of their low use efficiency and stimulatory effect on N2O emission. In contrast, the application of organic N stimulates CH4 emission because additional organic carbon is supplied for CH4 production. However, it is not sufficient to conclude that CH4 emission intensity would have been decreased by the replacement of organic N, which dominated traditional rice cultivations, with chemical N fertilizers, which are used in current rice cultivations, because the fertilizer replacement has also enhanced rice yields, which in turn affects CH4 production, oxidation and transport. Establishing quantitative relationships between N status in soil and CH4 production, oxidation and transport is essential to assess the effects of chemical N fertilizer application on CH4 emissions from rice fields.

Mechanisms for the retention of inorganic N in acidic forest soils of southern China

To understand the mechanism for spatial variation of CH(4) emissions from marshes grown with different type of plants in a region and plots within a certain marsh grown with one type of plants, we measured CH(4) emissions from a region in which eutrophic freshwater marshes were divided into three types: Carex lasiocarpa, Carex meyeruana and Deyeuxia angustifolia according to plant type as well as CH(4) concentration in porewater, aboveground plant biomass and stem density in situ in Sanjiang Plain of Northeast China in August 2001. Spatial variation of CH(4) emissions from both different marshes in a region and different plots within a certain marsh was high. The flux rates of CH(4) emissions from three marshes ranged from 17.2 to 66.5 mg CH(4) m(-2)h(-1) with 34.76% of variation coefficient, whereas the values in Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia marshes varied from 21.6 to 66.5 (39.61%), from 17.2 to 45.0 (29.26%) and from 19.1 to 33.0 mg CH(4) m(-2)h(-1) (17.51%), respectively. Both the flux rates and spatial variation of CH(4) emissions strongly increased as standing water depth increased significantly. Standing water depth greatly governed the spatial variation of CH(4) emissions from different marshes in a region by changing the amount of plant litters inundated in standing water, which provided labile organic C for methanogens and controlled CH(4) concentrations in porewater. Moreover, the aboveground plant biomass determined spatial variation of CH(4) emissions from plots within a certain marsh by controlling the pathways (stem density) of CH(4) emissions from the marsh into the atmosphere.