[show abstract][hide abstract] ABSTRACT: To quantitatively assess the effects of agricultural practices on methane (CH4) emissions from rice fields, a two-year (2005/2006) field experiment with 23 factorial designs was conducted to assess the effects of three driving factors on CH4 emissions in South China: continuously flooded (W0) and mid-season and final drainages (W2), straw (S1) and nitrogen fertilizer (N1) applications and their controls (S0, N0). Results showed that averaged across all the treatments about 75 % of the seasonal total CH4 occurred between the rice transplanting and booting stage, while constituted only 33 % of the seasonal total rice biomass during the same period. Averaged across the treatments in 2006, CH4 emissions were substantially decreased by mid-season drainage up to 60 % (15.6 vs. 39.0 g m−2). The decreased CH4 emissions represented almost all of the decrease in the total global warming potentials. Without straw incorporation CH4 emissions substantially decreased up to 59 % (15.9 vs. 38.7 g m−2). The stimulating effects of straw were significantly greater for W0 than W2 treatment, being also greater in the 2005 than in the 2006 season. A significant inter-annual difference in CH4 emissions was found when averaged across straw incorporation and N fertilizer applications for the W2 treatment (42.8 and 15.4 g m−2 in 2005 and 2006, respectively). Moreover, N fertilization has no significant effect on CH4 emissions in this study. Our results demonstrate that although straw effects varied greatly with specific management, both straw managements and water regimes are equally important driving factors and thus being the most promising measures attenuating CH4 emissions while achieving sustainable rice production.
Nutrient Cycling in Agroecosystems 05/2012; 93(1-10.1007/s10705-012-9503-3):103-112. · 1.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: Two-year (June 2003–May 2005) precipitation samples were collected from three monitoring sites with similar economy development
level in the Yangtze River Delta Region of China to investigate the spatial–temporal variation of inorganic N wet deposition.
The results showed that the Yangtze River Delta Region had higher inorganic N wet deposition than the northwestern, northern,
or southern China. There was spatial variation of inorganic N wet deposition. The positive relationship between inorganic
N deposition and precipitation suggested that rainfall amount might be an important factor influencing the wet deposition
of inorganic N. Deposition of inorganic N occurred mainly in the spring and summer season (March–August; 70% of the annual
total), which was in accord with seasonal distribution of precipitation. However, a negative logarithmic relation between
rainfall and inorganic N concentration in rainwater indicated the dilution effect of rainwater on inorganic N concentration.
Distinguished variation of NH4
− ratio in wet deposition existed in the different time scale. NH4
− ratio evidently decreased from 6 in 1980s to 1.2 in 2003/2005 and greatly varied between 0.3 and 9.9 within a year. NH4
− ratio peaked in accordance with nitrogen-fertilizing time during crop growing season. Annual alternate appearance of the
15N-enriched and 15N-depleted periods coincided with the temporal variation of NH4
− ratio, which was closely related to the timing of fertilization and seasonal climate changes, suggesting the effect of NH4
+ sources in the wet deposition.
Water Air and Soil Pollution 04/2012; 203(1):277-289. · 1.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: The main research results of nitrous oxide (N2O) emission from paddy fields in China were summarized. Paddy fields are an important source of N2O emission. Denitrification process exists not only in the upper flooded cultivated layer in paddy fields but also in the underground saturated soil layer. The cropping system with rice–wheat rotation and the water regime with mid-season aeration (MSA) in paddy fields of China are not only the controlling factors of N2O emission but also the main factors influencing methane (CH4) emission. There is a trade-off relationship between N2O and CH4 emissions from paddy fields. Straw amendment reduced N2O emission but promoted CH4 emission. Therefore, effects of both CH4 and N2O emissions from rice fields on the global warming potential (GWP) should be taken into consideration when any mitigation options are to be established.
[show abstract][hide abstract] ABSTRACT: Nitrogen (N) in wet deposition can provide significant nutrients to algae, which potentially contributes to eutrophication in waterbodies, and to nutrient surplus of rice–wheat crops in the Tai lake region, Jiangsu Province, China. Quantifying the N compounds in wet deposition and determining their sources is important to understand how to control eutrophication in lakes and to improve recommendations for fertilizer use. In this study, the concentrations of inorganic N, molar ratios of NH4+/NO3− and the natural 15N abundance of NH4+ (δ15NH4+) in wet deposition were determined for 78 precipitation events between June 2003 and July 2005. Samples were collected at two sites in Tai lake region, a watershed rice agroecosystem currently experiencing eutrophication. The average N wet deposition amounted to 27 kg N ha−1 yr−1, with 60% in the form of NH4+. Annually, two cycles of depleted and enriched δ15NH4+ indicate the shifting of main source of NH3 volatilization between chemical fertilizer and excreta of local residents and domestic animals, surface waters, and other organic N. The peak in NH4+/NO3− ratio, coupled with depleted δ15NH4+ in mid-June, coincided with the rice-transplanting period, which is indicative of surplus fertilizer application. Enriched δ15NH4+ values in August–October and in April–May were indicative of enhanced emissions from excreta and polluted waterbodies in the warmer seasons. Findings suggest that δ15NH4+ could be used to indicate the sources of NH3 volatilization, and the NH4+/NO3− ratio to indicate the intensity of wet N deposition.
[show abstract][hide abstract] ABSTRACT: Nitrous oxide (N2O) emissions resulting from Chinese vegetable production were measured. A site in suburban Nanjing (East coast; Jiangsu Province) was monitored from November 2001 to January 2003, in which five consecutive vegetable crops were sown. The crops consisted of radish, baby bok choy, lettuce, second planting of baby bok choy, and finally celery. Results suggested that N2O emission events occur in pulses. The average N2O-N flux for all five crops was 148±9μgNm−2h−1 and the average emission rate was 12±0.7kgNha−1. The average seasonal emission fluxes ranged from 37μgNm−2h−1 in the radish plot to 300μgNm−2h−1 in the celery plot. The celery field produced the greatest cumulative emission of 5.8kgNha−1 while the baby bok choy field had the lowest rate of 0.96–1.0kgNha−1. In total, 0.73% of applied fertilizer N was emitted as N2O-N as a whole. The lettuce field had the largest emission factor of 2.2%. Results indicate that emissions from vegetable field are a potential source of national N2O inventory.Temporal variation is much greater than spatial variation and the corresponding CV averaged 115% and 22%, respectively. Under the same total sampling quantity, increasing sampling frequency is more important than increasing spatial replicates.