| The field experiments were carried out in a typical paddy soil of the vegetable field where vegetable had been planted for more than 20 years and winter wheat field of rice-wheat rotation systems, which is located at the center of Taihu region that belongs to the Delta of Yangtze River. The soil is classified as anthropogenic-alluvial soil which is the main soil type of that region. Research on nitrous oxide (N2O) and nitric oxide (NO) emission from dry land is to provide a theoretical foundation for nitrogen cycle of the whole land ecosystem, besides it has significant meaning to the study of global nitrogen cycle.Using static chamber- gas chromatographic techniques and a chemiluminescence NOx analyzer manufactured by Thermo Environmental Instruments Inc. USA (model 42C), N2O and NO emissions from the unfertilized vegetable field and winter wheat field of rice-wheat rotation systems were carefully monitored during the whole period of winter wheat growth. The order and mechanism of the N2O and NO emissions under the different agriculture management practices and the same climate and soil condition were analyzed, which is to provide foundation for a precise assessment of N2O and NO emissions intensity of Chinese ago-ecosystem and to provide scientific foundation for agricultural and environmental sustainable development.By means of field investigation and sample analysis, the order of seasonal variation of N2O and NO emissions from vegetable field and winter wheat field of rice-wheat rotation systems in Taihu region was clarified, and the effects and mechanisms of soil moisture, soil temperature, and available N contents on it are discussed. Meanwhile, effects of the different agriculture management practices on N2O and NO emissions were analyzed. There were three field treatment schemes involved in this experiment: the non-tillage of winter wheat field, the tillage of winter wheat field and vegetable field. Fertilizer was not applied in all field treatments during the measurement period, and each treatment had three spatial replications. The result showed that N2O and NO emissions from vegetable field and winter wheat field of rice-wheat rotation systems in southeast China had different seasonal variation rules. Over the whole period of crop growth and following fallow, net emission of N2O and NO from vegetable field and winter wheat field was observed, while net uptake of N2O occurred within some one day or a certain period; soil moisture and soil temperature were important environmental factor which influenced N2O and NO emissions; impact of the tillage on N2O emission comprised of three procedure: reducing, not significant effect, and stimulating; vegetable field is a great agricultural source for N2O emission, and the total amount of N2O emitted from vegetable field increases by about 85% comparing to non-tillage treatment and about 99%comparing to the tillage treatment during the whole period of winter wheat growth.. This difference is most likely attributed to the significantly higher available nitrogen content, especially higher ammonium content in the soil of the vegetable fields .Over the whole period of winter wheat growth, the average seasonal emission fluxes of N2O from non-tillage treatment was21+4.1|igN20-N.m"2.h'1, the total amount of seasonal emission was l.l±0.21kgN2O-N.hm'2, and the average seasonal emission fluxes of N2O from tillage treatment was 19+l.lu.gN20-N.m'2.h'1, the total amount of seasonal emission was 1.0±0.06kgN2O-N.hm"2. Whether average emission fluxes of N2O or the total amount of seasonal emission, N2O emission from non-tillage treatment was greater than that of the tillage treatment but it was not significant between the two field treatments. For long time scales, it increases N2O emission. Over the whole period of measurement, the average seasonal emission fluxes of N2O from vegetable field was 40 + 5.0u.gN20-N.m"2.h'', the total amount of N2O emission was2.1 ±0.25kgN2O-N.hm'2.It was clear that significant difference of N2O emission between vegetable field and wheat field. Over the whole period of measurement, the average seasonal emission fluxes of NO from non-tillage treatment was 6.3 + 0.27fagN.m"2.h"' , the total amount of seasonal emission was 0.31 +0.013kgN.hm~2, and the average seasonal emission fluxes of NO from tillage treatment was 5.8 + 0.48ugN.m"2.h*', the total amount of seasonal emission was 0.28 + 0.023kgN.hm'2. The average emission fluxes of NO or the total amount of seasonal emission from non-tillage treatment was slightly greater than that of tillage treatment. Over the period of effective observation measurement at vegetable field, the average emission fluxes of NO was 7.6+0.91ngN.m*2.h'', and the total amount of emission was 0.26+ 0.032kgN.hm"2.During the whole period of winter wheat growth, soil moisture was one of the important factors to regulate N2O and NO emissions. Soil moisture had the same variation trend as N2O emission in a definite range, N2O emission was observed to increase vs. soil moisture, but when the soil moisture was higher than this range, there was a negative correlation between N2O emission flux and soil moisture. In addition, the dependence of N2O on soil moisture may be described with exponential function F=Ae during the period of lettuce growth at vegetable field. Over the whole period of measurement, the relationship between NO emission and soil moisture was analyzed, the result showed that there was all evidently negative correlation between NO emission flux and soil moisture at three field treatments.Over the whole period of measurement, the relationship of seasonal variation between N2O, NO emission and soil temperature was not evident. But N2O and NO emissions would depend on soil temperature to the extent in a certain period of crop growth, the result showed that the dependence of N2O emission on soil temperature may be described with exponential function F=Aeat at non-tillage,...
|
PDF Full Text Request