| Plastic film mulching cultivation is a revolutionary farming technology, which is widely used to improve soil conditions and crop yields. Moreover, N2O is an important greenhouse gas mainly coming from agriculture. The properties of farmland soil, such as soil moisture, temperature, microorganism and nutrients, were changed by film mulching, which would affect the production, transmission and emission of soil N2O. In this study, the common croping system（chili-radish rotation） in Southwestern China was selected as the research object, to explore the effects of cropland ecosystem on N2O emissions under film mulching and nitrogen application levels, and the effects on daily N2O emissions, N2O emissions pathes and N2O concentrations of different soil depth for film mulching. Meanwhile, to acknowledg the effects on soil environment of film mulching, the physical and chemical properties and active components of soil were monitored between mulching and non-mulching farmland. The correlation analysis, principal component analysis, stepwise regression analysis and path analysis, between the soil factors and soil N2O emissions, were applied to explain the N2O emission mechanism of mulching and non-mulching field, hoping to provide a theoretical basis for China’s farmland greenhouse gas emission reduction and improving the nitrogen fixing potential of soil and scientific supports for China’s environmental diplomacy. Results are displayed as follows:1. Effects of film mulching on N2O emission from farmland ecosystem（1） The average N2O emission fluxes were mulching（820.84μg·m-2h-1）< non-mulching（891.09μg·m-2h-1） under high nitrogen conditions; Common and low nitrogen condition were mulching（219.95、234.78μg·m-2h-1）< non-mulching（468.74、188.17μg·m-2h-1）, All were significantly higher than no nitrogen control, routine: 44.67μg·m-2h-1, film: 56.78μg·m-2h-1（P>0.05）. During the whole growing period, the peak of N2O emission were observed both in mulching and conventional field after fertilization or continuous precipitation. The N2O emissions in the pepper season were always higher than in the radish season.（2） During the pepper season, N2O emission coefficients of mulching and non-mulching farmland and nitrogen contribution rate of non-mulching farmland reached maximum, respectively 0.11%, 0.12% and 52.19%; the nitrogen contribution rate of mulching farmland was the biggest（57.14%） under normal nitrogen conditions; In radish season, N2O emission coefficients and nitrogen contribution rate of mulching and non-mulching farmland reached maximum, respectively 0.04% and 0.01%, 77.28% and 68.51%.（3） During pepper season,cumulative N2O emissions of low nitrogen conditions（film: 1.69 kg·hm-2, routine: 2.09 kg·hm-2） and normal nitrogen conditions（film: 1.32 kg·hm-2, routine: 3.11 kg·hm-2） reached peak in seedling stage, However, N2O emission crest emerged in blooming stage（high nitrogen conditions: film-9.85 kg·hm-2, routine-6.07 kg·hm-2; non-nitrogen conditions: routine-0.37 kg·hm-2） under high nitrogen and non-nitrogen conditions（P<0.05）; In radish season, the average N2O emission flux was highest in the seedling stage, but the highest cumulative N2O emissions were in the germination and seedling stage.（4） Daily N2O emissions from mulching farmland were higher than conventional treatment（P< 0.05）; N2O emission up to a peak of（210.53μg·m-2h-1） at 14:00 and to a discharge trough（99.44μg·m-2h-1） at 22:00 in mulching treatment; conventional farmland at 8:00 up to maximum 13.743μg·m-2h-1, and at 16:00 to a minimal value 42.69μg·m-2h-1.（5） When a large number of N2O was produced, mulching ridge（326.93μg·m-2h-1） and furrows（733.95μg·m-2h-1） were observed N2O emission peak, subsequently, N2O emissions of furrows greatly reduced, little difference with the conventional furrow emissions, slightly lower than mulching ridge（P>0.05）; indicating that effects of mulching on N2O transport between mulching and conventional farmland were slight, if there was no short-term N2O emissions surge.（6） both treatments’ N2O concentrations increased with soil depth; N2O emission from conventional farmland was significantly correlated with N2O concentrations in 10 cm, 20 cm and 30 cm depth; and only significantly correlated with N2O concentration of 30 cm depth in mulching farmland; significantly correlations were discovered between N2O concentrations of different soil depth, so were the same depth between two treatments.2. Effects of plastic film mulching on soil environmentMulching and conventional farmland respectively reached the maximum temperature of 33.50℃, 26.95℃ and the maximum soil water content rate were 24.84%, 22.81%. Soil ammonia nitrogen, nitrate nitrogen, alkaline hydrolysis nitrogen, DTN, TN contents basically conforms to the mulching treatment was higher than the conventional, and DON was just the opposite（P> 0.05）. In conventional farming, the highest SMBN and SMBC contents were appeared in chili season, reached 29.32, 304.60 mg·kg-1,the highest content of mulching farmland in radish season were respectively up to 30.98, 356.57 mg·kg-1. Urease activity of mulching soil was up to a maximum of 269.02 mg（NH4+-N）·kg-1, the lowest of 101.89 mg（NH4+-N）·kg-1; and urease activity of conventional soil was up to the highest 121.87 mg（NH4+-N）·kg-1, minimum of 73.96 mg（NH4+-N）·kg-1.3. Effects of plastic film mulching on farmland cropsMulching and high nitrogenous fertilizer were the keys to improve radish yield（mulching: 20.02 kg·m-2; non-mulching: 14.06 kg·m-2）（P< 0.05）, in addition, pepper’s and radish’s biomass, underground biomass and yield were little different in other conditions（P> 0.05）. TN contents of mulching and conventional farming pepper leaves were significantly higher than root and stem（P< 0.05）, and TN contents in roots, stems and leaves of mulching pepper were higher than conventional treatment（P< 0.05）, mulching radish in stems and leaves of TN contents were lower than the conventional treatment（P> 0.05）.4. Environmental factors of N2O emissions from conventional and mulching farmland ecosystemN2O emissions from mulching farmland were significantly positive relative with soil TN, DTN and ammonia nitrogen contents, similar relationships were observed between conventional farmland N2O emission and TN, DTN, nitrate nitrogen and underground temperature. Cumulative contribution ratio of three main factors in conventional N2O emission reached 79.46%, the factor 1 was the representative of soil nitrogen distribution, factor 2 was the characterization of soil carbon distribution and factor 3 reflected soil microbial activity. Four main factors were discovered in mulching N2O emission, reaching accumulative contribution ratio 83.42%, factor 1 was representative of soil nitrogen distribution and soil nutrient status and factor 2 was representative of soil organic carbon and microbial index, factor 3 was the characterization of soil microbial activity and factor 4 was soil organic carbon and nitrogen.TN（0.58） with the maximum value of the contribution limited conventional farmland N2O emissions, and the largest contribution of DTN（1.60） and ammonia（1.35） were related to mulching N2O emissions; indicating that the soil nitrogen was the biggest environmental factors for conventional and mulching farmland N2O emissions. |
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