| Agroecosystems play a vital role in the global balance of atmospheric greenhouse gases (GHGs) and net ecosystem carbon budget (NECB). Life cycle assessment is assessed with a whole analysis of total emissions from all inputs in a life cycle of production or consumption. For rice systems, the net global warming potential (NGWP) shoule include the CH4 and N2O emissions from rice growing seasons and seedling nurseries, soil organic carbon sequestration and carbon emissions from field management. Agricultural practices can be related to NGWP by estimating the NGWP per ton of crop yield, referred to as the greenhouse gas intensity (GHGI). How to increase the crop yield in unit area is important for the future food securigy. The integrated soil-crop system management (ISSM)cultivation patterns were established for improvement of crop yield and nitrogen use efficiency (NUE) involving different nitrogen application rates, different N split rations,organic rapeseed cake manure and different transplanting density, while few studies about the effect of ISSM on GHGs from double rice systems have been reported. Thus, this study is to evaluate the overall impacts of different ISSM cultivation patterns on double rice yield,NUE and NGWP from double rice systems in South China.With NN (no N cotrol) and FP (conventional farmer' practices) as the control, three integrated soil-crop system management (ISSM) cultivation patterns at different nitrogen rate were established (ISSM-N1, N rate reduced by 30 kg ha-1; ISSM-N2, N rate equal to FP; ISSM-N3, N rate increased by 30 kg ha-1). Methane and nitrous oxide fluxes and ecosystem respiration were measured with a static opaque chamber-gas chromatograph method over the three rice-rice-fallow rotations from April 2011 to April 2014. The objective of this study was to gain an insight into the effect of different ISSM cultivation patterns on greenhouse gas emissions, rice yield, NUE, NECB, Eo and Ei, NGWP and GHGI over the three years. Another field experiment was conducted in 2013 to evaluate the effect of different types of rice seedling nurseries (seedlings raised on wetland soil beds with continuous flooding, WSB; seedlings raised on dry land soil beds, DSB; and seedlings raised in wet conditions with moist irrigation on plastic trays, WPT) on CH4 and N2O emissions and global warming potential from rice seedling nurseries.The main results are listed as follows:1. All cultivation patterns showed similar temporal patterns in the CH4 fluxes from April 2011 to April 2014, which mainly occurred in rice growing seasons. Cumulative CH4 from late growing seasons were significantly higher than that from early rice growing seasons. Meanwhile, CH4 emissions during fallow seasons were much lower than rice growing seasons,which accounted for 2.0%?2.7% to annual cumulative CH4 emissions in different cultivation patterns. Significant positive liner relationships between CH4 emissions and the rice aboveground biomass were found for both early and late rice growing seasons. Annual CH4 cumulative emissions of each cultivation patterns ranged from 380 kg CH4 ha-1 yr-1 (NN) to 645 kg CH4 ha-1 yr-1 (ISSM-N3). Meanwhile, ISSM-N2 and ISSM-N3 significantly increased the annual CH4 cumulative emissions as relative to the other three cultivation patterns.2. During the experiment period from April 2011 to April 2014, N2O emissions were neglectful under waterflooding rice field, except for some separately sharp emission peaks.Seasonal dynamics of N2O were insignificantly infuenced by different cultivation patterns,while, annual N2O emissions were greatly affected by different cultivation patterns.Substantial N2O emissions were observed in the fallow seasons, although no fertilizer was applied, which accounted for 18%-27% to annual cumulative N2O emissions in different cultivation patterns. Annual N2O emissions average 0.34?1.03 kg N2O-N ha-1 yr-1 in different cultivation patterns. Compared with NN, the other four cultivation patterns significantly increased the N2O emissions, except for there was no significant difference between NN and ISSM-N1 for early rice seasons. And regression analysis showed that the annual cumulative N2O emissions were significantly exponentially correlated with the nitrogen rate.3. The annual increase of soil organic carbon (SOC) of different cultivation patterns were 0.13 t ha-1 yr-1 (NN), 0.29 t ha-1 yr-1 (FP), 0.49 t ha-1 yr-1 (ISSM-N1), 0.56 t ha-1 yr-1(ISSM-N2), 0.61 t ha-1 yr-1 (ISSM-N3). Compared with NN, the other four cultivation patterns significantly enhanced the annual SOC sequestration. In addition, compared with FP, the three ISSM cultivation patterns also significantly enhanced the annual SOC sequestration.Both early and late rice yield significantly varied with the years and different cultivation patterns. On average over the three years, the rice yield in different cultivations were ranged form 4.63 t ha-1 (NN) to 9.31 t ha-1 (ISSM-N3) in early rice seasons, and 6.22t ha-1 (NN) to 10.17 t ha-1 (ISSM-N3) in late rice seasons,respectively. Compared with NN,the other four cultivation patterns significantly increased the rice yields for both early and late rice seasons. Meanwhile, compared with FP, ISSM-N1, ISSM-N2 and ISSM-N3 significantly increased the annual rice yields and nitrogen use efficiency.4 The GWP induced by field management (Eo, Ei) of different cultivation patterns were 1267.5 kg CO2-eq(NN),2781.7 kg CO2-eq(FP),2719.7 kg CO2-eq(ISSM-N1),3439.1 kg C02-eq(ISSM-N2) and 4034.3 kg C02-eq(ISSM-N3). Compared with FP, ISSM-N1 decreased the Eo and Ei, but ISSM-N2 and ISSM-N3 increased the Eo and Ei. For double rice systems, the GWP induced by CH4 and N2O emissions from WSB, DSB and WPT were 1429.6, 3197.0 and 1032.2 kg CO2-equivalents, respectively. Compared to the traditional methods WSB and DSB, the new method significantly decreased the GWP by 28% and 68%, respectively. The new method for rice seedling, WPT can significantly decrease the GWP induced by CH4 and N2O emissions during the early rice seedling nurseries as relative to the two trandional methods DSB and WSB.5. For double rice systems,CH4 emissions dominated the NGWP in different cultivation patterns. The GWP of Eo and Ei were vital to the ecosystem's NGWP. In addition, the SOC sequestration can offset some global warming potential. On average, theannual NGWP and GHGI of FP were estimated to 18.72 t CO2 eq ha-1 and 1.23 kg CO2 eq kg grain-1. Compared with FP, ISSM-N1 decreased the NGWP and GHGI by 1.3% and 10.5%, ISSM-N2 and ISSM-N3 increased the NGWP by 27.4% and 32.7%, and GHGI by 3.6% and 3.9%, respectively.In conclusion, compared with the FP, the ISSM-N1 significantly increased the rice yields and NUE, in addition, decreased the NGWP and GHGI by 1.3% and 10.5%. But the other two ISSM cultivation patterns,ISSM-N2 and ISSM-N3 greatly increased the rice yields and NUE as compared with FP, but also increased the NGWP and GHGI. |
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