| Ratoon rice uses rice regeneration characteristics through a certain agronomic management measures after the first rice is harvested,and the living dormant buds in the first rice stubble are regenerated,grown,headed,matured and re-harvested.Planting ratoon rice is one of the effective measures to enhance the multiple cropping index and increase income.Because the studies are mainly focused on the morphology and physiology of ratoon rice,a series of soil environmental problems,such as increase of soil bulk density,imbalance of soil nutrients,high soil carbon emission and the idle of stubble stage caused by ratoon rice planting,have been neglected.Therefore,a field experiment was conducted in Farm Guanghua in Qianjiang to study planting ratoon rice effects on paddy soil fertility,greenhouse gas emissions,rice yield and its composition factors,nitrogen uptake and economic benefits,and three ratoon rice cultivation modes used included the conventional cultivation mode?first season machine transplanting+artificial fertilization+mechanical harvesting by Kubota harvester+leave 20 cm stubble after harvesting the first rice season+the first rice season straw covered in whole rice Pile row+conventional irrigation+winter vacancy?,optimization cultivation mode 1?first season machine transplanting+semi-automatic rotary table fertilizing machine+harvesting by Huanong harvester+leaving 20 cm stubble after harvesting the first rice season+crushing and returning the straw of the first rice season to the field+intermittent irrigation+winter vacancy?,and optimization cultivation mode 2?first season machine transplanting+semi-automatic rotary table fertilizing machine+harvesting by Huanong harvester+leaving 35 cm stubble after harvesting the first rice season+crushing and returning the straw of the first rice season to the field+intermittent irrigation+winter planting rapeseed?.The main experiment results are shown as follows:?1?Cultivation modes had no significant effect on soil pH,total nitrogen and total phosphorus content.The cultivation modes significantly affected soil bulk density,nitrate nitrogen,ammonium nitrogen,dissolve organic carbon,available phosphorus,available potassium and total potassium content after the rice was harvested.In the 0-5 cm soil layer after the first rice season,compared with conventional cultivation mode,nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,available phosphorus and total potassium content in optimization cultivation mode 1 were significantly increased by 57.1%,39.9%,38.5%,19.8%and 5.8%respectively,and nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,available phosphorus,available potassium and total potassium content in optimization cultivation mode 2 were significantly increased by 80.5%,105.0%,72.3%,32.0%,17.4%and 10.4%respectively.Compared with the conventional cultivation mode in the 5-10 cm soil layer after the first rice season,optimization cultivation mode 1 enhanced nitrate nitrogen and ammonium nitrogen content significantly by 34.1%and 22.0%respectively,and optimization cultivation mode 2increased nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,available phosphorus and available potassium content by 60.4%,143.5%,64.2%,25.4%and18.1%respectively.Compared with the conventional cultivation mode in the 10-20cm soil layer after the first rice season,nitrate nitrogen and ammonium nitrogen content in optimization cultivation mode 1 were significantly increased by 32.9%and76.4%respectively,and nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,available phosphorus,and available potassium content in optimization cultivation mode 2 were significantly increased 49.0%,178.9%,145.5%,24.3%,21.7%respectively.Compared with the conventional cultivation mode in the 0-5 cm soil layer of the ratooning rice season,the bulk density was significantly decreased by4.8%,while nitrate nitrogen,ammonium nitrogen,available phosphorus and available potassium content in optimization cultivation mode 1 were significantly increased by31.4%,30.0%,14.7%,and 9.7%respectively,and the bulk density was significantly decreased by 8.8%,while nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,available phosphorus and available potassium content were significantly increased by 34.6%,73.8%,56.8%,30.8%and 8.2%in optimization cultivation mode2 respectively.Compared with conventional cultivation mode in the 5-10 cm soil layer of the ratooning rice season,nitrate nitrogen,ammonium nitrogen and available phosphorus content were significantly increased by 19.2%,33.8%and 10.5%in optimization cultivation mode 1 respectively,and nitrate nitrogen,ammonium nitrogen and available phosphorus content were significantly increased by 32.5%,72.4%and 32.3%in optimization cultivation mode 2 respectively.Compared with conventional cultivation mode in the 10-20 cm soil layer of the ratooning rice season,nitrate nitrogen and ammonium nitrogen content were significantly increased by20.4%and 34.7%in optimization cultivation mode 1 respectively,and nitrate nitrogen,ammonium nitrogen,available phosphorus and available potassium content were significantly increased by 16.3%,60.3%and 25.7%in optimization cultivation mode2 respectively.?2?The methane?CH4?emissions from ratoon rice fields were mainly concentrated in the first rice season,and the peaks of CH4 fluxes were observed in the rice tillering and panicle differentiation stages.The CH4 emissions in the ratooning rice season were relatively low.The peaks of nitrous oxide?N2O?fluxes were observed mainly after N fertilization and floodwater drainage.Compared with the conventional cultivation mode in the first rice season,the cumulative N2O emissions in the optimized cultivation mode 1 and 2 were significantly increased by 71.0%and153.6%,respectively,while the cumulative CH4 emissions were significantly decreased by 27.0%and 28.1%,respectively.The cumulative CH4 emissions from optimized cultivation mode 2 in the ratooning rice season were significantly increased by 133.3%compared with the conventional cultivation mode.In addition,the cultivation modes had significant effects on cumulative N2O and CH4 emissions,global warming potential?GWP?and greenhouse gas emission intensity?GHGI?during the whole growth period of rice.Compared with the conventional cultivation mode,the cumulative N2O emissions in the optimized cultivation mode 1 were significantly increased by 36.4%,while the cumulative CH4 emissions,GWP and GHGI were significantly decreased by 25.8%,25.4%and 28.1%respectively,and the cumulative N2O emissions in the optimized cultivation mode 2 were significantly increased by 93.2%,while CH4 cumulative emissions,GWP and GHGI were significantly decreased by 25.0%,20.7%and 25.8%,respectively.The contribution of CH4 to GWP was greater than that of N2O.The contribution of CH4 to the global warming potential was 80.6%94.1%,obviously higher than that of N2O?5.9%19.4%?.Therefore,compared with the conventional cultivation model,the optimized cultivation mode could better mitigate greenhouse gas emissions and mitigate the environmental negative impact due to the greenhouse effect.?3?The cultivation modes significantly affected the yield and its components,the dry matter accumulation in the aboveground parts and the nitrogen uptake of the plants in first rice season and ratooning rice season.Compared with the conventional cultivation mode,the yield of the first rice season was significantly increased by 3.5%,the yield of the ratooning rice season was significantly increased by 30%,and the total yield of the two seasons was significantly increased by 9.8%in optimization cultivation mode 1.And the yield of the first rice season was significantly increased by 6.1%,the yield of the ratooning rice season increased significantly by 34.8%,and the total yield of the two seasons increased significantly by 13.5%in optimization cultivation mode 2.In terms of yield components,spikelets per panicle in the first rice season of optimization cultivation mode 2 was significantly higher than that of the conventional cultivation mode and the optimized cultivation mode 1,which increased by 8.0%14.1%.And panicles per hectare and spikelets per panicle in the ratooning rice season of optimization cultivation mode 2 both were significantly higher than the conventional cultivation mode and the optimized cultivation mode1,with an increase of 7.0%13.6%and 7.2%20.5%,respectively.The dry matter accumulation in the aboveground parts of the first rice season and the ratooning rice season showed that optimal cultivation mode 2>Optimized cultivation mode 1>Conventional cultivation mode.In addition,compared with conventional cultivation in first rice season,the total nitrogen accumulation,nitrogen uptake efficiency and partial factor productivity from applied nitrogen in the optimized cultivation mode 1 significantly increased by18.3%,20.3%and 3.6%,respectively,and in the optimized cultivation mode 2significantly increased by 29.4%,28.9%and 6.2%,respectively.Compared with conventional cultivation in ratooning rice season,the total nitrogen accumulation,nitrogen uptake efficiency and partial factor productivity from applied nitrogen in the optimized cultivation mode 1 significantly increased by 17.6%,18.2%and 27.1%,respectively,and in the optimized cultivation mode 2 significantly increased by 38.2%,38.8%and 34.5%,respectively.?4?The analysis of the cost and benefit of ratoon rice showed that the optimized cultivation mode 2 had the highest economic benefit,reached 10602.1 yuan/hm2,which is 1.76 times that of the conventional cultivation mode and 1.27 times that of the optimized cultivation mode 1.Taken together,our results show that the optimized cultivation modes are sustainable ratooning cultivation modes for fertilizing the soil,increasing grain yields of first and ratooning season,and increasing economic benefits while reducing the global warming potential.Morever,the optimized cultivation mode 2 is more effective and worthy of promotion in the rice area of Hubei Province. |
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