| In order to explore the difference in Cd accumulation and transportion characteristics between main crop and ratooning season of ratooning rice and the regulation effect of water and density,Xiangzaoxian 45,Y Liangyou 9918 and Yongyou 4149 were used as materials to study the difference in Cd accumulation and transportion characteristics between main crop and ratooning season of ratooning rice in 2018-2019,and through water management experiment(long-term flooding and intermittent irrigation),density experiment(medium density: 16.7 × 20.0 cm and low density: 20.0 × 20.0 cm),two factor experiment of water management(long-term flooding,intermittent irrigation and wet irrigation)and density(high density: 16.7 × 16.7 cm,medium density: 16.7 × 20.0 cm and low density: 20.0 × 20.0 cm)to study effects of water and density management on Cd accumulation and transportion of different ratooning rice varieties.The main results as follows:1.Comparison on yield and Cd accumulation characteristics between main crop and ratooning season.Under normal conditions,yield of ratooning season was significantly lower than that of main crop,mainly because the grains number per panicle and 1000-grain weight of ratooning season significantly decreased.However,in 2019,the seed setting rate of variety Y was significantly decreased due to heavy rain and flood in the earing and flowering period,and the yield was lower than the ratooning season.On the whole,the Cd content and transfer coefficient of each organ were larger in ratooning season,but there were some differences among different organs of different varieties at different stages.Cd content of brown rice in main crop and ratooning season showed the varietal and annual differences.In 2018,Cd content of brown rice in main crop and ratooning season of X and Y varieties was 0.16 mg/kg and 1.13 mg/kg,0.91 mg/kg and 0.44 mg/kg,respectively,while in 2019,that of Y and Z was 0.12mg/kg and 0.17mg/kg,0.08mg/kg and 0.13mg/kg,respectively.2.The regulation effect of water management on yield and Cd accumulation characteristics of ratooning rice.Compared with intermittent irrigation,flooding treatment significantly reduced the available Cd content in soil and rice organ Cd content and accumulation.The response of yield to water was differentbetween different varieties or different seasons of the same variety.The Cd transfer coefficient was different among varieties,that of X variety was bigger in flooding treatment,but that of Y variety was bigger in intermittent irrigation.Under flooding treatment,the Cd content of brown rice in main crop and ratooning season of X variety decreased by 37.9% and 43.9%,the Cd accumulation decreased by 52.41% and 53.40% respectively,and the available Cd in soil decreased by8.3% and 13.8%.The effects of flooding treatment on the Cd content,Cd accumulation and available Cd content of brown rice in rationing season of X variety were greater than those in main crop,while Y variety showed little difference.3.Regulation effect of density on yield and Cd accumulation characteristics of ratooning rice.Compared with medium density treatment,low density treatment could significantly reduce yield,Cd content and accumulation of rice organs,and its influence on ratooning season was greater than that onmain crop.The dry matter weight and Cd transfer coefficient of different varieties had different responses to density.The dry matter weight and Cd transfer coefficient of variety X were higher in medium density,but those of variety Y were higher in low density.Under the low density treatment,the Cd content of brown rice in main crop of X and Y varieties was 13.8% and 22.0%,7.69% and 9.09% lower than that in the ratooning season,respectively,and the Cd accumulation was 52.28% and 54.23%,17.22% and 29.24% lower.The effects of low density treatment on Cd content and Cd accumulation in ratooning season brown rice of varieties X and Y were greater than that in main crop,and the effects on the effective Cd content in soil were significantly different among different varieties in different seasons.4.The regulation effect of interaction of irrigation-density on yield and Cd accumulation characteristics of ratooning rice.Compared with intermittent and wet irrigation treatment,the effective panicle number significantly decreased but grain number per panicle and yield significantly increased in flooding treatment.The response of each yield component to density treatment was inconsistent,but the yield of both varieties was highest in high density treatment.In the ratooning season,the yield of two cultivars was the highest inwet irrigation treatment,but the response to density was different among varieties.The yield of variety Z was the highest in low density treatment,but that of variety Y was the highest in medium density treatment and the lowest in high density treatment.The effect of water treatment on Cd content in plants was obvious,while the effect of density and interaction of irrigation-density on Cd accumulation and transportion in rice and soil available Cd content was not obvious.Among water treatments,flooding treatment significantly reduced Cd content in plant organs,transfer coefficient,Cd accumulation and the effective Cd content in soil in main crop and ratooning season.Cd accumulation and accumulation rate in wet irrigation was the largest in main crop and ratooning season,Cd content in wet irrigation treatment was biggest in main crop,but for ratooning season,Cd content in each organ of variety Z was biggest in intermittent irrigation,while that of variety Y was biggest in wet irrigation treatment.There was no significant difference in the available Cd content of variety Z between intermittent and wet irrigation treatment,but that in wet irrigation treatment was the highest for variety Y.5.The difference in Cd content of ratooning rice from different nodes.In single factor experiment of water and density,Cd content in stems and sheathes of main crop decreased with the rising of node,and the leavesperformanced consistent with stems and sheathes at former stages,but Cd content in the lower leaves droped rapidly and that in the upper leaves increased at maturity.Cd content in organs of ratooning rice from lower nodes was higher than that of higher nodes.In irrigation-density interaction experiment,Cd content in the stems,sheathes and leaves of main crop decreased with the rising of node position,but there was no significant difference in Cd content among the organs from different nodes in ratoonging season.Panicle Cd content,of variety Y was higher in lower nodes,while that of variety Z was higher in higher nodes.Conclusion: In general,yield of main crop was higher than that of ratooning season,and its Cd content and transfer coefficient were lower than that of the ratooning season.The available Cd content in soil and Cd content and accumulation in rice plants were significantly reduced by flooding treatment and low-density treatment,and ratooning season showed more evident,and there existed varietal difference.The Cd content in stems and sheathes decreased with the rising of node position in main crop,while Cd content in all organs of ratooning season decreased with the rising of node position.Therefore,ratooning rice should be measures of lower density,flooding irrigation and higher stubble height could achieve the goal of reducing Cd-content in ratooning rice. |
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