| A pot experiment was conducted to study the effects of different concentrations of silicon fertilizer(Calculated on Si,0,20,40,80,160 mg/kg)on different growth stages(tillering stage,booting stage,filling stage,mature stage)of two different varieties of rice(Weiyou 46 and Xiangduan 12)in heavy metal Cd contaminated soil(0.5 mg/kg).The research includes the contents of Cd and Si in various parts of rice,and changes of pH value,available Si contents and TCLP-Cd and CaCl2-Cd contents in soil.The relationship between the accumulation of Si in rice and the transport coefficient of Cd from soil to rice was also discussed.The main results are as follows:(1)The effects of exogenous Si addition on Cd accumulation in different parts of two varieties of rice were different at mature stage.Among them,Si application had a significant effect on the accumulation of Cd in rice roots of Weiyou 46(p<0.05),but there was no significant effect on the accumulation of Cd in other parts of the rice(p>0.05).When the amounts of Si applied were higher than 40 mg/kg,the Cd content in rice roots of Weiyou 46 increased by 160.8%?304.3%,and the Cd content in rice roots of Xiangwanxian 12 increased and then decreased.For the two varieties of rice brown rice,the Cd content under each Si treatment was lower than the safety standard in the National Food Standards(Cd<0.2 mg/kg).(2)The addition of exogenous Si can increase rice yield of two rice varieties.Compared with CK,the application of Si at 20?160mg/kg could increase the rice yield of Weiyou 46 by 26.97%?55.71%(p<0.01),and the yield of rice in Xiangwanxian 12 increased by 12.2%?39.5%(p>0.05).When the amount of Si applied was 80 mg/kg and 160 mg/kg,the yield of two varieties of rice reached a maximum value,respectively.The accumulation of Si in brown rice of both varieties increased with the increase of Si application amount,and the effect of exogenous Si on the accumulation of Si in brown rice of Xiangwanxian 12 reached a significant level(p<0.05).When the amounts of Si applied were lower than 20 mg/kg,the rice yield of Xiangwanxian 12 was relatively higher;whereas when the amounts of Si applied were higher than 40 mg/kg,the rice yield of Weiyou 46 was relatively higher.(3)The application of exogenous Si significantly affected the soil pH values of two rice varieties(p<0.01),and the Si treatments with 20?160mg/kg increased the soil pH values as a whole.Under the same Si treatments,the soil pH value of Weiyou 46 was basically lower than that of Xiangwanxian 12.The addition of exogenous Si significantly increased available Si contents of the two rice varieties of paddy soil,and the highest levels increased from 73.13 mg/kg and 86.87 mg/kg to 121.28 mg/kg and 117.51 mg/kg,respectively,which increased by 0.66 and 0.35 times.There were extremely significant(p<0.01)and significant(p<0.05)positive linear correlation between available Si contents and the applied Si concentration in soils of two varieties of rice,and the correlation coefficients were 0.743 and 0.597,respectively.When the amounts of Si applied were 0?40 mg/kg,the Soil available Si content of Xiangwanxian 12 was relatively higher;whereas when the amounts of Si applied were 80?160 mg/kg,the Soil available Si content of Weiyou 46 was relatively higher.Simultaneously,Si application reduced the TCLP-Cd and CaCl2-Cd contents in the two paddy soils.(4)At different stages of rice growth,the amount of Si accumulated in each part of the two varieties of rice had different effects on the migration and transport of Cd in soil.At the rice tillering stage,there were negative correlation between the root Si accumulation in Weiyou 46 and Xiangwanxian 12 and the migration transport coefficient of Cd from the soil to the root and from the root to the stem and leaf,and the correlation coefficients were-0.249 and-0.521,respectively.the root Si accumulation inhibited the migration of Cd in soil to the root(p>0.05),and the effect of Weiyou 46 was relatively more obvious.At the rice booting stage,both stems,leaves and ears Si accumulation of Weiyou 46 inhibited Cd migration from underground to the ground(p<0.05),and ears Si accumulation could significantly inhibit the migration of Cd from stems and leaves to ears(p<0.05).The stems,leaves and ears Si accumulation of Xiangwanxian 12 promoted the migration of Cd from underground to the ground(p>0.05).At the rice filling stage,the ears Si accumulation of Weiyou 46 promoted the migration of Cd from soil to root(p<0.05),however,which inhibited the migration of Cd from root to stems and leaves(p<0.05)at the same time.The effect of Si accumulation in the ears of Xiangwanxian 12 on migration and transport of Cd was less significant than that of Weiyou 46.At the rice mature stage,stems and leaves Si accumulation of Weiyou 46 promoted the migration of Cd from the soil to root(p<0.05)and from stems and leaves to ears(p<0.01).On the other hand,it could also inhibit Cd migration from root to stems and leaves(p<0.05)and from ears to husks(p<0.05).In terms of Xiangwanxian 12,root Si accumulation promoted the migration of Cd from the soil to root(p<0.05).but stems and leaves as well as brown rice Si accumulation prevented the migration of Cd from ears to husks(p<0.05).(5)The effect of application of exogenous Si on Cd contents in brown rice of two varieties may be different.For Weiyou 46,it may be possible to increase the accumulation of leaves Si by increasing soil pH value and available Si contents,which promoted Cd enrichment from the soil to root and suppressed the migration of Cd from root to stems or leaves.In the combination of the above two factors contributed to the migration and transport of Cd.For Xiangwanxian 12,it may be possible to increase the accumulation of leaves Si by increasing soil pH value and available Si contents under exogenous Si application,which inhibited the transport of Cd from ears to husks.Considering rice yield and Cd contents in brown rice,it was recommended that the Si application be 80mg/kg for Weiyou 46 and 160 mg/kg for Xiangwanxian 12 under the Si conditions set in the experiment. |
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