Organic Water-Soluble Silicon Foliar Spraying To Reduce Cd Content In Rice And Its Mechanism

Rice is the main food crop in the south of China.The excessive content of heavy metals,especially cadmium,in the farmland soil seriously restricts the rice production safety in the Southern China due to mining,waste discharge,sewage irrigation and unreasonable application of fertilizer.How to safely use the farmland with moderately or seriously excessive cadmium content has drawn widespread attention in China.Agronomic measures are widely used for their advantages,including low cost,easy operation,no damage to the ecological environment of soil,and ability to fully exert self-restoration capability of soil and achieve sustainable development.In this paper,the effect of organic silicon water-soluble fertilizer sprayed to the leaves and soil matrixes on cadmium reduction in the soil from the farmland with excessive cadmium was studied through soil pot experiment and field plot experiment,its suitable concentration was selected,and the mechanism that the organic silicon water-soluble fertilizer reduced the cadmium absorption of rice was explored through the water culture experiment.The conclusions are as follows:1.The results of soil pot experiment show that(1)the different concentrations of organic silicon water soluble fertilizer sprayed to the leaf can promote the N,P and K absorption of rice,OWFSi3 shows much higher P content of the rice straw than the control after application in the booting stage,and OWFSi2 shows much higher P、K content of the rice straw than the control after application in the harvest stage;the inorganic silicon sprayed to the leaf could promote the P and K absorption of rice and reduce the N absorption of rice;ISi3 shows much higher K content of the rice straw than the control after application in the booting stage and harvest stage,and ISi2 shows much lower N content of rice straw than the control after application in the harvest stage;(2)both the organic silicon water soluble fertilizer and inorganic silicon fertilizer applied to the leaves increase the activity of SOD,decrease the content of MDA(except for OWFSi3),and have little effect on the activity of POD and CAT;(3)the analysis results of cadmium speciation in plants show that except from OWFSi1 and ISi3,both the organic silicon water soluble fertilizers and inorganic silicon fertilizers applied to the leaves show9.84%～ 31.98% lower extractable Cd content than the control;among the inorganic silicon fertilizers applied to the leaves,Na Cl and HCl shows 1.31～28.05% higher extractable Cd content(F Na Cl+F HCl)than the control,and HAc shows 9.97～23.87% lower extractable Cd content(F HAc)than the control;Si1and Si2 applied show 0.57%～15.60% lower(F H2O+F ethanol)than the control,and Si3 applied show higher(F H2O+F ethanol)than the control,especially OWFSi3 and ISi3 applied show higher 20.7% and 5.96%(F H2O+F ethanol)than the control;(4)the cadmium content of rice straw and rice during the harvest period decreased by 39.1%-55.1% and 49.3%-60.6%,and the 13.61% ～ 54.00%lower transport coefficient(from rice straw to rice)than the control(except for ISi1).2.The results of field plot experiments show that(1)the organic silicon water soluble fertilizer applied to soil matrixes and leaves shows 1.14% ～ 9.80% higher rice yield and 0.04% ～ 1.49% higher rice yield and 1000-grain weight than the control;among them,OWFSi1(containing 0.06% SiO2)has the best effect of increasing production;(2)the organic silicon water soluble fertilizer applied to soil matrixes and leaves shows 3.46% ～ 15.9% higher P content,1.80%～ 10.74%higher K content and 9.42% ～ 11.76% higher Si content of rice;(3)the organic silicon water soluble fertilizer applied to soil matrixes and leaves shows 0.29% ～17.53% higher SOD activity and 25.18%～ 41.73% higher GR activity,9.88% ～31.48% lower POD activity and 3.92% ～ 24.18% lower CAT activity,and0.60%～11.69% lower MDA content than the control;and(4)the organic silicon water soluble fertilizer applied to soil matrixes and leaves shows 6.42% ～ 23.26%and 15.38% ～ 41.54% lower Cd content of rice straw and rice,respectively and3.92% ～ 27.97% lower grain transport coefficient than the control;among them,the effect of Cd reduction is best treated by OWFSi2(containing SiO2 0.09%)on foliar treatment..3.The results of water culture experiment show that the organic silicon water soluble fertilizer(containing 0.09% SiO2)diluted 200 times and applied to leaves promotes the rice growth and development and shows 8.35% bigger plant height,58.35% bigger root length and 38.77% bigger dry matter weight;promotes the transportation of Ca,Mg,Fe,Mn and Cu elements to the shoot,and shows 93.37%higher Ca content,187.46% higher Mg content,112.93% higher Fe content,48.37% higher Mn content and 19.11% higher Cu content of the shoot than the control;weakens the Zn element transport to the shoot and shows 30.80% lower Zn content of the shoot than the control;shows 24.58% higher chlorophyll a content,23.40% higher chlorophyll b content and 4.77% higher carotenoid content,38.33%and 37.11 % lower Cd content of shoot and root system,respectively,and 1.29%lower transparent coefficient than the control;the results of fluorescent dye PTS test show that +Si applied shows 44.99% lower PTS transport to the shoot in the young rice plants and 28.40% Cd concentration of xylem sap than-Si applied,indicating that silicon can reduce the apoplastic transport permeability and inhibit the Cd transport and transfer from root to shoot.