Effects Of Different Potassium(K) Fertilizer On Heavy Metal Migration And Transformation In Soil-crop System Under Reclaimed Water Irrigation

Irrigation with reclaimed water containing traces of heavy metals may have an impact on the soil-crop system.Different potassium fertilizer and their accompanying anions interact with heavy metals in the soil-crop system could change the soil physical and chemical properties,which may influence the migration and transformation of heavy metals,and change the plant availability of heavy metals to some extent.Based on the effect of typical heavy metals Cd,Pb,Cu and Zn in reclaimed water irrigation on soil environment,crop quality and control measures,the effects of different potassium fertilizer on the contents of heavy metals in tomato plants,fruits,different depth soil layer and rhizosphere and non-rhizosphere soil were studied by field microplot and barrel experiment in this study.Under reclaimed water irrigation,we analysed the influence of different potassium fertilizer on the physicochemical properties of soil,on the migration and transformation of heavy metals in different soil forms,and on the accumulation of heavy metals and the quality of tomato plants and fruits.This research provides a theoretical basis for the potassium fertilizers in regulating Cd,Pb,Cu and Zn in soil and plants under reclaimed water irrigation.The main findings are as follows:?1?Under the condition of reclaimed water irrigation the effect of K₂SO₄ fertilizer inhibiting the accumulation of Cd and Zn in soil was the best.The SO₄^2-can be combined with H⁺to lower the pH of the soil after application of K₂SO₄,so that the effective state content of Cd and Zn in the soil can be increased,and the content of Cd and Zn in the soil can be reduced by carrying the Cd and Zn through the tomato plant body.Compared with K₂CO₃,KH₂PO₄ and KCl,K₂SO₄ promoted the accumulation of Cd in tomato plants by 44.79%.K₂SO₄ application reduced the content of soil Cd and Zn by 5.75%³8.09%and 3.01%⁴.11%.The application of K₂SO₄ in the barrel experiment reduced the soil bioavailable Cd by 13.63%²8.74%,and reduced the soil bioavailable Zn by 4.94%¹2.90%.?2?Under the condition of reclaimed water irrigation the application of KH₂PO₄ had the best inhibitory effect on soil Pb and Cu.The soil Pb and Cu contents were reduced by 6.90%¹8.43%and4.97%¹9.25%,respectively.KH₂PO₄ is mainly used to form a compound with lower solubility in the soil Pb ions so as to lower the active Pb content of the soil,and the negative charge of the soil surface is increased by the surface adsorption and the complexation,so that the active Cu content of the soil is reduced by the adsorption amount,and the KH₂PO₄ soil P is applied.The application of KH₂PO₄reduced the bioavailable Pb in soil by 2.44%²3.40%,and decreased the bioavailable Cu in soil by14.55%¹9.77%.The ability to uptake Pb and Cu was strongest in the tomato plans.Compared with K₂CO₃,KCl and K₂SO_4,KH₂PO₄ promoted the accumulation of Pb and Cu in tomato by 3.56%and5.72%.?3?Under the condition of reclaimed water irrigation short-time reclaimed water irrigation will not cause heavy metal pollution in soil.Potassium fertilizer can inhibit the accumulation of Cd,Pb,Cu,Zn in soil and the contents of heavy metals in soil is lower than the standard?GB 15618—2018?.For example,the accumulations of Cd,Pb,Cu and Zn in soil under reclaimed water irrigation were0.1366⁰.4231 mg/kg,14.18¹9.15 mg/kg,18.30²8.18mg/kg,95.92¹02.93 mg/kg,respectively,which are lower than the standard upper limit.?4?Under the condition of reclaimed water irrigation the effect of K₂SO₄ fertilizer inhibiting the uptake of Cd and Zn by tomato fruit was the best,and the effect of KH₂PO₄ inhibiting the uptake of Pb and Cu by tomato fruit was the best.The heavy metal contents in tomato fruit did not exceed the limit of standard for foods?GB 2762—2017?.The Cd content in tomato fruit was 0.0050⁰.0240 mg/kg,which was less than 0.05 mg/kg.The Pb content is far below 0.1 mg/kg?0.0084⁰.0106 mg/kg?.In tomato fruit,potassium fertilizer application could improve its taste flavor and nutritional quality compared with no fertilizer application,such as,the content of vitamin C,organic acid,protein,and soluble sugar was increased by 4.74%²4.77%,0.30%²4.08%,7.77%⁸0.46%,and 2.37%³3.41%,respectively.Tomato was improved taste flavor and nutritional quality.