Effects Of Long-term Fertilization On Phosphorus And Heavy Metals In Greenhouse Soil

In the past 20 years,greenhouse vegetables cultivation has been developing rapidly in China,especially in Liaoning Province,but its environmental conditions are different from those of open-air farmland.In addition,the long-term application of a large number of fertilizers,especially organic fertilizer and phosphorus fertilizer,has led to the accumulation of phosphorus and heavy metals in the soil.It is of great significance to study the effects of long-term fertilization on phosphorus and heavy metals in greenhouse soil for improving the quality of greenhouse soil and ensuring the safe production of agricultural products.This paper took the greenhouse soil of Shenyang Agricultural University's greenhouse tomato long-term fertilization positioning test base(established in 2009)as the research object,and collected basic soil samples in 2009,0-20 cm soil samples in 2014,2016,and 2018,and adopted the modified Hedley soil phosphorus classification method and Tessier continuous extraction method to study the change trend of phosphorus and heavy metals(Cu,Zn,Pb,Cd,Hg,Cr,and As)content and form in the greenhouse soil under the fertilization treatment of 10 different combinations of chicken manure(M),straw(R),K2SO4(K),quicklime(Ca)and compound fertilizer.In order to provide scientific basis for the quality management of greenhouse agricultural soil and the safety production control of agricultural products.The results showed as follow:(1)Different measures had different effects on soil total phosphorus content.Except for CK(non-fertilization)treatment,the total phosphorus content of the soil in the fertilization treatment groups(other treatments except CK treatment)increased with the increase of planting years.The application of chicken manure,straw,K2SO4 and compound fertilizer increased the total phosphorus of the soil,and the total phosphorus with the application of quicklime treatment was lower.By 2018,MRK treatment had the highest total phosphorus,an increase of 354%.MCa treatment was lower,with an increase of 278.55%.(2)Except for CK treatment,the content of various forms of phosphorus in the fertilization treatment groups increased with the increase of planting years.The content of inorganic phosphorus(H2O-P + Na HCO3-Pi + Na OH-Pi + HCl-P)increased a lot.By 2018,the proportion of HCl-P(the proportion of the sum of the various forms)was the highest(25.74%-31.09%),and the proportion of active phosphorus(H2O-P + Na HCO3-Pi + Na HCO3-Po)was as high as 29.15%-33.27 %.The effect of combined application of different materials was different.MRKCa treatment and MR treatment had a high proportion of active phosphorus(33.27% and 32.76% respectively),MCa treatment had a low proportion of active phosphorus at 30.76%.And the content of Residual-P in MRK treatment was high,accounting for 23.12% of total phosphorus.And the correlation study showed that the transformation of different forms of phosphorus in soil mainly occurred between the active phosphorus and Residual-P.(3)Different measures had different effects on the total amount of heavy metals in the soil.Except for CK treatment,the soil heavy metal content of the fertilization treatment groups increased with the increase in planting years.Zn increased the most,while Cd and Hg increased slightly.The application of chicken manure and straw increased the content of heavy metals in the soil.The application of compound fertilizer slightly promoted the growth of Pb,Cr and As.The application of K2SO4 mainly promoted the growth of Zn,Pb and Cr.And the application of quicklime may reduce the content of heavy metals in the soil.By 2018,the content of Cu,Pb and As in MR treatment was the highest,Zn,Hg and Cr in MRKCa treatment was the highest,Cd in MRK treatment was the highest,while heavy metal content in MCa treatment was less(Especially the content of Cd,Hg,Cr and As was very low).(4)Except for CK treatment,the content of heavy metals in the fertilization treatment groups fluctuated and increased with the planting years.By 2018,the proportion of heavy metals in different fertilization treatments(including CK treatment)was different,but they were mainly in the residue state,reaching more than 31.67%.The exchangeable states of Cd and Hg account for a large proportion of the total.The effect of combined application of different materials was different.By 2018,The active state(exchangeable + carbonate bound)of Pb,Cd,Hg and Cr in MR treatment accounted for a large proportion of the total amount,and the proportion of residual state was relatively low.The active state of Pb,Hg and Cr in MCa treatment accounted for a small proportion,and the proportion of residual state was high.After fertilization,both Cr and As showed a trend of increasing the proportion of active state and decreasing the proportion of residue state.(5)The correlation between soil phosphorus and heavy metals showed that total phosphorus,active phosphorus and residual phosphorus in the soil had a significant positive correlation with total heavy metals,the active state and residual state of heavy metals,respectively.In summary,long-term fertilization has caused continuous accumulation of phosphorus and heavy metals in greenhouse soil(Heavy metals did not exceed the screening value of agricultural land soil pollution risk),inorganic phosphorus has increased greatly,and activated the phosphorus.Different heavy metals had different form distribution ratios,but they were mainly in the residue state.There was a certain correlation between soil phosphorus and heavy metals.The effect of combined application of different materials was different.MCa treatment was not only beneficial to the utilization of soil phosphorus and reduced the accumulation of phosphorus,but also had low content of heavy metals in the soil and low activity of heavy metals in the soil(The activity of Pb,Hg and Cr was very low).