Effects Of Mushroom Residual Application On Heavy Metals Speciations And Bioavailability Under Rice-wheat Rotation System

The productivity of mushroom residue?MR?is very huge,and it contains rich nutrient contents.Studies have shown that application of MR can improve the quality of soil and crops.But at present,the recycling rate of MR is low,which caused resource waste and environment pollution.MR contains heavy metals,and long-term application of MR may cause heavy metal pollution risk.At the same time,the risk of heavy metals depends more on the speciations and bioavailability of heavy metals.Therefore,the experiment relied on the common rice-wheat rotation system in the Chengdu Plain to explore the effect of the application of MR on the speciations and bioavailability of heavy metals.In order to have consistency and comparability between field trials and general fertilization management,the test based on the conventional nitrogen application rate as the balance basis,the amount of nitrogen carried by MR used as the basis for the calculation of the amount of fertilizer,and the concentrations of heavy metal Cu,Cd,Pb,and Zn was calculated using the application of MR.There were eight treatments,including farmland soil system under no fertilizer?CK?,conventional fertilization?CF?,25%N from MR?M1?,50%N from MR?M2?,75%N from MR?M3?,100%N from MR?M4?,125%N from MR?M5?and 150%N from MR?M6?.The soil and crop samples were collected at the maturity of rice and wheat.The concentrations of Cu,Cd,Pb and Zn as well as BCR method for extraction of heavy metal in the state of acid extractable,reducible,oxidizable and residual were analyzed by using atomic absorption spectrometer,and analysis of the bioavailability of the speciations of heavy metals.Further evaluate the ecological pollution of the concentrations and speciation concentrations of heavy metals in the soil and evaluate the health risks of the crops,so as to obtain a suitable application rate of MR in rice-wheat rotation in the Chengdu Plain.Main conclusions of the study are as follows:?1?The concentrations of heavy metal Cu,Pb,Zn in rice and wheat soil increased with the increase of the MR application rate,and the concentrations of Cd in rice and wheat soil decreased first and then increased with adding MR application rate.Compared with the treatment of CF,the treatment of M1 and M2 can significantly reduce the concentrations of Cd of 6.60%and 4.51%in rice soil;the treatment of M1 and M2 can significantly reduce the concentrations of Cd of 7.64%and 6.15%in wheat soil.?2?Except for some heavy metals elements,the forms of heavy metals in soil were inert transformed after application of MR,which is transformed from a higher bioavailability form to a lower bioavailability form.Compared with the treatment of CF,the treatment of M2 can reduce the active partition coefficient of heavy metals in rice soil,the treatment of combined application of MR and chemical fertilizer?M1^M3?can reduce the active partition coefficient of heavy metal in wheat soil.?3?The concentrations of heavy metal in wheat grain are higher than that in rice grain.Under the treatment of M1^M6,the concentrations of heavy metals in grain increased with the increase of the MR application rate.Compared with the treatment of CF,the treatment of M1 can significantly reduce the concentrations of heavy metals Cu,Cd,Pb and Zn in rice grain and the concentrations of heavy metals Cd,Pb,Zn in wheat grain.?4?Linear regression analysis showde that the active form concentrations can be used to characterize the bioavailability of heavy metals in soil.By multiple linear regression equations analysis,the reducible state has great influence on the heavy metal concentrations of rice grain,and the bioavailability is high;the acid extraction and oxidizable state have great influence on the heavy metal concentrations of wheat grain,and the bioavailability is high.?5?Compared with the treatment of CF,the treatment of M1 can significantly increased the soil pH of 0.13 and 0.16 in rice and wheat soil;the treatment of M1^M6 can significantly increased the soil OM of 9.15%²1.19%and 8.32%¹6.67%in rice and wheat soil;the treatment of M1^M6 can significantly increased the soil CEC of 15.58%²0.77%and13.14%²0.52%in rice and wheat soil.The results of correlation analysis showed that the main factors influencing the active form concentrations of heavy metals in soil were pH and OM.There was a negative correlation between soil active form concentrations of heavy metals and soil pH,and a positive correlation with OM.CEC has a relatively weak effect on soil active form concentrations of heavy metals.?6?Evaluation results of Nemero index and comprehensive potential ecological risk index showed that soils in a non-pollution state under all treatments,and the soil contamination risk was the lowest under the treatment of M1.The results of ratio method of secondary phase and primary phase?RSP?showde that compared with the treatment of CF,the treatment of M1 and M2 can reduce the proportion of secondary phases of heavy metals and reduce the potential harm of heavy metals to the environment.The results of health risk assessment showde that compared with the treatment of CF,combined application of MR and chemical fertilizer?M1^M3?can reduce the threat of health for local people to eat rice,and the health risk of grain is the lowest under the treatment of M1.Proposal:Comprehensive evaluation methods,the risk of heavy metal pollution caused by M1 treatment is minimal.Therefore,application of MR 2408kg·hm^-2,urea fertilizer 245kg·hm^-2,calcium superphosphate fertilizer 121 kg·hm^-2,potash fertilizer 47kg·hm^-2in rice season;application of MR 2890 kg·hm^-2,urea fertilizer 293 kg·hm^-2,calcium superphosphate fertilizer 146 kg·hm^-2,potash fertilizer 56 kg·hm^-2in wheat season with meeting the demands of soil heavy metal safety.