Effects Of Long-term Different Fertilization On The Content Of Organic Carbon And Heavy Metals In Aggregates Of Purple Paddy Soil And The Absorption Of Heavy Metals In Crops

With the advantage of time scale,the long-term fertilization experiment field has the advantages of high reproducibility and high reliability for the study of the changes of soil fertility quality including the characteristics of aggregates and soil environmental quality(heavy metals)under different fertilization modes.Therefore,in this study,36 years of calcareous purple paddy soil in Yongxing Town,Chuanshan District,Suining City,Sichuan Province and 3 years of acid purple paddy soil in Huangzhuang,Yongxing Town,Jiangjin city,Chongqing city were selected as long-term fertilization test fields to study the changes of soil fertility quality under the regional,soil and fertilization mode differences,and to reveal the impact of fertilization management measures on soil fertility quality,especially the characteristics of aggregates The accumulation and availability of heavy metals in soils under different fertilization conditions,and the coupling relationship between the characteristics of aggregates and the accumulation and absorption of heavy metals were analyzed.The long-term fertilization experiment field in Chuanshan district,Suining City:In this study,the pH of fertilization reduced by 0.44-0.79 units,MNP and MNPK were the lowest,followed by NP and NPK and the concentration of soil organic matter(SOM)increased by 5.19%~29.24%,N increased least,cation exchange capacity(CEC)concentrations in the no fertilization were minimum,chemical fertilizer combined organic had a lower CEC content than the corresponding single fertilizer;total nitrogen(TN)and alkali hydrolyzed nitrogen(AN)contents increased by 25.33%~77.46%,6.16%~70.58%,it were much better in the applied organic fertilizer treatments,The content of total phosphorus(TP)and available phosphorus(AP)increased significantly with phosphorus fertilization.Taken togather,long-term application of NP and NPK decreased the values of pH and CEC,but increased the content of SOM,TN,TP,AN,and AP,and therefore,improved soil fertility.These effects were more profound in the NP and NPK treatments containing organic fertilizer.Under different long-term fertilization systems,the size of 1~2mm,0.25~1mm,0.053~0.25 mm,<0.053 mm aggregates,at 0~20cm soil depth,accounting approximately for 10%,20%~30%,20%,40%~50%,respectively.<0.053 mm aggregates were the main component and less affected by fertilization.The distribution of aggregates in different size increased with the decrease of grain.>0.25 mm water-stable aggregate mass fraction and MWD were minimum in CK,Compared with CK,fertilization improves soil structure and improves the stability of aggregate.The SOC content varied among different size soil aggregates,the lowest in <0.053 mm aggregates but the organic carbons were mainly distributed in the silt and clay in rice season.Chemical fertilizers did not change the total Fe,Mn,Cu,Zn,Pb,and Cd content in soils.Organic fertilizer along with chemical fertilizer significantly increased the Cu and Zn content but did not affect that of other metals.However,all these metals were under the limit prescribed by the Chinese Soil Environmental Quality of agricultural land(GB15618-2018).Amending the chemical fertilizers did not influence the availability of heavy metals except for treatments with chemical P fertilizer,which significantly increased available Fe,but decreased available Mn in soils.However,treatments with organic fertilizer increased soil available Cu,Pb,especially Cu.Correlation analysis showed that the relationships between the availability of heavy metals and the properties in the soil varied with elements.Fertilization reduced the Fe and Mn content of the aggregates,and the Fe content of the microaggregates was significantly lower than that of other grain grades.The Mn content of the rice season decreased with the decrease of the particle size and the opposite of the wheat season.The content of Cu and Zn in aggregates was the lowest,and the content of Cu and Zn in all grain grades increased by organic fertilizer,especially Cu.The content of Pb in each aggregate were different according to the difference of the planting crops,and the content of Cd was the lowest in micro-aggregates and powdery clay.The distribution of metal consistented with its aggregate size distribution,the effect of long-term fertilization on the content of heavy metals in crops were different due to different crop types,crop parts and metal elements.Individual fertilization has problems of excessive Pb and Cd in grains,so the safety of heavy metals in grains should be paid more attention.(2)The long-term fertilization experiment field of Huangzhuang village,Jiangjin district:The soil pH ranged from 4.96 to 5.24,with the lowest of straw application(SA),the content of SOM increased by 19.97%~41.16%,with the highest of SA,the content of CEC increased by 10.52%~25.17%,with the highest of optimized fertilization(OF).The content of TN,TP,AN,AP increased in different degrees compared with no fertilizer application(NF).The distribution of aggregate also increased with the decrease of particle size,the proportions of silt and clay were about 50%,which is in absolute advantage,and the mass fraction of water-stable aggregate >0.25 mm and the proportion of MWD in NF were the lowest.According to the organic carbon content of different aggregate particle sizes,the order was as follows: small agglomerates> large agglomerates > micro aggregate > silt and clay.The lowest content of silt and clay is also higher.Under the condition of fertilization,the content of organic carbon in different agglomerates increases.Of and SA can significantly affected soil pH,improve content of SOM and CEC and N and P nutrient,and enhanced the stability of soil aggregate structure.The content of heavy metals in soil was the lowest in NF,the highest content of Fe,Mn and Zn in OF,the highest content of Cu treatment in SA,the highest content of Pb and Cd treatment in CF.Except for Pb,the effective amount of heavy metals with fertilization was basically consistent with the response of the total amount of heavy metals to fertilization.The content of heavy metals in microaggregates was the lowest,and the content of heavy metals increases due to fertilization,and the distribution ratios of heavy metals were nearly 50%.Distribution ratio in micro-agglomerates and powder clay particles correspondingly decreased because of fertilization.