Effect Of Sludge Compost On Soil Nutrients And Crop Yield And Its Safety Evaluation

With the acceleration of urbanization and the increase of population,sewage treatment plant sludge production is increasing.At present,the commonly used method is composting,in this paper,the sewage sludge is made of sludge that from A nning sewage treatment plant of Lanzhou,we set different fertilization treatments,in order to study the soil heavy metal content in sludge compost applied to farmland and safety problem of the farmland,comparing the heavy metals accumulation of Cu,Zn,Cd,Cr,Pb,Hg and As in soil and crop seeds and the changes of crop yield under the treatments of the three consecutive years of chemical fertilizer(NPK),organic fertilizer(M),single application of sludge compost(W1)and different ratio of sludge compost and chemical fertilizer(W2-W5).The results show that :(1)Compared with CK treatment,sludge compost application increased the content of Cr and Zn in soil,had no significant effect to the content of other 3 kinds of heavy metals;The migration rate of heavy metals in soil was very slow.After continuous application of sludge compost,except for Cu and Zn which slightly downward move in soil,other kinds of heavy metals were accumulated in the surface layer.(2)Estimation based on the measured data showed that the maximum bearing years for Cu,Zn,Cd,Cr,Pb,Hg and As was 281,192,48,370,2857,170 and16 years in this region;if use the best fertilization plan W2,the maximum bearing years for Cu,Zn,Cd,Cr,Pb,Hg and As was 327,263,48,729,5045,225 and 18 years in this region.(3)The application of sludge compost could increase the content of total nitrogen,total phosphorus,total potassium,organic matter,available nitrogen,available phosphorus and available potassium in soil.Compared with the basic soil,the increase rate was 19.97%,16.02%,10.31%,15.40%,32.09%,32.79 %and 24.61%,Compared with the CK soil,the increase rate was41.81%,22.05%,12.04%,19.75%,43.1%,42.11% and 33.96%,Sludge compost can be used as a substitute for fertilizer and to achieve the purpose of fertilizing soil.(4)Application of sludge compost can significantly improve crop economic yield and biological yield,to achieve a certain increase in production,but has no significant effect on improving the economic coefficient of the crop.Applications of sludge compost,chemical fertilizer,and organic fertilizer all can achieve the effect of increasing yield.Compared with CK,the largest increase of crop yield under the single application of sludge compost can reach 51.The mixed application of sludge compost and chemical fertilizer is a reasonable and feasible way,not only reduces the risk of heavy metal pollution caused by sludge composting and reduces the amount of fertilizer applied,according to crop demand reasonable use of sludge compost can achieve a good yield effect.(5)After three years of continuous application of sludge compost,the content of heavy metals in grain was less than the national standard,therefore,the application of sludge compost has no bad effect on the quality and safety of agricultural product.(6)The content of Pb,Zn and Cr in pea seeds showed a significant positive correlation with the contents of Pb,Zn and Cr in soil,and the content of Hg in pea seeds showed a positive correlation with the content of Hg in soil;The content of Cu、Zn、Cr、Hg and As in broad beans showed a significant positive correlation with the contents of Cu、Zn、Cr、Hg and As in soil,and the content of Pb in broad beans showed a positive correlation with the content of Pb in soil;The content of Pb、Zn、Hg and As in flax seeds showed a significant positive correlation with the contents of Pb、Zn、Hg and As in soil,and the content of Cr in flax seeds showed a positive correlation with the content of Cr in soil.