Study On The Effects Of Sewage Sludge On The Growth Of Lettuce

With the emissions of sewage sludge increasing, environmental pollution, and growing, and thus endanger human health. So, it ibecome more important to disposal of sewage sludge and make good use of the sludge. The study on the sewage sludge application in agriculture, which is of great theoretical and practical value on the effective using of sewage sludge and reducing pressure on the environment.The sewage sludge in the experiment was taken from native sewage treatment plant (Bei shiqiao, xian) and lettuce was chosen as the experimental subjects. Through observing the germination and determining physiology and quality indicators of lettuce, we can come to the conclusions as follow.(1) In the first quarter of the pot test, it played a certain role in promoting lettuce growth in the low applicationrates of sludge (<12g/kg), but it inhibite the lettuce growth in the high applicationrates of sludge (> 12g/kg).1) The results of lettuce germination rate show that: the low applicationrates of sludge on the germination of lettuce has been facilitated in the sludge's applicationrates for the 6g/kg, the average germination rate (93%) than the one(75%) in the Comparison; but with the sludge's applicationrates increased, the average budding rate was inhibited and it was just 13% in the sludge's applicationrates of 18g/kg.2) The root activity test showed that: the volume, total absorption area, active absorption area of lettuce root and the percentage of active absorption area ncreased in low sludge's applicationrates. In the sludge's applicationrates for the 3g/kg and 6g/kg, the root volume and percentage of active absorption area were up to the maximum; when the sludge's applicationrates for the 9g/kg, the total absorption area and active absorption area reached their maximum.3) The content results of chlorophyll, soluble sugar and soluble protein showed that: The sludge can promote the synthesis of chlorophyll. And which reached its maximum of 13.863mg/g in the applicationrates for the 6g/kg. However, it would decreased chlorophyll content when sludge's applicationrates is too high (> 12g/kg); sludge had a limited impact on the soluble sugars. In the sludge's applicationrates for the 6g/kg, soluble sugar content was highest, but which was only about 3% higher the Comparison's. The inhibition is very clear that when the sludge's applicationrates is 12g/kg, the soluble sugar content was 3.378mg / g, and decreased by about 50% compared with the Comparison's. with the sludge's applicationrates increasing, soluble protein content increased significantly and reached the maximum in the applicationrates 9g/kg, which is 3 times higher than the Comparison's, but the soluble protein content started to decline when the sludge increasing. however, the soluble protein content of each treatment was still higher than the Comparison's.(2) The residual experiment showed that: the indexes of Lettuce appeared a trend of increasing and then discreasing with sludge application. the maximums of Chlorophyll, water content, soluble proteins appeared in the sludge's applicationrates for the 9g/kg, and were 91.9%,16.384 mg/g,25.26 mg/g respectively; when the sludge application was 21g/kg, the average sprouting rate came to the maximum of 67%; root volume, total absorption area, root area ratio, root active absorption area and root active absorption area of the highest percentages were 1.2cm3,0.632cm2,0.824%,0.199 cm2 and 41.61%. The soluble sugar's Maximum appears in the sludge's applicationrates for the 9g/kg and was 16.07mg/g.(3) through the experiment, we can come to the conclusion that: the sludge has a role in promoting the growth of Lettuce when its application lower than 9g/kg. So the application of the sludge, which converted to field application is about 1350kg / mu, can be used as the recommended value of farming.