Effects Of Municipal Sewage Sludge Compost On Heavy Metal Accumulation And Nutrient Uptake Of Soybean

Soybean has a high economic value; it is the worlds’s leading source of vegetable oil crops, but also an important source of quality protein for human. Therefore, the study on how to improve soybean yield and quality is very important. In recent years, the increasing dependence of pesticide and fertilizer use has caused series of problems such as the lack of the use of organic fertilizer, the imbalance of soil nutrient, soil compaction, the degradation of soil quality, river and underground water pollution and so on. Sewage sludge is rich in organic matter and nutrients for plant growth such as N, P, K and different kinds of trace elements, most of which are plant available. Humus decomposition of organic matter in the sludge can be effective in improving soil physical and chemical properties enhance soil retention of water and nutrients. It is a good soil conditioner; therefore sludge compost is currently in high profile in world’s environmental research project. Because heavy metal accumulation in soil can cause pollution, the heavy metal contents in the sludge is the limiting factor for the use of sludge in agriculture.In this experiment, a randomized block design was used to study the effect of municipal sewage sludge compost on the heavy metal accumulation and nutrient uptake of soybean. Seven treatments were set up, A was blank, B was conventional chemical fertilization, C, D, E, F, G were to utilize different levels of sludge (60000kg/hm2,12000kg/hm2,18000kg/hm2,24000kg/hm2and30000kg/hm2). The physical and chemical properties of the sludge and soil samples were determined before fertilization and the physical and chemical properties of soil were measured after soybean harvest. PTFE crucible was used to digest sludge and soil samples and high-pressure sealed digestion technique was used to digest plant samples. The heavy metal content of sludge, soil and mature soybean plant samples were determined by ICP-MS; the total N, P and K content of soybean in different growth periods were determined by dual-channel, fully automated continuous flow analyzer and the fat content of soybean grain was determined by soxhlet extraction method, they all provide a theoretical basis and technical support for municipal sewage sludge further used for agriculture. Through the experiment, the conclusions are as follows:1, After soybean harvest, soil nutrient content under sewage treatments were higher than the blank (no fertilizer treatment A), and slightly increased with increasing sludge application rate, soil pH was the opposite. Content of organic matter under treatment G was the highest compared with the blank and control (chemical fertilizer treatment B),and was4.84%higher than them (blank equals control); the total N and P content of treatment G were higher than the blank with10.16%and11.23%, the treatment E, F and G were higher than the control, treatment C and D were lower than the control; the available nitrogen content of treatment G and control had an increase of2.17 %and2.14%with blank, other sewage treatments were lower than the control; the available P and K content of control were highest compared with the blank increased by1.74%and4.00%, other sewage treatments were lower than the control; pH of all fertilization treatments compared to blank were reduced.2、The content of Pb, Cd, Cu and Zn of soil under different treatments were increasing with sludge application increased, the general order was G>F>E>D>C>B≈A, and none exceeded. The Cd content of treatment G was higher than the blank with19.89%and had significant difference with blank and control; the content of Cu was higher than the blank with24.08%and had significant difference with blank; the content of Pb was higher than the blank with10.93%and had significant difference with blank and control; the content of Zn element was also higher than the blank with69.47%and had significant difference with blank.3、The basic rule of the ground and underground part dry matter weight of soybean plant in different periods was F>E>G>B>D>C>A.4、The N, P and K content of soybean plant’s vegetative organs in the growing period were associated with the reproductive process of showing a decreasing trend, and in the grain handling from the drum tablets period to maturity was an increasing trend. The content on the general rule was F>E>G>B>D>C>A. N content of the mature grain of F was the highest and higher than the blank with9.30%, and showed significant difference with other treatments in addition to E and G; the highest rate of increase of P content was E, it was higher than the blank with24.36%, and showed significant difference with the other treatments; K content of F was the highest and higher than the blank with31.08%.5、Soybean plants to heavy metals content in different organs of the overall trend was increasing with increasing sludge application rate, that was G>F>E>D>C>B>A, and the three kinds of heavy metals (Pb not detected) content in grain of each treatment were not exceeded. Cu, Zn, Cd content of grain of all fertilization treatments in addition to the control and blank showed no significant difference, the other sewage treatments were significantly different with blank, which G was higher than the blank of28.26%,65.63%and410.14%, respectively.6、The distribution of Cu in different organs was grain> root> pod>stem, Zn was grain> root> pod> stem also and Cd was stem> root> pods> grain.7、Yield of all fertilization treatments were higher than the blank and showed significant difference with blank. The yield of F of all treatments was best and an increase of12.65%compared with the blank, so it could be determined as the best fertilizer treatment, the optimum sludge fertilization was24000kg/hm2. The fat content order of soybean grain of all fertilization treatments was G> F> C> E> D> B> A, the order of protein content was F> E> G> B> D> C> A.