| A pot culture experiment with single factor and completely randomized design was conducted to study the effects of different application rates of Taigu and Nongda sewage sludges on the organic matter, total N, available P, available K, and heavy metal (Cu, Zn, As, and Hg) contents of soil and the yield, nutrient contents, and heavy metal (Cu, Zn, As, and Hg) contents of pak-choi. It will be hope to provide theoretical foundation for safe and reasonable utilization of sewage sludge and using sewage sludge to produce complex fertilizer and soil amendment on calcareous soils. The results showed that:1. The plant height, root length, and fresh weight per plant of pak-choi all increased first and then reduced at two stubbles as the application rate of Taigu sludge increased, and when the sludge application rate was20g·kg-1, the plant height, root length, and freash weight per plant of pak-choi were all the bigest at two stubbles. The plant height, root length, and fresh weight per plant of pak-choi were all increased at two stubbles as the application rate of Nongda sludge increased. The average increase amplitudes of plant height and root length of pak-choi applied with the two sludges were both lower at second stubble than that at first stubble, but the average increase amplitude of fresh weight per plant of pak-choi applied with the two sludges was higher at second stubble than that at first stubble. The average increase amplitudes of plant height, root length, and fresh weight per plant of pak-choi apllied with Nongda sludge were all higher than that applied with Taigu sludge.2. The contents of N, P, and K in pak-choi were all increased as the application rates of the two sludges increased. The average increase amplitudes of N, P, and K in pak-choi applied with Taigu sludge were all lower at second stubble than that at first stubble, and the average increase amplitude of P in pak-choie was the highest at both of first stubble and second stubble. The average increase amplitude of N in pak-choi was higher at second stubble than that at first stubble, and the average increase amplitudes of P and K in pak-choi were lower at second stubble than that at first stubble, and the average increase amplitude of K in pak-choi was the highest in Nongda sludge treatment. The average increase amplitudes of nutrients in pak-choi were lower in Nongda sludge treatments than that in Taigu sludge treatments. 3. Application of the two sludges increased the contents of Cu, Zn, As, and Hg in both aboveground and underground parts of pak-choi. The contents of Cu, Zn, As, and Hg in both aboveground and underground parts of pak-choi increased as the application rate of sludge increased in Taigu sludge treatment. But the contents of Cu and Zn in both aboveground and underground parts of pak-choi increased and the contents of As and Hg in both aboveground and underground parts of pak-choi increased first and then reduced as the application rate of sludge increased in Nongda sludge treatments. The content of As in aboveground part of pak-choi was the highest at the sludge application rate of20g·kg-1, the contents of As in underground part of pak-choi and Hg in aboveground part of pak-choi both were the highest at the sludge application rate of40g·kg-1, and the content of Hg in underground part of pak-choi was the highest at the sludge application rate of80g·kg-1in Nongda sludge treatments. The average increase amplitudes of Cu, Zn, As, and Hg in both aboveground and underground parts of pak-choi were lower at second stubble than that at first stubble in the two sludge treatments. The average increase amplitudes of Cu in underground part of pak-choi and Zn in aboveground part of pak-choi were higher in Nongda sludge treatment than that in Taigu sludge treatment. The average increase amplitudes of Zn, As, and Hg in underground part of pak-choi and Cu, As, and Hg in aboveground part of pak-choi were lower in Nongda sludge treatment than that in Taigu sludge treatment. The contents of Cu, Zn, and Hg were higher in underground part of pak-choi than that in aboveground part of pak-choi, but the content of As were lower in underground part of pak-choi than that in aboveground part of pak-choi. The average increase amplitudes of Cu, Zn, As, and Hg were higher in underground part of pak-choi than that in aboveground part of pak-choi in Taigu sludge treatment. The average increase amplitudes of Cu, As, and Hg were higher in underground part of pak-choi than that in aboveground part of pak-choi in Nongda sludge treatment, but the average increase amplitude of Zn was higher in aboveground part than that in underground part at the first stubble pak-choi and that in underground part was higher than that in aboveground part at the second stubble pak-choi. In this experiment, the contents of Cu, Zn, As, and Hg in pak-choi were all under the acceptable range according to nation al vegetable safety standards (GB2762-2005)4. The contents of organic matter, total N, available P, and available K in soil were all increased as the application rates of the two sludges increased. The average increase amplitudes of soil organic matter, available P, and available K were lower at the second stubble than that at the first stubble, but the average increase amplitude of soil total N was higher at the second stubble than that at the first stubble in Taigu sludge treatment. The average increase amplitudes of soil organic matter, total N, available P, and available K were higher at the second stubble than that at the first stubble in Nongda sludge treatment. The average increase amplitude of soil organic matter was lower in Nongda sludge treatment than that in Taigu sludge treatment at the first stubble, but higher than that in Taigu sludge treatment at the second stubble. The average increase amplitudes of soil total N, available P, and available K were all lower in Nongda sludge treatment than that in Taigu sludge treatment at both first stubble and second stubble.5. The contents of Cu, Zn, As, and Hg in soil were increased as the application rates of the two sludges increased. The average increase amplitude of the four heavy metals in soil was Cu>Zn>Hg>As in Taigu sludge treatment, while The average increase amplitude of the four heavy metals in soil was Hg>Cu>Zn> As in Nongda sludge treatment. The average increase amplitudes of Cu, Zn, As, and Hg were all lower at the second stubble than that at the first stubble in both of the two sludge treatments. The average increase amplitudes of soil Cu and Zn were lower in Nongda sludge treatment than that in Taigu sludge treatment, and the average increase amplitudes of soil As and Hg were higher in Nongda sludge treatment than that in Taigu sludge treatment. In this experiment, the contents of soil Cu, Zn, As, and Hg were all under the acceptable range according to national vegetable safety standards (GB15618-1995). |
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