| Enzyme activities are important parameters for soil quality; they may be affected by heavymetal pollution. The North China Plain is an important base of lead （Pb） production in Chinaat present; however, the effect of heavy metal pollution on enzyme activities in this region hasnot been documented yet. Much crop straw with high heavy metal concentration are producednear lead smelters and applied into farming field every year, during this process, the heavymetals in the straw also enter the soil. However, the effect of the polluted straw on the soilquality has not been investigated. This work was conducted to investigate the relationbetween heavy metal and enzyme activities in soils near the lead smelter, and the effect ofapplying polluted crop straw on soil properties. Main findings include,i) The analysis of33topsoil samples from farming fields near a lead smelter in the NorthChina Plain indicated that, the average total Pb and Cd concentrations were144and5.59mgkg-1, respectively, those of DTPA-extractable Pb and Cd were54.1and0.964mg kg-1, thesevalues were much higher than those of average levels of un-polluted farming field soil.Significant negative correlations were found between catalase activities and the DTPA-Pb and-Cd concentrations, the total Pb concentrations （p<0.01）. The dehydrogenase activities weremore affected by the accumulation of Pb and Cd than pHospHotase and urease. The activitiesof protease and alkaline pHospHotase increased with increasing DTPA-Ni concentrations（p<0.1）, no significant correlation was found between urease activities and the total or DTPA-extractable concentrations of the heavy metals.ii) Polluted or clean crop straws were applied in un-polluted Chaotu soil at the rates of2%and4%and incubated. The results indicated that, concentration of Olsen-P increased2.66and7.81mg kg-1at the rate of2%and4%, respectively. No significant difference was observedfor the polluted straw at the rate of2%, however, at the rate of4%, Olsen-P increased by6.08mg kg-1, and the difference was statistically significant （p<0.05）. No obvious effect of theclean straw on heavy metal availability was observed. For the polluted straw amendment,concentrations of DTPA-Pb and Cd increased2.54and0.062mg kg-1at the rate of2%,respectively, at the rate of4%, these two values were4.72and0.107mg kg-1.iii) A Chaotu soil was spiked with500mg kg-1Pb, and amended with phosphate andpolluted or clean crop straw. The phosphorus availability was determined periodically during the following incubation. The results indicated that, the phosphorus availability increasedduring the30d incubation duration, the phosphorus amended soils increased about10-20mgkg-1, and these values were larger than those of non-phosphorus amended soils. The cropstraw amendment of non-lead-spiked soil increased soil phosphorus availability. Strawamendment of the lead-spiked soil increased soil phosphorus availability1d since theincubation, after that, the phosphorus availability of the straw amended soil graduallydecreased compared with the control. In most cases, there was no obvious difference inphosphorus availability between the clean and polluted straw amended soils.The results of this work suggest that, the total and available concentrations of Pb and Cd insoils near the lead smelter in the present study are higher than un-polluted soil, the activitiesof certain enzymes are affected by the accumulation of Pb and Cd; the application of cropstraw increased the phosphorus availability in soil, and the phosphorus availability increasedwith increasing incubation time, however, no substantial difference of the effects between thepolluted and clean straw on the phosphorus availability exists. Application of polluted cropstraw into Chaotu soil increased the availability of Pb and Cd, and the enrichment effectincreases with increasing dosages. |
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