Effects Of Long-term Fertilization On Heavy Metal Accumulation In Soils And Crops

Studies on effects of fertilizer application on heavy accumulation in surface soils (0-20cm) andcrops are critical for effective and safe application of fertilizers and manures. In this study, over20-yearlong-term fertilizer experiments in Black soil, Fluvo-aquic soil and Red soil under the cropping systemof maize, winter wheat-summer maize, winter wheat-summer maize, respectively, were used as thestudied materials. Soil and plant samples were collected from different fertilizer treatments includingcontrol without fertilizer (CK), NK, NPK and NPK plus manure (M). The contents of copper (Cu), zinc(Zn), cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), arsenic (As) and mercury (Hg) in collectedsoil and crop samples were analyzed. The fractions of Cu, Zn, Cd in soils and their relations to cropaccumulations were tested. The following results were obtained:1. Compared with CK, application of chemical fertilizers (NK and NPK) did notsignificantlyaffect Cu, Zn, Cd, Cr, Pb contents in Black soil, Cu, Zn, Cd, Cr, Pb, Hg, Nicontents in Fluvo-aquic soil, Cu, Zn, Cd, Cr contents in Red soil. Whereas combinedapplication of chemical fertilizer and manure (NPKM,1.5NPKM) significantly increased Cu,Zn, Cd contents in Black soil, Cu, Zn, Hg contents in Fluvo-aquic soil, Cu, Zn, Cd, As contentsin Red soil. Compared with NK, NPK did not significantly affected heavy metal contents in thethree types of soils, while NPKMsignificantly increased Cu, Zn, Cd, Pb contents in Black soil,Cu, Zn, Hgcontentsin Fluvo-aquic soil, Cu, Zn, Cd contents in Red soil. Application of NPKMsignificantly increased Cu, Zn, Cd, Pb contents in Black soil by88.9%,61.7%,449%,12.4%,increased Cu, Zn, Cd contents in Red soil by151%,74.0%,331%over NPK.2. Under current fertilization practices and cropping systems, NPKM treatment significantlyincreased Cu, Zn, Cd contents over CK and NPK treatments. Therefore, the average heavymetal contents of applied manures were estimated based on the difference ofmetal contents inNPKM and NPK treated soils, while the maximum bearing years of soils for metals werecalculated based on the difference ofmetal contents in NPKM and CK treated soils. Theaverage content of Cu, Zn, Cd was20.2,32.7and1.0mg·kg-1in manures applied in Black soil,5.4,20.2and0.1mg·kg-1in maures applied in Fluvo-aquic soil, and128.5,142.1and2.3mg·kg-1in manures applied in Red soil. Referring to the National Level Two SoilEnvironmental Quality Standard, the maximum bearing year for Cu, Zn and Cd was67,118and9years in Black soil,1042,2043and631years in Fluvo-aquic soil,10,46and0.5years inRed soil, respectively.3. In Fluvo-aquic soil, Zn contents in wheat grains and straws in NK treatment were significantlyhigher than other treatments. Cd andAs contents in wheat straws were higher in NPKMtreatment than CK and NPK treatment. In Red soil, NPK treatment significantly decreased Cu,Zn, Cd, Ni contents by29.9%,22.7%,31.3%,65.1%in wheat grain compared with CK,whereas NPKM treatment significanlty increased Cu, Zn, Cd contents in wheat grain by28.0%, 65.3%,81.8%, increased Zn, Cd, Hg contents in wheat straws by289%,103%,32.3%overNPK.4. Compared with CK, fertilizer application practices did not affect Cu, Cd, Cr contents in maizegrains in Black soil and Fluvo-aquic soil, as well as Cd, As contents in maize grains in Red soil.Comparing with NK, NPK significantly increased Pb contents in maize grains in Black soil andFluvo-aquic soil, and NPKM significantly increased Zn, Pbcontents in maize grains in Blacksoil, increased Pb contents in maize grains in Fluvo-aquic soil. The NPKM and1.5NPKMtreatments significantly increased Zn contents in maize grains in Black soil and Red soil overthe NPK. The Cu, Zn, Cd, Pb, As, Hg, Ni contents in maize straws of NPKM treatment weresignificantly more than NPK treatment in the Red soil.5. Fractionationsof Cu, Zn, Cd in soil samples by BCR extraction procedures indicated thatcompared with NK, the NPK treatment significantly increased reducible Zn contents andportions, decreased Zn contents in Black soil, decreased organic-bonded Zn contents andincreased residual Zn contents in Fluvo-aquic soil, increased acid extractable Zn, Cd andorganic-bonded Zn contents and portions in Red soil. Compared with NPK, application offertilizers and manures (NPKM or1.5NPKM) increased acid extractable, reducible andorganic-bonded Cu, Zn, Cd contents in Black and Red soil, increased residual Cu contents inFluvo-aquic soil and residual Cd contents in Red soil, decreased residual Zn contents inFluvo-aquic soil and Red soil.In Red soil the1.5NPKM treatment significantly improved acidextractable, reducible and organic-bonded Cu, Zn, Cd contents over NPKM treatment.Regression analysis indicated that the total and EDTA extractable Zn, Cu and Cd were the mainfactors influencing their fractionations in Black soil and Red soil.6. Stepwise regression analysis between the contents of heavy metals in crops and differentfractions in soils indicated that the main bioavailable fraction of Cu, Zn, Cd in Black soil wasacid extractable. The main bioavailable fractions of Zn and Cd in Fluvo-aquic soil werereducible and organic-bonded fractions. The bioavailable Cu, Zn and Cd in Red soil were acidextractable, reducible and organic-bonded fractions.