| With the development of industrialization, the surface runoff and underground runoff, thechromium in "three wastes" get into the environment, disturbing the original state soil, thecrop quality and safety were influenced, this will harm human health.On the basis of longterm fertilizer experiment about23years at “Chinese National Soil Fertiity and Fertilizer UseEfficiency Monitoring Base of Loess Soil”, we carried out a90days indoor cultivationexperiment. To show the transformation of chromium fraction in different fertilization soilsand the effect on different fertilizer, We spiked the four levels of Cr (Ⅲ)(0、250、500and1000mg/kg) to different fertilization soils which are CK, NPK and MNPK.It providestheoretical basis for establishing emergency measures to deal with pollution incidents. Thenwe add four levels of Cr (Ⅲ)(0、187.5、250and375mg/kg) to stiu soil. After100daysaging, we planted2years crops (wheat maize rotation). To provide reliable and realistic basisfor the safe production of regional agriculture, Cr content in wheat grain and soil, theenrichment coefficient, the changes of soil alkaline phosphatase, invertase and urease activitywere determined.During the90days of cultivation, the soil exchangeable and carbonate bound states ofchromium content of chromium decreased rapidly first and then decreased slowly, andCK>NPK>MNPK; soil bound to Fe Mn oxide, organic combination of content of chromiumand residue chromium were the fast rise and slow rise, performance content organic boundedchromium and residue chromium is: MNPK>NPK>CK, take30days as the critical value.Take500mg/kg chromium as an example, at the end of the incubation, compared with seconddays, CK, NPK, MNPK soil exchangeable chromium accounted for the proportion of addedweight decreased by39.7%,36.7%,30.9%; soil carbonates decreased by21.1%,20.7%24.8%respectively. Soil bound to Fe Mn oxides of chromium increased by52%,55.5%,43.2%; Soil organic bounded chromium accounted for the proportion of added weight wereincreased by6.7%,10.1%,15.5%; soil residue chromium accounted for in proportion to theamount added increased respectively by4%,4.6%,5.4%.It showed that the aging ofexogenous Cr in soil after90days, the effectiveness of chromium reduced gradually, transformate from unstable form to a more stable form, if the chromium converse to theresidual form may need longer time.The results showed that soil pH decreased by0.4to0.6units owing to Cr spiking.Long-term fertilization significantly reduced bio-availability of exogenous chromium. Soilbio-available chromium in NPK was lower than in CK by34%at same Cr level afterincubation, While which in MNPK was close to zero. Iron and manganese oxides boundedand organic bounded fraction was increased by12%and38%, respectively, in NPK relative toCK soil when exposed to Cr; the exchangeable chromium content was decreased by27%, nosignificant change was observed in carbonates bounded and residual chromium fractions.Contents of exchangeable, carbonates bounded, iron and manganese oxides bonded Cr weredecreased by100%,44%and29%in MNPK compared to NPK, respectively; but organicbounded and residual Cr was enhanced by72%and17%, respectively. These resultssuggested that long-term sound fertilizer management notably amendment of organic manurecan significantly improve the resilience of loess soil and thus alleviate the impairment ofchromium contamination.Cr content of wheat grain on exogenous chromium soil was not high (about0.1mg/kg).This value is far below the national standard GB2762-2012contaminants in food safety limitvalue of1mg/kg; Wheat grain Cr enrichment coefficient decreases with chromium pollutionincrease in soil. With the increase of chromium pollution concentration, alkaline phosphatase,invertase activity insoil was inhibited, while the soil urease activity is shown as "low or high"phenomenon. But these effects did not reach significant level. With Lou soil pollution ofchromium less than375mg/kg, the growth of wheat grain Cr content in line with nationalstandards for food safety. |
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