Possibility Of Planting Mulberry In Mining Polluted Farmland

In order to study the possibility of mulberry-sericulture model applied in mining pollution farmland, a field investigation of soil pollution characteristic, heavy metal content and quality of mulberry leaf was conducted in mulberry land of mining pollution area in Huanjiang county of Guangxi province. The thesis mainly studied the heavy metal content relation between soil and mulberry leaf, the quality of mulberry leaf effected by polluted soil, the bio-toxicity of polluted mulberry leaf. The main result can be summarized as follows:1) The soil heavy metal and acid pollution of contaminated mulberry land( submerged by flood with tailings) was severe in Guangxi Huanjiang. The content of Pb, Zn and As in contaminated soil was respectively 17.2, 3.8 and 3.5 times as the content of Pb, Zn and As in control soil( not submerged by flood with tailings, near polluted land). The over standard rate of Pb, Zn and As content was respectively 61.7%, 58.8% and 47.1%("Environmental quality standard for soils",â…¡). The polluted soil acidified extremely before acidity remediation. After primary acidity remediation, there was still about one third polluted land which was strong acid soil (pH<4.5). 2) Mulberry had a strong resistance of acid and toxicity of Pb, Zn and As in soil. Mulberry could grow normally in contaminated soil with 734mg/kg Pb, 1194mg/kg Zn, 53mg/kg As.3) The contents of Pb, Zn and As in the old mulberry leaf and the content of corresponding heavy metals in soil were significantly related. Pb and Zn content of pollution leaf were significant higher than the control leaf(p<0.01). But As content of pollution leaf and control leaf had no significant difference. The accumulation Pb, Zn and As ability of polluted mulberry leaf was nearly equivalent to normal plants.4) The accumulation of Pb, Zn and As in mulberry leaf increased with the. leaf growth cycle prolonging. The content of Pb, Zn and As between old leaf(5-8 leaf position) and tender leaf(above 4 leaf position) had significant correlation in polluted mulberry land. In unpolluted land, only the content of Zn and As between old leaf and tender leaf showed significant con-elation, but Pb was more easily accumulated by tender leaf.5) Not only the quality of mulberry leaf were not reduced, but also the protein content of old leaf in pollution land were significantly higher than the control. The soluble protein content and heavy metal content in mulberry leaf didn't show correlation, but the soluble protein content in mulberry leaf and pH in soil showed negative correlation. The soil acidity affected on acidity inside mulberry plant body. Acid environment inside plant body promoted the soluble protein content increasing. 6) The bio-toxicity of heavy metals in polluted mulberry leaf was low. The percentage of food ingestion and digestion between the polluted leaf and control leaf had no significant difference. There was significant difference of the good cocoon number between the polluted leaf and control leaf. But there was not significant difference of the good cocoon weight between the polluted leaf and control leaf. The rate of silk between the polluted leaf and control leaf also had no significant difference.7) The heavy metal content of silk from silkworm fed with polluted mulberry leaf was lower than the limit of heavy metals content seted by "Technical specification for ecological textiles(GBT18885-2002)". The heavy metal content of faecal from silkworm fed with polluted mulberry leaf was significant higher than the heavy metal content of faecal from silkworm fed with control leaf. But the heavy metal content of faecal from silkworm fed with polluted leaf was lower than the limit of heavy metals content seted by "Control standards for pollutants in sludges from agricultural use (GB4284-84)". The heavy metal content of silkworm chrysalis was lower than the limit of heavy metals content seted by "Hygienical standard for feeds(GB3078-2001)".8). To sum up, mulberry-sericulture is the model of the rational utilization of heavy metal polluted farmland.