Research On The Transformation Of Pig Manure With Heavy Metal By Black Soldier Fly And The Application Of Insect Frass On Maize

With the scale development of livestock and poultry breeding in China,a large number of livestock and poultry manure with excessive heavy metals is produced every year.It has a harmful effect on agricultural production,ecological environment and human health.Based on the above situation,the black soldier fly was adopted to transform the pig manure which contains heavy metals,and produced insect frass.The effects of black soldier fly on pig manure nutrients,heavy metals transformation,and the migration and accumulation of cadmium from pig manure to insect frass to soil to maize plants were investigated through the content of nutrients,heavy metals,morphologic change,and the effect of insect frass with different cadmium content on maize plants and heavy metals accumulation.The details of the conclusions were as follows:（1）The p H value of the insect frass was in the range of 7.99～8.19,which was 29.71%～33.61% higher than that of pig manure;the conductivity range from 6.82～7.05,which was31.70%～33.17% lower than that of pig manure.The total nitrogen content（1.21%～1.97%）in insect frass was 34.23%～56.12% lower than that in pig manure.The content of total potassium content（2.08%～2.33%）was increased by 11.98%～19.47%,and the significant change of organic carbon（46.54%～50.14%）and total phosphorus content（5.20%～5.59%）was not observed.After transformation,the total organic carbon,total nitrogen,total phosphorus and total potassium content in insect frass were decreased by 24.55%～32.38%,43.57%～53.06%,17.37%～22.88% and 11.25%～21.00% compared with pig manure,respectively.（2）With the increase of transformation days,the content of cadmium in the insects was increased,while the content of chromium and arsenic were decreased.The content of cadmium in the insect frass was decreased.And there was no significant change of arsenic content in insect frass.After transformation by black soldier fly,the available state distribution proportion of chromium decreased by 30.98% ～52.98%,and the available state distribution proportion of cadmium and exogenously added arsenic did not change.（3）Maize pot experiment suggested that the insect frass with low cadmium concentration had no effect on maize plants,while the insect frass with high cadmium concentration reduced the dry weight of maize plants,plant height,chlorophyll content and photosynthetic rate in the middle and late stages of maize.It It indicated that during the period of maize in the middle and late stages,high concentrations of cadmium inhibited maize growth and significantly reduced the phosphorus content in the roots of maize.（4）With the increase of cadmium content in insect frass,the cadmium content in maize plants and soil were increased,and the content of available cadmium in soil was increased.In conclusion,the effectiveness of chromium decreased,and the effectiveness of cadmium and arsenic did not change significantly after the transformation of pig manure containing cadmium,chromium and arsenic.The insect frass with low cadmium concentration had no effect on maize plants,and the insect frass with high cadmium concentration increased the migration of cadmium into the maize plant and inhibits plant growth.