Effect of insect feces (Hermetia illucens) on rice growth and heavy metal migration from polluted soil to rice plant.

Insect feces are a new kind of biological organic fertilizer. Little is known about the influences of insect feces on rice growth and heavy metal migration from soil to rice plant. In this study, the effects of different amounts (CK (0%), T1 (2%), T2 (4%), T3 (6%), and T4 (8%)) of black soldier fly larvae (BSFL) feces on the rice growth and the migration/accumulation of heavy metals (Cd and Pb) were investigated by pot experiments within 2 years. The application of insect feces remarkably increased the contents of soil pH, organic matter, ammonium nitrogen, available phosphorus, and potassium. Meanwhile, the insect feces application reduced the weak acid-soluble contents of soil Cd and Pb by 8.3-56.8%, but increased those in the oxidizable (by 22.4-165.7%) and residual (by 1.8-225.6%) states. Except for the T4 treatment in the first year, all fertilization treatments increased the rice yield (up to 43.7% and 195.5% higher than those of CK within 2 years). Moreover, the insect feces application reduced the contents of Cd (8.3-66.7%) and Pb (6.4-61.8%) in different parts of rice. Under the same treatment, the metal contents in each part of rice in the second year were lower than those in the first year. The insect feces application decreased the absorption coefficients (24.4-57.5%) and secondary transport coefficients (3.6-44.1%) of Cd and Pb by rice plant. The findings implied that the insect feces might act as effective organic fertilizers for rice plants as well as reducing heavy metal accumulation in rice plants growing in polluted soil.