Analysis of variance of the yield was shown in table 4-11.

Table 4-11 showed that there were significant differences between the yields of each treatment. Multiple comparisons of the eggplant yield among treatments were shown in table 4-12.

Notes: The significance of symbols were as same as table4-4.

Table 4-12. Multiple comparisons of the eggplant yield among treatments

The results showed that there were significant differences between B treatment of biogas residue fibre film and control, no significant differences between A, C treatment and control, significant differences between black film and control. There were extremely significant differences between the plastic film, A, C treatment and control, there were significant differences between plastic film and B treatment, no significant differences between plastic film and the black film. It can be seen, the yield of B treatment increased 47% as compared with control.

5. Conclusions

1. Biogas residue are mainly composed of the fiber, non-metallic minerals, minerals, their mass percentage are 64%, 35% and 1% respectively; cellulose, hemicellulose, lignin and ash are 44.8%,21.9%,15.6% and 17.7% respectively in the biogas residue fiber. The mass percent of biogas residue cellulose is over 5% more than that of rice straw, wheat straw and corn stalk; the mass percent of the hemicellulose is 5% less than that of rice straw, wheat straw and corn stalk.

2. An optimum factors combination is rosin 0.4%, bauxite 4% and wet tensile strength 1.8%, beating degree 40SR°, grammage 80 g/ m2, in this case, for the biogas residue fibre film, dry tensile strength can attain more than 30N, wet tensile strength can attain more than12N, the degradation period can attain 35 days to 60 days.

3. The rank of importance of the five factors on the dry tensile strength: grammage, beating degree, wet strength agent, bauxite and rosin; on the wet tensile strength: wet strength agent, bauxite, rosin, grammage and beating degree; on the degradation: grammage, wet strength agent, bauxite, rosin and beating degree.

4. Biogas residue fibre film has significant effect against weeds as compared with plastic film and bare field.

5. There was no significant difference of conserving moisture between biogas residue fiber mulching and the plastic film.

6. In the period of eggplant growth, the rank of the total accumulated temperature: plastic film, black film, biogas residue fibre film and bare field.

7. The eggplant yield of biogas residue fiber mulching whose grammage is 80g/ m2 is 47% more than bare field, and slightly lower than that of the plastic film.

8. It is feasible to make biodegradable mulching from the biogas residue, in accordance with the agronomic requirement