| Pesticide residues have become one of the potential security problems of straw silage utilization. It is unavoidable to have residues in crops by using pesticide, which may have some effect on straw silage. The present study systematically showed the pesticide residues effect of straw silage microorganism in many aspects from the microbial biomass, structure and genetic diversity, but there has been few reports so far.The experiment material was italian ryegrass, and the test consisted of two treatment groups:one was spraying pesticides that was used in corn, the other was spraying pesticides that used in rice, respectively called first treatment group and second treatment group. Each group has blank (CK, no pesticides),1.0 times (based on minimum amount),1.5 times and 2.0 times four concentration treatments, according to different pesticide recommended dosage and actual production. The test uses traditional pure culture technology and PCR-DGGE technology, studying the effect of pesticide on the raw material attached microorganism, and the quantity, diversity,dynamic changes of silage. The main results were as fellows:1.In the two treatment groups,the dynamic changes of the number of bacteria, mold and yeast attached on italian ryegrass in different stage has a characteristic:first restrain, recovery and then increasing, and the higher concentration of pesticide,the longer it lasted. Each test on different intensity of inhibition of bacteria, mold and yeast, with the concentration of pesticide increased, the amount of bacteria was reduced for the 1.0 times and 1.5 times, while the 2.0 times is between the two treatments. The quantity of mold and yeast were much lower in 2.0 times than in 1.5 times treatment of pesticides. There was only little lactic acid bacteria (LAB) in the field. Counts of attached LAB on material of italian ryegrass was significantly (p<0.05) lower than the contrast (CK). Under 1.5 times treatment of pesticide, the counts of bacteria was evidently decline (p<0.05). In the first treatment group, the number of mold and yeast was significantly (p<0.05) lower than the contrast CK, but not significant in different concentration pesticide. In the second treatment group, the number of mold and yeasts was decreased by 1.0 times, and significantly (P <0.05) lower than the contrast(CK).2. The two treatment groups have different effects on the dynamic changes of the pH value and microorganism quantity of italian ryegrass silage. In the process of italian ryegrass ensiling, pesticide can inhibit pH value descend. The number of LAB, bacteria,mold and yeast gradually changed with increasing concentration of pesticide, the quantity of LAB was much lower than the contrast (CK), but the quantity of bacteria, mold and yeast fluctuated above and below of the contrast(CK).3.The two treatment groups of italian ryegrass silage have different impact on LAB and bacterial diversity. In the two group,the diversity of LAB changes consistently. Pesticides have a great impact on the diversity of LAB. Effects-of different concentrations of pesticide treatments on LAB diversity italian ryegrass silage fermentation system are different. With the extension of silage fermentation time increasing, the similarity between every pesticide treatments and the contrast (CK) are enlarging. In these,2.0 times pesticide treatment has a greater impact on the treatment of LAB diversity than others. However, the two pesticide treatment groups effect silage bacterial diversity differently. In these two groups, the first group of bacterial similarity reached 0.55, the second group of bacterial similarity only reached 0.42. |
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