| With the general application of the drip irrigation technology of the cotton in Xinjiang, the diversity of the farmland has changed greatly, and also pests and diseases damage has been strengthened. What change to the diversity of weeds after the drip irrigation technology has been adopted in cotton field? How to use the diversity to prevent creatures effectively is significant. Abutilon theophrasti, which is a distributing weed abroad in cotton field, can not only effect the growth of cotton, but also bring very strong attractive effect to cotton bollworms, so it is a very potential creature prevention material to exploit. Therefore, based on the study on the composition variation of the diversity of the weed communities in soil seed banks from 0 year(flood irrigation) to 8-year drip irrigations in cotton field, the effect of the drip irrigations on the temporal and spatial distribution of weed community species is analyzed, and population dynamics are anatomized combining with the field investigation. Meanwhile, Abutilon theophrasti trapping band is set to study the mechanism of the Helicoverpa armigera, optimize attracting methods and explore the biological control measures using Abutilon theophrasti to prevent cotton bollworms. And some conclusions can be obtained as follows:(1) The drip irrigations had a larger effect on the seed bank of weeds in cotton fields, as the species number and seed density per unit area fluctuated significantly between the years. Continuous drip irrigations changed the structure and the composition of soil seed banks; number of species decreased from 27 species by flood irrigations to 20 and 15 species after 1 and 8 years of drip irrigation respectively. The Shannon-Wiener diversity index reached the lowest for the 8th year drip irrigation and seed density per unit area dropped substantially. With the increase of drip irrigation duration, the species—Setaria viridis, Chenopodium album, Solanum nigrum, A.retroflexus and Amaranthus lividus etc, which were found in dryer conditions, their wide time niche breadth and spatial niche breadth are big, which were found in dryer conditions. The ratio of these species in all seed banks increased gradually and they were the dominant weeds in the cotton fields. The seed banks of weeds were mainly distributed in the farming layer. The seed number was the lowest beyond the farming layer from 46cm to 50cm. Three sites on the northern slope of Tianshan Mountains, along the gradient from the oasis to the edges of desert, which the species were very similar. The irrigation methods, flood irrigation and drip irrigation, appeared to have greater impact on the species variation than the difference of geographical locations.(2) The time niche breadth and spatial niche breadth of Abutilon theophrasti is just less than Setaria viridis, Chenopodium album, Solanum nigrum, A.retroflexus and Amaranthus lividus. The ratio of Abutilon theophrasti increased in the former stage of drip irrigations, but seed banks became 0 when the drip irrigations had been applied for 8 years. And the space distributing instability of Abutilon theophrasti seeds in the soils increased, which caused by drip irrigations.(3) The relative abundance; field frequency; field density and field uniformity of Setaria viridis, Hibiscus trionum, Chenopodium album, and Solanum nigrum were much larger than other species by the investigation of weeds in 7 drip irrigation cotton fields. The total species number of gramineae, chenopodiaceae, malvaceae and solanaceae is the most in investigated weeds, and they were the main families in cotton weeds.(4) It could be seen from the comparison between the investigation and the soil seed banks that the species similarity is very high between them, and the weed status in cotton field could be reflected really from the seed banks. And they both indicated that Abutilon theophrasti adapted preferably by drip irrigations, and will have the latent to be the main weeds in cotton field. (5) The fecundity of attracting cotton bollworms of Abutilon theophrasti in the trapping band is much higher than cotton. The law of development, rotations and burst cycle of Helicoverpa armigera can be seen obviously from accumulated eggs on Abutilon theophrasti plants. It is found that cotton bollworms on the Abutilon theophrasti trapping band can produce 4 generations in the north of Xinjiang, but can produce 3 generations only on the cotton. Abutilon theophrasti trapping band has no obvious effects on the insect community, Aphis gossypii and natural enemies of cotton bollworms, but at the cotton area 0-10m far from the trapping band ladybirds eggs and lacewings eggs are much more than other cotton areas, and it has a certain effect on the breed of ladybirds and lacewings.(6) Optimized study of Abutilon theophrasti trapping Helicoverpa armigera showed that the higher the plants are, the better the trapping effects are, the number of accumulated eggs drop than 40cm>31~40cm>21~30cm>11~20cm>less than 10cm per 100 plants. In the amount of cotton bollworms eggs to different circumstances, the attracting effects of emerald plants are significantly better than dark green. After ageing of the abutilon leaves , cotton bollworms are more like tender fruit to egg. the accumulated eggs of 100 abutilon is 3 lines > 5 lines > 1 line for different wide trapping band, in total, the trapping amount is 5 lines> 3 lines> 1 line, The wider the trapping band is, the higher the trapping amount is, but the 3 lines is the best width in using the trapping band .The abutilon bundle have poor Trapping effect to attract the cotton bollworms, it show that abutilon trap cotton bollworms oviposition by using visual orientation behavior of Helicoverpa armigera.(7) The number of accumulated eggs of one hundred cottons in cotton field with Abutilon theophrasti trapping band is less than the comparing cotton field, and the number of accumulated eggs on the cotton near to the trapping band is more than that far from the trapping band, but it is not obvious. Comprehensive analysis shows that the trapping band can decrease the fecundity of cotton bollworms in cotton field, but it has no obvious effective protection distance.Some advices are proposed based on the research results as follows: (1) Based on Abutilon theophrasti have the latent to be the main weeds in cotton field.The supervision to the weeds that are fond of drought should be strengthened in cotton field, and the research work of the utilization value of the main weeds should be promoted. The seeds of Abutilon theophrasti should be controlled grimly at its maturity period when it is applied, which is to prevent Abutilon theophrasti bringing negative effect on the growth of the cotton. (2) Comprehensive analysis shows that abutilon trap cotton bollworms oviposition by using visual orientation behavior of Helicoverpa armigera, cotton bollworm larvae are beneficial to feed on the Abutilon theophrasti plants oviposition. Therefore the corresponding control measures of the cotton bollworm. Three lines of Abutilon theophrasti trapping band are planted around cotton field before sowing cotton. Cotton bollworms regulate water and fertilizer of the trapping band before the peak of each generation, which is to achieve the best effect on attracting cotton bollworms. Meanwhile medicine prevention should be carried out at the trapping band and the cotton area near to the trapping band when the oviposition peak period of cotton bollworms is just over. And the pupa should be destroyed at the trapping band areas in winter. |
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