Effects Of The Return To The Field Of Cotton Stalks Transformed By Insect-microorganism Composite Technology On The Growth And Development Of Cotton And The Occurrence Of Verticillium Wilt

In order to solve the problems of increasing Verticillium wilt in continuous cropping cotton fields,the low utilization rate of cotton stalks resource,and prominent disadvantages of direct return to the field,the effects of return of cotton stalks by insect-microorganism composite technology on the growth and development of cotton and the occurrence of Verticillium wilt were studied.To explore the potential of Protaetia brevitarsis Lewis in transforming cotton stalks and the return of larvae dung-sand（frass,larger particles called larvae dung-sand）to the field,the risk assessment of returning cotton stalks with Verticillium dahliae and larvae dung-sand to the field on the occurrence of Verticillium wilt,and the feasibility of combining larvae dung-sand with biological anti-microbial to prevent and control cotton Verticillium wilt.To optimize and verify the main technical parameters of cotton stalks transformed by insect-microorganism composite technology,to clarify the effects of the direct return of cotton stalks with V.dahliae and return of cotton stalks based larvae dung-sand on the amount of Verticillium wilt microsclerotia in the soil,the growth and development of cotton and the occurrence of the Verticillium wilt,and to explore the effects of the larvae dung-sand composite biological anti-microbial return to the field of cotton stalks after biotransformation on the growth and development of cotton and the occurrence of Verticillium wilt.This paper provided technical solutions and new ideas for off-field utilization of cotton stalks resources and the green prevention and control of cotton Verticillium wilt.The main results are as follows.1.The optimal technical parameters for transforming cotton stalks by insect-microorganism composite technology were as follows:40%ratio of cattle manure,selection of VT decomposition inoculants and fermentation for 25 days.We can concluded that for every 100 g of cotton stalks supplemented with 66.67 g of manure,104.75 g of mixed feed can obtain 70.92 g of larvae dung-sand after transformation by the 3rd instar larvae of the P.brevitarsis,and the weight gain of the dry larvae was 3.06 g,with 20.88 g residue remaining.Insect-microorganism compound systems can improve the nutrition indicators of cotton stalks as feed and fertilizer.The contents of protein and fat of the dry larvae were 52.49%and 11.7%.Compared with cotton stalks,the protein,fat and total energy of the larval body were 7.31,19.50 and 1.16 times higher,the free gossypol was reduced by more than 50%,and the crude fiber was less than 1/6.Dry larvae are high-quality,high-protein feed ingredients from an insect source.The total nitrogen,phosphorus,and potassium content was 9.04%,which was 1.95 times of the total nutrient of cotton stalk,and more than twice of the standard of organic fertilize（NY525-2021,NPK≥4%）,and the organic matter content of larvae dung-sand was 54.8%,which had the potential for fertilizer application.2.During the 70 d growth period of potted cotton,the growth and development of potted cotton in diseased soil was better than that in sterilized soil,in terms of plant height（46.78%～83.45%increase of B relative to M,the same below）,stem diameter（28.39%～51.83%）,number of fruit branches（17.19%～39.06%）,leaf age（17.19%～39.06%）and other growth indicators,the overall performance of the 7 treatments was as follows:cotton plants with V.dahliae>sterilized cotton plants>CK>root stubble with V.dahliae>Sterilized root stubble>cotton Stalks with V.dahliae>Sterilized cotton stalks.The full amount of cotton plants returned to the field can promote the growth and development of cotton,while the single return of root stubble and cotton stalks has a negative effect on the growth and development of cotton.The microorganisms carried by cotton plants and soil microorganisms had important effects on the growth and development of cotton.The direct return of cotton stalks and root stubble with V.dahliae increased the risk and degree of the occurrence of verticillium wilt in the current year.The number of cotton Verticillium wilt microsclertia in the rhizosphere soil of diseased field soils increased 0.16～8.37 times at the peak of Verticillium wilt occurrence compared with the initial soil sample,and the disease index of cotton Verticillium wilt occurrence and the number of microsclertia in the rhizosphere soil had a positive correlation trend.The negative influence of the return of root stubble with V.dahliae to the field on the occurrence of cotton Verticillium wilt was the greatest,with a 20.00%increase of disease index and an 8.37 fold increase of the number of soil microsclertia.No Verticillium wilt microsclerotium was detected in the cotton stalks and root stubble feed with V.dahliae fermented for more than 5 days and the larvae dung-sand transformed by P.brevitarsis.There was no risk of inoculation with microsclerotia of cotton Verticillium wilt when the larvae dung-sand returned to the field.For the cotton stalk and stubble mixed materials fermented for 25 days,the larvae of P.brevitarsis had good transformation ability.For every 1unit of dry larvae gain,it can take 27.47 times of feed and produce 23.88 times of larvae dung-sand,this translates into 3000 kg of larvae dung-sand and 120 kg of dry larvae per hectare of cotton stalks.3.Two years of experiments in the disease fields affected by cotton Verticillium wilt showed that the mode of cotton stalks off-field with larvae dung-sand and dung-sand compound biological anti-microbial return to the fields was feasible to ensure the growth,development and yield of the heavy Verticillium wilt disease field.In terms of the growth and yield of cotton,the diseased field（B）was superior to the field inoculated the microorganism（I）,there were no significant differences in plant height（the increase of B relative to I is 3.59%～9.58%,the same as below）,stem diameter（-8.11%～-6.17%）,leaf age（1.01%～1.55%）,chlorophyll content（-0.47%～1.35%）,first fruiting branch height（-8.40%～-0.58%）and number of fruit branches（9.66%～10.26%）in five treatments,including stalks removal/returning to field,larvae dung-sand and larvae dung-sand compound biological anti-microbial returning to field.The three treatments of stalks removal and larvae dung-sand and insect sand combined with biological anti-microbial returning to the field showed better overall performance in plant height,stem diameter,leaf age,number of fruit branches,number of cotton bells per plant（14.34%～24.31%）and yield（2.00%～6.77%）,the comprehensive increase was 4.74%～7.71%in 2 years.The cotton stalks off-field with larvae dung-sand and dung-sand compound biological anti-microbial return to the field for the following year to reduce the occurrence of cotton Verticillium wilt disease has a certain effect,and the comprehensive anti-efficiency was 33.96%～41.03%in 2 years.The number of microsclerotia of cotton Verticillium wilt was 3.81 to 8.05 CFU·g^-1in the tillage layer soil during the sowing stage of the experimental field.By the peak of Verticillium wilt occurrence,the number of microsclerotia of each treatment ranged from 2.24 to 12.67 CFU·g^-1.The number of microsclerotia of the stalks leaving the field and larvae dung-sand returning to the field treatment ranged from 2.24 to 7.48 CFU·g^-1,with an increase or decrease of-41.30%～79.17%,and the number of microsclerotia in the stalks return treatment ranged from 4.94～12.76 CFU·g^-1,with an increase or decrease of-25.97%～97.39%.The stalks leaving the field and larvae dung-sand returning to the field can prevent the growth of microsclertia in the rhizosphere soil to a certain extent,and the direct return of stalks has a risk of aggravating the accumulation of cotton Verticillium wilt microsclerotia.In summary,it can be concluded that:Supplementation with 40%manure,addition of 1‰VT inoculants,and fermentation for 25 days is the optimum technical parameters for transforming cotton stalks by insect-microorganism composite technology.The coupling application of cotton stalks for feed（high protein larval body）and fertilizer（high nutrient larvae dung-sand）is feasible.Direct return of cotton stalks and root stubble with Verticillium wilt microsclerotia to the field increased the risk of cotton Verticillium wilt（up to 20.00%）and increased the number of cotton Verticillium wilt microsclertia in the rhizosphere soil（up to 97.39%）.The pattern of cotton stalks off-field with the larvae dung-sand composite biological anti-microbial return to the field of cotton stalks after biotransformation could promote cotton growth,development and yield（increase4.74%～7.71%）,reduce the occurrence of verticillium wilt of cotton（41.03%）and reduce the accumulation of cotton Verticillium wilt microsclertia in the rhizosphere soil（up to 41.30%）.Cotton stalks through insect-microorganism composite technology to achieve resource utilization link cotton stalks off-field accompanied by larvae dung-sand or dung-sand composite biological anti-microbial to the field has potential application for the green prevention and control of cotton Verticillium wilt and the sustainable development of the cotton industry.As a new improved stalks returning technology,the indirect return of cotton stalk by the insect-microorganism composite technology improves the utilization effect of stalks resources,and prevents the direct return of stalks and stubble with V.dahliae from increasing the risk of increasing the number of cotton Verticillium wilt microsclertia in the rhizosphere soil and aggravating the disease of cotton Verticillium wilt..It is of great significance for the utilization of cotton stalks resource,reducing the occurrence of cotton Verticillium wilt and the healthy development of cotton planting industry.