Effect Of Subsurface Pipe Drainage System And Returning Straw Into Field On Greenhouse Soil Improvement And Cut Chrysanthemum Quality In Continuous Cropping System

Chrysanthemum(Chrysanthemum morifolium)is a perennial plant and originated in China,which is one of the most important ornamental plants with various color and inflorescence types.As one of the world's four major cut flowers,chrysanthemum occupies an extremely major market share of cut flowers in the world.With the increase of market demand for cut chrysanthemums,the accelerated development of the cut chrysanthemum industry in China,the area of cut chrysanthemum production has continued to expand,and the continuous planting years has accumulated.This has led to the increasing serious obstacles to continuous cropping of chrysanthemum,deterioration of soil physical and chemical properties and nutrient ratio,increase of secondary salinization of soil,reduction of production performance,and severely degrading the quality of cut chrysanthemums have become a difficult problem needed to be solved in chrysanthemum production.Under the actual production conditions,this experiment applied subsurface pipe drainage system and returning straw into field,to study the effect the different buried pipe spacing(2 m,4 m and 6 m)and the different straw returning amount(800 kg·hm-2,1600 kg·hm-2 and 2400 kg·hm-2)on soil organic matter content,available nutrients(available nitrogen,available phosphorus,and available potassium)content,salt content,soil enzyme activity(urease,sucrase,and catalase),the root activity,the quality and rhizosphere microorganisms of cut chrysanthemum 'Jimba'.The aim is to propose the best technical solution for the improvement of greenhouse soil and improving the quality of cut chrysanthemums.The main results were listed as follow:(1)In this study,under the condition of straw returning to field(800 kg.hm-2),the subsurface pipe drainage system was used to investigate the effects of different pipe spacing(2,4 and 6 m)on plough layer soil and the quality of cut chrysanthemum 'Jimba'.The results showed that the subsurface pipe drainage system could significantly enhance the root activity of the cut chrysanthemum.Compared with CK,the 2m,4m,and 6m pipe spacing treatment increases respectively by 36.1%,37.3%and 33.1%.And show a positive improvement in the main quality of cut chrysanthemum(plant height,stem diameter,flower diameter,ray floret number and shoot dry weight).Among the treatment evaluated,the 4m pipe spacing has the best treatment effect,which respectively increases by 22.2%,17.0%,13.9%,9.0%and 35.1%;The 4m pipe spacing treatment shows the significant improvement in soil organic matter and available nutrient content compared with 2m and 6m pipe spacing treatments.The 4m pipe spacing not only showed positive effect on groundwater depth controlling and desalination,but also showed significant effect on reducing the surface soil water content,electrical conductivity,total salt content and the main salt ions contents(Ca2+,Na+and SO42-).Soil water content in treated(2,4 and 6 m)decreased respectively by 299.9 mg·kg-1,264.3 mg·kg-1 and 268.1 mg·kg-1.With the decreasing of buried pipe spacing,the effect of groundwater depth controlling and desalination is more obvious.Combined with the initial cost of embedded buried pipe into account,the treatment of 4m pipe spacing can be the economic way to improve both soil and cut chrysanthemum quality in continuous cropping greenhouse.(2)To study the effect different straw returning amount(800 kg.hm'2,1600 kg·hm-2 and 2400 kg.hm-2)under conditions of subsurface pipe drainage(buried pipe spacing of 2 m)on the nutrient,cation exchange capacity and total salt content of tillage layer soil and the main physiological parameters of cut chrysanthemum 'Jimba'.The results showed that returning straw into field can significantly increase the organic matter,available phosphorus and available potassium in soil.While the content of available nitrogen decreased,the straw returning amount of 1600 kg·hm-2 was significantly lower than the straw returning amount of 800 kg·hm-2 and 2400 kg·hm-2.The application of rice straw can increase the cation exchange capacity of soil,and the straw returning amount of 1600 kg·hm-2 was the best,which was 8.30 cmol·kg-1 higher than that of CK.The treatment of returning straw into field can significantly reduce the total salt content and electrical conductivity of the surface soil.The reduction of 1600 kg·hm-2 straw returning amount was the largest,which was a drop of 88.48?s·cm-1;After treatment,the main physiological index such as plant height,stem diameter,ray florets,flower fresh weight,and biomass were significantly increased.Among them,the straw returning amount of 1600 kg·hm-2 treatment had significant effects on plant height,ray flowers,and biomass indicators above than the straw returning amount of 800 kg·hm-2 and 2400 kg·hm-2 treatments.The application of 1600 kg·hm-2 rice straw returning amount was the best treatment of this test,the soil environment was improved,the soil fertility was increased,and the quality of the cut flower chrysanthemum was significantly improved.(3)To study the effect different straw returning amount under conditions of subsurface pipe drainage(buried pipe spacing of 2m)on root activity,soil enzyme activity(urease,sucrase,catalase)and rhizosphere microorganisms of cut chrysanthemum 'Jimba'.The results showed that the root activity of cut chrysanthemum was significantly increased after rice straw was returned to the field.The treatment with straw returning amount of 1600kg·hm-2 increased-the most(33.34%).The soil urease activity decreases with the increase of straw returning amount;The catalase activity increased by 23.81%,54.22%,and 24.42%,respectively.The straw returning amount of 1600 kg·hm-2 was increased 76.86%,which was significantly higher than that of the treatment with straw returning amount of 800 kg·hm-2 and 2400 kg·hm-2.After the return of straw,the number of bacteria increased,the number of fungi decreased,and the B/F value increased significantly.The amount of fungi is inversely proportional to the amount of rice straw returned;B/F values increased 172.70%,257.74%and 210.26%,respectively.This indicates that straw returning to field under the condition of subsurface pipe drainage is conducive to improving the soil microbial community structure,from fungal type to bacterial type.The improvement effect of soil biological properties was obvious when the straw returning amount of 1600 kg·hm-2 was used to drain the buried pipe spacing of 2 m.