Study On The Composition And Nutrient Variation Characteristics Of Roof Greening Substrate

In order to solve the commonly used raw material perlite had different particle sizes,which made the physical properties of the substrate unstable,and the characteristics of nutrient changes during the use of light substrate were not clear and other issues,in this paper,perlite and fly ash were used as raw materials to prepare a mixed substrate.The effects of different particle size ratios of perlite and different additions of fly ash on the physical and chemical properties of the substrate were compared.The seed germination experiment verified the toxicity of substrates.After comprehensive analysis,two matching schemes of roof greening substrates were determined.Through the analysis of the cultivation effect of two species of Caryopteris clandonensis and Euonymus fortunei,the practicability of the roof greening substrates made of perlite and fly ash was explored.Then indoor leaching experiment and outdoor nutrient monitoring were carried out on the substrate with better plant cultivation effect,which could explore the characteristics of substrate nutrient changes.The main conclusions of this study are as follows:（1）The pore structure and saturated water bulk density of the substrate could be controlled by adjusting the perlite size and particle size ratio.For specific performance,when perlite with large particle size（3.35-1 mm）decreased and perlite with small particle size（<1 mm）increased,the total porosity and saturated water bulk density increased,and the size porosity ratio decreased.When the perlite size and particle size ratio is 7:3,the physical properties were the best,the total porosity was the highest 67.44%,the saturated water bulk density was about 0.75 g/cm3,and the size and pore ratio was about 0.41.According to the principal component analysis and comprehensive evaluation,when the ratio of perlite particle size（20 mesh:30 mesh）was 7:3 and the addition amount of fly ash was 15 g or 20 g,the physical and chemical properties of the mixed substrate were better.（2）The formula M _perlite:M _{fly ash}=100:15 was selected as substrate 1,and M _perlite:M _{fly ash}=100:20 was selected as substrate 2,and the perlite particle size ratio of the two substrates was 7:3.In the substrate 2 Caryopteris clandonensis and Euonymus fortunei plant height,fresh weight and dry weight on the ground,root dry weight,root volume,root diameter,root length and root area were significantly higher than that of substrate 1（P<0.05）.In conclusion,substrate 2 was the optimal substrate formula for the cultivation of Caryopteris clandonensis and Euonymus fortunei in this study.（3）In the indoor leaching experiment,after the same times of leaching,the leaching losses of ammonium nitrogen,nitrate nitrogen,total nitrogen,total phosphorus and total potassium in the substrate were 0.138 mg/L,7.733 mg/L,2.356 mg/L,0.195 mg/L and3.199 mg/L,respectively.The leaching loss of nitrate nitrogen was the largest,and the leaching loss of ammonium nitrogen was the least.According to the fitting equation,the five indexes were all in line with the linear regression model,that is,nutrient leaching concentration was significantly negatively correlated with the leaching times（P<0.05）.（4）Between July 15,2019 and November 29,2020,the contents of available phosphorus,available potassium,total phosphorus and total potassium in 0-20 cm and20-40 cm substrates were similar,and the changing trends were consistent.The content of available phosphorus in the substrate showed a"W"type change trend.The content of available potassium decreased first and then tended to be stable.The total phosphorus content fluctuated in the range of 0.35～0.48 g/kg,the total potassium content fluctuated from 30 g/kg～41 g/kg.（5）The organic matter content of 0-20 cm（Caryopteris clandonensis）substrate increased,and the organic matter content of 20-40 cm increased first and then decreased.The contents of organic matter and total nitrogen in 0-20 cm substrate were higher than those in 20-40 cm substrate;there was no stratification in the content of organic matter in the substrate（Euonymus fortunei）,and the organic matter content showed an increasing-decreasing-increasing trend.The total nitrogen content substrates showed an"increase-decrease-increase-decrease"trend,and the total nitrogen content of 0-20 cm substrate was higher than that of 20-40 cm substrate.