| With the rapid development of the national economy,people pay more and more attention to the ecological restoration of slopes.The ecological restoration of slopes can not only improve the ecological environment,but also plant roots have been shown to have a good reinforcement effect on soil and water conservation and stability of slopes.At present,most scholars have studied the reinforcement effect of plant roots and its influence on slope soil stability.However,there are few studies on the growth of plant roots and how to improve the reinforcement effect and then improve the stability of slope soil.Nutrients have a great influence on the growth state of plant roots,and the growth state of plant roots is uncertain.Therefore,this experiment seeks the influence of nitrogen and phosphorus content on slope ecological restoration by adding different nitrogen and phosphorus nutrients to plant pots,so as to obtain naturally growing plant roots.In addition,the influence law of plant root state on soil aggregate,shear strength and anti-disintegration performance was analyzed,the mechanism of nitrogen and phosphorus nutrient addition on slope ecological environment restoration was clarified,and the influence law of plant root state on slope stability was obtained,which provided the basis for ecological restoration of field road slope.In this thesis,plant biomass and root parameters were determined by drying method and photo method,soil microbial content was determined by dilution coated plate method,soil aggregate distribution was determined by dry screen and wet screen method,soil shear strength was determined by direct shear method,and disintegration resistance of soil was determined by immersion disintegration method.The following results were obtained:(1)The addition of nitrogen and phosphorus can increase soil nutrient content,plant biomass and soil microbial content.The results show that the addition of nitrogen can increase the content of nitrate nitrogen,ammonium nitrogen and organic matter in soil,and the addition of phosphorus can increase the content of available phosphorus and microorganisms in soil.Field experiment data showed that soil nutrient content at the bottom of the slope was highest,and plant biomass underground and root parameters at the bottom of the slope were highest,indicating that soil nutrient promoted plant root growth.However,indoor pot experiments showed that an appropriate amount of nitrogen and phosphorus(10 g/㎡)could promote plant growth,while a high concentration of nutrient content would limit plant growth.Comparing the soil nutrient content in the field with the indoor pot experiment,it can be seen that the ecological restoration work of the expressway slope needs to add appropriate nutrients.(2)Plant roots can increase the content of > 0.25 mm aggregates in soil mechanical and water stable aggregates,mainly by increasing the content of 0.5-1 mm aggregates.At the same time,it can enhance the stability of soil water stability aggregates by increasing the average weight diameter MWD.Mixed sowing of whisker-rooted and straight-rooted plants has the best effect on increasing the content and stability of large soil aggregates.The content of soil organic matter,actinomyces and fungi can effectively increase the content of soil aggregates > 0.25 mm,which is mainly achieved by increasing the content of 2-5 mm aggregates.In this thesis,through the redundancy analysis of particle size content of soil aggregates and plant root parameters,it was found that root mass density was the main factor affecting the distribution of aggregates in soil mechanical stability,while actinomyces content and root surface area density were the main factors affecting the distribution and stability of aggregates in soil water stability.(3)Plant roots can enhance soil shear strength,mainly by improving soil cohesion.The mixed sowing of bearded roots and straight root plants has the best lifting effect,and has little effect on the internal friction angle of the soil.Field sampling found that soil with roots was more cohesive than soil without roots,so it was known that plant roots could improve soil mass cohesion.When comparing soil cohesiveness with roots,it was found that the cohesiveness of the slope bottom was highest,and plant roots at the slope bottom were more developed than those at the top and bottom of the slope.Correlation analysis showed that the cohesiveness of plant roots and soil mass were positively correlated.Laboratory tests showed that soil cohesion was as follows:mixed-sowing > unicast tall fescue > unicast Medicago sativa L.> rootless.Therefore,the shear strength of whisker-root and straight root systems in mixed-sowing was stronger than that in unicast.(4)Plant roots can enhance soil anti-disintegration ability,and the mixed sowing effect of bearded roots and straight roots is the best.Field sampling found that the disintegration rate of soil containing roots was lower than that of soil without roots,so it was known that plant roots could enhance the anti-disintegration ability of soil mass.When comparing the anti-disintegration ability of soil mass containing roots,it was found that the anti-disintegration ability of the bottom slope was the strongest,and plant roots at the bottom slope were more developed than those at the top slope and on the slope,so the anti-disintegration ability of plant roots and soil mass showed a positive correlation.According to the results of laboratory tests,the relationship between soil disintegration residues was as follows: mixed-sowing > unicast tall fescue > unicast Medicago sativa L.> rootless.Therefore,the soil disintegration resistance of the mixed sowing of whiskers and straight roots was stronger than that of unicast.In conclusion,nitrogen and phosphorus supplementation of 10 g/㎡can effectively improve soil nutrient content,plant biomass and microbial content.Meanwhile,plant roots of herbaceous plants with mixed roots and straight roots grow best at N10P10,which has the best effect on the distribution and stability of soil aggregates,soil shear strength and anti-disintegration ability.It provides the basis for nutrient addition for the ecological restoration of Taihang Mountain expressway slope. |
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