| With the rapid development of highway in China, large areas of land have been temporarily occupied and damaged in recent years. In accordance with the ‘Land Reclamation Act’, these lands are required to be reclaimed and reused. However, due to the serious damage by digging, filling, pressing, and occupying during the highway construction, these lands are difficult and costly to reclaim. As soil is the basis of cultivated land, soil remediation is the key to the reclamation of damaged land in highway construction. To achieve ideal land reclamation, it is necessary to reconstruct the soil profile, improve soil physico-chemical and microbial properties so as to provide suitable site conditions for plant growth.In this study, the soils from five types of temporarily construction land of Jiangmen-Luoding Highway in Guangdong Province were collected to assess soil physico-chemical and microbial properties before and after construction and to explore the main limiting factors for land reclamation. Moreover, pot experiment was carried out to investigate the single and combined effect of organic fertilizer, earthworm, and Neyraudia reynaudiana on the soil physico-chemical and microbial properties of damaged land, and then provide scientific basis for the application of this combined technique of ‘organic fertilizer-earthworm-Neyraudia reynaudiana’ into the rapid remediation of damaged land. The main results are as follow:(1) The soil physico-chemical and microbial properties decreased dramatically after highway construction.The original vegetation and topsoils of the temporarily used land were removed during highway construction, and in part of this bare land the soil was highly compacted or concreted. Generally, the temporary land-use in highway construction caused lighter soil color, the disorder of soil structure and profile, the increase of bulk density, and the decrease of soil porosity, water content and field capacity. After temporary land-use, there was also a significant decrease in soil nutrient contents, such as organic matter, total nitrogen, available nitrogen and phosphorus, except a slight increase in the soil p H and the content of available potassium. Moreover, soil enzyme activities, microbial activities, and respiration were significantly decreased. As a whole, soil comprehensive quality was significantly declined(P < 0.001).(2) The main limiting soil factors for land reclamation varied among the types of temporarily land-use.For the reclamation of land used as borrow pit, the deficiency of organic matter, nitrogen, and phosphorus nutrient and the low enzyme activities were the main limiting factors; while the soil compaction and low porosity, water content, and field capacity was the main limiting factor for the reclamation of land which has been temporarily used as construction encampment, mixing station, and construction service road.(3) The application of vermicompost and cattle manure, manure application and earthworm inoculation had better effect on soil physico-chemical and microbial properties than that of chemical fertilizer.Compared with chemical fertilizer, vermicompost and cattle manure, manure application and earthworm inoculation was better for the improvement of both soil physico-chemical and microbial properties, and the effect became significant with the increase of fertilizer amount(P < 0.0001). Soil p H, bulk density and microbial C:N ratio was significantly decreased by the application of vermicompost and cattle manure, which was contrary to the changes in soil porosity, field capacity, the contents of organic matter and total nitrogen, soil microbial biomass, soil respiration, metabolic quotient, the population of bacteria, fungi and actinomycetes, and the activities of soil enzymes. Soil structure, water retention, permeability and fertilizers availability had been significantly improved by the application of organic fertilizer.(4) Both of the application of organic fertilizer and the inoculation of earthworms can promote the growth of Neyraudia reynaudiana and its accumulation of N, P, K nutrients.Compared with the control, the dry weight, plant height, tiller number, root morphology and nutrient accumulation of Neyraudia reynaudiana were significantly increased by the application of vermicompost, or cattle manure ± earthworms, and the effect became more significant with the increase of fertilizer amount(P < 0.0001). In the short term, the synergistic effect of manure application and earthworm inoculation was not significant, and the plant growth and nutrient accumulation was not improved by earthworm inoculation after manure application compared with manure application alone. The growth of Neyraudia reynaudiana was inhibited when chemical fertilizer was applied alone.(5) At the fertilizer rate of 2.5%, the application of vermicompost had better effect on soil comprehensive properties and the growth of Neyraudia reynaudiana.At smaller fertilizer rate, there was no significant difference in soil comprehensive properties and the growth of Neyraudia reynaudiana between the vermicompost and cattle manure treatments at the fertilizer rate of 5%; whereas at the fertilizer rate of 2.5%, the application of vermicompost had better effect on soil physico-chemical properties, the soil microbial properties, the enzyme activities, the growth of Neyraudia reynaudiana, and the nutrient accumulation than that of cattle manure(P < 0.0001).(6) At the fertilizer rate, the application of organic fertilizer was the best for the soil amelioration, following the manure application and earthworm inoculation; while the application of chemical fertilizer alone or earthworm inoculation alone is the worst for the soil amelioration.Factor analysis was used to evaluate the soil comprehensive quality after the inoculation of earthworms and the different fertilization, based on the selected 21 indexes that reflected soil physico-chemical and microbial properties were selected. The final soil comprehensive quality followed the sequence: 5% cattle manure > 5%vermicompost > 5% “Eisenia fetida+cattle manure” >2.5% vermicompost > 2.5% cattle manure > 2.5%“Eisenia fetida+cattle manure” > 5% chemical fertilizer > Eisenia fetida > 2.5% chemical fertilizer > CK. This sequence was consistent with that of Neyraudia reynaudiana biomass under different treatments. The results of cluster analysis by using minimum distance method indicated that At the fertilizer rate, the application of organic fertilizer was the best for the soil amelioration, following the manure application and earthworm inoculation; while the application of chemical fertilizer alone or earthworm inoculation alone is the worst for the soil amelioration.In summary, the soil physico-chemical and microbial properties of temporarily used land in highway construction were severely decreased. The application of small amount of vermicompost and cattle manure can improve the soil quality rapidly and also promote the plant growth, which can be the effective approach for the reconstruction and restoration of damaged soil by engineering construction. |
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