Background Disposal of residual soil and vegetation restoration in damaged areas emerged during transmission line tower foundation construction are the main factors restricting the project compliance of soil and water conservation. Unreasonable disposal scheme of residual soil and inadequate vegetation restoration effect would cause soil erosion during the construction period of transmission line project, and it is very difficult to rectify before soil and water individual acceptance. In order to solve the problems above, and to promote the acceptance of water and soil conservation of power transmission and transformation construction projects, it is of great significance to study the method of improving construction residual soil into planting soil.

Methods Experiment methods were determined by searching the keywords of "soil water and fertilizer conservation" "soil improvement materials" and "plant growth promotion", consulting the relevant literature and the actual situation of transmission line tower foundation construction, excluding the relevant research of tall trees, and focusing on the soil improvement methods for the growth of herbal plants. Indoor two factor gradient experiments were carried out to improve the residual soil by the mixed application of super absorbant polymer and organic fertilizer by setting nine improvement groups and one control group (CK), improvement groups were as follows: 25/50 (A1B1), 50/50 (A2B1), 100/50 (A3B1), 25/100 (A1B2), 50/100 (A2B2), 100/100 (A3B2), 25/150 (A1B3), 50/150 (A2B3), 100/150 (A3B3) according to the added grams of "super absorbant polymer/organic fertilizer", and the mechanism of soil improvement and plant growth was analyzed by principal component analysis method, in which nine indexes representing soil improvement and vegetation growth selected in this study were recombined into a group of unrelated comprehensive indexes through dimension reduction transformation.

Results 1) Soil improvement by using super absorbant polymer combined with organic fertilizer was significant, the content of soil organic matter increased synchronously with the increment of super absorbant polymer amount, and super absorbant polymer was conducive to improving the rapid degradation of nitrogen, phosphorus and potassium within organic fertilizer, but excessive application of super absorbant polymer would lead to the opposite effect. 2) Organic fertilizer promoted plant growth directly. With the increment of organic fertilizer addition, the plants aboveground and underground biomasses increased simultaneously. The aboveground and underground biomasses of plants decreased inversely with super absorbant polymer used excessively. And the effect of soil mixed improvement was more significant in the early period of vegetation restoration. 3) Through principal component analysis, it can be seen that the best effect of mixed application of super absorbant polymer and organic fertilizer on vegetation restoration was in A2B2 group, followed by A1B3 and A2B3 groups. 4) The outdoor experiment further confirmed that the vegetation restoration of the improved group was significantly better than that of the control group, and the vegetation restoration effect of the experimental group was basically consistent with the comprehensive score of the indoor experiment, which confirmed the reliability of the indoor experiment results.

Conclusions The results of this study reached the original goal in the background by providing an important reference for synchronously solving the two big problems of residual soil disposal and vegetation restoration of transmission line tower foundation construction. It also has found an appropriate theoretical and practical basis for improving the one-time success rate of water and soil conservation acceptance of power transmission and transformation construction projects.