*4.6. Evaluation of Di*ff*erent Soil and Water Conservation Measures Using the GCM*

The results of comprehensive evaluations can directly reflect the effects of soil and water conservation measures [22,44,45]. The order of gray comprehensive evaluation values in the eight conditions was as follows: S1 (0.7593) > S7 (0.6995) > S3 (0.6656) > S8 (0.6516) > S5 (0.6485) > S2 (0.6385) > S4 (0.6377) > S6 (0.6194) (Table 2). This indicates that in S1, the soil and water conservation benefits were highest, suggesting the use of this soil in restoration programs in this area. Basically, these results lead us to infer that weathered rock soil and collapsible loess can be used when repairing slopes. In terms of plant species, *C. korshinskii* and *H. rhamnoides* Linn. were planted separately to achieve the best soil and water conservation benefits. The gray comprehensive evaluation values of each index were VWS (0.7376) > TP (0.7284) > SPZ (0.7233) > SWC (0.5777) > SOM (0.466) > WrE (0.4294) > WdE (0.369). The relationship between soil bulk density and total porosity was the most significant one, indicating that soil porosity and soil bulk density have the greatest impact on the effect of soil and water conservation measures. When repairing slopes, organic fertilizer can be applied to enhance plant growth and improve soil conditions. Additionally, adequate irrigation is necessary to support plant development.

**Table 2.** Correlation degrees and correlation coefficients of each evaluation index. SPZ, VWS, TP, SWC, SOMC, WrE, WdE, and G (k) represent soil particle size, volume weight of the soil, soil water content, total soil porosity, soil organic matter, water erosion, wind erosion, and gray comprehensive evaluation value, respectively. The parameter ri and Wi indicate the degree of gray correlation and the coefficient of variation, respectively.


#### **5. Conclusions**

We observed significant differences in soil and water conservation benefits among different soil types and two shrubs species. When the gravel content of the soil exceeded 20% of the total soil volume, the changes in soil temperature are aggravated, resulting in a reduced water holding capacity. Based on the soil porosity in the area, water and organic matter conservation are not optimal, and in some sites, the soil condition was not suitable for plant growth. Although we found relatively different organic matter levels in the experimental sites, all levels were beyond the threshold values established by the second National Soil Census. Based on the poor water and organic matter status, plant growth is severely limited. Soil erosion resistance varied greatly among the different sites, and slope protection is crucial to ensure soil and water conservation in this area. The results of the comprehensive evaluation value indicate that the sites of S1 and S7 provide the best soil and water conservation benefits. This also shows that the region can achieve high soil and water conservation benefits through the two allocation modes for slope protection. Weathered rock soil and collapsible loess can be filled in to protect slopes in this area, and subsequently, the two shrub species *C. korshinskii* and *H. rhamnoides* Linn. can be planted separately to achieve optimum protection and to conserve soil and water.

**Author Contributions:** C.J. wrote the paper; B.-p.S. conceived and designed the experiments; X.Y. (Xinxiao Yu) and X.Y. (Xiaohui Yang) analyzed the data.

**Acknowledgments:** This research was supported by the National Natural Science Foundation of China (Grant No. 41430747), the National Science and Technology Support Project (2015BA0804219).

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**


© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

MDPI St. Alban-Anlage 66 4052 Basel Switzerland Tel. +41 61 683 77 34 Fax +41 61 302 89 18 www.mdpi.com

*Sustainability* Editorial Office E-mail: sustainability@mdpi.com www.mdpi.com/journal/sustainability

MDPI St. Alban-Anlage 66 4052 Basel Switzerland

Tel: +41 61 683 77 34

www.mdpi.com ISBN 978-3-0365-6396-1