Time effect of young shrub roots on slope protection of loess area in Northeast Qinghai-Tibetan plateau

To study the persistence effect of plant roots in slope protection of loess area in the northeast of Qinghai-Tibetan plateau, four shrubs Atriplex canescens、Caragana korshinskii、Nitraria tangutorum、Zygophyllum xanthoxylon were planted on the slopes of the test area. Field situ pull-out test was applied to test the four shrubs with one-year growth period or four-year growth period. The result showed that during the four years, the pull-resistance、lateral root quantity of Atriplex canescens were the largest, and the root diameter of Zygophyllum xanthoxylon increased fastestly among the four shrubs; and the root diameter of Zygophyllum xanthoxylon increased faster than that of the other three shrubs during the first year, and the root diameter of Atriplex canescens increased faster than that of the other three shrubs from the second year to the fourth year. There was a power function between average root diameter and growth time for Zygophyllum xanthoxylon and Nitraria tangutorum, an exponential function for Atriplex canescens and Caragana korshinskii, a power function between average lateral root quantity and growth time for Atriplex canescens and Nitraria tangutorum, a linear function for Zygophyllum xanthoxylon and Caragana korshinskii, a power function between the average root diameter and growth time for Atriplex canescens and Nitraria tangutorum, an exponential function for Zygophyllum xanthoxylon and Nitraria tangutorum, a power function between average pull-resistance and growth time for Atriplex canescens and Caragana korshinskii, and a linear function for Zygophyllum xanthoxylon, for Nitraria tangutorum was an exponential function. The research indicated that all the four shrubs showed a powerful persistent capability in slope protection.