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Root system distribution characteristics of plants on the terrace banks and their impact on soil moisture

2005; Elsevier BV; Linguagem: Inglês

1000-0933

Yu Zhang, Zhu Qing,

Environmental and Agricultural Sciences

The root system characteristics of plants are significant for plant species choice, spacing decision and management measures for agroforestry system. The objectives of this study are to understand root system characteristics of Tamarix ramosissima, Salix purpurea, Caragana korshinskii and Populus bolleana, which are extensively planted on the banks of terraces in arid Loess Plateau regions of northern China, and their competition for soil moisture. The study surveyed the characteristics of active roots by whole plant excavations based on selection of representative plant samples, observation of soil moisture on the selected site through soil coring in the layers of 0 ～ 200 cm in the dry season, and calculation of relative soil moisture deficit to describe changes in soil moisture near the banks.The results showed that the plant species mentioned above have quite different characteristics on root depth, biomass and length (B L) distribution of root systems and impact on soil moisture. Tamarix ramosissima has very deep roots reaching a depth of 757 cm; B L of roots decreases through the 0～100 cm layer, but its coarse roots are dominant in the whole root system; B L of fine roots is mainly concentrated in 0～40 cm layer. The main root distribution layer of Salix purpurea is (0～40 cm,) where the biomass accounts for 86.0% of the total root system, and the biomass of coarse roots overwhelms that of fine roots. Below the 40 cm layer (the greatest depth is 305 cm) B L reduces gradually, and the length of fine roots exceeds that of coarse roots. Noticeably, some of roots of Salix purpurea are distributed in the soil layer which is higher than the plant plane, and B L of fine roots dominate absolutely. Root distribution characteristics of Caragana korshinskii are similar to that of Salix purpurea; but it has more coarse roots than Salix purpurea. Populus bolleana has a shallow root system reaching to a maximum of 136 cm, and most roots are concentrated in the 0～40 cm layer, accounting for 77.2% in the total biomass. The biomass reduces sharply under 60 cm, and the length also reduces sharply below 80 cm. Throughout the distribution layers of the roots of Populus bolleana, notwithstanding the predominance of coarse roots in the biomass, fine roots are far longer than the coarse.The results also showed that there are obvious moisture deficits in the horizontal range near the banks with different plant species. The deficit distance (near the banks with Tamarix ramosissima, Salix purpurea, Caragana korshinskii and Populus bolleana) is 230 cm, 437 cm, 274 cm and 399 cm respectively. In the vertical range there is a layer in which soil moisture of the four sites observed increases from the surface to subsoil. This depth is about 30～70 cm and it varies in the distance to banks and plant species. Below that layer, soil moisture begins to decrease continuously; the point at which soil moisture deficit occurs ranges from 70cm to 200 cm,depending on the plant species planted and the distance to the banks. What the paper suggests is, (1) Tamarix ramosissima, with deep root systems and less impact on soil moisture,is an ideal species for agroforestry system in the Loess Plateau; (2) planting Salix purpurea on approximately 1/3 to 2/3 of bank height, where generally is the transition between loose layers and consolidated ones, and pruning at the time of crops maturity in autumn to balance the competition; (3) planting and management of Caragana korshinskii is similar to Salix purpurea; and (4) Populus bolleana, with shallow root distribution, has a big impact on soil moisture and survival is difficult except when planted on the top of banks. It is not a good plant species for growing on banks.