Research On The Distribution Patterns Of Soil Water And Salinity And Revegetation Of Bare Saline-alkali Patches In Songnen Grassland

The Songnen plain which is dominated by perennial Leymus chinensis, is one of the most important commodity grain and livestock industry in China. However, the L. chinensis grasslands have degraded as a result of overgrazing and reclamation. This research focuses on the seasonal movement and freeze-thawing period of water and salinity in different degraded and saline-alkalized grassland and bare patched. Further more, we adopt inserting corn stalk, making ridge, shallow harrowing in adapted time and Sowing Hordeum brevisublatum to revegetated the bare saline-alkaline patches. The major objectives of this research are exploring suitable methods with the advantage of effective, inexpensive and continuous, easy to operation and extend, for revegetating the bare saline-alkaline patches.Through the research, soil freeze-thawing causes the soil saline-alkalized. The results showed that during the melting process of the two-way-frozen layer, the upper melts faster than the lower. The upper frozen layer of the bare saline-alkalined patch melts faster than that of L. chinensis community. The strong moisture evaporation brings serious water loss in the surface (0-20cm) and caused the upward movement of salt in deeper soil. The salt accumulated in the surface like"eruption"in the early spring, on the base of the potential salt accumulation in the frozen period. Compared with L. chinensis community, the salt assembled in the surface is rooted from the deeper soil profiles and its level of salification is more intensive in the bare saline-alkaline patch.The movement of soil water and saline represents obvious seasonal dynamic influenced by continental monsoon climate in Songnen saline-alkalized grassland. The surface soil moisture is lower in spring and autumn, but higher in summer. The most content of soil moisture and the largest range of change lie in Phragmites australis community, and then L. chinensis community, the bare saline-alkalized patch is the lastest among the four communities. The soil profile salinity distributions of L. chinensis community, Puccinellia chinampoensis community and bare saline-alkaline patch were like a cuneiform with high in the above and low underneath respectively, while Ph. australis is low in the above and high underneath. The salinity contents of soil profiles from high to low were bare saline-alkaline patch, P. chinampoensis, L. chinensis community and Ph. australis in the four different habitats. The salinity contents of soil profile of bare saline-alkaline patch and P. chinampoensis changed apparently with season. The salinity contents of soil accumulated in the surface in spring, and remove to the deep layer in the rainy season, while accumulated again slightly in autumn. Different distributions of the soil water and salinity contents in different times and areas depend on the physical features and vegetative coverage conditions in the four different habitats. According to the features of the soil water-salt dynamics in the surface of soil profiles in bare saline-alkaline patch,we draw the conclusion that it is the best time to take some measures to recover its vegetative cover in the early of July. Deep harrowing for revegetation to moderate saline-alkalized grassland is not effective obviously. The biodiversity increases and the average coverage, the area especially the area of the perennial plant, the biomass of the perennial plant is higher than the other types. The close nursery is the best method to the restoration of the degraded grassland on contract of the methods of overgrazing and deep harrowing.The surface soil salinity decreases and increases with the periodic precipitation. The surface soil salinity is the lowest in later July, so it is the very better chance for Hordeum brevisublatum to germinate, successfully establish in bare saline-alkali patch by sowing H. brevisublatum in the bare patch after shallow harrowing. The method of applying shallow harrow and sowing H. brevisbulatum is suitable to re-establish vegetation in bare saline-alkali patch in Songnen Grassland, which is effective, low cost, sustainable economic benefit and easy to operate.The approach of revegetation in bare saline-alkali patches by ridging was effective, economic, and practicable. The ridge accumulated more precipitation to leach salinity from the surface soil to deep profile, and trapped sand particles and seeds carried by the wind, which provided a favourable micro site for seeds germination and seedlings growth. The operation of ridging plug litter speeded the establishment of vegetation, but the cost is more expensive. The narrow and high ridge meliorated more effectively the saline-alkali soil, and provided a more favorable micro site for the establishment of vegetation.Vegetation was restored well in terms of the above-ground biomass and coverage. Inserted cornstalks acted as safe sites that enhanced the plant survival rate in bare saline-alkali patch; they also enhanced the ability to contain seed movement, thus providing a seed source for initial revegetation. Along with initial revegetation, tussocks around cornstalks can provide better safe sites, which in turn can accelerate subsequent vegetation restoration in bare saline-alkali patch. The approach entails the strategic use of diverse seed sources and the construction of safe sites with agricultural byproducts (cornstalks); therefore, it is a low-cost method and can be used on a widespread scale. The results provide vigorous support in favor of vegetation restoration in bare saline-alkali patch and severely degraded grasslands in the region. In practice, this approach can be used in degraded ecosystems with compacted soil surfaces (including arid and salt-affected soils) to promote revegetation in various regions.