Study On Vegetation Restoration Technology Of Abandoned Sandy Fields

Sand field is one of the unique forms of traditional farming method against drought in northwest arid or semi-arid regions. The traditional farming process on Sand field is practically an aging process. Degrading sand field without renovation would make it impossible to grow food crops and cash crops any longer, thus the formation of large areas of abandoned sand fields. The study was made by combining field experiments, investigative observation and indoor analysis on basis of the soil moisture condition of sand fields. And the conditions for restoring vegetation and the possibility of re-utilization on abandoned sand fields were then analysed through shrub-planting experiments and observations on existing shrub lands within abandoned sand fields. Main conclusions are as following:(1) The results of the feasibility experiment of restoring-afforestation on abandoned sand fields show that,the survival rate of anti-drought trees planted on abandoned sand fields were respectively 93%,88%,72%,64%,48%,in line with Elaeagnus angustifolia, Tamarix ramosissima ramosissima, Caragana intermedia, Hedysarum scoparium and Calligonum mongolicum;Two years after planting on abandoned sand fields, the height growth of shrubs were: Tamarix ramosissima ramosissima> Calligonum intermedia >Hedysarum scoparium> Caragana mongolicum >Elaeagnus angustifolia; Diameter growth were: Tamarix ramosissima>Hedysarum scoparium> Calligonum mongolicum > Caragana intermedia > Elaeagnus angustifolia; Total root biomass of five shrubs is: Tamarix ramosissima> Hedysarum scoparium > Elaeagnus angustifolia> Caragana intermedia > Calligonum mongolicum. It showed that the five kinds of shrubs could survive with certain growth abilities.(2)Observations on the relationship between above ground and under ground growth of five kinds of shrubs show that, within five shrubs' infancy, root distribution mainly located in 0~40cm soil layer, and with deepening of soil, the root distribution of biomass decreases. The root distribution of biomass in 0~20cm soil layer are richest, noting the strongest ability on the use of soil moisture and nutrients in 0~ 20cm soil layer; Depth/Height and Root-range/Crown-diameter all surpassed 1; and below-/above-ground biomass valued also more than 1 except Calligonum. In dry conditions, the rate of plants' root growth rate is faster than the ground parts in certain circumstances so as to survive. It is necessary for plants to expand its root length and root range, extending horizontally and deeply, in order to absorb more moisture from soil for the growth of aerial parts. Hereby it was to some extent feasible to restore vegetation on abandoned sand fields through selecting shrubs with relatively strong viability against drought.(3) Observations over dynamic changes of soil moisture in abandoned sand field afforestation show that, in the whole observatory period, the soil moisture of 0 ~ 40cm layer averaged 12.6% in the abandoned sand field afforestation, higher than dry earth field 40.7%, indicating that the moisture retention capacity of abandoned sand fields was lower than new sand fields, but still better over dry earth field. We can infer that abandoned sand fields have the basic water condition necessary for using and restoring vegetation; within the whole growth period, the soil moisture of abandoned sand field afforestation fluctuated with overall downward trend, and the lowest turned up in July. And after the rainy season in October and September, the soil moisture was supplemented with a rapid increase, by which the conservation of water created basic conditions for tree growth upon abandoned sand fields in the coming year.(4) Through observations over the variation of soil moisture and its effect on the growth of shrubs after afforestation on abandoned sand fields, it can be indicated that: the highest height growth could occur in 4-year old tamarisk plants, the largest diameter growth in 6-year olds, whereas the annual growth of 12-year old plants was low. It is obvious that as age increases, the diameter and height growth of Tamarix ramosissima begins to slow at the age of 12 years, due to water restrictions and other factors required for its growth; 4-year old Tamarisk roots mainly exist in shallow soil (0~150cm), which provides the main soil moisture and depends on rainfall for its water supply. While the age increases, more water is needed for the growth of Tamarix ramosissima and the shallow layer water can not meet its needs when the plant's age reaches 6 years, hence the root growth toward deeper soil layer for more absorption and utilization of deep water; Throughout the growing season, the soil moisture was generally low in three Tamarisk afforestation of different age, of which the growth have not been significantly affected by low soil moisture content; it means that planted Tamarix ramosissima shrubs can still grow normally in sandy conditions without showing evident signs of recession as the age increases.(5) The most critical factor for successful vegetative restoration in arid areas is the water. Results of the experiment preliminary showed that the soil moisture of abandoned sand fields could meet the basic needs of shrub afforestation. So to some extent feasible to plant shrub to promote vegetation on abandoned sand fields.