【作者】 雷文文；

【导师】 王辉；

【作者基本信息】 甘肃农业大学 ， 水土保持与荒漠化防治， 2010， 硕士

【摘要】 砂田是我国西北干旱、半干旱地区独特的、传统的抗旱耕作形式之一。传统的砂田耕作过程实际上是砂田衰老的过程。砂田衰老退化以后若不能更新改造,就无法继续种植粮食作物和经济作物,便形成了大面积的弃耕砂田。本研究采用野外试验、调查观测与室内分析相结合的方法,从弃耕砂田的土壤水分条件入手,通过灌木造林试验和对已有弃耕砂田灌木林地的观测,分析研究弃耕砂田的植被恢复条件和再利用的可能性。其主要研究结论如下:(1)弃耕砂田人工造林恢复植被可行性试验结果表明,沙枣、多枝柽柳、柠条、花棒、沙拐枣等抗旱树种在弃耕砂田的造林成活率可分别达到93%、88%、72%、64%、48%;弃耕砂田造林后2年,5种灌木株高年生长量从大到小依次为:多枝柽柳>沙拐枣>花棒>柠条>沙枣,地径年生长量从大到小依次为:多枝柽柳>花棒>沙拐枣>柠条>沙枣,根系总生物量大小依次为:多枝柽柳>花棒>沙枣>柠条>沙拐枣,表明在弃耕砂田环境下,5种灌木不仅可以存活且能保持有一定生长能力。(2)对5种灌木地下与地上生长关系的观测表明,5种灌木幼林阶段根系主要分布在0~40cm土层中,而且随着土层的深入,灌木根系生物量分布呈下降趋势。0~20cm土层中根系分布最多,说明5种灌木幼林阶段在该土层中利用水分养分的能力最强;5种灌木的根深/株高、根幅/冠幅均大于1,5种灌木地下与地上生物量的比值分别为:1.62、1.4、1.05、1.15、1.3,也均大于1。5种灌木地下与地上生物量生长分配均有利于其在弃耕砂田干旱环境条件下对有限土壤水分的吸收和利用,这也是5种灌木适应弃耕砂田干旱立地环境的表现。由此可见,弃耕砂田通过选择具有较强抗旱能力的灌木树种进行人工造林以实现植被恢复具有一定的可行性。(3)弃耕砂田造林地水分动态变化观测结果表明:在整个观测期内,弃耕砂田造林地0~40cm层的土壤水分平均为12.6%,比旱作土田含水量高40.7%,说明虽然弃耕砂田的保水效果较新砂田有所下降,但较旱作土田仍具有较好的水分保持能力。研究认为,弃耕砂田具有植被恢复与利用必要的水分基础条件;在整个生长期内,弃耕砂田造林地土壤水分变化虽有波动,但总体呈下降趋势,7月份达到最低。而经过8~9月雨季后,土壤含水量得到补充而快速增加。这些土壤水分的良好保持就为来年弃耕砂田造林地的树木生长创造了基本条件。(4)对弃耕砂田人工造林后土壤水分条件的变化及对灌木生长影响的观测研究表明:4年生多枝柽柳株高年生长量最大,而6年生多枝柽柳地径年生长量最大,到12年生时,其株高、地径年生长量均较低。可见,随着树龄的增加,多枝柽柳在树龄达到12年以后,由于多枝柽柳生长所需水分等方面因素的限制,其地径和株高生长均变缓慢。4年生多枝柽柳根系主要分布在土壤浅层(0~150cm),其生长主要利用土壤浅层水分,这部分水分主要靠降雨补给,而随着树龄增加,多枝柽柳生长需要的水分也越多,到6年生时土壤浅层水分已不能满足其生长需要,多枝柽柳根系生长通过更多的向土壤下层延伸,以更多的吸收和利用土壤深层的地下水分。整个生长季内,3种不同林龄多枝柽柳林地土壤含水量普遍较低,但灌木的生长并没有因为较低的土壤含水量而受到明显的影响,也就是说在弃耕砂地环境条件下,人工多枝柽柳灌木林仍能基本正常生长,随着林龄增长尚未表现出显著的衰退迹象。(5)干旱区植被恢复成功与否的最关键因素是水分。试验研究结果初步表明,弃耕砂田的土壤水分条件基本上可以满足抗旱类灌木树种的生长需要。因此认为,通过营造人工灌木林来促进弃耕砂田的植被恢复具有一定的可行性。更多还原

【Abstract】 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.更多还原