【作者】 郭全恩；

【导师】 王益权；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2010， 博士

【摘要】 土壤盐渍化始终是世界性的土地资源与生态环境领域内亟待解决的重要问题之一,特别是在干旱和半干旱地区,仍然是制约人类生活的重要障碍性因素。以往土壤盐渍化过程是以土壤表层积盐为特征,盐渍化程度的划分也是以表层土壤盐分总量为依据,忽视了土壤内部积盐对于作物根系的危害性,尤其是在干旱半干旱地区、对类似于果树这样深根性植物而言,土壤耕作层以下的盐渍化过程及其危害未给予关注;以往对盐渍化危害性评价重视土壤盐分总量,而对于土壤盐分离子不平衡与分异所产生的危害研究较为欠缺;以往在水盐复合溶液体系中重视水分移动对盐分迁移的影响,而盐分对水分移动的制约关系研究较为贫乏;以往关于盐分累积对作物的危害性研究较多,而作物对盐分累积效应研究欠缺等等。基于上述问题,本研究以具有干旱、半干旱气候和环境特征的甘肃省秦安县果园次生盐渍化土壤为研究对象,采用了田间试验和室内模拟实验相结合,对土壤水盐运移参数、盐分离子之间的相关性、环境因子(果园近地面空气温度、相对湿度、潜在蒸发量、降雨量、土温、土壤水分)与土壤积盐的关系进行了研究,探讨了灌溉淋洗以及水分再分布过程和植被类型对土壤中盐分离子迁移及其分异规律,取得了如下主要结果:(1)针对盐渍化土壤的特征,以探索水盐关系为主要目标,研究得出在水盐复合溶液条件下,土壤水分动力学参数、水分特性曲线及其模型参数不仅取决于土壤基膜性状,也同样受溶液的盐分类型和矿化度的影响。以湿润峰迁移为特征的水分移动速度和以含水量为依据的水分扩散率受土壤盐分类型的影响是不同的。NaCl对水分移动速度有促进,但对于水分扩散率有抑制;而Na2SO4和Na2CO3对水分移动速度和水分扩散率均有抑制。实验证明由土壤水分特性曲线得到的土壤孔隙不应当是真正的土壤粒间孔隙和结构孔隙,而是用失水量获得的“概念孔隙”。NaCl对于土壤比水容量和毛管断裂的延迟效果要比NaSO4明显,且用比水容量的变化情况才能更为直观地看出各类盐分及其矿化度对于土壤持水性能的影响。在低吸力段,Na2SO4与温度的交互作用较NaCl与温度的交互作用对土壤持水性能的影响要明显。在不同水吸力条件下,不同矿化度的NaCl对土壤水分释放过程中HCO3-、SO42-、Ca2+、Mg2+含量有很大的影响,而不同矿化度的Na2SO4对土壤水分释放过程中Cl-、Ca2+、Mg2+含量有很大的影响。实验证实“盐随水来,盐随水去,盐水相随”存在着缺陷,在土壤体系内水盐互为协同、相互制约,“盐水相随程度”取决于盐分类型和盐分含量。(2)针对干旱地区土壤表面易形成干土层,不仅抑制蒸发也会抑制积盐特点,得出研究区土壤剖面盐分含量分布规律不同于一般盐渍化农田的“T”型分布,而是在一定土层内深层盐分含量相对较高,呈现“⊥”型分布。依据研究结果提出在气候干旱、土壤质地较轻的地区和一些作物根系分布较深的情况下,评价盐渍化土壤的危害性,仅看表层土壤积盐是不够的,更应当监测土壤内部积盐情况,才能做出科学的判断与准确的评价。(3)在干旱地区的农、林植被条件下,依据盐分在土体中累积的方式,提出“土表积盐”(T型)和“土内积盐”(⊥型)的概念。依据盐分迁移的驱动力,提出由于受近地层环境条件作用的土壤水分蒸发过程驱动的表层积盐,称之为“蒸发积盐”;受作物蒸腾耗水驱动的土内积盐,称之为“蒸腾积盐”。且指出一般蒸发积盐现象较为直观明显,易得到重视,防止水分蒸发过程就能达到抑制积盐效果;而蒸腾积盐在土壤表层没有外观表现,隐蔽性和欺骗性强,不易被人们所察觉,危害作物生育过程,尤其对于果树类作物的危害主要源于蒸腾积盐。(4)通过盐分离子剖面空间分布以及离子之间的相关性分析,在咸水灌溉盐渍化土壤上得出,HCO3-聚集于剖面上部土层,伴随着的K+与之形成碱性盐土特征,在SO42-聚集的下部各土层,伴随着的Ca2+与Mg2+、Na+之间形成中性盐土特征,氯化物盐分均匀分布在土壤剖面。同时,试验证实在自然情况下各类盐分离子的分化是客观存在的事实,盐分离子的分化常常成为盐渍化危害的主要原因之一。盐分的分化与沉积特征符合盐分类型的溶解度原理和受干旱地区水分剧烈变化双重影响。对于果树生长而言,其危害主要不是来源于表层碳酸盐区,而是来源于在较深层次的硫酸盐区,因为在较深层次有大量的Na离子聚集。(5)以钠离子和氯离子作为“指示剂”,研究不同土层对于环境因素与土壤性质响应机制,得出在0-25cm土层范围内,不同土层的Na+和Cl-对环境因子的响应不同。对土壤Na+迁移而言,提出0-5cm土层是地表环境因子与土体内部信息交流的“绝缘层”;且5-10cm土层是水溶性Na+对环境因子(蒸发量与降雨量)反应的“敏感层”;而果树在地上气候环境信息与土壤内部响应机制方面起到了“导体”的角色。对土壤剖面Cl-迁移累积与环境、土壤性质关系分析,得出在不同土壤层次具有不同的决定因子。表层0-5cm土层氯离子聚积主要依赖于自然环境的干湿度(水分亏值),在10-15cm土层氯离子聚积却主要依赖于土壤含水量;在15cm土层以下土壤氯离子变化与环境和土壤水分没有明显的响应性。(6)针对旱地土壤水分变化特征,研究了灌溉淋盐和水分再分布过程中盐分含量和离子变异的空间特征,得出灌溉淋洗全盐含量和水溶性Na+在淋洗前后有极显著的差异,Cl-和水溶性Ca2+在淋洗前后有显著的差异,K+、Mg2+、HCO3-、CO32-和SO42-在淋洗前后差异不显著。提出“盐渍化指数”的概念,对不同土层盐分离子淋洗的效果进行了综合评价。提出用“分形维数”作为土壤剖面盐分离子淋洗前后分异量化的指标,且通过分形维数进一步证实土壤剖面盐分离子在分异过程中始终要保持电荷平衡。果园灌溉量在2700-3600m3/ha之间时,灌溉有利于土壤剖面0-100cm土层盐分的淋洗,而灌溉量在1800 m3/ha以下时,灌溉则加速土壤表层盐分的累积。在水分再分布期间,受上层水分蒸发和下层水分深层移动双重的影响,在土壤剖面40-80cm土层出现了低含盐量区域,相当于土壤水分的“零通量面”位置,在水分再分配过程中,盐分“零通量面”位置逐渐向下移动,体现旱地土壤水分耗竭特征;在亚表层10-30cm是干旱地区积盐量最高区域。水分再分布过程对各类盐分离子的影响程度不同,导致土壤剖面盐分离子分化。(7)通过对裸露地、大麦、玉米、果树等不同植被土壤剖面盐分动态监测,研究不同植被与土壤剖面不同土层盐分离子迁移及其分异规律的关系。结果表明:裸露地块土壤盐分表聚比较明显。种植大麦可使土壤剖面0-100cm土层土壤盐分、Na+、Mg2+、Cl-和SO42-含量减小。种植玉米可以促使土壤盐分、Na+、Ca2+、Mg2+和HCO3-累积在60-100cm土层,而使0-40cm土层盐分减少。种植果树,在苹果生育期,土壤盐分累积有两个峰值,第一个峰值在5-6月份,土壤盐分主要累积在大约10-30cm土层;第二个峰值在8月中旬,土壤盐分主要累积在30-50cm土层。更多还原

【Abstract】 Soil salinization is always one of important and urgently solved problems in the domain of worldwide soil resource and entironment, especially in arid and semi-arid regions, it is still important obstacle factor that restricted human subsistence.Anciently, the course of soil salinization was according to characteristic of salt accumulation in topsoil, the degree of soil salinization was according as the content of salt in topsoil, ignored the damage of soil salt accumulation in substrate to crop root, especially in arid and semi-arid regions, as far as concerned deeper root plant, such as fruit tree, the damage and the process of soil salinization under the cultivation layer ought not to be given more attention; and the damage and appraisement of soil salinization was given more attention to total salt content, but the study on the damage of salt ions imbalance and diveraity was deficiency; and the influence of soil water movement to salt transfer was given more attention in water and salt complex solution, but the study on the interrelational constraint of salt transfer to water movement was deficiency; and the study on the damage of salt accumulation to crop was abundant, but the study the influence of crop to salt accumulation was deficiency.Base on above mentioned some questions, the object of study was orchards secondary salinization soil with the characteristics of arid and semi-arid climate and environment in Qin’an County of Gansu Province.We studied soil water and salt movement parameter, correlation of soil salt ions, relationship between soil salt ions accumulation in topsoil and environmental factors (air temperature, air relative humidity, latency evaporation, rainfall, soil temperature, soil moisture), and probled into the effect of soil salt transfer and diversity rule on under different condition (irrigation leaching, water redistribution and vegetation type) by field experiment and laboratory simulation. The results are as follows:(1)Aiming at the characteristics of soil salinization, the mostly object probed into the relationship of water and salt, the results showed that dynamics parameter of soil water and soil water characteristic curve were not only depended on soil basement membrane properties, but also was affected by salt type and content in water and salt complex solution. The influence of salt type on the velocity of soil water movement according to index of wet front transfer and the velocity of soil water diffusivity according to index of soil water content was different. NaCl accelerated the velocity of soil water movement, but it suppressed the velocity of soil water diffusivity; and both Na2SO4 and Na2CO3 were suppressed the velocity of soil water movement and soil water diffusivity. Experiment results proved that soil pore by soil water characteristic curve acquired was“concept pore”, it was not really soil intergrain pore and structure pore. The postponing effect of NaCl to specific soil water capability and capillary rupture were obvious than Na2SO4, and the effect of salt type and mineralization to soil water retention ability was observed according as specific soil water capability variety. The influence of Na2SO4 and temperature interaction on soil water retention ability was obvious than NaCl and temperature under low water suction condition. Under different water suction condition, NaCl influenced the content of HCO3-, SO42-, Ca2+, Mg2+ and Na2SO4 influenced the content of Cl-, Ca2+ and Mg2+ during the process of soil water release, respectively. The standpoint of“salt with water comes together, salt with water leaves together, salt stays along with water”was approved that there was in existence bug, and the relationship of salt and water was mutually promoted and restricted in soil system, and“salt stays along with water”depended on salt type and quantity.(2)Aiming at the characteristics of arid regions, the dry-soil depth is easy to form in topsoil and suppress evaporation and salt accumulation. The results showed that the regulation of salt accumulation was“⊥”type distributing in soil profile, and it was different from“T”type distributing of commonly farmland, and that the content of salt increased with soil depth increased. It was put forward that the damage of soil salinization was not only attached importance to salt accumulation in topsoil, but also should attached importance to salt accumulation in substrate under arid climate regions and crop deep root conditions, thus the scientific judgement and exact appraisement can be carried out.(3)Under conditions of agriculture and forest vegetation in arid regions, according to the way of salt accumulation in soil profile, the concept of“salt accumulating in topsoil”(T type) and“salt accumulating in substrate”(⊥type) were put forward. According to power of salt transfer, the concept of“salt evaporation accumulating”and“salt transpiration accumulating”was put forward. The course of“salt evaporation accumulating”was easy to directly perceive and obvious, and it was easy to be regarded, the process of prevent water from evaporation can be achieved success, but the course of“salt transpiration accumulating”with concealment and fraudulence was not easy to be perceived, the damage to crop was very serious, especially fruit trees.(4)Analysis spatial distributing characteristic of salt ions in soil profile and the correlation of salt ions.HCO3- was accompanied by K+ to congregate round topsoil, it formed alkalescence characteristic, SO42- were accompanied by Ca2+, Mg2+ and Na+ to congregate round substrate, it formed neutrality characteristic, chloride was equality distributing in soil profile, with salt-water irrigation. Meanwhile, salt ions in existence diversity in field by experiment approved, the diversity effect of salt ions was usually one of mostly reasons of salinization damage. During the course of soil salinization with salt-water irrigation, salt of the carbonate type distributed in topsoil, salt of the sulphate type distributed in substrate, the chloride was uniformity in soil profile. The characteristic of diversity and sediment of salt in soil profile was accorded with the double effect of the principle of solubility and water acute variety. As far as concerned fruit tree growth, the damage was not from carbonate zone in topsoil, and was sulphate zone in sbustrate, because a great deal of Na+ congregated round in substrate.(5)Taking Na+ and Cl- as“indicator”, the response mechanism was studied on the different soil layers to environment factor and soil basic properties, the results showed that the response of Na+ and Cl- in different soil layers to environment factors was different in range of the 0-25cm soil layer. As far as Na+ transfer, the 0-5cm soil layer was“insulated layer”of information communion between environment factors and soil profile. And the concept of“sensitive layer”presented in this paper was a good index to express the influencing intensity of environmental factors (evaporation and rainfall ) to soil water-solubility Na+ in the 5-10 cm soil layer, and fruit trees was play an role of“conductor”. Analysis the relationship of Cl- transfer accumulation, environment and soil basic properties, the results showed that there were different decision factors in the different soil layers. Cl- accumulation in the 0-5cm soil layer depended on the deficit value of water, but Cl- accumulation in the 10-15cm soil layer depended on soil water; the response of Cl- to environment factors and soil water under 15cm soil layer was not obvious.(6)Aiming at the characteristics of soil water variety in arid land, characteristic of spatial variety of salt and ions was studied during the courese of irrigation leaching salt and water redistributing. The results showed that there was a very marked difference between leaching before and after on soil total salt (P=0.001<0.01) and water-solubility Na+(P=0.000<0.01), and there was a marked difference on Cl- (P=0.040<0.05) and water -solubility Ca2+. But there was little difference on water-solubility K+, Mg2+, HCO3-, CO32- and SO42- between leaching before and after. The concept of“salinization index”was put forward, and the effect of leaching salt in different soil layers were integrated appraisement by“salinization index”. It was put forward that“fractal dimension”was considered index of salt diversity leaching before and after, and further the charge maintenance balance was approved by fractal dimension during the course of salt ions diversity. With an irrigation quantity ranging from 2700 to 3600m3/ha, irrigating was propitious to leaching salt in the 0-100cm soil layers. But irrigating could accelerate salt accumulating in topsoil when the irrigation quantity was under 1800m3/ha. During water redistributing, the 40-80cm soil layers was the lower salt zone under the double effects of water evaporation in superstratum and water movement down in substrate, the lower salt zone was equal to“zero flux surface”of soil water, the position of lower salt zone downwards movement during this course of water redistributing that opened out water exhaust characteristic. Salt accumulation quantity was the highest in the 10-30cm soil layer. The effcet of water redistributing to several ions was different, water redistributing induced salt ions diversity in soil profile.(7)The relationship of between vegetation and salt ions was studied by measured the dynamic variety of salt in different vegetation soil profile (nudity, barly, maize, apple fruit tree) in farmland. The results showed that soil salt congregated obviously in nudity farmland. Barly could suppressed salt accumulation in soil profile during the growth of barly, the content of Na+, Mg2+, Cl- and SO42- decreased in the 0-100cm soil layer. Maize could decreased salt in the 0-40cm soil layer, and drived salt, Na+, Ca2, Mg2+ and HCO3- gathering in the 60-100cm soil layer. There were two peak value of salt gathering during the growth of apple fruit tree. The first peak value, from May to June, soil salt mainly assembled in the 10-30cm soil layer; the second peak value, in the middle August, soil salt mainly congregated in the 30- 50cm soil layer.更多还原