The Response Mechanism Of Soil Salt Ions Transfer And Diversity Rule To Environment Factor

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.