| Object:The uneven effect of irrigation and evaporation space formed by mulched drip irrigation makes the farmland soil present the phenomenon of"interlaced spatial distribution of soil water and salt".The soil salt mainly accumulates outside the membrane and forms the characteristics of surface accumulation under evaporation,which weakens the leaching effect of irrigation on soil salt.However,under the condition of mulched drip irrigation,the phenomenon of soil salt accumulation and soil salt leaching coexists,which leads to a certain proportion between the amount of salt accumulating and salt leaching.Through the laboratory experiments and field tests,the process of salt crystallization at the interface of soil and gas under the action of water vapor two phase flow was discussed,and the proportion relationship and movement mechanism between soil salt leaching in the membrane and soil salt accumulation outside the membrane were studied.Based on this mechanism,the corresponding control technology was put forward,and the control effect of different tillage measures on the soil water and salt distribution under mulched drip irrigation was quantitatively analyzed.This study not only provides theoretical basis for revealing the phenomenon of soil salt accumulation under mulched drip irrigation,but also provides reference and technical support for effective governance of this phenomenon,and also provides beneficial basis for the long-term sustainable use of drip irrigation technology,which is of great scientific significance.Methods:This article takes saline-alkali soil as the research object through indoor experiments from 2016to 2019,the question of the effects of temperature treatment on the salt distribution of soil air interface,the migration and transformation mechanism of water,heat,salt under different evaporation intensity treatment(high evaporation intensity and low evaporation intensity),and the proportion of soil salt leaching and soil salt surface accumulation under different influence(irrigation amount,irrigation frequency,tillage method)were studied and analyzed.Through the field experiments from 2018 to 2019,the leaching efficiency of irrigation on salt under different tillage methods was analyzed,and the inhibition mechanism of horizontal tillage mode on soil salt was revealed.Results:(1)Salt surface accumulation is the result of soil water-heat-vapor-salt coupling movement.In the process of soil water vaporization,soil salt is retained on the surface of soil.Under the same temperature and irrigation amount,water vaporization rate faster in sandy soil than in loamy soil.The surface salt content of soil is positively correlated with temperature and negatively correlated with soil moisture content;the effect of soil moisture content on the surface salt content is higher than that of temperature.The two soils showed the characteristics of low salt accumulation rate under the low temperature treatment,and the peak value of salt accumulation rate under the suitable soil moisture content under the high temperature treatment.With the increase of temperature,the average accumulation rate of soil salt gradually increased,under the treatment of 20?,25?,30?,35?,40?,45?,the salt accumulation rate of sandy soil was1.74g·kg-1/h,2.02g·kg-1/h,6.01g·kg-1/h,7.13g·kg-1/h,7.17g·kg-1/h,8.67g·kg-1/h,respectively,and the corresponding values of loamy soil was 2.35g·kg-1/h,3.24g·kg-1/h,4.55g·kg-1/h,6.78g·kg-1/h,7.18g·kg-1/h,10.19g·kg-1/h,respectively.(2)Under the effect of uneven space between irrigation and evaporation,increasing evaporation intensity can increase the salt accumulation on the surface of soil outside the membrane.Under different evaporation intensity treatment,the proportion of surface accumulated salt content of the sandy soil was kept at 28.56%?33.07%,and that of the loam was kept at 33.07%?44.12%;under low evaporation intensity treatment and high evaporation intensity treatment,the proportion of the surface accumulated salt content of loamy soil was 5.14 and 11.05 percentage points higher than that value of sandy soil,respectively.Although increasing irrigation can reduce salt accumulation,it was difficult to eliminate the phenomenon of salt accumulation.Under different irrigation treatments,the proportion of salt accumulation in sandy soil was kept at 26.75%?40.64%,and that in loam was kept at 39.82%?56.95%.Under the treatment of irrigated 35mm,55mm and 75mm,the proportion of salt accumulation in loamy was 16.31,11.05 and 13.07 percentage points higher than that value of sandy soil,respectively.Under the same irrigation amount,increasing irrigation frequency can reduce the salt accumulation in topsoil,but at the same time increase the area of salt accumulation;under different irrigation frequency treatment,the proportion of surface salt accumulation in sandy soil was kept at 25.44%?33.61%,and that in loamy was kept at 38.45%?40.45%;under the irrigation frequency treatment of F1,F2,F4,the proportion of surface salt accumulation in loamy was 6.84,8.09 and 13.01 percentage points higher than value of sandy soil,respectively.(3)Horizontal tillage treatment can turn the high salinity soil of the position outside the film into the position beneathe the film,improve the initial salt content of the soil beneath the film before irrigation,and improve the solubility and dynamic carrying effect of the soil water inside the film to the salt by using the characteristics of the high temperature and water content of the soil beneath the film,so that the salt outside the film can be leached to the bottom inside the film under the comprehensive effect of tillage and mulched drip irrigation,resulting in the spatial distribution of soil salt gradually from the early"outside surface accumulation"profiles to the later"inside bottom accumulation"profiles,which provided a leaching way for the soil salt accumulation outside the membrane.In the soil bin experiment,the proportion of the surface salt accumulation of sandy soil and loamy soil under the horizontal tillage treatment was 9.92%and10.93%,respectively,which were 12.53 and 11.87 percentage points lower than that of the vertical tillage treatment,and 14.86 and 8.43 percentage points lower than that of the no tillage treatment.In field experiment,the leaching efficiency of the treatment of horizontal tillage 20cm,horizontal tillage 30cm and horizontal tillage 40cm was 0.11,0.09 and 0.29 percentage points higher than that of vertical tillage treatment at the same tillage depth in 0?40cm soil layer. |
PDF Full Text Request