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Study On Regulation And Numerical Simulation Of Soil Water And Salt Transport In Cotton Field With Tapical Drip Irrigation Under Mulch

Posted on:2019-03-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:G D YouFull Text:PDF
GTID:1480306026951209Subject:Water Resources and Hydropower Engineering
Abstract/Summary:PDF Full Text Request
Xinjiang is located in the northwestern region of China.It is characterized by arid and low rainfall,large evaporation,widespread saline soil,and scarce water resources.It is typical oasis irrigation agriculture.Therefore,the technique of water-saving drip irrigation under mulch has been widely used in Xinjiang.Nevertheless,the salinity still cannot be eliminated from the soil.Drip irrigation under mulch only adjusts the distribution of the soil salinity in plough layer.The accumulation and distribution of soil salinity in those cotton field that in the way of drip irrigating under mulch will influence the methods and developing direction of this irrigation methods.The existed research results have a good direction effects for the analysis and control of water and salinity.Because of complexity about water and salt migration in soil,diversity of the conditions and variability of the external environment in drip irrigation under mulch cotton field,it has been definitely needed continuously to strengthen the research about movement regulation of water and salt in cotton field that irrigated by drip irrigation under mulch.For the researching of the long-term characteristics of distribution and variation of soil water and salt in the drip irrigation under mulch cotton field,this thesis based on the data of soil water and salt change results that concluded by Xinjiang 121 regiment in 2011?2016 to analyse the distribution characteristics about water and salt in soil in both growth stage and nongrowth stage of drip irrigation under mulch cotton field;The researching of characteristics in those cotton field which is under autumn irrigation;The researching of the techniques about the salt discharge in cotton field drip irrigating-with combination of cultivating experiments and HYDRUS-2D simulation,the technique about the elimination of soil salt in drip irrigation under mulch cotton field were observed,analyzed and researched.The research conclusions are listed as follows:(1)The analysis of different salinity soils during the growth period from 2011 to 2013 revealed that when the low-salinity soil salinity becomes lower with desalination in 0?40cm layer.The high-salinity soil has a strong accumulation of salt in 0?60cm layer from 2011 to 2013.At the same time,we find that the salt accumulation between the mulch will become heavier when the soil salinity goes higher.(2)From the analysis of soil salt and groundwater level in drip-irrigated cotton field during the growth period,we found that the equationY2(28)-.002366(10).010854X-.002113X2matches the law of change.Cluster analysis was used to qualitatively analyze the soil salinity before and after irrigation.The results showed that the active layer depth of soil salinity was 0?40cm before irrigation and the depth of active layer was 0?20cm after irrigation.The depth of soil salt stability layer increased after irrigation.(3)The study on the spatial distribution of soil salinity during growth period revealed that the soil salinity in 0?20cm,0?40cm,0?60cm,0?100cm respectively reduced 0.06%,0.08%,0.07%,and 0.10%contrast with the beginning of growing season;For the 6th,10th,12th,and 17th years of plots,which planting cotton continuous ever year,the average soil salinities during growth period were 0.73%,0.53%,0.39%,and 0.59%.The soil salinity of the plots aged 6 to 17 years showed a V-shaped change trend.The soil with different cultivating years shows the regulation that it eliminates salt firstly and accumulates finally.(4)Based on the field trials conducted during the non-birth period from 2014 to 2015,it was found that the soil temperature during freezing and thawing period was negatively correlated with soil water and salt;The salinity depth in severe salinized soil was 0?100cm,and the salinity in mild salinized soil was0?40cm.The analysis of spatial distribution of soil salinity in non-growing period revealed that the soil salt content of 0?10cm at the end of non-growth stage was greater than 0.70%,the number of soil samples increased by 2.70%,and the soil average salt content at 0?10cm and 0?20cm increased by 0.12%and0.09%,respectively.Shallow soil salt showed an increasing trend in the non-birth period.(5)In view of the problem of soil salt accumulation in cotton fields under drip irrigation in northern Xinjiang in the last several years,spatial-grid sampling method was used to analyze the distribution of soil water and salt in autumn.The results showed that the soil water content in autumn soil plots at 0?20cm and0?40cm in seedling stage increased by 4.90%and 5.33%,and the increase in autumn irrigation quota of2400 m3·hm-2could increase soil moisture in seedling stage.Compared with the untreated land,the soil salinity at 0?20cm,0?40cm,and 0?100cm decreased by 0.28g·kg-1,0.23g·kg-1,and 0.19g·kg-1,respectively,in the seedlings of the following year after 20 days of the fall irrigation.0?100cm soil total salt reduced0.50g·kg-1.The soil salinity T test at the seedling stage showed that the difference between the autumn and un-falling plots was extremely significant.(6)The salt-water migration and salinization effects in drip-irrigated cotton fields were studied when the depth of salt drains was set with 10,20,and 30cm.It was concluded that in the depth of 0?25cm,salinity in membrane soil with 20cm-deep brine ditch greatest increased from beginning-growth stage to the finish-growth stage.Using HYDRUS-2D model to predict salt salinity in different depths of silty soil during the growth period,it was found that the effect of salt excretion in the depth of 5?15cm is the best.
Keywords/Search Tags:drip irrigation of cotton field under mulch, water and salt movement, autumn irrigation, salt removal technology, HYDRUS-2D
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