| Xinjiang belongs to the typical arid and semi-arid regions, soil water and salt severely impacts the development of agriculture in this region. Characterizing by high crop yield, water conservation, salt inhibition and deep infiltration reducing, drip irrigation has become the best way in solving water conservation and soil salt inhibition issues. Drip irrigation techonology has been introduced to Xinjiang for 19 years, it is limited to soil salt regulation in drip irrigation moist area, but salt is still exist in plough layer soil, so whether drip irrigation in long-term continuous farming soil would lead to new environmental problems and whether it could be sustainably applied in arid regions have become concern issues of scholars today. In order to study the water-salt transport rules of long-term continuous farming cotton field soil, soil salinity of 6 fixed plots in cotton field that applied drip irrigation for 1 to 15 years in the 121 Regiment, Shihezi, Xinjiang has been continuouly measured from 2009 to 2012. In addition, spatial variability of soil salt of 2014 in the test site has been studied as well. Moreover, in order to study the water-salt transport rules of drip irrigated cotton field in winter, non-fertile phase experiment in winter has beem carried out in Water conservation Tesing Station of Shihezi University, and this explored the water-salt transport rules of drip irrigation cotton field under snow and low temprature condition in north Xinjiang. In order to find the method to drain soil salt using drip water, drip irrigating cotton field under mulch and drainage salt between mulches techonology has been studied, and to futher understand the water-salt transport rules of this techonology, analysis has been carried out based on combination of testing and model method. The main conclusions are as follows:(1) Based on the four year field measured data of Xinjinag cotton, soil salt changes in non-fertile phase(March and October) in mulch drip irrigation cotton field in different years has been studied. By contrasting the changes of soil salt in mulch drip irrigation cotton field in two different non-fertile phases and years, the preliminary conclusions are: the features of soil salt ratio in different soil lyaer in under mulch drip irrigated cotton field in March and October are as follows: in 0 ~ 60 cm deep soil layer, soil salt ratio in October is greater than that in March, but in 60 ~ 100 cm deep layer, soil salt ration changes without obvious rules. The change trend of soil salt ration in the four successive years is: with the increase of drip irrigation years, soil salt ratio in mulch drip irrigation cotton field presents an increasing trend. Treating the cotton field that started to apply mulch drip irrigation in 1998, 2001, 2003, 2005, 2007 and 2009 as a series, soil salt ratio of the 6 testing plots in the four successive years has been analyzed, and concluded the changing trend of soil salt ratio of cotton field that applid under mulch drip irrigation in 2009, 2011 and 2012: with the increase of cultivation years, soil salt ratio in mulch drip irrigation cotton field decrease first and then increase. The changing trend of soil salt ratio of c mulch drip irrigation cotton field in 2010 is: with the increase of cultivation years, soil salt ratio in mulch drip irrigation cotton field shows an decreasing trend.(2) In order to study the influence of temperature and snowmelt water in winter on soil salt trasport, based on setting two defferent test pits that with and without mulching, and monitoring the soil temperature and salt of the test pits during the winter, the features of soil temperature and salt under different setting conditions has been measured. The change of the temperature has certain influence on soil temperature, with the increase of soil depth, the influence of temperature on soil decreased gradually. Mulching has certatin heat-preservation function on soil, in spring, each soil layer is leached by snowmelt water, and salt in surface layer decrease to some extent, but intensive evaporation start after snow melting, and salt accumulate in surface layer again. Test pits with mulches will not be affected by snow outside, but it is found that soil salt increase in different depth.(3) In long-term continuous cropping cotton field as the research object, research in March, July, October 0~40cm in drip irrigation cotton field cultivated soil moisture content in space, and the spss19.0 software was used to the classical statistics of tillage layer soil water content, sample data variation function theory modeling using statistical software ArcGIS10.1, the distribution map of interpolation Kriging space, spatial heterogeneity of soil electrical conductivity in March 20 cm minimum tillage layer soil electrical conductivity, 0cmvalue of the maximum; in July the tillage layer soil conductivity value of the minimum 40 cm,0cm maximum soil electrical conductivity; October 40 cm of plough layer soil electrical conductivity value of the minimum and maximum 0cm soil electrical conductivity; the average value of different seasons in tillage layer depth is close to 20 cm in different seasons, different depth of soil tillage layer conductivity has no obvious regularity. Each month the 0cm soil electrical conductivity coefficient of variation is small, strong variability; the coefficient of variation of soil electrical conductivity performance of each month: March July20 cm October and strong variability, moderate variability; the coefficient of variation of soil electrical conductivity performance of each month: March and July 40 cm October moderate variability, moderate variability.(4) In March, mainly in non salinized soil and salinized soil, moderate salinization soil was 15.38%, moderate soil salinization accounted for a larger proportion. 20 cm soil layer mainly by non salinized soil and light soil salinization. 40 cm soil layer mainly by non salinized soiland light soil salinization. The July 0cm to 40 cm soil layer in non saline soil, the classification of saline soil increases with depth showed increasing trend, October 0cm to 40 cm soil layer in non saline soil, with the increase of depth showed a tendency to increase, in March, July,October three months of soil salt content, 0cm and 40 cm the soil non saline soil tillage layer,in March the overall salinity minimum, followed in October, is the largest in July, July and October from soil salinization degree of saline soil in increasing order to non saline soil.(5) Adopting mulch drip irrigation techonology in arid agricultural area, and excavating soil salt draining ditches in barren area between mulches, the soil salt transport rules under mulching drip irrigation condition and the surface draining salt effect of the draining ditches has been studied under the contion of arranging salt draining ditches. The effect of salt draining ditches of mulching drip irrigation is obvious, salt dilution zone formed near the dripper, massive salt accumulated at the slope of salt draining ditches. In 0 ~ 40 soil depth, it shows that soil salt in the mulch ceter(dripper) is generally higher than that in mulch edge and salt accumulation at the barren area of draining ditches is sinificant. The change of wetting front of drip irrigation infiltration and features of soil solute transport has been simulated under the technological condition of using mulch drip irrigation and salt draining between mulches based on HYDRUS-3D model. It found that the salt draining effect of mulch drip irrigation and salt draining ditches is obvious, salt accumulation at the slope of salt draining ditches is significant, and HYDRUS-3D model could well simulate the changing process of wetting front of drip irrigation infiltration. |
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