| With water resource scarcity, the situation of drought and soil salinity get even worse in Hetao Irrigation District in Inner Mongolia. Based on the idea of irrigation for saving water as well as controlling salinity in field scale, and regulating groundwater level to decrease evaporation and salt accumulation by combining well and canal, this research investigated distribution and transportation of water and salinity under different mulched drip irrigation schedule in maize field; compared the influence of different irrigation patterns (border irrigation with yellow river water[H], border irrigation with groundwater[J], drip irrigation with groundwater[D]) on transformation of irrigation water-soil water-groundwater, soil temperature and salt balance, and maize growth and yield; analyzed typical corn irrigation schedule and water-salt balance in canal-irrigation and well-irrigation area, and influence of combining well and canal on groundwater depth and soil salt. The main results are listed as follows:(1)As Hetao Irrigation District in Inner Mongolia is arid, rainless, and intense evaporation, soil water was evaporated through uncovered area and crops transpiration. Soil salt migrated with water and its profile distribution was uneven. Soil salt migrated from the central to the peripherial of the film horizontally and from the lower to the upper soil layers vertically, tending to accumulate in surface soil layer outside the film. Soil temperature was influenced by air temperature, corn cover degree(LAI), irrigation practice and soil moisture content compreehensively, which droped sharply after irrigation practice, and recovered 2-3 days later. The effect of salt-leaching irrigation with 180mm Yellow River water in non-crop growth period was remarkable, and 0-100cm soil salt profile distribution was even which decreased by 10.86%～26.14%. Salt regulation of mulched drip irrigation in Hetao Irrigation District should be drip irrigation schedule for water-saving and salt-controlling combined with salt leaching irrigation with Yellow River water in non-crop growth period.(2)Soil water and salt of different irrigation patterns was fluctuation under the effect of irrigation, rainfall and evapotranspiration. The transformation of irrigation water-soil water-groundwater was strong. The quantity of utilizing groundwater by crop of H、J and D in growth period s 64.0、46.5、27.9mm and the recharge coefficients of one irrigation of H、 J and D to groundwater were 0.13.0.10 and 0. respectively. The crops would consume water stored in deep soil layers and groundwater during two irrigation practice. Considering evapotranspiration and reusing of invalid water which has percolated down to lower soil layers of the root zone of the crop by the latest irrigation practice, the modified field irrigation efficiency of H、J、D was 82.95%.88.13% and 100.00%. which was 92.07%,50.79% and 45.45% higher than traditional field irrigation efficiency. ET of H、J、 D was 512.6、［463、392.85mm. separately. Irrigation Water Production (IWP) of H、J、D was2.84、3.18.4.96kg/m3. and Water Production(WP) was 2.90.3.26,4.16kg/m3. Soil accumulated temperature in 0-40cm layer of H、J, D was 2647.08、2615.14.2586.18℃ respectively, which was Little difference in growth period. While the influence of irrigation practice to soil temperature was obvious, and descend range was J> H> D. Soil salt of H in whole crop growth period was accumulated. Soil salt of J was accumulated in lower layers while upper soil layers was desalted, and D was accumulated at the edge of the film. Considering soil salt balance in 0-100cm in crop growth period comprehensively, it is 2 years that drip irrigation should have a salt leaching irrigation practice. The results of Irrigation schedule and water-salt monitoring in typical farmland in well-canal area showed that large irrigation quota could keep soil salt balanced in crop growth period and autumn irrigation every year is not needed.(3)The regulation effect of well-canal project on groundwater depth and soil salt is significantly effective. The higher probability of groundwater depth ranged from 2.3m to 2.44m in Longsheng well-canal area, which is influenced by natural and human factors including precipitation(P), water intake(Y), ETo as well as well-canal project(WC). The data of path analysis presented that WC has the biggest influence on WL and R2 was 0.810. which is the main factor leading groundwater level descending; the direct and indirect impact of ETo on WL is equal, which ranks the second; the total indirect path coefficient of Y on WL via P. ET0. WC was 0.990, and R2 was-0.229:P has little influence on WL for the less precipitation and less rainfall intensity. From time, the area average soil salt in the later stage (from 2009 to 2015) of well-canal project was decreased by 32.31% than that of the early stage (from 2002 to 2005). Meanwhile, the soil salt in well area decreased intensively than that of the canal area at the early stage and multi-year average was reduced by 18.56%. Form space, the average soil salt in 0-lOOcm in well area was 0.293ds/m. which was 16.33% lower than than of in canal area. There was a significant cubic polynomia relationship between groundwater depth and soil salt in Longshneg well-canal area, and when groundwater depth was more than 2 m. as the groundwater level descending, the soil salt was diminished. The descending of groundwater level is the main factor of soil salt reduction, so regulation of groundwater level is the main way to control soil salinity in arid and semi-arid shallow groundwater area.The regulation strategy and suggestions for soil water and salt of mulched drip irrigation in well-cannal area of Hetao Irrigation District in Inner Mongolia are listed as follows. The irrigation schedule in crop growth period should be combined with leaching irrigation with Yellow River water in non growth period in well irrigation area with mulched drip irrigation, which should be made in order to gain high production and no salt accumulation in root zone inside plastic. However, because of the complicated hydrogeologic condition and the impact of freeze-thaw in Hetao irrigation district, when leaching irrigation in non growth period is needed as the accumulation of salt with mulched drip irrigation and what is the most suitable leaching irrigation schedule need to be investigated further. The present irrigation schedule in crop growth period and autumn irrigation practice should be adopted in order to maintain the balance of soil salt and the stability of groundwater in canal irrigation area. |
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