| Hetao Irrigation District(HID)is the typical saline irrigation area,faced with water shortage,low water and fertilizer utilization efficiency,and unreasonable water and fertilizer configuration,at the same time,the amount of water diverted from the Yellow River has decreased sharply in recent years,which has limited the sustainable development of agriculture in the irrigation area.Therefore,It has the significant practical meaning for the sustainable development of the agricultural production in the irrigation area By studying the mechanism of water saving,nitrogen reduction,Obtain high productivity in agricultural production under border irrigation with different sand depth,to determine reasonable water and nitrogen amount and optimize irrigation schedule.In this study,spring maize was used as the study subject,the experiment of water and nitrogen reduction was carried from 2016 to 2017 To investigate the water and salt transport in soils,crop growth,root distribution and yield,compare and analyze the differences under two different sand depth and using the HYDRUS-1D model to optimize the better water and fertilizer application as well.A water and fertilizer experiment with different irrigation methods under different sand inter-layered soil was taken in 2018 to study the water and salt transport in soils,crop growth,root distribution and yield.It is important to scientifically guide the efficient use of agricultural water and fertilizer in HID.The main results are as follows:1.The effect of different water saving and nitrogen reduction on soil water content and electrical conductivity under two types of sand inter-layered soil.The soil water content and electrical conductivity(Ec)in sand was lower than those in the soil that obtained above and below the sand layer.The water content and Ec under different sand-layered basically do not be influenced fluctuate by irrigation,evaporation and rainfall(except the sand layer buried at depth of 20-40 cm).The deeper the sand layer buried,the more water retention of the soil.Compared with the shallow buried sand layer(S2),the water content and Ec in the 0-40 cm soil layer increased under the deep buried sand layer(S1).The average soil water content under S1 increased by 7.28% to 24.83% and Ec increased by 6.92% to 21.59% in 0-40 cm soil compared with S2 by border irrigation.Compared with the sand inter-layered soil,the Homogenous soil can increase the water content by 13.27%～19.24% and 2.61%～21.91% of Ec.The water content under drip irrigation is higher than under border irrigation and has lower Ec.2.The effect of different water saving and nitrogen reduction on maize growth index and yield and water use efficiency(WUE)under two sand burial depths.Under border irrigation,plant height of S1 increased by 2.63% to 6.24% compared to S2.And 3.08%～18.58% of leaf area index(LAI).The height and LAI under drip irrigation is higher than under border irrigation.The yield under S1 increase by 20.78%～49.61% And1.88%～15.20% of WUE than S2.Drip irrigation increased yield by 0.35% to 31.15% and WUE by 1.88%～20.69% compared to border irrigation.3.The effect of different sand layer structures on water saving and nitrogen reduction on the root growth distribution of maize.Root growth has the characteristic of "stopping when touched the sand".72.46%～87.37%of root distributed in the 0-40 cm soil layer.The percentage of root length in the bottom increased by 24.61% to 83.17% compared to the sub-bottom layer.Homogeneous soils are more conducive to root growth than sand inter-layered soil.72.46%～92.40% obtained in the0-40 cm.Root length density(RLD)has a high fit as a cubic function of relative standardized root depth.The model can describe the root distribution well under different sand interlayered soil with water-saving and nitrogen-reducing.It is good for the root growth with "wide and deep" by Reducing the amount of irrigation and nitrogen input.The root surface area,root length in narrow rows of 20 cm,and root length in 10-20 cm vertically were more closely related to yield and WUE,and better reflected the differences in yield and WUE of spring maize under different water and fertilizer in the sand interlayered soil;The correlation between root length and yield and WUE in the 40-50 cm soil layer was not significant.4.The simulation of water-salt dynamics in typical sand inter-layered soil by HYDRUS and optimize the schedule of maize.Four depths of sand inter-layered soil,the upper boundary of sand layer is mostly recharged by infiltration.The upper boundary of sand layer is mainly recharged by water upward under the depth of 40-60 cm.It is still mainly recharged by soil upward under the irrigation quota of 54 mm and 63 mm,and turns to the soil water leakage when the irrigation quota is more than 72 mm.Under the burial depth of four different sand layers,the upper boundary of sand layer is mostly recharged by infiltration;when the burial depth is 40-60 cm,the upper boundary of sand layer is mainly recharged by water upward;when the burial depth is 60-80 cm,the upper boundary of sand layer is still mainly recharged by soil when the irrigation quota is 54 mm and 63 mm,and when the irrigation quota is more than 72 mm,the soil water leakage is mainly;the lower boundary of sand layer and 1 m soil interface are mainly recharged by The lower boundary of the sand layer and the 1 m soil interface are dominated by soil water infiltration,and there is no upward water recharge due to the influence of the sand layer.The bottom of the sand and the 1 m soil interface are dominated by soil water seepage,and there is no Upward recharge of water because of the sand inter-layered soil.The maximum amount of water stress to the root system accounted for 56%-68%;The total water stress on the roots gradually decreased with increasing depth of sand burial,and the deeper the sand burial,the lower the water stress on the roots.Compared with the sand layer burial depth of 20-40 cm,the total water stress of the root system was reduced by 10.76%to 45.63% in other sand layer burial depths.The bottom boundary salt flux increased by 0.17%to 447.38%,when the with increasing irrigation quota and the deeper sand inter-layered soil.The Ec in the surface soil and root layer increased after harvest.Considered the soil water and salt distribution,It is recommended to irrigate three times during the whole fertility period at the pulling stage,male extraction stage and filling stage,when the depth of sand inter-layered 20-40 cm and 40-60 cm are 63～72 mm and 81～90 mm respectively,and the depth of sand inter-layered 60-80 cm and 80-100 cm are 72～90 mm. |
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