| In order to explore the influence of different leaching irrigation modes of brackish water on the water and salt transport law of severe saline-alkali soil in southern Xinjiang,four leaching irrigation modes were set up through indoor soil column experiments,including brackish water irrigation with different salinity,mixed irrigation with salty water,alternate irrigation with salty water and intermittent irrigation with salty water.The effects of three kinds of salinity(0 g/L,3 g/L and 5 g/L),three kinds of mixed irrigation ratio of salty and fresh water(1:4,1:1 and 4:1),two irrigation orders(salty before light,salty after light)and three kinds of intermittent time(intermittent 0 min,120 min and 360 min)on soil were analyzed.(1)When brackish water with different salinity and the same irrigation quota is used for leaching irrigation,fresh water lasts for 8160 min,which is the longest;When leaching irrigation is carried out with the same infiltration time and different proportions of mixed irrigation of salt and fresh water,the higher the proportion of salt water,the greater the infiltration quantity;The cumulative infiltration of saline water first is greater than that of fresh water first when irrigation is carried out in different sequences of saline and fresh water alternately.The shorter the intermittent time,the greater the cumulative infiltration.When the intermittent time is 0 min,it takes the shortest time to reach the same irrigation quota.At the initial stage of infiltration,the migration trend of wetting front in each treatment is basically the same,but with the passage of time,the difference between different treatments is more obvious.When the irrigation quota is reached,the wetting front moves fastest and lasts the shortest when the salinity is 5 g/L;With the increase of infiltration time,the migration speed of wetting front in the treatment with relatively small salt water gradually slows down;It takes less time to reach the same migration depth of wetting front after salting first and then salting second.The end time of irrigation infiltration in intermittent leaching irrigation increases with the increase of intermittent time.The fitting result of Kostiakov formula can better reflect the actual situation of infiltration rate,and the fitting degree R2 of all treatments reaches 0.85.(2)Under different irrigation modes of brackish water,with the increase of salinity of brackish water,the soil moisture content increases and the desalination rate decreases;The proportion of salt and fresh water has a great influence on soil desalination.The smaller the share of salt water,the smaller the water content and the higher the desalination rate.The sequence of first salty and then salty irrigation can reduce the salt content of the upper soil,while the sequence of first salty and then salty irrigation can increase the water content of the lower soil.Under the condition of intermittent irrigation with salinity of 3g/L and 5g/L in the middle and upper soil layers(0-30cm),there is no obvious difference among the treatments,and the soil salt content is small,which is located in the intermittent irrigation mode with salinity of 3 g/L and 5g/L in the middle and lower soil layers(30-60cm).With the increase of intermittent time,the soil salt content and water content increase.(3)Using HYHRUS-1D model to construct the equation of water movement and solute transport,and set specific initial conditions and boundary conditions to simulate the distribution process of water content and salt content under different salinity brackish water leaching irrigation conditions.The measured values of soil water content and salt content after different salinity brackish water leaching irrigation are basically consistent with the simulated values,and the simulated values of soil water content and salt content gradually decrease with the increase of depth.The determination coefficient(R~2)of the simulated values of different treatments all reached above 0.93,and the root mean square error(RMSE)was in a low level.The model was tested and calibrated,which proved that the simulated values could better reflect the actual situation.(4)Different irrigation modes of brackish water have different effects on the changes of main ions of chlorine,calcium,magnesium and sodium in soil.Under different salinity brackish water leaching irrigation modes,the whole soil is dechlorinated within the depth of0-40cm.The higher the salinity,the higher the calcium ion content in each soil layer.The leaching effect of 3g/L brackish water direct irrigation on magnesium ions is better than that of 5g/L brackish water direct irrigation.When the salinity exceeds 3g/L,the sodium leaching effect becomes worse.Under the mixed irrigation mode with different proportions,chlorine,calcium,magnesium and sodium ions were effectively leached in the soil depth range of0-30cm,and the ion content was at a low level.The greater the proportion of fresh water,the higher the leaching efficiency of each ion.Under different alternate order leaching irrigation modes,the order of salty first and then light irrigation can improve the leaching efficiency of ions in the middle and upper soil,and the order of light first and then salty is beneficial to improve the leaching efficiency of ions in the deep soil.Under different intermittent leaching irrigation modes,the main ions in the depth range of 0-30cm soil layer in each treatment were fully leached,and with the increase of intermittent time,the main ions migrated further with infiltration.In the lower soil layer of 30-50cm,the content of main ions in each treatment increased gradually with the increase of intermittent time. |
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