Study On The Law Of Soil Water And Salt Transport Under The Mode Of Straw Interlayer Combined With Different Surface Mulch

Unreasonable irrigation mode and large evaporation drop ratio in arid and semi-arid areas are the main reasons for the secondary salinization of cultivated land.In order to curb the secondary salinization of cultivated land in arid and semi-arid areas,improve water resource utilization efficiency,this paper will pass the indoor soil column test,study the contents of two experimental stages:In the first stage,five control treatments are set up:pure soil（CK）,straw interlayer and no soil surface covering（G）,straw interlayer and sand and gravel covering on the soil surface（S）,straw interlayer and straw covering on the soil surface（J）,straw interlayer and plastic film covering on the soil surface（M）,the effects of straw interlayer combined with different soil surface coverings on the characteristics of water infiltration,evaporation and water and salt transport of the tested soil samples were studied,the stratification rate of soil salt reserves was analyzed,and select the optimal model of soil moisture conservation and salt suppression（J）;In the second stage,based on the optimal mode（J）,three control treatments were set:soil surface straw mulch and straw interlayer thickness of 3cm（T₁）,soil surface straw mulch and straw interlayer thickness of 6cm（T₂）,and soil surface straw mulch and straw interlayer thickness of 9cm（T₃）,comprehensively explore the effects of different straw interlayer thickness on the water infiltration,evaporation and water salt transport characteristics of the tested soil samples under the optimal mode,establish a suitable infiltration and evaporation model,analyzing the profit and loss of soil salt,and finally determine the conservation tillage mode（T₂）that is more in line with the sampling area.The main research results are as follows:1.Phase I research results:（1）In the stage of water infiltration,the average migration rate of soil water wetting peak is CK>G>S>J;The cumulative infiltration of G,S and J increased by9.8%,24.3%and 42.6%respectively compared with CK;The results show that:straw interlayer will attenuate the movement rate of wetting peak and increase the cumulative infiltration of soil water,the“upper cover and lower partition”mode shows a good effect of water retention and seepage resistance in the stage of water infiltration,and the J mode is the best.In the stage of water evaporation,the average daily evaporation is CK>G>S>J>M;The cumulative evaporation under G,S,J and M modes is reduced by 28.4%,59.8%,73.5%and 77.6%respectively compared with CK mode,the highest steam inhibition rate of M mode is 77.5%,followed by J mode;The results showed that the effect of straw interlayer was better,and the effect of“upper cover and lower compartment”mode was obvious.The effect of M mode was the best,followed by J mode.（2）The movement laws of soil water and salt were significantly different under the five modes,48h after the end of infiltration stage,the average soil moisture content at 0-25cm under CK,G,S and G modes is J>S>G>CK,the average conductivity is CK>G>S>J,the leaching rate of J mode was the highest,29.2%.After the evaporation stage,the average soil moisture content at 0-25cm under the five modes is M>J>S>CK>G,and the average conductivity is CK>G>S>J>M,the salt inhibition rate of M mode was the highest,23.1%,followed by J mode;The stratification rate of soil salt reserves is analyzed,the salt peaks of each model are distributed at 25-37.5cm.The results showed that after the infiltration stage,the straw interlayer significantly increased the moisture content of the soil above the straw interlayer and improved the desalination effect of the soil;After the evaporation phase,the“upper cover and lower partition”mode shows obvious effects of steam,desalination and salt suppression,among which the effect of M mode is the best,followed by J mode.（3）The significant analysis of the water retention effect of S,J and M modes shows that the F statistic value of S～J and S～M combination is more than F crit,P-value less than 0.01,while the F statistic value of J～M combination is less than F crit,P-value more than 0.05,this shows that the steam inhibition effect of M and J mode is very significant compared with S mode,but M is not significant compared with J mode;Considering that plastic film mulching will pollute the soil environment,J model is considered to be the best model.2.Phase II research results:（1）In the infiltration stage,the average migration rate of soil moisture wetting peak of the three treatments was T₁>T₂>T₃;The results show that with the increase of straw interlayer thickness,the migration rate of wetting peak will gradually decline,the power function equationy（28）m?tⁿcan well reflect the variation of soil moisture peak migration distance with time under different straw interlayer thickness under the optimal mode;Philip and Kostiakov infiltration models can better fit the relationship between soil water cumulative infiltration and time under different straw interlayer thickness under the optimal mode;EquationI（28）Kx（10）Bhas a good fitting effect on the relationship between the migration distance of wetting peak and cumulative infiltration under three treatments.In the stage of water evaporation,the average daily evaporation of the three treatments was T₁>T₂>T₃;The cumulative evaporation of soil water under T₂and T₃treatment decreased by 3.8%and 9.7%respectively compared with T₁mode,and the highest vapor suppression rate of T₃treatment was 76%;The results showed that with the increase of straw interlayer thickness,the average daily evaporation of soil gradually decreased,and the cumulative evaporation of soil water gradually decreased.The greater the inhibition rate of soil water evaporation,the better the inhibition effect;Rose evaporation model has a good fitting effect on the variation law of soil water cumulative evaporation with different straw interlayer thickness under the optimal mode.（2）Under the optimal mode,the movement laws of water and salt in the three treatments were significantly different,48h after the infiltration stage,the average soil moisture content at 0-25cm under T₁,T₂and T₃modes is T₃>T₂>T₁,the average conductivity is T₁>T₂>T₃,the highest leaching rate of T₃treatment was 32.8%;After the evaporation stage,under the three modes,the average soil moisture content at0-25cm is T₃>T₂>T₁,the average conductivity was T₁>T₂>T₃,and the salt inhibition rate of T₃treatment was the highest,which was 24.7%;The salt profit and loss analysis of the three treatments showed that the salt discharge rate（（35）s/s _a）was T₃>T₂>T₁;The results show that in the stage of water infiltration,with the increase of the thickness of straw interlayer,the water above the straw interlayer will increase,and the water below the straw interlayer will decrease,and the effect of soil desalination and salt leaching will be better;In the water evaporation stage,with the increase of straw interlayer thickness,the more obvious the effect of inhibiting soil water evaporation,the better the effect of inhibiting soil deep salt return,and the higher the salt discharge rate.（3）The water retention effects of the three treatments were analyzed.The F statistics of T₁～T₂,T₁～T₃and T₂～T₃are less than F crit,P-value more than 0.05,the steam inhibition effect of the three treatments was not significant;Considering its water and salt transport law,practicability and ease of operation,T₂model is considered to be a more reasonable conservation tillage model,the results can provide a theoretical basis and reference for the conservation tillage model in Yongjing County,Linxia Hui Autonomous Prefecture,Gansu Province.