| Hetao irrigation area of Inner Mongolia is one of the largest saline area in China with a saline area of 394,000hm~2,accounting for 68.65%of total arable land in this irrigation area,which has a huge development potential.In Our previous studies,buried straw layer plus plastic mulching under the surface 35-40cm has been recommended as an effective practice for reducing soil salinity and enhancing crop productivity.At present,this technology has been accepted widely.However,this technology has a lot of space to improve,and the controlling effect of this technology is likely to be determined by the characteristics and structure of the straw layer.If the shape of straw layer changed,its physical properties will also change,that might affect water infiltration and the distribution of salt.Moreover,the straw will gradually decompose,exerting an effect on physical and chemical properties of soil.However,these problems about straw layer lack of experimental verification.In addition,about the evaluation index,people evaluate the saline soil improvement effect by measuring soil salt content,actually the soil salt concentration and salt ion as index to diagnose the salt injury to plant will be more accurate.So it is necessary to study on soil solution concentration and the change of ion.Therefore,this paper carries out the research through the three parts:the indoor soil column simulation experiment,the micro-plot field experiment and the auxiliary field experiment with straw decomposition in natural stage,were conducted to investigate the effect of straw layer on soil solution and ion movement.The result will provide a theoretical base to reveal the mechanism on the effect of salinity control by straw layer,and it also provides the basis for further optimization on this technology.1.This paper designed a series of indoor soil column experiment which contain ten treatments including CK(soil with no maize straw layer),L5/L3/L1.5(original maize straw cut into 5cm,3cm and1.5cm,respectively),SK(maize straw pellet layer),SF(maize straw powder layer),SR(maize straw layer of horizontal composition),SL(maize straw layer of vertical composition),HRS(half decomposed maize straw layer)and RS(completely decomposed maize straw layer).The experiment aimed to research the effect of different straw layer on water infiltration and soil salt.The main results are as follows:Compared to CK,straw layer with different shape and decomposing degree all reduced water infiltration and then increased salt leaching.With the straw cut to shorter slice,the water infiltration rate was lower and the desalting efficiency in 0-40cm soil layer was higher.Compared to straw layer composed with original 5cm-long straw,SK showed the poor effect on reducing water infiltration.Water content of 0-40cm layer under SK was decreased by 10.96%,and the sodium content was decreased by 11.29%.SF further slowed water infiltration,and the water and chloridion content were decreased by 2.48%,11.82%,respectively,while the sodium content was increased by 8.6%.The rate of water infiltration was slow under SR,which saved more water,and the soil salt,sodium and chloridion content were decreased by 6.06%,18.31%and 16.79%compared with L5.SL showed poor performance on storing water because of the vertical porosity.But the soil salt content and ion content have no significant difference with L5.The water infiltration rate was high on HRS soils,so that the soil water content on 0-40cm layer were decreased by 6.25%,while there were much more salt and ions.The rate of water infiltration was slow on RS,which saved more water,and the soil salt,sodium and chloridion content were decreased by 5.48%,12.75%,9.38%compared with L5.2.The different straw layer burial level(CK:non layer,S400:400kg/667m~2,S800:800kg/667m~2,S1200:1200kg/667m~2)were settled by micro plot experiment to study the influence of straw layer on the soil solution concentration.Two year results showed that the straw interlayer could improve desalinization rate.With the increase of straw interlayer dosage,the effect of water storage and salt-leaching were better,and the soil solution concentration was lower after irrigation.The straw interlayer can also significantly reduce the content of sodium and chloride ions in soil solution.The content of soil salinity,sodium and chloride ions in soil solution under S1200 reduce 35.61%,34.24%and 53.59%than CK after irrigation in 2015,while the soil salinity,sodium and chloride ions under S1200 reduced 27.54%,43.85%and 52.96%than CK after irrigation in 2016.The straw interlayer could break the capillary,restrain salt and water up,and reduce the soil solution of salt and ionic content in the root distribution layer.The content of soil salinity,sodium and chloride ions under S1200 reduce30.23%,13.32%and 38.66%than CK after harvest in 2005,and 36.35%,39.01%and 31.70%than CK after harvest in 2016.However from crop growth point,S1200 treatment obstructs the moisture below the straw barrier due to the excessive usage of straw,so that crop could not get enough water.Wihle straw usage of S800 was moderate,and it could both regulate soil salt and supply enough water for crop,and finally got the highest production.The plant height,disc stem,root height,hundred-grain weight and yield were higher 7.75%,6.22%,15.25%,4.56%,11.72%than CK respectively.3.Collecting soil samples from auxiliary field experiment which has buried straw layer for two and three years.The result showed that after years of decomposition,straw interlayer effectively improved soil aggregate in the 35-40cm soil layer,and the micro-aggregate were composed to macro-aggregate.Moreover,decomposed straw layer helped increased organic matter,humus,available nitrogen and available potassium,promoting the soil fertility.Straw layer still play the effect of restraining water and salt,but the salt controllingeffect under buried straw treatment was gradually weakened from 2015 to2016 because of the increase of micro-aggregate,reforming capillary ascension again. |
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