Regulation Effect Of Straw Mulching On Soil Water Salt Distribution And Cotton Growth Under Drip Irirgation In Arid Region

In order to explore the effect of straw mulching on soil water salt distribution in cotton growth andyield under drip irrigation in North Xinjiang.2009-2012with wheat straw as the material, the effect ofdifferent quantity of straw mulching, straw mulching position and straw length on soil profile water-saltdistribution in the case of soil column one-dimensional vertical infiltration and evaporation werecomparatively studied through soil column experiments in lab. Meanwhile combining four years test-pitexperiments, the effect of surface coverage, coverage below the surface30cm and no coverage on cottongrowth, root system and yield under drip irrigation respectively in the condition of nonsaline alkali soilsand saline-alkali soil on was studied. Motion process of soil moisture and temperature under straw mulchhas been simulated using HYDRUS. The main conclusions are as follows.（1）Ponding infiltration moist soil moisture in the treatment of no coverage and surface coveragegradually Reduce, from top to bottom, from saturated water content to initial value. Both cumulativeinfiltration and wetting front in one-dimensional vertical infiltration increase with the time. At thebeginning of infiltration, cumulative infiltration and wetting front increase rapidly. But its increasing trendgradually become slow over time and continue. The model of no cover one-dimensional vertical waterinfiltration is built.（2）Deep straw mulching which can block infiltration flow make infiltration flow detained in the soilabove straw mezzanine and it also has the permeability reduction which make infiltration water’s andinfiltration front’s wetting velocity reduced. Meanwhile it also affects salinity and ion migration. Salinityrises gradually from top to bottom. After infiltration, change rule of Cl^-and change rule of total salinity isthe same in profile. Sensitivity of HCO₃^-to the straw interlining is stronger than SO₄^2-.（3）Straw mulching has a significant effect on soil temperature field. Straw layer can stop or absorb partof heat energy at any position. The bigger surface cover, more slowly profile temperature changes and thebigger temperature difference than no cover. In the treatment of, temperature variation characteristics is thesame with no cover in the rage of0-40cm and heat transfer performance of straw laminated is greater thanthe surface coverage. The temperatures of the treatment of surface coverage are all lower than coveragebelow the surface20cm in the rage of0-20cm. In the0-40h, the temperatures of the treatment of coveragebelow the surface20cm are all lower than surface coverage in the rage of20-40cm. But endothermic effectof the treatment of coverage below the surface20cm reduces after40h and temperature rise rate is higherthan the treatment of surface coverage in the rage of entire depth. The general function of the soiltemperature with the depth and time is fitted.（4）Straw mulching shows significant influence on soil water distribution. And the location of strawmulching has a remarkable effect on the distribution of soil moisture content after the evaporation ofone-dimensional soil column. Straw coating can effectively restrain water loss from evaporation. The morethe surface of straw mulching quantity is, the stronger inhibition on the surface and the upper evaporationof soil moisture content is. Straw mulching of5cm length and12000kg/hm²or more could inhibit theevaporation loss by52.21%or much better. Soil moisture content of the treatment of surface coverage ishigher than coverage below the surface20cm in0-20cm, and coverage below the surface20cm is higherthan the surface coverage in20-40cm. The more the straw mulching quantity is, the more obvious thephenomenon is. Variance analysis shows that straw mulching quantity under the condition of surfacecoverage influences cumulative evaporation, averaging moisture content of0-15cm and averaging a saltcontent of0-15cm most significantly.When the straw cover is20cm, it only has the biggest influence on theaveraging moisture content of0-15cm.（5） Under the conditions of one-dimensional vertical evaporation, straw mulching affects or reduces saltup accordingly. The position of straw mulching mainly influences salt movement in the lower soil closelyconnected to the cover, the salt accumulating under straw layer in a certain range. Surface soil salinity gradient decreases with the increase of straw mulching. When the amount of straw mulching is far morethan12000kg/hm², it inhibits soil salt significantly. And the depth of inhibition is about20cm. Coveragebelow the surface20cm reduces the upward migration of salinity, rendering the upper salinity rate reduce.And the salinity rate within the scope of the following10cm straw layer is to rise. Straw cover of5cmlength is more, the effect of the inhibition on the upper soil salt is better. The soil salinity gradient is higherthan coverage below the surface20cm within0-20cm soil layer, and the depth of20cm is higher within20-25cm.（6） Drip irrigation cotton trials in Straw mulching test pit showed that straw mulching affected themigration and distribution of soil salt indirectly. Surface of straw mulching has obvious effect on inhibitingwater loss. It can reduce the evaporation in the medium loam soil and saline-alkali soil within0-20cm. Theeffect of protecting water is better.30cm deep Straw mulching stalk （for about100days） has obviousinhibition on water and salt migration upwards in deep layer before rot.0-20cm.Soil salt content within0-20cm is lower and mainly gather in the deep of the30to40cm, which is beneficial for the cotton rootzone to form desalting area. The effect of inhibiting salt is higher than the surface coverage, thus play a rolein interlayer, inhibiting salt and improving saline soil. But the effect of the inhibition on evaporation andsalt is not obvious in the late cotton growth.（7） Straw mulching significantly affected the density distribution of root length, and has a greaterimpact on deep root system distribution. The root system distribution in medium loam is deeper. Reducingroot weight density distribution proportion in plow layer by0to28cm, or increasing root length density,prompted the development and distribution of fine roots of cotton in plow layer and taproot in deep layerrespectively.Surface coverage promotes root development in plow layer. The cover of30cm limits upperroot development, whereas promotes lower root development. Cotton root system in saline alkali soil isusually thin and long, and fine roots are more in per unit volume of soil. Under salinity stress, straw covercan promote the root to develop more and longer, increasing root length density distribution.（8） Straw mulching has certain influence on drip irrigation cotton growth and yield, especially under thecondition of saline alkali soil. The saline alkali soil straw mulching on drip irrigation for cotton plant leafarea index and yield is relatively high coverage for promoting effect was not significant.The effect of strawmulching on the plant height,leaf area index and yield of drip irrigation cotton is not significant innon-saline alkali soils. But the surface covered comprehensive control effect is better than that of coveragebelow the surface30cm especially during the later period of cotton growth （the blooming period）.However,the effect of straw mulching on the plant height, leaf area index and yield of drip irrigation cotton issignificant in saline alkali soils, especially in the middle. The effect of salt suppression in surface cover ismore significant than coverage below the surface30cm. The effect of coverage below the surface30cm isobvious at the early stage of the cotton growth （seedling stage, bud stage）, and weakens during the laterperiod （flowering and boll setting stage）.The cotton yield of surface coverage has increased respectively by3.2-17.9%and3.1-16.3%than no cover and coverage below the surface30cm.（9） Using HYDRUS to compare the results of simulated values and measured values about soilmoisture and motion temperature of straw mulching is more ideal. It can reflect the law that how soilmoisture content is changing with the factors such as irrigation and evaporation during the test period muchbetter. And it could be used to study and predict how soil water salt and heat move under the conditions ofstraw mulching.As a try to explore how to ease membrane fouling in Xinjiang farmland and develop efficientecological agriculture, the combine of straw mulching and drip irrigation in cotton crops in saline-alkaliland has the possibility of application and prospect. However, technologies related still need furtherresearch.