| Soil salinization is the major causes of declining agriculture productivity in the Hetao IrrigationDistrict of Inner Mongolia, China. In the circumstances of local shallow groundwater table, highevaporation, low precipitation and coupled with main upward movement of soil salt and severe saltaccumulation in the surface soil in this area, how to control the salt accumulation is very practical andurgent. This paper has proposed a new technique to restrain soil evaporation, retain moisture and controlsalinization thus helping to improve the saline soils and increase sunflower (Helianthus annuus L.) yieldthrough burying a straw layer in the soil and combing with plastic film mulch. In order to reveal effectsof plastic film mulch and buried straw layer on soil water, salt transport and sunflower growth, threetrails were conducted from2011to2013with maize straw as the experimental material. With the help ofsoil columns, the impacts of different straw parts, lengths and burial depths on soil water infiltration,evaporation, upward movement of capillary water and phreatic water evaporation were comparativelystudied in laboratory, as well as the distribution and transportation of soil water and salt during theprocesses. Meanwhile, a three-year micro-plot experiment was conducted to evaluate the effects ofstraw layer and its thickness and burial depth on soil water and salt transportation under planting.Moreover, a two-year field experiment was conducted to investigate the effects of plastic film mulchand straw layer burial on sunflower growth and yield. The main results are as follows:1. Results from the soil column simulation experiment showed that the combined application ofplastic film mulch and straw layer burial treatment altered the distribution and transportation of soilwater and salt in soil profile, including retaining more moisture in the topsoil layer, enhancing saltleaching, reducing the soil water and phreatic water evaporation, preventing the upward movement ofsoil water and salt, reducing sal accumulation.(1) In infiltration process, straw layer treatments effectively retarded water-flow and had anobvious effect of retaining water and leaching salts which in the topsoil. In infiltration process, the strawlayer treatments not only reduced the water infiltration rate and advanced wetting velocity, but alsoinduced the instability of wetting front, i.e., appearance of preferential flow. However, the benefit effectdeclined significantly with the decrease difference in hydraulic conductivity between straw layer andsoil layer. Then, the relationship between cumulative infiltration and time was converted fromnon-linear process into linear infiltration process. Meanwhile, straw layer treatments displayedsignificant long-term effect of storing soil water in the upper soil layer thereby helping to leach soil salt.Primarily, its effectiveness relates to the structure of straw layers, and it has more to do with strawinternal porosity which will make a difference in water conductivity. The more the internal porosity instraw layers the less inhibiting effect on water infiltration.(2) In evaporation process, straw layer treatment had an obvious effect of reducing soil evaporationand preventing the upward movement of soil water and salt. During the early days of evaporation, thesurface soil layer easy to be dried under intensive evaporation. Then, it can improve the soil temperature thereby to speed up the vaporized water movement and increase the proportion of gas in the straw layers.Consequently, it increased the effect on preventing soil water evaporation, and retained more water inthe subsoil layers. In addition, the salt upward movement in the straw layer treatments was controlled,and thus more salts been blocked in deep soil layers. Neverthless, the effect of straw layer on preventingthe upward movement of soil water and salt related to its internal porosity and burial depth. On the onehand, with the increase of internal porosity in straw layers, the inhibitory effect on preventing soil waterevaporation decreased in the early days while increased in the later. On the other hand, with the increasein straw layers burial depth, the inhibitory effect on preventing soil water evaporation decreased.(3) Compared to non-straw layer control, the height of capillary water was decreased in the strawlayer treatments. Also the rate of capillary water upward movement in the soil layers below straws waslowed. Capillary water did not cross the straw layers if it with5cm thick, but their bottom side weresoaked wet. With the increase of internal porosity in straw layers, the inhibitory effect on capillary waterupward movement increased; in contrast, the rate of capillary water upward movement increased in thesoil layers below straws.(4) Aside from the aforementioned, straw layer treatments dramatically reduced the evaporationfrom phreatic water under shallow groundwater table. During the30days of experiment, the cumulativeevaporation from phreatic water in the straw layer treatment decreased by96.82%, compared to uniformsoil. Plastic film mulch also reduced the evaporation relative to non-mulch. However, the straw layertreatment had94.02%lower evaporation than plastic film mulch. Moreover, the combined applicationof straw layer and plastic film mulch treatment performed better to against water evaporation than eithernon-mulch, or the individual use of straw interlayer or plastic film mulch. Therefore, the straw layerburial and plastic film mulch treatment had more moisture and less salt in the infiltration process, andreduced the soil water and phreatic water evaporation in the evaporation process, compared to othertreatments. In our experiment, straw layer had obvious effect on preventing groundwater evaporation ifits burial depth was equal to or less than60cm under plastic film mulch when the groundwater tablewas below1m. No significant differences in evaporation inhibitory effect were observed among thedifferent burial depth treatments. Nervertheless, with the increase of straw layers burial depth, the waterstorage capacity enhanced while the salinization control effect decreased.2. Results from the micro-plot experiment showed that the combined application of plastic filmmulch and buried straw layer treatment not only significantly enhanced water storage capacity of the0~40cm soil layer, but also continuously controlled salt accumulation.(1) In our experiment, the soil water content of0-20and20-40cm soil layer was4.01%and3.10%higher while the soil salt content was21.23%and29.60%lower in the straw layer treatments than innon-straw layer treatments before sowing, respectively. During the sunflower growing seasons, thestraw layer treatments had a higher soil water content of0-40cm soil layer than that of control on30days after sowing. However, the water retention effect sustained to approximately60days after sowingin the combined application of plastic film mulcha and straw layer burial treatment, particularly in wetyear. On the other hand, the plastic film mulch and straw layer burial treatment had a consistently and significantly lower soil salt content and soluble salt concentration of0-40cm soil layer than that ofother treatments throughout the growing season. Thus, it provided a better edatope for plants andimproved the development of sunflower.(2) In the fields, the desalinization effect increased significantly and service year also extendedremarkable with the thickness of straw layer when combined with plastic film mulch. It also observedthat the deeper the straw layer burial, the more water retention. However, the preferable burial depth forstraw layer to control salinization was40cm, which was in conformity with the actual agriculturalproduction.3. Results from the field experiment showed that the straw layer burial and plastic film mulchtreatment significantly improved emergence rate and sand establishment, promoted the growth ofsunflower and increased seed yield. Compared to neither straw layer nor mulch control, the straw layerburial and plastic film mulch treatment increased dry matter accumulation rate by35.30%at seedlingstage, shorted growth phases by4-12d and increased net photosynthetic rate by4.87%-11.90%,respectively. Moreover, the straw layer burial and plastic film mulch treatment increased plant height,stem diameter, leaf area and dry matter by36.62%,16.44%,49.05%and42.60%at maturity stage,respectively; it significantly increased seed yield by24.57%. |
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