Abstract This article mainly covers the agricultural technology and traditional technology of plastic film mulching in China through the contrast and analysis. The mechanism and effect of plastic mulching technology is expounded， and the main use， positive role and development prospects of the technology in agricultural production， as well as the technology of agricultural soil conservation are introduced. In addition， existing problems and countermeasures are put forward to promote the development of agriculture in arid areas.
　　Key words Mulching； Mechanism； Result； Prospects
　　Traditional cover agriculture has a history of several thousand years in China； but due to the limitations of the nature and source of traditional cover materials， it is difficult to popularize and apply in large areas. The appearance of plastic film as a cover material in China has resulted in qualitative changes in traditional cover agriculture， and significant changes in agricultural cultivation techniques， and a profound impact on Chinas traditional agricultural technology have been produced， accelerating the development of traditional agriculture in China to modern agriculture[1-2]. The area of arid and semiarid regions in China is vast， accounting for approximately 51% of the countrys total land area. Sixtyfive percent of the 51 million hm2 of farmland has no irrigation conditions. The semiarid region centered on the Loess Plateau is dominated by rainfed agriculture in Chinas drylands （rainfed）. In the main distribution area of agriculture， natural precipitation is the only source of moisture for agricultural production in dryland in the area. Research shows that the distribution of natural precipitation on the underlying surface of the Loess Plateau is： 20% to 25% of primary productivity， 10% to 15% of soil erosion， and 60% to 70% of ineffective evaporation[3]. Therefore， adopting the necessary protective cultivation techniques， ground cover technologies， and catchment and irrigation technologies will play an active role in agricultural production in arid regions.
　　Application and Development of Plastic Film Mulching Technology
　　Plastic film cover technology was developed in the middle of the 20th century with the rise of the plastics industry. Some developed countries in the world are widely using plastic film covering cultivation techniques， first applied to vegetables， and gradually expanded to other crops later. In 1951， Japan began experimenting with the use of plastic film instead of oil paper and glass， and its application in agriculture has since grown rapidly. In the United States in the early 1950s， mulching was first applied in Hawaii. In 1963， the black film was covered with a laminating machine in Arizona. The laminating machine was able to continuously perform two operations： film laying and sowing， and planting two weeks in advance. Cotton production increased significantly. 　　Since 1978， China began to introduce mulching techniques for plastic mulching. The mulch cultivation experiment began in 1979. When it was tested in 44 provinces， municipalities and districts in the country with 44 hm2 of vegetablebased crop tissues， it was fully successful. In the 1980s， the multipoint trial was transformed into largescale promotion. Since then， the mulching area has rapidly expanded throughout the country. According to incomplete statistics， the cultivated area of mulching in China reached more than 6.667 million hm2. It has become the largest country in the world for mulching film cultivation， and there are about 60 kinds of crops covered by mulching. The cultivation theory and technology have achieved major breakthroughs and innovations. Plastic film mulching technology has developed rapidly since it was introduced into China. It has been widely used in economic crops and food crops， especially in wheat. Gansu， Shanxi， and Shandong have successively studied film mulching and ridge cover interfilm fine singling. The application of cover cultivation techqnieus in dry land has been expanded to the whole growth period of crops.. In Chinas arid and semiarid regions， mulching technology has been widely used. It has become an important mean for increasing agricultural production， and it has revealed in terms of ecological effects， plant physiological ecology， ploughing soil effect， utilization of water and fertilizer， and water conservation and soil conservation. The law of production and application of plastic mulching covers the formation of a relatively complete farming system[4-6]. Han Siming and Liao Yuncheng conducted indepth research on dryland cultivation in summer and winter， farmland water harvesting and conservation tillage systems， dualcoverage cultivation techniques for dry wheat in the whole process of microwater gathering and deepfilmside furrow sowing techniques for stubblecovered wheat[7-8].
　　Application Mechanism of Mulching
　　Effective conservation and use of water
　　Plastic film coverage in arid regions due to the provision of a gasimpermeable membrane on the surface of the soil prevents vertical evaporation of soil moisture， promotes lateral migration of water， effectively preserves soil moisture， reduces evaporation， coordinates crop growth， eases water demand conflicts， and promotes the use of deep water. According to Han Siming et al.s study in the Weibei Arid Regions， the treatment of mulching with water and covering straw in the trenches began in the summer and early summer， and the soil water storage capacity in the 0-200 m soil layer at the end of summer was 63.2 mm higher than that in plain tillage. The natural precipitation conservation rate during leisure period was 25.9% higher than that of plain tillage. Because of the functions of steam suppression， polywater， and water retention， the membrane side ditching is superior to the sowing on the membrane in the soil moisture， and it has a good effect of increasing production. However， in particularly arid years and semiarid droughtprone areas， no rain can be accumulated， and the temperature and water retention effects of flat film sowing are obvious[7]. Zhang Zhengmao et al.s study in the Weibei anaerobic field showed that winter wheat mulching in the winter， the 0-50 cm storage volume side membrane ditch was 14.1 mm higher than the control， 6.1 mm higher than the film sowing； in the harvest period， the reservoir was 23.6 mm higher than that of the control， and 20.6 mm higher than that on the membrane. Coverage in the field had a great influence on soil evaporation in the early stage of crop growth[3]. According to the study of the gate flag and other studies， it was concluded that the mulching film coverage increased from 35% to the current maximum coverage rate of 90%， the interforest evaporation decreased by 51.8%， and the soil evaporation in the bare land decreased by 74.6%. Therefore， it is better not to remove the film before the crop is ridged to reduce the evaporation of soil between the trees and increase the effective transpiration of the crop， but the high field coverage is not conducive to the accumulation and infiltration of rainwater[9]. He Zhijian et al. studied the moisture dynamics of mulching in terraced fields in Jinxi and found that in an extremely dry year， the soil with a greater effect on soil moisture is 0-100 cm soil layer， and 100-200 cm can be absorbed and used effectively[10]. While mulching with water mulching， the development of effective water production potential has been continuously improved[11]. 　　Increase the temperature of the tillage layer
　　The mulching film has a significant influence on the soil temperature， while the plough layer temperature has a great influence on the root growth of the crop. Wang Shusen[12]believes that the main mechanisms for increasing the temperature of mulch are： ① The mulch isolates the exchange of moisture between the soil and the outside and inhibits the latent heat exchange； ② The mulch weakens the sensible heat exchange between the soil and the outside； ③ The water layer adhering to the surface of plastic film weakens the longwave antiradiation and slows down the nighttime temperature drop. Covering the mulching film promotes the crops to make full use of the abundant light and heat resources and increases the accumulated temperature during crop growth. According to the measurement of dryland membrane millet， the temperature of 0-15 cm soil layer in seedling stage is 1.3-2.3 ℃ higher than that in open soil， 0.3-3.0-1.0 ℃ in jointing stage， and 150-200 ℃ in whole growth period. According to the survey data of winter wheat fields in Wenxi County， Shanxi Province， on November 30， 1996， the field temperature of 5 cm covered fields was 1.2 ℃ higher than that of the control. On February 18， 1997， the soil temperature at 5 cm was 2.3 ℃ higher than the control. The increase in ground temperature delays the wintering of wheat by 17 days compared with the open season， and it is half a month earlier than the return to green in the following year. For spring crops， low temperatures in early spring can affect seed germination and morphogenesis at seedling stage. Film coverage can effectively solve this problem by eliminating latent heat and sensible heat losses from the soil and the outside world and slowing down the rate of soil temperature decline. The study showed that the mulch film coverage of spring wheat could be increased by more than 5 ℃ 30 days after sowing， but the high temperature in the later period was not conducive to the absorption and utilization of water and nutrients by crops. The warming effect of mulching film changes with the change of crop groups. The coverage of early crops is low， the effect of warming is significant； and the coverage of later crops is increased， and the warming effect is reduced. Studies on cotton mulch cover showed that the narrowfilm or widefilm cover increased the accumulated temperature in the cotton field by 105 ℃ and 195 ℃ in the early growing period （from late April to the end of June）， and the soil temperature increased by 0.7 to 3.2 ℃， but this heat effect was associated with fertility. The arrival of the latter period weakened. The mulching effect of mulching film decreases with the increase of soil depth. In the cold and arid regions， low temperature becomes the limiting factor for agricultural production， followed by moisture. For highfertilizer and warmtowarm crops， the warming effect of plastic film coverage is greater than the contribution of ridgelift water collection to yield[13-15]. 　　Application Effect of Plastic Film
　　Effect of plastic film mulching on production
　　Plastic film mulching technology can greatly increase the economic output of crops due to the effects of warming， water retention， and water transfer. Even when the crops are exposed to drought and early frost， they can still obtain better yields. At the Yuci floodplain experimental site in the eastern part of Jindong， the average yield of waterpermeable plastic film reached 8 226 kg/hm2， which was 13.8% higher than that of conventional plastic film， 43.7% higher than that of straw mulching， and 46.5% higher than that without mulching. The study on wheat mulching in Weibei dryland has shown that in 1997， the sowing on film and sidegroove sowing increased the yield by 12.9% and 36.3%， respectively； in 1999， the sowing on film and the sowing of film on the lateral groove increased the yield by 22.3% and 40.1%， respectively. Membranous furrow sowing is better than film sowing， which is inconsistent with the infiltration of precipitation by the flat film covering pattern， resulting in inefficient evaporation， resulting in poor soil moisture status[16-17]. The threedimension and highefficiency cultivation of dry land not only improves the crop multiple cropping index and the effect of increasing production， but also can be used for a dual purpose. Domestic and foreign scholars have not yet seen this research. Studies have shown that the drycultivation of the ridge cultivation （wheat） trench cover （corn） is better than the current trench cultivation （wheat） ridge cover （corn） with the planting form， the former than the latter increased by 9.0% to 12.5%. The increase in grain output not only solves the problem of food for the farmers in the dry areas， but also increases the income of the farmers[18].
　　Promote crop growth and development
　　Plastic film mulching also has a great influence on the morphogenesis of crop growth. It can enable crops to emerge earlier and advance the crop growth process； mulching can improve the microhabitat of the plough layer and near the ground， which is conducive to the growth of the early root system and the increase in activity of the root system. It has a significant effect on the growth of the crops aboveground and underground parts[19-21]. In potato seedling stage， the 40 cm and 50 cm mulching treatments， compared with the control， increased the plant height by 27.2% and 31.0%， increased the dry matter by 27.4% and 37.6%， increased the root length by 20.86% and 27.3， and increased the photosynthate by 56.1% and 58.9%. Root vigor， coated with 40 cm and 50 cm treatments were 0.71 mg/（h·strain） and 0.91 mg/（h·strain）， respectively， higher than controls[22]. The increase of physiological indicators directly laid the foundation for the high yield of crops[23]. 　　Microbial effects
　　Plastic film coverage improves the microenvironment of the farmland and the water and heat conditions of the soil， affects the soil microbial activity and enzyme activity， and promotes the effectiveness of soil nutrients. The study on winter wheat mulching in Weibei karst showed that the swell pattern was 15.38 times more bacterial， 0.33 times more fungus and 0.61 times more actinomycetes than the soil exposed in open field sowing in March. The sowing pattern was 5.52 times more than that in open field sowing soil， 0.13 times more fungi， actinomycetes more than 0.24 times. It was determined that soil nutrients in mulched wheat increased compared with the control， in which organic matter increased by 26%， total nitrogen increased by 0.014%， and available phosphorus increased by 16.1 mg/kg. Studies have shown that the coating has an effect on the activities of soil enzymes such as catalase， urease， etc[24].
　　Main Technical Modes in Production
　　Membrane ditch planting technology
　　The filmcovered sowing planting technology has better warming effect and conservation effect， and increases the accumulated temperature of the effective crop growth period[25]. Studies have shown that the cumulative temperature of winter wheat covered by filmmulched holes increases by 68-105 ℃. This technology is suitable for dry areas that are insufficient in two seasons and more than one season， and some highcold arid areas， which can increase the multiple cropping index and water use efficiency. Ineffective evapotranspiration is an effective transpiration in wheat， corn， cotton， millet， etc[9].
　　Cultivation techniques for ridge cover
　　The ridge and cover film planting technology has good water storage and water collection effects. The technology is applicable to a wide range of crops. Artificial manmade production in the fields is used to form superimposed precipitation to improve crop moisture conditions. Through field microwater harvesting techniques， it is possible to reduce heavy rain and reduce precipitation， effectively reduce precipitation and improve water use efficiency[26]. In addition， the fertilizer can be used in a centralized manner and soil erosion in the farmland is also controlled. This technology has been widely promoted in Shaanxi， Gansu， and Ningxia in recent years. In arid regions， corn and wheat harvesting techniques have been relatively successful， resulting in significant yield increase. For corn， in the cold and cool areas， membrane cultivation should be adopted to meet the accumulated temperature during the growth period， but the efficiency of precipitation utilization is not as good as that of the membrane side. Zhao Jubaos experiments in Shouyang， Shanxi Province showed that the microwater harvesting and soil conservation technology has the effect of regulating the evapotranspiration of farmland， and has obvious effect of increasing production （the drought year is more pronounced， reaching 59.3%， and the general year increases production by 26.3%-28.1%）[27]. 　　Full miniature polywater binary coverage technology
　　The fullscale miniature polywater dual coverage technology is a comprehensive production increase technology proposed by Professor Han Siming of the Northwest A&F University and other staff members at the Experimental Station of Qian County， Shaanxi Province[7]. It is mainly used in the dryland production areas in northern China， such as the Weibei dryland area in Shaanxi Province， which has the advantage of accumulating natural precipitation in the summer and maximal period in the soil， coordinating the release and maintenance of soil water and fertilizer， and saving water and soil moisture. This technology is mainly applied to the cultivation of winter wheat， and has high requirements for site preparation， burrowing on ridges， and seedlings in trenches. The effect of yield increase is obvious. Tests have shown that largescale field cultivation increases yield by 40.4% and water use efficiency reaches 17.0 kg/（mm·hm2）. The effective cultivation technology system for collecting water and soil moisture was covered on the anniversary of dryland[7-8].
　　Other technical modes
　　In the current production， the first two kinds of technology models have a large area of application， and the third model is mainly applied to Weibei dryland in Shaanxi Province. In addition， according to the precipitation conditions and topography of the arid area combined with the actual production， there are also many new planting patterns， such as the staged mulching and the covering of the whole growing period， which mainly change from the former two models. The ultimate goal is to make full use of precipitation， preserve soil moisture and increase water use efficiency， such as corn lowhole planting technology， Shuanglonggou cultivation technology， Yangpo mulching film covering cultivation techniques， and covering cultivation technology during the leisure period. The development of waterpermeable plastic film provides a new way for the development of agriculture in arid areas[28-30].
　　Problems in Development and Solutions
　　Pollution of farmland ecoenvironment by waste plastic film
　　According to research， although the use of mulch film coverage， in the short term has a good conservation capacity and significant increase in production， the reduced annual soil water and fertilizer in the slope will intensify soil erosion and residual film on the plough layer[28]. In contrast， wheat straw cover is more conducive to the sustainable development of agriculture in arid regions. At present， the residue of agricultural mulch in China is quite serious. About 10% of the total agricultural film remains in the soil every year， because the raw materials of the mulch are mostly macromolecular compounds， which are difficult to decompose under natural conditions. Residues of plastic film affect the soil. The granule structure and the activity of soil microbes are not conducive to farming and pollute the ecological environment of farmland. Therefore， the use of photolysis membranes， biodegradable membranes， double membranes， and liquid plastic membranes are advocated as alternatives to plastic films. In order to solve the problem of residual plastic film more effectively， at the same time， mechanized recycling and reuse technologies for residual film have been developed actively to completely eliminate "white pollution"[29-30]. 　　Phenomenon of premature aging of crops
　　The reason for the decrease in yield caused by mulching of spring wheat mulch film is that mulch film coverage promotes root growth， wheat grows too vigorously during seedling period， and soil moisture is consumed too quickly. At the same time， precipitation is insufficient in the later period， resulting in serious water shortage in late growth period and yield decline[31]. In the middle and late stages of crop growth， some crops have premature aging， which is mainly due to the fact that under the covering conditions， the decomposition rate of soil fertilizers is fast and the utilization rate is high， but the supplementation of fertilizers is insufficient in the later period， thus causing premature aging. Care should be taken to properly arrange the area of nutrition， not to overclose the plant， to ensure that the population is ventilated and exposed to light， and to take appropriate measures to remove the film[32-33].
　　Mechanization degree and quality of mulching film need to be improved
　　Artificial mulching not only wastes a lot of agricultural operation time， but also virtually increases agricultural investment. Mechanized coating greatly improves the efficiency of coating and reduces production costs. For example， in Xiji County， Ningxia， there were 104 laminating machines in 1998， covering an area of 69.33 hm2， which accounted for only 10% of the covered area. This figure has slightly increased. The semiarid areas are mostly secondorder ladders in China. The topography is complex and there are many types of landforms that affect the process of mechanized coating. At the same time， the poor quality of the mechanized coating and the waste of the plastic film limit the speed of its promotion.
　　Outlook
　　Plastic film cover technology is a highinput， highoutput agricultural cultivation technology that can significantly increase crop yields and improve farmland ecological environment. Combining diversified film cover technology and seeding technology， we will further improve and ensure the simultaneous production of highyielding cultivation techniques such as crop varieties， sowing dates， sowing rates， plant density， fertilization techniques， pest and disease control， and weed control in the field， while vigorously promoting catchment irrigation technology， following the principle of adapting to local conditions， adopting different plastic film coverage methods and other measures for water conservation， water collection， and water conservation in different topography， landforms， and precipitation conditions[34-35]. With the further development of the mulching technology experiment and demonstration work， the warming， conservation， and highyield effects demonstrated by more and more people have been recognized by more and more people， which has brought new opportunities for the promotion of mulching technology. In order to ensure the sustainable production of agroecosystems， the recovery of common mulch membranes， the development and application of water permeable membranes and biodegradable membranes， and the promotion of other mulching cultures should be carried out in depth， and the degree of mechanization needs to be further improved. 　　References
　　[1]XIA ZQ， ZHAO SL. Effects of plastic film mulching on soil temperature and water and water saving benefits[J]. Journal of Hohai University （Natural Sciences）， 1997（2）： 39-45.
　　[2]GAO YJ， LI SX. Reasons and mechanism of crop yield reduction under straw mulching in dryland[J]. Journal of Agricultural Engineering， 2005， 21（7）： 15-19.
　　[3]ZHANG ZM， REN GX， YU AC. Preliminary study on different cultivation methods of winter wheat in Weibei dryland[J]. Journal of Arid Land Research， 1999， 17（4）： 36-40.
　　[4]ZHANG JM， LIU JH， ZHANG LJ. Preliminary results of degradable plastic film covering spring maize and fluecured tobacco[J]. Shaanxi Journal of Agricultural Sciences， 2000（3）： 10-12.
　　[5]WANG JH， DING NF. The effect report of liquid film use[J]. Zhejiang Agricultural Sciences， 2002， 1（1）： 18-19.
　　[6]WANG SS， DENG GY. Study on the mechanism of warming in plastic film mulching[J]. Chinese Journal of Agricultural Sciences， 1991， 24（3）： 74-78.
　　[7]HAN SM， YANG CF， SHI JT， et al. Study on coverage tillage of dryland residues[J]. Arid Zone Agriculture Research，1988（3）.
　　[8]LIAO YC， WEN XX， HAN SM， et al. Study on the effect of covering and covering wheat in Loess Plateau dryland[J]. Chinese Journal of Agricultural Sciences， 2003， 36（5）： 548-552.
　　[9]MEN Q， LI Y， FENG GP. Effect of plastic film mulching on soil evaporation[J]. Journal of Irrigation and Drainage， 2003， 22（2）： 17-20.
　　[10]HE ZJ，WEI ZX. Study on soil moisture dynamics of terraced field covered with microfarming cultivation[J]. Shanxi Science and Technology of Soil and Water Conservation， 2000（3）：12-15.
　　[11]WANG Q， ZHANG EH， LI FM. Rainfall collection efficiency of film ridges and soil ridges in semiarid area and comparison of soil moisture during different rain collection periods[J]. Chinese Journal of Ecology， 2004， 24（8）：1816-1819.
　　[12]WANG SS， DENG GY. Study on the mechanism of temperature increase in plastic film mulching[J]. Chinese Journal of Agricultural Sciences， 1991， 24（3）：74-78.
　　[13]LI JQ. Effect of plastic film mulching on yield and quality of spring maize[J]. Journal of Maize Sciences， 2008， 16（5）：87-92.
　　[14]YANG QH， HAN JF， HE DX， et al. Study on water conservation effect of liquid film coating[J]. Journal of Soil and Water Conservation， 2004， 18（4）： 29-32.
　　[15]WEN XX， HAN SM， ZHAO FX， et al. Ecological effects of film mulching in dryland wheat[J]. Chinese Journal of EcoAgriculture， 2003， 11（2）： 93-95. 　　[16]WANG HQ， HAN SM， TANG YH， et al. Study on super highyield cultivation techniques of film covering winter wheat in Weibei dryland[J]. Arid Zone Agriculture Research，1998（1）： 24-30.
　　[17]ZHANG DQ， LIAO YC， JIA ZK. Research progress and prospects of plastic film mulching in arid areas[J]. Arid Areas Agriculture Research， 2005， 23（1）： 208-213.
　　[18]WANG XB， CAI DX. Study on the comprehensive techniques of conservation tillage in dryland farmlandliquid membrane and fertilizer[J]. Chinese Journal of Agricultural Engineering， 2005， 21（6）：22-25.
　　[19]JIN JT， SHI SL， CAI ZS. Effects of cultivation with furrow and rain on the growth characteristics and quality of alfalfa on dry land[J]. Chinese Journal of Agricultural Sciences， 2010， 43（24）： 5028-5036.
　　[20]ZHANG J， JIA ZK， LI GL， et al. Effects of different materials on the biological characteristics of maize[J]. Journal of Northwest A&F University： Natural Science Edition， 2010， 38（12）： 133-140.
　　[21]WANG JP， MA L， JIANG J， et al. Cropland microwater harvesting in semiarid areas of southern Ningxia[J]. Journal of Northwest Agricultural University， 1999， 27（3）：22-27.
　　[22]WANG Q， ZHANG EH， LI FM， et al. Determination of the optimal ratio of furrows and ridges for planting microcollection of rainwater in the ridges and furrows in semiarid areas[J]. Chinese Journal of Agricultural Engineering， 2005， 21（2）： 38-41.
　　[23]BU YS， MIAO GY， SHAO HL， et al. Analysis of growth and yield of corn covered with plastic film and straw[J]. Acta Agronomica Sinica， 2006， 32（7）：1090-1093.
　　[24]LI SQ， LI FM， SONG QH， et al. Effects of different plastic mulching periods on soil nitrogen availability in semiarid areas[J]. Chinese Journal of Ecology， 2001， 21（9）： 1519-1526.
　　[25]CHEN SY， ZHANG XY， YAN D， et al. Effect of straw mulching on soil evaporation and soil temperature in summer maize field[J]. Journal of Irrigation and Drainage， 2004， 23（4）： 32-36.
　　[26]HAN QF， LI XT， WANG JP， et al. Simulated study on the effect of microwater harvesting on the regulation of farmland moisture[J]. Journal of Agricultural Engineering， 2004， 20（2）：78-82.
　　[27]LIU XY， LI YZ， LI QZ， et al. Effect of harvesting rain on the physiology， growth and yield of winter wheat[J]. Journal of Agricultural Engineering， 2006， 22（9）： 64-69.
　　[28]ZHANG CY， YANG XM. Effect of liquid film on growth and yield of maize[J]. Journal of Qingdao Agricultural University （Natural Science）， 2008， 25（3）： 227-230. 　　[29]CARTER D， MILLER S. Three years experience with an onfarm macrocatchment water harvesting system in Botswana[J]. Agricultural Water Management， 1991， 19（3）： 191-203.
　　[30]SHEN LX， WANG Y， ZHANG LL. Effects of degradable plastic film on soil， temperature， moisture and corn growth and development[J]. Chinese Journal of Agricultural Engineering， 2011， 27（6）： 25-30.
　　[31]ZHAO AQ， LI ZZ， GONG YS. Effects of biodegradable plastic film on corn growth and field degradation[J]. Journal of China Agricultural University， 2005， 10（2）： 74-78.
　　[32]MORENO MM， MORENO A. Effect of different biodegradable and polyethylene mulches on soil properties and production in a tomato crop[J]. Scientia Horticulturae， 2008， 116（3）： 256-263.
　　[33]ZHAO AQ， LI ZZ， GONG YS. Effects of biodegradable plastic film on the growth of corn and its field degradation[J]. Journal of China Agricultural University， 2005， 10（2）： 74-78.
　　[34]ZHU GQ， SHI XG， LI QZ. Study on microcatchment technology of spring wheat farmland in semiarid region of Dingxi[J]. Chinese Journal of Agrometeorology， 2001， 22（3）：6-9.
　　[35]ZHAO JB， MEI XR， XUE JH， et al. Effect of straw mulching on water use efficiency of dryland crops[J]. Chinese Journal of Agricultural Sciences， 1996， 29（2）： 59-66.
　　Editor： Tingting XU Proofreader： Xinxiu ZHU