Jing Dang，Weili Liang*，Guiyan Wang，Pengfei Shi，Dan Wu

Faculty of Agronomy，Agricultural University of Hebei，Baoding，Hebei 071001，China

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A preliminary study of the effects of plastic film-mulched raised beds on soil temperature and crop performance of early-sown short-season spring maize（Zea mays L.）in the North China Plain

Jing Dang，Weili Liang*，Guiyan Wang，Pengfei Shi，Dan Wu

Faculty of Agronomy，Agricultural University of Hebei，Baoding，Hebei 071001，China

A R T I C L E I N F O

Article history:

Received in revised form

29 February 2016

Accepted 15 March 2016

Available online 30 March 2016 Keywords:

Raised bed

Film mulch

Spring

Short-season

Maize

North China Plain

A B S T R A C T

To identify a strategy for earlier sowing and harvesting of spring maize（Zea mays L.）in an alternative maize-maize double cropping system，a 2-year field experiment was performed at Quzhou experimental station of China Agricultural University in 2014 and 2015.A short-season cultivar，Demeiya number 1（KX7349），was used in the experiment.Soil temperature to 5 cm depth in the early crop growth stage，crop growth，crop yield，and water use of different treatments（plastic film-mulched raised bed（RF）and flat field without plastic film mulching（CK）in 2014；RF，plastic film-mulched flat field（FF），and CK in 2015）were measured or calculated and compared.Soil temperature in the film-mulched treatments was consistently higher than that in CK（1.6-3.5°C in average）during the early growth stage.Crops in plastic film-mulched treatments used 214 fewer growing-degree days（GDDs）in 2014 and 262 fewer GDDs in 2015.In 2014，the RF treatment yielded 32.7% higher biomass than CK，although its 9.4%higher grain yield was not statistically significant.Also，RF used 17.9%less water and showed 33.1%higher water use efficiency（WUE）than CK.In 2015，RF and FF showed 56.2%and 49.5%higher yield，15.0%and 4.5% lower water use（ET），and 63.4%and 75.7%higher WUE，respectively，than CK.RF markedly increased soil temperature in the early crop season，accelerated crop growth，reduced ET，and greatly increased crop yield and WUE.Compared with FF，RF had no obvious effect on crop growth rate，although soil temperature during the period between sowing and stem elongation was slightly increased.However，RF resulted in lower ET and higher WUE than FF.Effects of RF on soil water dynamics as well as its cost-effectiveness remain topics for further study.

?2016 Crop Science Society of China and Institute of Crop Science，CAAS.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license（http://creativecommons.org/licenses/by-nc-nd/4.0/）.

1.Introduction

Plastic film mulching is a widely used practice in field crop production，supported by many research publications.Major proven effects of plastic film mulching include conserving soil water，increasing soil temperature，accelerating crop growth and development，and raising crop yield and water use efficiency（WUE）［1-10］.A new form of plastic film mulching is“completely mulched alternating narrow and wide ridges with furrow planting，”which has greatly increased crop yield and WUE in dryland cultivation［5-9］.It has also been reported for this practice that irrigated maize mulched with plastic film between rows had higher yield and WUE than that mulched on rows［6-10］.

With wheatcultivation in the North China Plain（NCP）having been criticized for water consumption in a water-scarce environment，the wheat growing area has been forcibly reduced，confronting the conventional wheat（Triticum aestivum L.）-maize（Zea mays L.）double-cropping system with a challenge.Some farmers in the area have attempted alternative cropping systems，suchasspringmaize-summermaizesystem.However，in the northern part of the NCP，two sequentially sown crops of currently popular maize cultivars cannot reach full maturity before harvesting owing to inadequate growing degree days（GDDs），even under plastic film mulch［11］.With the proven effects of plastic film mulching on increased maize yield and WUE［12-15］，shorter-seasoncultivarstogetherwithearlysowing under plastic film in spring are essential for meeting the crop GDDdemand forsuccessfulmaize-maizedoublecroppinginthe northern NCP.

The practice of growing crops on raised beds has long been adopted in the NCP and has proven to be water-efficient and convenient for residue retention.In recent years，some farmers have started planting spring maize on the slope between the furrow and the top of plastic film-mulched raised beds（RF），planting the succeeding summer maize crop on the top surface after harvesting the spring crop.However，the effects of this practice on crop growth，yield，soil temperature，water use（ET），and other characters have not yet been reported.This paper presents a preliminary analysis of the effects of RF on soil temperature，crop growth，yield，and WUE using data from a 2-year field experiment.

2.Materials and methods

2.1.The experimental site

The two-year field experiment was conducted on a sandy loam fluvo-aquic soil at the research station of China Agricultural University in Quzhou county（114.93°E，36.7°N），Hebei province，China，in2014and2015.Theareaischaracterizedbyatemperate semi-humid continental monsoon climate:cold and dry in winter，hot and rainy in summer，and windy and dry in spring. Inthe66 yearsfrom1948to2014，theareahadanaverageannual temperature of 13.4°C，212 frost-free days，4472.0-degree days cumulative temperature（above 10°C），and 499.3 mm annual rainfall（among which 1/3 occurred in July-September）.Soil organic matter sampled in 2014 in the experimental field was 10.8 g kg-1，total N was 0.88 g kg-1，available P（P2O5）was 3.2 mg kg-1，and available K（K2O）was 145.3 mg kg-1in the top 20 cm.

2.2.Experimental design

A randomized block design with three replications was employed and a hybrid maize cultivar，Demeiya number 1（KX7349），was used in both experimental years.In 2014，two treatments:raised bed with plastic film mulch（RF）and flat field without plastic film mulch（control，CK）were applied to plots of size 31.3 m×7.3 m.The RF treatment was sown on March 21 and the CK on April 20，the conventional sowing date for spring maize.In 2015，to evaluate the effects of raised beds，one more treatment，film-mulched flat field（FF），was added，the plot size was enlarged to 47.0 m×9.8 m，and all plots were sown on March 27.Land was prepared and crops were sown in south-north row orientation in both years.

A non-filmed raised bed treatment as control was lacking from the experimental design.The reasons for this absence are as follows.First，the purpose of this study was to identify feasible，effective measures for early sowing and obtaining more cumulative temperature for the maize crop under current climate conditions.Given that plastic film mulching on flat fields has been shown to be effective for increasing soil temperature and conserving soil water，the experimental design in this study was aimed at investigating the effects of plastic film-mulched raised beds.Thus，among the three treatments，two could be treated as controls for RF.Second，theoretically，the top surface of a bare raised bed is subject to salinization and rapid soil water loss in the field，with high surface exposure in early spring to windy and dry air that impede seed emergence and seedling growth.Also，the focus of this study was on the effects of plastic film-mulched raised bed rather than plastic film-mulching and raised bed.For these reasons，bare raised beds were not included as a treatment.

The experimental field was irrigated in early spring before land preparation.Diammonium phosphate（375 kg ha-1；18% N and 46%P2O5）and potassium sulfate（187.5 kg ha-1）were applied immediately prior to plowing.Beds were raised with a specially designed plow drafted by a 25 hp four-wheel tractor after the land was plowed and harrowed.Seeds were sown by hand in RF plots and with a planter in FF and CK plots，at a density of 8.3 plants m-2（60 cm in row×20 cm between plants）.Degradablepolyethylenefilm90 cmwideand 0.004 mm thick was manually laid to cover furrows and part of the top surface of the beds（Fig.1）in the RF treatment，and two sown rows in the FF treatment.At two leaves after emergence，holes were made by hand in the polyethylene film to free the seedlings.Urea（112.5 kg ha-1）was top-dressed at nine leaves in both years.

The experimental plots were irrigated twice in 2014，once before land preparation on March 17 and again on May 27（nine leaves of a total leaf number of 12 was observed in the cultivar），with a total quantity of 125 mm of water.In 2015，two irrigations were given to the experimental plots at the same stages as in 2014，on March 20 and May 29，respectively，with a total water amount of 182 mm.Total amounts of 150.4 mm and 215.6 mm rainfall were received in the RF andcontrol treatments respectively in 2014，and 134.0 mm rainfall was received in all plots in 2015 during the maize growing period.

Fig.1-Schematic diagram of planting pattern in plastic film-mulched raised beds（left）and operation of laying plastic film（right）.

2.3.Observations and measurements

2.3.1.Phenostages

Dates of emergence，stem elongation，nine leaves（when the top leaves of the plant were trumpet-shaped，indicating the beginning of reproductive growth.A total of 12 leaves in the cultivar were observed in the 2-year experiment），silking，and maturity were observed and recorded.

2.3.2.Weather data

Daily weather data for the experimental area，issued by the ChinaMeteorologicalDataSharingServiceSystem（cdc.nmic.cn），were recorded.

2.3.3.Soil temperature

One thermometer（detector）was placed in a plant row in each plot at 5 cm soil depth to measure soil temperature（Tsoil）. The thermometers were placed under polyethylene film in film-mulched plots before films were laid.In 2014，a digital thermometer（Shengli model DM6801A，manufactured by Shengli Instruments Company Ltd.of Shenzhen）assorted with thermo sensors（Shengli model TP02K），was used and data were read three times daily，at 8:00，14:00，and 20:00，after planting until May 15 when all the crops passed the stage of stem elongation.Fourtec MicroLite temperature USB loggers（model Lite5032P，manufactured by Fourier Technologies）were used in 2015 to record soil temperature every hour after planting until June 2，when the crop reached silking. Recorded data were downloaded to a computer after the data loggers were removed from the soil.Daily Tsoilwas calculated by averaging all the observations during 1 day:3 observations in 2014 and 12 in 2015.

2.3.4.Yield

Plants in two rows of 10 m long in each plot were sampled and harvested at maturity.Numbers of plants and ears in the samples were counted，and ears and stalks were weighed separately after harvesting.Twenty ears were selected from the harvested ears in the sample from each plot and weighed after air drying，and kernel rows per ear and kernels per row were counted，after which the cobs were threshed and grain weighed.Three 500-kernel samples from each 20-ear sample were taken，weighed，and oven-dried at 85°C.Three stalks from each plot were sampled for measurement of moisture content using oven drying at 85°C.Grain yield of each plot was calculated at 14%moisture content，following the equation below:

Grain yield（ Y；kg ha-1）=（weight of air-dry grain from 20 ears

× （1-moisture content of air-dry grain）/20

×number of ears in the two 10-m sampled rows

/0:6 m（ row spacing）×10；000 m2）

/（1-14%moisture content）

Biomass yield=ear biomass+stalk biomass

2.3.5.ET and WUE

Soil samples were taken with an auger immediately before sowing and after harvesting to measure moisture content to a depth of 200 cm.Soil samples were weighed，oven dried at 100°C，and weighed again to calculate gravimetric moisture content.Volumetric soil moisture content was calculated by multiplying gravimetric moisture content with bulk density of thesoil layer.ET（mm）=irrigation waterduringthe time period（mm）+rainfall during the time period（mm）+soil water storage at harvesting（mm）-soil water storage at sowing（mm），and WUE=Y/ET.

Microsoft Excel 2007 was used for editing the data and for calculation，and IBMSPSSStatisticsV21.0wasusedfor statistical analysis.

3.Results and analysis

3.1.Effect on soil temperature

Higher soil temperatures in early spring increase crop growth［16］.The daily mean soil temperature（Tsoil）dynamics of all the treatments to the depth of5 cmare illustrated inFig.2.Itcan be seen that，in 2014，Tsoilin the RF treatment was consistently higher（3.5°C on average，see Table 1）than in the control treatment between sowing and stem elongation.Average daily mean soil temperature（averageTsoil）inthe RFplots was 19.9°C duringtheperiodfrom sowing to emergence，4.2°C higherthan in the control，whereas average Tsoilin the RF treatment was22.9°C，3.4°C higher than in the control during the period from emergence to stem elongation.In 2015，average Tsoilin RF and FF treatments during the time period from sowing to nine leaves were 2.3°C and 1.6°C higher，respectively，than in the control，whereas this advantage in soil temperature of the two plastic film-mulched treatments remained at 3.3°C and 1.9°C，respectively，betweenemergence and stem elongation.No clear difference in Tsoilbetween the three treatments was observed after stem elongation inthe 2 experimentalyears，inagreement with the results of Hai et al.［17］.This similarity may reflect the increased canopy size，which reduced solar radiation reaching the soil surface.Narrowed differences in Tsoilbetween plastic film-mulched and non-film-mulched treatments on rainy and overcast days were observed.

Fig.2-Dynamics of daily mean soil temperature.RF，plastic film-mulched raised bed；FF，film-mulched flat field；CK，flat field withoutfilm；S，sowing；FM-S，sowingoffilm-mulchedcrop；CK-S，sowingofcrop inthecontrol；FM-E，emergenceoffilm-mulched crop；CK-E，cropemergence inthecontrol；FM-J，stemelongationoffilm-mulchedcrop；CK-J，stemelongationofcropinthe control.

Table 1-Average daily mean 5-cm soil temperature during different growth stages.

3.2.Effect on maize growth rate

Dates of appearance，duration in days，and GDD of each growth stage of the treatments are presented in Table 2.In 2014，given that the control was sown 29 days later and grew in a warmer environment，it is hard to make a direct comparison.Still，the RF treatment was 2 days earlier and required 41 fewer degree days for emergence than the control，whereas crops in the RF treatment required 2 days fewer to reach stem elongation from emergence，corresponding to 202 fewer degree days.

In 2015，the improved experimental design made it easier to compare crop growth rate between treatments.It can be seen in Table 2 that there was no obvious difference in crop growth rate between the two plastic film-mulched treatments，whereas crops in the two film-mulched treatments emerged 4 days earlier and required 34 fewer degree days than the control.Although all three treatments required 40 days to reach stem elongation，the two film-mulchedtreatments used 45 fewer degree days than the control，given that they were 4 days earlier，thus reaching the stage in cooler weather.This precocity was further assisted by warmer soil temperature under polyethylene film.With this cumulative advantage，maize crops in the two plastic film-mulched treatments completed their life cycle in 106 days，10 days shorter than in the control，and required 262 fewer degree days.In other words，polyethylene film mulching added 262 more degree days for maize growth.

Table 2-Comparison of crop growth rates under different treatments.

3.3.Effects on yield and WUE

Grain yield，ET，and WUE of all treatments are listed in Table 3. In 2014，although the 9.4%higher grain yield of the RF treatment was not significantly different from that of the control，the 32.7%higher biomass，which was significantly different from that of the control at 95%probability，suggests a potentially much higher productivity of the RF treatment than the control.Also，the RF treatment used 17.9%less water and showed a 33.1%higher WUE than the control.In 2015，grain yields of the RF and FF treatments were 56.2%and 49.5% larger，ET were 15.0%and 4.5%lower，and WUE were 63.4% and 75.7%higher，respectively，than the control.Reasons for which the RF treatment showed slightly lower maize grain yield than the FF treatment may include the following:sowing by hand resulted in less even sowing depth，row and plant spacing，and thus lower plant uniformity than the flat field treatment；soil moisture loss caused by raising beds before sowing resulted in slightly less favorable soil condition for crop growth before the first irrigation.The yield difference between the plastic film-mulched treatment and the control was greater in 2015 than in 2014，possibly owing to lower adaptability of the early-sown crop without plastic film mulch.

Table 3-Grain yield，ET，and WUE of different treatments in 2014 and 2015.

4.Discussion

Plastic film mulching increases air and soil temperatures below the mulch and reduces evaporation from soil［18］. Transparent film allows solar radiation to reach the soil surface with little reflection［19］，and water droplets attached to the inner side of the film together with higher air moisture content beneath the film impede the escape of long-wave radiation from the soil to the open air，thereby delaying soil temperature decrease after sunset.Those effects are greater when temperature is low in a growing season［16，20］.

Plastic film mulching has the greatest effect on increasing temperatures at the seedling stage when the crop canopy is sparse and solar radiation can reach soil surface with little interception［21］.Temperature beneath the mulch cannot greatly increase in overcast and cloudy weather，so that there is no difference between temperatures beneath the mulch and in the open field.

Plastic film mulching had the greatest effect on conserving soil water at the early crop growth stage，and the earlier the greater.The biomass WUE of film-mulched maize crop could be 5.61-7.67 times that in the open field before stem elongation.There was no appreciable difference in ET，but mulched crops maintain higher biomass WUE after stem elongation.Plastic film mulching improved crop nitrogen uptake and increased apparent nitrogen recovery rate and output/input ratio［12，17］.All of the above effects of plastic film mulching may have contributed to accelerating growth rate and conferring higher yield.

The short-season cultivar used in this study，Demeiya number 1，is reported to have a growth duration of 115 days at high（50°15′N）latitude［22］.The film-mulched crop of the cultivar in this study matured in 104 days in 2014 and 106 days in 2016，whereas the non-mulched crop required 8 more days in 2014 and 10 more days in 2016 to reach maturity and used more GDD than the mulched crop.The growth rate of the cultivar appears to be slower and more GDD is required when it is exposed to cooler temperatures when sown in early spring.

Plastic-mulched flat field increased soil temperature more than did mulched-ridge furrowing in a field in which maize was planted in furrows［23］.Differences in reported results may reflect variation in soil moisture，climate，row direction，and other factors，at different experimental sites.

As it is grown in windy and droughty weather，spring-sown maize may not be more water efficient than winter wheat. However，with the ease of adaptation of the well-developed and popular plastic mulching technique to maize，water use can be greatly reduced and WUE increased.The plastic film-mulchedtreatmentsused43.3 mmlesswaterand yielded 2447 kg ha-1of grain than the non-filmed treatment over 2 years.Plastic film-mulched raised bed could be a possible approach to developing more water-efficient alternative double-cropping systems in the northern NCP.

The difference between 2014 and 2015 in soil temperature，crop growth，biomass，yield components，and other characters may come from two sources:climate variation and difference in sowing time of the control，which led to differences in environmental air temperature，solar radiation，and soil water regime for the crop.However，the data in the 2 years were similar and led to the same conclusion.

5.Conclusion

Plastic film mulching increases soil temperature before stem elongation，shortens crop growth duration，reduces water use，and increases yield and WUE of short-season maize sown in early spring.This method thus increases the feasibility of a potential alternative maize-maize double-cropping system in the northern part of the North China Plain.

The plastic film-mulched raised bed slightly increased soil temperature over that of the film-mulched flat field but did not markedly change the growth rate of the maize crop. However，it had an advantage in WUE，reflecting its lower crop water use.The film-mulched raised-bed system deserves further in-depth study of the mechanisms behind the observations.

Acknowledgements

The study presented in this paper was financially supported by the Special Fund for Agro-scientific Research in the Public Interest（No.201103001）.We thank Mr.Shukui Zhang at the station for looking after the experimental field.

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25 January 2016

*Corresponding author.

E-mail address:lwl@hebau.edu.cn（W.Liang）.

Peer review under responsibility of Crop Science Society of China and Institute of Crop Science，CAAS.

http://dx.doi.org/10.1016/j.cj.2016.02.002

2214-5141/?2016 Crop Science Society of China and Institute of Crop Science，CAAS.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license（http://creativecommons.org/licenses/by-nc-nd/4.0/）.