Experimental study on water-saving and emission-reduction effects of controlled drainage technology

2015-12-31

Water Science and Engineering 2015年2期

关键词：本科毕业教育工作者执业

* Corresponding author.

Meng-hua Xiao*,Xiu-jun Hu,Lin-lin Chu

Research Center of Fluid Machinery Engineering and Technology,Jiangsu University,Zhenjiang 212013,PR China

Received 8 May 2014; accepted 20 January 2015 Available online 9 May 2015

* Corresponding author.

Abstract

Field experiments and laboratory analysis were carried out to determine the effects of controlled drainage (CTD)and conventional drainage (CVD)technologiesondrainagevolume,concentrationsofandtotalphosphorus(TP),nitrogenandphosphoruslosses,riceyield,and water utilization efficiency.Results show that CTD technology can effectively reduce drainage times and volume;and TP concentrations,from the first to the fourth day after four rainstorms decreased by 28.7%e46.7%,37.5%e47.5%,and 22.7e31.2%,respectively,with CTD.These are significantly higher rates of decrease than those observed with CVD.CTD can significantly reduce nitrogen and phosphorus losses in field drainage,compared with CVD; the reduction rates observed in this study were,respectively,66.72%,55.56%,and 42.81% forand TP.Furthermore,inthe CTDmode,the riceyieldwas cut slightly.Inthe CVDmode,thewater productionefficiencies inunit irrigationwaterquantity,unitfieldwaterconsumption,andunitevapotranspirationwere,respectively,0.85,0.48,and1.22kg/m3,whileinthe CTD mode they were 2.91,0.84,and 1.61 kg/m3din other words,3.42,1.75,and 1.32 times those of CVD.Furthermore,the results of analysis of variance (ANOVA)show that the indicators in both the CVD and CTD modes,including the concentrations ofand TP,the losses ofand TP,irrigationwaterquantity,andwaterconsumption,showedextremelysignificantdifferencesbetweenthemodes,butthe rice yield showed no significant difference.

Keywords:Controlled drainage; Nitrogen; Phosphorus; Rice yield; Drainage volume; Water utilization efficiency

This work was supported by the National Natural Science Foundation of China (Grant No.51409124),the Natural Science Foundation of Jiangsu Province (Grant No.BK20140564),and the Open Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering (Grant No.2013490711).

E-mail address: menghuaxiao@aliyun.com (Meng-hua Xiao).Peer review under responsibility of Hohai University.

http://dx.doi.org/10.1016/j.wse.2015.04.009

1.Introduction

To ease the tension between supply and demand of water resources,water-saving irrigation techniques for paddy fields were widely investigated (Tabbal et al.,2002; Belder et al.,2004).As China is the largest producer and consumer of synthetic fertilizers in the world,large amounts of nitrogen have entered its water bodies through various means,resulting in water eutrophication in China (Li et al.,2008; Chirinda et al.,2010).However,paddy fields can achieve the effect of water purification through maintenance of a proper water level for a certain number of days after fertilization,pollutant control,and heavy rain.Therefore,controlled drainage (CTD)technology for paddy fields has attracted attention of researchers (Wesstr€om et al.,2001),and been a focus of study for agricultural water environment protection.This technology can effectively improve the utilization efficiency of irrigation water and water productivity (Zhang et al.,2003),ease the tension between supply and demand of water resources,reduce nitrogen and phosphorus losses from paddy fields,improve the water environment,maintain the nutrient cycle of paddy fields,improve the utilization efficiency of rainfall,effectively reduce the concentrations of nitrogen and phosphorus in drainage,and maintain the yield (Peng et al.,2009; Li et al.,2008).

With the development of the theory and practice of modern irrigation and drainage technology,people have fully realized that it would be more conducive to improving the efficiency of rice production by combining water-saving irrigation with CTD (Peng et al.,2011; Xiao et al.,2013).Through the combination of existing water-saving irrigation and CTD theories for paddy rice,an irrigation-drainage technology that saves water,reduces emissions,and generates a high yield can be developed.Based on its characteristics as a semi-aquatic plant,we can make full use of the stress of drought and,especially,water-logging on rice to coordinate the stress degree (Xiao et al.,2012).While the lower irrigation limit is maintained,appropriately increasing the upper rain water storage limit can make full use of rainfall,thus reducing the irrigation quota as well as nitrogen and phosphorus loads (Yu et al.,2002).While meeting the requirements of no significant reduction of crop yield and quality,CTD technology can also achieve the goals of saving water and reducing emissions (Ng et al.,2002; Ju et al.,2009).According to the research on the key supporting technologies of large-scale agricultural watersaving improvement projects in China,research on watersaving irrigation and CTD systems was carried out,and the results show that the water level in the paddy field can be used as an efficient irrigation and drainage indicator (Xie et al.,2007; Yang et al.,2009).

In this study,an experiment was conducted in Suqian City,in Jiangsu Province,China to further confirm the environmental effect of CTD.The aims of this study were to investigate the application of CTD technology and water level control rules in farmland experiments,to improve rice irrigation-drainage systems,to verify the water-saving and emission-reduction effects of CTD,and to provide a scientific basis for optimal design of irrigation-drainage projects in rice irrigation districts.

2.Materials and methods

2.1.Experimental site

An experiment was conducted from October 2011 to October2012,inthe Sankeshuexperimental fieldinthe Yunnan irrigation district,which is located in the Sucheng District of Suqian City,in China (Fig.1).The experimental site has a warm temperate zone monsoon climate,with four distinct seasons and mild average temperatures.The average annual rainfall is 892.3 mm,and the average annual amount of rainfall days is 120 d,with rainfall in the main flooding season accounting for nearly 70% of the total.The average annual evaporation amount is 900 mm,the annual average temperature is 14.1 C,the highest monthly average temperature is 27.2 C,the average annual amount of sunshine hours is 2 314 h,and the annual non-frost period is 211 d.The topsoil (from 0 to 30 cm),with a pH value of 6.95,contains 2.35% of soil organic matter,0.894 5 g/kg of total nitrogen (TN),27.95 mg/kg of available nitrogen,0.34 g/kg of total phosphorus (TP),and 12.2 mg/kg of available phosphorus.

Fig.1.Layout of experimental site and experimental management.

2.2.Experimental design

The variety of rice used in the experiment was Japonica rice,according to the local custom.There were two irrigationdrainage modes,conventional drainage (CVD)and CTD.Each mode included three replications.Plastic isolating film was used at each experimental plot at 50 cm below the balk,in order to avoid water exchange.The fertilizer regime was determined according to the local custom.There were three fertilizer applications: a base fertilizer on June 25,a tillering fertilizer on July 9,and an earing fertilizer on August 10,with pure nitrogen amounts of 120,60,and 60 kg/hm2,respectively,for a total of 240 kg/hm2.In addition,a total of 50 kg/hm2P2O5and K2O were applied to each mode.

Water management of a paddy field in CVD was based on local custom.The water level control indicators in CVD are shown in Table 1,while those in CTD are shown in Table 2.2.3.Experimental mechanism and methods

Table 1　Water level control indicators at each growth stage in CVD mode.

Table 2　Water level control indicators at each growth stage in CTD mode.

In this study,the evapotranspiration for a paddy field was calculated based on the water balance principle as follows: where ET is the evapotranspiration (mm); P is the precipitation (mm),which was recorded daily by an automatic weather station in the experiment; I is the irrigation water quantity (mm),which was recorded with water meters installed on the pipes in each plot; W is the flooding depth or the soil water content in the root zone (mm),with the soil water content measured with a time domain reflectometer (TDR)in this study,and the flooding depth measured with a vertical ruler; t represents the day of measurement; and D represents the drainage volume or the underlying root leakage (mm).Since the bottom of each lysimeter was closed with concrete,surrounded by an impervious isolation board,the underlying root leakage was not considered in this study.

2.4.Statistical analysis

A t-test was used to evaluate the differences in measured variables from different plots.The software package SPSS 16.0.0 was used for analysis of variance (ANOVA).

3.Results and discussion

3.1.Field drainage volume in different irrigationdrainage modes

Water was drained through the drainage exit when the rainfall exceeded the allowed water depth,according to the highest water depth in field surface.The drainage dates and volumes in different irrigation-drainage modes are shown in Table 3.There was only one controlled drainage in CTD,but five in CVD in 2012,owing to heavy rainfall and rainfall concentration.In 2012,the total rainfall was 720.6 mm,and there were four rainstorms (larger than 50 mm in 24 h),which resulted in field drainage.Table 3 also shows that the total drainage volume in the CTD mode was 6.60 mm,which was far below that in CVD (59 mm)and accounted for 11.19%.This shows that the CTD mode can improve the rainfall utilization efficiency.

Table 3　Drainage volumes in CTD and CVD during rice-growing period.

Fig.2.Changes of NHþ4-N concentration in different drainage modes after four rainstorms.

Fig.3.Changes of NO3-N concentration in different drainage modes after four rainstorms.

3.4.Changes of TP concentration in field drainage

TP concentrations in different drainage modes after four rainstorms are shown in Fig.4.On the first day after a rainstorm,the TP concentration in CVD was higher than that in CTD.This was mainly because the allowed water depth in CTD was higher.In CVD,after a rainstorm,the TP concentration showed a trend of first decreasing and then increasing,to a level even higher on the fourth day than on the first day after a rainstorm.This is due to the fact that the water level in CVD gradually decreased,resulting in the rising of the TP concentration.Meanwhile,in CTD,the TP concentration decreased day by day,showing that CTD can reduce the TP concentration in drainage.For the four rainstorms,the average TP concentrations in CVD were 1.51,1.63,1.69,and 1.88 mg/L,respectively,while in CTD they were 1.23,1.20,1.22,and 1.24 mg/L,respectively,only 81.5%,73.6%,72.1%,and 66.0%of the respective concentrations in CVD.Compared with the first day after rainstorm,the TP concentration on the fourth day in CVD decreased by 8.3% and 3.4%,respectively,for the first and second rainstorms,but increased by 8.8% and 7.2% for the third and fourth rainstorms,while in CTD the TP concentration decreased by 22.7%,28.4%,24.3%,and 31.2%,respectively,across the four rainstorms,showing a significant decrease.

3.5.Nitrogen and phosphorus losses

Nitrogen and phosphorus losses in different drainage modes were investigated in this experiment.The results show thatwas the main form of nitrogen losses in both drainage modes,whilecontributed a little.In CVD,the averageloss was 5.80 kg/hm2,accounting for 53.70% of nitrogen losses,while in CTD it was 1.93 kg/hm2,accounting for 53.61%.This was 3.87 kg/hm2lower than the loss in CVD,a reduction rate of 66.72%.In CVD,the averageloss was 0.63 kg/hm2,accounting for 5.83% of TN,while in CTD it was 0.28 kg/hm2,accounting for 7.78%.This was 0.35 kg/hm2lower than the loss in CVD,a reduction rate of 55.56%.Theloss in paddy field drainage was affected by the fertilizer level and irrigation management mode; at a given fertilizer level,CTD can effectively reduce theloss in a paddy field.Theloss was rather low,which was mainly due to the lowcontent in the paddy field soil.Thecontent in drainage was mainly from what remained from the wheat-growing season,rainfall,and irrigation.In the rice-growing season,thecontent was lower,and this was mainly because the paddy field was flooding and soil had a low oxygen content,low levels of nitrifying bacteria activity,and a low nitrification rate,resulting in a small portion of nitrogen fertilizer converting toafter converting toPhosphorus runoff loss was one of the main losses in the paddy field,another important reason for eutrophication.In this experiment,the average TP loss in CVD was 2.85 kg/hm2,accounting for 5.70% of the phosphorus fertilizer input,while in CTD it was 1.63 kg/hm2,accounting for 3.26%.This was 1.22 kg/hm2lower than the loss in CVD,a reduction rate of 42.81%.Thus,CTD can significantly reduce TP losses in field drainage.Phosphorus fertilizer was always applied as base fertilizer.At that time,rice had not yet become green,and the root had low phosphorus absorption ability.If a rainstorm or drainage occurred,the phosphorus loss was huge.Thus during the first week after base fertilizer application,field drainage should be avoided in order to reduce the phosphorus loss.Fractionated fertilization may be used to reduce the TP concentration in field drainage to reduce phosphorus runoff loss.

3.6.Rice yield and water utilization efficiency changes

Rice production is the ultimate goal of rice cultivation; water-saving and reduction of nitrogen and phosphorus losses cannot occur at the expense of the rice yield.Reasonable irrigation-drainage modes and fertilizer management practices will play an important role in maximizing the water and fertilizer utilization efficiencies.Therefore,analysis of indicator systems of different irrigation techniques on rice yield is important.The rice yield and water utilization efficiency in different drainage modes are shown in Table 4.In CVD,the rice yield was 7 143.6 kg/hm2,while in CTD it was 6 856.4 kg/hm2.The rice yield decreased slightly in CTD (4.0%).This was mainly because of different years,regions,or varieties.

Fig.4.Changes of TP concentration in different drainage modes after four rainstorms.

Table 4　Rice yield and water utilization efficiency in different drainage modes.

According to final rice yield,the water utilization efficiency in a paddy field was calculated using irrigation amount,water consumption,and evapotranspiration throughout the growth stage (Table 4).It is found that the unit irrigation water quantity,unit water consumption,and unit evapotranspiration in CTD were significantly lower than in CVD.In CVD in 2012,the water utilization efficiencies for unit irrigation water quantity,unit water consumption,and unit evapotranspirationrespectively)were,respectively,0.85,0.48,and 1.22 kg/m3,while in CTD they were 2.91,0.84,and 1.61 kg/m3,respectively,about 3.42,1.75,and 1.32 times those in CVD.This shows that CTD technology can reduce water consumption,improve water utilization efficiency,ensure rice yield,and realize efficient use of water resources.Reasonable soil water control using CTD technology can not only reduce irrigation times and irrigation amount,but also promote the growth of rice roots,significantly reduce surface evaporation and field leakage,effectively reduce transpiration of the rice plant,and realize water saving.3.7.ANOVA in CVD and CTD modes

医学生培养要与国家执业医师考试接轨已成为医学教育工作者的共识[1]，为了更好地培养医学生，服务于我国的医疗事业，我们国家近几年进行了执业医师考试改革。执业医师考试改革前，医学生在本科毕业至少满一年后才能报考，自从近几年进行执业医师考试改革后，执业医师考试分为两个阶段，第一阶段是在校生实习之前，另一阶段是毕业工作一年后。这两个阶段均包括技能和理论考试。理论考试采用计算机答题，考试难度有所增加，主要体现在出题思路的转变上，以前主要考查学生的记忆能力，改革后则更注重考查知识点的应用能力，尤其是与临床密切相关的基础知识，是第一阶段考查的重点[2-3]。

The ANOVA results for each indicator of the CVD and CTD modes are shown in Table 5.The indicators in the CVD and CTD modes of the concentrations of ,and TP,losses of ,and TP,irrigation water quantity,and water consumption showed extremely significantdifferences,but the rice yields in the CVD and CTD modes showed no significant difference from one another.This indicates that,although the rice yield decreased slightly in the CTD mode,the concentrations of and TP,the losses of ,and TP,irrigation water quantity,and water consumption were effectively reduced.

Table 5　ANOVA results for each indicator in CVD and CTD modes.

4.Conclusions

(1)Under the experimental conditions,the CTD mode can effectively reduce drainage times and increase the rainfall utilization efficiency.In 2012,the CTD mode included only one drainage but the CVD mode included five times of drainage.The total drainage volume in CTD was 6.60 mm,which was far less than that in CVD.

(2)The CTD mode can effectively reduce nitrogen and phosphorus concentrations in drainage.Compared with the first day,,and TP concentrations on the fourth day decreased by 28.7%e46.7%,37.5%e47.5%,and 22.7%e 31.2%,respectively,in CTD,significantly higher rates of decrease than those in CVD.

(3)CTD can significantly reduce nitrogen and phosphorus losses in field drainage: the averageand TP losses decreased by 3.87,0.35,and 1.22 kg/hm2,respectively,compared with CVD,and the reduction rates were,respectively,66.72%,55.56%,and 42.81%.contributed most to the nitrogen loss,whilecontributed least.

(4)In the CTD mode,the rice yield was cut slightly.The CTD mode can not only reduce water consumption,but also improve the water utilization efficiency,ensuring economic yield of rice and realizing efficient utilization of farmland water resources.

(5)The ANOVA results showed that the indicators in both CVD and CTD modes of the concentrations ofand TP,the losses ofand TP,irrigation water quantity,and water consumption showed extremely significant differences between the modes,but the rice yield showed no significant difference.

(6)The results of the present study should help promote the application of the CTD technology and water level control rules in farmlands; contribute to water savings,emission reduction,high yield,and fertility conservation of paddy rice irrigation-drainage systems; verify water-saving and pollutantreduction effects of CTD; and provide a scientific basis for optimization of irrigation-drainage project design in rice irrigation districts.

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