The Effect of Water Saving and Production Increment by Drip Irrigation Schedules

Vol.9 No. 42004 493-497WUJNSWuhan University Journal of Naturai SciencesArticle ID: 1007-1202(2004)04-0493-05The Effect of Water Saving and ProductionIncrement by Drip Irrigation Schedules0IntroductionC ] QIU Yuan-feng, LUO Jin-yaot，MENG GeState Key Laboratory of Water Resources and Hydropowerhe irrigation schedule of drip irrigation system is aEngineering Science， Wuhan University， Wuhan 430072，Hubei, Chinafunction of water requirement, the output of the irri-gation system, the allowed deficit condition and the irriga-tion application eficiencyI"]. The irigation application effi-Abstract: Drip irigation system can achieve high uniformity.When the system is designed for uniformity cofficient equal orciency is determined from the emitter flow variation of themore than 70%，the water application in the field can be ex-drip irigation system and the allowable deficit of water ap-pressed as a normal distribution and further simplfied to a linearplication. The total emitter flow variation that is mainly af -distribution. This paper will describe the irrigation schedulingparameters, percent of deficit, application efficiency and coffi-fected by hydraulic design and manufacturer’ s variation cancient of variation by simple mathematical model. Using this ef-be considered as a normal distribution [1.2]. This can befective model and the irrigation application, the total yield affect-justified when the manufacturer's variation is normally dis-ed by the total water application for different uniformity of irri-gation application can be determined. More over, this paper usestributed and the hydraulic variation contributes only a smallthe cost of water, price of yield, uniformity of the drip irigationportion in the total variationl2. In 2000，the study of tes-system, crop response to water application and environmentalting normality of drip irrigation emitter flow through a com-concerns of pollution and contamination to determine the optimalirrigation schedule. A case study shows that the optimal iriga-puter simulation of about 2000 combinations showed thattion schedule can achieve the effect of water saving and produc-the emitter flow can be presented as normal distribu-tion increment compared with the conventional irrigation scheduletion[2.3]. The cumulative frequency curve of the normal dis-in which the whole field is fully irrigated.Key words: drip rrigation;linear cumulative frequency curve;tribution shows that a percentage of area receives irrigationoptimal irrigation schedule; water saving ; production incrementequal or less than a given depth of water. With a known re-CLC number: TV 139. 1quired irrigation application, this curve can indicate the are-as over irrigated and under irrigated. This curve can beused to evaluate application efficiency for drip irrigation aswell as sprinkler irigation-31. The curve from a normal dis-tribution can be approximated by using a straight line 41.This linear cumulative frequency curve offers a direct andReceived date: 2003-05-16easy solution of irrigation application efficiency and schedu-Foundation item: Supported by the National Natural Science Foundationof China (59379407)ling5]. This paper is a further evaluation of this approachBiography: QIU Yuan feng(1973-), male, Ph. D, research direction:of linear中国煤化工r distribution and willwater saving rrigation theory and techniques. E- mail: yfqiu @ wuhee.edu. cnuse the li片CNMHGurvetomakeananaly-t To whom correspondence should be addressed. E-mail: Luojy@ wuhee.sis on the effect of water saving and production incrementdu. cnby drip irrigation. .493Wuhan Unprpys数rnal of Natural Sciences Vol.9 No.4 20041 Material Methodsferent cofficient of variations can be plotted by calculat-ing b from Eq. (2). As shown in Fig. 2, two parametersDrip irigation system can achieve high uniformity.a and b can be used to characterize the linear cumulativeWhen the system is designed for a cofficient of variation,frequency straight line; a+b is the intercept and b is theCv，equal or less than 30% or uniformity coefficient,slope. When a required relative depth X is superimposedUc，equal or more than 70%，the water application inon Fig. 2, the percent area fully irrigated, the deficit are-the field can be expressed as a normal distribution anda，the percent of deficit and irrigation efficiency can befurther simplified to a linear straight line distributionE6] .calculated. A linear equation can be used to express theThe cumulative frequency curve of a normal distributionstraight line .for the coefficient of variation (Cv) as0. 1 is plotted di-X= (a+b)-bPx(4)mensionless as shown in Fig. 1. The dimensionless plotwhere X is a depth ratio and a, b are two cofficients andshows the relationship between the percent of area PAPA is the percent of area.and the relative irrigation depth X which is the ratio ofFromFig.2，itcanbeseenthataandbcanbethe amount of water required for the maximum yield tcexpressed by the following equationthe total amount of water application. A linear cumula-a= 1-6/2tive frequency straight line is drawn for the same CvThe percent of area under deficit can be shown as(0.1) and superimposed on the curve in Fig. 1. It is(1- PA) and expressed ashoped that the straight line can approximate the curve.Ap= (x-a)/bThe linear cumulative frequency is produced from awhere Ap is the percent area under deficit. The percentuniform frequency distribution whose density function isof deficit by volume can be expressed as,rectangle. The cumulative frequency is a straight linePr= (x- a)2/(26X)(7)shown in Fig. 2 with a minimum value a, a maximumwhere Pp is percent of deficit. The application efficiencyvalue a+b and the slope of the line b. The cofficient ofwhich is defined as the irrigation water store in the zonevariation Cv can be evaluated through the two equal tri-divided by the total amount applied.angles in Fig. 2 by integrating Ox2 along the base， forE= X(1- Pp)(8)simplicity, using the base as t, therefore .' Jwhere E is the irrigation application efficiency.The slope of the straight line, b, will indicate the(C、)2=2| (Ox)2 dt(1)uniformity of the emitter flow distribution. If the slope isby substituting △x=b. t and integrating, the Cv can be0 the straight line is a horizontal line and the uniformityexpressed as a function of b only,is 100%. The main advantage of using the linear cumula-Cv=0.2888b.(2)tive frequency approach solution is that the required paVc=1- 0.288 8b(3)rameters in the irrigation scheduling, such as the percentwhere Uc is uniformity coefficient. The linear cumulativeof deficit， cofficient of variation and irrigation applica-frequency straight line plotted in Fig. 1 is determinedtion efficiency can be expressed by simple equations.from Eq. (2). The linear cumulative frequency for dif-2.0 (飞2.0t 1.5, Rcquired relative depth X1.04x0.一- Linear distributionLinear dstribuion...... Normal distribution02(406[8100中国煤化工~ 608(Fig. 1 The comparison of normal distribution withP/%YHCNMHG_e frequencylinear straight line for Cv=0. 10 (PA: Percent of Area)model (PA: Percent of Area)494QIU Yuan-feng et al: The Effect of Water Saving and Production ....石一21l_1\c _ K,(Xr-a)22 Method to Solve the ModelsK26X。1厂b(10)2.1 Drip Irrigation Schedules2abX-(a+b- X.)x]C.Drip irrigation schedule expressed as a horizontalwhere Zo is the optimum return, Za is total return underline in Fig.2 is a key figure to show the efficient waterconventional irigation scheduling, K, is a reduction coef-use based on the amount of water in the root zone, per-ficient which is a constant for a given crop, K is a coffi-cent of deficit and the volume of deep seepage. If the re-cient, Xo is the required depth of water when reachingquired irigation depth is determined by the depth tothe optimum benefits, C，and C, are two cost ratios.achieve maximum yield, the relative irrigation depth, X,K, X，Cn and Cr, are defined by the following equa-tion[1.2]can be shown as .X= wm/(Q. T)(9)_YmaWm(11)ETwhere W is the amount of water required to achieve theETmpuwmaximum yield and QT is the total amount applied (Q is(12)YmPythe capacity of the irrigation system and T is the irriga-ETmpstion time). The dimensionless value X is, in fact, a pa-Ympy(13)rameter for irrigation scheduling. Each individual decisiona2+2lC,/K, +(a+b)*C,/R,on irrigation scheduling will be presented as a horizontalK。=(14)1+C,/K,line in Fig. 2. Different drip irrigation schedules ex-pressed by X are explained as follows57.8]① Xa+b. Too lit-Xo is always larger thana, Eq. (15) will produce a re-tle irigation is scheduled. The whole field is in deficit ir-sult with a positive sign. This means water savingrigation condition in which there is no deep seepage forthrough optimum irrigation scheduling. It is important tothe whole field. Among all the irigation schedules, theemphasize that optimum irrigation scheduling comparedfirst (Xa+b) are impractical andwith the conventional schedule, will not only produce anot recommended. The two most important schedules arehigher return but also achieve water saving at the samethe conventional (X