Yield Response of Corn to Deficit Irrigation in a Semiarid Climate

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1 University of Nebrsk - Lincoln DigitlCommons@University of Nebrsk - Lincoln Biologicl Systems Engineering: Ppers nd Publictions Biologicl Systems Engineering Yield Response of Corn to Deficit Irrigtion in Semirid Climte José O. Pyero University of Nebrsk-Lincoln, jpyero@clemson.edu Steven R. Melvin University of Nebrsk-Lincoln, smelvin1@unl.edu Sut Irmk University of Nebrsk-Lincoln, sut.irmk@unl.edu Dvid Trklson University of Nebrsk-Lincoln, dtrklson@unl.edu Follow this nd dditionl works t: Prt of the Biologicl Engineering Commons Pyero, José O.; Melvin, Steven R.; Irmk, Sut; nd Trklson, Dvid, "Yield Response of Corn to Deficit Irrigtion in Semirid Climte" (006). Biologicl Systems Engineering: Ppers nd Publictions This Article is brought to you for free nd open ccess by the Biologicl Systems Engineering t DigitlCommons@University of Nebrsk - Lincoln. It hs been ccepted for inclusion in Biologicl Systems Engineering: Ppers nd Publictions by n uthorized dministrtor of DigitlCommons@University of Nebrsk - Lincoln.

2 Published in Agriculturl Wter Mngement 84:1 (July 16, 006), pp ; doi: /j.gwt Copyright 006 Elsevier B.V. Used by permission. A contribution of the University of Nebrsk Agriculturl Reserch Division, Lincoln, NE Journl Series No Accepted Jnury 3, 006; published online Mrch 9, 006. Yield response of corn to deficit irrigtion in semirid climte José O. Pyero, Steven R. Melvin, b Sut Irmk, c nd Dvid Trklson University of Nebrsk Lincoln, West Centrl Reserch nd Extension Center, 461 West University Drive, North Pltte, NE 69101, USA b University of Nebrsk Lincoln Coopertive Extension, Curtis, NE, USA c Deprtment of Biologicl Systems Engineering, University of Nebrsk Lincoln, 34 L.W. Chse Hll, Lincoln, NE , USA Corresponding uthor J. O. Pyero, tel , fx , emil jpyero@unl.edu Abstrct Irrigtion wter supplies re decresing in mny res of the U.S. Gret Plins, which is requiring mny frmers to consider deficit-irrigting corn (Ze mys L.) or growing crops like winter whet (Triticum estivum L.) tht require less wter, but tht re less profitble. The objectives of this study were to: (1) quntify the yield response of corn to deficit irrigtion, nd () determine which of severl sesonl wter vribles correlted best to corn yield in semirid climte. Eight (T1 T8) nd nine (T1 T9) deficit-irrigted tretments (including drylnd), were compred in 003 nd 004 in North Pltte, Nebrsk. The ctul sesonl crop evpotrnspirtion ( ) (clculted with procedures in FAO-56) for the different tretments ws 37 79% in 003 nd 63 91% in 004 compred with the sesonl crop evpotrnspirtion when wter is not limited (ET w ). Quntittive reltionships between grin yield nd severl sesonl wter vribles were developed. Wter vribles included, irrigtion (I), totl wter (W ll ), rin + irrigtion (W R+I ), evportion (E), crop evpotrnspirtion ( ), crop trnspirtion (T d ), nd the rtios of nd T d to evpotrnspirtion nd trnspirtion when wter is not limited (ET w nd T w ). Both yers, yield incresed linerly with sesonl irrigtion, but the reltionship vried from yer to yer. Combining dt from both yers, hd the best correltion to grin yield (yield = , R = 0.95), nd the wter vribles could be rnked from higher to lower R when relted to grin yield s: (R =0.95) > T d(r =0.93) > (R =0.90) = T d (R =0.90) > W ll(r =0.89) > E (R =0.75) > W R+I(R =0.65) > I (R =0.06). Crop wter productivity (CWP) (yield per unit ) linerly incresed with (R = 0.75), which suggests tht trying to increse CWP by deficit-irrigting corn is not good strtegy under the conditions of this study. Keywords: evpotrnspirtion, deficit irrigtion, corn, mize, crop wter productivity, wter vrible, wter use efficiency 1. Introduction Irrigtion wter supplies re decresing in mny res of the Gret Plins of the USA. Some of the resons for this decrese include extended drought periods, decline in groundwter levels (McGuire, 004; McGuire nd Fischer, 1999), litigtion mong sttes relted to surfce wter lloctions, nd diversion of wter from irrigtion to environmentl uses (Lingle nd Frnti, 1998). This sitution is forcing frmers to consider the options of deficit-irrigting crops like corn or growing lterntive crops like winter whet tht require less irrigtion wter, but tht re generlly less profitble. Knowing the quntittive response of crops to limited wter supplies under specific environments is criticl to be ble to 101

3 10 P y e r o et l. in Agriculturl Wter Mngement 84 (006) perform economic comprisons mong locl cropping options. In the US Gret Plins, developing locl nd current informtion on wter yield reltionships is prticulrly importnt for corn (Ze mys L.), since this crop covers more irrigted re thn ny other crop in the region (Norwood, 000). Deficit irrigtion cretes wter stress tht cn ffect the growth nd development of corn plnts. The response of corn plnts to wter stress hs been shown to chnge with hybrid (Lorens et l., 1987) nd cn be ffected by improving technologicl level (Dle nd Dniels, 1995). Effects of wter stress on corn include the visible symptoms of reduced growth, delyed mturity, nd reduced crop yield. For instnce, wter stress hs been shown to reduce corn cnopy height (Denmed nd Shw, 1960; Gvloski et l., 199; Trore et l., 000), lef re index (NeSmith nd Ritchie, 199; Trore et l., 000), nd root growth (Gvloski et l., 199; Jm nd Ottmn, 1993). Jm nd Ottmn (1993) found tht stressing corn during the vegettive stge in n rid environment hindered root development, which restricted deep wter uptke. However, in wetter environment in estern Nebrsk, Newell nd Wilhelm (1987) found tht lthough fully irrigted corn tretment hd greter totl profile (0 1.5 m) nd surfce ( m) root length t the reproductive stge, drylnd nd deficit-irrigted tretments hd reltively greter root length prolifertion deep in the soil profile. The effect of wter stress on reducing corn grin nd biomss yields hs lso been studied (Denmed nd Shw, 1960; Trore et l., 000). Grin yield cn be reduced by decresing yield components like er size, number of kernel per er, or the kernel weight. Clssen nd Shw (1970) observed tht stress before or during silking nd pollintion resulted in reduced kernel number, while stress during or fter silking reduced kernel weight. NeSmith nd Ritchie (199) ttributed yield loss from wter stress during pre-nthesis to reduction in the number of well-developed kernels. Brynt et l. (199) indicted tht wter stress reduces yield by reducing ccumulted biomss nd the hrvest index (rtio of grin yield to boveground plnt dry weight). Trore et l. (000), however, found tht the hrvest index ws ffected by wter deficit only when stress ws imposed during nthesis. Mny reserchers hve evluted the effect of stress timing on corn yield (Robins nd Domingo, 1953; Denmed nd Shw, 1960; Brnes nd Woolley, 1969; Downey, 1971; Clssen nd Shw, 1970; Jurgens et l., 1978; NeSmith nd Ritchie, 199; Brynt et l., 199; Jm nd Ottmn, 1993). Others hve developed models to quntify the effect of stress timing on yield (Jensen, 1968; Nirizi nd Rydzewski, 1977; Doorenbos et l., 1979; Doorenbos nd Kssm, 1979; Meyer et l., 1993, 1993b). For instnce, Doorenbos et l. (1979) proposed tht the effect of wter stress on yield could be quntified by liner function where the slope of the line (ky) ws n empiricl yield response fctor tht vried depending on the growth stge when wter stress occurred. For corn, they reported ky vlues of 0.4, 1.5, 0.5, nd 0. for the vegettive, flowering, yield formtion, nd ripening stges, indicting tht yield ws more ffected by wter stress during the flowering stge thn t ny other stge. This model suggests tht if wter is limited, the irrigtor should time irrigtion to coincide with the most sensitive stge. Despite the body of evidence indicting tht stress timing hs n effect on corn yield, there is lso indiction tht corn yield is just liner function of sesonl evpotrnspirtion (ET) or trnspirtion (T), with no regrd for stress timing. For instnce, good liner reltionship between corn yield nd sesonl ET hve been reported by Robins nd Domingo (1953), Hnks (1974), Hnks et l. (1976), Gilley et l. (1980), Schneekloth et l. (1991), Brrett nd Skogerboe (1978), Stone (003), nd Klocke et l. (004). The dt reported by Benoit et l. (1965) lso follow liner yield-et function with R Brrett nd Skogerboe (1978) pointed out tht the sctter in the published crop yield versus wter use dt lrgely resulted from the time of occurrence of wter deficits in reltion to the stge of growth. However, they lso stted tht if these yields re plotted versus sesonl ET rther thn the quntity of wter pplied, the dt would likely fll on stright line. The objectives of this study were to: (1) quntify the grin yield response of corn to deficit irrigtion nd () determine which of severl sesonl wter vribles correlted best to corn grin yield under deficit irrigtion conditions in the semirid climte of West-Centrl Nebrsk.. Mterils nd methods.1. Site description Field dt for this study were collected in 003 nd 004 t the University of Nebrsk Lincoln West Centrl Reserch nd Extension Center, North Pltte, Nebrsk (41.1 N, W, 861 m bove se level). The soil t North Pltte is Cozd silt lom (Fluventic Hplustolls) with field cpcity of 0.9 m 3 m 3 nd permnent wilting point of 0.11 m 3 m 3 (Klocke et l., 1999). The corn hybrid DeKlb C57-40 RR ws plnted t 0.76-m row spcing in 003 nd Renze 9363 Bt RR ws plnted in 004. These hybrids hd comprtive reltive mturities tht re commonly plnted in the re nd were chosen for being the top yielding hybrids in locl vriety trils during the previous yer. In 003 corn ws plnted on My 13, nd hrvested on October 13. In 004, corn ws plnted on My 10 nd hrvested on November 15. The experimentl plots were locted within reltively lrge irrigted re. Plots were irrigted using solid-set sprinkler system, which ws rrnged in grid with sprinkler hed instlled on 3.35-m riser t ech corner of ech plot. Ech experimentl plot ws 1. m 1. m (148.8 m ) in size, which ccommodted 16 corn rows. The center four rows of ech plot were hrvested using plot combine. Experimentl plots were seprted from ech other by 1.-m wide border strips tht were lso plnted to corn. Wter for the system ws pumped from the Oglll quifer, using n electric turbine pump with cpcity of 600 GPM t 483 kp of pressure. The minline t the pumping sttion ws instrumented with two pressure guges, two flow meters, pressure relief vlve, chemigtion check vlve, nd high nd low pressure switches. The flow meters mesured both the instntneous flow rte nd the cumultive volume of wter pumped. The irrigtion system hd n utomtic control pnel hrd-wired to electric vlves instlled t ech plot. Ech electric vlve controlled the four sprinklers of ech plot. The control pnel ws lso connected

4 Y i e l d response of corn to deficit irrigtion in semirid climte 103 Tble 1. Averge of dily vlues of mximum ir temperture (T mx ), minimum ir temperture (T min ), verge ir temperture (T ), solr rdition (R s ), reltive humidity (RH), wind speed t -m height (u ), nd grss reference evpotrnspirtion (ET o ) for the month of My October t North Pltte, NE during 003 nd 004 Month T mx ( C) T min ( C) T ( C) R s (MJ m d 1 ) RH (%) u (m s 1 ) ET o (mm d 1 ) 003 My June July August September October Averge My June July August September October Averge to mnul rely pnel, which llowed both mnul nd utomtic opertion of the irrigtion system. This design llowed irrigting ech individul plot independently, nd chnging the rndomizing of the plots from yer to yer to ccommodte different experimentl designs. The verge wether conditions t North Pltte during the study re shown in Tble 1. In generl, wether conditions were cooler nd wetter during the 004 growing seson thn in 003. Although the verge ir temperture during June October ws only 0.6 C cooler in 004, it ws pproximtely. C cooler during the months of June, July, nd August. These cooler wether conditions during 004 delyed crop mturity nd hrvest bout month compred with 003. Wrmer conditions, however, previled in 004 compred with 003 during the months of My nd September. Although wether conditions were cooler in 004, the verge of the dily grss-reference evpotrnspirtion (ET o ) vlues for the entire My October period ws only 0.0 mm d 1 lower during 004 (Tble 1). In 004, the verge dily ET o vlues were lower thn 003 during the months of July, August, nd October, nd higher during My, June, nd September. Averge dily ET o vlues in 004 were prticulrly lower thn 003 during the months of July nd August, which re usully the months with the pek ET o vlues for the North Pltte re. Rinfll ws significntly less in 003 thn 004 (Figure 1). A totl of rinfll events occurred during the 003 growing seson, which totled 138 mm of wter. In 003, the totl in-seson rinfll ws only enough to supply pproximtely 19.4% of sesonl crop wter requirements (ET w ). In 004, however, there were 39 rinfll events, lmost twice s mny s in 003. Rinfll in 004 totled 414 mm, which supplied more thn hlf (54.5%) of the sesonl crop wter requirements... Irrigtion tretments The experiment ws conducted using rndomized complete block design with four replictions. Eight irrigtion tretments (T1 T8) were pplied in 003 nd the number of tretments ws incresed to nine (T1 T9) in 004. Ech yer, tretments included drylnd tretment (tretment T8 in 003 nd T9 in 004) (Tble ), which received no irrigtion. This mny tretments were included to obtin enough dt points nd wide enough rnge of wter stress levels to be ble to develop meningful quntittive reltionships between grin yield nd severl sesonl wter vribles, including irrigtion, totl wter, rin + irrigtion, evportion, evpotrnspirtion, nd trnspirtion, mong others. Irrigtion to the different tretments ws scheduled trying to crete differences in soil wter depletions of pproximtely 10 mm between irrigted tretments, within the rnge of mm. This rnge of soil wter depletion represents between 50 nd 85% of totl vilble wter in the mximum crop rooting depth. No irrigtion ws pplied during the vegettive growth stge, following common prctice in the re, nd to mke sure tht there would be some sesonl crop stress despite potentil rinfll occurring lter in the Figure 1. Dily nd cumultive rin during the 003 nd 004 corn growing sesons t North Pltte. % of ET w is the percent of sesonl crop evpotrnspirtion when soil wter is not limiting tht ws supplied by in-seson rinfll.

5 104 P y e r o et l. in Agriculturl Wter Mngement 84 (006) Tble. Irrigtion (mm) pplied to corn t North Pltte during 003 nd 004 for ech irrigtion tretment (T1 T9). Dte T1 T T3 T4 T5 T6 T7 T8 T /10/ Drylnd Not included 7/11/ /17/ /18/ // /6/ /9/ /30/ /31/ /8/ /9/ /11/ /13/ /18/ /19/ /5/ /6/ /1/ // /3/ /9/ Totl % of ET w /9/ Drylnd 8/11/ /1/ /13/ /17/ /19/ /3/ /4/ /5/ /7/ /8/ Totl % of ET w % of ETw is the percent of sesonl crop evpotrnspirtion when soil wter is not limiting tht ws supplied by irrigtion. growing seson. Depths nd timings of irrigtion events pplied to ech irrigtion tretment during the 003 nd 004 growing sesons re shown in Tble. Due to more in-seson rinfll, sesonl irrigtion mounts nd the number of irrigtion events per tretment were significntly less in 004 thn 003. In 003, sesonl irrigtion depths per tretment rnged from pproximtely 45 to 395 mm. These sesonl irrigtion depths supplied between 34.7 nd 55.7% of sesonl crop wter requirements (ET w ). In 004, sesonl irrigtion depths rnged from 34 to 161 mm, representing between 4.7 nd 1.% of sesonl ET w. In 003, the first irrigtion to some of the irrigted tretments ws pplied in erly July. In 004, rinfll erly in the seson llowed delying the first irrigtion to ny of the tretments until erly August. The lst irrigtion during both yers ws pplied in erly September. Irrigtion scheduling t both sites ws done using scheduling spredsheet tht used the clculted dily corn evpotrnspirtion s input to estimte dily soil wter content in the crop root zone. When ctul soil wter mesurements were vilble, they were used to djust the spredsheet estimtes. Soil wter mesurements were mde pproximtely every weeks during the growing seson using the neutron scttering method. Soil wter redings were tken from 50-mm dimeter luminum ccess tubes instlled t the center of two of the four replictions for ech tretment. Redings were tken t 0.3-m depth increments to depth of 1.8 m. Wether dt for this study were obtined from n utomtic wether sttion locted within 1.5 km from the reserch site. This wether sttion ws prt of the High Plins Regionl Climte Center (HPRCC) wether network. Dily wether dt were downloded from the HPRCC web site ( including dily mximum nd minimum ir temperture, reltive humidity, wind speed, rinfll, solr rdition, reference ET, nd crop ET for different crops, including corn..3. Dt nlyses The sttisticl nlyses of yield dt, which included nlysis of vrince (ANOVA) nd seprtion of mens by

6 Y i e l d response of corn to deficit irrigtion in semirid climte 105 the Duncn s new multiple rnge test, were conducted using the SAS System for Windows sttisticl softwre (SAS Institute, Inc., Cry, NC). A computer progrm ws written in Microsoft Visul Bsic to model the dily soil wter sttus. Bsic input to the progrm included dily wether dt, rinfll, irrigtion, the soil wter profile t crop emergence, nd crop-specific nd site-specific informtion such s plnting dte, mturity dte, soil prmeters, mximum rooting depth, etc. Bsed on these inputs, the wter blnce in the crop root zone ws clculted on dily bsis. Similr soil wter blnce models hve previously been used by Robinson nd Hubbrd (1990), Swn et l. (1990), nd Brynt et l. (199) to estimte dily wter sttus nd yield for corn. The computer progrm clculted evpotrnspirtion using the procedure presented in FAO-56 (Allen et l., 1998). Since this is lengthy procedure, reders re referred to the originl source for detils. According to this procedure, crop evpotrnspirtion cn be obtined s the product of the evpotrnspirtion of reference crop (ET o ) nd crop coefficient (K c ). ET o is clculted using the dily wether dt s input to the Penmn Monteith eqution, nd the K c is used to djust the estimted ET o for the reference crop to tht of other crops t different growth stges nd growing environments. ET o is the evpotrnspirtion of hypotheticl reference crop with n ssumed crop height of 0.1 m, fixed surfce resistnce of 70 s m 1 nd n lbedo of 0.3. The reference surfce closely resembles n extensive surfce of green grss of uniform height, ctively growing, completely shding the ground nd with dequte wter (Allen et l., 1998). The dul crop coefficient pproch ws used to seprte the two components of evpotrnspirtion, nmely evpottion (E) nd trnspirtion (T) (Wright, 198). For corn, this procedure linerly reduced crop evpotrnspirtion when the root zone depletion exceeded 55% (tken from Tble in FAO-56) of totl vilble wter, which ws used to quntify the effect of wter stress on corn wter use. The dul crop coefficient procedure lso ccounts for the shrp increses in evportion due to wet soil surfce following rin or irrigtion. This procedure permitted clcultion of the crop evpotrnspirtion nd trnspirtion when soil wter is not limiting (ET w nd T w ), nd the ctul crop evpotrnspirtion, trnspirtion, nd evportion (, T d, nd E). From the sesonl vlues, the sesonl nd T d rtios were clculted for ech tretment. It ws expected tht the sesonl nd T d rtios would relte to crop yield. Additionlly, in FAO-56, n eqution ws presented to estimte the frction of totl vilble soil wter in the root zone (p) tht cn be depleted from the root zone before moisture stress (reduction in ) occurs. This eqution estimtes vrible p (p clc ) s function of dily ET w s: where, p tble is the p vlue tken from Tble in FAO-56, nd ET w is in mm dy 1 nd 0.1 p clc 0.8. This eqution suggests tht s ET w for given dy decreses, it is esier for the crop to sustin ET w rtes, nd therefore, higher soil wter depletion levels could be llowed without yield loss, s previously proposed by Doorenbos et l. (1979). This wy of clculting vrible p vlue differs from the common procedure of using fixed p vlue for given crop for the entire growing seson. In this study, the dily p clc vlues were clculted, which were tken s the theoreticl optimum depletion vlue for given dy. Also, dily ctul p (p ctul ) ws clculted s: p ctul = D/TAW (8) TAW = 1000(θ FC θ PWP )Z r (9) where D is the soil wter depletion in the crop root zone (mm), θ FC the soil wter content t field cpcity (m 3 m 3 ), θ PWP the soil wter content t permnent wilting point (m 3 m 3 ), Z r the crop rooting depth (m), nd TAW is the totl vilble soil wter in the crop root zone (mm). A mximum rooting depth of 1.7 m ws ssumed for corn (tken from Tble in FAO-56). In this study, it ws expected tht p dif f = (p ctul p clc ) ccumulted for the entire seson only for dys when p diff > 0 (sesonl p diff ) would be good indictor of the level of crop stress nd would, therefore, relte to crop yield. The greter the sesonl p diff for given tretment the greter the level of wter stress. Sesonl p diff ws therefore clculted for ech tretment. The effect of irrigtion tretments on crop yield ws lso evluted by clculting the crop wter productivity (CWP) (Zwrt nd Bstinssen, 004) s: CWP = [Y /(sesonl )]/10 (10) where Y is the crop yield (kg h 1 ), sesonl the sesonl ctul crop evpotrnspirtion (mm), nd CWP is in kg m 3. Since 1 h-mm = 10 m 3, 10 is needed to convert CWP from units of kg h 1 mm 1 to kg m 3. The CWP is sometimes p clc = p tble (5 ET w ) (7) Figure. Dily soil wter depletion in the crop root zone for the different irrigtion tretments (T1 T9) t North Pltte during the 003 nd 004 growing sesons. TAW is the totl vilble wter in the crop root zone nd RAW is the redily vilble wter (RAW = 0.55TAW).

7 106 P y e r o et l. in Agriculturl Wter Mngement 84 (006) Tble 3. Sesonl clculted vlues of severl wter vribles obtined for corn t North Pltte during 003 nd 004 for ech irrigtion tretment (T1 T9) Tret. ET ET W W ( W E T T D ET /ET E/ET E/ET p T /T CWP d (mm) w (mm) ll (mm) R+I (mm) soil (mm) (mm) w (mm) d (mm) p (mm) d w d w diff d w (kg m 3 ) 003 T T T T T T T T T T T T T T T T T ET w, sesonl crop evpotrnspirtion when soil wter is not limiting; W ll, wter vilble to the crop from ll sources, including irrigtion, rinfll nd wter lredy stored in the soil t crop emergence; W R+I, rinfll plus irrigtion wter; W soil, wter stored in the soil profile t crop emergence, to depth equl to the mximum root depth; T d, sesonl ctul trnspirtion; T w, sesonl trnspirtion when soil wter is not limiting; E, sesonl evportion; D p, sesonl deep percoltion; p diff, dily positive difference between the ctul nd the theoreticl frction of totl vilble soil wter in the root zone tht cn be depleted before moisture stress occurs, ccumulted for the entire seson, nd CWP, crop wter productivity., sesonl ctul crop evpotrnspirtion.

8 Y i e l d response of corn to deficit irrigtion in semirid climte 107 equivlent to wter use efficiency (WUE) s defined by Howell (000), lthough sometimes reserchers define WUE in terms of sesonl irrigtion pplied insted of sesonl. This study lso evluted the reltionships between severl other wter vribles nd corn grin yield. These vribles included sesonl, T d, E, irrigtion pplied (I), rin + irrigtion (W R+I ), nd totl wter vilble to crop during the growing seson (W ll ). Grin yields were lso normlized by clculting the % yield potentil (%Y p ) nd the % mximum yield (%Y mx ). The mximum yield obtined within ech seson ws tken s reference to clculte %Y mx. The potentil yield for ech seson ws estimted using the Hybrid- Mize simultion model developed by Yng et l. (004). 3. Results nd discussion 3.1. Yield response to wter deficit Irrigtion tretments resulted in differences in dily soil wter depletions in the crop root zone s shown in Figure. To void wter stress, best mngement prctices commonly recommend mintining root zone depletion below the redily vilble wter (RAW) line (Figure ). Figure, however, shows tht in 003, delying irrigtion until erly July resulted in wter stress for ll tretments occurring fter mid June. Limited wter inputs fter tht time lso resulted in wter stress levels for the different tretments tht rnged from mild to severe. In 004, except for the drylnd tretment, stress to most tretments only occurred fter mid July. Limited wter inputs in 004 lso resulted in some level of stress for ll tretments, especilly lte in the growing seson. In 004, similrly to 003, the drylnd tretment suffered from wter stress during most of the growing seson, lthough the level of stress t the end of the growing seson for this tretment ws more severe in 003 thn 004. Irrigtion tretments lso resulted in differences in sesonl vlues of severl wter vribles s shown in Tble 3. Although the 004 growing seson ws cooler nd wetter thn 003, the sesonl vlues of ET w were higher in 004 due to the longer growing seson, resulting from delyed crop mturity, nd to incresed soil evportion due to more frequent wetting of the soil surfce by rinfll. Vlues of sesonl for the different tretments were lso higher in 004 since there ws more wter vilble to the crop compred with 003. The sesonl vlues of per tretment rnged from 0.37 to 0.79 in 003 nd from 0.63 to 0.91 in 004. The vlues of the rtio indicte tht ll tretments experienced some wter stress during the growing seson. No deep percoltion (D p ) occurred during the study for ny of the irrigtion tretments. In 004, there ws slightly more sesonl evportion (E) for ll tretments compred with 003. The vlues for E in Tble 3 show tht the sesonl evportion represented bout 1/3 of ET w during both sesons for ll tretments. This is significnt mount of wter tht does not directly contribute to crop yield. In this study, however, most of the evportion resulted from rinfll insted of irrigtion. Most of the E lso occurred erly in the growing seson when there ws prtil cnopy cover nd the soil surfce ws exposed to direct solr energy. To chieve the objective of producing more crop yield per unit of wter there is still potentil for reducing the evportion component of ET w in ddition to the ppliction of other wter-sving techniques (Kijne et l., 003). Irrigtion tretments lso resulted in differences in grin yields s shown in Tble 4. Higher yields were obtined in 004 since there ws more wter vilble to the crop in ll tretments compred with 003. The nlysis of vrince resulted in significnt yield differences during both growing sesons. However, during the 003 seson the seprtion of mens nlysis resulted in five different groups of tretments, while in 004 only the drylnd tretment (T9) hd significntly lower grin yield thn the other tretments. Running the Hybrid-mize simultion model of Yng et l. (004) ssuming dequte irrigtion, potentil yields for corn t North Pltte were estimted t 13.3 Mg h 1 for 003 nd 16.9 Mg h 1 for 004. These potentil yields were used to clculte the % potentil yield (%Y p ) shown in Tble 4. The mximum yield ws 10.1 Mg h 1 in 003 nd 14. Mg h 1 in 004. Bsed on these Tble 4. Corn grin yields, % potentil yield (%Y p ), nd % mximum yield (%Y mx ) for ech irrigtion tretment (T1 T9) obtined t North Pltte during 003 nd 004 Irrigtion tretment Yield (Mg h 1 ) %Y p %Y mx Yield (Mg h 1 ) %Y p %Y mx T T 8.9b T3 9.b T4 8.3bc T5 8.5bc T6 7.9bc T7 7.3c T8.4d T9 8.0b The %Y p vlues re bsed on estimted yield potentil vlues of 13.3 Mg h 1 for 003 nd 16.9 Mg h 1 for 004 using the Hybrid-Mize simultion model (Yng et l., 004). ANOVA ws used to determine significnce of tretment min effect for yield for ech yer. The Duncn New Multiple Rnge test ws used to seprte mens when the tretment min effect ws significnt. For given yer, yields with the sme letter re not significntly different.

9 108 P y e r o et l. in Agriculturl Wter Mngement 84 (006) Figure 3. Reltionships mong different vribles for corn obtined t North Pltte during 003 (solid circles) nd 004 (open circles). nd T d re ctul crop evpotrnspirtion nd trnspirtion, ET w nd T w re crop evpotrnspirtion nd trnspirtion when soil wter is not limiting, p diff is dily positive difference between the ctul nd the theoreticl frction of totl vilble soil wter in the root zone tht cn be depleted before moisture stress occurs, ccumulted for the entire seson, nd CWP is crop wter productivity. The solid nd dshed lines re liner regression lines.

10 Y i e l d response of corn to deficit irrigtion in semirid climte 109 Tble 5. Results of liner regression nlysis for corn t North Pltte for 003, 004, nd combining dt from both yers Independent vrible Dependent vrible Slope Intercept R RMSE 003 Irrigtion Grin yield W ll Grin yield W R+I Grin yield Grin yield T d Grin yield Evportion Grin yield Grin yield p diff Grin yield T d Grin yield CWP %Y p %Y p %Y mx Irrigtion Grin yield W ll Grin yield W R+I Grin yield Grin yield T d Grin yield Evportion Grin yield Grin yield p diff Grin yield T d Grin yield CWP %Y p %Y p %Y mx nd 004 combined Irrigtion Grin yield W ll Grin yield W R+I Grin yield Grin yield T d Grin yield Evportion Grin yield Grin yield p diff Grin yield T d Grin yield CWP %Y p %Y p %Y mx ET w, sesonl crop evpotrnspirtion when soil wter is not limiting; W ll, wter vilble to the crop from ll sources, including irrigtion, rinfll nd wter lredy stored in the soil t crop emergence; W R+I, rin + irrigtion, T d, sesonl ctul trnspirtion; T w, sesonl trnspirtion when soil wter is not limiting, p diff, dily positive difference between the ctul nd the theoreticl frction of totl vilble soil wter in the root zone tht cn be depleted before moisture stress occurs, ccumulted for the entire seson; CWP, crop wter productivity (kg m 3); %Y p, % yield potentil; %Y mx, % mximum yield for ech seson, grin yield is in Mg h 1, nd ll wter vribles re in units of mm. RMSE is the root men squred error., sesonl ctul crop evpotrnspirtion. mximum yields, the % mximum yield (%Y mx ) per tretment ws lso clculted (Tble 4). The %Y p for the different irrigtion tretments rnged between 17.7 nd 75.9% in 003 nd from 47.4 to 83.8% in 004. During both yers, soil wter deficit ws the min yield-limiting fctor. 3.. Effect of sesonl wter vribles on grin yield The reltionships between yield nd severl sesonl wter vribles obtined during 003 nd 004 re shown in Figure 3. Results of regression nlyses for the different wter vribles re shown in Tble 5, which include the results of the regression nlyses for ech yer nd lso combining dt for both yers. Figure 3 nd Tble 5 indicte tht in 003 there were very good liner reltionships mong ll the yield nd wter vribles. The poorest reltionships were between evportion nd grin yield, which resulted in R = 0.58, nd between nd CWP, which resulted in R = All other reltionships resulted in R > Among ll vribles, the ones relting best to grin yield in 003 were irrigtion, W ll, nd rin + irrigtion, nd, which ll resulted in high R vlue of 0.94.

11 110 P y e r o et l. in Agriculturl Wter Mngement 84 (006) For 004, however, irrigtion, rin + irrigtion, nd evportion were ll poorly relted to grin yield. Also, ws poorly relted to CWP in 004, which could be due to the smll rnge of CWP vlues obtined tht yer. All other vribles were well-correlted to grin yield during 004, resulting in R The poor reltionship between irrigtion nd grin yield during 004 could be due to severl fctors. First, the smll sesonl irrigtion mounts pplied during 004 did not provide lrge enough rnge of irrigtion mong tretments to be ble to observe significnt yield differences, with the only exception of the drylnd tretment. Second, some of the irrigtion wter my hve been pplied too lte in the seson to some of the tretments to be ble to mke n impct on crop yield. For instnce, no grin yield increse resulted from pplying n dditionl 48 mm of irrigtion to tretment T1 lte in the growing seson (on September 8, 004) compred to tretment T5, which received the lst irrigtion on August 5, 004 (Tble ). Both of these tretments produced the sme yield, lthough T1 received 161 mm of irrigtion, while T5 only received pproximtely 6 mm. The difference ws tht there ws higher mount of soil wter left in the T1 tretment t the end of the seson compred to T5 (Figure ). Figure shows tht t the end of the growing seson, there ws still some wter vilble in the soil profile tht the crop did not hve time to use becuse it resulted from rinfll or rin tht occurred too lte in the growing seson to hve n impct on crop yield. Norwood (000) in 4-yer study with corn in Knss found tht considerble wter remined in the soil profile fter hrvest. These results point out the importnce of pplying ll irrigtions erly enough in the growing seson so tht the crop hs time to use the wter nd convert it into grin. Figure 3 reflects the considerble vritions in the reltionship between grin yield nd irrigtion tht cn occur from one seson to the next, s previously reported by Norwood (000). These vritions depend on how much wter is stored in the soil profile t crop emergence, nd the mount nd distribution of in-seson rinfll. These results lso point out the importnce of clculting vribles tht relte crop yield to vilble soil wter (i.e., CWP or wter use efficiency) in terms of wter vribles tht re more stble thn sesonl irrigtion. Some of these more stble wter vribles include sesonl, T d,, W ll, T d, or p diff. Figure 4. Liner reltionships between corn grin yield nd ctul sesonl evpotrnspirtion ( ) reported in the literture nd tht obtined in this study. When dt for 003 nd 004 were combined, irrigtion hd the poorest reltionship to grin yield (R = 0.06) mong ll vribles, followed by rin + irrigtion (R = 0.65) (Tble 5). Even evportion ws better relted to grin yield thn the two previous vribles (R = 0.75). Although evportion itself might not contribute to crop yield directly, it is well-correlted to (R = 0.69), which does contribute to yield. All the remining vribles were highly correlted to grin yield. Combining both yers, hd the best correltion to grin yield, nd the wter vribles could be rnked from higher to lower resulting R when relted to grin yield s: (R =0.95) > T d(r =0.93) > (R =0.90) = T d (R =0.90) > W ll(r =0.89) > P diff(r =0.87) > evportion (R =0.75) > rin + irrigtion (R =0.65) > irrigtion (R =0.06). The rnking of these vribles, however, could chnge for other loctions, when combining dt for more thn one loction, or when considering n individul yer or seson. For instnce, it ws previously shown tht during the dry 003 seson, irrigtion, W ll, nd rin + irrigtion hd the highest correltion to crop yield of ll the vribles, while irrigtion nd rin + irrigtion hd poor correltion to yield when dt for the two sesons were combined. Normlizing grin yield s %Y mx or %Y p did not produce significnt improvement in the reltionships between yield nd the sesonl wter vribles compred in this study. Figure 3 shows tht in this study, it took pproximtely 180 mm of sesonl for the crop to strt producing grin yield. This number cn be derived from the eqution of the line obtined using the 003 nd 004 dt combined in Tble 5 (yield = ), ssuming grin yield = 0 Mg h 1 (sesonl = 5.04/0.08 = 180 mm). The slope of the line indictes tht grin yield incresed with sesonl t rte of 0.08 Mg h 1 mm 1. Figure 4 shows comprison of the yield- liner reltionship obtined in this study nd those functions reported by other reserchers. This plot seems to suggest tht corn response to wter could chnge with environment nd time s new crop hybrids re developed nd mngement prctices improve. The slope of the line obtined in this study, however, is very similr to those reported by Schneekloth et l. (1991) nd Klocke et l. (004) for the sme loction. Schneekloth et l. (1991) reported n verge yield- slope for two corn crop rottions (continuous corn nd whet corn soyben) during three-yer study of Mg h 1 mm 1. Klocke et l. (004) lso reported yield- slope for corn t North Pltte of Mg h 1 mm 1, lthough the intercept of the line ( 8.5 Mg h 1 ) ws smller thn the one obtined in this study ( 5.04 Mg h 1 ). For the sme loction, Hergert et l. (1993) lso reported n verge mrginl return for corn from the ppliction of deficit irrigtion tretment of 150 mm of wter of 0.07 Mg h 1 mm 1, which ws very similr to the slope of the yield- line obtined in this study. Stone (003), however, reported long-term yield- slope for corn in Knss of Mg h 1 mm 1, which is slightly higher thn the slope found in this study. This difference could be due to differences in techniques used to quntify sesonl nd yield, differences in climte between loctions (especilly the mount nd distribution of in-seson rinfll), differences in crop vrieties nd culturl prctices, irrigtion method, differences in irrigtion scheduling prctices, etc.

12 Y i e l d response of corn to deficit irrigtion in semirid climte 111 The CWP incresed with, resulting in R = 0.75 when dt for both yers were combined (Tble 5). These results suggest tht trying to increse CWP by using deficit irrigtion might not be beneficil strtegy under the conditions of this study s suggested by other reserchers. For instnce, Zwrt nd Bstinssen (004) reviewed mesured CWP for severl crops round the world, including corn, nd concluded tht the CWP could be significntly incresed if irrigtion ws reduced nd crop wter deficit ws intentionlly induced. Deficit irrigtion would probbly increse CWP only in situtions where crops re being over-irrigted. The results of this study suggest tht if the crop is lredy deficit-irrigted, lowering irrigtion inputs would only contribute to further reduce yields, lowering CWP. Howell (000) showed tht WUE (clculted the sme s CWP in this study) for corn incresed s yield incresed. It is importnt, however, to point out tht the objective of most frmers is not to mximize CWP, but to mximize profits. Therefore, there could be very good resons for pplying deficit irrigtion other thn trying to mximize CWP. For exmple, Norwood (000) concluded tht for corn, deficit-irrigtion combined with proper fertility nd plnt popultion ws vible lterntive to drylnd in Knss where groundwter resources re declining. Some economic justifictions for deficit irrigtion strtegies for corn in Nebrsk hve been reported by Klocke et l. (004) nd Schneekloth et l. (1995). 4. Conclusions Quntittive reltionships between grin yield nd severl sesonl wter vribles were developed. Sesonl wter vribles included, irrigtion (I), totl wter (W ll ), rin + irrigtion (W R+I ), evportion (E), ctul crop evpotrnspirtion ( ), ctul crop trnspirtion (T d ),, T d, nd p diff. Severl of the wter vribles were lso relted to grin yield normlized s % mximum yield nd % potentil yield. A reltionship between crop wter productivity (CWP) nd ws developed. Results indicted tht E ccounted for bout 1/3 of sesonl ET w, which indictes tht technologies to minimize E should be developed nd implemented. The liner reltionship between grin yield nd some of the wter vribles chnged significntly from yer to yer, while others were very consistent. Combining dt from both yers, hd the best correltion to corn grin yield (yield = , R = 0.95). The wter vribles could be rnked from higher to lower R when relted to grin yield s: (R =0.95) > T d(r=0.93) > (R =0.90) = T d / T w(r =0.90) > W ll(r =0.89) > P diff(r =0.87) > E (R =0.75) > W R+I(R =0.65) > I (R =0.06). The CWP linerly incresed with (R = 0.75). These results indicte tht trying to increse CWP by imposing deficit irrigtion for corn might not be beneficil strtegy under the conditions of this study. However, it is recognized tht there could be other good justifictions for deficit irrigting corn in this environment, other thn incresing CWP. References Allen et l., 1998 Allen, R. G., Pereir, L. S., Res, D., Smith, M., Crop Evpotrnspirtion Guidelines for Computing Crop Wter Requirements. Irrigtion nd Dringe Pper No. 56. Food nd Agriculture Orgniztion of the United Ntions (FAO), Rome, Itly. Brnes nd Woolley, 1969 D. L. Brnes nd D. G. Woolley, Effect of moisture stress t different stges of growth. I. Comprison of single-ered nd two-ered corn hybrids, Agron. J. 61 (1969), pp Brrett nd Skogerboe, 1978 J. W. H. Brrett nd G. V. Skogerboe, Effect of irrigtion regime on mize yields, J. Irrig. Drin. Div. 104 (1978), pp Benoit et l., 1965 G. R. Benoit, A. L. Htfield nd J. L. Rglnd, The growth nd yield of corn. III. Soil moisture nd temperture effects, Agron. J. 57 (1965), pp Brynt et l., 199 K. J. Brynt, V. W. Benson, J. R. Kiniry, J. R. Willims nd R. D. Lcewell, Simulting corn yield response to irrigtion timings: vlidtion of the Epic model, J. Prod. Agric. 5 (199), pp Clssen nd Shw, 1970 M. M. Clssen nd R. H. Shw, Wter deficit effects on corn. II. Grin components, Agron. J. 6 (1970), pp Dle nd Dniels, 1995 R. F. Dle nd J. A. Dniels, A wether-soil vrible for estimting soil moisture stress nd corn yield probbilities, Agron. J. 87 (1995), pp Denmed nd Shw, 1960 O. T. Denmed nd R. H. Shw, The effects of soil moisture stress t different stges of growth on the development nd yield of corn, Agron. J. 5 (1960), pp Downey, 1971 L. A. Downey, Effect of gypsum nd drought stress on mize (Ze mys L.). I. Growth, light bsorption nd yield, Agron. J. 63 (1971), pp Doorenbos nd Kssm, 1979 Doorenbos, J., Kssm, A. H., Yield response to wter. In: Johl, S. S. (Ed.), Irrigtion nd Agriculturl Development: Bsed on n Interntionl Expert Consulttion, Bghdd Irq. Pergmon Press, New York, NY. Doorenbos et l., 1979 Doorenbos, J., Kssm, A. H., Bentvelsen, C., Uittenbogrd, G., Yield response to wter. FAO Irrigtion nd Dringe Pper No. 33, FAO, Rome, Itly. 193 pp. Gvloski et l., 199 J. E. Gvloski, G. H. Whitfield nd C. R. Ellis, Effect of restricted wtering on sp flow nd growth in corn (Ze mys L.), Cn. J. Plnt Sci. 7 (199), pp Gilley et l., 1980 J. R. Gilley, D. G. Wtts nd C. Y. Sullivn, Mngement of Irrigtion Agriculture with Limited Wter nd Energy Supply, Institute of Agriculture nd Nturl Resources, University of Nebrsk-Lincoln (1980) pp Hnks, 1974 R. J. Hnks, Model for predicting plnt yield s influenced by wter use, Agron. J. 66 (1974), pp Hnks et l., 1976 R. J. Hnks, J. Keller, V. P. Rsmussen nd G. D. Wilson, Line source sprinkler for continuous vrible irrigtion-crop production studies, Soil Sci. Soc. Am. J. 40 (1976), pp

13 11 P y e r o et l. in Agriculturl Wter Mngement 84 (006) Hergert et l., 1993 G. W. Hergert, N. L. Klocke, J. L. Petersen, P. T. Nordquist, R. T. Clrk nd G. A. Wicks, Cropping systems for stretching limited irrigtion supplies, J. Prod. Agric. 6 (1993), pp Howell, 000 T. A. Howell, Irrigtion s role in enhncing wter use efficiency, Proceedings of the Fourth Decennil Symposium ASAE, Phoenix, Arizon, November (000), pp Jm nd Ottmn, 1993 A. O. Jm nd M. J. Ottmn, Timing of the first irrigtion in corn nd wter stress conditioning, Agron. J. 85 (1993), pp Jensen, 1968 M. E. Jensen, Wter consumption by griculturl plnts. In: T. T. Kozlowski, Editor, Wter Deficits nd Plnt Growth, Acdemic Press, New York (1968), pp. 1. Jurgens et l., 1978 S. K. Jurgens, R. R. Johnson nd J. S. Boyer, Dry mtter production nd trnsloction in mize subjected to drought during grin fill, Agron. J. 70 (1978), pp Kijne et l., 003 Kijne, J. W., Tuong, T. P., Bennett, J., Boumn, B., Oweis, T., 003. Ensuring food security vi improvement in crop wter productivity. In: Chllenge Progrm on Wter nd Food: Bckground Ppers to the full proposl. The Chllenge Progrm on Wter nd Food Consortium, Sri Lnk. Klocke et l., 1999 N. L. Klocke, D. G. Wtts, J. P. Schneekloth, D. R. Dvison, R. W. Todd nd A. M. Prkhurst, Nitrte leching in irrigted corn nd soyben in semi-rid climte, Trns. ASAE 4 (1999), pp Klocke et l., 004 N. L. Klocke, J. P. Schneekloth, S. Melvin, R. T. Clrk nd J. O. Pyero, Field scle limited irrigtion scenrios for wter policy strtegies, Appl. Eng. Agric. 0 (004), pp Lingle nd Frnti, 1998 Lingle, G. R., Frnti, T. G., Wht is the Coopertive Agreement for Endngered Species Hbitt Along the Centrl Pltte Rive? NebFct NF University of Nebrsk-Lincoln Coopertive Extension Publiction, vilble t: unl. edu/wildlife/nf375. htm (5 pp.) Lorens et l., 1987 G. F. Lorens, J. M. Bennett nd L. B. Loggle, Differences in drought resistnce between two corn hybrids. II. Component nlysis nd growth rtes, Agron. J. 79 (1987), pp McGuire nd Fischer, 1999 McGuire, V. L., Fischer, B. C., Wter-level Chnges, nd Sturted Thickness, , in the High Plins Aquifer. Fct Sheet U. S. Geologicl Survey, Lincoln. McGuire, 004 McGuire, V. L., 004. Wter-level Chnges in the High Plins Aquifer, predevelopment to 00, , nd Fct Sheet U. S. Geologicl Survey, Lincoln. Meyer et l., 1993 S. J. Meyer, K. G. Hubbrd nd D. A. Wilhite, A crop-specific drought index for corn. I. Model development nd vlidtion, Agron. J. 85 (1993), pp Meyer et l., 1993b S. J. Meyer, K. G. Hubbrd nd D. A. Wilhite, A crop-specific drought index for corn. II. Appliction in drought monitoring nd ssessment, Agron. J. 85 (1993), pp Nirizi nd Rydzewski, 1977 S. Nirizi nd J. R. Rydzewski, Effects of dted soil moisture stress on crop yields, Exp. Agric. 13 (1977), pp NeSmith nd Ritchie, 199 D. S. NeSmith nd J. T. Ritchie, Short- nd long-term responses of corn to pre-nthesis soil wter deficit, Agron. J. 84 (199), pp Newell nd Wilhelm, 1987 R. L. Newell nd W. W. Wilhelm, Conservtion tillge nd irrigtion effects on corn root development, Agron. J. 79 (1987), pp Norwood, 000 C. A. Norwood, Wter use nd yield of limited-irrigted nd drylnd corn, Soil Sci. Soc. Am. J. 64 (000), pp Robinson nd Hubbrd, 1990 J. M. Robinson nd K. G. Hubbrd, Soil wter ssessment model for severl crops in the High Plins, Agron. J. 8 (1990), pp Robins nd Domingo, 1953 J. S. Robins nd C. E. Domingo, Some effects of severe soil moisture deficit t specific growth stges in corn, Agron. J. 45 (1953), pp Schneekloth et l., 1991 J. P. Schneekloth, N. L. Klocke, G. W. Hergert, D. L. Mrtin nd R. T. Clrk, Crop rottions with full nd limited irrigtion nd drylnd mngement, Trns. ASAE 34 (1991), pp Schneekloth et l., 1995 J. P. Schneekloth, R. T. Clrk, S. A. Cody, N. L. Klocke nd G. W. Hergert, Influence of whet-feed grin progrms on riskiness of crop rottions under lternte irrigtion levels, J. Prod. Agric. 8 (1995), pp Stone, 003 L. R. Stone, Crop wter use requirements nd wter use efficiencies, Proceedings of the 15th nnul Centrl Plins Irrigtion Conference nd Exposition Colby, Knss, Februry 4 5 (003), pp Swn et l., 1990 J. B. Swn, J. A. Strick, M. J. Shffer, W. H. Pulson nd A. E. Peterson, Corn yield response to wter stress, het units, nd mngement: model development nd clibrtion, Soil Sci. Soc. Am. J. 54 (1990), pp Trore et l., 000 S. B. Trore, R. E. Crlson, C. D. Pilcher nd M. E. Rice, Bt nd Non-Bt mize growth nd development s ffected by temperture nd drought stress, Agron. J. 9 (000), pp Wright, 198 J. L. Wright, New evpotrnspirtion crop coefficients, J. Irrig. Drin. Div. 108 (198), pp Yng et l., 004 H. S. Yng, A. Dobermnn, J. L. Lindquist, D. T. Wlters, T. J. Arkebuer nd K. G. Cssmn, Hybridmize mize simultion model tht combines two crop modeling pproches, Field Crops. Res. 87 (004), pp Zwrt nd Bstinssen, 004 S. J. Zwrt nd W. G. M. Bstinssen, Review of mesured crop wter productivity vlues for irrigted whet, rice, cotton nd mize, Agric. Wter Mng. 69 (004), pp

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