Wter Resources Mnement VI 497 Deficit irrition of pech trees to reduce wter consumption D. Wn USDA-ARS, Wter Mnement Reserch Unit Prlier, Cliforni, USA Abstrct Lck of wter is mjor limitin fctor for production tree fruits such s peches in the Sn Joquin Vlley of Cliforni nd mny other rid- or semi-rid reions in the world. Deficit irrition cn be used in some croppin systems s wter resource mnement strtey to reduce non-productive wter consumption. A difficulty in usin deficit irrition is the lck of techniques for quickly nd ccurtely mesurin plnt wter sttus so s not to cuse irreversible dme on the plnts, especilly in perennil species such s vine nd tree crops. Field mesurements nd nlyses were crried out in multi-yer experiment to evlute deficit irrition strteies for mnin posthrvest reduced wter ppliction of pech trees. Micrometeoroloicl vribles were collected ner the center of the orchrd for enery blnce computtions nd infrred temperture sensors were instlled in different field res which received full or deficit irrition tretments. Results indicted tht with pproximtely 30-40% of the full sesonl wter use, deficit irrition with furrows produced pech yield similr to full irrition. With subsurfce drip irrition, deficit wter ppliction t 25-30% of the full rte reduced the yield in the first yer but not the second yer. Smller fruit sizes were found under the severe deficit tretment in the subsurfce drip irrition method. Mesured middy cnopy to ir temperture differences in the wter-stressed posthrvest deficit irrition tretments were consistently hiher thn tht in the full irrition control tretments. Crop wter stress index ws estimted nd consistently hiher vlues were found in the deficit irrition thn in the full irrition control tretments. The study clerly showed tht with crefully mesured wter stress levels, deficit irrition is potentil mnement strtey for reducin wter consumption in rowin peches. Keywords: crop wter use, wter mnement, cnopy temperture, evpotrnspirtion, wter productivity. doi:10.2495/wrm110431
498 Wter Resources Mnement VI 1 Introduction Fresh wter is becomin less vilble to riculture with incresin demnds from urbn, industril, nd environmentl or recretionl needs. In ddition, enerlly ccepted wether pttern in recent decdes is the reduced totl nnul precipittion such s in pre-loned drouht or incresed frequency in extreme precipittion events tht exceeds the surfce wter store cpcities resultin in loss of wter for riculture use durin pek wter demnd period of the rowin seson. For perennil crops, controlled plnt wter stress could be used to improve crbohydrte prtitionin from the non-reproductive prts to reproductive prts such s fruits or berries thus incresin the yield or used s strtey to control excessive cnopy rowth [1] or used s technique to mnipulte crop qulity such s in wine rpes [2, 3]. Deficit irrition hs been studied s mens of reducin totl crop wter consumption for fruit trees becuse fruit yield nd qulity t hrvest my not be sensitive to wter stress t some developmentl stes such s durin non-fruit berin posthrvest seson [4]. Althouh the concept nd methods hve been developed, deficit irrition is not widely used due prtilly to the lck of effective nd fst methods for mesurin plnt wter stress nd determinin ssocited risks of pplyin deficit irrition. When crops re mned under deficit irrition, the mrin of error in timin nd mount of wter ppliction becomes smller before cusin yield losses. Monitorin the soil nd plnt wter sttus is more criticl for reducin risks for cusin crop filure or permnent dme to the trees. However, current estblished techniques of monitorin the soil nd plnt wter sttus such s neutron probe redins of soil wter profile, stem wter potentil mesurements, or trunk dimeter shrinke mesurements re lbor intensive, nd lck the timeliness needed for dy-to-dy irrition decisions [5]. Usin cnopy-temperture bsed pproch, the crop wter stress index (CWSI) ws developed by Jckson et l. [6] nd Jckson [7] for nnul crops tht my be used to quntify wter stress in mnin deficit irrition of perennil riculturl crops. A key component in pplyin CWSI is the mesurement of cnopy temperture. Sometimes the reltive deree of cnopy to ir temperture difference my be used s n indirect mesure of crop wter stress. Usin cnopy temperture mesurements, the cnopy nd ir temperture difference ws relted to the ir vpor pressure deficit in pech trees [8] nd lso reflected in stomtl responses to wter stress. Wter stress in wine rpes ws estimted usin CWSI when both therml nd visible imes of the vine cnopy were mesured [9]. In short-sesoned nnul crops the cnopy temperture bsed wter stress method ws pplied to mesure irrition uniformity [10] nd extended to crete wter mnement strteies such s schedulin irrition for cotton [11]. Approximtely 10,000 h of commercilly-rown pech trees in centrl Cliforni depend on irrition s the primry source of wter in the pek summer rowin seson. A potentil solution for mnin wter shorte is to
Wter Resources Mnement VI 499 use deficit irrition in rowth stes not sensitive to some deree of wter stress. However, there is limited informtion vilble in the literture on mnin deficit irrition in Prunus crops such s peches. The objective of this study ws to evlute effect of deficit irrition on yield nd qulity of erlyripenin peches. CWSI ws determined to evlute the deree of wter stress of the deficit irrition tretments used in the study. 2 Experiment 2.1 Field description A multi-yer field experiment ws crried out to evlute deficit irrition strteies for mnin posthrvest reduced wter ppliction in pech trees. The deficit irrition tretments included furrow irrition nd subsurfce drip irrition to replce portion of the crop evpotrnspirtion (ETc). For the furrow deficit irrition tretment, wterin event ws initited when stem wter potentil pproched -2 MP. For the subsurfce drip deficit irrition tretment, one fourth of the full mount of ETc ws pplied durin ech irrition event. A non deficit control ws used for both the furrow nd the subsurfce drip tretments where 100% ET ws pplied for the experiment. The vlues of ETc were determined by multiplyin the potentil evpotrnspirtion (ETp) with crop coefficients for the sme vriety of pech crop developed from nerby weihin lysimeter mesurements. The study ws conducted durin 2007-2009 in 1.6 h pech orchrd locted ner Prlier, Cliforni, USA. The trees were erly-ripenin Crimson Ldy (Prunus persic (L.) Btsch) pech trees on Nemurd rootstock plnted in April 1999. The trees were spced 1.8 m prt within rows nd 4.9 m between rows. Ech tretment plot consisted of three rows with eiht trees per row. The middle six trees in the center row were used for mesurements, includin yield nd fruit qulity ssessments. A totl of six replictions were used, with ech repliction includin the four irrition tretments or totl of 24 tretment plots for the study. The soil t the study site is Hnford sndy lom soil (corselomy, mixed, thermic Typic Xerorthents). To fcilitte wter stress ssessment, cnopy temperture ws mesured from 12 of the 24 tretment plots (or three replictions per irrition tretment) usin infrred thermometers. These temperture sensors were instlled in ech plot by mountin them on lvnized metl pipes extendin bove the orchrd cnopy. The center of field of view for ech sensor ws imed t the middle three trees of the center row for ech mesurement plot. The imin ws chieved by mountin webcm cmer in prllel with the infrred sensors. A dtloer system ws used to record temperture redins. 2.2 Evpotrnspirtion nd CWSI clcultions To compute ET p for irrition schedulin nd CWSI for wter stress, ir temperture nd other meteoroloicl prmeters were obtined from wether
500 Wter Resources Mnement VI sttion instlled ner the center of the orchrd. Estimtion of ET p ws crried out with the modified Penmn-Monteith eqution [12]: ET p s ( Rn vdv G) * s * / p (1) where s = slope of the sturtion model frction t pprent tmospheric pressure (p ), R n =net rdition, G=soil het flux, γ* = pprent psychrometer constnt, λ = ltent het of vporiztion of wter, v = vpor conductnce of the cnopy, nd D v = vpor pressure deficit. Prmeters s nd D v re determined usin mesurements of ir temperture (T ) nd reltive humidity (h r ) nd the Tetens formul for sturtion vpor pressure: s bc 2 p ( c T ) bt exp c T (2) bt D v ( 1 hr ) exp (3) c T where coefficients = 0.611 kp, b = 17.502, nd c = 240.97 C. Vpor conductnce of the cnopy ( v ) ws computed from stomtl conductnce ( s ) nd boundry lyer erodynmic conductnce ( ): v 1 s 1 1 (4) The erodynmic conductnce ws clculted usin k 2 ˆ u( z) (5) z d z d ln M ln H zm zh where k = von Krmn constnt (0.4), ρˆ = molr density of ir, u=wind speed, z = heiht of wind mesurement, d = zero-plne displcement heiht, z M,H nd Ψ M,H re rouhness lenths nd profile dibtic correction fctors for momentum nd het, respectively. The crop wter stress index (CWSI) ws computed usin the enery blnce method of Jckson [7]: 1 * c (6) CWSI 1 c
Wter Resources Mnement VI 501 c Rn ( T c T )( ) D c p 1 Rn ( T c T ) c p bc e s T c T 2 v (7) (8) where is psychrometric constnt (0.0652 kp ºC -1 ), e s = sturtion vpor pressure t T = (T c + T )/2, nd T c nd T re cnopy nd ir temperture, respectively. 2.3 Pech hrvest mesurements Pech fruit yield ws mesured in 2008 nd 2009 from the center six trees of the 24 tretment plots. Fruits were picked by locl commercil hrvestin crew followin typicl frmin procedures. A totl of three picks, bout three dys prt, were used durin ech seson. The totl number of peches per tree nd weiht per tree were mesured for ech tretment plot. Avere weiht per fruit or fruit size ws obtined by dividin the weiht per tree with number peches per tree. Sttisticl comprisons were mde for weiht per tree nd fruit size between different irrition methods nd deficit tretments for ech yer. 3 Results nd discussion Becuse ech yer pech hrvest ws completed ner the end of My, therefore the deficit irrition tretments were initited ner the beinnin of June nd lsted until bout November when irrition ws no loner needed. The cumultive irrition pplied for the 2007 nd 2008 posthrvest seson (June November) is summrized in Tble 1. As shown in the tble, under furrow irrition the 100% ET tretment required more thn 1000 mm of wter durin this period. The deficit furrow tretment received 39% nd 33% of the full irrition in 2007 nd 2008, respectively. Under subsurfce drip irrition, the 100% ET tretment required pproximtely 900 mm of wter. The deficit subsurfce drip tretment received only 25% nd 30% of the full irrition mount in 2007 nd 2008, respectively. The imposed deficit irrition tretments clerly received sinificntly reduced mount of irrition wter thn the full irrition control tretments. To delinete the sesonl chnes in irrition wter ppliction with respect to the crop wter needs or ET, the cumultive ET nd irrition in 2008 ws compred in Fiure 1 for the durtion of 1 Mrch to 30 September 2008. The fiure clerly shows the initition of deficit irrition fter 30 My where the cumultive mount of irrition in furrow nd subsurfce drip deficit tretments strted to fll behind the full irrition (100% ET) tretments. Also seen
502 Wter Resources Mnement VI Tble 1: Cumultive irrition pplictions durin June-November. Tretment 2007 (mm) 2007 (%) 2008 (mm) 2008 (%) Furrow, 100% ET 1030 100 1111 100 Furrow, deficit 405 39 366 33 Subsurfce drip,100% ET 977 100 870 100 Subsurfce drip, deficit 241 25 259 30 from the fiure is tht the furrow nd subsurfce drip deficit tretments trcked well on the rph nd the finl totl mounts were 366 nd 259 mm, respectively. The furrow full irrition tretment ppered to follow the ETp while the subsurfce drip full irrition mtched the ETc curve. This discrepncy is likely ttributed to differences in methods of irrition, e.. furrow vs. subsurfce drip, nd the ctul opertion of the irrition mnement durin the experiment. Cummultive ET or pplied wter (mm) 1,500 ETp ETc 1,200 Furrow, 100% ET Furrow, deficit 900 Subsurfce drip, 100% ET Subsurfce drip, deficit 600 300-3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 2008 dte Fiure 1: Cumultive potentil evpotrnspirtion (ETp), crop ET (ETc), nd pplied irrition wter for the 100% ET (non-deficit) nd deficit tretments by furrow nd subsurfce drip irrition methods. No sttisticl difference ws found in fruit weiht per tree between the deficit irrition nd 100% ET tretments with furrows in either 2008 or 2009 (Tble 2). With subsurfce drip irrition, the deficit irrition tretment reduced pech yield in 2008 but not sinificntly different from the 100% ET tretment in 2009. The weiht per fruit ws not different between the deficit irrition nd 100% ET tretments with furrows in 2008 but smller fruits were found in 2009. With subsurfce drip irrition, the deficit irrition tretment reduced pech fruit size
Wter Resources Mnement VI 503 in both 2008 nd 2009. These results indicte tht deficit irrition with furrow ppliction triered t -2 MP stem wter potentil did not cuse yield losses (weiht per tree or per re bsis). Deficit irrition by subsurfce drip t 25% ETc could led to yield losses (sinificntly reduced yield for one yer but not the second yer). The different response to deficit irrition between furrow nd drip irrition my be ttributed to the numeric differences in cumultive mount of irrition wter pplied: 405 mm vs. 241 mm in 2008 nd 366 mm vs. 259 mm in 2009 (Tble 1). The severe deficit likely exceeded the stress threshold in the drip tretments wheres the furrow deficit irrition ws on the bounder before cusin yield losses. The other possibility tht led to different response to deficit irrition between furrow nd drip irrition my be reduced wettin in the root zone when wter ws pplied more frequently nd delivered vi pointsource emitters compred to furrows tht pplied wter less frequently tht would enerte deeper penetrtion or infiltrtion of irrition wter so less prone to wter stress. Tble 2: Fruit yield fter deficit irrition. Different letters indicte sttisticl sinificnce t P = 0.05 usin the Tukey s studentized rne (HSD) test. Tretment 2008 weiht (k/tree) 2008 size (/fruit) 2009 weiht (k/tree) 2009 size (/fruit) Furrow, 100% ET 22 123 12 128 Furrow, deficit 22 121b 11 120bc Subsurfce drip,100% ET 21 124 11 126b Subsurfce drip, deficit 18b 115b 10 118c Deficit irrition tretments clerly incresed pech cnopy wter stress shown s hiher CWSI vlues thn in the non-wter stressed 100% ET tretments with both furrow nd subsurfce drip irrition. For exmple, in 2008 similr CWSI vlues (0.5-1.5) were found mon ll irrition tretments t the beinnin of the posthrvest seson (i.e., 1 June, Fiure 2). Wheres the CWSI vlues remined bout 0-0.1 from 1 June to 15 Auust 2008 in the 100$ ET control tretments, the stress index incresed to pproximtely 0.4 for furrow deficit nd 0.3 for drip deficit in July 2008. The comprison showed tht CWSI my be used s n indictor to monitor wter stress when pplyin deficit irrition in peches. The study showed tht deficit irrition is potentil mnement technique for reducin crop wter use t non criticl stes of rowth. The questions remin in the determintion of optimum mount of deficit without cusin yield losses or losses in product qulity, such s fruit size. There is likely crop specific effect on the tolerble deficit but fundmentl physioloicl principles my be pplied to extrpolte to different crop types. The other question is the
504 Wter Resources Mnement VI 0.6 0.5 0.4 Furrow, 100%ET Furrow, deficit Subsurfce drip, 100% ET Subsurfce drip, deficit CWSI 0.3 0.2 0.1 0.0-0.1 6/1 6/16 7/1 7/16 7/31 8/15 2008 dte Fiure 2: Dily crop wter stress index (CWSI) clculted for 1300 hour pcific stndrd time in 2008 of both non-deficit nd deficit irrition tretments. timin for pplyin deficit irrition. For some crops the timin could be criticl in minimizin risks in yield nd qulity losses. A bsic ssumption for ny deficit irrition is tht soil wter will be replenished some time durin hydroloic cycle such s throuh lre precipittion or mn-mde infiltrtion events. References [1] Chlmers, D.J., Mitchell, P.D. & vn Heek, L., Control of pech tree rowth nd productivity by reulted wter supply, tree density nd summer prunin. Journl of Americn Society of Horticulturl Science, 106, pp. 307-312, 1981. [2] Willims, L.E., Dokoozlin, N.K. & Wmple, R., Grpe. Hndbook of Environmentl Physioloy of Fruit Crops, eds. B. Schffer & P.C. Andersen, CRC Press, Inc., Bco Rton, FL, 1994. [3] Brvdo, B. & Nor, A., Effect of wter reime on productivity nd qulity of fruit nd wine. Act Hort, 27, pp. 15-26, 1996. [4] Johnson, S.R. & Hndley, D.F., Usin wter stress to control veettive rowth nd productivity of temperte fruit trees. HortScience, 35, pp. 1048-1050, 2000. [5] Goldhmer, D.A., Fereres, E., Mt, M., Giron, J. & Cohen, M., Sensitivity of continuous nd discrete plnt nd soil wter sttus monitorin in pech trees subjected to deficit irrition. Journl of Americn Society of Horticulturl Science, 124, pp. 437-444, 1999.
Wter Resources Mnement VI 505 [6] Jckson, R.D., Idso, S.B., Reinto, R.J. & Pinter, Jr., P.J., Cnopy temperture s crop wter stress indictor. Wter Resource Reserch, 17, pp. 1133-1138, 1981. [7] Jckson, R.D., Cnopy temperture nd crop wter stress. Advnces in Irrition, 1, pp. 43-85, 1982. [8] Glenn, D.M., Worthinton, J.W., Welker, W.V. & McFrlnd, M.J., Estimtion of pech tree wter use usin infrred thermometry. Journl of Americn Society of Horticulturl Science, 114, pp. 737-741, 1989. [9] Moller, M., Alchntis, V., Cohen, Y., Meron, M., Tsipris, J., Nor, A., Ostrovsky, V., Sprintsin, M. & Cohen, S., Use of therml nd visible imery for estimtin crop wter sttus of irrited rpevine. Journl of Experimentl Botny, 58, pp. 827-838, 2007. [10] Sdler, E.J., Cmp, C.R., Evns, D.E. & Millen, J.A., Corn cnopy temperture mesured with movin infrred thermometer rry. Trnsctions of Americn Society of Ariculturl Enineers, 45, pp. 581-591, 2002. [11] Wnjur, D.F. & Upchurch, D.R., Accountin for humidity in cnopytemperture-controlled irrition schedulin. Ariculturl Wter Mnement, 34, pp. 217-231, 1997. [12] Cmpbell, G.S. & Normn, J.M., An Introduction to Environmentl Biophysics. 2 nd Edition. Spriner, New York, NY, 1998.