Assessment of yield and water use efficiency of durum wheat as affected by irrigation practices and

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1 IOSR Journl Of Environmentl Science, Toxicology And Food Technology (IOSR-JESTFT) e-issn: 9-,p- ISSN: Volume 7, Issue (Nov. - Dec. ), PP -9 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd soil properties in the irrigted re of oued rmel in Tunisi Smi Bhouri Khil, Bouthein Douh, Amel Mguidiche, Mohsen Mnsour, Abdelhmid Boujelben (Higher Agronomic Institute of Chott Mriem. BP 7, Chott Mriem, Sousse. Tunisi) (Regionl Reserch Center in Horticulture nd Orgnic Frming, BP.7,, Chott Mriem, Sousse, Tunisi) Abstrct: This work ims to study the impct of totl vilble soil wter in the root zone (TAW) on the reltion between irrigtion regime nd wter use efficiency of durum whet (Triticum durum Desf. Vr. Krim.) cultivr in the pedoclimtic conditions of the irrigted re of Oued Rmel in Tunisi. After clibrtion, STICS model ws used to simulte effects of two irrigtion scenrios on wter use efficiency of durum whet over -yer period with regrd to frmers irrigtion prctices in the study re. To crry out the study, three types of soil in the Oued rmel irrigtion scheme were chosen on the bsis of their TAW. Two scenrios of irrigtion scheduling were designed through the STICS model: (i) irrigtion ws scheduled when % of the TAW ws depleted (I); (ii) irrigtion ws scheduled when % of the TAW ws depleted (I). Results showed tht lowest vlues of grin yield were obtined in soil hving low TAW s consequence of frequent wter stress occurring during the reproductive stge of whet. The highest vlues of WUE, s determined t grin nd biomss bsis (WUE g nd WUE bio indexes), were obtined when irrigtion ws scheduled t % of the TAW depletion. In I nd I scenrios, highest WUEg, verging respectively. nd. kg m - ws obtined in soil hving high TAW. As noticed for WUEg, highest vlues of WUE bio were registred in soil hving high TAW. Keywords: crop model, durum whet, irrigtion, wter use efficiency, I. INTRODUCTION In Tunisi, cerel yields re subject to significnt fluctution, given the internnul vribility of rinfll, in ddition to sesonl moisture deficits tht my previl, even during wet yer []. Obtining high yields of cerels require, in ddition to chemicl tretments, irrigtion nd use of minerl fertilizers [], [], [] []. However, in Tunisi, s in countries with semi-rid climte, shortge of wter is ever one of the min limittions for griculturl development []. Reserch on better use of vilble rinfll nd the interctions between effects of soil, nd field mngement on cerel production is required. Scientists should provide technicl informtion to guide frmers nd policy mkers in mking decisions tht optimize the dul objectives of high crop yield nd low environmentl degrdtion [7]. Thus, Cerels occupy plce in the primry griculturl reserch progrms in Tunisi. This plce is prticulrly importnt s the country wnts to chieve stble grin production in prticulr for durum whet [8]. Fced with demogrphic chnge, the frgility of the griculturl sector nd the scrcity of wter resources, it is cler tht the chllenge is to mximize the crop wter use efficiency [9]. Wter use efficiency is useful indictor for quntifying the impct of irrigtion scheduling decisions with regrd to wter mngement []. It hs been shown tht the vribility observed in determining wter use efficiency, my be lrgely ttributed to the wter regime pplied []; []; []; [];[9]. However, [] showed tht, when providing opertionl suggestions to optimize irrigtion mngement, the impct of climte nd of soil properties should ttentively be considered since they cn provide certin mount of settlements. In the lst yers, crop growth models hve been widely used s n importnt tool to investigte the responses of crops nd vrieties in different pedoclimtic conditions []. Crop growth models cn be used s tool for incresing wter productivity with pproprite irrigtion mngement []. Simultion models, driven by dily climtic dt, cn be used to predict the impct of long-term climte vribility on the probbility of success of rnge of crop, wter nd soil mngement strtegies thus providing n opportunity of ccelerted lerning compred with the trditionl multi-loction, multi-sesonl nd multi-fctoril field trils []. The potentils nd limits of dynmic simultion models s predictive tools hve been discussed [];[7]; [8], concluding tht crop modeling could provide unique dvntges in severl situtions [9]. In this work, STICS model [] ws clibrted with the objective of nlyzing the combined effects of irrigtion scheduling nd the soil totl vilble wter in the root zone (TAW) on yield nd wter use efficiency of durum whet in the pedoclimtic conditions of the irrigted re of Oued Rmel in Tunisi. Pge

2 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd II. MATERIALS AND METHODS.. The study re The nlysis hs been chieved on the Oued Rmel irrigtion scheme ( N- E) locted in Northestern prt of Tunisi. The scheme covers n irrigted re of bout 77 h. The Oued rmel scheme is supplied by the Oued Rmel dm, locted in dominnt position with respect to the served re. Its reservoir hs totl cpcity of 7 Mm. The overll mount of wter withdrwn from the Oued Rmel reservoir for irrigtion purpose vries from Mm to Mm sincce nnul distribution of precipittion is very irregulr. Wter is distributed to frmers by mens of lrge-scle pressurized distribution system, operted by locl Wter Users Assocition. The irrigtion delivery service usully strts from mid October nd lsts up to the end of June. Freqeuncy nd mount of wter delivered depends on the dm wter level. The dominnt crops re fruit trees nd cerels, minly durum whet. Whet is generlly sown between mid November nd mid December, depending on climtic conditions nd the strt of the rinfll seson Figure. Loction of the study re In the study re, the climte is typiclly Mediterrnen with hot-dry summers nd mild-riny winters. According to long term wether dt (98-), mximum monthly tempertures rnge between nd C nd minimum monthly temperture vry from 7 to C. Men reltive humidity vry from % to 7%. Monthly rinfll rnges between nd 8 mm Tble. Long term men (98- ) meteorologicl dt in the study re (source: Ntionl Meteorologicl Institute of Tunisi) Averge of temperture ( C) Men reltive wind speed Tmx Tmin humidity (%) (m.s - ) Jnury Februry Mrch April My June July....8 August September Otober November December Pge

3 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd (mm) monthly totl of precipittion monthly men temperture ( C) jnury februry mrch pril my june july ugust september october november december Figure. Long term men monthly rinfll distribution nd men ir temperture in the study re. To crry out the study, three types of soil (S, S nd S) in the Oued rmel irrigtion scheme were chosen on the bsis of their vilble soil wter in the root zone (TAW) nd their significnt representtiveness in the region. According to [], these soils show contrsting chrcteristics in terms of totl vilble soil wter in the root zone. Tbles, nd summrize the min chrcteristics of these soils. Soil properties Tble : min chrcteristics of the soil S depth Cly (%) 9 8 Snd (%) Silt (%) 9 Apprent density (g.cm - ).... Wter content t field cpcity (% in volume) Wter content t wilting point (% in volume) 7 7 Totl vilble wter in the soil depth explored by the 8 root zone (mm) Tble : min chrcteristics of the soil S Soil properties depth Cly (%) 9 7 Snd (%) Silt (%) 8 Apprent density (g.cm - )... Wter content t field cpcity (% in volume) Wter content t wilting point (% in volume) Totl vilble wter in the soil depth explored by the root zone (mm) Pge

4 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd Tble : min chrcteristics of the soil S depth Soil properties Cly (%) Snd (%) Silt (%) Apprent density (g.cm - )... Wter content t field cpcity (% in volume) Wter content t wilting point (% in volume) Totl vilble wter in the soil depth explored by the root zone (mm) 7 The TAW describes the vilble wter storge in the soil which my be exploited by the root system. It is defined s the difference between the soil wter contents t field cpcity nd t wilting point, multiplied by the depth of the root system []. The wter content t field cpcity nd t wilting point depends on the specific physicl properties of the soil, especilly its texture. The soil depth which my be explored by the root system is specific chrcteristic of ech cultivted species []. As for durum whet, [] proved tht the soil depth explored by the root system is not deeper thn m... Model description STICS (Simulteur Multidisciplinire des Cultures Stndrds), hs been developed since 99 t INRA (Frnce) in collbortion with other reserch or professionl institutes []. From the chrcteriztion of climte, soil, species nd crop mngement, it computes output vribles relted to yield in terms of quntity nd qulity, environment in terms of dringe nd nitrte leching, nd to soil chrcteristics evolution under cropping system []. STICS is widely used in lot of gro-environmentl contexts []; [7]; [8]. It ws retined in this study s it showed wider scope, serving t the sme time for reserch nd mngement objectives. In ddition, some tests crried out in the South of Frnce showed tht the STICS model correctly simulted winter whet crop behviour under wter shortge conditions [9]. The model is composed of number of modules (see figure ). There re modules tht del with: i) the physiology of the boveground plnt prts, ii) the interctions between the crop mngement nd the soil-crop system, iii) the micro-climte, nd iv) the interctions between soil nd subsurfce plnt prts [] 7.8 Figure. Overview of the model system nd its components [] The model requires informtion bout initil nd permnent conditions of soil, plnt functioning nd crop mngement nd is driven by dily climtic dt (solr rdition, minimum nd mximum temperture, precipittion nd reference evpotrnspirtion) []. STICS simultes the crop growth from sowing to hrvest, focusing on the evolution of the LAI t few selected vegettive stges []. Crop growth is driven by the plnt crbon ccumultion []: solr rdition intercepted by the folige nd then trnsformed into boveground biomss tht is directed to the hrvested orgns during the finl phse of the crop cycle. Dily ccumultion of boveground biomss is function of the intercepted rdition ccording to prbolic lw involving the mximl rdition use efficiency (RUE) []. A more detiled description of the model, its structure nd interlinkges is given in [], []. 8 Pge

5 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd.. Model evlution Model evlution is n essentil step in the modelling process becuse it indictes if the implementtion of the clcultions involved reproduces the conceptul model of the system to be simulted (model relibility) nd the level of ccurcy of the model in reproducing the ctul system (model usefulness) []. Model evlution includes ny ction in which the goodness of mthemticl model is estblished [], []. The topic of model evlution hs long ttrcted considerble debte mongst members of the scientific community. Much debte hs stressed over the mening of terms such s testing, vlidtion, verifiction nd clibrtion s prt of the process collectively referred to s evlution []. Model clibrtion could be defined s the estimtion of some model prmeters by fitting the overll model to field dt []. Prmeter estimtion for complex process models used in gronomy or the environmentl sciences is importnt, becuse it is mjor determinnt of model predictive power, nd difficult, becuse the models nd ssocited dt re complex []. A dtbse from 8 experiments conducted on durum whet (Triticum durum Desf. Vr. Krim.) cultivr ws used to evlute nd clibrte the model. As shown in tbles nd, the dt sets for these experiments re chrcterized by vribility of loction, soil chrcteristics nd crop mngement. Since the cultivtion prctices ffect the development, growth nd grin yield. The model will be evluted in vrious conditions, Tble. Some mngement prctices crried out during the experiments used for model vlidtion Experiments were crried out in Tunis ( 8 N- E) during nd growing sesons, Nbeul ( 'N- 'E) during growing seson nd Bizerte (7 ' N-9 8' E) during growing seson. The cmpigns of mesures during the trils hve concerned phenologicl stges, bove-ground biomss, finl grin yield nd soil wter content. Experiments from to hve been described by [7]. Experiments nd hve been described in detil by [8]; while experiments 7 nd 8 hve been described by [9]. Tble. Men chrcteristics of the soils observed t the experimentl sites experiment Experiment Loction Sowing dte clibrtion Irrigtion Fertiliztion (mm) (kg.h - ) Nbeul //99 //99 none Nbeul //99 //99 none Nbeul //99 //99 none none Nbeul //99 //99 vlidtion Bizerte //998 //999 8 Tunis 7//998 //999 7 Tunis //99 //99 none 8 Tunis //99 9//99 none soil depth (cm) Seed number.m - Hrvest dte Cly (%) Snd (%) Silt (%) Apprent density (g.cm - ) Wter content t field cpcity (% in volume) Wter content t wilting point (% in volume) experiments from to experiment.7 experiment 7. experiment 7. experiment 8. 7 STICS ws run fter prepring the input dt files consist of meteorologicl dt, irrigtion, plnt, nd soil informtion for the eight experiments. Model evlution ws conducted using root men squre of error (RMSE), model efficiency (ME), coefficient of determintion (R ) nd men Biis (MB) criterions obtined s follows: 9 Pge

6 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd ( )( ) [ ( ) ][ ( ) ] () ( ) () () ( ) ( () ) Where Yi is the predicted vrible, Xi is the observed vlue, is the predicted men, is the mesured men, nd n is the number of observtion. R represents the proportion of vrition in the smple dt tht is explined by the regression model. It is only n estimte of the proportion of vrition in the popultion tht is explined by the regression model []. Prctitioners would be dvised to void selecting model bsed solely on the criterion of observing high R vlue. This is especilly true when mny terms re included in model to fit reltively smll number of observtions []. The RMSE indictes the error of prediction of the model by giving more weight to high errors. A low vlue of RMSE mens good prediction bility of the model. Also, ME rnges from negtive infinity to positive ; the closer to, the more robust the model. RMSE provides quntittive estimtes of the devition of modelled outcomes from mesurements []. [], likewise, indicted RMSE s stble sttistics. The modelling efficiency sttistic [], interpreted s the proportion of vrition explined by the model, hs been extensively used in plnt nd hydrology models [], [], nd cn certinly be used in biologicl nd ecologicl models []. Moreover, visul comprison of modelled nd mesured dt, nd experience-bsed judgement on the prt of the modeller hve been deemed importnt by reserchers for ssessing model vlidity nd pplicbility in decision mking []. After clibrtion the model ws used to ssess the frmer s irrigtion in durum whet cultivr (Triticum durum Desf. Vr. Krim.) compred to rinfed system in the study re. In fct, frmers generlly irrigte winter whet one time t sowing. Usully, the mount of irrigtion wter pplied is equl to mm. Fertilizer (mmonium nitrte.%) is generlly pplied t rte of kg.h-. Simultions were performed yer by yer during the 98 period t the three identified soils, under experimentl neutrlity (sme sowing dte nd fertilistion). Precipittion ws obtined from recorded mesurements on the test site itself while other climte dt were documented using records from the nerby Oued Souhil wether sttion ( km wy). Collected dt in this study were nlyzed nd exmined sttisticlly using nlysis of vrince (ANOVA) from the Sttisticl Anlysis System (SPSS 7. for Windows) (SPSS inc., Chicgo, IL, USA). Mens were compred by the SNK Test t the % level of significnce.. Wter use efficiency The term wter use efficiency origintes in the economic concept of productivity. Productivity mesures the sme mount of ny given resource tht must be expended to produce one unit of ny goods or service [7]. The WUE terms re presented s non-dimensionl vlues nd they do not represent n output/input rtio of only one entity. In fct, they describe the processes in which wter is consumed nd/or used to produce new entities (e.g. biomss, yield, etc) [8]. Some uthors dopt it to express the wter productivity of the irrigtion wter [9]. Excluding experimentl errors relted to the determintion of yield nd ET, the vribility in determining WUE (Fig. ) cn hve minly three sources: () gro-techniques: wter nd fertilizer pplied to crops nd nlysed in terms of quntity nd qulity; () plnt: differences between species, vriety effects, phenologicl stge sensitivity to wter constrints; () environment: soil nd climte []. Wter use efficiency (WUE) hs been the most widely used prmeter to describe irrigtion effectiveness in terms of crop yield [9]. Two pproches cn be considered to determine wter use efficiency: i) the ecophysiologicl pproch, bsed on the nlysis t given instnt of the reltionship between photosynthesis nd trnspirtion per lef unit re, t the lef scle, crop cnopy scle, nd territoril scle [], ii) the gronomicl pproch bsed on wter consumption nd yield concept []. The time scle considered is the whole vegettive cycle. Eco-physiologicl nd gronomic pproches re relly linked, s recently showed by []. Since the study of de Wit (98), different expressions (WUE, crop wter productivity) hve been proposed nd discussed [], [];; [7]; [8]; [9]; [9]; [];[]. In generl, WUE cn be written s follows []: () () Pge

7 Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd Yield in eqution cn be indicted by two prmeters: () globl dry mtter yield; () mrketble crop yield. In durum whet, the mrketble crop yield is criterion more interesting thn dry mtter. In fct, for species like durum whet, yield cn vry significntly s result of genetic improvement []. Figure. Schemtic overview of the prmeters involved in the determintion of WUE [] Furthermore, to nlyse crop wter use efficiency in reltion with the irrigtion mngement nd soil properties, two indexes hve been proposed: () Where WUEbio= crop wter use efficiency t biomss bsis (kg.m-), WUEg= crop wter use efficiency t grin bsis (kg.m-), Y = grin yield (kg.h-), B= dry mtter t hrvest (kg.h-), ET= sesonl evpotrnspirtion (m.h-) III. Results And Discussion.. Model clibrtion Model clibrtion ws conducted by chnging the crop prmeters nd bsed on the best mtching between simulted nd mesured dry biomss nd grin yield. The initil cultivr prmeters were chosen bsed on defult vlues for the durum whet cultivr nmed Aclou included in the model. The totl number of crop prmeters is very lrge in crop simultion model such s STICS model []. Thus, in some prmeters, the recommended defult vlues by model guidelines were considered. Clibrtion concerned prmeters defining the course of development between two successive stges (stlevmf, stmflx, stlevdrp, stdrpmt) nd the hrvest index growth rte (vitircrbt). The clibrted prmeters vlues were determined by testing rnge of vlues s suggested by []. The selected vlues were those which minimized the difference between simultions nd mesurements. Through repeted simultion runs nd output comprison of simulted versus observed yield nd biomss, set of four conservtive prmeters ws obtined which seemed most pproprite nd gve stisfctory results of situtions simulted (tble 7). () Tble 7. Adjusted model prmeters prmeter Stlevmf Stmflx Stlevdrp stdrpmt definition The sum of development units between the dy of seedling emergence nd the dy of mximum ccelertion in the growth of LAI (degree-dys) sum of development units between the dy of mximum ccelertion in the growth of LAI nd the first dy of mximum LAI (degree-dys) sum of development units between the dy of seedling emergence nd the first dy of seed filling (degree-dys) sum of development units between the first dy of seed filling nd the first dy of seed filling nd physiologicl mturity (degree-dys) Evlution rnge Initil Vlue Vlue fter clibrtion STICS performed with stisfctory precision in terms of whet yield nd biomss. This is confirmed by the sttistics displyed in Tble 8. Vlues of RRMSE, ME, R nd ND indicte tht the clibrted model performed Pge

8 grin yield clculted by STICS (t h - ) dry biomss clculted by STICS (t h - ) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd with stisfctory precision in terms of whet yield nd biomss. According to [9] nd [8], vlues of MB nd ME indicte tht the clibrtion is stisfctory. Furthermore, R ws higher thn the generlly cceptble vlue of. []; []. Tble 8 Sttisticl indices for evluting the performnce of STICS model in predicting grin yield nd dry biomss fter clibrtion grin yield dry biomss RMSE.8.8 RRMSE (%) MB.. ME.7.7 R..8.. Model vlidtion... Grin yield nd dry biomss Generlly, there ws close greement between the mesured nd simulted dry biomss. These qulittive findings re confirmed by the sttistics (figure ). The coefficient of determintion is lrger thn.9, ME is.9 nd RMSE is. t.h - representing % of the verge observed vlue of dry biomss. Furthermore, the simultion is considered good s the normlized RMSE is greter thn % nd less thn % [] Figure. Comprison of simulted nd mesured dry mtter using vlidtion dt set Figure shows the comprison of the simulted nd observed grin yield. RMSE ws. t.h which represented % of the verge observed mesured yield nd MB ws.8. According to [] nd [9], these vlues indicte resonble greement between mesured nd simulted yield R² =.97 8 mesured dry biomss (t h - ) R² =.8 8 mesured grin yield (t h - ) Figure. Comprison of simulted nd mesured grin yield using vlidtion dt set... soil wter content Figure 7 shows the comprison of the simulted nd observed soil wter content (SWC). We notice tht the performnce of STICS is stisfctory s the coefficient of determintion is greter thn. []; []. Comprtive nlyses of the observed nd simulted SWC hd ME of.7, nd MB of.. This highlights comprtively good fit between the observed nd the simulted results, s [8] nd [9] consider tht simultion is cceptble if ME is greter thn. nd MB is lower thn.. The good greement between mesured nd Pge

9 grin yield (t.h - ) soil wter content clculted by STICS (mm) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd simulted is lso reflected in the RMSE vlue which represents % of the verge SWC observed vlue []. These results show the bility of STICS to simulte SWC under vrious irrigtion regimes. R² =,8 mesured soil wter content (mm) Figure 7. Comprison of simulted nd mesured soil wter content These results prove the bility of STICS to study the effect of loction, soil type nd irrigtion mngement on crop production under rinfed nd irrigted griculture. The ptitude of the STICS model in predicting yield nd biomss, in Mediterrnen environment, is therefore cceptble.. Model ppliction... Grin yield Grin yield ws incresed by incresed irrigtion mounts for the three soils. Figure 8 indictes tht I nd I resulted, in higher grin yield s compred to frmers irrigtion prctice. Incresed yield with incresed irrigtion mounts shows positive effect of irrigtion on grin yield. These results corroborte the findings of severl studies [] [] [7] nd [8]. Higher grin yield obtined in I nd I could be ttributed to higher grin weight with incresing irrigtion [9] [7]. Compred to tretment (I), tretment (I) exhibited between nd % grin yield decrese. 8 I I frmers irrigtion prctice 7 S S S Figure 8. Averge nd stndrd devitions vlues of grin yield, simulted by the STICS model, in the three soils s function of wter mngement Low grin yield obtined for frmers irrigtion prctices could be explined by n intensive wter stress during grin filling period. This contributes highly in reducing grin weight [7]. The highest vlues of grin yield were obtined in soil hving high TAW. In I nd I scenrios, highest grin yield, verging respectively.8 nd. t h - ws obtined in S, while S hd the lowest yield vlue. In S, the reduction in grin yield my be consequence of crop wter stress occurring during the reproductive stge of whet, much more frequent in soil hving low totl vilble wter. It seems tht soil with high TAW cretes more suitble conditions in the root zone re for plnt production. Pge

10 dry mtter yield (t.h - ) grin yield (t.h - ) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd 7 b S S S Figure 9. Averge (98 period) nd stndrd devitions vlues of grin yield, simulted by the STICS model, in the three soils for (I) irrigtion scenrio Figure. Averge (98 period) nd stndrd devitions vlues of grin yield simulted by the STICS model, in the three soils for (I) irrigtion scenrio For I (figure ), whet conducted in S nd S produced in verge respectively nd 7% lower grin yield with regrd to S. While for I (fig.), S nd S resulted respectively in lmost nd % reduction in grin yield respect to S. No sttisticl difference ws found in grin yield between S nd S for the two irrigtion scenrios. This could be explined by the fct tht wter stress conditions, during criticl stge of whet, ffected yield similrly in plnts conducted in S nd S... Dry mtter yield Figure indictes tht I nd I resulted, in higher totl dry mter t hrvest s compred to Frmers irrigtion prctice. In the two irrigtion scenrios, dry mtter t hrvest ws incresed, depending on the soil type, from % to % respect to frmers irrigtion prctices. This is in greement with the results reported by [7] who indicted tht biologicl yield ws incresed s irrigtion incresed. 8 8 I I frmers irrigtion prctice S S S Figure. Averge nd stndrd devitions vlues of eril dry mtter t hrvest, simulted by the STICS model, in the three soils s function of wter mngement Generlly, lowest vlues of dry mtter t hrvest were recorded in the soil with low TAW vlue. Moreover, highest difference in bove ground biomss, resulting from the two irrigtion scenrios respect to the frmers Pge

11 WUEbio (kg.m-) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd irrigtion prctices, ws obtined in soil with lowest TAW. Indeed, in S, the biologicl yield incresed by 8% on verge, moving from frmer s irrigtion prctice to I tretment. While in S hving highest TAW, the dry mtter vlues incresed by % on verge moving from frmer s irrigtion prctice to I tretment.. For I (figure ), highest vlues were obtined in soil hving high TAW with. t.h -. While, for I (figure ), verge eril dry mtter, ws.97,.8 nd 9.89 t.h - respectively in S, S nd S. Figure. Averge (98 period) nd stndrd devitions vlues of dry mtter yield simulted by the STICS model for I scenrio in the three soils Figure. Averge (98 period) nd stndrd devition vlues of dry mtter yield simulted by the STICS model for I irrigtion scenrio in the three soils.. Wter use efficiency t biomss bsis Figure shows the effects of different irrigtion tretments on crop wter use efficiency in the three soils. It indictes tht I nd I resulted, in higher WUE bio s compred to frmers irrigtion prctice. In S, the WUE bio vlues incresed by 7% (from. to.97 kg.m - ) on verge, moving from frmer s irrigtion prctice to I. WUE vlues were therefore higher thn those observed in the other two soils. While in S hving lowest TAW, the WUE bio vlues incresed by % on verge moving from to frmer s irrigtion prctice to I. WUE bio vlues were therefore lower thn those observed in the other two soils. This confirms the findings of [7] showing tht wter use efficiency incresed with incresing wter supply. In I nd I scenrios, highest WUE bio, verging respectively.7 nd.97 kg m - ws obtined in S, while S hd the lowest WUE bio vlue. For I (figure ), whet conducted in S nd S produced in verge respectively nd 7% lower WUE bio with regrd to S. While for I (figure ), S nd S resulted respectively in lmost nd % reduction in WUE bio respect to S. No sttisticl difference ws found in grin yield between S nd S for the two irrigtion scenrios. I I frmers irrigtion prctice S S S Figure. Averge nd stndrd devitions vlues of WUE bio simulted by STICS in the three soils s function of wter mngement Pge

12 WUEg (kg.m-) WUE bio (kg.m - ) WUE bio (kg.m - ) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd b S S S Figure. Averge vlues of WUE bio simulted by STICS in the three soils for I irrigtion scenrio b S S S Figure. Averge vlues of WUE bio simulted by STICS in the three soils for I irrigtion scenrio.. Wter use efficiency t grin bsis Figure 7 show the effects of irrigtion mngement on crop wter use efficiency s function of irrigtion mngement. As noticed for WUE bio, highest vlues of WUE g were registred in I nd I. Averge WUE g, for I, ws.,.8 nd.9 kg.m - respectively in S, S nd S (figure 9). These vlues re higher thn verge wter use efficiency observed for the whole Mediterrnen region [7]. Moreover when compring effects of irrigtion on crop wter use efficiency, it should be kept in mind tht the generic term irrigted crops cn include, in relity, extremely different situtions of plnt wter supply []. I I frmers irrigtion prctice... S S S Figure 7. Averge nd stndrd devitions vlues of WUE g simulted by STICS in the three soils s function of wter mngement Figure 8 showed tht, in I, WUE g vried ccording to soil type. Highest WUE g ws obtined in soil hving high TAW with. kg.m - nd the lowest one ws found in soil with lowest TAW with.8 kg.m -. No sttisticl difference ws found in grin yield between S nd S for the two irrigtion scenrios. This could be explined by the fct tht wter stress conditions, during criticl stge of whet, ffected yield similrly in plnts conducted in S nd S. Pge

13 WUEg (kg.m-) WUEg (kg.m-) Assessment of yield nd wter use efficiency of durum whet s ffected by irrigtion prctices nd. b.. S S S Figure 8. Averge vlues of WUE g simulted by STICS in the three soils for I irrigtion scenrio. b.. S S S Figure 9. Averge vlues of WUE g simulted by STICS in the three soils for I irrigtion scenrio Generlly, lowest vlues of WUEg were recorded in the soil with low TAW vlue. This is consistent with the findings of []. The reduction in WUEg vlues, my be consequence of more intense wter deficit during criticl stges, s suggested by []. In order to verify this hypothesis, the vlues of stomtl wter stress indice (SWFAC) clculted by the STICS model, during vegettive nd reproductive stges, s the rtio between ctul trnspirtion nd mximum trnspirtion were summrized in Tble 9. It should be noticed tht vlues of SWFAC rnge between (no stress) nd (intense wter stress). Tble 9. Averge vlues of the stress index (SWFAC), simulted by the STICS model in the three soils s function of wter mngement I I S S S S S S Vegettive stge Reproductive stge In I nd I irrigtion scenrios, the wter stress index shows close vlues in the three soils during the vegettive stge. Contrrily, this index is weker during the reproductive stge. IV. Conclusion In this study the impct of totl vilble soil wter in the root zone on the reltion between wter regime nd WUE of durum whet cultivr ws exmined. After its vlidtion, the STICS model ws retined to simulte the vribles required for the study. The results of STICS evlution indicted tht this model performed with stisfctory precision in terms of whet yield nd biomss. This study highlighted the existence of consistency nd convergence in the results obtined with the grin yield nd WUE indexes (WUE g nd WUE bio ). It ws determined tht totl vilble wter in the root zone my significntly modulte the response of whet wter use efficiency, performed through the WUE g nd WUE bio indexes, to the wter regime. According to the reserch results, it ws found tht irrigtion t sowing hd positive effect on crop wter use efficiency. Moreover, highest difference in WUE ws obtined in soil with highest TAW. Further studies should be conducted, tking into ccount the effects of vrious irrigtion wter schedules, in terms of crop wter use efficiency, in soils hving different properties. 7 Pge

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