Growth and Yield of Six Rice Cultivars under Three Water-saving Cultivations

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1 Plnt Production Science ISSN: X (Print) (Online) Journl homepge: Growth nd Yield of Six Rice Cultivrs under Three Wter-sving Cultivtions Noki Mtsuo & Toshihiro Mochizuki To cite this rticle: Noki Mtsuo & Toshihiro Mochizuki (29) Growth nd Yield of Six Rice Cultivrs under Three Wter-sving Cultivtions, Plnt Production Science, 12:4, , DOI: /pps To link to this rticle: 29 Tylor & Frncis Published online: 3 Dec 215. Submit your rticle to this journl Article views: 93 View relted rticles Citing rticles: 21 View citing rticles Full Terms & Conditions of ccess nd use cn be found t Downlod by: [ ] Dte: 7 July 216, At: 2:19

2 Plnt Prod. Sci. 12(4) : (29) Growth nd Yield of Six Rice Cultivrs under Three Wter-sving Cultivtions Noki Mtsuo 1 nd Toshihiro Mochizuki 2 ( 1 Grdute School of Bioresource nd Bioenvironmentl Sciences, Kyushu University, Ksuygun, Fukuok , Jpn; 2 Fculty of Agriculture, Kyushu University, Ksuygun, Fukuok , Jpn) Downloded by [ ] t 2:19 7 July 216 Abstrct : We evluted the genotypic differences in growth, grin yield, nd wter productivity of six rice (Oryz stiv L.) cultivrs from different griculturl ecotypes under four cultivtion conditions: continuously flooded pddy (CF), lternte wetting nd drying system (AWD) in pddy field, nd erobic rice systems in which irrigtion wter ws pplied when soil moisture tension t 15 cm depth reched 15 kp (A15) nd 3 kp (A3). In three of the six cultivrs, we lso mesured bleeding rte nd predwn lef wter potentil (LWP) to determine root ctivity nd plnt wter sttus. Soil wter potentil (SWP) in the root zone verged 1.3 kp t 15 cm in AWD, -5.5 nd -6.6 kp t 15 nd 35 cm, respectively, in A15, nd 9.1 nd 7.6 kp t 15 nd 35 cm, respectively, in A3. The improved lowlnd cultivr, Nipponbre gve the highest yield in CF nd AWD. The improved uplnd cultivr, UPLRi-7, nd the trditionl uplnd cultivr, Sensho gve the highest yield in A15 nd A3, respectively. The yields of trditionl uplnd cultivrs, Sensho nd Beodien in A3 were not lower thn the yields in CF. However, the yields of the improved lowlnd cultivrs, Koshihikri nd Nipponbre, were mrkedly lower in A15 nd A3. Totl wter input ws 2145 mm in CF, 176 mm in AWD, 84 mm in A15, nd 627 mm in A3. The wter productivity of uplnd rice cultivrs in erobic plots ws 2.2 to 3.6 times higher thn tht in CF, while those of lowlnd cultivrs in erobic plots were lower thn those in CF. The bleeding rte of Koshihikri ws lower in A15 nd A3 thn in CF nd AWD, nd its LWP ws significntly lower in A15 nd A3 thn in CF nd AWD, but Sensho nd Beodien showed no differences mong the four cultivtion conditions. We conclude tht erobic rice systems re promising technologies for frmers who lck ccess to enough wter to grow flooded lowlnd rice. However, lowlnd cultivrs showed severe growth nd yield reductions under erobic soil conditions. This might result from poor root systems nd poor root function, which limits wter bsorption nd thus decreses LWP. More reserch on the morphologicl nd physiologicl trits under erobic rice systems is needed. Key words : Grin yield, Lowlnd rice, Uplnd rice, Wter productivity, Wter-sving cultivtion. Rice is the mjor stple food in Asi, where bout 92% of the world s rice is produced nd consumed (IRRI, 22). However, the qulity of irrigtion wter is being reduced by chemicl pollution nd sliniztion, nd the wter resource itself is being depleted by flling groundwter tbles, silting of reservoirs, nd incresed competition from urbn nd industril uses (Guerr et l., 1998). We must grow more rice with less wter to sustin the continuing popultion growth (Guerr et l., 1998; Tuong et l., 25). Field techniques to sve irrigtion wter include direct (dry) sowing, keeping soils t sturtion, nd lternte wetting nd drying systems (AWD). Reserchers in Chin found tht AWD significntly reduced wter input nd incresed yields (Wu, 1999; Li, 21). Boumn nd Tuong (21) reported tht AWD in the tropics reduced wter input, but yields usully declined when the soil wter potentil (SWP) during the non-submerged phse reched vlues between 1 nd 4 kp. However, it is uncler how much wter input cn be sved without plnt growth nd grin yield penlty in AWD. A new development in wter-sving technologies is erobic rice systems (Boumn 21; Boumn et l., 25), in which fields remin unsturted throughout the seson. Mny studies hve focused on drought resistnce in rice under temporl wter stress (Turner, 1986; Ludlow nd Muchow, 199; Fuki nd Cooper, 1995; Jckson et l., 1996; Cooper, 1999; Lfitte et l., 23). However, it is uncler whether effective trits for drought resistnce to temporl wter stress re useful for erobic rice systems or not. The trget environments of erobic rice systems re irrigted lowlnds where wter is insufficient to keep fields flooded, nd fvorble uplnds with ccess to supplementry irrigtion in which plnts re not imposed by severe wter stress, nd yields of 7% 8% of high-input flooded rice re chievble (Belder Received 5 June 28. Accepted 9 April 29. Corresponding uthor: N. Mtsuo (n_mtsuo@frm.kyushu-u.c.jp, fx ). Abbrevitions : A15, erobic rice system 15; A3, erobic rice system 3; AWD, lternte wetting nd drying system; CF, continuously flooded pddy; DAS, dys fter sowing; DAT, dys fter trnsplnting; LAI, lef re index; LWP, predwn lef wter potentil; RLD, root length density; RWD, root weight density; SWP, soil wter potentil.

3 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 515 Tble 1. Bckground of plnt mterils used in this study. Nme Group Origin Ecosystem History Sensho Jponic Jpn Uplnd Trditionl Htminorimochi Jponic Jpn Uplnd Improved Beodien Indic Vietnm Uplnd Trditionl UPLRi-7 Indic Philippines Uplnd Improved Koshihikri Jponic Jpn Lowlnd Improved Nipponbre Jponic Jpn Lowlnd Improved Downloded by [ ] t 2:19 7 July 216 et l., 25). Irrigtion cn be pplied by flush or furrow irrigtion or by sprinklers, nd ims t keeping the soil wet but not flooded or sturted. In prctice, irrigtion is pplied to bring the soil wter content to field cpcity fter it hs reched certin lower threshold level, such s 3 kp (Boumn et l., 25; Peng et l., 26). Therefore, soil moisture conditions in erobic rice systems should be quite different from those of temporl wter deficit under drought uplnd environments. The potentil wter svings when rice cn be grown s n uplnd crop re lrge, especilly on soils with high seepge nd percoltion rtes (Boumn et l., 21). In ddition, evportion decreses, since there is no wter surfce, nd the lrge mount of wter used for lnd preprtion is eliminted. In Asi, uplnd rice is lredy grown erobiclly with miniml input in uplnd fields, but mostly s low-yielding subsistence crop to give stble yield under the dverse environmentl conditions (Lffite et l., 22). Uplnd rice cultivrs hve droughtresistnt chrcteristics (e.g., deep root nd high root-shoot rtio) to void plnt wter shortge by extrcting wter with deep or extensive root systems, but hve low yield potentil nd tend to lodge under high levels of fertilizer nd irrigtion. Highyielding lowlnd rice cultivrs grown in erobic soil with supplementl irrigtion hve been shown to sve wter, but t severe yield penlty (Blckwell et l., 1985; Wescott nd Vines, 1986; McCuley, 199). To chieve high yield under irrigted erobic conditions, we need new cultivrs tht hve the drought-resistnt chrcteristics of uplnd cultivrs nd the high yielding chrcteristics of lowlnd cultivrs (Lffite et l., 22). In Chin, breeders hve produced erobic rice cultivrs with n estimted yield potentil of 6 7 t h -1, nd reserch is under wy to study the wteruse nd yield potentil of these cultivrs under welldefined hydrologicl conditions (Yng et l., 25). In the Philippines, De Dtt et l. (1973) grew the lowlnd cultivr, IR2, in erobic soil with furrow irrigtion. Aerobic culture sved 45% of wter input compred with flooded conditions, but yield fell from bout 8 t h -1 under flooded conditions to 3.4 t h -1 under erobic conditions. In Jpn, Kto et l. (26) reported genotypic differences under erobic conditions. However, there is little informtion on the difference in crop performnce between erobic nd flooded conditions nd on the optimum threshold for reirrigtion when cultivrs tht re dpted to erobic conditions re grown. Furthermore, the physiologicl bsis of the yield gp between erobic nd flooded rice hs not been studied extensively. Such informtion is crucil to identify the morphologicl nd physiologicl trits for the selection nd breeding of high-yielding erobic rice cultivrs. In the present study, we evluted the growth nd yield response of six cultivrs from different griculturl ecotypes (two jponic uplnd, two indic uplnd, nd two jponic lowlnd) to different wtersving cultivtions. The objectives were to determine how much wter could be sved nd to nlyze the genotypic differences in plnt growth, grin yield nd wter productivity. We lso determined the bleeding rte nd predwn lef wter potentil (LWP) of three of these six cultivrs to determine the root ctivity nd plnt wter sttus. Mterils nd Methods 1. Experimentl design All experiments were conducted t the Experimentl Frm of Kyushu University, Fukuok, Jpn (33º 37 N, 13º 27 E) in 26. The soil contined 2.7% cly, 23.2% silt, nd 56.1% snd (cly-lom) in the lowlnd fields nd 21.7% cly, 12.8% silt nd 68.6% snd (sndy cly-lom) in the uplnd fields. Four wter tretments were imposed: continuously flooded pddy (CF); lternte wetting nd drying systems (AWD) in the lowlnd field; nd erobic rice systems where irrigtion wter ws pplied when SWP t 15 cm depth reched 15 kp (A15) nd 3 kp (A3). The decision of irrigtion ws mde bsed on the verge redings of four tensiometers (see below). A rndomized complete design with three replictions ws conducted within tretment. Ech tretment covered 58.2 m 2. Six rice cultivrs (i.e. jponic trditionl uplnd cultivr, Sensho; jponic improved uplnd cultivr, Htminorimochi; indic trditionl uplnd cultivr, Beodien; indic improved uplnd cultivr, UPLRi-7, jponic improved uplnd cultivr, Koshihikri nd Nipponbre; Tble 1) were selected bsed on our previous study (Mtsuo et l., 27), which ssessed

4 516 Plnt Production Science Vol.12, 29 Downloded by [ ] t 2:19 7 July 216 grin yields of 12 rice cultivrs under temporl wter deficit condition round flowering stge. In CF nd AWD, seeds were sown in seed beds on June 1 nd 21-d-old seedlings were trnsplnted t one seedling per hill t spcing of 3 cm 15 cm on 1 July. Plots were puddled 2 d before trnsplnting. In both plots, the wter depth bove soil surfce ws initilly 2 mm. A flsh irrigtion of bout 5 mm depth ws pplied whenever the surfce wter disppered in CF nd SWP t 15 cm depth reched -5 kp in AWD. SWP ws mintined bove -5 kp in AWD, except for 1 wk during the mid-vegettive stge, for mid-seson dringe (Mo, 1993). We instlled plstic sheets down to 6 cm between CF nd AWD to prevent seepge nd wter flow between the plots. Nitrogen fertilizer ws pplied three times: 4 g m -2 s bsl fertilizer 2 d before trnsplnting, 4 g m -2 s topdressing t 25 d fter trnsplnting (DAT), nd 2 g m -2 t 56 DAT. Phosphorus (12 g m -2 ) nd potssium (12 g m -2 ) were lso pplied 2 d before trnsplnting. In erobic rice systems (A15 nd A3), plnts were grown under rinout shelter from sowing to 17 September, when typhoon hit the experimentl site. Becuse there is much precipittion in the summer seson in Jpn, we used the rinout shelter to control the mount of irrigtion wter nd to reproduce the environments of erobic rice systems. The experiment ws crried out without the rinout shelter fter 17 September. Three to four pre-germinted seeds were sown t spcing of 3 cm 15 cm on 19 June. The erobic plots were dry-ploughed nd hrrowed 2 d before sowing. The soil ws irrigted 1 d before sowing (2 mm), nd irrigtion wter of 1 mm ws pplied everydy for the first 2 wk to keep SWP t 15 cm depth bove 1 kp for promoting crop estblishment. Afterwrd, bout 2 mm of wter ws pplied whenever SWP t 15 cm depth reched -15 kp in A15 nd 3 kp in A3. Irrigtion wter ws pplied by line source sprinklers which were plced between every two rows. Seedlings were thinned to one per hill t 21 d fter sowing (DAS). Nutrients were pplied in the sme wy s in CF nd AWD. A combintion of insecticide, herbicide nd mnul weed control ws used to mximize yields in the experiment. 2. Mesurements nd clcultion A wether sttion set up ner the field recorded dily men temperture, rdition, nd rinfll. The mount of irrigtion wter pplied ws mesured with flow meters (RK5S, KOFLOC Co., Ltd, Tokyo, Jpn) connected to the irrigtion hoses. Four guged tensiometers (DIK-3126, Diki Rik Kogyo Co., Ltd, Sitm, Jpn) were instlled t 15 cm depth in AWD nd t 15 nd 35 cm depth in A15 nd A3 for dily mesurement of SWP. The plces where tensiometers were instlled were selected rndomly. The depth of ponded wter in CF nd AWD ws mesured dily by using perforted PVC pipes (inner dimeter, 3 cm; height, 6 cm) instlled down to 4 cm from the soil surfce. Crop smples were tken five times in CF nd AWD (t 21, 53, 65, 84, 17 DAS) nd four times in A15 nd A3 (t 45, 57, 76 nd 99 DAS) to determine totl dry biomss nd lef re index (LAI). Plnts of four hills per repliction were collected t ech smpling. LAI ws determined with lef re meter (AAM- 9, Hyshi Denko Co. Ltd., Tokyo, Jpn). Then, dry biomss ws determined fter oven-drying t 7 C for t lest 3 d. At mturity, plnts of eight hills per repliction were smpled to determine boveground biomss, yield, nd yield components. The number of pnicles per hill ws counted to determine the pnicle number per m 2. Pnicles were hnd-threshed, nd filled spikelets were seprted from unfilled spikelets by submerging them in tp wter. Spikelets per pnicle, grin-filling percentge (1 filled spikelet number per totl spikelet number), nd wter productivity (g grin per kg input wter) were clculted. The grin moisture content within ech plot ws determined with grin moisture tester (Riceter m, Kett Electric lbortory Co. Ltd., Tokyo, Jpn) to convert the smples to 14% moisture content. We mesured the bleeding rte in Sensho, Beodien, nd Koshihikri from 7 to 11 on 14 August in ll plots, becuse bleeding rte hs been used s n index of root ctivity in mny studies (e.g., Ymguchi et l., 1995). One dy before bleeding rte mesurements, irrigtion wter, imposed by the design of irrigtion tretment, ws pplied in ech tretment. Shoots were cut with shrp rzor t height of pproximtely 1 cm from the soil surfce, nd pre-weighed cotton pds were ttched to the cut surfce nd cotton pds were covered with plstic film seled with rubber bnds to protect ginst wter loss. Ech sp smple ws collected for 12 min nd then cotton pds were weighed to determine bleeding rte. Then, we clculted bleeding rte on lef re bsis to nlyze the reltion with the recovery of plnt wter sttus during night. We mesured LWP (3-53) in Sensho, Beodien, nd Koshihikri with dewpoint psychrometer (WP4, Decgon Devices Inc., Pullmn, WA, USA) on 24 August in ll plots. Two fully expnded youngest leves on the min stems were smpled rndomly from ech repliction for mesurement of LWP. One dy before LWP mesurements, irrigtion wter, imposed by the design of irrigtion tretment, ws pplied in ech tretment. Results 1. Wether Tble 2 shows the men monthly wether dt in 26 nd during 1996 to 25. The men monthly temperture ws lower in 26 thn the 1-yr verge

5 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 517 Tble 2. Averge monthly temperture, solr rdition, nd ccumulted totl rinfll from June to November in 26 nd during t the Experimentl Frm of Kyushu University. Men temperture (º C) Solr rdition (MJ m -2 d -1 ) Rinfll (mm) 26 Averge 26 Averge 26 Averge June July August September October November () () 12 (b) Downloded by [ ] t 2:19 7 July 216 Rinfll (mm) Irrigtion (mm) Irrig gtion (mm) (c) (e) Irrig gtion (mm) Irrigtion (mm) (d) Dy of yer Dy of yer Fig. 1. Amount nd timing of irrigtion ppliction in CF (), AWD (b), A15 (c) nd A3 (d), nd rinfll (e). throughout the experiment. Solr rdition ws lower in June nd July nd higher in August, October, nd November in 26 thn the 1-yr verge. Sufficient rin fell in June to September in Hydrologicl conditions Fig. 1 shows the ctul irrigtion nd rin inputs in ll plots. Irrigtion wter ws pplied 25 times in CF, 15 times in AWD, 36 times in A15, nd 25 times in A3. The mount pplied ech time ws smller in A15 nd A3 thn in CF nd AWD nd verge totl mount of irrigted wter ws 1119, 679, 663, nd 486 mm in CF, AWD, A15 nd A3, respectively (Tble 3). The totl mount of input wter ws clculted by including totl mount of irrigted wter nd rinfll nd it ws on verge 2146, 176, 84 nd 627 mm, in CF, AWD, A15 nd A3, respectively. Totl mount of input wter ws 2.5% less in AWD thn in CF, 62.5% less in A15,

6 518 Plnt Production Science Vol.12, 29 Tble 3. Averge sesonl wter inflow in CF, AWD, A15, nd A3. CF AWD A15 A3 Rinfll (mm) Irrigtion (mm) Totl input (mm) Irrigtion rte (%) Totl input rte b (%) The rtio of irrigtion wter in AWD, A15 nd A3 to tht in CF. b The rtio of totl input wter in AWD, A15 nd A3 to tht in CF. Downloded by [ ] t 2:19 7 July 216 epth (mm) De CF AWD Dy of yer Fig. 2. Ponded wter depth in CF nd AWD. Negtive vlues indicte tht the wter surfce is below the soil surfce. nd 7.8% less in A3. The rinout shelter over the erobic plots from sowing to 17 September kept the rin wter inputs smll. The dynmics of the wter tble in CF nd AWD re given in Fig. 2. The wter tble ws nerly lwys t or bove the soil surfce in CF. AWD hd periods of 3-1 d without surfce-ponded wter. Fig. 3 shows SWP t 15 cm in AWD nd tht t 15 nd 35 cm in A15 nd A3. In AWD, SWP t 15 cm styed mostly within -5 kp, but dropped to 3 kp once, when mid-seson dringe ws imposed. In A15, SWP t 15 cm styed mostly within 15 kp, s intended, nd dropped below 15 kp six times. At 35 cm, SWP ws smller thn tht t 15 cm nd fluctuted mostly between nd 1 kp. The mximum vlue recorded ws 33 kp t 15 cm nd 2 kp t 35 cm. In A3, SWP t 15 cm styed mostly within 3 kp nd dropped below 3 kp six times. At 35 cm, the tension ws smller thn tht t 15 cm nd fluctuted mostly between nd 15 kp. The minimum vlue recorded ws 36 kp t 15 cm nd 19 kp t 35 cm. The verge SWP ws 1.3 kp t 15 cm in AWD; 5.5 kp t 15 cm nd 6.6 kp t 35 cm in A15; nd 9.1 kp t 15 cm nd 7.6 kp t 35 cm in A3. 3. Phenology Tble 4 shows the phenology of the crops. The jponic cultivrs hd similr flowering dtes nd growth durtions in ll tretments, differing by 4 to 7 SWP (kp) SWP (kp P) SW WP(kP) Dy of yer () () (b) (c) Fig. 3. Soil wter potentil (SWP) t 15 cm ( ) nd 35 cm ( ) depth in AWD (), A15 (b), nd A3 (c). The men stndrd error of the mesurements ws ± 7 in AWD, ±1.6 in A15, nd ±3. in A3 plots t 15 cm, nd ±1.7 in A15 nd ± 2.2 in A3 plots t 35 cm. SWP in AWD ws mesured only t 15 cm depth. d. However, the flowering dte ws lter nd growth durtion ws longer in indic uplnd cultivrs thn in the jponic cultivrs. Flowering dte in CF nd AWD ws erliest in Koshihikri (23 August), nd it ws 2 d lter in Sensho nd Nipponbre, 4 d lter in Htminorimochi, 16 d lter in UPLRi-7, nd 19 d lter in Beodien. In A15, Sensho nd Htminorimochi hd the erliest flowering dte (3 September), nd it ws 3 d lter in Nipponbre, 6 d lter in Koshihikri, 13 d lter in UPLRi-7, nd 26 d lter in Beodien. In A3, Sensho hd the erliest flowering dte (1 September),

7 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 519 Tble 4. Flowering nd physiologicl mturity dtes of the six rice cultivrs in CF, AWD, A15, nd A3. CF AWD A15 A3 Flowering Sensho 25 August 25 August 3 September 1 September Htminorimochi 27 August 27 August 3 September 2 September Beodien 11 September 11 September 29 September 18 September UPLRi-7 8 September 8 September 16 September 16 September Koshihikri 23 August 23 August 9 September 6 September Nipponbre 25 August 25 August 6 September 5 September Downloded by [ ] t 2:19 7 July 216 Mturity Sensho 13 October 13 October 23 October 19 October Htminorimochi 13 October 13 October 22 October 21 October Beodien 29 October 29 October 5 November 5 November UPLRi-7 26 October 26 October 5 November 5 November Koshihikri 6 October 6 October 24 October 26 October Nipponbre 6 October 8 October 24 October 23 October Growth durtion (dys) Sensho Htminorimochi Beodien UPLRi Koshihikri Nipponbre LAI () Sensho Htminorimochi Beodien UPLRi-7 Koshihikri Nipponbre (b) 2 8 (c) (d) LAI Dy of yer Dy of yer Fig. 4. Lef re index (LAI) of six rice cultivrs in CF (), AWD (b), A15 (c) nd A3 (d). Brs indicte the stndrd error (n = 3).

8 52 Plnt Production Science Vol.12, 29 Bio omss (g m -2 ) () Sensho Htminorimochi Beodien UPLRi-7 Koshihikri Nipponbre (b) Bio omss (g m -2 ) 15 (c) (d) Downloded by [ ] t 2:19 7 July Dy of yer Fig. 5. Shoot dry biomss of six rice cultivrs in CF (), AWD (b), A15 (c) nd A3 (d). Brs indicte the stndrd error (n = 3). nd it ws 1 d lter in Htminorimochi, 4 d lter in Nipponbre, 5 d lter in Koshihikri, 15 d lter in UPLRi-7, nd 17 d lter in Beodien. 4. Crop growth Fig. 4 shows the LAI vlues. In CF, LAI reched mximum of 4 to 5, except for tht of UPLRi-7, which exceeded 6. LAI in indic uplnd cultivrs Beodien nd UPLRi-7 peked lter thn those in jponic cultivrs due to the longer growth durtion. The sme tendency ws seen in AWD. LAIs of the uplnd cultivrs in the erobic plots were the sme s or slightly lower thn those in CF nd AWD, but those of lowlnd cultivrs were mrkedly lower. The biomss ccumultion shows the sme trend s in LAI (Fig. 5). The lowlnd cultivrs, Koshihikri nd Nipponbre, showed significntly lower biomss thn uplnd cultivrs in A15 nd A3. The difference in shoot growth between lowlnd nd uplnd cultivrs were observed fter 57 DAS in erobic plots (t second smpling). 5. Yield components Tble 5 shows the yield components. Lowlnd cultivrs, Koshihikri nd Nipponbre, hd more pnicles per m 2 thn uplnd cultivrs in CF nd AWD. Pnicle numbers were lmost identicl in CF nd AWD. However, they decresed in erobic plots in ll cultivrs, especilly in the lowlnd cultivrs. UPLRi-7 hd the lrgest number of spikelets per pnicle in ll tretments. The spikelet number in Koshihikri ws mrkedly decresed in erobic plots reltive to tht in CF nd AWD, wheres tht of uplnd cultivrs Dy of yer tended to increse in erobic plots. In CF nd AWD, Nipponbre hd the highest percentge of filled grin. In erobic plots, the percentge of filled grin ws mintined in Sensho nd Htminorimochi, incresed in Beodien nd UPLRi-7, nd decresed in Koshihikri nd Nipponbre reltive to those in CF nd AWD. Genotypic differences in grin weight were pprent: Sensho hd the heviest grin weight followed by Beodien in ll tretments. Grin weights of Beodien, UPLRi-7, Koshihikri, nd Nipponbre tended to decrese in erobic plots. 6. Yield nd wter productivity Grin yield nd wter productivity re shown in Tble 6. Although Nipponbre hd the highest grin yield in CF nd AWD, no sttisticlly significnt differences were detected mong cultivrs. Grin yield in AWD ws higher (on verge 13%) thn in CF in ll cultivrs except Sensho. The yields of Koshihikri nd Nipponbre were considerbly reduced in erobic plots. Grin yields of Sensho, Beodien, nd UPLRi-7 were higher in A15 thn in CF. Yields of Htminorimochi nd UPLRi-7 were pproximtely 25% lower in A3 thn in CF, wheres those of Sensho nd Beodien were the sme s in CF. Nipponbre hd the highest wter productivity in CF nd AWD. Averge wter productivity in AWD (.3) ws higher thn tht in CF (.21), probbly owing to lower wter input nd higher yield in AWD thn in CF. In erobic plots, however, the lowlnd cultivrs, Koshihikri nd Nipponbre, hd significntly lower wter productivity thn uplnd cultivrs owing to the considerble yield

9 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 521 Tble 5. Yield components of six rice cultivrs in CF, AWD, A15, nd A3. CF AWD A15 A3 Men Pnicle number (m -2 ) Sensho 258 bc 233 b Htminorimochi 269 b 268 b Beodien 214 bc 22 b UPLRi c 199 b b 178 Koshihikri b 9 b 235 Nipponbre b 125 b 255 Men Downloded by [ ] t 2:19 7 July 216 Spiklet number per pnicle Sensho 96 b 12 b 121 b 127 b 112 Htminorimochi 96 b 96 bc 121 b 114 b 17 Beodien 81 bc 88 bcd 123 b 16 b 1 UPLRi Koshihikri 81 bc 85 cd 59 c 46 c 68 Nipponbre 71 c 73 d 56 c 62 c 65 Men Percentge of filled grin (%) Sensho 53.9 c 55.8 d 63.4 b 56.8 bc 57.5 Htminorimochi 62.2 bc 64.8 c 57.2 b 59.1 bc 6.8 Beodien 75.5 b 75.7 b UPLRi c 62.4 cd 71.4 b 7.8 b 65.6 Koshihikri 58.7 c 68.9 bc 46.4 b 42.5 c 54.1 Nipponbre b 42.3 c 64. Men grins weight (g) Sensho Htminorimochi 24.9 cd 25.4 b 25.1 bc 25.8 bc 25.3 Beodien 28.2 b 28.2 b 26.9 b 27.7 b 27.8 UPLRi c 26.8 b 24.6 cd 23.8 cd 25.3 Koshihikri 24.2 d 24.7 b 22.3 e 21.5 e 23.2 Nipponbre 24.1 d 24.4 b 23. de 23.2 de 23.7 Men Within column for ech prmeter, mens followed by different letters re significntly different t P =.5 ccording to Tukey s test. reduction. In uplnd cultivrs, miniml yield reduction nd low wter input cused 2.2 to 3.6 times higher wter productivity in erobic plots thn in CF. UPLRi-7 (.71) showed the highest wter productivity, followed by Sensho (.66) in A15, nd Sensho (.71) showed the highest wter productivity followed by Beodien nd UPLRi-7 (.6) in A3. 7. Bleeding rte nd LWP No significnt differences in bleeding rte per lef re were observed mong wter regimes in trditionl uplnd cultivrs, Sensho nd Beodien, but significnt differences were observed in Koshihikri (Fig. 6): bleeding rtes of Koshihikri in erobic plots were significntly lower thn those in CF nd AWD. LWP investigted 1 d fter the mesurements of bleeding rte showed the similr trend (Fig. 7). Sensho nd Beodien showed identicl vlues in ll wter regimes (on verge.34 nd.37 Mp, respectively). In Koshihikri, however, LWP ws significntly lower in

10 522 Plnt Production Science Vol.12, 29 Tble 6. Grin yield nd wter productivity of six rice cultivrs in CF, AWD, A15, nd A3. CF AWD A15 A3 Men Grin yield (g m -2 ) Sensho b Htminorimochi b Beodien b UPLRi Koshihikri c 38 b 267 Nipponbre c 82 b 38 Men Downloded by [ ] t 2:19 7 July 216 min -1 cm -2 ) eeding rte (mg Ble Wter productivity (g grin kg -1 wter) Sensho.2 b.26 b.66 b Htminorimochi.19 b.28 b.44 b Beodien.17 b.24 b.62 b.6.41 UPLRi-7.23 b.31 b Koshihikri.21 b.34.1 c.6 b.18 Nipponbre c.14 b.22 Men Within column for ech prmeter, mens followed by different letters re significntly different t P =.5 ccording to Tukey s test. Sensho Beodien Koshihikri Fig. 6. Bleeding rte of Sensho, Beodien, nd Koshihikri in CF, AWD, A15, nd A3 on 14 August. Mens followed by different letters re significntly different t P =.5 mong wter regimes in ech cultivr by Tukey s test. Brs indicte the stndrd error (n =3). b b CF AWD A15 A3 LWP (MP) Sensho Beodien Koshihikri CF AWD A15 A3 Fig. 7. Predwn lef wter potentil of Sensho, Beodien, nd Koshihikri in CF, AWD, A15, nd A3 on 24 August. Mens followed by different letters re significntly different t P =.5 mong wter regimes in ech cultivr by Tukey s test. Brs indicte the stndrd error (n = 3). Bleeding rte is expressed on lef re bsis. b b erobic plots (.69 MP in A15 nd.8 MP in A3) thn in CF nd AWD (on verge.43 MP). Discussion In AWD, reduction in soil wter potentil ws very smll (Fig. 3), thus LAI nd biomss ccumultion differed little from those in CF (Figs. 4, 5). Grin yield in AWD tended to be higher (13% on verge) thn in CF (Tble 6). Moreover, AWD sved 2% of totl wter input in comprison with CF (Tble 3), resulting in higher wter productivity thn in CF (39% on verge, Tble 6). Intermittent irrigtion is believed to improve oxygen supply to rice roots, with potentil dvntges for nutrient uptke (Stoop et l., 22), nd to void ccumultion of toxic substnces such s ferrous iron nd hydrogen sulfide, which re potentilly toxic to root growth. Yng et l. (24) reported tht, in rice plnts, ctive bsorption re of root nd root ctivity prmeters (root α-nphthylmine oxidtion nd root surfce phosphtse) in AWD tended to be higher thn those in CF (though insignificnt) t the lte growth stge (9 nd 12 DAT). High root ctivity secures high photosynthetic rte by

11 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 523 Downloded by [ ] t 2:19 7 July 216 supplying sufficient mount of nutrients to shoot, thus ensure high productivity (Oski et l., 1997). We mesured bleeding rte only once in this experiment nd sttisticl significnce ws not observed between CF nd AWD in three cultivrs (Fig. 6). It my be worthwhile to further investigte bleeding rte nd nutrients in root sp t the lter growth stge. The bsence of yield reduction in AWD in comprison with CF ws consistent with the results obtined in Chin nd the Philippines (Belder et l., 25b). However, the threshold t which plnt growth nd yield begn to decrese ws uncler in this experiment. Therefore, further investigtions re needed to clrify the threshold of re-irrigtion to sve much wter without reduction in plnt growth nd grin yield in AWD. Although erobic rice systems could sve more thn 6% of input wter (Tble 3), there were lrge genotypic differences in plnt growth nd grin yield. Grin yields of Sensho, Beodien, nd UPLRi-7 incresed in A15, where the soil ws wet throughout the growth phse, reltive to those in CF. Furthermore, yields of Sensho nd Beodien (trditionl uplnd cultivrs) in A3 were the sme s in CF, indicting the existence of promising trditionl uplnd cultivrs for erobic rice systems. Mny studies on erobic rice systems hve used improved uplnd cultivrs (Belder et l., 25; Boumn et l., 25; Peng et l., 26). In A3, the spikelet number per pnicle of Sensho nd Beodien incresed by up to 3%, lthough pnicle number per m 2 decresed by 3%, reltive to tht in CF. Thus, decresed sink size cused by reduction of pnicle number might be compensted by increse of spikelet number per pnicle. Peng et l. (26) pointed out tht mong yield components, sink size contributed more to the yield gp between erobic nd flooded rice thn the percentge of filled grin nd the 1-grin weight. Therefore, sink size my be importnt to chieve high yield under erobic rice systems. Even in reltively wet erobic soil, yields of Htminorimochi nd UPLRi-7 were 25% lower in A3 thn in CF. In this respect, these two cultivrs behved similrly to the tropicl cultivrs used in Philippine by Boumn et l. (25) nd to the temperte cultivrs used in the USA by Wescott nd Vines (1986) nd McCuley (199) nd in Austrli by Blckwell et l. (1985). Trditionl uplnd cultivrs my hve more stble yield thn improved uplnd cultivrs under erobic rice systems where the threshold for reirrigtion is lower. The lowlnd cultivrs, Koshihikri nd Nipponbre, hd mrkedly lower yields in erobic soil conditions, resulting in reduced wter productivity. Boumn et l. (25) reported tht totl wter input in erobic rice systems ws from 696 to 1341 mm nd could be sved 11.5 to 5.7% in comprison with flooded lowlnd conditions, nd tht yield nd wter productivity of uplnd rice cultivrs under erobic rice systems rnged from 2.92 to 5.66 t h -1 nd.2 to.67 g grins kg -1 wter, respectively. In their study, however, yield (2.55 to 6.3 t h -1 ) nd wter productivity (.32 to.72 g grin kg -1 wter) of lowlnd cultivrs were equl to those of uplnd cultivrs. The much lower grin yield in lowlnd cultivrs thn in uplnd cultivrs under erobic rice systems (on verge 87 vs. 482 g m -2 in A15 nd 6 vs. 37 g m -2 in A3) in the present study ws not in line with their results. Yng et l. (25) conducted field experiments with five wter tretments under erobic rice systems in Chin nd reported tht totl wter input in erobic rice systems ws from 469 to 917 mm nd could be sved from 26.9 to 65.3% in comprison with flooded lowlnd conditions. The yield nd wter productivity of erobic rice cultivrs, Hn Do 297 nd Hn Do 52, under erobic rice systems rnged from 2.5 to 5.7 t h -1 nd.53 to.82 g grins kg -1 wter, respectively, nd the yield nd wter productivity of the lowlnd cultivr were on verge 54% lower thn those of two erobic rice cultivrs. These results showed similr tendencies to those in the present study, lthough the reduction rte of grin yield of lowlnd cultivrs (on verge 82% in A15 nd 84% in A3) ws much higher in the present study. The totl evpotrnspirtion ws clculted with the Penmn Monteith eqution (Allen et l., 1998) only for CF, nd rnged from 548 to 62 mm mong cultivrs (dt not shown). Assuming the mount of evpotrnspirtion in erobic plots ws the sme s in CF, the wter input ws higher thn the evpotrnspirtion demnd for ll cultivrs even in A3. Nevertheless, the reductions in plnt growth nd yield of lowlnd cultivrs were serious under erobic rice systems. Thus, future studies should ddress the genotypic differences of physiologicl mechnism responsible for the gps of plnt growth nd yield between uplnd nd lowlnd rice cultivrs under erobic rice systems. This informtion will help breed new rice cultivrs for erobic rice systems. The bleeding rte of Koshihikri ws lower thn those of Sensho nd Beodien in erobic plots, nd those of Koshihikri in erobic plots were significntly lower thn tht in CF nd AWD (Fig. 6). Moreover, bleeding rte of Koshihkri decresed s wter input decresed. These results suggest tht the root ctivity of Koshihikri decresed in wter-sving cultivtions, especilly in erobic rice systems. Therefore, it might be difficult for the root systems of Koshihikri to extrct enough soil wter, explining the significntly lower LWP mesured bout 1 h fter irrigtion ppliction (Fig. 7). Mtsuo et l. (28), who mesured root systems of these three cultivrs with minirhizotron, reported tht the root systems of Sensho nd Beodien reched depth of 8 cm nd tht of Koshihikri reched depth of 6 cm. In n unpublished experiment under erobic rice systems, we found tht root length density (RLD) nd root weight density (RWD) concentrted in the top -2

12 524 Plnt Production Science Vol.12, 29 Downloded by [ ] t 2:19 7 July 216 cm depth in three cultivrs nd RLD nd RWD t -2 cm depth were the lrgest in Beodien, followed by Sensho, nd Koshihikri in this order. Therefore, these quntittive differences of root systems mong cultivrs might result in the genotypic difference of bleeding rte nd LWP. On the other hnd, in Chin, Boumn et l. (26) investigted root systems of two erobic rice cultivrs nd one lowlnd rice cultivr under erobic rice systems nd reported tht there were no significnt differences in rooting depth, distributions, RLD nd RWD mong the cultivrs, lthough yield of the lowlnd cultivr ws lower thn those of the erobic rice cultivrs. Mtsuo et l. (29) mesured the root hydrulic conductnce, which is often regrded s wter uptke bility of root systems (e.g. Clrkson et l., 2), for these three cultivrs grown erobiclly under two wter regimes (well-irrigted nd repetitive cycles of wet nd dry conditions) in pot experiment. They reported tht (1) root hydrulic conductnce of Koshihikri ws the lowest mong three cultivrs under both wter regimes, (2) the reduction rte of the conductnce in Koshihikri (the rtio of the vlue in the repetitive wrer stress condition to tht in the well-irrigted condition) ws the highest mong three cultivrs, nd (3) root hydrulic conductnce ws significntly nd positively correlted with shoot dry weight only in repetitive wter stress conditions. Trillo nd Fernández (25) lso reported tht root hydrulic conductivity of whet plnts subjected to repetitive cycles of wet nd dry condition ws significntly lower thn tht of well-irrigted plnts. These results suggested tht repetitive wter stress hd negtive effects on root ctivity or function nd its effects vried with the cultivr, resulting in genotypic differences in the bleeding rte nd LWP. Arki nd Iijim (25), who investigted wter extrction pttern of root systems of n uplnd rice cultivr in pot experiments, reported tht when wter content of the shllow lyer (-25 cm depth) ws mple, more thn 9% of wter ws extrcted from shllower lyer, nd wter extrction re sifted to deeper lyer s surfce soil dried out. Integrting these reports on root function, besides the quntittive difference in root systems mong cultivrs (described bove), qulittive difference in root function mong cultivrs my be one of the importnt trits under erobic rice systems. Since studies on root morphologicl or physiologicl trits under erobic rice systems re still limited, further studies re needed to clrify the suitble trits for good crop performnce under erobic rice systems. Conclusion AWD could sve more thn 2% of totl input wter nd erobic rice systems could sve 6%, reltive to CF. Although yields tended to increse in AWD in comprison with CF, genotypic differences in yield ws lrge under erobic rice systems. In A15, where the soil ws kept wet throughout the growth period, yields of the uplnd cultivrs Sensho, Beodien, nd UPLRi-7 incresed in comprison with CF, but those of the lowlnd cultivrs, Koshihikri nd Nipponbre, decresed mrkedly. Moreover, yields of Sensho nd Beodien in A3 were the sme s in CF, suggesting tht promising cultivrs exist mong trditionl uplnd cultivrs. The yield reduction in the lowlnd cultivrs in erobic rice systems might be due to chnges in root ctivity or function s well s root morphology. AWD is esier for frmers to use thn erobic rice systems, which need extr irrigtion equipments. The selection of technique lrgely depends on the sitution of the frmers. Further study should exmine the optimiztion of irrigtion wter input (mount nd timing of irrigtion to mximize yield) in AWD. Aerobic rice systems cn sve more wter thn AWD nd promise wter svings for frmers in environments where wter vilbility is low or wter is too expensive to grow flooded lowlnd rice. Further breeding is required to develop cultivrs tht cn chieve high yield under erobic rice systems. Understnding how to mintin high yields under erobic rice systems will be crucil. However, the concept of erobic rice is new, nd there is yet little informtion to support the breeding of new cultivrs. Future studies should ddress morphologicl nd physiologicl trits under erobic rice systems. References Allen, R.G., Pereir, L.S., Res, D. nd Smith, M Crop evpotrnspirtion for computing crop wter requirements. FAO Irrigtion nd Dringe Pper 56. FAO, Rome. Arki, H. nd Iijim, M. 25. Stble isotope nlysis of wter extrction from subsoil in uplnd rice (Oryz stiv L.) s ffected by drought nd soil comction. Plnt Soil 27 : Belder, P., Boumn, B.A.M., Spiertz, J.H.J., Peng, S., Cstñed, A.R. nd Vispers, R.M. 25. Crop performnce, nitrogen nd wter use in flooded nd erobic rice. Plnt Soil 273 : Belder, P., Spiertz, J.H.J., Boumn, B.A.M., Lu, G. nd Tuong, T.P. 25b. Nitrogen economy nd wter productivity of lowlnd rice under wter-sving irrigtion. Field Crops Res. 93 : Blckwell, J., Meyer, W.S. nd Smith, R.G Growth nd yield of rice under sprinkler irrigtion on free-drining soil. Aust. J. Exp. Agric. 25 : Boumn, B.A.M. 21. Wter-efficient mngement strtegies in rice production. Int. Rice Res. Notes 26 : Boumn, B.A.M. nd Tuong, T.P. 21. Field wter mngement to sve wter nd increse its productivity in irrigted lowlnd rice. Agric. Wter Mnge. 49 : Boumn, B.A.M., Peng, S., Cstñed, A.R. nd Vispers, R.M. 25. Yield nd wter use of irrigted tropicl erobic rice systems. Agric. Wter Mnge. 74 : Boumn, B.A.M., Yng, X.G., Wng, H.Q., Wng, Z.M., Zho,

13 Mtsuo nd Mochizuki Growth nd Yield of Rice under Wter-sving Cultivtions 525 Downloded by [ ] t 2:19 7 July 216 J.F. nd Chen, B. 26. Performnce of erobic rice vrieties under irrigted conditions in Chin. Field Crops Res. 97 : Clrkson, D.T., Crvjl, M., Henzler, T., Wterhouse, R.N., Smyth, A.J., Cooke, D.T nd Steudle, E. 2. Root hydrulic conductnce : diurnl quporin expression nd the effects of nutrient stress. J. Exp. Bot. 342 : Cooper, M Concepts nd strtegies for plnt dpttion reserch in rinfed lowlnd rice. Field Crops Res. 64 : De Dtt, S.K., Krupp, H.K., Alvrez, E.I. nd Modgl, S.C Wter mngement in flooded rice. In : Wter Mngement in Philippines Irrigtion Systems : Reserch nd Opertions. IRRI, Los Bños, Philippines, Fuki, S. nd Cooper, M Development of drought resistnce cultivrs using physio-morphologicl trits in rice. Field Crops Res. 4 : Guerr, L.C., Bhuiyn, S.I., Tuong, T.P. nd Brker, R Producing more rice with less wter from irrigted system. SWIM Pper 5. IWMI/IRRI, Colombo. IRRI 22. Rice Almnc, 3rd ed. IRRI, Los Bños, Philippines. Jckson, P., Robertson, M., Cooper, M. nd Hmmer, G. L The role of physiologicl understnding in plnt breeding; from breeding perspective. Field Crops Res. 49 : Kto, Y., Kmoshit, A., Ymgishi, J. 26 Growth of rice (Oryz stiv L.) under uplnd conditions with different levels of wter supply. 2. Grin yield. Plnt Prod. Sci. 9 : Lfitte, R., Blum, A., Atlin, G. 23. Using secondry trits to help identify drought-tolernt genotypes. In K. S. Fischer, R. Lfitte, S. Fuki, G. Atlin, B. Hrdy eds., Breeding Rice for Drought-Prone Environments. Interntionl Rice Reserch Institute, Los Bños, Philippines Lffite, R.H., Courtois, B. nd Arrudeu, M. 22. Genetic improvement of rice in erobic systems : progress from yield to genes. Field Crops Res. 75 : Ludlow, M.M. nd Muchow, R.C Criticl evlution of trits for improving crop yields in wter-limited environment. Adv. Agron. 43 : Li, Y.H. 21. Reserch nd prctice of wter-sving irrigtion for rice in Chin. In R. Brker, R. Loeve, Y. Li nd T.P. Tuong eds., Proc. Int. Workshop on Wter-sving Irrigtion for rice, Mrch 21, Wuhn Mo, Z Study on evlution of irrigtion performnce in Chin. Mintennce nd Regionl Symposium, Beijing Mtsuo, N., Nhn, D.Q. nd Mochizuki, T. 27. Effect of deep tillge on growth nd yield of rice cultivrs grown under wter deficit. J. Fc. Agric. Kyushu Univ. 52 : Mtsuo, N., Ozw, K. nd Mochizuki, T. 28. Genotypic differences of the response to erobic rice cultivtion in rice (Oryz stiv L.). 2. Root length density nd root hydrulic conductivity. Jpn. J. Crop Sci. 77 (Extr Issue 1) : 24-25*. Mtsuo, N., Ozw, K. nd Mochizuki, T. 29. Genotypic differences in root hydrulic conductnce of rice (Oryz stiv L.) in response to wter regimes. Plnt Soil 316 : McCuley, G.N Sprinkler vs. flooded irrigtion in trditionl rice production regions of southest Texs. Agron. J. 82 : Oski, M., Shimono, T., Mtsumoto, M., Zheng, T. nd Tdno, T A root-shoot interction hypothesis of high productivity of field crops. Soil Sci. Plnt Nutr. 43 : Peng, S., Boumn, B.A.M., Vispers, R.M., Cstñed, A., Nie, L. nd Prk, H. 26. Comprison between erobic nd flooded rice in the tropics : gronomic performnce in eight-seson experiment. Field Crops Res. 96 : Stoop, W.A., Uphoff, N. nd Kssm, A. 22. A review of griculturl reserch issues rised by the system of rice intensifiction (SRI) from Mdgscr : opportunities for improving frming system for resource-poor frmers. Agric. Syst. 71 : Trillo, N. nd Fernández, R.J. 25. Whet plnt hydrulic properties under prolonged experimentl drought : stronger decline in root-system conductnce thn in lef re. Plnt Soil 277 : Tuong, T.P., Boumn, B.A.M. nd Mortimer, M. 25. More rice, less wter Integrted pproches for incresing wter productivity in irrigted rice-bsed systems in Asi. Plnt Prod. Sci. 8 : Turner, N.C Crop wter deficit : decde of progress. Adv. Agron. 39 : Wescott, M.P. nd Vines, K.W A comprison of sprinkler nd flooded irrigtion for rice. Agron. J. 78 : Wu, X Populriztion of wter sving irrigtion technique to frmers. In Z. Xu ed., Proc. Int. Symp. Wter-Sving Irrigtion for Pddy Rice, 1 14 October 1999, Guilin Ymguchi, T., Tsuno, Y., Nkno, J. nd Mno, R Anlysis of fctors concerning bleeding rte from the bsl prt of stem in rice plnts. Jpn. J. Crop Sci. 64 : 73-78**. Yng, C., Yng, L., Yng, Y. nd Ouyng, Z. 24. Rice root growth nd nutrient uptke s influenced by orgnic mnure in continuously nd lterntely flooded pddy soils. Agric. Wter Mnge. 7 : Yng, X., Boumn, B.A.M., Wng, H., Wng, Z., Zho, J. nd Chen, B. 25. Performnce of temperte erobic rice under different wter regimes in north Chin. Agric. Wter Mng. 74 : * In Jpnese. ** In Jpnese with English bstrct.