Growth and physiological performance responses to drought stress under non-flooded rice cultivation with straw mulching

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1 Growth nd physiologicl performnce responses to drought stress under non-flooded rice cultivtion with strw mulching J. Qin 1, X. Wng 2, F. Hu 3, H. Li 3 1 Institute of Soil Science, Chinese Acdemy of Sciences, Nnjing, P.R. Chin 2 Nnjing Institute of Environment Science, MEP, Nnjing, P.R. Chin 3 College of Resources nd Environmentl Sciences, Nnjing Agriculturl University, Nnjing, P.R. Chin ABSTRACT A field experiment ws performed to investigte the growth performnce nd the growth stge-dependent chnges in ctivities of ntioxidtive enzymes nd concentrtion of mlondildehyde (MDA) in leves of rice sujected to tretment with () or without strw mulching (NF-WM) under non-flooded conditions compred with continuously flooded tretment (). Compred with the NF-WM tretment, mulch ppliction significntly incresed the flg lef re per plnt efore heding, tillers numer nd plnt height t the erly period of tillering stge. There ws no significnt difference etween the yield of the NF-WM nd tretment. However, the yield of NF-WM tretment ws significntly lower thn nd tretments. Significntly higher ctivities of peroxidse (POD) nd ctlse (CAT) ut lower concentrtion of superoxide dismutse (SOD) nd mlondildehyde (MDA) were oserved in strw mulching tretment thn in tretment without mulching t elongtion, heding nd grin filling stges. The chnge tendency of ntioxidnt enzyme ctivity nd MDA level ws in line oth with soil moisture sttus nd rice yields of different tretments. Keywords: non-flooded rice; strw mulching; drought stress; ntioxidnt enzymes; yield Rice (Oryz stiv L.) production is chllenged y the incresing shortge of wter resource in the world nd y the limittion of wter resource in the sesonl drought res. Conventionl flooded rice cultivtion in Asi provides more thn 75% of the world s rice supply for hlf the erth s min stple food (Cngon et l. 22). However, rice production consumes out 3% of ll freshwter used worldwide. In Asi, flood-irrigted rice consumes more thn 45% of totl freshwter used (Brker et l. 1999). By 225, 15 out of 75 million hectre of Asi s flood-irrigted rice crop will experience wter shortge (Tuong nd Boumn 23). Alterntives to the conventionl flooded rice cultivtion were developed worldwide to reduce wter consumption nd produce more rice with less wter. Non-flooded rice cultivtion hs een proven to e n effective mesure to reduce wter consumption. In this pper, non-flooded rice refers to rice grown in non-flooded condition with supplementl irrigtion when rinfll is insufficient, in which rice is grown like n uplnd crop. Non-flooded rice cultivtion my decrese wter demnd nd promise sustntil wter svings y minimizing seepge nd percoltion nd gretly reducing evportion (Boumn et l. 22, Hung et l. 23). However, compred with continuously flooded rice system, rice cultivtion under non-flooded conditions leds to less stle productivity nd lower grin yield (De Dtt et l. 1973). In Philippines, rpid yield decline under continuous uplnd rice cropping ws documented (Peng et l. 26). The disdvntges rising from this cn e overcome Supported y the CAS-piloted tril implementtion of the Knowledge Innovtion Progrm (KIP) Soil qulity mintennce nd improvement, effective nd sustinle modern gronomicl piloted tril implementtion in Jingxi province, Grnt No. KSCX1-YW-9-8. PLANT SOIL ENVIRON., 56, 21 (2):

2 to certin extent y n lterntive wy of growing lowlnd rice using rice strw mulch under nonflooded conditions (Hung et l. 23, Qin et l. 26). Crop residue mulch hs the potentil to retin soil moisture (Enrique et l. 22) nd mintin the non-flooded rice production (Hung et l. 23, Qin et l. 26). Root development nd prolifertion depend on soil moisture (Gjri nd Prihr 1985) nd grin yield under mulches is higher due to longer rooting nd higher moisture content in the upper soil lyers (Bonfil et l. 1999). It is ovious tht wter-sving production systems (mulch ground cover) will not entirely replce trditionl pddy fields, ut in wter-scrce environments or under conditions when concurring wter demnd of non-griculturl users forids extensive wter consumption in griculture, wter-sving ground cover rice production systems my e promising lterntive tht gretly reduces seepge nd evportion (To et l. 26). Previous work showed tht non-flooded rice cultivtion reduced wter consumption y lmost 5 7% compred with the continuously flooded system (Hung et l. 23, Qin et l. 26). However, there were only limited reports on mechnisms involved in wter use efficiency nd wter stress physiology in prticulr in nonflooded rice cultivtion with mulching (Ling et l. 23). Although much work ws done on the reltionships etween ntioxidtive enzymes nd drought tolernce in plnts, most of such work ws undertken within shorter experimentl durtion (from hours to dys) under lortory conditions (Ling et l. 23). Ling et l. (23) studied the ntioxidtive defenses nd wter deficit-induced oxidtive dmge in rice growing on non-flooded pddy soils with plstic- nd pper-mulching. However, the study of Ling et l. (23) did not involve the ground mulching type of rice strw. Furthermore, strw mulching is more sustinle nd cceptle thn the plstic or pper mulching. Hence, in this study we performed field trils sujected to non-flooded cultivtion to investigte the yield nd growing performnce, especilly the growth-stge-dependent chnges in ntioxidtive enzyme ctivity of rice sujected to with or without mulching under non-flooded conditions compred with continuously flooded system. For etter understnding the mechnisms of the dptive responses of rice to wter deficit stress, the im of this study is to exmine the effects of strw mulching on rice growing performnce nd oxidtive dmges in wter-stressed rice grown under non-flooded pddies. MATERIALS AND METHODS Soil nd climte The field experiment ws conducted t the Yujing county, Jingxi province, Chin (N28 15', E116 55') in lte rice seson (July Octoer) of 24. The reserch re is representtive of typicl sutropicl moist climte with men nnul temperture of out 17.7 C; mximum dily temperture of round 4 C in summer; n verge of 262 frost-free dys nd rinfll of 175 mm, out 5% of which flls from Mrch to erly July. The uneven distriution of rinfll cuses strong sesonl droughts in summer nd/or utumn. The soil ws developed from lluvil deposits nd used for rice cropping for more thn 5 yers. The soil is nthropogenic soil nd the soil horizons include A-P-W1-W2. The initil ploughed soil ( 2 cm) chrcteristics of the experimentl field, which were mesured y using routine methods (Lu 1999), re given in Tle 1. Experimentl design nd wter mngement The crop system ws erly rice followed y lte rice. The rinfll for the erly rice ws plentiful nd wter mngement tril ws performed in the lte rice. The erly rice ws mnged under the controlled flooded cultivtion, lwys keeping stnding wter depth in the field until two weeks efore hrvest. In lte rice sesons, conventionl flooded cultivtion () tretments nd Tle 1. Initil soil chrcteristics of the field experiment conducted t Yujing County Prmeter Men SD ph Orgnic C (g/kg) Totl N (g/kg) Aville N (mg/kg) Aville P (mg/kg) Aville K (mg/kg) Totl S (g/kg).26.1 EC (µs/cm) CEC (cmolc/kg) eff Bse sturtion (%) Cly (%) Silt (%) Snd (%) PLANT SOIL ENVIRON., 56, 21 (2): 51 59

3 non-flooded cultivtion tretments (NF), which included non-flooded cultivtion with strw mulching () nd without strw mulching (NF-WM) tretments, were crried out in fields. Rice cultivr Zhongxun 1 ws used in this experiment. All the tretments were rrnged with rndomized design. Ech tretment ws triplicte in the field. Plot size ws 6 m 2 (6 m 1 m). In lte sesons, rice strw ws pplied t 5 kg/ hm 2 in dry weight fter trnsplnting. Seedlings grown in nursery for month were then trnsplnted on 26 th of July t density of 18 hills/m 2 nd two or three plnts per hill. Fertilizers of ure, superphosphte nd potssium chloride were pplied t the rtes of kg N, 39.3 kg P nd 62.2 kg K/h s sl fertilizer fter trnsplnting nd thoroughly incorported in the soils y hnd. Additionl ure ws spred over the surfce soil t rte of 45 nd 67.5 kg N/h t the tillering nd heding periods, respectively. Irrigtion wter ws pumped from n djcent well nd induced through irrigtion chnnel to the experimentl plots. The irrigtion system nd the device to mesure the mount of irrigtion wter were descried efore (Qin et l. 26). Mesurement nd dt collection Soil moisture. Volumetric soil wter content ws mesured using frequency domin reflectometer proes (MP-46), which were emedded to the depth of 1 cm in the soil. Three proes were used s replictes in ech plot. Rice growth performnce nd grin yield. Plnt height nd tillers numer were mesured on three different dys, seprtely on 1 th nd 25 th of August nd 15 th of Septemer. 2 plnts were rndomly selected for mesurements ech time. Before heding, CI-23 AREA METER (Cid, INC.USA) ws used to mesure flg lef re nd men lef re in ech plot (3 plnts were selected rndomly). The crop ws hrvested from net re of 4 m 2 when the ers were ripe nd strw hd turned yellow. Grin yields were recorded fter threshing of rice. Extrction nd ssy of enzymes. The second youngest fully expnded lef from 2 plnts per tretment ws tken t tillering, elongtion, heding nd grin filling stges respectively. One grm of frozen lef segments (< 2 mm) ws homogenized in 5 ml of ice cold 5 mmol/l N-phosphte uffer (PBS) (ph 7.8) contining.2 mmol/l ethylene dimine tetrcetic cid (EDTA) nd 2% (w/v) polyvinylpyrrolidone (PVP). The smples were centrifuged t 1 g for 2 min t 4 C. After centrifugtion, the otined superntnt smple ws used for further processing. SOD (EC ) ctivity ws ssyed y the photochemicl method descried y Ginnopolitis nd Ries (1977). One unit of SOD ctivity ws defined s the mount of enzyme, which produced 5% inhiition of the rte of NBT (ρ-nitro Blue Tetrzolium Chloride) reduction t 56 nm. POD (EC ) ctivity ws mesured y monitoring the increse in sornce t 47 nm. The rection mixture consisted of.5 ml enzyme extrct, 2.55 ml 1 mmol/l 7. PBS (contined.1 mmol/l EDTA),.2 ml 1% guicol nd.3 ml 1 mmol/l H 2. One unit of POD ctivity ws defined s n sornce chnge of.1 units/min t 47 nm [U/ min g/(fw)] (Zou 2). CAT ctivity (EC ) ws determined y monitoring the disppernce of H 2, which ws crried out y mesuring the decrese in sornce t 24 nm. Activity ws expressed s units (µmol of H 2 decomposed per min) per mg of protein (Zou 2). The rection mixture contined 5 mmol/l potssium phosphte uffer (ph 7.), 1 mmol/l H 2 nd 2 µl of enzyme extrct in 3-ml volume. MDA content ws determined y the thiorituric cid (TBA) rection ccording to the method of Heth nd Pcker (1968). The rection mixture contined 2. ml enzyme extrct nd 2. ml TBA regent [.5% (w/v) TBA dissolved in 1% (w/v) trichlorocetic cid (TCA)]. All the enzymes were expressed s units per mg of protein. Protein ws ssyed using ovine serum lumin s reference stndrd mteril (Brdford 1976). Sttisticl nlysis. All the dt were sujected to sttisticl nlysis nd the mens were tested y the lest significnt difference (LSD) nd/or the Duncn s Test t 5% level of significnce. All the sttisticl nlyses were conducted using the sttisticl pckge SPSS RESULTS Plnt height nd tillering. In totl, the rice crop ws the highest in the tretment, followed y the M nd ZM tretments (Tle 2). On the 1 th of August, the rice crop height of the tretment ws significnt higher thn the non-flooded tretments. It ws shown tht rice growth ws ffected gretly y wter stress during the erly period of tillering. The crop height on the 15 th of Septemer ws not significntly different mong the three tretments. So, the difference cn e reduced in the lte period of tillering. The tillers PLANT SOIL ENVIRON., 56, 21 (2):

4 Tle 2. Plnt height nd tillering numer of different periods in the cropping seson Tretment Plnt height (cm) Tillering numer 1 th Aug. 25 th Aug. 15 th Sep. 1 th Aug. 25 th Aug. 15 th Sep NF-WM c Within column for ech prmeter, mens followed y different letters re significntly different t.5 proility level ccording to the lest significnt difference (LSD) test numer vried mong the tretments nd the vrition ws similr to the trend of rice crop height. However, there ws no significnt difference etween the nd tretments during the three periods. The tillers numer oth of the nd tretments ws significntly greter thn the NF-WM tretment. Lef re. The effect of rice grown in non-flooded plots on flg lef re ws very gret (Figure 1). Compred to the tretment, the flg lef re ws decresed significntly in NF-WM tretment. However, there ws no significnt different for men lef re mong the three tretments. In order to llevite the effect of wter stress, lef re ws decresed to reduce trnspirtion in the non-flooded plots. Sheng et l. (24) reported tht strw mulching cn increse lef re index (LAI) compred with the tretment without mulching under non-flooded rice cultivtion system. Grin yields. There ws no significnt difference etween the yields of the tretment nd the tretment (Figure 2). Both of them were significntly higher thn the yield of NF-WM tretment. In the non-flooded plots, mulching cm NF-WM cm Flg lef re Men lef re Figure 1. Effect of ground mulching tretment on flg lef nd men lef re efore heding stge of rice grown under non-flooded nd flooded conditions. Dt re mens of three replictes. The mens mrked with different letters t the sme growth stge re significntly different t P <.5 y the Duncn s New Multiple Rnge Test 1 8 Yield (kg/hm 2 ) 2 ) NF-WM Figure 2. Grin yield of rice grown under non-flooded conditions with or without mulching nd under continuously flooded condition 54 PLANT SOIL ENVIRON., 56, 21 (2): 51 59

5 Tle 3. Wter content (v/v, %) of cultivted soil horizon t different growth stges of rice grown under nonflooded nd flooded conditions Tretment Tillering Elongtion Heding Grin filling ± ± ± ± ± ± ± ±.2 NF-WM ± ± ±.25 c ±.12 Within column for ech prmeter, mens followed y different letters re significntly different t.5 proility level ccording to the lest significnt difference (LSD) test with rice strw cn mintin high production of rice. Furthermore, in this tril, strw mulching tretment significntly incresed soil moisture content t ll stges compred to the tretment without mulching (Tle 3). SOD ctivity. In totl, SOD ctivity ws higher in non-flooded cultivtion thn in continuously flooded condition (Figure 3). At tillering stge, no significnt difference in SOD ctivity ws noted mong the three tretments. At other three stges, SOD ctivity in NF-WM tretments ws highest, followed y the nd tretments. At lst three stges, SOD ctivity in NF-WM tretment ws significntly higher thn in tretment However, there ws no significnt difference etween the nd tretments t elongtion nd heding stges. At grin filling stge, SOD ctivity in tretment ws significntly lower thn in nd NF-WM tretments, while in tretment it ws lso significntly lower thn in NF-WM tretment. POD ctivity. No significnt difference in POD ctivity ws noted mong the three tretments t tillering stge (Figure 4). POD ctivity in nd tretments ws significntly higher thn in NF-WM tretment t elongtion, heding nd grin filling stges. At elongtion stge, POD ctivity in -tretment ws significntly higher thn in tretment. However, there ws no significnt difference etween the nd tretments. At heding nd grin filling stges, POD ctivity in tretment ws the highest, followed y nd NF-WM tretments. CAT ctivity. In the tril, no significnt difference ws noted etween nd tretments in CAT ctivity t four growing stges (Figure 5). At tillering stge, there ws no significnt difference mong the three tretments. At elongtion nd heding stges, CAT ctivity in tretment ws highest, followed y nd NF-WM tretments. Differently, CAT ctivity in tretment ws highest, followed y nd NF-WM tretments t grin filling stge. CAT ctivity oth in nd tretments ws significntly higher thn in NF-WM tretment t elongtion, heding nd grin filling stges. SOD ctivity (U.mg (U/mg -1 protein) NF-W M Tillering Elongtion Heding Grin filling Growth stge c Figure 3. SOD ctivity of rice growing with or without strw mulching under non-flooded condition compred with continuously flooded system. Dt re mens of three replictes. The mens mrked with different letters t the sme growth stge re significntly different t P <.5 y the Duncn s New Multiple Rnge Test PLANT SOIL ENVIRON., 56, 21 (2):

6 POD Pod ctivity (? (? sor.mg protein. protein/min) -1 ) NF-W M c Figure 4. POD ctivity of rice growing with or without strw mulching under non-flooded condition compred with continuously flooded system. Dt re mens of three replictes. The mens mrked with different letters t the sme growth stge re significntly different t P <.5 y the Duncn s New Multiple Rnge Test Tillering Elongtion Heding Grin Grin filling filling Growth stge MDA. At four growing stges, MDA concentrtion in NF-WM tretment ws the highest, significntly higher thn tretment (Figure 6). MDA concentrtion in NF-WM tretment ws significntly higher thn in tretment t elongtion, heding nd grin filling stges, except t tillering stge. At erly stges (tillering nd elongtion stges), MDA concentrtions in ll tretments were reltively low compred to the lte stges (heding nd grin filling stges). DISCUSSION Compred to the tretment without mulching, strw mulching cn keep soil moisture nd reduce the differences etween nd non-flooded tretments in flg lef re, plnt height, tillers numer nd grin yield. The soil moisture content in tretment without mulching rnged from only 84. to 94.7% of tretment, while tht of strw mulching tretment from 91.9 to 96.7% of tretment, suggesting less severe wter deficit stress in strw mulching tretment. Rice growth ws deferred gretly in the non-flooded plots. In our previous study, we lso found tht in non-flooded condition, rice growth time ws longer thn in the flooded plots (Qin et l. 26). In non-flooded condition, rice growth ws deferred during the tillering nd heding stges. Our results coincided with those of Hung et l. (23) who reported tht, in non-flooded condition, the growth time ws 5 dys longer thn under flooded conditions. The resons for this were s follows: (1) during erly periods, rice grew etter in flooded plots, nd sored more nitrogen from soil. So efore CAT ctivity (U. (U.mg/protein) NF-WM Tillering Elongtion Heding Grin filling Growth stge Figure 5. CAT ctivity of rice growing with or without strw mulching under non-flooded condition compred with continuously flooded system. Dt re mens of three replictes. The mens mrked with different letters t the sme growth stge re significntly different t P <.5 y the Duncn s New Multiple Rnge Test 56 PLANT SOIL ENVIRON., 56, 21 (2): 51 59

7 MDA MDAconcentrtion (nmol.g (nmol/g -1 FW) FW) NF-WM c Figure 6. MDA ctivity of rice growing with or without strw mulching under non-flooded condition compred with continuously flooded system. Dt re mens of three replictes. The mens mrked with different letters t the sme growth stge re significntly different t P <.5 y the Duncn s New Multiple Rnge Test 5 Tillering Elongtion Heding Grin filling Growth stge hrvesting, nitrogen content in the non-flooded soil ws higher thn in the flooded plots. (2) In non-flooded plots, wter stress delyed the tillering in erly growth period (Tle 2), which cused whole growth to e delyed. Mulching with rice strw lso incresed the flg lef re nd improved the grin yield of rice significntly compred to the NF-WM tretment. Compred to the tretment without mulching, strw mulching could gretly reduce the effect induced y wter deficit stress in non-flooded condition. This ws supported y the decresed concentrtion of MDA, n end product of lipid peroxidtion (Figure 6). MDA is one of the min products of lipid peroxidtion. Its content reflects the degree of lipid peroxidtion. The MDA s lipid peroxidtion product cn ct with mny ingredients of plnt cells esily nd dmges enzymes nd memrne system severely. In this study, it is proposed tht the incresed memrne dmge induced y elevted ctive oxygen species could e llevited y strw mulching vi the striking efficiency in the mintennce of soil moisture (Tle 3). Higher MDA concentrtion in NF-WM tretment (Figure 6) t ll growing stges ws closely relted to the decline in ctivities of POD nd CAT (Figures 4 nd 5). In contrst, significntly higher SOD ctivity (Figure 3) ws oserved t elongtion stge nd onwrd in NF-WM tretment. In this study, SOD ctivity in NF-WM tretment ws significntly higher thn in tretment t lst three stges, which is in line with the findings reported y Kocsy et l. (1991) in whet nd y Ling et l. (23) in tril with rice under wter deficit stress in On the contrry, the decline in SOD ctivity under stressed conditions ws thought to e ssocited with oxidtive dmge (Gogorcen et l. 1995). In other words, the SOD ctivity should e in line with the ctivity of POD nd CAT. For exmple, it ws reported tht SOD ctivity decresed in drought-stressed pe nodules (Gogorcen et l. 1995) nd in wter deficit stressed rice. In fct, the ility of plnts to dpt to environmentl stresses does depend not only upon SOD ut lso on the rice cultivr nd the whole ntioxidtive defense system (Ling et l. 23). It ws reported tht POD ctivity plyed n importnt role in droughtstressed plnts (Zheng nd Hn 1997). In the present study, lowest POD ctivity ws oserved in the NF-WM tretment nd ws followed y the tretment, highest POD ctivity ws noted in tretment t ll stges (Figure 4). Similr chnge ws noted in CAT with growth stge (Figure 5). This ws generlly coincident with the results of Ling (Ling et l. 23). Thus it cn e ssumed tht higher concentrtion of H 2 formed in the removl of superoxide free rdicls y higher SOD in NF-WM tretment could not e eliminted y its lower POD nd CAT ctivities (Figures 4 nd 5), thus dmging cell memrne lipids (Figure 6). Higher ctivities of ntioxidtive enzymes in rice plnts (Figures 3 5) in strw mulching tretment effectively protected the plnt tissues from memrne oxidtive dmge induced y wter stress. Except for the tillering stge, the chnges in ntioxidtive enzymes nd MDA with growth stges (Figures 3 6) were in line with the severity of wter stress in soils, flg lef re nd rice productivity (Figures 1 nd 2), suggesting tht ntioxidtive defenses nd lipid peroxidtion cn well reflect the sttus of wter deficit stress of the field plnts t lst PLANT SOIL ENVIRON., 56, 21 (2):

8 three growing stges. At tillering stge, there ws no significnt difference in ntioxidtive enzymes nd MDA concentrtion mong ll the tretments (Figures 3 6). The results were different compred to the report of Ling et l. (23); lthough wter stress ffected the tillers numer, the different smpling time for tillers numer recording nd enzymes ssy cused the different results. The erliest dte of tillers numer recording ws on 1 th August. However, lef smples for enzymes ssy t tillering stge ws smpled on 1 st August, only 5 dys fter trnsplnting. Before trnsplnting, soil preprtion ctivities in ll the tretments egin with pre-sturtion irrigtion to sturte the topsoil lyer nd to crete ponded wter lyer (out 5 cm) for lnd soking. Then, plowing nd puddling ws pplied y hnd under sturted soil conditions in different plots (Qin et l. 26). On 1 st August, rice growing ws not ffected gretly y wter stress compred to lst three growing stges. Therefore, no significnt difference ws oserved in ntioxidtive enzymes nd MDA concentrtion mong ll the tretments s result of sence of severe wter stress t tillering stge. Rice yield ws significntly lower in NF-WM tretment thn in tretment, s well s the ntioxidtive defenses nd oxidtive dmge etween NF-WM nd N tretments. The min reson is tht rice growth nd yield is determined not only y soil wter supply ut lso y mny other fctors including soil nutrient vilility, light intensity, soil temperture etc. The resons for the eneficil effect of crop residue mulch on non-flooded rice were tht: (1) for loss of wter y evportion from mulched soil, wter must chnge from liquid to vpor t the soil surfce. The wter vpor must then diffuse through the thickness of mulch, which significntly reduces the rte of wter loss when compred with re soil surfce. The mulch reduces the quntity of direct solr rdition reching the soil surfce, therey reducing the mount of energy ville for chnge of stte of wter from liquid to wter. (2) Mulches lso ct s insultors to downwrd conduction of het into the soil. Mulching tretment cn effectively decrese soil temperture in erly stges (tillering nd elongtion stges) nd keep soil temperture in lte growing stges (heding nd grin filling stges). (3) Strw mulching increses the input of orgnic mtter. Use of orgnic mendments is generlly seen s key issue for soil helth nd sustinility in intensive rice-sed systems, oth in terms of mintining the mount nd qulity of soil orgnic mtter nd in terms of supplying importnt micronutrients (Ydv et l. 2, Timsin nd Connor 21). Retention of crop residues on the soil surfce incresed orgnic C nd totl N in the top 5 15 cm of the soil (Rsmussen nd Collins 1991), while strw mulching cultivtion resulted in mintined rice yields (Liu et l. 23, Fn et l. 22). Rsmussen nd Collins (1991) reported tht slowly decomposing crop residues on the soil surfce incresed orgnic C nd totl N in the top 5 15 cm of the soil while protecting the surfce soil from erosion. In conclusion, strw mulching enhnced ntioxidtive defenses nd reduced wter deficit-induced oxidtive dmge nd yield decline in rice grown under non-flooded pddy soils compred to the tretment without strw mulching. REFERENCES Brker R., Dwe D., Tuong T.P., Bhuiyn S.I., Guerr L.C. (1999): The outlook for wter resources in the yer 22: chllenges for reserch on wter mngement in rice production. In: Assessment nd Orienttion towrds the 21 st Century. Proceedings of the 19 th Session of the Interntionl Rice Commission, 7 9 Septemer 1998, Ciro, Egypt. Food, Agriculture Orgniztion, Bonfil D.J., Mufrdi I., Klitmn S., Asido S. (1999): Whet grin yield nd soil profile wter distriution in no-till rid environment. Agronomy Journl, 91: Boumn B.A.M., Wng H., Yng X., Zho J., Wng C. (22): Aeroic rice (Hn Do): new wy of growing rice in wtershort res. In: Proceedings of the 12 th Interntionl Soil Conservtion Orgniztion Conference, My, 22, Beijing, Chin. Tsinghu University Press, Brdford M.M. (1976): A rpid nd sensitive method for the quntittion of microgrm quntities of protein utilizing the principle of protein-dye inding. Anlyticl Biochemistry, 72: Cngon R.J., Tuong T.P., Adullh N.B. (22): Compring wter input nd wter productivity of trnsplnted nd directseeded rice production systems. Agriculturl Wter Mngement, 57: De Dtte S.K., Aily W.P., Klwr G.N. (1973): Wter stress in flooded tropicl rice. In: Wter Mngement in Philippine Irrigtion Systems: Reserch nd Opertions. IRRI, Los Bńos, Philippines, Enrique S.S., Rodriguez J.A.L., Hernndez M.F., Vzquez C.V. (22): Nitrogen recovery nd uptke y whet nd sorghum in stule mulch nd no tillge systems. Agrocienci, 36: Fn X.L., Zhng J.P., Wu P. (22): Wter nd nitrogen use efficiency of lowlnd rice in ground covering rice production system in south Chin. Journl of Plnt Nutrition, 25: PLANT SOIL ENVIRON., 56, 21 (2): 51 59

9 Gjri P.R., Prihr S.S. (1985): Rooting, wter use nd yield reltions in whet on lomy snd nd lom soils. Field Crop Reserch, 12: Ginnopolitis C.N., Ries S.K. (1977): Superoxide dismutse in higher plnts. Plnt Physiology, 59: Gogorcen Y., Iture-Ormetxe I., Escuredo P.R., Becn M. (1995): Antioxidnt defenses ginst ctivted oxygen in pe nodules sujected to wter stress. Plnt Physiology, 18: Heth R.L., Pcker L. (1968): Photoperoxidtion in isolted chloroplst I. Kinetics nd stoichemistry of ftty cid peroxidtion. Archives of Biochemistry nd Biophysics, 125: Hung X.Y., Xu Y.C., Shen Q.R., Zhou C.L., Yin J.L., Dittert K. (23): Wter use efficiency of rice crop cultivted under wterloggednd eroic soil mulched with different mterils. Journl of Soil nd Wter Conservtion, 17: (In Chinese) Ling Y.C., Hu F., Yng M.C., Yu J.H. (23): Antioxidtive defenses nd wter deficit-induced oxidtive dmge in rice (Oryz stiv L.) growing on non-flooded pddy soils with ground mulching. Plnt nd Soil, 257: Liu X.J., Wng J.C., Lu S.H., Zhng F.S., Zeng X.Z., Ai Y.W., Peng S.B., Christie P. (23): Effects of non-flooded mulching cultivtion on crop yield, nutrient uptke nd nutrient lnce in rice-whet cropping systems. Field Crops Reserch, 83: Lu R.K. (1999): Anlyticl Methods for Soils nd Agriculturl Chemistry. Chin Agriculturl Science nd Technology Press, Beijing. (In Chinese) Kocsy G., Gli G., Sutk J. (1991): In vitro system to study slt nd drought tolernce of whet. Act Horticulture, 289: Peng S., Boumn B., Vispers R.M., Cstňed A., Nie L., Prk H.K. (26): Comprison etween eroic nd flooded rice in the tropics: gronomic performnce in n eight-seson experiment. Field Crops Reserch, 96: Qin J.T., Hu F., Zhng B., Wei Z.G., Li H.X. (26): Role of strw mulching in non- continuously flooded rice cultivtion. Agriculturl Wter Mngement, 83: Rsmussen P.E., Collins H.P. (1991): Long-term impcts of tillge, fertilizer, nd crop residue on soil orgnic mtter in temperte semi-rid regions. Advnces in Agronomy, 45: Sheng H.J., Shen Q.R., Feng K. (24): Popultion development chrcteristics of rice crop cultivted on eroic soil with mulching. Chinese Journl of Applied Ecology, 15: (In Chinese) To H.B., Brueck H., Dittert K., Kreye C., Lin S., Sttelmcher B. (26): Growth nd yield formtion of ricez (Oryz stiv L.) in the wter-sving ground cover rice production system (GCRPS). Field Crops Reserch, 95: Timsin J., Connor D.J. (21): Productivity nd mngement of rice-whet cropping systems: issues nd chllenges. Field Crops Reserch, 69: Tuong T.P., Boumn B.A.M. (23): Rice production in wterscrce environments. In: Proceedings of the Wter Productivity Workshop. Interntionl Wter Mngement Institute, Colomo, Sri Lnk. Ydv R.L., Dwivedi B.S., Prsd K., Tomr O.K., Shurpli N.J., Pndey P.S. (2): Yield trends nd chnges in soil orgnic-c nd ville NPK in long-term rice-whet system under integrted use of mnures nd fertilisers. Field Crops Reserch, 68: Zheng Y.Z., Hn Y.H. (1997): Effect of high temperture nd/or drought stress on the ctivities of SOD nd POD of intct leves in two soyen cultivrs. Soyen Genetics Newsletter, 24: Zou Q. (2): Plnt Physiology: A Lortory Mnul. Chinese Agriculture University Press, Beijing. Received on July 27, 29 Corresponding uthor: Dr. Jingto Qin, Chinese Acdemy of Sciences, Institute of Soil Science, 218 Nnjing, P.R. Chin phone: , e-mil: jtqin@isss.c.cn PLANT SOIL ENVIRON., 56, 21 (2):