Control of Micronutrients Availability in Soil and Concentration in Rice Grain through Field Water Management

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1 Journl of Agriculturl Science; Vol. 7, No. 5; 215 ISSN E-ISSN Published by Cndin Center of Science nd Eduction Control of Micronutrients Avilbility in Soil nd Concentrtion in Rice Grin through Field Wter Mngement Jun Dmin Mrques Fong 1, Tsugiyuki Msung 1 & Kuniki Sto 1 1 Fculty of Life nd Environmentl Science, Shimne University, Mtsue, Jpn Correspondence: Tsugiyuki Msung, Fculty of Life nd Environmentl Science, Shimne University, 16 Nishikwtsu, Mtsue, Shimne , Jpn. Tel: E-mil: msung@life.shimne-u.c.jp Received: Februry 9, 215 Accepted: Mrch 19, 215 Online Published: April 15, 215 doi:1.5539/js.v7n5p163 URL: Abstrct A pot experiment ws conducted under different wter mngements, nmely control (continuous flooding condition), 2,3,4WAH (wter ws drined t two to four weeks fter heding), nd FCp (the soil moisture ws kept t field cpcity level, to mintin erobic soil condition). We exmined the influence of the estblishment of erobic soil condition t different timing of rice post-heding stge. The results showed tht wter mngements chnged soil redox potentil nd ph tht were known to be responsible of micronutrients vilbility in soil. Trnsition from flooding condition to erobic condition during rice post-nthesis stge, reduced ph towrd its initil vlue s well s Fe vilbility in soil. Although soil ws re-oxidized in 2,3,4WAH tretments, which reduced Fe vilbility in soil from the level of control tretment, concentrtion of Fe in grin did not differ between control nd drined tretments. Correltion nlyses exhibited tht the reduction of Fe vilbility in soil under erobic condition in 2,3,4WAH nd FCp enhnced Zn nd Cu vilbilities in soil nd incresed concentrtion of Zn, Cu nd Mn in grin. The results point up towrd tht, enhncement of micronutrient vilbility in soil during post-heding stge re strongly ssocited with its grin micronutrient concentrtion. Estblishment of erobic condition from two weeks fter heding incresed the grin Zn, Cu nd Mn concentrtion by 11, 2 nd 35 percent respectively over the vlues in flooding condition, without negtive effects on yield prmeters. Unlike control nd 2,3,4WAH tretments, FCp tht kept erobic soil condition performed high concentrtion of grin micronutrients but its low yield. Keywords: grin filling stge, micronutrients concentrtion, soil vilbility, rice, wter mngement 1. Introduction Micronutrient deficiencies in soil hve been identified s one of min fctors ffecting crop yield, food qulity nd humn helth (Yng et l., 27; Allowy, 28). In recent yers, emphsis on griculture, environment, demogrphic growth nd micronutrient mlnutrition hs incresingly tken center stge in policy discussions on food security in developing countries. The inhbitnts of these countries re prone to suffer from undernourishment, cused by indequte food intke or intke of foods of poor nutritionl qulity (Bin et l., 213). New pproches hve been pplied in chieving sustinble improvements in the micronutrient sttus of vulnerble popultions. One of them is the genetic biofortifiction which hs been ccepted s cost-effective nd sustinble strtegy in order to meliorte the mlnutrition (Ckmk, 28; Meenkshi et l., 27). The development of new improved crops vrieties, through dvnced breeding techniques s well s the screening of germplsm, hs llowed for identifiction of vrieties with high potentil of ccumulting micronutrient in edible prts. Some of the mjor successes hve been observed in crops such s whet, mize, bens, sweet potto, cssv nd rice. Rice (Oryz stiv L.) is the min stple crop for more thn hlf of the world popultion (FAO, 213). In spite of its high consumption, the low content of micronutrient in rice required to meet whole dietry elements necessry to keep blnced diet in humns, clls for concern. Rice s mjor cerel therefore hs become priority for current reserch works. New findings suggest tht micronutrients content in rice grin depends not only on genotypic vribles, but lso on environmentl fctors, such s the endogenous soil minerl contents, soil properties ( Ckmk, 28; Sperotto et l., 213) wter mngement (Dobermnn & Firhurst, 2; Lio et l., 213) nd climte conditions (Njfi-Ghiri et l., 213). Agronomic biofortifiction through the ppliction of fertilizer (inorgnic or orgnic), modifiction of 163

2 Journl of Agriculturl Science Vol. 7, No. 5; 215 cultivtion systems, soil mngement nd new irrigtion strtegies hve proved effective in enriching micronutrients content in rice grin by controlling the vilbility of soil micronutrients for plnt (White & Brodley, 29). Unlike genetic biofortifiction, the gronomic biofortifiction hs shown to be short-term pproch, more ccessible for developing countries which re fcing the burden of mlnutrition nd where the dvnced technologies (e.g. plnt breeding nd genetic engineering) still remin unrechble (Ckmk, 28). Since soil micronutrient vilbility is highly ssocited with the contents in plnt nd grin qulity; its vilbility hs become the key limittion fctor to productivity, stbility nd sustinbility of rice production in mny countries such s Austrli, Chin, Indi nd United Sttes (Bell & Dell, 28). Studies conducted by Yng et l. (27) in Chin, reported tht such deficiencies in soil overlpped res where popultion exhibits helth micronutrients imblnce, ffecting more thn 4% of the popultion. Usully those deficiencies re fforded by the pplictions of chemicl fertilizer (edphic nd folir) or orgnic mendment. The ppliction of Zn fertilizer hs hd positive response in whet (Triticum estivum L.), (Ckmk, 28), sorghum (Sorghum bicolor L.) nd rice (Go et l., 212). Iron is nother importnt micronutrient for plnt nd humn helth. Mjor Fe deficiencies hve been reported minly in sndy nd clcreous soils (Brdy & Weil, 214). However, under such condition ppliction of inorgnic Fe fertilizer often results in ineffective prctice due the conversion to ferric form (Rengel et l., 1999). Besides tht, the micronutrients content in grin could be controlled by genetic fctor mening tht the ppliction of fertilizer even in excess could not increse the content in grin nd would rther trigger toxicity symptoms. Likewise micronutrient demnd for physiologicl processes nd plnt uptke rtes could lso vry in function of different growing stges nd environmentl condition (Mschner, 212). Rice s well s other crops needs essentil micronutrients in very smll mount compred to mcronutrient. Almost ll the soil contins enough micronutrients to support the plnts growth demnds, however, micronutrients vilbility often is governed by some soil properties (White & Brodley, 29). For exmple, chnges in soil redox potentil nd ph re the most importnt properties tht could ffect micronutrient vilbility in pddy (To et l., 27; Brdy & Weil, 214). Likewise, soil orgnic mtter nd its decomposition processes hve significnt nd direct impct on the vilbility of micronutrients (Mrschner & Rengel, 27). Other fctors such s synergistic nd ntgonist interctions mong micronutrients nd essentil elements could lso often ffect micronutrient uptke by crops (Fgeir, 22). In order to increse the contents of micronutrients in grin, understnding the dynmics of micronutrient t different growing stges is lso very importnt. Some studies hve pointed out tht the period between pnicle initition to mturity is considered s high demnd for grin micronutrient ccumultion. For instnce, concerning Zn uptke, Jing et l. (27) reported tht 36% of totl Zn in rice grin ws tken up directly from soil between nthesis nd mturity stges, similr ptterns hs been described in whet during grin filling stge (Person & Rengel, 1994). For Fe, s Inoue et l. (29) observed, Fe-trsnporter gene OsYSL15 ws highly expressed during the nthesis nd seed formtion stge, these stges probbly re the ctive Fe uptke period of rice. Copper (Cu) on the other hnd is essentil in flower fecundtion (Dobermnn & Firhurst, 2). Therefore, its demnd should significntly increse t nthesis. With regrds to bove fctors influencing the micronutrient vilbility in soil, plnt uptke nd the content in rice grin, little informtion is vilble bout the effect of wter mngement over micronutrient concentrtion in grin during grin filling stge. Since chnges in soil wter condition re strongly ssocited with micronutrient vilbility nd plnt uptke; shifting soil wter condition could be suitble pproch to control soil micronutrient vilbility nd to improve the nutritionl vlue of rice in developing countries where frmers do not hve esy ccesses to fertilizers or other costly pproches. Therefore, the im of this present study ws to ssess the effect of wter mngement on the micronutrient contents in rice grin nd vilbility of soil t grin filling stge. 2. Mterils nd Methods The effects of wter mngement on soil properties nd micronutrients content in rice grin, were evluted through pot experiment conducted in greenhouse t Shimne University (35 29 N E), from during rice growing seson in Jpn (My 15th/Oct 15th). Plstic bucket (Ø = 24 cm 25 cm height) were filled with 7.5 kg of ir dry Gry Lowlnd soil Typic Fluvquent (USDA, 21). The generl soil chrcteristics re presented in Tble 1. The semi-dwrf (cv. Koshihikri) rice vriety ws used in this study. 2.1 Experimentl Design The pot experiment ws lid out in rndomized block design of five wter irrigtion tretments (Figure 1) with four replictions. Control ws flooded from trnsplnting to hrvest. The heding stge (5% of the pnicle exertion) ws the benchmrk for the next customized irrigtion tretments where flooded-irrigtion ws stopped 164

3 Journl of Agriculturl Science Vol. 7, No. 5; 215 during the post-heding t four week fter heding 4WAH, three week fter heding 3WAH, nd two weeks fter heding 2WAH, nd kept in soil 1evel pproximtely 35±3% (v/v) moisture, equivlent to ±8% of its field cpcity level. The lst tretment ws kept t the sme moisture condition, 8% of field cpcity conditions FCp throughout growth period in order to mimic the conditions of uplnd systems. Tretments under flooding condition were ±5 cm wter depth. Distilled wter ws used for irrigtion to void micronutrient supply through it. Chemicl fertilizer (N:P:K) t doses of 45:65:6 kg h -1 respectively ws pplied bsed on crop demnd s follows: N ws split in four ppliction, 1 st -2% bsl, 2 nd -3% t tillering stge, 3 rd -4% t pnicle initition nd 4 th -1% 15 dys fter pnicle initition (PI). P ws pplied 1% of dose bsl. K ws split in two ppliction 5% bsl nd 5% t pnicle initition. Tble 1. Physicl-chemicl properties of Typic fluvquent soil Gry lowlnd collected t pddy field in Shimne prefecture, Jpn Soil chrcteristics Vlue Snd (%) 22.8 Silt (%) 37.8 Cly (%) 39.4 ph 4.85 EC (msm -1 ) 3.87 Bulk Density (g cm -3 ) 1.39 Totl C ( g kg -1 ) 17.6 Totl N ( g kg -1 ) 1.6 NH 4 -N (mg kg -1 ) 4.91 NO 3 N (mg kg -1 ) 8.22 Avilble P (mg kg -1 ) 34.9 Figure 1. Schemtic representtion of rndomized block design t with different irrigtion tretments were pplied during the growth seson. (I) Sowing, (II) Trnsplnting, (III) Tillering, (IV) Heding, (V) Mturity Stge, (VI) Hrvest. Period between ( ) IV nd V ws considered s grin filling stge 165

4 Journl of Agriculturl Science Vol. 7, No. 5; Plnt nd Rice Grin Chemicl Anlysis Plnt smples were collected t hrvest. Flg leves were first wshed with tp wter nd twice with distilled wter. Therefter they were oven dried t 4 C for 48 hours nd dehusked in rotting rubber roll, (Stke THU35B, Jpn). For micronutrient nlysis, flg leves nd grin smples were ground into fine powder in gte grinding jrs, using mixer mill (MM2, Retsch GmbH, Hn, Germny). Grin nd plnt smples were oven-dried 12 hours t 8 C. Subsequently.5 g of smple ws digested in 2.5 ml HNO 3 within Teflon vessel. All smples were oven heted t 16 C for 4 hours, kept resting overnight nd diluted with distilled wter up to 25 ml (Koym & Sutoh, 1987). The concentrtions of Fe, Zn, Cu nd Mn were determined by Inductive Coupled Plsm Spectroscopy (ICPE-9, Shimdzu, Jpn). 2.3 Soil Smpling nd Anlysis Soil smples were collected from 5, 1 nd 15 cm depth in the bucket fter hrvest. They were immeditely stored in ZIPLOC hermetic plstic bg nd refrigerted in order to mintin originl chemicl soil properties. Portions of ech smple ws oven dried t 15 C to mesure the moisture content to clculte the necessry mount for ll the subsequent nlyses following stndrd nlyses methods (Jpn Soil Environment Anlysis Methods Committee, 23). The concentrtion of micronutrients (Fe, Zn, Cu nd Mn ws nlyzed by mixing 1 g of soil with 2 ml of diethylene trimine pentcetic cid (DTPA-TEA) extrcting solution (Linsy & Norvel, 1978). The solution obtined ws filtered nd nlyzed in ICPE-9. Soil ph ws determined by the soil-wter rtio of 1:2.5 nd electric conductivity (EC) soil-wter rtio of 1:5 using electrode method (D-24 HORIBA, Jpn). Redox potentil ws mesured in situ from trnsplnting period to 25 DAT t 1cm depth using electrode method (PNR-41, DKK-TOA Co., Jpn). 2.4 Sttisticl Anlysis To determine the influence of wter mngement on soil properties, micronutrient concentrtion in soil, plnt nd rice grin ccumultion, dt were sttisticlly nlyzed by one wy nlysis of vrince (ANOVA). Significnt differences mong the tretments were determined by Turkey s honestly significnt difference (HSD) test (P <.5) for multiple mens comprison. Correltion nlysis between grin micronutrient concentrtion nd soil properties ws done using Person Product Moment Correltion (PPMC). All sttisticl nlysis ws performed using IBM SPSS Sttistic v2. (IBM SPSS, 211. Chicgo IL, USA). 3. Results 3.1 Soil Properties Effects of flooding on soil redox potentil (Eh) (Figure 2) were observed from trnsplnting until erly tillering stge (25 DAT). There ws shrp decrese over time in the Eh t the 1 cm depth, from +467 to -379 mvolt (mv). This suggested tht depletion of O 2 nd n increse in electron ctivity medited by microorgnisms respirtion ws highly mrked in the first five dys. However, fter 17 dys Eh vlues chieved n pprent stbility, without significnt chnges. As result of chnges in the soil electricl conductivity in the flooded tretments, the ph incresed from initil ph 4.85 (trnsversl dshed line) t trnsplnting (Figure 2b). In the control which ws flooded throughout the growth stge, ph ws 6.18 t the hrvest stge, significntly higher thn tht of the other tretments tht were drined fter heding t 4, 3, 2 WAH. In the drined tretments, ph rnges declined between without significnt differences mong them. Results show tht ph cquires specific vlues t specific soil moisture. FCp tretment showed the lower ph of

5 Journl of Agriculturl Science Vol. 7, No. 5; 215 Eh mv Dys fter flooding Figure 2. Influence of soil flooding on soil electrochemicl properties. ) Soil Redox Potentil; b) Soil ph(h 2 O). [dshed line represent the pre-flood ph vlue] ph (H 2 O) b b b b Control 4WAH 3WAH 2WAH FCp Tretments c 3.2 Influence of Wter Mngement on Grin Micronutrient Contents nd Yield One wy nlysis of vrince (ANOVA) showed tht, there were sttisticlly significnt differences between mens of micronutrient concentrtion in grin (P-vlue <.5) Tble 2. Therefore resulted in rejection of the null hypothesis which stted tht ll the dt cme from groups with the sme men. In this cse, subsequent nlysis will help us to find significnt difference between pirs of mens in t lest one of the tretments. Tble 2. One Wy nlysis of vrince (ANOVA) for the concentrtion of micronutrients in grin Sum of Squres df Men Squre F Sig. Grin-Fe Concentrtion Between Groups Within Groups Totl Grin-Zn Concentrtion Between Groups Within Groups Totl Grin-Cu Concentrtion Between Groups Within Groups Totl Grin-Mn Concentrtion Between Groups Within Groups Totl The concentrtion of micronutrients in rice grin (Figure 3) differed significntly mong irrigtion tretments. The Fe concentrtion in grin rnged from 19.1 mg kg -1 to mg kg -1. 4WAH, Control nd 2WAH showed the higher Fe concentrtion with no lrge significnt differences, while 3WAH nd FCp were 1% nd 23% respecctively lower thn Control. In contrst to Fe, Zn concentrtion in rice grin ws more sensitive to chnges in wter mngement (Figure 3b). Tretments FCp nd 2WAH showed vlues 35.4 mg kg -1 nd 33.7 mg kg -1 respectively, representing 18% nd 11% significntly higher thn Control. The concentrtion of Cu in grin clerly rose due the estblishment of erobic condition (Figure 3c). Tretments FCp nd 2WAH showed higher concentrtions of 4.82 nd 4.11 mg kg -1 respectively without significnt difference between them. Both tretments lmost doubled their concentrtion in comprison with Control, 4WAH nd 3WAH which were not significntly different. The trend observed for Mn grin concentrtion ws not s we expected for the different wter tretments. As soil nerobic conditions were more prolonged, grin Mn concentrtion decresed. Vlues vried from mg kg -1 to mg kg -1, tretments 2WAH nd FCp rose their Mn concentrtion by 65-76% respectively higher thn Control (Figure 3d). 167

6 Journl of Agriculturl Science Vol. 7, No. 5; 215 ) 25 Fe b b 2 bc c Control 4WAH 3WAH 2WAH FCp Tretments Fe-Grin Conc.(mg kg ¹) b) Zn 4 b c c bc 35 Zn-Grin Conc.(mg kg ¹) Control 4WAH 3WAH 2WAH FCp Tretments c) Cu 6 Cu-Grin Conc.(mg kg ¹) 5 4 b b b d) Mn-Grin Conc.(mg kg ¹) b Mn b c c Control 4WAH 3WAH 2WAH FCp Tretments Control 4WAH 3WAH 2WAH FCp Tretmetns Figure 3. Concentrtion of micronutrients (Fe, Zn, Cu nd Mn) in rice grin, influenced by wter mngement The effects of soil dringe on grin micronutrient concentrtion during erly grin filling stge, round 75-8 DAT, ws beneficil prticulrly from tretment 2WAH where the period of flooding ws the shortest. Tht period ws identified s high demnd for micronutrient cquisition nd ccumultion. Despite of chnges in soil properties, the trnsition from flooded to erobic conditions incresed grin yield nd root density by 7% nd 7.3 % respectively compred to the control (Tble 3). Although boveground plnt biomss (lef nd stem weight) showed higher vlues for drined tretments, we observed tht the increse ws due the emergence of some new shoots fter of the erobic conditions were estblished. These tillers did not produce pnicle t the time of hrvest. Tble 3. Comprison of dry mtter weight mong different wter mngements. Vlues represent mens of dry mtter weight, on ech prt of the rice plnt Control 4WAH 3WAH 2WAH FCp. Grin yield (g plnt -1 ) 3.1 b 3.5 b 31.3 b c Lef & Stems weight (g plnt -1 ) 11. b 18.6 b c Roots weight (g plnt -1 ) b b Note. * Mens followed by different lowercse letter represent the significnt difference t P <.5 mong tretments. 3.3 Soil Micronutrient Avilbility nd Wter Mngement Soil micronutrient vilbilities were clerly influenced by wter mngements. The Fe vilbility (Figure 4) significntly decresed from Control to FCp. The decresing chnge ws more evident fter the re-oxidtion of tretments 4, 3, 2 WAH where the concentrtion ws reduced by more thn 2%. Tretments 3WAH, 2WAH nd FCp showed slight increse in Zn vilbility by 6, 11nd 12% over Control, respectively, lthough differences were not sttisticlly significnt (Figure 4b). 168

7 Journl of Agriculturl Science Vol. 7, No. 5; 215 ) Fe 25 b Fe Avil.(mg kg ¹) c b d b) Zn 4 Zn Avil.(mg kg ¹) Control 4WAH 3WAH 2WAH FCp Tretments Control 4WAH 3WAH 2WAH FCp Tretments c) Cu 4 Cu Avil. (mg kg ¹) 3 b 2 1 d) Mn Avil. (mg kg ¹) Mn b Control 4WAH 3WAH 2WAH FCp Control 4WAH 3WAH 2WAH FCp Tretments Tretments Figure 4. Micronutrients vilbility (Fe, Zn, Cu nd Mn) in soil Cu vilbility incresed shrply s erobic condition were estblished. Figure 4c shows how Cu vilbility increse from flooded condition to 4WAH in short time. Cu vilbility reched its pek vlues s result of decresing ph which is mintined cross subsequent tretments. Avilbility of Cu did not show significnt difference between the drined (4, 3, 2WAH) nd FCp tretments. FCp nd 2WAH were >2% significntly higher thn Control. Likewise, Mn vilbility (Figure 4d) remined high cross ll the tretments regrdless of flooding schedule. These tretments did not showed significnt differences mong them. Avilbility of Mn rnge from 187 mg kg -1 to 228 mg kg -1. Control ws six fold higher in vilble Mn thn FCp. 4. Discussion At first, for better understnding of the results of present study, we simply summrize the effect of Soil Eh nd ph chnge with wter mngement on micronutrient vilbility in soil. Soil flooding conditions cused modifictions in soil ph nd Eh. After its estblishment, soil pores were wter sturted nd Eh strted to decrese progressively (Figure 2). The depletion of O 2, triggered new processes driven minly by strict fculttive nerobic microbes tht thrive under these environments. They tke over further biochemicl rections, using substnces other thn O 2 s the terminl electron cceptor to metbolize orgnic compounds (Berkowitz, 214). In the present study, the ph increse under flooding condition (Figure 2b), could be led by Eh reduction nd the hydrogen consumption, during the reduction process of MnO 2 nd Fe(OH) 3 nd other trnsition elements demnded in microbes metbolism (Brdy & Weil, 214). The trnsition from flooding to erobic condition during grin filling stge, reduced ph suggesting tht estblishment of erobic condition could hve ffected the Eh nd therefore ph could be progressively restored towrd its initil vlue, s soil is re-oxidized (Zhou et l., 214). Redox rections (i.e. gin nd losses of electrons) cn define both the soil ph nd the vilbility of micronutrients (White & Brodley, 29). 4.1 Fe Dynmics In our result, Fe vilbility (Figure 4) ws over the criticl level in soil (5 mg kg -1 ) for deficiency nd below 3 mg kg -1 in lef for toxicity (Dobermnn & Firhurst, 2). The vilbility of Fe in soil ws significntly higher in flooded thn drined tretments, which implies tht Fe vilbility in soil depends on soil Eh. Therefore wter mngement becomes the mjor controlling fctor to consider in promoting Fe plnt uptke. Results lso showed tht even when soil becme erobic, Fe vilbility decresed t 2, 3 nd 4WAH, but the grin Fe concentrtion ws kept comprble in ll the tretments except FCp. Moreover, trnsition from 169

8 Journl of Agriculturl Science Vol. 7, No. 5; 215 flooding to erobic nd re-oxidtion of Fe 2+ to less soluble form t 2WAH nd the other drined tretments, did not ffect substntilly the concentrtion of Fe in grin. Remobiliztion of Fe from tissues to the grin my explin this phenomen. Studies conducted on rice by Sperotto et l. (213) suggested tht leves were the min source to supply Fe to the seeds by remobiliztion from old tissues. Besides, relese of orgnic cids (phytosiderophores) in rhizosphere might lso contribute to Fe cquisition under erobic condition nd deficiency stress (Nozoye et l., 213). Rice plnt, during the tillering nd reproductive stges is ble to ccumulte Fe s ferritin Fe-reserve protein (D Silveir et l., 29). This Fe is remobilized vi phloem by metl-trnsporters such s OsIRT1, OsIRT2, OsYSL15, nd OsNRAMP5 which enhnce their ctivity during grin filling stge (Bshir et l., 213). In ddition, the enhncement of Fe vilbility in soil, inhibited the vilbility of Zn nd Cu in soil (Dobermnn & Firhurst, 2) nd the concentrtion of Zn, Cu nd Mn in grin s showed correltion mtrix (Tble 4) therefore the re-oxidtion of Fe to less soluble form from 2WAH, might fcilitte the uptke of such micronutrients nd improve the concentrtion in grin 4.2 Zn Dynmics Regrding vilble Zn vlues, in soil were bove the criticl levels (.8 mg kg -1 ) for deficiency (Dobermnn & Firhurst, 2). The concentrtion of Zn in grin s well s the concentrtion in soil ws the highest in FCp, nd lso tended to increse by trnsition from Control, to 2, 3,4WAH (Figures 3b nd 4b). These enhncements in grin positively correlted (P <.1) with the Zn vilbility in soil (see Tble 4). Although Zn vilbility in soil might be ffected by severl fctor (Sdeghzdeh, 213) pprently, the reestblishment of erobic condition, ph declining nd reduction of Fe to less vilble form were the mjor fctor controlling Zn vilbility. The timing in which irrigtion ws stopped, lso plyed n importnt role for Zn cquisition. Unlike FCp, which chieved high grin Zn but low yield, 2WAH showed the best performnce in terms of Zn grin concentrtion nd grin yield (Tble 3). The period in which soil ws re-oxidized coincided with grin filling stge, which hs been identified s high demnd period not only for the uptke nd remobiliztion of Zn but lso other essentil elements (Person & Rengel, 1994; Bshir et l., 213) Mny reserchers found tht Zn is trnslocted from old tissues to flg lef nd fterwrds remobilized to the grin (Rengel et l., 1999; Wu et l., 21). However, the higher percentge of Zn moved into the grin is tken up directly by root, during post-heding stge (Jing et l., 27; Sperotto et l., 213). Although the vilbility in soil did not show significnt differences with control, 2WAH responded more positively thn other tretments. In comprison with 2WAH, tretments 3 nd 4WAH did not increse their Zn grin concentrtion even when erobic condition could hve fcilitted vilbility of Zn. Under flooding condition, Zn cn be precipitted s ZnS nd Zn(OH) 2 or reduced its trnsport nd root uptke by HCO 3 which is the predominnt nion t such condition (Dobermnn & Firhurst, 2). The smll enhncement in root density (Tble 3) observed in 2WAH, lso could be nother positive fctor tht fcilitted lrger soil contct re (Yng et l., 24) nd therefore, increse Zn uptke by plnt. 4.3 Cu Dynmics Avilble Cu in soil is held minly s free cupric ion (Cu 2+ ) which is the preferred form for plnt (Hong et l., 28). In our results the Cu behvior in soil nd grin ws brodly similr with the trend observed in Zn. Results showed tht the wter condition t this period in which soil ws re-oxidized t erly grin filling stge, i.e. two weeks fter heding, ws determining fctor controling the Cu contents in grin. Figures 3c nd 4c, showed close reltionship between soil Cu vilbility nd grin concentrtion. Furthermore, the shifting from nerobic to erobic condition promote enhncement of Cu solubility nd biovilbility s well s better root uptke (Lio et l., 213). On the other hnd the lower Cu vilbility observed in tretments where nerobic condition ws kept longer, could be scribed to the formtion of Cu-ferrite (Cu 2 Fe 2 O 4 ), orgnic mtter bound nd formtion of insoluble CuS (Dobermnn & Firhurst, 2). Soil Zn vilbility did not significntly increse when the erobic conditions were estblished, but Cu did (Figures 4b nd 4c). This suggested tht Cu is ble to increse in vilbility esier thn did Zn. Grnett et l. (25) reported tht more thn 6% of Cu in grin ws bsorbed t filling stge, which explins the importnce of timing in wter mngement to increse grin Cu concentrtion. Enhncement of Cu vilbility is dvisble in soils where Cu do not exceed toxic level for plnt nd humns (Xu et l., 26). 4.4 Mn Dynmics Despite of estblishment of erobic condition, scheduled t 2, 3,4 WAH, soil Mn vilbility remined high (Figure 4d) without significnce chnges compred with control. Since Mn is reduced t higher potentil (+4~ -1mV) thn Fe (+2~ -2 mv) (Kyum, 1997), the Mn vilbility in soil cn be kept stble longer thn Fe in drined tretments of which the moisture condition chnged. Although Fe nd Mn tke ctive prts in redox rections in soil nd both re ble to increse their vilbility fter soil flooding, presumbly, high Fe 17

9 Journl of Agriculturl Science Vol. 7, No. 5; 215 vilbility observed in soil, dversely inhibited Mn uptke by roots, becuse of the ntgonist interction in soil (Dobermnn & Firhurst, 2; Millleo et l., 21; Ds, 214). Alm (1985) reported tht concentrtion of Mn in leves nd stems of 7 weeks plnts were incresed when Fe ppliction rnged -3 mg kg -1 in soil, but bove 3 mg kg -1 ppliction reduced Mn concentrtion in plnt. Other studies conducted by Person nd Rengel, (1994) concluded tht Mn concentrtion in flg lef nd other ctive leves incresed during grin filling stge, but remobiliztion to the grin ws not crried out, regrdless of the lef concentrtion. Suggesting tht, continuous uptke from soil seems to be the min source of grin Mn. However its behvior still remins uncler, therefore further investigtions re needed to elucidte this issue. 4.5 Reltionship mong Soil, Plnt nd Grin Micronutrients Composition. The effect of wter mngement on soil micronutrients vilbility nd its reltionship with the concentrtion in grin nd flg lef re shown in Tble 4. The vilbility of Fe, Zn nd Cu in soil significntly correlted with their respective concentrtions grin. Soil ph, redox rections, plnt physilogy (Growth stge) nd rhyzosphere ctivity re the min fctors controlling the vilbility in soil nd concentrtion of micronutrients in grin (Dobermnn & Firhurst, 2; Go et l., 212; Mrchner, 212) medited by the trnsition from flooding to erobic condition. Mn detected in soil did not correlte with Mn concentrtion in flg lef nd showed negtive correltion with grin Mn (p <.5). Fe vilbility in soil correlted negtively with the concentrtion of Zn nd Cu in plnt nd grin (p <.1). This observtion suggested tht vilbility of Fe in soil could be ttributed to ntgonistic interction, nmely inhibition of Zn, Cu nd Mn uptke (Dobermnn & Firhurst, 2) Negtive effects of Fe excess on Cu nd Mn shoots concentrtion hve been observed in Indic vrieties (Yoshihr et l., 21). Concentrtion of Fe, Zn, Cu nd Mn in flg lef correlted positively with their respective concentrtion in grin. Moreover, concentrtion of Zn, nd Cu in grin nd flg lef correlted significntly (p <.1) mong ech other. Studies conducted by Ishimru et l. (25) reveled tht the expression of ZIP s gene fmily re ctively relted with the Zn nd Cu uptke nd trnsport system. The sme mechnism my control the behvior of Zn nd Cu in plnt, which brought the similr results of Zn nd Cu in the present study. Tble 4. Correltion mtrix between soil micronutrients vilbility nd micronutrient concentrtion in flg lef nd grin Soil Micronutrient Flg lef Micronutrient Grin Fe Zn Cu Mn Fe Zn Cu Mn Fe Zn Cu Zn -.33 * Cu -.77 **.43 ** Mn.71 ** -.47 ** -.47 ** Fe Zn -.68 ** ** -.14 Cu -.74 **.47 *.61 ** -.81 **.2.77 ** Mn *.59 ** ** ** Fe.63 ** -.38 * -.41 **.55 ** ** -.61 ** -.27 Zn -.61 **.39 *.46 ** -.58 ** **.86 **.76 **.25 Cu -.57 **.45 **.51 ** -.66 ** **.93 **.8 ** ** Mn -.53 **.48 **.59 ** -.34 *.46 * **.85 ** **.79 ** Note. ** nd * represent significnt correltion t P <.1 nd P <.5 respectively. Soil Flg lef Grin 5. Conclusions Soil wter mngement chnges the soil Eh nd ph, which control the vilbility of micronutrient in soil nd consequently the concentrtion in rice grin. When those chnges occur during grin filling stge, micronutrients such s Zn, Cu nd Mn increse their concentrtion in the grin, likely due the reduction of ph nd their interction with other soil properties. Although wter mngement did not exerted significnt chnges on soil Fe vilbility, its re-oxidtion to less vilble form, promoted the increse of Zn, Cu nd Mn in grin. Although reserchers hve been focused to increse the concentrtion of micronutrient in grin through breeding 171

10 Journl of Agriculturl Science Vol. 7, No. 5; 215 strtegies, if soil mngement in reltion to wter condition is not pplied, those strtegies inevitbly will fil. Therefore estblishment of erobic condition strting from 2 weeks post-nthesis till mturity by proper wter mngement such s intermittent irrigtion, seems to be the most fesible strtegy to increse the concentrtion of micronutrients in rice grin. Furthermore, this technique did not result in grin yield losses. Our results exhibited the importnce of soil environmentl mngements in reliztion of the biofortifiction progrm. Plnt breeding strtegies must work longside gronomic biofortifiction techniques. In this prticulr cse of rice, the combintion between wter mngement nd plnt breeding could be the most vible option in order to ensure the supply of micronutrients from the soil nd overcome mlnutrition in vulnerble popultions. Acknowledgements This study ws supported by Jpn Society for the Promotion of Science (Grnt-in-Aid Scientific Reserch No ). The uthor is highly grteful to the members of the Pedosphere Eco-Engineering Lbortory, Fculty of Life nd Environmentl Science, Shimne University. References Alm, S. M. (1985). Effects of iron nd mngnese on the growth of rice nd on the contents of these elements in rice plnts. Agronomie. Retrieved Jnury 7, 215, from Allowy, B. J. (28). Micronutrient deficiencies in globl crop Production. Springer Sci., Dordrecht. Bin, L. E., Awh, P. K., Gerldine, N., Kindong, N. P., Sigl, Y., Bernrd, N., & Tnjeko, A. T. (213). Mlnutrition in Sub Shrn Afric: Burden, cuses nd prospects. The Pn Africn Medicl Journl, 15, Bshir, K., Tkhshi, R., Nknishi, H., & Nishizw, N. K. (213). The rod to micronutrient biofortifiction of rice: progress nd prospects. Frontier Plnt Science, 4, Bell, R.W., & Dell, B. (28). Micronutrients for Sustinble Food, Feed, Fibre nd Bioenergy production. Interntionl Fertilizer Industry Assocition IFA, Pris, Frnce. Berkowitz, B. (214). Biologicly nd medited trnsformtion. In B. Berkowitz, I. Dror, & B. Yron (Eds.), Contminnt geochemistry. Interctions nd trnsport in the Subsurfce environment (2nd ed., pp ). Springer. Brdy, N. C., & Weil, R. R. (214). The Nture nd Properties of Soil (14th ed.). Person Eduction Limited, USA. Ckmk, I. (28). Enrichment of cerel grins with zinc: Agronomic or genetic biofortifiction? Plnt Soil, 32, D Silveir, V. C., Fdnelli, C., Sperotto, R. A., Stein, R. J., Bsso, L. A., Sntos, D. S.,... Fett, J. P. (29). Role of Ferritin in the Rice Tolernce to Iron Overlod. Scienti Agricol, 66, Ds, S. K. (214) Role of Micronutrient in Rice Cultivtion nd Mngement Strtegy in Orgnic Agriculture A Repprisl. Agriculturl Sciences, 5, Dobermnn, A., & Firhurst, T. (2). Rice: Nutrient disorders nd nutrient mngement. Singpore nd Los Bños: Potsh & Phosphte Institute (PPI), Potsh & Phosphte Institute of Cnd (PPIC), nd Interntionl Rice Reserch Institute (IRRI), Philipine. Fgeri, N. K. (22). Influence of micronutrients on dry mtter yield nd interction with other nutrients in nnul crops. Pesquis. Agropecuri Brsileir, 37, Food nd Agriculture Orgniztion (FAO). (213). In feeding the world. FAO Sttisticl Yerbook. Retrieved Jnury 7, 215, from Go, X., Hofflnd, E., Stomph, T., Grnt, C. A., Zou, C., & Zhng, F. (212). Improving zinc biovilbility in trnsition from flooded to erobic rice: A review. Agronomy for Sustinble Development, 32, doi.org/1.17/s x Grnett T. P., & Grhm R. D. (25). Distribution nd Remobiliztion of Iron nd Copper in Whet. Annls of Botny, 95, Hong, T. C., Rogevich, E. C., Rnd, G. M., Grdinli, P. R., Frkes, R. A., & Brgr, T. A. (28). Copper 172

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