AJCS 6(12):163-1636 (212) ISSN:1835-277 Grin yield nd dry mtter ccumultion response to enhnced pnicle nitrogen ppliction under different plnting methods (Oryz stiv L.) Song Chen 1*, Xiufu Zhng 1, Guoping Zhng 2, Dngying Wng, Chunmei Xu 1, 1 Chin Ntionl Rice Reserch Institution, Hngzhou, 3129 Chin 2 Agronomy Deprtment, Zhejing University, Hngzhou, 3129 Chin *Corresponding uthor: chis.zju@gmil.com Astrct A four-yer field experiment (26-29) ws conducted to ssess the effect of enhnced pnicle nitrogen ppliction on rice yield nd its dry mtter ccumultion chrcteristics in direct-seeded (R) nd trnsplnted rice (R). The field experiment included two plnting ptterns (R nd R) nd four nitrogen tretments: () low pnicle nitrogen fertilizer (PNF) with high totl nitrogen mount (TNA; 225kg N h -1 ); () low PNF with low TNA (15kg N h -1 ); () high PNF with high TNA; () high PNF with low TNA. There ws little difference in men yield of plnting ptterns etween nd. However, the men yield in ws 1.15% greter thn in. The men totl dry mtter in ws 12.% greter thn in. These results indicted tht enhnced PNF might enefit dry-mtter ccumultion ut led to yield decline. We found tht rice yield ws linerly correlted with grin filling percentge (R 2 =.47, p <.1) s well s grins m -2 (R 2 =.55, p <.1). Grins m -2 ws qudrticlly correlted with stem dry mtter t the heding stge, which suggests tht over-ccumulted dry mtter in the stem efore grin filling might ply negtive role in grin yield. Grin filling percentge nd grin m -2 were found to e linerly correlted with lef dry mtter t the heding stge, which suggests tht lef growth t pnicle initition nd heding stge might e criticl chrcteristics in yield performnce. Keywords: Rice; Grin yield; Plnt dry mtter; Direct seeding; Trnsplnting, Pnicle Nitrogen fertilizer. Arevitions: R: Trnsplnted rice; R: Direct-seeded rice; PNF: Pnicle nitrogen fertilizer; TNA: Totl nitrogen mount; MT: Mid-tillering stge; HS: Heding stge; PI: Pnicle initition stge; GFP: Grin filling percentge 1. Introduction The mount of N sored during pnicle initition mkes the most effective contriution to spikelet production s well s grin filling. A lrger mount sored increses specific lef weight nd N content in leves, which leds to enhncement of photosynthetic cpcity nd promotion of crohydrte ccommodtion in culms nd lef sheths (Me, 1997). Therefore, hevy nitrogen fertiliztion during pnicle development, so clled pnicle nitrogen fertilizer (PNF), hs een populr in Chin to improve popultion dynmics, mke fertilizer use more efficient nd enhnce grin yield in recent yers (Jing et l., 24; Lin, 2). In ddition, switch in plnting methods from trnsplnting to direct seeding hs occurred in Chin (nd mny other countries) s lor costs hve risen nd the need to intensify rice production through doule nd triple cropping hs provided economic incentives (Dwe, 25; De Dtt, 1986; Nklng, 1996; Pndey et l., 22). Menwhile, most high-yielding rice vrieties relesed in Chin in the lst decde hve een chrcterized s hving high nitrogen tolernce with high dry mtter production (Lin et l., 29; Ottis et l., 28). Moreover, frmers hve discovered tht pplying enhnced fertilizer t mid-tillering (MT) encourges erly popultion development of rice nd sves lor y reducing the time needed for topdressing, especilly in Southest Chin. As result, the totl nitrogen fertilizer mount hs incresed to very high level to mintin yield performnce, which hs led to huge wste of nitrogen fertilizer followed y series of environmentl prolems. Whether PNF could help to mintin yield or minimize yield loss in rice pddies when the totl nitrogen is reduced is still unknown. R cultivtion provides completely different growth environment for rice, prticulrly t the seedling stge, compred with tht under the trnsplnting system. The proportion of plnt N derived from pplied fertilizers is out 4-6% in young seedlings (Me, 1997). Nitrogen sored during the vegettive period minly promotes the erly growth of the plnt nd increses the numer of tillers (Mkino et l., 1984). In ddition, R hs shorter time from seeding to emergence (Pndey et l., 22), stronger root ctivity (De Dtt nd Nntsomsrn, 1991), higher grin-setting percentge nd greter iomss production in the erly period (Nklng, 1996) compred to R. These differences ffect nitrogen sorption nd physiologicl utiliztion. In ddition, higher PNF results in reduced MT nitrogen fertilizer topdressing, which might depress the erly development of R. However, literture out the effects of PNF on the erly growth nd enhnced reproductive stge of R is limited. Until now, most rice vrieties hve een specificlly red for trnsplnted conditions. Nitrogen fertiliztion strtegies hve lso een developed sed on the gronomy prctice of trnsplnting nd hve een widely dopted to improve rice yield with high totl nitrogen level. In fct, grin yields of most rice vrieties re chieved y high nitrogen input in Chin. With incresing use of pnicle fertiliztion, there hs een less fertiliztion pplied t sl or topdressing in MT, ut responses of rice yield nd dry mtter ccumultion in R nd R hve een little studied. Thus, it is of urgent importnce to understnd the reltionship etween plnting pttern nd nitrogen mngement under the Chinese system. The ojective of this study ws to determine the effects of 163
nitrogen fertiliztion strtegies on R yield in terms of dry mtter ccumultion nd redistriution nd to test the PNF effect on R when the totl nitrogen level ws reduced. This would help high-yielding rice vrieties to estlish the proper N fertiliztion strtegy for R with the im of improving nitrogen use efficiency nd mintining high yield level. 2. Results 2.1 Effect of N tretments on grin yield In generl, the men yield cross the fertiliztion of R ws slightly decresed compred with tht of R. The difference mong the men yields of N tretments ws significnt: >,, in nd > >, in R. However, rice yield ws vrile cross yers. The men yields of cross the yers were 11%-18% nd 11%-19% higher thn tht of other N tretments in R nd R, respectively. The highest yield of R ws 11.1 t/h otined y mngement in 29, nd the highest yield of R ws 1.43 t/h otined y in 29 (Tle 2). Rice yield cross yers ws lso influenced y the totl nitrogen mount nd PNF levels. The interction etween plnting ptterns (PP) nd nitrogen fertiliztion tretments (NF) ws significnt (Tle 2). Apprently, grin yield depended on the totl nitrogen mount, especilly in R, where rice yield t the rte of 225 kg N h -1 ws greter thn tht of 15 kg N h -1 in oth PNF levels except in 27. However, in R, the effect of totl nitrogen mount ws only found in low PNF. The PNF effect on grin yield vried within different totl nitrogen mounts. In comprison with low PNF, rice yield in high PNF ws reduced when the mount ws 225 kg N h -1 nd styed consistent when the mount ws 15 kg N h -1. However, the PNF effect on yield difference etween R nd R ws not significnt. The yer s effect on yield difference etween R nd R ws significnt, so it is difficult to drw conclusions out the PNF effect on yield difference etween R nd R cross the yers. Furthermore, rice yield ws significntly decresed due to unusul climtic conditions during 27 (extremely high temperture during reproductive phse). Effects of N mngement on totl dry mtter ccumultion nd hrvest index The N mngement effect on the totl dry mtter ccumultion nd hrvest index (HI) under R nd R re shown in Tle 2. In generl, totl dry mtter ws greter in R thn in R, while the opposite ws found for HI. Significnt differences in totl dry mtter ccumultion nd HI were found mong N tretments, with greter thn the other methods regrdless of plnting ptterns. The PNF effect on totl dry mtter vried depending on the totl nitrogen mount. Totl dry mtter in high PNF ws greter thn tht in low PNF when the mount ws 225 kg N h -1. However, little difference ws found etween low nd high PNF when the mount ws 15 kg N h -1. The PNF effect on HI vried with different N mngements, eing > >,. Compred with low PNF, high PNF in HI ws incresed when the mount ws 15 kg N h -1, ut decresed when the mount ws 225 kg N h -1. Becuse the interctions of PP nd NF on totl dry mtter nd HI were not significnt, little difference etween R nd R in N mngement effect ws found in totl dry mtter nd HI. Effects of N mngement on dynmic chnge of plnt dry mtter ccumultion Dynmic totl dry mtter ccumultions in different N mngements were determined for R nd R methods (Figure 1). Before MT, dry mtter ccumultion ws generlly greter in R thn in R, ut the opposite ws found from MT to HS in ll yers except for in 27 nd in 29. On verge, dry mtter ccumulted in R ws 43% greter thn in R efore MT, nd 23% less from MT to HS. Little difference in dry mtter ccumultion ws found etween totl nitrogen mount of 15 nd 225 kg N h -1 in oth R nd R regrdless of growth periods. The PNF effect on dry mtter ccumultion vried with plnting ptterns nd growth periods. R produced more dry mtter during PI to HS with high PNF ( nd ) thn with low PNF ( nd ) in ll yers nd plnting ptterns except for 26 in R. R produced more dry mtter in the vegettive phse, while R produced more in the reproductive phse. Self-regultion of plnt group might prtly explin the different dry mtter ccumultion rtes. Effects of N mngement on net photosynthetic nd SPAD vlue Flg lef net photosynthetic rte nd lef SPAD vlue were determined to evlute the cpcity of lef CO 2 ssimiltion nd nitrogen sttus (Figure 2). In generl, flg lef net photosynthetic rte ws greter in R thn in R when high PNF ws pplied in ll the yers except 27 (Figure 2). However, the difference etween R nd R ws not significnt when low PNF ws pplied. Furthermore, flg lef net photosynthetic rte in high PNF ws greter thn in low PNF when the sme TNI ws pplied in oth R nd R in ll yers except for 26 nd 28 in R nd 27 in R. The effect of N mngement on lef SPAD vlue vried y yer (Figure 2). The difference in SPAD vlue etween nd ws significnt when high PNF ws pplied, with R significntly greter thn R; however, little difference ws found when low PNF ws pplied, except in 29. Menwhile, the effect of TNI on the difference in SPAD vlue etween R nd R ws not significnt. Reltionships of rice yield nd dry mtter ccumultion Reltions etween yield components nd grin yield were nlyzed to determine the component fctors tht might influence the finl grin yield. We found tht grin filling percentge (GFP) nd grins m -2 were linerly relted with grin yield in oth R nd R. The reltionship etween yield nd GFP is shown in Figure 3; no sustntil difference etween R nd R ws found. However, there ws cler difference etween R nd R in the reltionship etween grins m -2 nd grin yield (Figure 3). Grins m -2 for given grin yield ws 1% lrger in R thn in R on verge. Further nlysis ws crried out to evlute the reltionships etween dry mtter ccumultion chrcteristics nd grins m -2 /GFP. For grins m -2, chrcteristics of totl plnt dry mtter t MT, lef dry mtter t PI nd HS ws linerly relted with grins m -2 (Figures 4,, c). Moreover, qudrtic curve reltionship ws found etween stem dry mtter t HS nd grins m -2 (Figure 4d). There ws cler difference etween R nd R in the reltionship etween GFP nd lef dry mtter, with GFP out 14% lrger in R thn in R. 1631
Tle 1. Fertilizer ppliction tretment (kg N h -1 ) for R nd R. Fertilizer tretment Bsl c Topdressing Rte Totl N TNA PNF dressing MT PI 225 1% of TNA 3:6:1 225 67.5 135 22.5 15 1% of TNA 3:6:1 15 45 9 15 225 3% of TNA 2:5:3 225 45 112.5 67.5 15 3% of TNA 2:5:3 15 3 75 45 : The proportion of N fertilizer ppliction rte t sl, MT nd PI. : Compound Fertilizer (N:P:K=15%:15%:15%), c: Ure. Note: R: direct seeding rice; R: trnsplnting rice; TNI: totl nitrogen mount; PNF: pnicle nitrogen fertilzer; 2 Before MT PI-HS MT-PI HS-MS 2 2 1 1 1 1 2 c 2 d 2 2 1 1 1 1 Fig 1. Plnt totl dry mtter ccumultion efore MT, from MT to PI, from PI to HS nd from HS to MS of rice under nd with different nitrogen fertiliztion in Jixing Chin from 26 to 29 ( - d). Discussion PNF effect on grin yield nd totl dry mtter with different plnting ptterns To improve nitrogen use efficiency (NUE) in order to increse frmers profitility nd reduce negtive environmentl externlities, studies hve previously een performed on spects of rice yield nd N utiliztion under different N ppliction rtes nd ptterns. However, the conclusions hve een inconsistent (Jing et l., 27; Li nd Zhng, 1981; Shi et l., 28; Tn et l., 1981). Recently, pnicle N fertiliztion ws recommended for use in rice production in Chin to increse grin yield nd reduce nitrogen loss in the field (Ling, 2). Belder et l. (24), Jing et l. (24), Jing et l. (27), nd Shi et l. (28) ll used differentil responses to N mngement of rice cultivrs (inred rice, two-line hyrid, nd three-line hyrid, etc.), ssuming tht higher pnicle nitrogen frction would e sound strtegy for improving NUE nd yield. However, our results showed tht enhnced pnicle nitrogen fertilizer hd negtive effect on the yield production of rice vriety Xiushui 9 in oth R nd R, especilly when the totl nitrogen mount ws high (225kg N h -1 ). Furthermore, the grin yield depended on the nitrogen mount: rice yield ws greter t the rte of 225kg N h -1 thn t the rte of 15kg N h -1. Cultivr s differentil responses to nitrogen mngement in rice yield, dry mtter nd nitrogen ccumultion nd redistriution hve een reported y previous reserchers (Bufogle et l., 1997; Jing et l., 1995; Souz et l., 1998). Jing et l. (24) lso pointed out tht rice vrieties with long growth durtion could increse grin yield y ppropritely incresing pnicle nitrogen rte. The dominnt cultivr in South Chin, Xiushui 9, hs long growth durtion of 15-155 dys. Improving the pnicle nitrogen rte incresed the plnt dry mtter significntly; however, the yield ws drmticlly decresed. These results imply tht growth durtion might not e good indictor for choosing the pproprite nitrogen strtegy. Most previous studies of pnicle nitrogen fertilizer were conducted sed on the proper totl nitrogen input for trditionlly trnsplnted rice ut ignored the fct tht high rice yield ws otined y overuse of erly nitrogen topdressing nd incresed totl nitrogen input (Cheng, 212). It is still not cler whether nitrogen mngement options developed for trditionlly trnsplnted rice re unsuitle for direct-seeded rice ecuse direct-seeded rice is suject to more diverse nd heterogeneous soil environments thn trnsplnted rice (De Dtt nd Nntsomsrn, 1991). The current study showed tht the men yield cross fertiliztion methods in R ws slightly decresed compred with tht in R (Tle 2), nd little difference in the effect of nitrogen mngement etween 1632
Tle 2. Grin yield, ove dry mtter nd HI of rice under nd with different N tretments. PP NF Yield (t h -1 ) 26 1.5 9.64 9.85 9.23 1.77 9.67 1. 9.34 27 7.91 6.3 6.23 6.49 7.98 6.8c 6.33 6.54 28 1.21 8.49 9.85 8.77 1.98 8.85c 9.9 9.1c 29 1.43 9.38 9.9 9.45 11.1 9.54c 1.7 9.5c Averge 9.65 8.38c 8.95c 8.48c 1.21 8.53c 9.7 8.62c 8.86 9.11 NF 147.8** Y 839.9** NF*Y 5.2* PP*Y*NF.55ns ANOVA PP 32.99** PP*NF 5.44* PP*Y 4.12* Totl dry mtter (t h -1 ) 26 2.8 19.7 22.9 21.6 2. 19.1 22.6 21.6 27 16.8 16.7 17.4 16.1c 16.2 16.2 16.9 16.c 28 2.7 21.4 24.1 17.4c 2.7 2.4 22.9 17.2c 29 19.4 19.3 2.8 19.8 18.7 19.2 2.4 19.4 Averge 19.4 19.3c 21.3 18.7c 18.9 18.7c 2.7 18.5c 19.7 19.2 ANOVA NF 1.22** Y 32.63** NF*Y 2.2ns PP*Y*NF 1.56ns PP 15.2* PP*NF.35ns PP*Y.39ns HI 26.5.49.42.43.54.5.44.44 27.47.36.36.4.49.37.37.41 28.52.4.41.5.53.43.43.54 29.55.46.48.48.59.47.49.5 Averge.51.43c.42c.45.54.44c.43c.47.45.47 ANOVA NF 36.4** Y 245.25** NF*Y 4.6* PP*Y*NF 1.8ns PP 63.78** PP*NF 1.15ns PP*Y 1.69ns Notes: Mens of N tretments followed y the sme letter for ech plnting pttern re not significntly different t the 5% level y Tukey test, n=4; The effect plnting pttern (PP), nitrogen fertilizer (NF), Yer (Y) effects s well s their interction effects ws tested y Tukey test; ns=not significnt; *=P<.5; **=P<.1. Net Photosynthetic Rte (µmol CO 2 m -2 s -1 ) 25 2 15 1 26 27 28 29 55 5 45 4 35 3 25 2 15 1 26 27 28 29 Fig 2. Net photosynthetic rte () nd SPAD vlue () of rice t heding stge t Jixing from 26 to 29. Error r represent SE, n=4. SPAD vlue R nd R ws found. We lso found tht R hd greter dry mtter ccumultion in the erly stge, consistent with previous reports (Dwe 25; De Dtt 1986; Nklng 1996; Pndey et l. 22). In generl, the nitrogen pplied t sl nd mid-tillering ws 22% less in high PNF thn in low PNF (Tle 1). Our results showed tht there ws little difference in dry mtter ccumultion etween low nd high PNF t the mid-tillering stge in oth R nd R regrdless of nitrogen mount, ut significnt differences were found t PI etween low nd high PNF in R (except in 29), with low PNF greter thn high PNF nd differences rnging from 8.5-16.8% (Figure 1). These results indicted tht pproprite reduction in nitrogen topdressing in the erly stge might not ffect the plnt dry mtter ccumultion in oth R nd R. A slightly improved effect of high PNF on grin yield ws lso oserved t 225kg N h -1 compred with tht t 15kg N h -1 in R. However, there ws little difference etween the rtes of 15 nd 225 kg N h -1 under high PNF in R. The extr nitrogen input hd little effect on the yield improvement ut significntly improved the totl dry mtter. These results imply tht incresed PNF might led to n excessive plnt growth t the pnicle growth stge, which ultimtely ffects the yield performnce Reltionships etween yield components nd dry mtter ccumultion chrcteristics The yield improvement of recently relesed vrieties comes from two sources: improved dry mtter ccumultion nd greter HI (Dingkuhn et l., 1991; Horie et l., 21; Peng et l., 1996; Yoshid, 1981). Generlly, R produced more dry 1633
75, 7, : Y = 312.9x + 3389 R 2 =.4435, P<.1 1 95 : Y = 3.2439x + 54.716 R 2 =.2, P<.1 65, 9 Grins m -2 6, 55, 5, 45, 4, 35, : Y = 3739.7x + 18183 R 2 =.5472, P<.1 Grin filling percentge (%) 85 8 75 7 65 : Y = 3.3361x + 55.53 R 2 =.4721, P<.1 3, 4. 6. 8. 1. 12. Grin yield (t h -1 ) 6 4. 6. 8. 1. 12. Grin yield (t h -1 ) Fig 3. Reltionship etween grins m -2 (), grin filling percentge () nd yield of nd rice grown from 26 to 29 t Jixing. 7 : Y =.4x + 28.93 R 2 =.5925, P<.1 : Y =.52x + 67.7 R 2 =.4195, P<.5 Totl dryweight t MT (g m -2 ) 4 3 2 1 : Y =.32x - 22.762 R 2 =.5999, P<.1 Lef dryweight t PI (g m -2 ) 4 3 2 1 : Y =.45x + 76.652 R 2 =.4788, P<.5 3, 4, 5, 6, 7, 8, Grins m -2 3, 4, 5, 6, 7, 8, Grins m -2 55 : Y =.47x + 178.63 R 2 =.311, p<.5 85 8 : Y = -1E-6x2 +.1231x - 372.5 R 2 =.466, P<.5 75 Lef dryweight t HS (g m -2 ) 45 4 35 3 25 : Y =.45x + 76.652 R 2 =.4788, P<.5 Stem dryweight t HS (g m -2 ) 7 65 55 : Y = -9E-7x2 +.116x - 264.9 R 2 =.6476, P<.5 2 3, 4, 5, 6, 7, 8, Grins m -2 c 3, 4, 5, 6, 7, 8, Grins m -2 d Fig 4. Reltionships etween totl dry weight t MT (), lef dry weight t PI (), lef dry weight t HS (c), stem dry weight t HS (d) nd grins m -2 of nd rice grown from 26 nd 29 t Jixing. mtter ccumultion ut lower HI compred to R (De Dtt, 1986; De Dtt nd Nntsomsrn, 1991; Nklng, 1996; Pndey et l., 22), which ws consistent with our results. Anlyzing the reltionships etween grin yield nd yield components, we found tht the yield ws linerly correlted with grin filling percentge nd grins m -2 (Figure 3). In sink-source theory, the grin filling percentge is determined y the sink size (grins m -2 ), source cpcity (lef photosynthetic rte, photosynthesis durtion, solr rdition, ir temperture nd so on.) nd crohydrte flow etween sink nd source (dry mtter trnsporttion from strw to spikelets during the grin filling period; Cssmn et l., 1998; Mkino et l., 1984; Peng et l., 1996; Ying et l., 1998). In the current study, we found tht high PNF significntly improved the flg lef photosynthetic rte compred with low PNF in the heding stge regrdless of plnting pttern nd yer (Figure 2), which is consistent with reports of the physiologicl effect of nitrogen ppliction on the lef photosynthesis t pnicle initition (Me, 1997). However, the result tht grin m -2 ws qudrticlly correlted with 1634
Lef dryweight t HS (g m -2 ) 55 45 4 35 : Y = 6.5616x + 151.67 R 2 =.3384, <.1 3 : Y = 7.223x + 8.56 R 2 =.567, P<.1 25 6. 7. 8. 9. 1. Grin filling percentge (%) Stem dryweight t HS (g m -2 ) 85 8 75 7 65 55 : Y = -.1337x 2 + 29.943x - 861.41 R 2 =.5784, P<.1 : Y = -.2189x 2 + 43.44x - 1419.8 R 2 =.5376, P<.1 45 6. 7. 8. 9. 1. Grin filling percentge (%) Fig 5. Reltionships etween lef dry weight t HS (), stem dry weight t HS () nd grins filling percentge of nd rice grown from 26 nd 29 t Jixing. stem nd sheth dry mtter ccumultion t the heding stge (Figure 4d) provides evidence tht over-ccumultion of dry mtter in the stem nd sheth might hve negtive effect on sink size production nd result in yield decline. Dry mtter ccumulted in strw efore heding is thought to e crohydrte storge for the dry mtter redistriution during the grin filling period (Ying et l., 1998). However, excess nitrogen pplied to the crop could result in prolems such s over-stimultion nd excessive growth which ttrcts pests, delyed mturity, reduction in the qulity of the crop, or lodging of rice plnts (Yoon et l. 21). In ddition, the concentrtion of nitrogen required vries depending on the crop s well s its growth stge; high nitrogen levels my e eneficil during erly growth stges ut my cuse yield losses during the lter flowering nd fruiting stges (Ayres nd Westcot, 1994). These resons might prtly explin the lower yield in PNF. Mteril nd Method Site description Field experiments were conducted t the experimentl frm of the Jixing Agriculture Reserch Institute, Chin (3 17 N, 12 45 E, 6 m ltitude) from 26 to 29. Prior to plnting, the soil t the experimentl site ws lluvil sndy cly lom, with ph 6.8, orgnic C 3.3 g/kg, totl N 2.4 g/kg, ville P 32.5 mg/kg nd ville K 58.6 mg/kg. Soil properties were determined ccording to stndrds set y the Lortory Mnul for Agriculture nd Soil Anlysis (Po, 25). Experimentl tretment The rice (Oryz stiv L.) vriety used ws Xiuyou 5 (Xiushui 11 Xiuhui 69), jponic hyrid relesed y Jixing Crop Reserch Institute. Two plnting ptterns were used: direct sowing (R) nd trnsplnting (R). For R, seeds were mnully rodcst on the plowed plots t seeding rte of 15 kg h -1 in erly June. For R, seedlings with three expnded leves (out 25-3 d fter sowing) were trnsplnted into the field t density of 25 hills m -2 (2 cm 2 cm) with two plnts per hill. Sowing of R ws 1-15 dys erlier thn R to meet the dte for the heding period. Four tretments of nitrogen fertilizer ppliction were evluted s follows: : TNA of 225 kg N h -1 comined low PNF; : TNA of 15 kg N h -1 comined low PNF; : TNA of 225 kg N h -1 comined high PNF; : TNA of 15 kg N h -1 comined high PNF (Tle 1). Bsl pplictions were mde week efore trnsplnttion/sowing. Totl Potssium of 135 kg h -1 ws pplied to ll plots, with 5% eing sl dressing in the form of compound fertilizer nd 5% s topdressing t PI in the form of Potssium Chloride. Phosphorous ws not supplied ecuse of its sufficient level in the soil. A split plot design ws used with the plnting pttern s min plot nd fertilizer ppliction s su-plot. The size of ech su-plot ws 5.5 4.5 m, with three replictions for ech tretment. Weeds, insects nd diseses were controlled s required to void yield loss. Smpling nd mesurement In this pper, the full-heding period ws defined s the time when 8% of the pnicles hd emerged. After mesurement of the SPAD vlue of individul leves (SPAD-52, Minolt, Tokyo, Jpn), net photosynthetic rtes were mesured using LI-64 portle photosynthesis system (LI-COR, Lincoln, NE, USA) on the uppermost fully expnded leves. The crop ws considered to hve reched mturity when 95% of the spikelets hd turned yellow. Twelve representtive hills (hills with men vlue of tillers per hill from ech plot were collected t ech smpling for mesurement of dry weight of constituent orgns (the hills were seprted into lef ldes, culms plus lef sheths nd pnicles). All smples were oven-dried t 8-15 C for severl dys, weighed nd powdered. At the time of hrvest, twelve representtive hills with the men vlue of pnicles per hill from ech plot were collected nd hnd-threshed for mesurement of the numer of filled nd unfilled spikelets. The filled spikelets were seprted y sumerging the hnd-threshed spikelets in NCl solution with specific grvity (g m -3 ) of 1.6. The filled spikelets were then hulled nd oven-dried t 15 C to constnt weight in order to determine grin dry weight. A survey of yield ws crried out s follows: hills were collected from the center prt of ech plot of 5 m 2. Unhulled (rough) rice ws otined fter reping, threshing nd wind selection. The weight of rough rice ws djusted to moisture content of 14%. Sttisticl nlysis All dt were sujected to ANOVA using sttisticl softwre 1635
SAS 8. for Windows. Comprisons were mde etween the tretments using Tukey s test; p vlues <.5 nd.1 were considered significntly different. Acknowledgments This reserch ws prtly supported y grnts from the 'Five-twelfth' Ntionl Science nd Technology Support Progrm (211BAD16B14), the Ntionl Nturl Science Foundtion of Chin (3117152), the Zhejing province Nturl Science Foundtion of Chin (LQ12C131) nd MOA Specil Fund for Agro-scientific Reserch in the Pulic Interest of Chin (212396). Reference Ayres RS, Westcot DW (1994) Wter Qulity for Agriculture. FAO Irrig. Drin p. 29 Rev 1. Rome, Itly: Food nd Agriculture Orgniztion Belder P, Boumn BAM, Cngon R, Lu GA, Li YH, Spiertz JHJ, Tuong (24) Effect of wter-sving irrigtion on rice yield nd wter use in typicl lowlnd conditions in Asi. Agric. Wter Mnge. 65: 193 21 Bufogle A, Bollich PK, Kovr JL, Mcchivelli RE, Lindu CW (1997) Rice vriety differences in dry mtter nd nitrogen ccumultion s relted to plnt stture nd mturity group. J. Plnt Nutr. 2: 123 1224 Cssmn KG, Peng S, Olk DC, Ldh JK, Reichrdt W, Doermnn A, Singh U (1998) Opportunities for incresed nitrogen-use efficiency from improved resource mngement in irrigted rice systems. Field Crops Res. 56: 7-39 Cheng S (21) Chinese super rice reeding. Science Press in Chin, Beijing. Dwe D (25) Incresing wter productivity in rice-sed systems in Asi pst trends, current prolems, nd future prospects. Plnt Prod. Sci. 8: 221-23 De Dtt SK (1986) Technology development nd the spred of direct-seeded flooded rice in Southest Asi. Exp. Agri. 22: 417-426 De Dtt SK, Nntsomsrn P (1991) Sttus nd prospects of direct seeded flooded rice in tropicl Asi. Pper presented t Interntionl Rice Reserch Conference on Direct seeded flooded rice in the tropics, Interntionl Rice Reserch Institute, Mnil, Philippines Ding YF, Wng QS, Zho CH (23) Effect of ppliction stge of pnicle fertilizer on rice grin yield nd the utiliztion of nitrogen. J. Nnjing Agri. Uni. 26: 5-8 Dingkuhn M, Schnier HF, De Dtt SK, Dorffling K, Jvelln C (1991) Reltionships etween ripening-phse productivity nd crop durtion, cnopy photosynthesis nd senescence in trnsplnted nd direct-seeded lowlnd rice. Field Crops Res. 26: 327-345 Horie T, Peng S, Hrdy B (21) Incresing yield potentil in irrigted rice: reking the yield rrier. Pper presented t Proceedings of the Interntionl Rice Reserch Conference on Rice reserch for food security nd poverty llevition. Interntionl Rice Reserch Institute (IRRI), Los Bños, Philippines Jing L, Di T, Jing D, Co W, Gn X, Wei S (24) Chrcterizing physiologicl N-use efficiency s influenced y nitrogen mngement in three rice cultivrs. Field Crops Res. 88: 239-25 Jing LG, Wng WJ, Xu ZS (1995) Studies on the developing lw of dry mtter production nd yield of Indic rice vrieties. J. Huzhong Agric. Univ. 14: 549 554 Jing TB, Di D, Jing WX, Co XQ, Gn SQ (24) Chrcterizing physiologicl N-use efficiency s influenced y nitrogen mngement in three rice cultivrs. Field Crops Res. 88: 239 25 Jing Q, Boumn BAM, Hengsdijk H, Vn Keulen H, Co W (27) Exploring options to comine high yields with high nitrogen use efficiencies in irrigted rice in Chin. Eur. J. Agron. 26: 166 177 Li YZ, Zhng DC (1981) High-yielding constitution nd regultion of hyrid rice Frm. Inf. Res. 21: 31 33 (in Chinese with English strct) Lin QH (2) Crop Popultion Qulity. Shnghi Science &Technology Press, Shnghi. pp. 96-17 Lin X, Zhu D, Chen H, Cheng S, Uphoff N (29) Effect of plnt density nd nitrogen fertilizer rtes on grin yield nd nitrogen uptke of hyrid rice (Oryz stiv L.). J. Agri. Biotech. Sustin. Dev. 1: 44-53 Me T (1997) Physiologicl nitrogen efficiency in rice: Nitrogen utiliztion, photosynthesis, nd yield potentil. Plnt nd Soil. 196: 21-21 Mkino A, Me T, Ohir K (1984) Reltion etween nitrogen nd riulose-1, 5-isphosphte croxylse in rice leves from emergence through senescence. Plnt nd Cell Physiol. 25: 429 Nklng K (1996) Growth of rice cultivrs y direct seeding nd trnsplnting under uplnd nd lowlnd conditions. Field Crops Res. 48: 115-123 Ottis BV, Hrrell DL, Gerrd PD, Bond JA, Wlker TW (28) Hyrid rice response to nitrogen fertiliztion for midsouthern United Sttes rice production. Agron. J. 1: 381-386 Pndey S, Velsco LE, Suphnchimt N (22) Direct seeding: reserch strtegies nd opportunities (eds). In Economics of direct seeding in Asi: ptterns of doption nd reserch priorities. Interntionl Rice Reserch Institute (IRRI), Los Bños, Philippines Po SH (25) lortory mnul for griculture nlysis. Chin griculture Press, Beijing Peng S, Grci FV, Lz RC, Snico AL, Vispers RM, Cssmn KG (1996) Incresed N-use efficiency using chlorophyll meter on high-yielding irrigted rice. Field Crops Res. 47: 243-252 Shi HR, Zhng WZ, Xie WX, Yng Q, Zhng ZY, Hn YD, Xu ZJ, Chen WF (28) Anlysis of mtter production chrcteristics under different nitrogen ppliction ptterns of jponic super rice in north Chin. Act Agron. Sin. 34: 1985 1993 (in Chinese with English strct) Souz SR, Strk EMLM, Fernndes MS (1998) Nitrogen remoiliztion during the reproductive period in two Brzilin rice vrieties. J. Plnt Nutr. :249 263 Tn ZH, Ln TY, Jin WM, Hung GJ, Wn YL (1981) Effect of on yield formtion fctors medium hyrid rice under different nitrogen supply period. Sci. Tech. Sichun Agric. 2: 8 11 (in Chinese with English strct) Ying J, Peng S, He Q, Yng H, Yng C, Vispers RM, Cssmn KG (1998) Comprison of high-yield rice in tropicl nd sutropicl environments: I. Determinnts of grin nd dry mtter yields. Field Crops Res. 57: 71-84 Yoon CG, Soon KK, Jong HH (21) Effects of Treted Sewge Irrigtion on pddy. Rice Culture nd its Soil. Irrig. Drin. 5: 227-236 Yoshid S (1981) Fundmentls of rice crop science. Internitonl Rice Reserch Institute, Los Bños, Philippines 1636