Radiation interception, extinction coefficient and use efficiency of wheat crop at various irrigation and nitrogen levels in a semiarid

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1 Ind J Plnt Physiol. (July Septemer 2018) 23(3): ORIGINAL ARTICLE Rdition interception, extinction coefficient nd use efficiency of whet crop t vrious irrigtion nd nitrogen levels in semirid loction S. Prdhn 1,2 V. K. Sehgl 2 K. K. Bndyopdhyy 2 P. Pnigrhi 1 C. M. Prihr 2 S. L. Jt 3 Received: 23 Octoer 2016 / Accepted: 17 Septemer 2018 / Pulished online: 29 Septemer 2018 Ó The Author(s) 2018 Astrct Field experiments were conducted to study the effect of irrigtion nd nitrogen levels on rdition use efficiency (RUE), rdition extinction coefficient (j) nd temporl vrition of lef re index () nd frction intercepted photosyntheticlly ctive rdition (). The of whet incresed with increse in irrigtion nd nitrogen levels. The lso followed trend similr to. The nd showed logrithmic reltionship with R 2 vlue of 0.92 nd 0.93 for the yers nd , respectively. The j vlue vried etween 1 nd 0.78 nd ws significntly ffected y nitrogen levels ut ws not influenced y irrigtion levels. The grin nd ove ground iomss (AGB) yields of whet were not ffected significntly y irrigtion levels. However, ppliction of 160 kg N h -1 (N160) registered higher grin (12 33%) nd AGB (22 25%) yeilds s compred to tht with ppliction of 40 kg N h -1 (N40). Similr to AGB, the totl intercepted photosyntheticlly ctive rdition (TIPAR) ws not ffected y irrigtion levels ut N160 tretment registered 9 20% higher TIPAR compred to N40 tretment. The liner reltionship etween TIPAR nd AGB reveled tht 83 86% vrition in AGB yield of whet cn e explined y TI. The RUE of whet under three irrigtions (I3) ws 6 nd 18% higher (P \ 5) thn the five (I5) nd two (I2) irrigtion & S. Prdhn sntn28@gmil.com ICAR-Indin Institute of Wter Mngement, Bhuneswr, Odish , Indi ICAR-Indin Agriculturl Reserch Institute, New Delhi, Delhi , Indi ICAR-Indin Institute of Mize Reserch, New Delhi, Delhi , Indi tretments, respectively for the yer However, there ws no significnt effect of irrigtion on RUE of whet in the yer N160 tretment registered 5 13% higher RUE thn the N40 tretment. Thus whet my e grown with three irrigtions (CRI, flowering nd grin filling) nd 160 kg N h -1 for higher RUE without significnt reduction in AGB of whet compred to five irrigtion levels in semi-rid loction of Delhi region. Keywords Rdition interception Rdition extinction coefficient RUE Whet Introduction Whet is the second most importnt cerel crop of Indi covering n re of 30 million h with production of 94 million tons in the yer Wter nd fertilizer (nitrogen) re the two most importnt inputs, which gretly contriute to whet productivity more specificlly in the rid nd semi-rid trct of Indi where whet is grown s dry seson crop (Prdhn et l. 2014d). Trditionlly, crop responses to irrigtion nd nitrogen levels hve een reported y mny workers (Bndyopdhyy et l. 2010; Prdhn et l. 2014,, d; Rnjn et l. 2015) ut there re very few studies evluting the integrted effect of irrigtion nd nitrogen supply on the ecophysiologicl determinnts of ove ground iomss (AGB) production of whet. The AGB production of crop is directly relted to the mount of intercepted photosyntheticlly ctive rdition (IPAR) y the crop cnopy during its life cycle (Monteith 1977; Ate et l. 1997; Sndñ et l. 2009; Prdhn et l. 2014d). The AGB per unit of totl IPAR is clled s rdition use efficiency (RUE) (Sinclir nd Muchow

2 Ind J Plnt Physiol. (July Septemer 2018) 23(3): ). The RUE of cerels is constnt in non-stressful environments (Gllgher nd Biscoe 1978; Sinclir nd Muchow 1999). Therefore, AGB produced cn e expressed s product of the cumultive IPAR during the crop growth cycle nd RUE (Sndñ et l. 2009). This pproch is commonly employed in rdition use efficiency sed crop growth models (Ritchie nd Otter 1985; Jones et l. 1991; Keting et l. 1997; Brisson et l. 2003; Stöckle et l. 2003; Aggrwl et l. 2004) nd remote sensing estimtion of iomss (Csnov et l. 1998). The cumultive totl IPAR of crops is mostly controlled y frction of the incoming photosyntheticlly ctive rdition y the cnopy, which is function of green lef re index () nd the efficiency with which the green lef re intercepts solr rdition, descried y the light extinction coefficient (j) (Plénet et l. 2000; Muurinen nd Peltonen- Sinio 2006; Mssignm et l. 2009; Sndñ et l. 2009). Severl studies hve shown tht totl IPAR is negtively relted to oth wter nd nitrogen deficiencies in whet (Prdhn et l. 2014d; Dreccer et l. 2000; Slvgiotti nd Mirlles 2008). The j vlues for whet vries etween 0.37 nd 2 (Yunus et l. 1993; O Connell et l. 2004; Muurinen nd Peltonen-Sinio 2006). Thoms (2013) oserved tht effect of irrigtion ws not significnt on j of whet in semi-rid loction of Indi. Similr to irrigtion, mny uthors hve reported tht nitrogen did not effect j significntly (Green 1987; Muurinen nd Peltonen-Sinio 2006). Though there re studies on the effect of irrigtion nd nitrogen on totl IPAR nd light extinction coefficient in isoltion, studies on interctive effect of irrigtion nd nitrogen on these prmeters re limited. Besides species nd cutivrs, RUE is mostly ffected y the mngement fctors such s wter nd nitrogen ppliction (Sinclir nd Muchow 1999; Stöckle nd Kemnin 2009; Muurinen nd Peltonen-Sinio 2006). Under nonstressed conditions, the RUE vlues of whet vries from 1.46 to 2.93 (Gregory et l. 1992; Yunus et l. 1993). Wter stress reduces RUE y reducing the utiliztion of photosynthtes for growth s lower intercepted phtosyntheticlly ctive rdition occurs from reduced (Wilson nd Jmieson 1985; O Connell et l. 2004). Negtive responses of RUE to wter stress hs een presented y mny workers for whet (Hn et l. 2008; Li et l. 2008; Thoms 2013). RUE is lso ffected y the nutrient ppliction (Sinclir nd Horie 1989; Plénet et l. 2000) nd mong ll the nutrients, nitrogen influences RUE the most (Muurinen nd Peltonen-Sinio 2006). RUE reduction under lower nitrogen ppliction conditions is relted to lower specific lef nitrogen content nd RUE increses linerly with nitrogen ppliction till the specific lef nitrogen stys under sturting N content (Sinclir nd Muchow 1999). The negtive effect of nitrogen ppliction to RUE of whet is well documented (Prdhn et l. 2014d; Muurinen nd Peltonen-Sinio 2006). However, similr to IPAR nd j, the study on interctive effect of irrigtion nd nitrogen on RUE is lso limited. Successful modeling of plnt growth nd remote sensing estimtion of iomss relies on ccurte description of, light extinction coefficient for IPAR nd RUE. Keeping these in view, the ojectives of this study were to determine the interctive effect of irrigtion nd nitrogen on () temporl vrition in nd frction IPAR nd, () totl IPAR, grin nd AGB yield, j nd RUE of whet in semi-rid loction of Indi. Mterils nd methods Study re nd experimentl detils Field experiments were conducted during dry seson (winter) of nd t the experimentl frm of the Indin Agriculturl Reserch Institute (IARI), New Delhi ( E Longitude, N Ltitude nd m ove men se level), with whet (Triticum estivum L.) s test crop. The re comes under semi-rid sutropicl climtic elt. The texture of the study site ws sndy lom (Typic Hplustept), low in orgnic cron nd ville nitrogen nd medium in ville P nd K content. The ulk density vried from 1.56 to 1.74 Mg m -3, sturted hydrulic conductivity from 9 to 2 cm h -1 nd sturted wter content from 0.38 to 2 m 3 m -3 in the upper 0 0 m soil lyer. The soil moisture content vried etween 26 29% t 0.33 MP (field cpcity) nd 8 11% t 1.5 MP (permnent wilting point) in different lyers of 0 0 m soil depth. The experiment ws lid out in split-plot design with irrigtion levels s min plot tretments nd nitrogen levels s su-plot tretments, replicted three times. The suplot size ws 5 9 5m 2. The irrigtion levels were I2: two irrigtions (CRI nd flowering stges), I3: three irrigtions (CRI, flowering nd grin filling stges) nd I5: five irrigtions (CRI, tillering, Jointing, flowering nd grin filling stges). In ech irrigtion, n mount of 60 mm wter ws pplied through surfce irrigtion. The irrigtion mount ws mesured y Prshll Flume. The mount of irrigtion wter pplied for I2, I3 nd I5 were 60, 120, nd 240 nd 120, 120 nd 240 mm for the yers nd , respectively. The nitrogen levels were N40: 40 kg N h -1 nd N160: 160 kg N h -1. The source of nitrogen fertilizer ws ure. Nitrogen ws pplied in three splits (Bsl: 50% N; CRI: 25% N nd flowering stge: 25% N). All the plots received recommended sl dose of phosphorous nd potssium (60 kg P 2 O 5 h -1 s single super phosphte nd 60 kg K 2 Oh -1 s murite of potsh). Whet crop (cv. HD 2967) ws sown on 26th nd 18th

3 418 Ind J Plnt Physiol. (July Septemer 2018) 23(3): Novemer in the yers 2013 nd 2014, respectively, y trctor drwn seed drill (t depth of 4 5 cm) with row spcing of 22.5 cm nd seed rte of 100 kg h -1. The crop ws hrvested on 15th nd 20th April in 2013 nd 2014, respectively. Lef re index () Lef re index ws mesured t regulr intervls using plnt cnopy nlyzer (-2000, LI-COR, Lincoln, NE, USA). The timing of oservtion coincided with the timing of oservtion for photosyntheticlly ctive rdition (PAR). Cnopy rdition extinction coefficient (j) Both incoming nd outgoing photosyntheticlly ctive rdition (PAR) vlues were mesured periodiclly t the top nd ottom of the whet cnopy throughout the seson using line quntum sensor LI-191SA (LICOR Inc., Lincoln, NE, USA). The frction intercepted PAR () ws clculted s (Monteith 1981): Io I ¼ ð1þ I where Io is incident PAR t the top of cnopy nd I is the trnsmitted PAR t the ottom of the cnopy. The cnopy nd were relted y the reltionship given elow (Monsi nd Seki 1953): ¼ 1 e ð jþ ð2þ where, j is the cnopy rdition extinction coefficient nd is the lef re index. The j ws determined with lest-squre regression y clculting the slope of the reltionship etween ln(1 - ) nd (Roertson et l. 2001) with intercept set to zero. Yield The net plot (5 m 9 5 m) ws hrvested mnully y cutting the plnts close to ground fter leving the order rows. The plnt smples were dried nd weighed for AGB yield nd expressed in kg h -1. Threshing of whet ws done mechniclly nd the grin yield ws expressed in kg h -1. Rdition use efficiency (RUE) Vlues for for ech dy fter sowing were interpolted etween ctul mesurements y liner interpoltion throughout the crop seson (Prdhn et l. 2014c, d; Sh et l. 2015). Dily incoming solr rdition ws clculted y using right sunshine hours in the Angstrom eqution (Allen et l. 1998). The dily incoming solr rdition ws multiplied y fctor 8 (Monteith 1972) to get incoming incident PAR. Then the dily incident PAR vlues were multiplied y corresponding dily vlues to compute dily intercepted PAR (IPAR). The dily IPAR ws integrted for the whole crop seson to get totl IPAR (TIPAR). The RUE ws clculted y dividing totl AGB (g m -2 ) with the TIPAR (MJ m -2 ) for the whole crop durtion (Prdhn et l. 2014c, d). Sttisticl nlysis The dt were sttisticlly nlyzed using nlysis of vrince (ANOVA) s pplicle to split-plot design (Gomez nd Gomez 1984). F test ws employed to see the significnce of the tretment effects. The difference etween the mens ws estimted using lest significnce difference nd Duncn s multiple rnge tests t 5% proility level. Regression nlyses were performed using the dt nlysis tool pck of MS Excel (2007). Results nd discussion Wether Men monthly temperture, reltive humidity, solr rdition, rinfll nd reference evportion (Allen et l. 1998) re presented in Tle 1. The men monthly temperture ws lmost similr in oth the yers of study except for the month of Ferury. The men monthly temperture of Ferury ws 3.1 C higher thn tht of the yer It coincides with the flowering nd milk stge of whet crop growth. The whet crop growth period of (315.8 mm) received significntly higher rinfll thn the yer (169.2 mm). More specificlly, Mrch month of received mm rinfll compred to 63.5 mm of the yer However, the Ferury month of received 63.5 mm rinfll in four spells wheres the yer did not receive ny rinfll for the sme period. The men monthly reltive humidity ws lmost similr for oth the yers of study except for the month of Ferury. The Ferury month of the yer registered 10% higher reltive humidity compred to the yer It could e ttriuted to the higher Ferury rinfll of the yer compred to the yer The solr rdition received for the study period of the yer (2617 MJ m -2 ) ws lmost similr to the yer (2639 MJ m -2 ). Similrly, the reference evpo-trnspirtion for the study period of (523 mm) nd (512 mm) were lmost similr. The higher reference evpo-trnspirtion for the month of

4 Ind J Plnt Physiol. (July Septemer 2018) 23(3): Tle 1 Wether condition during the period of study Months Men temperture ( C) Men reltive humidity ( C) Totl solr rdition (MJ m -2 ) Totl rinfll (mm) Totl reference evpotrnspirtion (mm) Nov Dec Jn Fe Mr Apr Ferury (75 mm) compred to the yer (59 mm) my e ttriuted to the higher solr rdition received during the sme period corresponding to the previous period. On the whole, whet crop of the yer experienced more congenil wether compred to the whet crop of the yer Lef re index () I2 I3 I5 The temporl vrition in of whet crop for irrigtion nd nitrogen tretments of oth the yers of study re presented in Figs. 1 nd 2. The vlue incresed stedily till dys fter sowing nd then declined. The Dys er sowing Dys er sowing I2 I3 I5 N40 N160 Fig. 1 vrition of whet t different dys fter sowing (DAS) for irrigtion () nd nitrogen () tretments Dys er sowing Dys er sowing increse in my e ttriuted to folige expnsion ecuse of development of new leves nd enlrgement of existing leves (Mndl et l. 2005). The pek vlue of in the present experiment coincided with the ooting to flowering stge of whet. This finding is in greement with Akrm (2011) nd Bssu et l. (2011) for whet. The decrese in during lter prt of crop growth is scried to lef senescence (Thoms 2013; Mndl et l. 2005; Prdhn et l. 2013; Bndyopdhyy et l. 2010). Averged over nitrogen tretments, the highest for I5, I3 nd I2 tretments were 4.69, 4.24 nd 3.42 in nd 5.35, 4.41 nd 4.05 in , respectively. In the yer , the effect of irrigtion levels were significnt N40 N160 Fig. 2 vrition of whet t different dys fter sowing (DAS) for irrigtion () nd nitrogen () tretments

5 420 Ind J Plnt Physiol. (July Septemer 2018) 23(3): (P \ 5) only on mesured t 128 dys fter sowing. However, in the yer , irrigtion effects were significnt (P \ 5) on mesured t 83, 90, 122 nd 129 dys fter sowing. In oth the yers of study, the of reproductive stge of whet ws highest in I5 followed y I3 nd I2. Incresed wter stress due to differentil level of irrigtion ppliction might hve led to incresed scission rte nd hence decresed in (Akrm 2011; Thoms 2013). Averged over irrigtion levels, the highest for N40 nd N160 tretments were 3.39 nd 4.84 in nd 4.14 nd 5.06 in , respectively. Nitrogen tretment significntly (P \ 5) ffected of whet t ll stges of mesurement except t 34 dys fter sowing for the yer However, in the second yer, the significnt effect of nitrogen levels on were oserved only t 83, 90, 102, 114 nd 122 dys fter sowing. Higher with incresed N ppliction could e ttriuted to significnt increses in lef expnsion (length nd redth) resulting from cell division nd cell enlrgement t higher N rtes. Similr results were reported y Wright (1982) nd Kr nd Kumr (2015) for mize, nd Shfi et l. (2011) for rley. The interction effect of irrigtion nd nitrogen on ws not significnt for oth the yers of study. Frction intercepted PAR () The temporl vrition of of whet for irrigtion nd nitrogen tretments of oth the yers re presented in Fig. 3 nd 4. The incresed continuously till 98 DAS in nd 102 DAS in nd then decresed with progress of seson. Prdhn et l. (2014c) lso reported curviliner reltionship etween nd dys fter sowing for whet. The temporl vrition of followed the trend similr to tht of. Jh et l. (2012) nd Serrno et l. (2000) hve lso oserved tht temporl vrition in showed the trend similr to for mustrd nd whet, respectively. The grphicl reltionship etween nd for oth the yers of study re presented in Fig. 5. The nd showed logrithmic reltionship with R 2 vlue of 0.92 for nd 0.93 for In oth the yers, incresed with increse in, initilly t higher rte nd then t lower rte nd finlly flttening. This could e scried to the lower rte of chnge of to higher rte of chnge of fter chieving the peks of nd, respectively (Thoms 2013). The irrigtion levels did not ffect significntly throughout the crop growth period of nd (Fig. 3 nd 4). Averged over nitrogen tretments, the highest (%) for I5, I3 nd I2 tretments were 85.5, 9 nd 91.3% in nd 91.3, 92.3 nd 96.2% in , respectively. However, the nitrogen levels significntly Dys er sowing Dys er sowing N40 I2 I3 I5 N160 Fig. 3 vrition of whet t different dys fter sowing (DAS) for irrigtion () nd nitrogen () tretments Dys er sowing Dys er sowing I2 I3 I5 N40 N160 Fig. 4 vrition of whet t different dys fter sowing (DAS) for irrigtion () nd nitrogen () tretments

6 Ind J Plnt Physiol. (July Septemer 2018) 23(3): y = 70ln(x) + 59 R² = 0.92 Exinc on coefficient (κ) I2 I3 I Fig. 6 Extinction coefficient (j) of whet t different irrigtion levels for nd Columns mrked y sme letters re not significntly different t P \ 5 in yer 0 y = 39ln(x) + 54 R² = Fig. 5 nd reltionship for () nd () Ex nc on coefficient (κ) N40 N160 (13 21% in nd 4 32% in ) ffected t lmost ll stges of its mesurement (Figs. 3 nd 4). Averged over irrigtion tretments, the highest (%) for N160 nd N40 tretments were 82.2 nd 95.8% in nd 91.6 nd 95.0% in , respectively. The lower in N40 tretments compred to N160 tretments cn e ttriuted to lower in the former thn the lter. Bssu et l. (2011) hs lso oserved lower in durum whet due to lower. The interction effect of irrigtion nd nitrogen were not significnt on for oth the yers of study. Light extinction coefficient (j) The cnopy light extinction coefficient [the slope of ln(1 - ) nd reltionship] ws otined for ech tretment nd sujected to sttisticl nlysis nd presented in Figs. 6 nd 7. The j vried etween 0.51 (I2N40) to 5 (I3N160) in nd 7 (I2N40) to 0.58 (I2N160) in (dt not presented). The estimted j vlues fll within the rnge of 1 nd 0.78 reported for red whet (Yunus et l. 1993; O Connell et l. 2004; Muurinen nd Peltonen-Sinio 2006). The irrigtion levels hd no significnt effect on j for oth the yers of study (Fig. 6). This result is in greement with the Thoms (2013). However, j ws significntly (P \ 5) lower in N40 (16% in nd 9% in ) compred to 0 N160. It indicted tht under nitrogen stress condition, the lef ecomes more erect resulting in etter penetrtion of PAR into the cnopy nd hence lower nd RUE (Kiniry et l. 1989; Brekke et l. 2011; Bssu et l. 2011; Sh et l. 2015). Yield Fig. 7 Extinction coefficient (j) of whet t different nitrogen levels for nd Columns mrked y sme letters re not significntly different t P \ 5 in yer The grin nd ove ground iomss (AGB) yields re presented in Tle 2. The grin yield vried etween 2750 (I2N40) nd 5500 (I5N160) kg h -1 with n verge vlue of 4340 kg h -1 for nd 3285 (I2N40) to 4001 (I5N160) kg h -1 with n verge vlue of 3732 kg h -1 for Similr to grin yield, the AGB vried etween 8125 (I2N40) nd 14,500 (I5N160) kg h -1 with n verge vlue of 11,833 kg h -1 for nd 8625 (I2N40) to 13,500 (I5N160) kg h -1 with n verge vlue of 10,993 kg h -1 for The men grin yield ws 14% lower in s compred to However, the men AGB yield ws 7% lower in s compred to The decrese in

7 422 Ind J Plnt Physiol. (July Septemer 2018) 23(3): Tle 2 Aove ground iomss (kg h -1 ), TIPAR (MJ m -2 ) nd RUE (g MJ -1 ) of whet for different irrigtion nd nitrogen levels Grin yield (kg h -1 ) Aove ground iomss (kg h -1 ) TIPAR (MJ m -2 ) RUE (g MJ -1 ) Effect of irrigtion I c 2.03 I I Effect of nitrogen N N Effect of irrigtion 9 nitrogen I2 N c c 8625c 367c 440c I2 N c c I3 N c 425c 480c I3 N c I5 N c c I5 N yield of whet in compred to cn e ttriuted to the higher rinfll (201.8 mm) cusing ertion stress during the Mrch month of Thoms (2013) hs lso reported decrese in yield of whet due to ertion stress. The grin yield ws not significntly (P \ 5) ffected y the irrigtion levels for oth the yers of study. The N160 tretment registered 33% higher (P \ 5) grin yield compred to N40 tretment in However, in the N160 nd N40 tretments were sttisticlly t pr. Similr to grin yield, the AGB ws not significntly (P \ 5) ffected y irrigtion levels for oth the yers of study (Tle 2). However, the AGB of whet ws significntly ffected y nitrogen levels. N160 tretment registered 25% nd 22% higher AGB compred to N40 tretment during the yers nd , respectively. The incresed yield in N160 tretment compred to N40 tretment cn e ttriuted to incresed (Figs. 1 nd 2), green spikes re nd crop durtion with greenness, which resulted incresed interception of rdition (Ltiri-Souki et l. 1998; Prdhn et l. 2014d). The interction effect of irrigtion nd nitrogen tretments ws significnt on the grin yield of nd AGB of oth the yers of study. The highest grin nd AGB yield ws oserved in I5N160 nd lowest in I2N40 tretment for oth the yer of study. The grin yield of I5N160, I3N160 nd I3N40 were sttisticlly t pr. The I3N40, I3N160, I5N40 nd I5N160 tretments in nd I2N160, I3N160, I5N40 nd I5N160 tretments in were sttisticlly t pr with respect to AGB. Totl intercepted PAR (TIPAR) The totl intercepted PAR (TIPAR) is one of the most importnt fctors of crop production (Monteith 1981). In the present experiment, TIPAR vried etween 367 (I2N40) nd 536 (I5N160) MJ m -2 with men vlue of 467 MJ m -2 in nd 440 (I2N40) to 574 (I5N160) MJ m -2 with men vlue of 506 MJ m -2 for the yer (Tle 2). The higher (8%) TIPAR in crop seson compred to crop seson my e ttriuted to longer crop durtion nd etter in thn The TIPAR ws not significntly ffected y irrigtion levels in the first yer (Tle 2). However, in the second yer, significntly higher TIPAR ws oserved in I5 (555 MJ m -2 ) compred to I3 (489 MJ m -2 ) nd I2 tretments (474 MJ m -2 ), nd I3 nd I2 tretments were sttisticlly t pr with respect to TIPAR. The nitrogen levels significntly (P \ 5) ffected TIPAR for oth the yers of study (Tle 2). N160 registered higher TIPAR thn the N40 tretments y 20% nd 9% for the yer nd , respectively. The higher TIPAR t higher irrigtion nd nitrogen levels is ttriuted to higher (Hn et l. 2008; Bssu et l. 2011). The reltionship etween AGB nd TIPAR of whet t vrious irrigtion nd nitrogen tretments re presented in Fig. 8. These reltionships re liner in nture. The TIPAR ws significntly (P \ 1) nd positively correlted with the AGB yield of whet (r = 0.93** for the yer nd.91** for the yer ). The liner reltionship etween TIPAR nd AGB depicts 86 nd 83% vrition in AGB yield of whet cn e explined

8 Ind J Plnt Physiol. (July Septemer 2018) 23(3): Aove ground iomss (kg h -1 ) y = x R² = 595 y = x R² = TIPAR (MJ m -2 ) showed good correltion (8) in nd poor correltion (7) in with grin yield. The poor correltion etween RUE nd grin yield for cn e scried to the non-significnt vrition in grin yield mong the tretments due to excess rinfll. These findings re in greement with the findings of Whitfield nd Smith (1989), Li et l. (2008) nd Hn et l. (2008) for whet. The interction effect of irrigtion nd nitrogen levels on RUE were not significnt for oth the yers of study. Fig. 8 TIPAR versus ove ground iomss of whet for the yer nd y TIPAR for the yer nd , respectively. Similr reltionship hs een oserved in mny crops (pigeon pe, chickpe, mustrd, whet, soyen, mize) y vrious workers (Singer et l. 2011; Prdhn et l. 2014c, d; Sh et l. 2015; Kr nd Kumr 2015). Rdition use efficiency (RUE) The rdition use efficiency (iomss produced per unit intercepted rdition) of whet vried etween 1.97 (I2N40) nd 2.42 (I3N160) g MJ -1 in with n verge vlue of 2.51 g MJ -1 nd 2.21 (I2N40) nd 2.73 (I3N40) g MJ -1 with n verge vlue of 2.16 g MJ -1 for the yer (Tle 2). In the present experiment, our estimted RUE vlues were within the rnge of 0 nd 2.93 g MJ -1 reported in literture for whet cross rnge of environments (Kiniry et l. 1989; Siddique et l. 1989; Gregory et l. 1992; Gregory nd Esthm 1996). In , the significntly highest (P \ 5) RUE ws oserved in I3 (2.70 g MJ -1 ) followed y I5 (2.55 g MJ -1 ) nd I2 (2.29 g MJ -1 ). However, in , I5 (2.23 g MJ -1 ), I3 (2.22 g MJ -1 ) nd I2 (2.03 g MJ -1 ) irrigtions levels were sttisticlly t pr (P \ 5) with respect to RUE. However, even though RUE vlues were not significntly different mong nitrogen levels (Tle 2), they showed decresing trend (5% in nd 13% in ) with decrese in N levels. It cn e ttriuted to the lower AGB nd higher root iomss in N40 which is commonly oserved under stressful environments resulting lower RUE (Siddique et l. 1989; Hmlin et l. 1990; Jmieson et l. 1995). The decrese in RUE (sed on AGB) mong the tretments ws mostly due to the vrition in AGB thn the vrition in TIPAR. This is cler from the good correltion etween the AGB of whet with the RUE (4 for nd 8 for ) thn TIPAR with the RUE (0.57 for nd 1 for ). However, the RUE Conclusion It ws concluded tht of whet followed curviliner reltionship with time similr to tht of lef re index. There ws increse in nd with the increse in the irrigtion level up to five irrigtions nd with the increse in nitrogen does up to 160 kg N h -1. There ws no significnt difference in the TIPAR mong the irrigtion tretments in high rinfll yer ut in norml rinfll yers, TIPAR incresed significntly up to five irrigtion level. However in oth the yers TIPAR of whet incresed up to 160 kg N h -1. There ws no significnt difference mong the irrigtion tretments with respect to extinction coefficient ut it increse significntly due to increse in N dose up to 160 kg N h -1. During norml rinfll yer 5 irrigtion with 160 kg N h -1 registered highest grin nd iomss yield of whet which is t pr with 3 irrigtions with 160 kg N h -1. However during high rinfll yers though five irrigtions with 160 kg N h -1 registered highest iomss yield of whet yet grin yield ws not ffected y irrigtion nd N levels. During norml rinfll yers 3 irrigtions registered highest RUE ut in high rinfll yers effect irrigtion ws not significnt on RUE of whet. So whet my e grown with three irrigtions t criticl stges nd 160 kg N h -1 in the semirid region of Delhi region without ny significnt yield reduction compred to five irrigtions nd to chieve higher rdition use efficiency under norml rinfll sitution. Open Access This rticle is distriuted under the terms of the Cretive Commons Attriution 4.0 Interntionl License ( tivecommons.org/licenses/y/4.0/), which permits unrestricted use, distriution, nd reproduction in ny medium, provided you give pproprite credit to the originl uthor(s) nd the source, provide link to the Cretive Commons license, nd indicte if chnges were mde. Funding Funding ws provided y Indin Agriculturl Reserch Institute, New Delhi, Indi.

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