Field Crops Research

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1 Field Crops Reserch 130 (2012) Contents lists ville t SciVerse ScienceDirect Field Crops Reserch jou rnl h om epge: Agronomic productivity nd nitrogen requirements of lterntive tillge nd crop estlishment systems for improved weed control in direct-seeded rice C.M. Pittelkow,, A.J. Fischer, M.J. Moechnig,1, J.E. Hill, K.B. Koffler, R.G. Mutters, C.A. Greer, Y.S. Cho,2, C. vn Kessel, B.A. Linquist Deprtment of Plnt Sciences, University of Cliforni, Dvis, One Shields Ave, Dvis, CA 95616, USA University of Cliforni Coopertive Extension, Division of Agriculture nd Nturl Resources, 1111 Frnklin St, Oklnd, CA 94607, USA r t i c l e i n f o Article history: Received 30 Decemer 2011 Received in revised form 14 Ferury 2012 Accepted 14 Ferury 2012 Keywords: Direct-seeded rice Crop estlishment Tillge Weeds Grin yield Nitrogen fertilizer mngement s t r c t Weed control is primry concern in direct-seeded rice, prticulrly for hericide-resistnt weed species which stnd to threten the long-term sustinility of Cliforni rice systems. In four-yer field study we evluted the potentil for improved weed control using no-till stle seeded prctices in wterseeded () nd drill-seeded (DS) rice estlishment systems. In ddition, s the gronomic performnce of lterntive tillge nd crop estlishment methods is not well understood, we ssessed the productivity of these systems nd estimted economic optimum nitrogen (EON) rtes sed on yield response to nitrogen (N) trils. Estlishment system tretments included: wter-seeded conventionl tillge ( conventionl), wter-seeded conventionl tillge stle seeded ( stle), wter-seeded no-till stle seeded ( no-till stle), drill-seeded conventionl tillge (DS conventionl), nd drill-seeded no-till stle seeded (DS no-till stle). Compred to the conventionl system, stle nd no-till stle tretments significntly reduced sedge weed iomss y 59 nd 95%, respectively. Although redstem (Ammnni spp.) ws not controlled, lterntive systems reduced grss weed iomss y more thn 99% when present. Within DS systems, no-till stle seeded prctices significntly reduced wtergrss (Echinochlo spp.) iomss y 75% in the first two yers ut did not improve wtergrss control during the second hlf of the study. Grin yields were not different for conventionl nd lterntive rice estlishment systems ech yer when N ws pplied t 168 kg N h 1 nd weeds were fully controlled. However, yields were significntly lower for lterntive estlishment systems compred to the conventionl system when no N fertilizer ws pplied, likely s result of greter soil N losses. The response of grin yield to N rte ws significntly different mong systems nd estimted EON rtes indicted tht stle nd no-till stle systems required n increse of kg N h 1 to mximize yields nd returns to N compred to the conventionl system. Results from this experiment demonstrte tht lterntive tillge nd crop estlishment systems cn led to improved weed control while remining vile from n gronomic nd economic stndpoint in Cliforni. Provided N rtes re close to optiml nd nd DS estlishment methods re selected to trget weed species of concern, these findings suggest tht no-till stle seeded prctices should e considered s component of integrted weed mngement strtegies in direct-seeded rice moving forwrd Elsevier B.V. All rights reserved. 1. Introduction Alterntive rice (Oryz stiv L.) estlishment systems sed on innovtive technologies nd mngement prctices to reduce Arevitions:, wter-seeded; DS, drill-seeded; EON rte, economic optimum nitrogen rte. Corresponding uthor. Tel.: , fx: E-mil ddress: cpittelkow@ucdvis.edu (C.M. Pittelkow). 1 Present ddress: Deprtment of Plnt Science, South Dkot Stte University, Agriculturl Hll, Box 2207A, Brookings, SD 57007, USA. 2 Present ddress: Deprtment of Agronomy, Gyeongnm Ntionl University of Science nd Technology, Chilm-Dong 150, Jinju-City, Kore. humn lor requirements nd externl inputs while mintining or incresing economic productivity hve een developed in recent yers, primrily in Asi. For exmple, zero tillge direct-seeded rice systems re eing dopted to void mnul trnsplnting requirements nd llevite soil degrdtion prolems (Frooq et l., 2011; Ldh et l., 2009). However, direct-seeded systems re distinct from trnsplnted rice in tht weeds nd rice emerge in closer temporl proximity nd greter efforts re required to mnge weed popultions nd prevent yield loss (Bhgt et l., 1996; Hill et l., 1994). Therefore, weed control in directseeded rice remins significnt concern nd strtegies to reduce weed popultions re needed (Ldh et l., 2007; Ro et l., 2007) /$ see front mtter 2012 Elsevier B.V. All rights reserved. doi: /j.fcr

2 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) In Cliforni, rice is grown on pproximtely 200,000 h nd direct-seeded systems hve een used for close to century to vrying degrees, with wter-seeded () rice eing the primry estlishment prctice since the lte 1920s. Lnd preprtion typiclly consists of 3 to 5 tillge events using chisel-plow nd disc, followed y severl psses with triplne nd roller to crete uniform, level seeded. Reltive to cerel production systems utilizing reduced or no-till prctices, intensive tillge cn increse energy consumption nd equipment costs (Mutters et l., 2007; Shrwt et l., 2010) nd contriute to ir qulity prolems (Mdden et l., 2008). Fertilizer is commonly pplied y ground rig nd pre-germinted rice seed is erilly seeded onto flooded fields. Crop rottions re not common due to hevy cly soils in the region, thus culturl nd chemicl weed control prctices generlly remin similr yer to yer. Weed mngement strtegies re focused on chieving erly weed control fter seeding, ut this is ecoming incresingly difficult nd numerous hericide pplictions my e required (Fischer nd Hill, 2004). Continuous selection pressure hs led to the development of hericide-resistnt weed species (Fischer et l., 2000), with Cliforni rice hving mong the highest numer of hericide-resistnt iotypes compred to ny other crop or region in the U.S. (Hep, 2011). Hericide-resistnt weeds represent mjor chllenge fcing growers in the region y reducing yields nd incresing production costs (Fischer et l., 2000; Fischer nd Hill, 2004). In ddition, with greter pulic demnds for production systems tht minimize environmentl impcts, more stringent regultions re limiting the hericides tht cn e used long with how they cn e pplied (Hill et l., 2006). To ensure the long-term sustinility of Cliforni rice systems, shift in mngement prctices is needed to develop more effective weed control strtegies nd promote resource conservtion nd environmentl qulity relted to intensive tillge prctices. With integrted culturl nd chemicl weed control prctices, lterntive rice estlishment systems my help reduce weed pressure. Weed emergence in rice systems is lrgely driven y wter mngement during crop estlishment, thus seeding methods with contrsting wter regimes llow for different weed species to e recruited (Bhgt et l., 1999). In drill-seeded (DS) rice systems, eroic conditions re mintined prior to the permnent flood which my help suppress qutic weed species tht dominte rice systems in Cliforni (Hill et l., 1994) nd llow for new hericides with different modes of ction to e used, for which resistnce hs not yet evolved (Fischer et l., 2000). Another weed control option tht hs gined populrity is to implement stle seeded prior to plnting in comintion with reduced tillge or no-till prctices (Hrrell et l., 2011; Hill et l., 1994). With this technique fields re irrigted fter lnd preprtion to promote weed germintion nd then weeds re eliminted efore seeding using non-selective hericide to which weeds re not resistnt. Stle seededs hve een shown to reduce weed popultions common to direct-seeded rice (Ro et l., 2007) nd my e especilly effective when comined with no-till prctices s weed seeds tht re not eliminted prior to rice seeding remin uried in the seeded (Chuhn et l., 2006). Additionlly, ecuse no-till prctices hve the potentil to reduce externl inputs nd production costs (Bhushn et l., 2007; Ldh et l., 2009), lterntive estlishment systems my represent n importnt option for enhncing the sustinility of Cliforni rice systems. However, there re potentil issues with switching estlishment systems tht must e ddressed, especilly concerning gronomic productivity nd nitrogen (N) fertilizer mngement prctices to optimize yield. Previous studies hve determined tht DS systems reduce N uptke nd N recovery efficiency compred to systems (Westcott et l., 1986), s well s reduce yields in some cses ut not others (Bufogle et l., 1997; Singh et l., 2011). No-till prctices hve lso een shown to cuse yield reductions in direct-seeded rice (Bzy et l., 2009; Gthl et l., 2011; Singh et l., 2011), possily due to poor germintion nd crop estlishment or the reduced efficiency of pplied N fertilizer (Ll, 1986). Accumultion of orgnic mtter ner the soil surfce cn cuse immoiliztion of N fertilizer (Rice nd Smith, 1984) nd lrge mounts of surfce residue my increse N losses through mmoni voltiliztion (Griggs et l., 2007). Furthermore, N is typiclly pplied to the soil surfce in no-till systems, wheres in conventionl systems it cn e incorported with tillge which hs een shown to reduce losses (Co et l., 1984). These fctors my contriute to reduced crop N uptke nd yields in no-till systems (Kundu nd Ldh, 1999; Ll, 1986). In ddition, lthough ntive soil N is n importnt nutrient source for rice nd its vilility in flooded soils hs een thoroughly investigted (Cssmn et l., 1996; Doermnn et l., 1994), little is known out the effects of no-till prctices. Strw is generlly either not incorported or incorported to lesser extent which my influence ntive soil N vilility nd lter N fertilizer requirements (Egle et l., 2000; Linquist et l., 2006). When ntive soil N supply is low nd N uptke y rice is limited, incresed N fertilizer is often required to rech mximum yield (Cssmn et l., 1996; Ki et l., 1984). To ddress the growing prolem of hericide resistnce in Cliforni rice production systems while ensuring limited environmentl impcts, this study ws conducted to ssess the potentil for improved weed control using no-till stle seeded prctices in nd DS rice estlishment systems. Agronomic performnce nd N fertilizer requirements of ech system were lso investigted. The specific ojectives were to (i) evlute weed dynmics s influenced y estlishment system, (ii) ssess system productivity over time, nd (iii) estimte economic optimum N rtes for ech system sed on the yield response to N fertilizer. 2. Mterils nd methods 2.1. Site description nd experimentl design A four-yer field experiment ws conducted from 2004 to 2007 t the CA Rice Experiment Sttion ner Biggs, CA ( N, W). The experimentl re ws 4 h in size. Soils t this site re clssified s n Esquon-Neerdoe Complex (fine, smectitic, thermic Xeric Epiquerts nd Durquerts). Selected soil chrcteristics for the 0 15 cm depth include: ph 5.0, 34.2 cmol c kg 1 CEC, 1.06% orgnic C, 0.08% totl N, 0.36 ds m 1 EC, 29% snd, 26% silt, nd 45% cly. Annul precipittion followed typicl ptterns for Mediterrnen climte with n verge of 541 mm of rinfll occurring primrily outside the growing seson. Averge mximum nd minimum tempertures during the growing seson were 29.2 nd 12.7 C, respectively. The field tril ws rrnged s rndomized complete lock design with four replictions. Rice estlishment systems were implemented in individul 0.2 h size plots (i.e. rice sins) tht were seprted y levees nd ditch to prevent lterl wter movement etween plots. In ddition to weed control chrcteristics, gronomic performnce nd N fertilizer requirements were investigted to etter understnd the yield potentil of these systems nd develop improved fertility mngement prctices. Therefore, the lyout for ech sin included (i) the min plot under typicl fertility nd weed control prctices, (ii) n re for weed recruitment which received no hericides with the exception of preplnt glyphoste in stle seeded tretments nd (iii) set of N fertility trils (Fig. 1). The loction of N trils moved ech yer ut weed recruitment zones were permnent. Other spects of this experiment were previously reported on y Linquist et l. (2008).

3 130 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) Fig. 1. Experimentl plot lyout. Individul sins were 0.2 h in size nd contined (i) the min plot, (ii) permnent re for weed recruitment which received no hericides except preplnt glyphoste in stle seeded tretments, nd (iii) N fertility trils which moved loctions ech yer Rice estlishment systems Five estlishment systems were evluted in this experiment (Tle 1). The tretment lyout did not chnge over the course of the experiment, thus ech sin ws under 4 yers of continuous system mngement. Ech estlishment system represented unique comintion of tillge (conventionl or no-till), seeded preprtion (regulr or stle seeded), nd rice seeding method ( or DS). The five tretments were wter-seeded conventionl tillge ( conventionl), wter-seeded conventionl tillge stle seeded ( stle), wter-seeded no-till stle seeded ( notill stle), drill-seeded conventionl tillge (DS conventionl), nd drill-seeded no-till stle seeded (DS no-till stle). Agronomic mngement for ech system followed typicl N fertilizer (168 kg N h 1 ) nd weed control prctices for the region in ccordnce with current recommendtions for Cliforni rice production (Fischer nd Hill, 2004; Willims, 2010). N fertilizer ws pplied s ure except for topdress pplictions where N ws pplied s mmonium sulfte. To ensure tht other nutrients were not limiting, 22 kg P h 1 s triple super phosphte nd 45 kg K h 1 s potssium chloride were pplied ech spring prior to tillge or the previous fll fter hrvest. Conventionl tillge prctices consisted of severl psses with chisel-plow nd disc, followed y finl seeded preprtion with triplne nd roller. No-till prctices in this study referred specificlly to spring tillge events prior to crop estlishment. In ll systems nd yers, sins were seeded with Clrose medium grin rice vriety widely grown in the region (M-202). To determine grin yield, n re of 33 m 2 ws hrvested t rice physiologicl mturity with smll plot comine. Following hrvest, comine ruts in the field were eliminted nd strw ws incorported with disc except in the first yer where strw ws removed. All sins were flooded ech winter to promote strw decomposition. The conventionl tretment represented the conventionl rice estlishment prctice for Cliforni nd served s the control when ssessing gronomic performnce nd weed control chrcteristics of lterntive estlishment systems. Pre-germinted rice seed ws rodcst in ll systems t 168 kg seed h 1, which reflects commercil rice production prctices in the region nd is well within the rnge of seeding rtes to otin mximum tiller density nd grin yield (Miller et l., 1991; Mutters et l., 2007). Bsins were flooded severl dys prior to seeding nd permnent flood of cm ws mintined until the field ws drined pproximtely one month prior to hrvest. Two lterntive estlishment systems, oth using the stle seeded technique, were ssessed. Weed recruitment irrigtion flushes were performed to implement stle seededs the month prior to seeding. Depending on the yer, rice sins were flooded nd drined either once or twice to mximize weed emergence. Glyphoste ws pplied t rte of 1.5 kg.e. h 1 severl dys efore plnting to eliminte weeds tht hd emerged. The stle tretment consisted of conventionl tillge s descried ove followed y stle seeded prctices. For the no-till stle tretment, no-till mngement ws comined with stle seeded prctices (Tle 1). Following seeding, wter mngement nd weed control prctices were similr for tretments throughout the growing seson. Depending on the yer, comintions of post-emergence hericides (clomzone (0.7 kg.i. h 1 ), propnil (6.7 kg.i. h 1 ), ensulfuron (0.04 kg.i. h 1 ), penoxsulm (0.04 kg.i. h 1 )) were pplied for rod spectrum control of primrily sedge nd rodlef weed species in systems (Fischer nd Hill, 2004). Two DS tretments were evluted in this experiment. The DS conventionl tretment consisted of conventionl tillge s descried ove followed y DS crop estlishment prctices. For the DS no-till stle tretment, no-till mngement ws comined with stle seeded prctices (Tle 1). All DS systems were seeded with M-202 t 112 kg seed h 1 using grin drill with 19 cm spcing etween rows. Although it hs een shown tht seeding rtes of kg h 1 cn e used successfully in DS systems (e.g. Gthl et l., 2011; Jt et l., 2009), this rte ws selected sed on previous reports indicting tht pnicle density nd yields re mximized in DS systems etween pproximtely 90 nd 140 kg seed h 1 (Hrrell nd Blnche, 2010; Jones nd Snyder, 1987). During stnd estlishment, sins were flooded nd drined 2 4 times nd

4 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) Tle 1 Crop estlishment prctices for wter-seeded () nd drill-seeded (DS) rice estlishment systems nd corresponding dtes of mngement ech yer. Yer System Tillge initited Weed recruitment flush 1 Weed recruitment flush 2 Glyphoste ppliction Seeding dte Permnent flood Hrvest 2004 conventionl 24 April 17 My 14 My 1 Octoer stle 24 April 14 My 26 My 31 My 4 June 2 June 6 Octoer no-till stle No-till 14 My 26 My 31 My 4 June 2 June 11 Octoer DS conventionl 24 Apr 12 My 5 June 30 Septemer DS no-till stle No-till 14 My 26 My 31 My 3 June 23 June 12 Octoer 2005 conventionl 18 April 31 My 28 My 5 Octoer stle 18 April 5 My 26 My 31 My 28 My 5 Octoer no-till stle No-till 5 My 26 My 31 My 28 My 5 Octoer DS conventionl 18 April 27 My 28 June 12 Octoer DS no-till stle No-till 5 My 26 My 27 My 28 June 12 Octoer 2006 conventionl 1 My 1 June 31 My 11 Octoer stle 1 My 11 My 29 My 1 Jun 31 My 11 Octoer no-till stle No-till 11 My 29 My 1 June 31 My 11 Octoer DS conventionl 1 My 30 My 16 June 11 Octoer DS no-till stle No-till 11 My 29 My 30 My 16 June 11 Octoer 2007 conventionl 2 April 31 My 22 My 15 Octoer stle 2 April 1 My 13 My 29 My 1 June 31 My 15 Octoer no-till stle No-till 1 My 13 My 29 My 1 June 31 My 15 Octoer DS conventionl 2 April 30 My 16 June 22 Octoer DS no-till stle No-till 1 My 13 My 29 My 30 My 16 June 22 Octoer Prior to the permnent flood in DS systems, sins were flooded nd drined severl times for crop estlishment. the permnent flood generlly occurred d fter seeding (Tle 1). Wter levels were mintined t cm throughout the growing seson nd fields were drined pproximtely one month prior to hrvest. Weed control prctices were similr for DS tretments following seeding nd depending on the yer comintions of hericides (pendimethlin (1.1 kg.i. h 1 ), cyhlofop-utyl (0.3 kg.i. h 1 ), propnil (6.7 kg.i. h 1 )) were pplied efore the permnent flood for rod spectrum control in DS systems (Fischer nd Hill, 2004) Weed recruitment zones To investigte the potentil for improved weed control using no-till nd stle seeded prctices in nd DS rice systems, weed recruitment zones were estlished in ech rice sin. While ll other mngement prctices remined the sme s the min plot, hericides were not pplied to n re of pproximtely 300 m 2 ech yer with the exception of preplnt glyphoste in stle seeded tretments (Fig. 1). In the sence of chemicl weed control fter rice seeding, weed growth in these zones remined unchecked throughout the growing seson. The loction of this zone within ech sin remined the sme ech yer. Weed seed nk dynmics, erly seson emergence, nd competition with rice were monitored throughout the experiment. A full nlysis of these results is eyond the scope of the present pper nd will e reported elsewhere. To ssess the effects of ech estlishment system on weed control, weed iomss ws determined t hrvest. Nine oveground iomss smples were otined from ech weed recruitment zone using 0.09 m 2 qudrts in rndomly selected loctions. Weed iomss ws seprted into the following species nd susequently dried to constnt weight t 65 C: wtergrss (Echinochlo spp.), sprngletop (Leptochlo fsciculris), smllflower umrell sedge (Cyperus difformis), ricefield ulrush (Schoenoplectus mucrontus), nd redstem (Ammnni spp.) Nitrogen fertility trils Optimum mngement of N fertilizer ws investigted using N fertility trils in ech estlishment system (Fig. 1). Trils were rrnged s split-plot design nd were moved to new loction within min plots ech yer to void the residul effects of N fertilizer over time (Reddy nd Ptrick, 1978). N fertilizer in the form of ure ws pplied to 37.2 m 2 su-plots t the following rtes: 0, 112, 168, nd 224 kg N h 1. Due to differences in wter mngement etween nd DS systems s well s requirements for no-till nd stle seeded estlishment prctices, timing nd plcement of N pplictions vried mong systems. In systems, N fertilizer ws either pplied completely preflood (i.e. prior to the permnent flood t plnting) or split etween preflood nd midseson (i.e. topdressed etween mid-tillering nd pnicle inittion). Previous work in DS systems hs suggested there re numer of wys to split N pplictions with the potentil to improve yields or N uptke y rice (Reddy nd Ptrick, 1976). Therefore, in DS systems N fertilizer ws either pplied preflood, split etween preplnt (i.e. directly efore seeding) nd preflood, or split etween preflood nd midseson. For conventionl nd DS conventionl systems, preplnt N ws incorported into the soil with hrrow. For ll other systems nd midseson pplictions, N ws rodcst on the soil surfce or into the floodwter. At physiologicl mturity, yields were determined in N su-plots from n re m 2 in size depending on the yer. All grin yield results reported represent rough rice yields djusted to 14% grin moisture content Dt nlysis Anlysis of vrince ws performed on weed iomss nd grin yield results using the PROC GLM procedure of SAS softwre, version 9.1 of the SAS System for Windows (SAS Institute Inc., 2004). If results violted ANOVA ssumptions they were trnsformed ccordingly using log 10 or power functions. For presenttion of results ll mens were de-trnsformed where necessry. Significnt differences etween systems were determined using LS MEANS pirwise comprisons (P < 0.05). For weed iomss results, weed species were considered to e present when the men ws significntly different from zero. Anlysis of vrince for weed iomss nd grin yields ws initilly performed cross yers ut results were susequently nlyzed y yer when significnt yer y tretment interctions were detected. Nitrogen fertility tril results were used to evlute the reltionship etween grin yield nd N rte. Bsed on recent work indicting tht qudrtic yield response functions provide the est model fit nd re the most relile cross soils nd vrieties for

5 132 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) Weed iomss (kg h -1 ) conventionl stle ) sedge c no-till stle conventionl stle ) redstem no-till stle conventionl stle c) grss no-till stle Estlishment system Fig. 2. Weed iomss in weed recruitment zones of systems t rice hrvest. Mens for () sedge species (smllflower umrell sedge nd ricefield ulrush) nd () redstem were verged over s there ws no yer y system interction. Mens for (c) grss species (wtergrss nd sprngletop) were verged over s grsses were not present in See Tle 1 for tretment descriptions. Within ech pnel, rs with the sme letter re not significntly different t P < Weed iomss (kg h -1 ) DS conventionl DS no-till stle ns ) wtergrss ) sprngletop ns ns ns ns Yer Yer Fig. 3. Weed iomss in weed recruitment zones of DS systems t rice hrvest. Mens for () wtergrss nd () sprngletop re presented y yer due to significnt yer y system interction. Aqutic weed species (smllflower umrell sedge, ricefield ulrush, nd redstem) were not present in DS systems. See Tle 1 for tretment descriptions. Within ech yer, rs with the sme letter re not significntly different t P < rice production systems (Wtkins et l., 2010), qudrtic yield response function including fixed nd rndom effects ws fit to N fertility tril dt for using the PROC MIXED procedure of SAS softwre, version 9.1 (SAS Institute Inc., 2004). The finl model included fixed effects of N rte, N rte N rte, System, nd System N rte. Yer nd lock were designted s rndom effects with rndom slope nd intercept estimted for ech lock-yer comintion using n unstructured covrince mtrix (Linquist et l., 2009; Miguez nd Bollero, 2006). Terms for nonsignificnt effects were removed to increse model prsimony (this included system N rte N rte nd system yer interctions). In few cses, where N ws either pplied in mnner inconsistent with estlished est mngement prctices or tretment N rtes chnged over time, tretments were excluded from the nlysis (e.g. severl N rtes in 2004 were experimentl nd not repeted in lter yers, thus only yield results for 0 nd 168 kg N h 1 plots were included). Anlysis of vrince ws performed with the regression model nd contrsts were used to further prtition the sum of squres. Intercepts nd initil slopes (i.e. N rte coefficients) were considered significntly different etween systems t P < Economic optimum nitrogen (EON) rtes were clculted for ech estlishment system using the qudrtic yield response functions descried ove. EON rtes re sed on the price of rice nd cost of N fertilizer nd reflect the point t which mximum returns to N re chieved for given yield function. Model coefficients were used to determine EON rtes following Bullock nd Bullock (1994) nd Wtkins et l. (2010). Economic input vlues included the verge price of rice in Cliforni nd the verge cost of ure fertilizer over the durtion of the study period (USDA Ntionl Agriculturl Sttistics Service, 2011), s well s the cost of custom service N fertilizer ppliction for rice grown in this region (Mutters et l., 2007). Since the reltionship etween N fertilizer cost nd rice price cn vry sustntilly yer to yer, multiple N cost/rice price rtios were considered. EON rtes were estimted using the rnge of N cost/rice price rtios oserved in Cliforni for the period to enle growers to mximize returns to N despite price fluctutions (Doermnn et l., 2011). 3. Results 3.1. Weed recruitment zones In weed recruitment zones, grss weed species (wtergrss nd sprngletop) represented more thn 99% of totl weed iomss cross yers in DS systems. Aqutic weed species (smllflower umrell sedge, ricefield ulrush, nd redstem) were not present in DS systems. In systems, qutic species (smllflower umrell sedge, ricefield ulrush, nd redstem) represented more thn 95% of totl weed iomss during the first two yers nd 80% during the second two yers (dt not shown). Grss species (wtergrss nd

6 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) Tle 2 Rice grin yield for min plots where 168 kg N h 1 ws pplied nd full weed control occurred. Men vlues for re presented under seprte column s there ws no yer y system interction. Within column, vlues followed y the sme letter re not significntly different t P < System Grin yield, kg h Men conventionl 10, stle no-till stle 10, DS conventionl 10, DS no-till stle 10, , Grin yield (kg h -1 ) ANOVA results ns ns ns ns P = sprngletop) were not present in systems the first two yers, ut ecme prolem in the conventionl system nd represented pproximtely 55% of totl weed iomss in the lst two yers (Fig. 2). In oth DS nd systems, weed control ws significntly improved when lterntive estlishment prctices were implemented (Figs. 2 nd 3). In the conventionl system, sedge species (smllflower umrell sedge nd ricefield ulrush) produced pproximtely 600 kg iomss h 1 ech yer. Stle seeded nd no-till stle seeded prctices significntly reduced sedge iomss y 59 nd 95%, respectively (Fig. 2). Alterntive systems reduced grss iomss y more thn 99% when present, ut the qutic redstem escped control (Fig. 2 nd c). In DS systems, weed dynmics differed nd significnt yer y tretment interction ws oserved. Wtergrss nd sprngletop represented 90% nd 10%, respectively, of totl grss weed iomss (Fig. 3). The DS no-till stle system significntly reduced wtergrss iomss y 75% compred to the DS conventionl system in the first two yers, ut these effects were not consistent over time nd reductions were not oserved during the lst two yers (Fig. 3). Sprngletop only represented minor portion of grss weed iomss nd the DS no-till stle system improved sprngletop control in one yer (Fig. 3) System productivity Outside of weed recruitment zones where N ws pplied t 168 kg N h 1 nd weeds were controlled in ccordnce with current recommendtions, grin yields were not different for conventionl nd lterntive rice estlishment systems ech yer (Tle 2). However, when nlyzed over the durtion of the study period, yields for the stle system were significntly lower thn the other four systems. Men yields rnged from 8273 kg h 1 in the stle system to 9520 kg h 1 in the DS no-till stle system, with nd DS conventionl systems producing 8954 nd 9130 kg h 1 on verge, respectively. Overll, men yields from this experiment were very close to sttewide yield verges oserved during this period (USDA Ntionl Agriculturl Sttistics Service, 2011) conv. stle n.t. stle DS conv. Estlishment system DS n.t. stle Fig. 4. Rice grin yield when no N fertilizer ws pplied nd full weed control occurred. Vlues for were verged s there ws no yer y system interction. See Tle 1 for tretment descriptions. Brs with the sme letter re not significntly different t P < Nitrogen mngement When no N fertilizer ws pplied, yields for control plots were significntly lower for lterntive estlishment systems compred to the conventionl system (Fig. 4). Yields without N fertilizer rnged from 3580 kg h 1 in the stle system to 4343 kg h 1 in the DS no-till stle system, with the conventionl system producing 5424 kg h 1 on verge. The response of grin yield to N rte ws significntly different mong systems (Fig. 5 nd Tle 3). The regression nlysis indicted significnt liner nd qudrtic effect of N on grin yield, s well s significnt system N rte interction (Fig. 5). The qudrtic prmeter of the model ws not significntly different etween systems, thus it ws held constnt t for EON clcultions. In systems, modeled intercepts were lower for oth stle nd no-till stle systems s compred to the conventionl system. The yield response to N rte ws similr for conventionl nd DS conventionl systems (Tle 3). Estimted EON rtes were lowest for the conventionl system nd highest for stle nd no-till stle systems (Tle 4). Depending on the N cost/rice price rtio, stle nd notill stle systems required round kg N h 1 more thn the conventionl system. In contrst, oth DS systems required similr mount of N fertilizer s the conventionl system to mximize returns. Predicted yields nd returns to N were comprle mong systems, with the no-till stle system hving slightly lrger nd the DS no-till stle system hving slightly smller vlues with respect to the conventionl system. When the N cost/rice price rtio incresed or decresed reltive to the verge vlue of 6, EON rtes shifted pproximtely kg N h 1 nd differences etween systems remined similr in mgnitude. Tle 3 Regression nlysis results for the response of grin yield to N rte in wter-seeded () nd drill-seeded (DS) rice estlishment systems. A qudrtic yield response function ws fit to N fertility tril dt for using mixed-effects model. ANOVA Model coefficients Contrsts P-vlue Fixed effect P-vlue System Intercept SE Liner SE Intercept Liner N < conventionl conv. vs. stle < N N < stle conv. vs. no-till stle System no-till stle stle vs. no-till stle System N DS conventionl conv. vs. DS conv DS no-till stle DS conv. vs. DS no-till stle

7 134 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) Tle 4 Economic optimum nitrogen (EON) rtes, predicted grin yields, nd returns to N fertilizer for the rnge of N cost/rice price rtios oserved in Cliforni during System N cost/rice price rtio EON (kg h 1 ) Yield (kg h 1 ) Returns ($ h 1 ) EON (kg h 1 ) Yield (kg h 1 ) Returns ($ h 1 ) EON (kg h 1 ) Yield (kg h 1 ) Returns ($ h 1 ) conventionl stle no-till stle , , , DS conventionl DS no-till stle Discussion 4.1. Weed recruitment zones A more detiled nlysis of weed emergence, competition with rice, nd community dynmics s ffected y estlishment system will e reported in nother pper. Three key concepts sed on weed iomss results t rice hrvest will e discussed here. First, rice seeding method hd significnt impct on weed recruitment. Aqutic weeds were primrily present in systems while grsses were exclusively present in DS systems. Therefore, oth DS systems provided complete control of qutic weeds reltive to the conventionl system. This cn e ttriuted to differences in wter mngement prctices during crop estlishment nd corresponding soil moisture nd temperture conditions tht re known to influence weed germintion (Cton et l., 2002; Jurimi et l., 2011). In terms of long-term weed mngement strtegies for Cliforni, these results suggest tht lternting etween nd DS estlishment systems my form prt of n ecologicl pproch for suppressing qutic weed species. Second, while stle seeded prctices significntly improved sedge nd grss weed control in systems, when comined with no-till prctices even more drmtic reductions were chieved (Fig. 2 nd c). On the contrry, Chuhn nd Johnson (2009) reported tht no-till prctices lone incresed weed germintion nd Shd nd De Dtt (1986) found totl weed iomss ws often greter nd decresed yields. Therefore, no-till prctices on their own my not e n effective weed mngement tool nd should e comined with stle seeded prctices nd other integrted weed mngement strtegies (Murphy nd Lemerle, 2006; Ro et l., 2007). In prticulr, strtegies for lte-seson rodlef control re needed s lterntive systems did not reduce redstem iomss (Fig. 2), likely due to poor germintion of redstem during stle seeded implementtion nd delyed emergence with respect to rice. Third, no-till stle seeded prctices were more effective in compred to DS systems. Although the DS no-till stle system reduced wtergrss iomss y 75% during the first two yers of this study, it performed similr to the DS conventionl system during the second hlf. This is most likely ecuse the seeded is distured y drill openers t plnting in DS systems, ringing more weed seeds to the surfce where germintion rtes re higher (Chuhn nd Johnson, 2009). In ddition, ecuse weeds were not controlled ech seson in weed recruitment zones, seeds likely ecme concentrted t the soil surfce over time (Chuhn et l., 2006). Incresed germintion of surfce seeds in no-till systems my hve potentilly outweighed weed control enefits oserved in the first two yers. Alterntively, further fine-tuning of stle seeded prctices to specificlly trget shllow seeds might llow for sustntil portion of the seed nk to e eliminted prior to rice seeding in no-till systems. Along with other weed control considertions, these spects of nd DS systems must e evluted to determine the most suitle estlishment system for given context (e.g. in res where mnul or mechnicl weeding is prcticed insted of chemicl weed control, DS systems with defined rows nd inter-rows my e fvored over rodcst systems) System productivity Results from this four-yer field experiment indicte tht under recommended fertility nd weed control prctices, lterntive rice estlishment systems consistently produce grin yields similr to conventionl estlishment prctices (Tle 2). This is n importnt finding in light of the pressing glol need for development nd doption of rice production systems tht mintin gronomic productivity while conserving nturl resources (Gupt nd Seth, 2007; Timsin nd Connor, 2001). In support of our findings, prior reserch hs shown tht nd DS systems with conventionl tillge produce equl yields Wter-seeded Drill-seeded Grin yield (kg h -1 ) conventionl stle no-till stle DS conventionl DS no-till stle N rte (kg h -1 ) N rte (kg h -1 ) Fig. 5. The response of rice grin yield to N rte in wter-seeded nd drill-seeded rice estlishment systems s modeled y mixed-effects qudrtic yield response function fit to N fertility tril dt for Regression nlysis results re displyed in Tle 3.

8 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) (Choudhury et l., 2007; Westcott et l., 1986). Moreover, while evluting no-till mngement for rice systems, Bhttchryy et l. (2008) found no differences in yield etween conventionl nd no-till prctices over four-yer period. Likewise, Shrwt et l. (2010) reported tht comprle yields were chieved in systems with conventionl tillge nd DS systems under notill mngement. Along with prior work in the region (Bhushn et l., 2007), Shrwt et l. (2010) indicted tht lterntive systems significntly reduced mchine lor nd other inputs which led to higher net returns. Although not directly quntified in our study, it ws oserved tht considerle svings in lor nd energy were ssocited with no-till prctices while yields remined similr, suggesting net returns my lso increse with no-till prctices in Cliforni. The economic performnce of lterntive estlishment systems is importnt nd further reserch on this topic is wrrnted. More recently, four-yer study on lterntive seeding nd tillge prctices reported inconsistent yield results cross sites in northern Indi (Singh et l., 2011). In one portion of the study lterntive estlishment systems mintined yield levels of conventionl systems t multiple reserch loctions. In contrst, t the primry reserch site it ws found tht DS systems with conventionl tillge yielded significntly lower thn systems nd furthermore, tht no-till prctices reduced yields within DS systems. Our results do not support this dt; however, these differences my in prt e explined y irrigtion prctices. In our study permnent flood ws mintined in oth nd DS systems fter crop estlishment, wheres in Singh et l. (2011) crops relied on rinfll nd supplementl irrigtion. These uthors noted tht similr yields mong systems were primrily chieved t sites which received lrge mounts of supplementl irrigtion, suggesting tht the potentil for yield loss under lterntive estlishment prctices my increse in res where it is difficult to meet crop wter demnds. Importntly, yields for lterntive estlishment systems did not decline over this four-yer study. Yield stility is criticl spect of lterntive cropping systems tht hs received little ttention despite the potentil for no-till prctices to influence soil properties nd therefore gronomic productivity over time (Jt et l., 2009; Timsin nd Connor, 2001). Although some vrition ws oserved in our results, yields for no-till systems in prticulr remined consistent. Gthl et l. (2011) reported similr findings from seven-yer study on no-till DS systems, with dditionl dt indicting tht soil physicl properties relevnt to crop production improved under no-till mngement. If these systems re to e dopted y growers in the future, yield nd yield stility need to e mintined in ddition to soil qulity. Indeed, short-term monetry gin rther thn resource conservtion tends to e the primry driver of on-frm experimenttion nd doption (Erenstein et l., 2008) Nitrogen mngement Our results indicte tht grin yield response to N is significntly different mong systems (Tle 3), with lterntive estlishment prctices generlly requiring more N fertilizer to ttin yields similr to conventionl systems (Tle 4). Efficient N mngement is n importnt spect of environmentl qulity tht hs often een overlooked in previous studies on lterntive systems (Frooq et l., 2011), nd these results highlight the need for creful considertion of N inputs nd mngement when undertking reserch nd extension efforts in the future. In control plots where no N fertilizer ws pplied, grin yields were lower for lterntive estlishment systems. In prticulr, when stle seeded prctices were comined with conventionl tillge, yield ws reduced y pproximtely 1800 kg h 1 compred to the conventionl system. Since other nutrients were not limiting in this study, the oserved differences in grin yield suggest there ws decrese in soil N supply under lterntive estlishment prctices. Preseson wter mngement including flood drin events during stle seeded implementtion my hve contriuted to greter N losses prior to rice seeding (George et l., 1993). When soil is sujected to eroic neroic cycles, nitrte concentrtions tend to increse during eroic periods ut then rpidly decrese when fields re flooded, with soil nitrte presumly lost through denitrifiction processes (Becker et l., 2007; Linquist et l., 2011). These cycles hve een shown to significntly reduce the totl N content of soil (Ptrick nd Wytt, 1964), therey decresing soil N ville to the crop. Moreover, ecuse tillge increses soil N minerliztion nd nitrifiction processes (Grce et l., 1993), it is likely tht preseson N losses were excerted in the stle system where stle seeded flushes directly followed spring tillge. This potentilly explins why yields from control plots were lowest for this system. While preseson N losses re known to occur nd cn e sustntil for rice systems (George et l., 1993), it is lso possile tht there were differences in N vilility following seeding (Kundu et l., 1996). Overll these results suggest tht soil N supply, which underpins the gronomic productivity of flooded rice production (Cssmn et l., 1996), is strongly influenced y estlishment system nd further reserch on this topic is needed. Bsed on yield response to N functions nd three different rtios for the cost of N reltive to the price of rice, estimted EON rtes for the conventionl system were in greement with current recommendtions for Cliforni rice production (Willims, 2010). However, EON rtes for lterntive systems indicted tht n increse of kg N h 1 ws needed to mximize yields nd returns to N in stle nd no-till stle systems. It hs previously een documented tht higher N rtes re required s result of no-till prctices in trnsplnted rice (Gthl et l., 2011; Ll, 1986), ut few investigtions hve een conducted in systems. Reductions in ntive soil N supply, evidenced y low yields from control plots s discussed ove, likely contriuted to the incresed need for N fertilizer in lterntive systems. For exmple, the stle system hd the lowest yield without ddition of N fertilizer nd in turn required the highest N rte to ttin yields equivlent to the conventionl system (Fig. 4; Tle 4). The higher N requirements of the stle system likely explin why grin yields were significntly lower when 168 kg N h 1 ws pplied in min plots compred to the conventionl system over the four-yer study period (Tle 2). Conversely, yield differences in min plots were not oserved for DS systems compred to the conventionl system, s estimted EON rtes for these systems more closely mtched ech other (Tle 4). Overll, within DS systems our results re consistent with prior work showing N requirements re similr for conventionl tillge nd reduced or no-till stle seeded prctices (Griggs et l., 2007; Hrrell et l., 2011). Moreover, they re supported y conclusions for DS systems on cly soils where mximum yields nd returns to N were chieved round 180 kg N h 1 (Wtkins et l., 2010). Despite higher EON rtes in some cses, our results show tht predicted yields nd returns to N were comprle mong systems nd remined reltively stle cross wide rnge in N fertilizer cost/rice price rtios. This indictes tht lterntive systems re vile from n economic stndpoint provided N rtes re close to optiml (Wtkins et l., 2010). Furthermore, these results suggest tht improvements in N fertilizer efficiency my led to greter returns in lterntive systems. One option to increse N recovery nd yield y rice is to split N pplictions (De Dtt, 1987; Ptrick nd Reddy, 1976); however, within our N fertility trils yield results for split N rtes were inconsistent mong estlishment systems nd vried y yer (dt not shown). Therefore, further reserch on

9 136 C.M. Pittelkow et l. / Field Crops Reserch 130 (2012) N timing is needed to etter synchronize N vilility with crop N demnd in lterntive systems, prticulrly those hving greter N requirements. 5. Conclusions Adequte weed control to prevent yield loss is primry chllenge in direct-seeded rice. This study evluted weed recruitment nd iomss dynmics, gronomic productivity, nd N mngement strtegies to meet yield potentil in rnge of lterntive nd DS rice estlishment systems in Cliforni. No-till stle seeded prctices were effective t reducing weed popultions in the first two yers in DS systems nd throughout the study in systems. These findings suggest tht long with lternting etween nd DS systems, no-till stle seeded prctices my form prt of n ecologicl pproch for long-term weed control in Cliforni. Adding to growing ody of literture, our results demonstrte tht gronomic productivity ws similr for lterntive tillge nd seeding prctices ssessed in this study. However, likely due to differences in wter mngement nd corresponding soil N losses, estimted economic optimum N rtes were kg N h 1 higher in lterntive compred to conventionl systems. Despite higher N requirements, predicted yields nd returns to N were similr mong estlishment systems nd cross rtios for the price of rice reltive to the cost of N fertilizer. These results highlight the fct tht lterntive estlishment systems re cple of providing improved weed control while remining vile from n gronomic nd economic stndpoint, yet creful considertion of N inputs nd mngement is needed when undertking reserch nd extension efforts relted to these systems in the future. Acknowledgements This work ws funded y the Cliforni Rice Reserch Bord nd the Stte Wter Resources Control Bord (Grnt numer: ). We re grteful to Dr. McKenzie nd employees t the Cliforni Rice Experiment Sttion for providing the experimentl site nd ssistnce throughout the project. We pprecite the help of UC Dvis Stff Reserch Assocites Jmes Eckert nd Ry Wennig with field opertions nd dt collection. We thnk the Deprtment of Plnt Sciences, UC Dvis for supporting K. Koffler nd C. Pittelkow with grdute student reserch ssistntships. The no-till seeder used in this study ws generously provided y collorting grower, J. Thompson. References Bzy, B.R., Sen, A., Srivstv, V.K., Plnting methods nd nitrogen effects on crop yield nd soil qulity under direct seeded rice in the Indo-Gngetic plins of estern Indi. Soil Till. Res. 105, Becker, M., Asch, F., Mskey, S.L., Pnde, K.R., Shh, S.C., Shresth, S., Effects of trnsition seson mngement on soil N dynmics nd system N lnces in rice whet rottions of Nepl. Field Crops Res. 103, Bhgt, R.M., Bhuiyn, S.I., Moody, K., Wter, tillge nd weed interctions in lowlnd tropicl rice: review. Agric. Wter Mnge. 31, Bhgt, R.M., Bhuiyn, S.I., Moody, K., Wter, tillge nd weed mngement options for wet seeded rice in the Philippines. Soil Till. 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