Agglomerating seeds to enhance native seedling emergence and growth

Transcription

1 Journl of Applied Ecology 2012, 49, doi: /j x Agglomerting seeds to enhnce ntive seedling emergence nd growth Mtthew D. Mdsen 1 *, Kirk W. Dvies 1, C. Json Willims 2 nd Tony J. Svejcr 1 1 United Sttes Deprtment of Agriculture, Agriculturl Reserch Service, Estern Oregon Agriculturl Reserch Center, A Hwy 205, Burns, OR 97720, USA; nd 2 United Sttes Deprtment of Agriculture, Agriculturl Reserch Service, Northwest Wtershed Reserch Center, 800 Prk Blvd., Boise, ID 83712, USA Summry 1. Restortion in rngelnds is constrined y low estlishment of species sown from seed. Noniotic soil-surfce crust is one of the mjor fctors limiting reseeding success y cting s rrier to seedling emergence. 2. The ojective of this study ws to determine whether seedling emergence could e improved y gglomerting multiple seeds into single pellet, so tht the seedlings growing from the pellet will collectively generte sufficient force to penetrte the soil crust. To evlute this technology, we compred seedling emergence nd iomss production from gglomerted, single nd non-coted seed (control) of Pseudoroegneri spict. In the greenhouse, seeds were sown in either crust-forming cly or non-crusting sndy soil nd studied for 25-dy period. Strting seed density ws constnt cross tretments. 3. In the cly soil, seedling emergence from the gglomertion tretment ws 1Æ3 nd 1Æ9 times higher thn the single seed coting nd control, respectively. In the sndy soil, the gglomertion nd single seed coting responded similrly, producing 1Æ4 times more seedlings thn the control. 4. Biomss production followed similr trend s plnt density. In the cly soil, incresed iomss of the gglomertion tretment ws not only ecuse of higher plnt densities ut ws lso product of hving greter iomss per plnt. 5. Synthesis nd pplictions. This short-durtion proof-of-concept study indictes tht oth the seed coting mterils used to form the gglomertes nd the ct of gglomerting the seeds together improve P. spict emergence nd plnt growth. These results lso demonstrte tht in the erly seedling stge, fcilittion outweighs competition in gglomertion plntings. Additionl reserch is needed to verify these results in the field. Key-words: fcilittion, ntive plnts, restortion, seed coting, seeding, seedling emergence, soil physicl crust Introduction Rngelnds constitute nerly hlf of the Erth s lnd surfce nd provide multiple ecosystem services eneficil to humn life (Asner et l. 2004; Hvstd et l. 2007). These services re diminished when the functionl integrity of rngelnd systems *Correspondence uthor. E-mil: mtthew.mdsen@oregonstte.edu Mention of proprietry product does not constitute gurntee or wrrnty of the product y USDA or the uthors nd does not imply its pprovl to the exclusion of the other products tht lso my e suitle. USDA is n equl opportunity provider nd employer. The Estern Oregon Agriculturl Reserch Center is jointly funded y the USDA Agriculturl Reserch Service nd Oregon Stte Agriculturl Experiment Sttion. is compromised. The loss of ntive vegettion is one of the most significnt lnd degrdtion issues fcing the world tody (Ninn 2001). In mny situtions, these lnds hve een degrded to point where utogenic recovery is impired nd energy-intensive restortion mesures re required to restore ecosystem function (Bestelmeyer 2006; Kinyu et l. 2010). It is common prctice for lnd mngers to seed distured res to fcilitte the recovery of desirle vegettion (Allen-Diz & Brtolome 1998; Mrtin & Wilsey 2006; Epnchin-Niell, Englin & Nlle 2009). Unfortuntely, the success of these seeding efforts is typiclly less thn desirle, especilly in rid nd semi-rid ecosystems (Seloom et l. 2003; Lysne & Pellnt 2004; Jmes, Svejcr & Rinell 2011). Demogrphy reserch on rngelnd seedings in the Gret Bsin region of the western United Sttes hs shown tht seedling emergence represents Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA.

2 432 M. D. Mdsen et l. mjor developmentl ottleneck in the progression from seed to n estlished plnt (Jmes & Svejcr 2010; Jmes, Svejcr & Rinell 2011). One fctor tht cn ct s significnt rrier to seedling emergence is the presence of non-iotic soil-surfce crusts (U-nger 1984; Awdhwl & Thierstein 1985; Belnp 2003). Soil physicl crust is chrcterized y dense, reltively impermele soil-surfce feture, which impedes seedling emergence, while decresing wter infiltrtion nd gs exchnge (Belnp 2003). To effectively ddress physicl soil crust prolem, expensive mngement prctices must often e performed to increse ggregte stility (Belnp 2003). Where resources re ville, this cn e chieved y incorporting orgnic mtter or other soil mendments such s gypsum (e.g. Shinerg et l. 1989) or polycrylmide (e.g. Ben-Hur 1994) into the soil. Seedling emergence cn lso e incresed through short-term tretments, such s irrigtion to mintin moist soil surfce (Unger 1984), or use of equipment (i.e. rotry hoe) to mechniclly rek up the soil crust (Bilro & Wnjur 1982). While these pproches my work in intensive gronomic opertions, typiclly they re imprcticl for the revegettion of extensive rngelnd systems of reltively low economic vlue. Consequently, there is need for the development of cost-effective seeding technologies tht will enhnce seedling emergence in the presence of soil physicl crust (Jmes & Svejcr 2010). Seed coting technology provides severl options for enhncing germintion nd seedling growth (Tylor & Hrmn 1990). A common pproch for pplying the cotings to the seed is through the use of rotry (or rotostt) seed coter. In generl, seeds re coted through this technology using centrifugl forces to mix the seeds, while dhesives (or stickers) re pumped to the centre of the coting chmer onto n tomizing disc, which redirects the liquid outwrd in smll droplets onto the seed. With inder providing tcky se, seed coting powder is delivered through n uger feeder onto the moist seeds. Trditionlly, coting formultions nd ppliction rtes hve een pplied in mnner tht produces the desired coting properties (e.g. density, hrdness, plsticity nd moisture uptke), while keeping the seeds from sticking or clumping together during the coting processes (Gregg & Billups 2010). Mdsen, Petersen & Tylor (2010) proposed in US ptent ppliction coting technology tht lters the trditionl pproch to seed coting y developing method tht uses rotry seed coting technology to promote the uniform clumping of seeds into pellets (or gglomertes) (Fig. 1). Becuse the penetrtion force of emerging seedlings increses with the numer of seeds sown in the sme loction (Edwrds 1966; Awdhwl & Thierstein 1985), gglomerted seeds should hve improved seedling emergence y hving multiple seedlings collectively generting greter emergence force thn single seed (Fig. 1). Higher seedling densities my increse mortlity s result of competition for limited resources (Connell & Sltyer 1977; Stchowicz 2001); this my e especilly true with the plntings of gglomerted seed where cohorts of the sme species re occupying the sme microsite (i.e. complete niche overlp). It my lso e possile tht positive interctions (or fcilittion) my extend eyond seedling emergence nd provide other enefits ssocited with clustered growth ptterns tht will outweigh competition nd enhnce seedling estlishment (Hunter & Arssen1988; Fjrdo & McIntire 2011). The ojective of this study ws to determine whether seedling emergence of perennil unchgrss species could e improved y gglomerting multiple seeds into single pellet. Comprisons were mde using gglomerted seed, coted seed (which ws not gglomerted) nd non-coted seed (control). The three tretments were evluted in cly-lom soil tht ws susceptile to crusting, nd non-crusting sndy soil. We tested the following hypotheses: (i) gglomerted seeds would hve higher emergence thn single coted or single non-coted seeds in cly ut not snd, nd (ii) intrspecific competition would result in lower per-plnt iomss in the gglomerted tretment, reltive to the other two tretments. Mterils nd methods Evlutions were performed on the ntive species Pseudoroegneri spict (Prush.) Löve, which is often mjor component of ntive plnt communities in the Intermountin West, USA, nd is commonly used for restortion of rngelnd systems in this region (Ogle, St John & Jones 2010). Pseudoroegneri spict hs wide ecologicl ptitude growing in reltively low elevtion, dry Artemisi L. communities nd up to high elevtion, moist sgerush-grsslnds (Dvies, Btes & Miller 2006; Dvies & Btes 2010). SEED COATING Seed coting ws performed t the Estern Oregon Agriculturl Reserch Center (EOARC) in Burns, OR, USA. The tretments descried erlier were pplied using RP14DB Ò rotry seed coter (BrceWorks Automtion nd Electric, Lloydminster, SK, Cnd). () () Fig. 1. () Illustrtion of seedling emergence eing impeded y physicl soil crust lyer, nd () gglomerte pellet with multiple seedlings collectively generting sufficient force to penetrte through the soil crust. Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

3 Ntive seed gglomertion technology 433 Agglomertes were creted similr to methods proposed y Mdsen, Petersen & Tylor (2010). Mterils used in this process included the dhesive inder, Selvol-205 Ò (Sekisui Specilty Chemicls Americ 2009), nd the powder filler mteril, ditomceous erth (Perm- Gurd, Inc., Aluquerque, NM, USA). Selvol-205 ws prepred with n 8% solid content, ccording to Sekisui Specilty Chemicls solution preprtion guidelines (Sekisui Specilty Chemicls Americ 2009). After evluting severl common seed coting powder mterils (i.e. limestone, tlc, entonite cly nd montmorillonite cly), we generlly felt ditomceous erth formed gglomertes most consistently. Ditomceous erth is composed of fossilized ditom remins tht hve shrp nd jgged microscopic edges. The structure of the ditomceous erth my id in the formtion of gglomertes y decresing the flowility of the coted seed nd promoting seed clumping. A detiled description of the mount nd ppliction rte used to form the gglomerted seeds is shown in Tle 1. First, we pplied se coting comprised of Selvol-205 nd ditomceous erth. In this phse, Selvol-205 nd ditomceous erth were pplied using typicl seed coting methods tht llows for the product to dhere to the seed nd prevent seeds from clustering together. In the second phse, seeds were gglomerted together y incresing the rte of Selvol-205, nd only pplying ditomceous erth in periodic short ursts. Generlly speking, through this pproch, gglomertion size (i.e. numer of seeds per pellet) is primrily dependent upon the mount nd rte tht Selvol-205 Ò is pplied while withholding or limiting ditomceous erth. Lstly, the gglomertes were coted using methods descried in phse 1 erlier, to provide dditionl structure to the gglomerted seed. After coting, gglomerted seeds were plced on forced ir drier t 25 C for 4 min. From this tch, we selected gglomertes tht hd exctly five seeds to e used in the tril. Single coted seeds were mde using the sme mount of mterils used to form the gglomertes. In this tretment, the coting mteril ws pplied t rte sufficient to keep the seeds from clustering together. SOIL Evlutions were performed on cly (31% snd, 22% silt nd 47% cly) nd sndy (91% snd, 5% silt nd 4% cly) textured soils. The cly soil ws otined from the USDA Agriculturl Reserch Services (ARS), Northern Gret Bsin Experimentl Rnge (NGBER; Lt: N, Long: W), 67 km west of Burns, Oregon, USA. This soil ws clssified s clyey, montmorillonitic, frigid nd shllow Xeric Argidurids. Soil ph ws 7Æ8, nd orgnic mtter content ws 1Æ9% (Soil Survey Stff 2011). We collected the sndy soil from site 17Æ6 km south of Burns, OR, USA (Lt: N, Long: W). At this loction, the soil is clssified s fine snd, mixed, frigid Xeric Hplocmids. Soil ph ws 7Æ2, nd orgnic mtter content ws 0Æ25% (Soil Survey Stff 2011). At oth sites, the vegettion community ws co-dominted y Artemisi tridentt spp. wyomingensis (Beetle & A. Young) S.L. Welsh nd perennil unchgrsses, such s Agropyron cristtum, Stip thurerin, Agropyron spictum nd Po sndergii. STUDY DESIGN Seed tretments were evluted in the greenhouse t the EOARC using rndomized lock split-plot design, with five locks. Ech lock contined two 0Æ2 m )2 continers (0Æ5 0Æ4 m on side, with depth of 0Æ1 m), one with snd nd the other with cly soil. Within ech continer, we hnd sowed the three seed tretments, in seprte rows, eqully spced, with the loction of the row rndomized mong the tretments. Ech row ws 0Æ4 m long nd contined 15 seeds, plnted 1 cm elow the surfce. For the rows designted for noncoted nd single coted seeds, we evenly distriuted the seed cross the row. In the rows designted for gglomerted seeds, we sowed three pellets, which ech contined five seeds. RAINFALL SIMULATION AND WATER REGIME Prior to seeding, we sturted the soil from the ottom-up nd then llowed the soil to drin for 24 h. We then seeded the oxes nd plced them on 5% slope, where we pplied 15 mm (3Æ0 L continer )1 ) of wter using portle oscillting-rm rinfll simultor, s descried y Meyer & Hrmon (1979). To promote soil crust formtion, we rined on the soil with n ppliction intensity of 24Æ7 mmh )1, which pproximted the rinfll intensity for 15-min period, with 2 yer return intervl, for the NGBER (Miller, Frederick & Trcy 1973). Over the reminder of the study, pots were wtered with fine mist spryer. To stimulte seedling germintion, the soil ws misted once dy with 1Æ5 mm(0æ3 L continer )1 ), for 5 dys fter seeding. After dy 5, the soil ws wtered weekly with 3Æ4 mm (6Æ8 L continer )1 ) tht is pproximtely hlf the verge weekly Tle 1. Btch recipe used to cot 227 g of Pseudoroegneri spict seed. The Tle shows the time the seed coter s pump, nd powder feeder ws turned on nd off to pply Selvol-205 nd ditomceous erth, long with their ssocited rtes nd mount of mteril delivered. The mount of Selvol-205 in the tle contins 8% y weight of ctive ingredient. The Tle lso shows the different speeds the coting pn ws run during the coting process Selvol-205 Ditomceous erth Rotor speed Time (s) Strt stop Rte (g s )1 ) Sutotl (g) Time (s) Strt stop Rte (g s )1 ) Sutotl (g) Time (s) Strt stop Rte (% of mx.) Æ000 29Æ Æ Æ833 65Æ Æ65 52Æ Æ Æ Æ Æ490 19Æ Æ Æ Æ Æ Æ18 43Æ48 Totl 238Æ68 209Æ61 Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

4 434 M. D. Mdsen et l. mount of precipittion received in the spring (Mrch My) t the NGBER (Western Regionl Climte Center 2010). MEASUREMENTS We mesured volumetric soil wter content nd crust penetrtion resistnce to frcture the soil surfce, in-etween the rows, t three loctions per ox, pproximtely every 3 dys. Soil wter content ws mesured from the soil surfce down to 60 mm, with n ML2x Thet Proe (Delt-T Devices, Cmridge, UK). On the dys the soil ws designted to e wtered, soil wter content ws mesured prior to wtering. Crust penetrtion resistnce ws determined using 4Æ76-mm dimeter flt point hndheld penetrometer (Model 719-5MRP; John Chtillon & Sons, Kew Grden, NY, USA). Eleven dys fter seeding, we mesured the thickness of the soil crust using vernier clliper, t three smple loctions per ox continer. Seedling density of ll live seedlings in ech row of the ox continers ws lso recorded t the sme time tht the soil wter content nd crust penetrtion resistnce ws mesured t c. 3 dy intervls. At the conclusion of the study (25 dys fter seeding), we weighed stnding ove-ground iomss fter oven-drying t 65 C for 72 h. DATA ANALYSIS Seedling density dt were nlysed using repeted mesures mixedmodel nlysis with n utoregressive order 1 covrince (ss Version 9.2; SAS 2006). In the model, seed tretments nd soil type were considered fixed fctors, smpling period ws designted s repeted mesure, nd locks were rndom. We used mixed-model nlysis to nlyse totl iomss, nd per-plnt iomss. Agin, locks were considered rndom, while seed tretments nd soil type were considered fixed fctors. When significnt min or interctive effects were found, men vlues were seprted using the LSMEANS procedure (SAS 2006). Prior to nlysis, normlity nd homogeneity ws tested using the Shpiro Wilk test nd Levene s test, respectively (PROC UNIVARIATE; SAS 2006). Ech dt set ws log-trnsformed to reduce prolems with devince from normlity. For ll comprisons, significnce level of P <0Æ01 ws used. In the text nd figures, mens re reported with either unique letters to denote significnces or with ssocited stndrd error. Results Soil wter content (%) Soil wter content (%) wiltingpoint Cly Dys from seeding Snd wiltingpoint Dys from seeding Fig. 2. Men ± SE soil wter content (closed circles) nd penetrtion resistnce (open circles) over the course of the study. Dshed line represents permnent wilting point ()1Æ5 MP). Tle 2. P-vlues from mixed-model nov nlysis for the effect of seed coting tretments, nd soil type, on plnt density, totl plnt iomss, nd iomss per plnt Effect Density Totl iomss Penetrtion resistnce (MP) Penetrtion resistnce (MP) Biomss per plnt Seed tretment 0Æ018 <0Æ001 0Æ008 Soil <0Æ001 0Æ077 <0Æ001 Soil seed tretment <0Æ001 0Æ621 0Æ833 Time <0Æ001 Time soil 0Æ912 Seed tretment time 0Æ387 Seed tretment soil time 0Æ294 VOLUMETRIC WATER CONTENT AND SOIL CRUST Soil moisture in oth soil types ws t sturtion t the strt of the study, nd y the end of the experiment, it hd declined to ner wilting point ()1Æ5 MP) (Fig. 2). In the cly soil, crust penetrtion resistnce incresed rpidly s soil moisture declined, until round dy 15. During this period, crust penetrtion resistnce rnged from 0Æ13 MP (dy 3) to 0Æ23 MP (dy 15). After dy 15, crust strength ws highly vrile nd on verge decresed with time (Fig. 2). Crust thickness of the cly soil mesured on dy 11 ws 9Æ3 ±0Æ6 mm.thesndy soil did not form physicl crust (Fig. 2). PLANT DENSITY Plnt density mong seed tretments differed y soil type (Tle 2). In the cly soil, on verge, the gglomerted seeds emerged erlier nd over longer period of time thn the control (Fig. 3). This generlly resulted in the gglomertion tretment hving higher plnt densities thn the control. Finl plnt density in the cly soil showed the gglomertion tretment hving pproximtely two times (1Æ9 times)more seedlings thn the control. Seedling emergence for the single coted seed tretment ppered to hve een impired y physicl soil crust similr to the control, for the first hlf of the study. Between dy 14 nd 19, this tretment incresed in plnt density y 35%, while density in the control remined constnt. Finl seedling density for the single cotings produced n intermedite response when compred to the other two tretments, with single cotings hving 1Æ4 times more seedlings thn the control. Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

5 Ntive seed gglomertion technology 435 Seedling density (plnts m 2 ) Seedling density (plnts m 2 ) Cly Snd control single gglomertion Dys from seeding control single gglomertion Dys from seeding c c viility 214 (plnts m 2 ) viility 214 (plnts m 2 ) Tle 3. Aove-ground iomss nd per-plnt iomss of Pseudoroegneri spict grown from non-coted (control), single coted nd gglomerted seeds, sown in cly nd sndy soil Tretment tretments (Tle 3). On verge, the single seed nd gglomerted tretments produced 1Æ7 nd 2Æ1 times more iomss thn the control, respectively. Per-plnt iomss followed similr pttern s totl iomss, with oth single seed nd gglomerted tretments producing similr vlues, which were 1Æ4 nd 1Æ6 times greter thn the control, respectively. Discussion SEEDLING DENSITY Biomss (mg) Biomss per plnt (mg) Cly Control 396Æ3 6Æ1 Single 742Æ3 7Æ1 Agglomertion 1083Æ4 8Æ9 Snd Control 330Æ9 3Æ0 Single 585Æ1 4Æ2 Agglomertion 682Æ9 4Æ8 Mens with different letters re significntly different (P < 0Æ01). Fig. 3. Comprison of Pseudoroegneri spict plnt density over the course of the study grown from none-coted (control), single coted nd gglomerted seeds, sown in cly nd sndy soil. Plots were sown with 214 PLS m )2. Significnt differences (P <0Æ01) etween men density vlues t ech smpling dte re shown y unique letters. In the sndy soil, gglomerted nd single coted seed tretments hd similr plnt densities t ech mesurement period (Fig. 3). There ws some indiction tht these tretments cn improve the rte of seedling emergence in the sndy soil, with erly plnt density vlues nerly doule tht of the control. However, towrds the end of the study, the gp etween the coting tretments nd the control decresed resulting in sttisticlly similr finl plnt densities (Fig. 3). ABOVE-GROUND BIOMASS Differences in iomss were primrily influenced y seed coting tretments nd to lesser extent, soil type (Tle 2). In the cly soil the gglomertion tretment hd 1Æ5 timesmoreiomss thn the single coted seed tretment nd 2Æ7 times more iomss thn the control (Tle 3). On per-plnt sis, the control nd single coted seed tretments remined similr while the gglomertion tretment hd 1Æ4 times more iomss thn the control ut ws not sttisticlly higher thn the single seed coting tretment. In the sndy soil, there ws greter iomss in the single seed coting nd gglomertion tretments when compred to the control; however, in this soil type, there ws no sttisticl difference etween single coted nd gglomerted seed The results of this study confirmed our hypothesis tht gglomerting perennil unchgrss seeds into pellets enhnces seedling emergence in the presence of crusting soil (Fig. 3). Our dt further indicte tht the coting mterils used to gglomerte seeds together lso enhnces seedling emergence (Fig. 3). The mechnism y which the gglomertion tretment improves seedling emergence is illustrted in the comprison of seed tretments y soil type. In the cly soil, seedling emergence ws limited y crusting soil nd drought (Fig. 2). Within this soil type, the single seed coting tretment (which hs the sme mount of coting mteril s the gglomertion tretment) hd less emergence thn the gglomertion tretment yet ws greter thn the control (Fig. 3). However, in the sndy soil, emergence ws limited y drought only (Fig. 2). Within this soil type, the gglomertion nd single seed coting tretment oth produced similr increse in seedling emergence over the control (Fig. 3). Greter seedling emergence in the cly soil is proly the result of hving multiple seedlings collectively generting sufficient force to penetrte through the soil crust. Seedling emergence force increses when multiple seeds re plnted in the sme loction (Edwrds 1966; Awdhwl & Thierstein 1985). In the sndy soil where crust ws not limiting fctor. The single seed coting nd gglomertion tretments performed similrly, which my e due to the coting mteril enhncing drought tolernce y incresing the mount nd durtion of plnt ville wter. As explined previously, the coting mteril used in this study ws comprised of Selvol-205, nd ditomceous erth. Selvol- 205 is prtilly hydrolysed polyvinyl lcohol product, formulted for incresed wter sorption (Sekisui Specilty Chemicls Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

6 436 M. D. Mdsen et l. Americ 2009). Ditomceous erth hs high wter sorption nd retention properties (Li et l. 2000; Shwkeh & Tutunji 2003). These two coting mterils my id in the sorption nd retention of moisture round the seed. Presuming this wter ws thermodynmiclly ville to the seed, incresed moisture vilility round the seed would enhnce seed imiition, germintion nd erly seedling growth, in wter-limited environment. Incresed moisture provided y the coting my lso help mintin plnt turgor pressure nd susequently promote seedling emergence thrust through the soil. Ditomceous erth my lso hve ided in seedling emergence nd survivl y providing source of silicon. The chemicl composition of oven dried ditomceous erth typiclly contins etween 80% nd 90% silicon dioxide (Antonides 1997). The ppliction of silicon fertilizer to cerel crops hs een shown to increse seedling resistnce to oth iotic nd iotic stresses (Ahmd, Zheer & Ismil 1992; Ling 1998; Tun et l. 2008). However, review of the literture indictes tht moisture enhncing seed cotings generlly fil to improve rngelnd reseeding (i.e. Hull & Klomp 1967 nd references therein; Kocher & Stuendieck 1986; Mngold & Sheley 2007). Therefore, the positive response in seedling emergence from the seed coting mterils used in this study merits dditionl reserch to verify the mechnisms nd controlling vriles. BIOMASS PRODUCTION As with plnt density, incresed iomss, in prt, cn proly e ttriuted to the gglomertion tretment improving seedling emergence (Fig. 3, nd Tle 3). Interestingly, in the cly soil, incresed ove-ground iomss in the gglomertion tretment is not only ecuse of greter plnt densities ut is lso product of hving greter iomss per plnt (Tle 3). Such response is contrry to our hypothesis tht intrspecific competition would lower iomss production on per-plnt sis. These results my indicte tht under the conditions of this study, fcilittion plyed more importnt role thn competition. Fcilittion often outweighs competition effects in hrsh nd resource-limited environments (Hunter & Arssen1988; Bertness & Cllwy 1994; Cllwy & Wlker 1997; Brooker & Cllghn 1998; Fjrdo & McIntire 2011). As n exmple, Fjrdo & McIntire (2011) compred Nothofgus pumilio tree seedlings plnted in clusters nd spced prt from ech other long stress grdient in forest pririe ecotone in Ptgoni, Chile. As stress incresed, seedlings plnted in dense clusters hd higher survivl thn solitry seedlings (Fjrdo & McIntire 2011). It is prole tht the increse in iomss in our gglomertion tretment my e due, in prt, to the ility of this technology to etter mimic the wy plnts hve evolved to grow in nturl systems. Seeds typiclly grow within groups or clusters ecuse of nturl process depositing them within the sme microsite. For instnce, seeds cn e collected within litter mteril, holes nd crcks in the soil surfce, or other fetures tht trp wind-lown seeds (Eckert et l. 1986; Stmp 1989; Chmers, McMhon & Hefner 1991; Chmers 2000). Seeds cn lso e grouped together s result of cching ctivities y grnivores. Seed cching is considered the primry mechnism of seedling estlishment y Purshi tridentte (Pursh) DC (ntelope itterrush) nd Achntherum hymenoides (Roemer & J.A. Schultes) Brkworth (Indin rice grss), with two or more mture plnts typiclly growing together (West 1968; Vnder Wll 1994). This study provides justifiction for dditionl reserch to determine wht specific fcilittive interctions in the gglomertion tretment improved plnt growth, in ddition to multiple seedlings incresing emergence thrust. For exmple, erly emergence (Fig. 3) my hve llowed the seedlings to grow deeper root systems to etter utilize moisture resources from rpidly drying wetting front (Nicotr, Bick & Westoy 2002; Leck, Prker & Simpson 2008). Moisture vilility my lso hve een improved s result of incresed plnt cover in the gglomertion tretment promoting greter soil infiltrtion, nd from the fllow spces etween groups of plnts prolonging the durtion of ville moisture. Multiple seedlings growing within cluster my indirectly increse the vilility of nutrients through promoting microil ctivity. We did not mesure root growth, ut greter ove-ground growth would presumly trnslte into higher elow-ground growth s well. More root growth in the gglomerte tretment should result in greter exuded sustrte from the roots, which stimultes rhizospheric microil ctivity (Whipps 1990). This in turn promotes higher soil minerliztion rtes nd susequent nutrient vilility (Mrschner 1995; Hmilton & Frnk 2001). The gglomertion tretment my lso moderte microsite tempertures, s the plnts collectively provided greter insulting ffect from extreme tempertures. Conclusions nd future reserch To our knowledge, this is the first seed coting tretment specificlly designed to improve seedling emergence in crusting soil y gglomerting multiple seeds together within single pellet. Enhnced emergence of the gglomertion tretment is most likely to e function of the coting mteril decresing the emergence time, lleviting drought conditions nd result of the greter emergence thrust generted y the seedlings collectively growing from the gglomerted pellet compred with single seedling. In ddition to the gglomertion tretment improving seedling emergence in crusting soils, this reserch lso provides evidence tht seedlings growing from gglomertes fcilitte greter growth thn cn e chieved y single seedling. These results indicte tht current gronomic prctices tht evenly spce seeds my not e the most effective technique for reseeding rngelnds with crusting soils. Use of seed gglomertion technology my provide lnd mngers with the ility to efficiently plnt seeds within clusters using stndrd seed drills. Fcilittion ssocited with coting mterils nd clustered plnt growth my increse the proility of the plnt estlishing on site, nd thus lower the proility of restortion filure. Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

7 Ntive seed gglomertion technology 437 Further development nd evlution of this technology is needed efore it cn e recommended s ntive plnt restortion tretment. Future studies should include: (i) determintion of how gglomertion size (i.e. numer of seeds per pellet) influences seedling emergence, plnt survivl nd iomss production cross different stress grdients; (ii) nlysis of the gglomertion procedure, with focus on how emergence is ffected y vriility in the mterils, ppliction rtes nd other inputs into the coting process; (iii) evlution of how seed nd plnt physiologicl chrcteristics of different species function within n gglomertion tretment; (iv) quntifiction of the long-term survivl nd plnt community structure of gglomertion plntings nd (v) determintion of the mechnisms tht influence seedling growth from n gglomerted pellet (i.e. wter infiltrtion nd moisture vilility, therml response to extreme tempertures, microil response nd nutrient vilility). Acknowledgements We would like to cknowledge Fred Pierson (USDA-ARS, Boise, ID, USA) for technicl dvice nd use of rinfll simultor. We would lso like to thnk Kristen Mundy, Aron Inouye, nd Suznne Bichrt for their ssistnce in conducting this reserch. We re grteful to Brend Smith nd Brett Binghm (USDA-ARS, Burns, OR, USA) for reviewing erlier versions of this mnuscript. References Ahmd, R., Zheer, S.H. & Ismil, S. (1992) Role of silicon in slt tolernce of whet (Triticum estivum L.). Plnt Science, 85, Allen-Diz, B. & Brtolome, J.W. (1998) Sgerush-grss vegettion dynmics: compring clssicl nd stte-trnsition models. Ecologicl Applictions, 8, Antonides, L.E. (1997) Ditomite: U.S. Geologicl Survey Minerl Commodity Summries. pp Asner, G.P., Elmore, A.J., Olnder, L.P., Mrtin, R.E. & Hrris, A.T. (2004) Grzing systems, ecosystem responses nd glol chnge. Annul Review of Environment & Resources, 29, Awdhwl, N.K. & Thierstein, G.E. (1985) Soil crust nd its impct on crop estlishment: review. Soil nd Tillge Reserch, 5, Belnp, J. (2003) Comprtive structure of physicl nd iologicl soil crusts. Biologicl Soil Crusts: Structure, Function nd Mngement (eds J. Belnp & O.L. Lnge), pp Springer-Verlg, Berlin. Ben-Hur, M. (1994) Runoff, erosion, nd polymer ppliction in moving-sprinkler irrigtion. Soil Science, 158, Bertness, M.D. & Cllwy, R.M. (1994) Positive interctions in communities. Trends in Ecology & Evolution, 9, Bestelmeyer, B.T. (2006) Threshold concepts nd their use in rngelnd mngement nd restortion: the good, the d, nd the insidious. Restortion Ecology, 14, Bilro, J.D. & Wnjur, D.F. (1982) Soil crusts nd cotton emergence reltionships. Trnsctions of the ASAE, 25, Brooker, R.W. & Cllghn, T.V. (1998) The lnce etween positive nd negtive plnt interctions nd its reltionship to environmentl grdients: model. Oikos, 81, Cllwy, R.M. & Wlker, L.R. (1997) Competition nd fcilittion: synthetic pproch to interctions in plnt communities. Ecology, 78, Chmers, J.C. (2000) Seed movements nd seedling ftes in distured sgerush steppe ecosystems: implictions for restortion. Ecologicl Applictions, 10, Chmers, J.C., McMhon, J.A. & Hefner, J.H. (1991) Seed entrpment in lpine ecosystems: effects of soil prticle size nd dispore morphology. Ecology, 72, Connell, J.H. & Sltyer, R.O. (1977) Mechnisms of succession in nturl communities nd their role in community stility nd orgniztion. The Americn Nturlist, 111, Dvies, K.W. & Btes, J.D. (2010) Vegettion chrcteristics of mountin nd Wyoming ig sgerush plnt communities in the northern Gret Bsin. Rngelnd Ecology nd Mngement, 63, Dvies, K.W., Btes, J.D. & Miller, R.F. (2006) Vegettion chrcteristics cross prt of the Wyoming ig sgerush llince. Rngelnd Ecology nd Mngement, 59, Eckert Jr, R.E., Peterson, F.F., Meurissee, M.S. & Stephens, J.L. (1986) Effects of soil surfce morphology on emergence nd survivl of seedlings in ig sgerush communities. Journl of Rnge Mngement, 39, Edwrds, F.E. (1966) Cotton seedling emergence. Mississippi Frm Reserch, 26,4 5. Epnchin-Niell, R., Englin, J. & Nlle, D. (2009) Investing in rngelnd restortion in the rid west, USA: countering the effects of n invsive weed on the long-term fire cycle. Journl of Environmentl Mngement, 91, Fjrdo, A. & McIntire, E.J.B. (2011) Under strong niche overlp conspecifics do not compete ut help ech other to survive: fcilittion t the intrspecific level. Journl of Ecology, 99, Gregg, B.R. & Billups, G.L. (2010) Seed Conditioning Volume Two, Technology-Prt A. pp Science Pulishers, Enfield, NH USA. Hmilton, E.W. & Frnk, D.A. (2001) Cn plnts stimulte soil microes nd their own nutrient supply? Evidence from grzing tolernt grss. Ecology, 82, Hvstd, K.M., Peters, D.P.C., Skggs, R., Brown, J., Bestelmeyer, B., Fredrickson, E., Herrick, J. & Wright, J. (2007) Ecologicl services to nd from rngelnds of the United Sttes. Ecologicl Economics, 64, Hull Jr, A.C. & Klomp, G.J. (1967) Thickening nd spred of crested whetgrss stnds on southern Idho rnges. Journl of Rnge Mngement, 20, Hunter, A.F. & Arssen, L.W. (1988) Plnts helping plnts. BioScience, 38, Jmes, J.J. & Svejcr, T.J. (2010) Limittions to postfire seedling estlishment: the role of seeding technology, wter vilility, nd invsive plnt undnce. Rngelnd Ecology nd Mngement, 63, Jmes, J.J., Svejcr, T.J. & Rinell, M.J. (2011) Demogrphic processes limiting seedling recruitment in ridlnd restortion. Journl of Applied Ecology, 48, Kinyu, D., McGeoch, L.E., Georgidis, N. & Young, T.P. (2010) Short-term nd long-term effects of soil ripping, seeding, nd fertiliztion on the restortion of tropicl rngelnd. Restortion Ecology, 18, Kocher, E. & Stuendieck, J. (1986) Brodcsting grss seed to revegette sndy soils. Journl of Rnge Mngement, 39, Leck, M.A., Prker, V.T. & Simpson, R.L. (2008) Seedling Ecology & Evolution. pp Cmridge University Press, Cmridge, UK. Li, D., Joo, Y.K., Christins, N.E. & Minner, D.D. (2000) Inorgnic soil mendment effects on snd-sed sports turf medi. Crop Science, 40, Ling, Y.C. (1998) Effects of silicon on lef ultrstructure, chlorophyll content nd photosynthetic ctivity in rley under slt stress. Pedosphere, 8, Lysne, C. & Pellnt, M. (2004) Estlishment of Aerilly Seeded Big Sgerush Following Southern Idho Wildfires. pp. 14. Tech. Bull U.S. Deprtment of the Interior, Bureu of Lnd Mngement, Idho Stte Office, Boise, ID. Mdsen, M.D., Petersen, S.L. & Tylor, A.G. (2010) Seed coting compositions nd methods for pplying soil surfctnts to wter-repellent soil. Pu. No. WO Interntionl Appliction No. PCT US Mngold, J.M. & Sheley, R.L. (2007) Effect of soil texture, wtering frequency, nd hydrogel on the emergence nd survivl of coted versus uncoted crested whetgrss seeds. Ecologicl Restortion, 25, Mrschner, H. (1995) Minerl Nutrition of Higher Plnts, 2nd edn. Acdemic Press, Sn Diego, CA. Mrtin, L.M. & Wilsey, B.J. (2006) Assessing grsslnd restortion success: reltive roles of seed dditions nd ntive ungulte ctivities. Journl of Applied Ecology, 43, Meyer, L.D. & Hrmon, W.C. (1979) Multiple-intensity rinfll simultor for erosion reserch on row sideslopes. Trnsctions of the ASAE, 22, Miller, J.F., Frederick, R.H. & Trcy, R.J. (1973) Precipittion-Frequency Atls of the Western United Sttes. pp. 43. NOAA Atls 2, Volume X-Oregon, Ntionl Wether Service, Silver Spring, MD. Nicotr, A.B., Bick, N. & Westoy, M. (2002) Seedling root ntomy nd morphology: n exmintion of ecologicl differentition with rinfll using phylogeneticlly independent contrsts. Oecologi, 130, Ninn, L. (2001) Fighting ginst ourselves: efforts to comt desertifiction & lnd degrdtion. Currents Interntionl Trde Lw Journl, 65, 66. Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,

8 438 M. D. Mdsen et l. Ogle, D.G., St John, L. & Jones, T.A. (2010) Plnt Guide for Blueunch Whetgrss (Pseudoroegneri spict). pp. 5. USDA-Nturl Resources Conservtion Service, Idho nd Wshington Plnt Mterils Progrm. SAS Institute Inc. (2006) Softwre Version 9.2. SAS Institute Inc, Cry, NC. Seloom, E.W., Borer, E.T., Boucher, V.L., Burton, R.S., Cottinghm, K.L., Goldwsser, L., Grm, W.K., Kendll, B.E. & Micheli, F. (2003) Competition, seed limittion, disturnce, nd reestlishment of Cliforni ntive nnul fors. Ecologicl Applictions, 13, Sekisui Specilty Chemicls Americ, LLC (2009) SelvolÒ Polyvinyl Alcohol... A Verstile High-Performnce Polymer. pp. 16. North Americn Distriutions, Sekisui Specilty Chemicls Americ, LLC, Dlls, TX. Shinerg, I., Sumner, M.E., Miller, W.P., Frin, M.P.W., Pvn, M.A. & Fey, M.V. (1989) Use of gypsum on soils: review. Advnces in Soil Science, 9, Shwkeh, R.A. & Tutunji, M.F. (2003) Experimentl study nd modeling of sic dye sorption y ditomceous cly. Applied Cly Science, 24, Soil Survey Stff, Nturl Resources Conservtion Service, United Sttes Deprtment of Agriculture (2011) We Soil Survey. Aville t: (ccessed on 5 July 2011). Stchowicz, J.J. (2001) Mutulism, fcilittion, nd the structure of ecologicl communities. BioScience, 51, Stmp, N.E. (1989) Seed dispersl of four symptric grsslnd nnul species of Erodium. Journl of Ecology, 77, Tylor, A.G. & Hrmn, G.E. (1990) Concepts nd technologies of selected seed tretments. Annul Review of Phytopthology, 28, Tun, A.L., Ky, C., Higgs, D., Murillo-Amdor, B., Aydemir, S. & Gergon, A.R. (2008) Silicon improves slinity tolernce in whet plnts. Environmentl Experimentl Botny, 62, Unger, P.W. (1984) Tillge effects on surfce soil physicl conditions nd sorghum emergence. Soil Science Society of Americ Journl, 48, Vnder Wll, S.B. (1994) Seed fte pthwys of ntelope itterrush: dispersl y seed-cching yellow pine chipmunks. Ecology, 75, West, N.E. (1968) Rodent-influenced estlishment of ponderos pine nd itterrush seedlings in centrl Oregon. Ecology, 49, Western Regionl Climte Center (2010) Historicl climte informtion. Aville t: (ccessed on 5 My 2010). Whipps, J.M. (1990) Cron economy. The Rhizosphere (ed. J.M. Lynch), pp Wiley, Chichester. Received 29 August 2011; ccepted 8 Ferury 2012 Hndling Editor: Brin Wilsey Pulished This rticle is U.S. Government work nd is in the pulic domin in the USA. Journl of Applied Ecology, 49,