ORGANIC CARBON AND TOTAL NITROGEN IN THE DENSIMETRIC FRACTIONS OF ORGANIC MATTER UNDER DIFFERENT SOIL MANAGEMENT 1

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1 Universidde Federl Rurl do Semi-Árido Pró-Reitori de Pesquis e Pós-Grdução ISSN -316X (impresso) ISSN (online) ORGANIC CARBON AND TOTAL NITROGEN IN THE DENSIMETRIC FRACTIONS OF ORGANIC MATTER UNDER DIFFERENT SOIL MANAGEMENT 1 MARCELO RIBEIRO VILELA PRADO 2, FABRICIO TOMAZ RAMOS 2*, OSCARLINA LÚCIA DOS SANTOS WEBER 2, CAIO BATISTA MÜLLER 2 ABSTRACT The evlution of lnd use nd mngement y the mesurement of soil orgnic mtter nd its frctions hs gined ttention since it helps in the understnding of the dynmics of their contriution to soil productivity, especilly in tropicl environments. This study ws conducted in the municiplity of Colordo do Oeste, stte of Rondôni, Brzil nd its im ws to determinethe quntity of orgnic cron nd totl nitrogen in the light nd hevy frctions of orgnic mtter in the surfce lyers of typic hpludlf under different lnd use systems: Ntive Forest: open evergreen forest, reference environment; Agroforestry System 1: tek (Tecton grndis LF) nd kudzu (Puerri montn); Agroforestry System 2: coffee (Coffe cnephor), mrndu plisde grss (Brchiri riznth cv. Mrndu), pinho cuino (Prki multijug), tek nd kudzu.; Agroforestry System 3: tek nd coco (Theorom cco); Silvopsture System: tek, coco nd mrndu plisde grss; nd Extensive Grzing System: mrndu plisde grss. The experimentl design ws rndomized lock in split-split plots (use systems versus soil lyers of -.5 nd.5-. m) with three replictions. The results showed tht reltive to Ntive Forest, the Agroforestry System 2 hd equl- nd greter mounts of orgnic cron nd totl nitrogen respectively (light nd hevy frctions) in the soil orgnic mtter, with the light frction eing responsile for storge of pproximtely 45% nd 7% of the orgnic cron nd totl nitrogen, respectively. Therefore, the light densimetric frction proved to e useful in the erly identifiction of the generl decline of the soil orgnic mtter in the lnd use systems evluted. Keywords: Silvopsture system. Agroforestry system. Forest cultivtion. CARBONO ORGÂNICO E NITROGÊNIO TOTAL NAS FRAÇÕES DENSIMÉTRICAS DA MATÉRIA ORGÂNICA SOB DIFERENTES MANEJOS DO SOLO RESUMO - A vlição de sistems de uso e mnejo dos solos por meio d mtéri orgânic e seus comprtimentos tem gnhdo pelo, pois jud entender dinâmic do seu porte, principlmente em mientes tropicis. Ojetivou-se neste trlho determinr, no município de Colordo do Oeste, Rondôni, lterção do crono orgânico e nitrogênio totl ns frções leve e pesd d mtéri orgânic d cmd superficil de um ARGISSOLO VERMELHO-AMARELO Eutrófico típico so diferentes usos do solo: Florest ntiv (FN): Florest Omrófil Aert, como miente referênci; sistem groflorestl 1: tec (Tecton grndis L. F.) e kudzu (Puerri montn); sistem groflorestl 2: cfé (Coffe cnephor), pstgem (Brchiri riznth cv. Mrndu), pinho cuino (Prki multijuc), tec e kudzu; Sistem grossilvopstoril: Tec, ccu (Theorom cco) e pstgem; sistem groflorestl 3: Tec e ccu; pstgem extensiv: (B. riznth cv. Mrndu). O delinemento empregdo foi o de locos csulizdos em esquem de prcels sudividids (diferentes coerturs vegetis versus cmds de solo à -,5 e,5-, m) com três repetições. Verificou-se que: comprdo florest ntiv houve umento e iguldde n quntidde de crono orgânico e nitrogênio totl d frção leve e pesd d mtéri orgânic do solo no sistem groflorestl 2 ; frção leve foi responsável pelo rmzenmento de proximdmente 45% e 7% do crono orgânico e nitrogênio totl do solo, respectivmente. Portnto, o dignóstico d frção densimétric leve é o mis indicdo pr identificção precoce do declínio gerl d mtéri orgânic do solo. Plvrs-chve: Sistem grosilvopstoril. Sistem groflorestl. Cultivo florestl. *Corresponding uthor 1 Received for puliction in 7/3/214; ccepted in 1/25/216. Pper extrcted from the doctorl thesis of the fourth uthor. 2 Postgrdute Progrm in Tropicl Agriculture, Universidde Federl de Mto Grosso, Cuiá, MT, Brzil; vilelmrcelo@yhoo.com.r, friciotomzrmos@gmil.com, oscrlinweer@gmil.com, ciomuller@hotmil.com. Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,

2 INTRODUCTION Deforesttion in the Amzon region hs een closely ssocited with the expnsion of the griculturl frontier since the 197s. Most of the clered res re now occupied y pstures eing grzed extensively y smll numer of nimls per hectre. This is recurring prolem in other regions of Brzil nd it demnds chnges in pulic policies tht would help to increse oth the resilience nd the profitility of griculturl systems, which in turn would ese the pressure to cler new res (MMA, 213). Deforesttion cuses the loss of iodiversity in flor nd fun nd lso decreses the sequestrtion of C-CO 2 (g), therey ggrvting the greenhouse effect (WHITE, 26). One lterntive recommended to reduce deforesttion is the use of groforestry systems, which comine crops, orchrds, extrctive forests nd/or grzing lnd s wy to mke etter economic use of the lnd (SANTOS et l., 2); nd increse soil fertility y incresing soil orgnic mtter (SOM) (FÁVERO et l., 28; IWATA et l., 212). A dependence reltionship exists etween SOM nd vrious chemicl, physicl nd iologicl processes in terrestril ecosystems (STRICKLAND; ROUSK, 2). Severl uthors hve stressed the importnce of orgnic mtter in determining soil qulity ecuse it influences, mong other properties, the stility of the ggregtes nd the structure of the soil (HICKMANN et l., 212; RAMOS et l., 213); the rte of wter infiltrtion nd retention (RAWLS et l., 23); iologicl ctivity nd ction exchnge cpcity (SILVA; MENDONÇA, 27); the complextion of metls (BEZERRA et l., 29); the cycling nd vilility of nutrients to plnts (SILVA et l., 29); nd the relese of CO 2 nd other gses (LAL; BRUCE, 1999). The frctions of the SOM cn e chrcterized y physicl nd/or chemicl methods, depending on the purpose of the investigtion. Physicl methods involve seprtion of the constituents ccording to their reltive densities (clled densimetry), while chemicl methods re sed on the dimeters of the prticles or ggregtes in the soil (ROSCOE; MACHADO, 22; MARTINS et l., 29). There re siclly two frctions: the first is prticulte SOM (light-density frction), either free or occluded, depending upon whether it is locted within or etween the soil ggregte. It is n importnt source of lile nutrients to plnts due to its rpid minerliztion rte (GOLCHIN et l., 1994). The hevy-density frction is the SOM ssocited with the minerl prticles in the soil, forming orgn minerl complexes. It is composed of orgnic residues with high specific densities nd rtes of decomposition. These re importnt fctorsin the sequestrtion of C-CO 2 (g) (WHITE, 26; ROSCOE et l., 26). In view of this ckground, the im of this study ws to determine the vritions in orgnic cron nd totl nitrogen of the light nd hevy frctions of the surfce orgnic mtter of n ARGISSOLO VERMELHO-AMARELO Eutrófico típico (TYPIC HAPLUDALF) under different use systems: ntive forest, three groforestry systems, silvopsture system nd extensive cttle grzing. MATERIALS AND METHODS Study site The study ws crried out t the Estrel frm, locted 9.5 km from the Escondido River in the municiplity of Colordo do Oeste, in the southern region of the stte of Rondôni, t the geogrphic coordintes 13º9 29,4 S nd 6º37 5,6 W, t n ltitude of 333 meters. The region s climte is Am ccording to the Köppen clssifiction tropicl hot nd humid with n verge nnul temperture of 24 C (minimum 12 C nd mximum 36 C) nd therml mplitude of C. The verge yerly rinfll is 2,234 mm, with Jnury to Mrch eing the wettest months. The soil in the study re is clssified s n ARGISSOLO VERMELHO- AMARELO Eutrófico típico (or TYPIC HAPLUDALF), moderte horizon A, medium/cly texture, nd the terrin is gently rolling (SANTOS et l., 213). Experimentl design The experimentl design ws rndomized lock in split-split plots (use systems versus soil lyers of -.5 nd.5-. m), with three replictions. The experimentl unit consisted of six djcent lnd plots under different use systems (descried in Tle 1). 264 Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun., 216

3 Tle 1. Lnd use history of the experimentl plots in Colordo do Oeste, Stte of Rondôni, Brzil. 1 Plnt cover/use Symol History Nturl Forest (open evergreen forest) Agroforestry System 1: Tek nd kudzu. Agroforestry System 2: Coffee, mndru plisde grss, pinho cuino, tek nd kudzu. Silvipstoril System: Tek, cco, nd mndru plisde grss. Agroforestry System 3: Tek nd cco. Extensive Grzing: Mndru plisde grss NF AFS 1 AFS 2 SPS AFS 3 EG In ech tretment, n re covering pproximtely 2,5 m 2 (5 5 m) ws demrcted to smple the soil in rndom zigzg pttern, with strip meters wide etween ech plot. At ech smpling point, monolithic soil smples were collected in two lyers ( to.5 nd.5 to. m). Three smll trenches were opened in the form of steps. The soil smples were immeditely plced in hermeticlly seled rigid plstic continers to preserve the initil moisture nd structure during trnsport to the soil physics lortory of the Federl University of Mto Grosso in Cuiá, Brzil. Lortory nlysis In the lortory, the monoliths were further moistened y pplying distilled wter with sprinkler to ttin frile consistency nd to rek the soil structure on the wek surfces, s descried y Slton et l. (212). The smples were then irdried nd the ggregtes were seprted into two prts (prticles smller thn 2 mm, nd prticles igger thn 2 mm) y sifting through sieve with 2- mm mesh ttched to n electromgnetic shker Are covered y open tropicl forest (semideciduous, sumontne, emerging dossel), with 2 to 5% of the leves remining during the dry seson. Tek (Tecton grndis L. F.) plnted without fertiliztion of the soil in Decemer 21, cultivted in n re of 7. h with spcing of 3 2 m, fter mnul removl of the primry forest in 1998 followed y urning. In the first two yers (1999 nd 2), rice, corn, nd ens were grown in comintion in lternting rows, without soil correction or fertiliztion. In Ferury 2, the soil ws seeded with kudzu (Puerri montn), which remined until 27, the yer of the smpling. Tek plnted in 1998, where the primry forest hd een removed in June 1975 followed y urning, fter which coffee (Coffe cnephor) ws plnted, long with rice, corn nd ens in lternting rows etween the rows of coffee nd grown for four yers without fertiliztion. In the fifth yer, grss ws introduced (Brchiri riznth cv. Mrndu), nd in 1984 pinho cuino (Prki multijug) ws plnted, in n re of hectres with spcing of 3 5 m. Some seedlings died, however, so tek ws plnted s replcement. The psture ws mnged with rotting grzing of cttle (2 nimls h -1 ) nd in the dry seson, when the grss hd low renewl cpcity, the nimls were trnsferred to the extensive grzing re. In Decemer 2, kudzu ws plnted to replce psture, nd remined until 27, the yer of the smpling. Tek plnted without fertiliztion of the soil in Decemer 1998, cultivted in n re of 5. h with spcing of 3 2 m where the primry forest hd een mnully removed in 1998, followed y urning. In Decemer 2, cco (Theorom cco) ws plnted etween the rows of trees, long with grss (B. riznth). The psture mngement ws the sme s AFS 2, nd grzing continued until 27, the yer of the smpling. Tek plnted without fertiliztion of the soil in Decemer 1998, cultivted in n re of 5. h with spcing of 3 2 m where the primry forest hd een mnully removed in 1998, followed y urning. In Decemer 2, cco ws plnted etween the rows of trees, nd remined until 27, the yer of the smpling. An re covering pproximtely hectres clered in 21 y mnul removl of the forest followed y urning nd seeding of grss (B. riznth) without ppliction of fertilizer nd soil correction. After the estlishment of the psture, cttle were extensively grzed (under 2 nimls per hectre), resulting in n uneven pttern of grss cover, with some res undergrzed nd others overgrzed. The grzing system ws mintined until 27, the yer of the smpling. (Endecotts Limited, Octgon Digitl D2, London, Englnd), djusted to the medin virtion setting of 5, for one minute. The root mteril ws then removed nd the smples were stored in plstic trys. Preliminry tests showed tht in order to otin sufficient quntities of low-density orgnic mtter, nmely, the light frction (LF; descried ove) for the cron nd nitrogen nlyses, it ws necessry to use 3 g of soil from the surfce lyer ( to.5 m) nd 6 g from the susurfce lyer (.5 to. m). The quntities of ggregtes used tht were lrger thn or equl to 2 mm (LA 2 mm) + smller thn 2 mm (SA < 2 mm) were clculted sed on the verge result of the dry sifting of the smples collected from ech lnd use re, in the proportion of 6% LA to 4% SA. For ech clss of ggregtes, the light nd hevy frctions of the SOM were seprted y flottion in solution of NI t density of 1.7 g L -1 (densimetric method), dpted from Roscoe nd Mchdo (22), s depicted in Figure 1. The ph of the NI ws djusted to 4. with solution of 1. mol L -1 HCl so tht the orgnic mtter would not dissolve. Two mounts of soil (3 g nd 6 g) were Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,

4 weighed out from the surfce nd susurfce lyer. These smples were plced in 5 ml glss ekers (VAT no. 42) contining 5 nd ml of the NI solution respectively. The ekers were then plced in horizontl gittor (Tecnl, TE-167, Pircic, SP, Brzil) for 14 h t 4 rpm, providing sufficient time to rek up the soil clumps. The light frction (LF) ws skimmed off the top fter flottion then filtered through qulittive filter pper nd set side, while the filtrte (NI) ws returned to the eker nd stirred with glss rod to -,5 m 3 g de AG + AP, 5 ml of NI solution decompose the pellet for recovery of the LF. This ws followed y recentrifuging nd filtrtion to seprte the LF. This process ws repeted two or three times until no more flocculted LF remined fter spinning. The recovered LF ws filtered gin nd wshed with 4 ml distilled wter nd ml of.1 mol L -1 CCl 2 to remove the NI. The LF ws then dried in circulting-ir chmer for 24 t 5 ºC then weighed, mcerted nd set side for the determintion of the quntities of orgnic cron nd totl nitrogen.,5-, m 6 g de AG + AP, ml of NI solution MFL (retined on the filter) Shke Filter the superntnt Repet 3 times or until stop the floccultion of MFL 4 ml of distilled wter Filter ml de CCl 2,1 mol L -1 Filter Solution of NI Add the filtrte (NI) in the tue nd shke MFP (pellet) MFP (fter 3 filterings) 4 ml of distilled wter Centrifuging nd discrding the superntnt ml of CCl 2,1 mol L -1 Drying t 5 ºC Centrifuging nd discrding the superntnt Cron nd Nitrogen nlysis Figure 1. Flowchrt showing the process of seprting the light nd hevy orgnic mtter frctions. Remrk: LA nd SA = ggregtes equl to or lrger thn 2 mm (LA 2 mm) nd smller thn 2 mm (SA < 2 mm) respectively; LF nd HF = light nd hevy frctions of soil orgnic mtter respectively. To remove the NI from the HF, the mteril ws wshed five times with 8 ml distilled wter nd once with ml of.1 mol L -1 CCl 2. With ech wshing, the pellet ws homogenized with glss rod to relese the NI dhering to the prticles. After the CCl 2 wshing, the HF ws dried in circulting-ir chmer t 5 ºC for 48 h, mcerted nd set side for the nlysis of the orgnic cron nd totl nitrogen (Figure 1). The orgnic cron (OC) content of the light nd hevy frctions ws quntified y moist comustion in solution of potssium dichromte in n cid medium (H 2 SO 4 ) with heting in lock digester. The excess potssium dichromte ws titrted with mmonium iron (II) sulfte using ferroin s the indictor (YEOMANS; BREMNER, 1988). In this method, it is the recommended to use to 5 mg of the soil smple, ecuse the quntity of orgnic cron in the smple should not exceed 8. mg. For the LF, which contins lrger 266 Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun., 216

5 quntity of orgnic mtter, we used 2 mg. The results were expressed in g kg -1. The totl nitrogen (TN) of the light nd hevy frctions ws mesured y the Kjeldhl method, s descried in Tedesco (1995). For oth frctions, 5 mg were used nd the results were expressed in g kg -1. Sttistics nlysis cording to the Shpiro-Wilk test (p >.5), the dt otined were not normlly distriuted, so n nlysis of vrince ws run using SigmPlot version 12.5 pplying the F-test (Fischer), nd the mens of the smples from the different lnd use res were compred y the Tukey test (p <.5) ccording to Lrson nd Frer (2). RESULTS AND DISCUSSION Orgnic cron nd totl nitrogen in the light nd hevy frctions With respect to the proportions of light nd hevy frctions in the initil 3 g soil smple, the mss of LF in the smples drwn from the different lnd use res vried from 3.75 to 6.96 g in the -.5 m lyer nd 2.3 to 5.91 g in the.5-. m lyer (Figure 2). Light nd hevy frctions (g) 5 HF LF A AB A A A A A AB A AB NF AFS 1 AFS 2 SPS AFS 3 EG Lnd use systems Figure 2. Mss of light frctions (LF) nd hevy frctions (HF) (g) in ech lnd use system nd soil lyer smpled. Remrk: Ntive Forest (NF): open evergreen forest, s reference environment; Agroforestry System 1 (AFS 1): tek (Tecton grndis LF) nd kudzu (Puerri montn); Agroforestry System 2 (AFS 2): coffee (Coffe cnephor), mrndu plisde grss (Brchiri riznth cv. Mrndu), pinho cuino (Prki multijuc), tek nd kudzu; Agroforestry System 3 (AFS 3): tek nd coco (Theorom cco); Silvopsture System (SPS): tek, coco nd mrndu plisde grss; nd Extensive Grzing (EG) [System]: mrndu plisde grss. Cpitl letters compre the lyers (m) in the sme system while smll letters compre the systems in the sme soil lyer, y the Tukey test (P <.5). The verge concentrtions of orgnic cron (OC) nd totl nitrogen (TN) in the light nd hevy frctions of orgnic mtter re presented in Figure 3. It cn e seen tht for the light frction in the surfce lyer, the smples from the AFS 1, AFS 2 nd SPS res contined the highest mounts of OC, while in the susurfce lyer, AFS 1 nd AFS 2 were the stndouts (Figure 3A). For the hevy frction, AFS 2 nd EG in the surfce lyer nd in the susurfce lyer cn e considered the est soil mngement systems ecuse they hd levels of CO closer to tht of ntive forest (NF) (Figure 3B) thn did the others. Bsed on this oservtion nd the quntities of OC, only the AFS 1 nd AFS 2 systems did not differ in the verge OC vlues of the light frction, regrdless of the lyer, nd in oth cses they were greter thn tht of the ntive forest (NF) (Figure 3A). With respect to the hevy frction, AFS 2 lso did not differ in OC content etween the two lyers, ut ws equl in terms of OC to the NF re in the surfce lyer nd to the EG re in the susurfce lyer (Figure 3B). In reltion to the TN, when contrsting the systems t the level of the sme lyer, the highest TN levels in the light frction were found in the surfce lyer of the AFS 1 re, nd in the susurfce lyers of the NF nd AFS 2 res (Figure 3C). For the hevy frction, the AFS 3 nd EG res retined the highest TN levels, in oth lyers (Figure 3D). Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,

6 OC of light frction (g kg -1 ) A Bc B A Bd LF Bd A OC of hevy frction (g kg -1 ) NF AFS 1 AFS 2 SPS AFS 3 EG HF A Bc A B A A B TN of light frction (g kg -1 ) NF AFS 1 AFS 2 SPS AFS 3 EG Coertur vegerl LF A A B B Ad B B Bc Bcd C TN of hevy frction (g kg -1 ) NF AFS 1 AFS 2 SPS AFS 3 EG Bcd A Bc Coertur vegerl NF AFS 1 AFS 2 SPS AFS 3 EG Lnd use systems Bd AB Figure 3. Orgnic cron (OC) nd totl nitrogen (TN), in the light nd hevy frctions under different lnd use systems: Ntive Forest (NF): open evergreen forest, s reference environment; Agroforestry System 1 (AFS 1): tek (Tecton grndis LF) nd kudzu (Puerri montn); Agroforestry System 2 (AFS 2): coffee (Coffe cnephor), mrndu plisde grss (Brchiri riznth cv. Mrndu), pinho cuino (Prki multijuc), tek nd kudzu; Agroforestry System 3 (AFS 3): tek nd coco (Theorom cco); Silvopsture System (SPS): tek, coco nd mrndu plisde grss; nd Extensive Grzing (EG) [System]: mrndu plisde grss. Cpitl letters compre the lyers in the sme system while smll letters compre the systems in the sme soil lyer, y the Tukey test (P <.5). HF B D 268 Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun., 216

7 The verge vlues of orgnic cron (OC) found in the light frction vried from 4.7 to 13.5 g kg -1 (Figure 3A) nd from 4.8 to 26.8 g kg -1 for totl nitrogen (TN) (Figure 3C). In the hevy frction, the rnge ws 6.1 to 16.8 g kg -1 (Figure 3B) for OC nd 1.2 to.3 g kg -1 for TN (Figure 3D). An interesting oservtion is tht lthough the light frction hd lower proportion of the totl mss thn did the hevy frction (Figure 2), sed on the dt of Figure 3, it ccounted for pproximtely 45% (-.5 m) nd 44% (.5-. m) of the OC, nd 74% (-.5 m) nd 71% (.5-. m) of the TN, when considering the verges of the vlues under the lnd use systems for ech lyer evluted. These results re similr to those reported y Freixo et l. (22). It ppers, therefore, tht the light frction lone is le to store lrge prt of the OC nd TN. cording to Roscoe nd Mchdo (22) nd Silv et l. (29), the light frction is n importnt source of lile nutrients for plnts due to the reltively fster decomposition, minerliztion nd nutrient cycling in this zone. The mesurement of these nutrients is therefore very useful for plnning techniques tht will reduce the decomposition of these nutrients nd, over time, mintin or increse the qulity nd quntity of orgnic mtter. Regrdless of the soil lyer, the light frctions of the AFS 1 nd AFS 2 use systems did not differ in terms of verge OC vlues, nd their verge OC levels were greter thn those of the ntive forest (NF) (Figure 3A). With respect to the OC content of the hevy frction, however, only the AFS 2 soil did not differ etween the two lyers. The NF, AFS 1 nd EG systems were equl to the AFS 2 in this respect, ut only in the susurfce soil lyer (Figure 3B). It cn thus e deduced tht the longer cultivtion time nd greter heterogeneity of cultures in the groforestry system AFS 2 (Tle 1) fvored greter equilirium with time etween the OC of the light (Figure 3A) nd hevy frction (Figure 3B) thn did the less diverse lnd use. In generl, the surfce lyer stored more nitrogen thn did the susurfce lyer, proly ecuse, ccording to White (26), microorgnisms nd orgnic residues re more plentiful in the surfce lyer thn they re in the lower strt. Furthermore, up to 95% of the nitrogen in the soil is found in orgnic form (RANGEL; SILVA, 27). In light of these findings, the quntity of cron in the soil cn e mintined or even incresed to higher quntities thn in ntive environments with the use of more vried production systems wherein different plnts nd nimls re comined s is the cse of AFS 2 (Tle 1) (ARAÚJO et l., 211). This rgument is justified ecuse, s reported y Rngel nd Silv (27), Iwt et l. (212) nd Mglhães et l. (213), systems tht fvor the constnt production of plnt or niml iomss increse the content of cron nd vrious nutrients in the soil including nitrogen. The cultivtion of psture cused OC to ccumulte in the hevy frction of the surfce lyers in the AFS 2, EG nd NF res (Figure 3B). TN levels were equl in the light frctions of oth the EG nd NF systems (Figure 3C) wheres TN ws greter in the hevy frction of EG thn it ws in NF (Figure 3D). cording to D Andre et l. (24) nd Rossi et l. (212), productive systems tht include grsses such s Brchiri sp. re efficient in storing cron minly ecuse grsses hve n undnt nd voluminous rnched root system with continuous renovtion, entrnce nd cycling. cording to Fávero et l. (28), lthough the totl orgnic cron content of soil under psture cn e higher [thn it is in other lnd use systems], in soil under groforestry systems the less stle orgnic frctions (light frctions) re more dynmic thn they re elsewhere which, ccording to Iwt et l. (212), increses the vilility of nutrients to plnts. cording to Redin et l. (211), the urning of orgnic wstes ccelertes their minerliztion nd cuses the loss of C vi the relese of CO 2. It is therefore nturl tht plnts initilly develop vigorously ut this effect wnes due to the loss of C-CO 2 through microil respirtion, soil erosion nd the leching of nutrients from the shes. This phenomenon especilly holds true in the cse of monocultures, which, ccording to Rmos et l. (2), cn cuse n imlnce in the soil s microiot. Therefore, it is likely tht urning ctlyzed the decomposition of the light frction of the SOM, therey incresing the quntity of the hevy frction. Since the EG re is n indequtely mintined monoculture however, it ws lredy showing signs of degrdtion during the study period (Tle 1). cording to Gicomini et l. (23), plnt nitrogen supply nd demnd should e synchronized. In other words, even fter ntive forests re cler-cut, the use of polycultures (such s groforestry systems) cn rise OC nd TN levels (Figure 3). The results lso indicted tht not only is it importnt to know the generl concentrtions of OC nd TN, ut it is lso necessry to know their proportions of light nd hevy frctions (Figure 3). Since the ccumultion of the hevy frction depends on the input of the light frction, nd therefore the ctivity of soil orgnisms, the cron/ nitrogen rtio (C/N) cn e used to mke inferences out soil qulity (SILVA; MENDONÇA, 27). The rte of degrdtion of orgnic residues in ech type of lnd use system strongly influences the cycling of nutrients such s nitrogen nd hence, y extension, their vilility to plnts (GIACOMINI et l., 23; WHITE, 26). Rtio of cron to totl nitrogen in the light nd hevy frctions Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,

8 It is known tht in order for nutrients such s nitrogen derived from orgnic wstes to ecome ville (minerlized) to plnts, the orgnic mtter must first need to e decomposed y soil microorgnisms. Ech microorgnism, however, hs its own idel demnd for chemicl elements such s C nd N (WHITE, 26). Soil microorgnisms use N s n energy source nd C to form cells nd tissues. Assuming tht the C/N rtio of fungi nd cteri is 8:1, s proposed y White (26), when the wste mtter hs C/N rtio of out 24:1, there is n equilirium etween the sorption nd the relese of N (immoiliztion). When the wste hs C/N rtio of round 9:1, nitrogen is tken up y the soil (deficit). When the wste hs C/N rtio of out 9:1, nitrogen is relesed from the soil (minerliztion). Therefore, the higher the C/N rtio, the lower the rtes of decomposition, minerliztion nd the vilility of N to plnts. In view of the ove informtion, the lnd use res with highest C/N rtios (Figure 4) were the light frctions of the surfce lyer of the SPS nd the susurfce lyers of the AFS 2 nd the SPS. For the hevy frctions the highest vlues were found in the surfce lyer of the AFS 1 re nd the susurfce lyers of the NF, AFS 1 nd AFS 2 res. 8 Light frction Hevy frction -.5 m.5-. m -.5 m.5-. m C/N rtio NF AFS 1 AFS 2 SPS AFS 3 EG NF AFS 1 AFS 2 SPS AFS 3 EG FNF AFS 1 AFS 2 SPS AFS 3 EG Lnd use systems NF AFS 1 AFS 2 SPS AFS 3 EG Figure 4. Rtio of cron to totl nitrogen (C/N) in the light nd hevy frctions under different lnd use systems: Ntive Forest (NF): open evergreen forest, s reference environment; Agroforestry System 1 (AFS 1): tek (Tecton grndis LF) nd kudzu (Puerri montn); Agroforestry System 2 (AFS 2): coffee (Coffe cnephor), mrndu plisde grss (Brchiri riznth cv. Mrndu), pinho cuino (Prki multijuc), tek nd kudzu; Agroforestry System 3 (AFS 3): tek nd coco (Theorom cco); Silvopsture System (SPS): tek, coco nd mrndu plisde grss; nd Extensive Grzing (EG) [System]: mrndu plisde grss. Cpitl letters compre the lyers (m) in the sme system while smll letters compre the systems in the sme soil lyer, y the Tukey test (P <.5). Arorel species produce leves, rnches nd stems with higher C/N rtios thn those found in grsses, which in turn hve higher C/N rtios thn those of leguminous plnts. Therefore, wste mtter from rorel species decomposes more slowly thn tht derived from other plnt species (MOREIRA; COSTA, 24). This tendency explins the oservtion in this study tht the systems which ccumulted the most OC nd/or TN in the light nd hevy densimetric frctions of the soil were not necessrily those with the highest C/N rtios (Figure 4). C/N rtios were higher in the surfce lyers nd lower in the susurfce lyers for ll lnd use systems except the SPS regrding in terms of its C/N rtio in the light frction nd AFS 1 in the hevy frction. Therefore the C/N rtios differed depending upon the lnd use system nd the soil lyer evluted proly due to the time- sensitive chnges in the qulity nd quntity of orgnic mtter entering them (Tle 1). These results my e useful in the process of plnning lnd uses nd techniques tht could reduce the minerliztion of orgnic wste. The ppliction of such strtegies is prticulrly importnt for sndy soils ecuse their higher oxygention rtes nd their lower surfce res nd lod densities my impir the formtion of orgnominerl complexes nd mke them more susceptile to leching due to fster minerliztion of orgnic wstes (ROSCOE; MACHADO, 22; WHITE, 26). Therefore, if it is true tht the higher the C/N rtio, the slower the decomposition, minerliztion nd vilility of N to plnts, then ll of the lnd use systems in this study would relese nitrogen from the soil t C/N rtio of 9:1 (Figure 4), s descried in White (26). Nevertheless, the light frction hd lower C/N rtio thn did the hevy frction in ll of the lnd use systems evluted. A similr finding ws lso reported y Roscoe nd 27 Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun., 216

9 Mchdo (22), nd y Silv nd Mendonç (27). cording to White (26), the decomposition rte is determined not only y the C/ N rtio ut lso y other chrcteristics of the plnt in question such s its chemicl composition, size, distriution, shoot nd root rnching, s well s the soil texture nd temporl vritions in gs nd wter content of gses nd wter with time, etc. nd the tmosphere (evpotrnspirtion rtes for ech type of plnt cover, etc.). For exmple, in the EG lnd use re, the C/N rtio ws sttisticlly low in oth the light nd hevy frctions in comprison to the other systems. cording to Mrtins et l. (29), soils in psture res hve less reclcitrnt orgnic mtter thn do those contining orgnic mtter derived from the stlks nd rnches of rorel species ecuse the ltter hs greter content of lignin, which is chemicl precursor of reclcitrnt humic sustnces. cording to Gicomini et l. (23), griculturl systems consisting of comintion of species should produce dry mtter with C/N rtio intermedite etween tht of ech species lone in order to produce longer-lsting soil cover with greter synchrony etween plnt nitrogen supply nd demnd. cording to Texeir et l. (29), in tropicl res, where wethering processes re strong nd soils re highly susceptile to lnd mngement nd use prctices, it is importnt to mintin sufficient orgnic mtter on the ground in ll production systems, e they griculturl, forestry or groforestry. Soil conservtion prctices cn fvor this mintennce system y occluding orgnic mtter within soil ggregtes or micropores (ROSCOE; BUURMAN, 23). Furthermore, the protection of the orgnic mtter depends upon the qulity of the wste s well s its quntity. Since the nture of the orgnic mtter vries with plnt species, different humifiction routes must e ctivted vi the interdependent ctivities of vrious soil micro, meso nd mcroorgnisms (SILVA; MENDONÇA, 27). CONCLUSIONS In comprison with the ntive forest, there were increses in oth orgnic cron nd totl nitrogen in the light nd hevy frctions of the soil orgnic mtter in the Agroforestry System 2 re. This lnd use system ws the most diverse of ll of those studied. This finding indictes tht more diversified groforestry mngement system is preferle to improve effectively soil qulity over time fter deforesttion. Although the hevy orgnic mtter frction constituted over 9% y mss of the soil smples, the light frction ws responsile for storing pproximtely 45% nd 7% of the orgnic cron nd totl nitrogen in the soil respectively. Therefore, it is importnt to know not only the generl levels of orgnic cron nd totl nitrogen ut lso their reltive presence undnce in the light nd hevy frctions. Finlly, mesurement of the light densimetric fction is indicted for the erly identifiction of the generl decline of orgnic mtter in the soil. REFERENCES ARAÚJO, E. A. et l. Impcto d conversão florestpstgem nos estoques e n dinâmic do crono e sustâncis húmics do solo no iom Amzônico. t Amzônic, Mnus, v. 41, n. 1, p , 211. BEZERRA, P. S. S.; TAKIYAMA, L. R.; BEZERRA, C. W. B. Complexção de íons de metis por mtéri orgânic dissolvid: modelgem e plicção em sistems reis. t Amzônic, Mnus, v. 39, n. 3, p , 29. D ANDRÉA, A. F. et l. Estoque de crono e nitrogênio e forms de nitrogênio minerl em um solo sumetido diferentes sistems de mnejo. Pesquis Agropecuári Brsileir, Brsíli, v. 39, n. 2, p , 24. FÁVERO, C.; LOVO, I. C.; MENDONÇA, E. DE SÁ. Recuperção de áre degrdd com sistem groflorestl no vle do Rio Doce, Mins Geris. Revist Árvore, Viços, v. 32, n. 5, p , 28. FREIXO, A. A. et l. Estoques de crono e nitrogênio e distriuição de frções orgânics de Ltossolo do Cerrdo so diferentes sistems de cultivo. Revist Brsileir de Ciênci do Solo, Viços, v. 26, n. 2, p , 22. GIACOMINI, S. J. et l. Mtéri sec, relção C/N e cúmulo de nitrogênio, fósforo e potássio em misturs de plnts de coertur de solo. Revist Brsileir de Ciênci do Solo, Viços, v. 27, n. 2, p , 23. GOLCHIN, A. et l. Study of free nd occluded prticulte orgnic mtter in soils y solid stte 13C CP/MAS NMR spectroscopy nd scnning electron microscopy. Austrlin Journl of Soil Reserch, Clyton South, v. 32, n. 2, p , HICKMANN, C. et l. Atriutos físico-hídricos e crono orgânico de um rgissolo pós 23 nos de diferentes mnejos. Revist Cting, Mossoró, v. 25, n. 1, p , 212. IWATA, B. DE B. et l. Sistems groflorestis e seus efeitos sore os triutos químicos em Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,

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11 TEIXEIRA, W. et l. Decifrndo Terr. 2. ed. São Pulo, SP: Compnhi Editor Ncionl, p. WHITE, R. E. Principles nd Prctice of Soil Science: The soil s nturl resource. 4th ed. Mlden, Mss.: Blckwell, 26, 363 p. YEOMANS, J. C.; BREMNER, J. M. A rpid nd precise method for routine determintion of orgnic cron in soil. Communictions in Soil Science nd Plnt Anlysis, Athens, v. 19, n. 13, p , Rev. Cting, Mossoró, v. 29, n. 2, p , r. jun.,