Soil Respiration, Nitrification, and Denitrification in a Wheat Farmland Soil under Different Managements

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1 Communitions in Soil Siene nd Plnt Anlysis, 44: , 2013 Copyright Tylor & Frnis Group, LLC ISSN: print / online DOI: / Soil Respirtion, Nitrifition, nd Denitrifition in Whet Frmlnd Soil under Different Mngements Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Z. H. HU, 1 H. LING, 2 S. T. CHEN, 2 S. H. SHEN, 1 H. ZHANG, 2 AND Y. Y. SUN 2 1 Yle-NUIST Center on Atmospheri Environment nd Jingsu Key Lortory of Agriulturl Meteorology, Nnjing University of Informtion Siene nd Tehnology (NUIST), Nnjing, Chin 2 Shool of Environmentl Siene nd Engineering, Nnjing University of Informtion Siene nd Tehnology, Nnjing, Chin A field experiment ws onduted during the 2010 to 2011 winter whet growing seson to understnd the soil respirtion (R s ), nitrifition, nd denitrifition rtes in winter whet frmlnd soil under no-tillge (NT) tretment with rie strw inorportion. The experimentl tretments inlude NT, NT with rie strw overs on the surfe (NTS), onventionl tillge (CT), nd CT with strw inorportion (CTS). No-tillge nd strw inorportion tretments did not hnge the sesonl ptterns of R s,gross nitrifition (Gn), nd denitrifition (D) rtes ompred with CT. Compred with the CT tretment, the NT, NTS, nd CTS tretments signifintly redued R s (P < 0.01), nd the NT nd NTS tretments signifintly inresed Gn nd D (P < 0.01). CTS lso signifintly inresed Gn (P < 0.01) ut hd no signifint effet on D (P > 0.05). Further nlysis showed tht the temperture sensitivity of soil respirtion (Q 10 )ofct, NT, NTS, nd CTS were 4.26, 1.86, 3.25, nd 2.36, respetively. Our findings suggest tht, ompred with CT, the NT nd strw inorportion tretments redued R s nd Q 10 nd inresed Gn nd D. Keywords Denitrifition, nitrifition, no-tillge, rie strw inorportion, soil respirtion, winter whet Introdution The ron (C) ontent in the soil pool is more thn 1,750 Gt or pproximtely three times the vegettion C pool nd twie the tmospheri pool (Grnier et l. 2000). Therefore, ny smll hnges in the soil C pool n dversely ffet glol C yling. The soil C pool in roplnds is n importnt prt of the overll terrestril eosystem C pool. Cron sequestrtion from roplnds plys n importnt role in glol hnge (Smith 2004). Menwhile, roplnds re one of the most tive eosystems ffeted y humn tivities. Soil respirtion, inluding the utotrophi respirtion of plnt roots nd heterotrophi respirtion of soil miroorgnisms, plys key role in glol C yling (Buhmnn 2000; Shlesinger nd Andrews 2000). In ddition, soil respirtion nd glol wrming losely Reeived 9 Mrh 2012; epted 9 April Address orrespondene to Z. H. Hu, 219 Ningliu Rod, Nnjing, Chin. E-mil: zhhu@nuist. edu.n 3092

2 Soil Respirtion, Nitrifition, nd Denitrifition 3093 Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 influene eh other (Sánhez et l. 2003; Shlesinger nd Andrews 2000). Nitrifition nd denitrifition re importnt proesses involving nitrogen (N) turnovers nd removls from griulturl eosystems (Currie 1996; Müller, Stevens, nd Lughlin 2004; Cookson et l. 2006). Moreover, these proesses re the min soures of nitrous oxide (N 2 O) nd nitri oxide (NO) from soils (Russow, Spott, nd Stnge 2008; Ski, Smith, nd Fowler 1993). Agriulturl mngement ffets the soil respirtion rte (R s ) (Ding et l. 2007). Strw inorportion is n importnt strtegy in orgni-mtter mngement in frmlnds (Nie et l. 2007) s it n inrese the soil orgni C ontent (Freiuer et l. 2004) nd influene R s (Duong, Bumnn, nd Mrshner 2009; Iql et l. 2009). Compred with onventionl tillge (CT), the no-tillge (NT) pproh n protet the struture of soil ggregtes (Pikul et l. 2009; Olhin et l. 2008), strengthen soil minerliztion, nd inrese soil C storge pity (Jos et l. 2010). Previous studies hve suggested tht different tillge pprohes ould ffet the soil N minerliztion potentil nd N trnsformtion (Kheyrodin nd Antoun 2009; Murugnndm, Isrel, nd Rorge 2010). These pprohes ould lso lter the quntity nd miroil tivity of soil miroorgnisms, therey ffeting the soil N yle (Murugnndm, Isrel, nd Rorge 2010; Mhí et l. 2007). To our knowledge, only Gesh et l. (2007) nd Dexter et l. (2000) hve doumented the effets of tillge nd plnt residue mngement on the soil respirtion of griulturl soil. Thus, the possile impts of tillge nd strw inorportion on soil respirtion, nitrifition, nd denitrifition in typil roplnds need further investigtion. In this study, we hypothesized tht NT nd strw inorportion pprohes might redue the R s nd inrese the gross nitrifition (Gn) nd denitrifition (D) rtes in frmlnd soil. To test this hypothesis, we performed field experiment on winter whet frmlnd. The ojetive ws to investigte the effets of NT nd strw inorportion tretments on the R s,gn, nd D in roplnd soil. Mterils nd Methods Experimentl Site The field experiment ws onduted in frmlnd t the Eologil nd Agriulturl Meteorology Experimentl Sttion (32.16 N, E), Nnjing University of Informtion Siene nd Tehnology, Southest Chin. Annul rottions, suh s pddy rie (Oryz stiv) winter whet (Tritium estivum) nd soyen (Glyine mx) winter whet, re the min griulturl ropping systems in this re. The nnul verge temperture nd rinfll in this site re 15.6 C nd 1,100 mm, respetively. The soil (0 m to 20 m) is lssified s hydromorphi, ontining 26.1% ly with n initil ph (H 2 O) level of 6.20, totl orgni C of g kg 1, nd totl N of 0.77 g kg 1. Field Experiments The field experiments were onduted during the winter whet growing seson. A lol previling winter whet ultivr, Yngmi 12, ws sown on 3 Novemer 2010 nd hrvested on 1 June Tle 1 shows the different growth stges nd fertiliztion of whet. The experiment followed ompletely rndomized plot design, with three replite plots (1 m 2 m re eh) for every tretment. The tretments inlude NT, NT with rie strw overs on the surfe (NTS), onventionl tillge (CT, with depth of pproximtely 15 m), nd CT with rie strw inorportion (CTS, where the strws were

3 3094 Z. H. Hu et l. Tle 1 Min growth stges nd fertiliztion shedules of winter whet Dte Growth stges Dte Fertiliztion 3 Novemer 2010 Sow 3 Novemer kg N h 1 (ure), 78 kg Ph 1, 100 kg K h 1 28 Deemer 2010 Tillering 16 Jnury kg N h 1,21kgPh 1, 27 kg K h 1 4 Ferury 2011 Turning green 21 Ferury kg N h 1 17 Mrh 2011 Elongtion 9 April 2011 Booting 17 April 2011 Heding 23 April 2011 Flowering 28 April 2011 Grin filling 1 June 2011 Hrvest Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 uried fter plowing). The rie strws were ut into short setions (2 m to 3 m in length), nd the dry weight of the rie strws employed ws 225 g m 2. Determintion of Soil Respirtion R s ws mesured using the LI-8100 utomted soil CO 2 flux system (LI-8100, LI-COR, Linoln, Ne., USA). An integrted pump irultes the hedspe ir from the hmer to the nondispersive infrred gs nlyzer during the losed stte of the hmer, nd the CO 2 onentrtion dt nd lulted flux rtes in the system re reorded. Before the mesurement, the PVC soil ollrs (outer nd inner dimeters of 21.3 nd 20.3 m, respetively) were inserted 1 to 2 m deep into the soil, with the top edges kept t pproximtely 7 to 8 m ove the soil surfe. The ollrs were left on the field throughout the experiment. However, ll plnts inside the ollrs were removed during the study period. Eh tretment hd three soil ollrs s replites, nd 12 soil ollrs were rndomly pled in the experimentl field. R s ws mesured one week during the no-rin period. The R s mesurements strted t 8:00 in the morning to minimize errors due to temperture. The soil temperture nd moisture (5 m depth) were simultneously mesured using proes equipped with LI Determintion of Gn nd D The Gn nd D rtes during three ruil growth stges of whet (turning green elongtion, ooting flowering, nd grin filling ripening stges) were determined using the BPS tehnique. The BPS system ws equipped with ontiner holding mximum of seven soil ores (Ingwersen et l. 1999). Cirulr stinless overs (7 m in dimeter) were used to ollet soil smples. Twelve intt soil smples were tken from eh tretment, nd four ores were simultneously mesured in the BPS ontiner. In other words, three prllel replites were set for eh tretment. BPS is sed on the determintion of the CO 2,O 2, nd totl gs lnes of the soil smples. Nitrifition nd denitrifition re the min iologil proesses responsile for gs pressure hnges inside suh n isotherml nd gs-tight system (Breuer, Kiese, nd Butterh-Bhl 2002). The Gn nd D n e lulted sed on gs nd inverse lne

4 Soil Respirtion, Nitrifition, nd Denitrifition 3095 pprohes. The unit of Gn nd D is μg Nkg 1 h 1, whih represents the mount of N prodution per dry weight of soil (kg) per hour. A detiled desription on BPS nd relevnt mesuring proesses n e found in the ppers of Ingwerson et l. (1999) nd Breuer et l. (2002). Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Sttistil Anlysis The verge Rs, Gn, D, nd stndrd errors (SEs) were lulted sed on triplite mesurements. One-wy nlysis of vrine (ANOVA) ws used to test the dt vriility mong different tretments. To exmine the temperture sensitivity of soil respirtion, we performed regression nlysis using y = e x, where y is the R s,xis the soil temperture, oeffiient is the interept of respirtion t 0 C, nd oeffiient represents the temperture sensitivity of soil respirtion. The exponentil regression ws used to nlyze the reltionship etween the dt (Rs, Gn, nd D) nd the environmentl ftors (soil temperture nd moisture). In this study, signifine implies P = 0.05 unless stted otherwise. All sttistil nlyses were onduted using SPSS 13.0 (SPSS In., Chigo, Ill., USA). Results nd Disussion Effets of NT nd Strw Inorportion on Soil Respirtion The R s vlues of the different tretments re shown in Figure 1. Compred with CT, the NT nd strw inorportion tretments did not hnge the sesonl pttern of R s.inthe turning green elongtion stge, the R s vlues of the four tretments were reltively lower. During the ooting flowering nd grin filling ripening stges, the R s vlues inresed. Figure 2 shows the verge R s of the four tretments in different growth stges. The verge R s vlues of NT nd CT were signifintly different (P < 0.05). Compred with CT, NT signifintly deresed the verge R s. The NT nd NTS results during the turning green elongtion nd ooting flowering stges were signifintly different. The CT nd CTS results during the turning green elongtion nd grin filling ripening stges were lso Soil respirtion rte (µmol m 2 s 1 ) NT NTS CT CTS Dte(mm-dd) Figure 1. Temporl vrition of soil respirtion rte (R s ) in different soils tretments. Vlues re expressed s mens (± SE), with the error rs showing SE.

5 3096 Z. H. Hu et l. 10 Averge soil respirtion rte (µmol m 2 s 1 ) NT NTS CT CTS 0 Turning green-elongtion stge Booting-flowering stge Growth stges Grin filling-ripening stge Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Figure 2. Averge soil respirtion rte (R s ) vlues in different growth stges. Different letters represent signifint differenes etween tretments. Vlues re expressed s mens (±SE), with the error rs showing SE. different, inditing tht strw inorportion redued R s. Menwhile, strw inorportion in CT signifintly inresed R s ompred with tht in NTS. In ll growth stges, the verge R s of CT ws the gretest. No-tillge soils hd greter soil orgni C thn CT soils (Jos et l. 2010), whih improved the utiliztion effiieny of the miroil C soure (Cookson, Murphy, nd Roper 2008; Wng et l. 2008). This improvement leds to more redued soil CO 2 emissions under NT nd NTS, ompred with CT nd CTS. Further nlysis showed tht the verge R s of CTS ws greter thn tht of NT. This differene my e ttriuted to the ft tht the disruption of soil ggregtes hs stronger influene on the effiieny of C stiliztion thn the pplition of strw into the soil profile (Olhin et l. 2008). Effets of NT nd Strw Inorportion on the Temperture Sensitivity of Soil Respirtion Regression nlysis indites tht R s inresed exponentilly with inresing soil temperture (Figure 3), therey showing tht soil respirtion is positively orrelted with soil temperture. This result is onsistent with the findings of previous studies tht soil temperture is the min ftor ffeting soil respirtion, long with soil orgni mtter (Ussiri nd Ll 2009; Chen et l. 2010). The re-estimted vlues were used to lulte the soil respirtion quotient (Q 10 = e 10 ). The Q 10 vlues of different tretments were 4.26 (CT), 3.25 (NTS), 2.36 (CTS), nd 1.86 (NT). In ontrst to CT, the NT nd strw inorportion (NTS nd CTS) tretments redued Q 10, inditing tht the NT nd strw inorportion tretments redued the temperture sensitivity of soil respirtion. Our results suggest tht the Q 10 vlue of soil respirtion ws signifintly ffeted y NT nd strw inorportion (P < 0.01). Further studies on plnt hemistry nd the deomposition proesses in soil re needed to understnd the mehnisms of the effets of NT nd strw inorportion on the temperture sensitivity of soil respirtion. Further studies on the different responses of utotrophi nd heterotrophi respirtion to NT nd strw inorportion should lso e onduted.

6 Soil Respirtion, Nitrifition, nd Denitrifition 3097 Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Figure 3. Soil respirtion rte (R s ) in reltion to soil temperture. Effets of NT nd Strw Inorportion on Gn nd D The Gn rtes of the different tretments re shown in Figure 4. In the turning green elongtion stge, ompred with CT, the NT nd NTS tretments signifintly inresed Gn y 124% (P < 0.01) nd 252% (P < 0.01), respetively. Menwhile, CTS inresed Gn y 58% (P > 0.05). In the ooting flowering stge, the Gn rtes in NT, NTS, nd CTS soils were 6.62, 8.66, nd 3.47 times greter thn tht in CT soil (P < 0.01), respetively. In the grin filling ripening stge, the Gn rtes in NT, NTS, nd CTS soils were 3.07, 4.97, nd 1.62 times greter thn tht in CT soil (P < 0.01), respetively. Figure 5 shows the D rtes of the different tretments. In the turning green elongtion stge, the D rtes in NT nd NTS soils were 4.30 nd 6.21 times greter thn tht in CT soil (P < 0.01). In the ooting flowering stge, ompred with CT, the NT nd NTS tretments signifintly inresed D y 393% nd 476% (P < 0.01), respetively, wheres the CTS tretment did not inrese D (P > 0.05). In the grin filling ripening stge, the NT nd NTS tretments inresed D y 66% nd 189% (P < 0.01), respetively, wheres the CTS tretment deresed D y 62% (P < 0.01). The Gn rtes of the different tretments were NTS > NT > CTS > CT. The D rtes were NTS > NT > CT CTS. Two proesses of N yle exhiited similr hrteristis. This similrity my e ttriuted to the lose ssoition mong the different trnsformtion proesses involved in the N yle (Nnnipieri nd Pul 2009). The NTS nd NT tretments hd higher Gn nd D rtes, wheres CT tretment hd lower Gn nd D rtes. This disrepny my e due to the vrying N ontent in the different treted soils. Groffmn (1985) lso found tht nitrifition nd denitrifition tivities were greter t the upper 5 m of NT soils thn in CT soils. In ontrst to CT, NT nd strw inorportion tretments hd greter N trnsformtion nd minerliztion rtes (Kheyrodin nd Antoun 2009; Murugnndm, Isrel, nd Rorge 2010). Moreover, NT nd strw inorportion

7 3098 Z. H. Hu et l. Gross nitrifition rte (µg N kg 1 h 1 ) NT NTS CT CTS d 0 Turning green-elongtion stge Booting-flowering stge Groth stges Grin filling-ripening stge Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Figure 4. Gross nitrifition rtes (Gn) of different tretments soils during different growth stges. Vlues re expressed s mens (±SE), with the error rs showing SE. Denitrifition rte (µg N kg 1 h 1 ) Turning green-elongtion stge Booting-flowering stge Growth stges NT NTS CT CTS d Grin filling-ripening stge Figure 5. Denitrifition rtes (D) of different tretments soils during different growth stges. Vlues re expressed s mens (±SE), with the error rs showing SE. ould inrese the quntity nd miroil tivities of soil miroorgnisms nd thus elerte the soil nitrogen yle (Murugnndm, Isrel, nd Rorge 2010; Mhí et l. 2007; Phillips 2008). In generl, the mount of ville inorgni N is one of the ftors regulting D rtes in soils (Phillips 2008). Clrk et l. (2009) lso suggested tht the nitrifition proess is onsequently limited y nitrte (NO 3, nd mmonium (NH 4 + ) vilility in soil. Furthermore, the Gn nd D rtes in different tretments hd similr sesonl ptterns, showing greter vlues in the erly growth period, whih then deresed grdully. This phenomenon my e ttriuted to the freezing nd thwing in the erly spring seson, whih re enefiil to the minerliztion, nitrifition, nd denitrifition of N in soils nd strw (Su, Kleineidm, nd Shloter 2010). Moreover, the sesonl vrition of

8 Soil Respirtion, Nitrifition, nd Denitrifition 3099 Tle 2 Effets of no-tillge nd strw inorportion on the reltionships etween gross nitrifition rte (Gn) nd soil temperture nd moisture Prmeter Tretment Gn R 2 P vlue Soil temperture (t) NT 868.2e 0.128t <0.01 NTS e 0.124t <0.01 CT 272.5e 0.138t <0.05 CTS 700.7e 0.148t <0.01 Soil moisture (θ v ) NT 37.7e 0.160θv <0.01 NTS 82.0e 0.060θv <0.01 CT 9.0e 0.374θv <0.01 CTS 11.9e 0.273θv <0.01 Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Tle 3 Effets of no-tillge nd strw inorportion on the reltionship etween denitrifition rte (D) nd soil temperture nd moisture Prmeter Tretment D R 2 P vlue Soil temperture (t) NT 215.3e 0.065t <0.01 NTS 233.2e 0.048t <0.01 CT 16.8e 0.022t >0.05 CTS 30.4e 0.041t >0.05 Soil moisture (θ v ) NT 45.2e 0.077θv <0.01 NTS 85.2e 0.022θv <0.01 CT 23.2e 0.002θv >0.05 CTS 8.8e 0.096θv >0.05 Gn rtes in soils n e redily predited y soil moisture nd temperture (Stnge nd Neue 2009; Kiese, Hewett, nd Butterh-Bhl 2008). In the urrent study, ll Gn nd D rtes, exept the D rtes of CT nd CTS, re negtively orrelted with soil temperture nd positively orrelted with soil moisture (Tles 2 nd 3). These results re onsistent with previous studies (Stnge nd Neue 2009; Kiese, Hewett, nd Butterh-Bhl 2008; Chen et l. 2011). Rie nd Smith (1983) lso found tht nitrifition rtes re greter in NT soils thn in CT soils euse the former type hs more fvorle soil moisture onditions. Conlusions Compred with CT, NT nd strw inorportion tretments did not hnge the sesonl pttern of soil respirtion. However, they redued the R s vlues nd Q 10 vlues. The Gn nd D rtes of the different tretments hd the sme sesonl pttern, suggesting greter vlues in the turning green elongtion stge, whih then deresed grdully in the ooting flowering nd grin filling ripening stges. The NT nd strw inorportion signifintly inresed the Gn nd D rtes. Therefore, Gn nd D rtes re negtively orrelted with soil temperture nd positively orrelted with soil moisture.

9 3100 Z. H. Hu et l. Aknowledgments This work ws supported y the Ntionl Nturl Siene Foundtion of Chin ( , ), the Ministry of Edution of Chin (Grnt PCSIRT), nd the Meteorologil Industry Reserh Fund (GYHY ). Referenes Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Breuer, L., R. Kiese, nd K. Butterh-Bhl Temperture nd moisture effets on nitrifition rtes in tropil rin-forest soils. Soil Siene Soiety of Amerin Journl 66: Buhmnn, N Bioti nd ioti ftors ontrolling soil respirtion rtes in Pie ies stnds. Soil Biology nd Biohemistry 32: Chen, S. T., Y. Hung, J. W. Zou, Q. R. Shen, Z. H. Hu, Y. M. Qin, H. S. Chen, nd G. X. Pn Modeling internnul vriility of glol soil respirtion from limte nd soil properties. Agriulturl nd Forest Meteorology 150: Chen, Y. T., W. Borken, C. F. Stnge, nd E. Mtzner Effets of deresing wter potentil on gross mmonifition nd nitrifition in n id oniferous forest soil. Soil Biology nd Biohemistry 43: Clrk, K., M. H. Chntigny, D. A. Angers, P. Rohette, nd L. E. Prent Nitrogen trnsformtions in old nd frozen griulturl soils following orgni mendments. Soil Biology nd Biohemistry 41: Cookson, W. R., P. Mrshner, I. M. Clrk, N. Milton, M. N. Smirk, D. V. Murphy, M. Osmn, E. A. Stokdle, nd P. R. Hirsh The influene of seson, griulturl mngement, nd soil properties on gross nitrogen trnsformtions nd teril ommunity struture. Austrlin Journl of Soil Reserh 44: Cookson, W. R., D. V. Murphy, nd M. M. Roper Chrterizing the reltionships etween soil orgni mtter omponents nd miroil funtion nd omposition long tillge disturne grdient. Soil Biology nd Biohemistry 40: Currie, W. S., J. D. Aer, W. H. MDowell, R. D. Boone, nd A. H. Mgill Vertil trnsport of dissolved orgni C nd N under long-term N mendments in pine nd hrdwood forests. Biogeohemistry 35: Dexter, A. R., J. Arvidsson, E. A. Czyz, A. Trutner, nd B. Stenerg Respirtion rtes of soil ggregtes in reltion to tillge nd strw-mngement prties in the field. At Agriulture Sndinvi, Setion B 49: Ding, W. X., L. Meng, Y. F. Yin, Z. C. Ci, nd X. H. Zheng CO 2 emission in n intensively ultivted lom s ffeted y long-term pplition of orgni mnure nd nitrogen fertilizer. Soil Biology nd Biohemistry 39: Duong, T. T. T., K. Bumnn, nd P. Mrshner Frequent ddition of whet strw residues to soil enhnes ron minerliztion rte. Soil Biology & Biohemistry 41: Freiuer, A., M. D. A. Rounsevell, P. Smith, nd J. Verhgen Cron sequestrtion in the griulturl soils of Europe. Geoderm 122:1 23. Gesh, R. W., D. C. Reiosky, R. A. Gilert, nd D. R. Morris Influene of tillge nd plnt residue mngement on respirtion of Florid Evergldes Histosol. Soil nd Tillge Reserh 92: Grnier, A., E. Ceshi, C. Dmesin, E. Dufrene, D. Epron, P. Gross, S. Leue, V. Le Dnte, N. Le Goff, nd D. Lemoine The ron lne of young Beeh forest. Funtionl Eology 14: Groffmn, P. M Nitrifition nd denitrifition in onventionl nd no-tillge soils. Soil Siene Soiety of Ameri Journl 49: Ingwrsen, J., K. Butterh-Bhl, R. Gshe, H. Ppen, nd O. Rihter Brometri proess seprtion: New method for quntifying nitrifition, denitrifition, nd nitrous oxide soures in soils. Soil Siene Soiety of Amerin Journl 63:

10 Soil Respirtion, Nitrifition, nd Denitrifition 3101 Downloded y [Z. H. Hu] t 06:40 30 Otoer 2013 Iql, J., R. G. Hu, S. Lin, R. Htno, M. L. Feng, L. Lu, B. Ahmdou, nd L. J. Du CO 2 emission in sutropil red pddy soil (Ultisol) s ffeted y strw nd N-fertilizer pplitions: A se study in southern Chin. Agriulture, Eosystems nd Environment 131: Jos, A., M. Helfrih, S. Hnish, U. Quendt, R. Ruer, nd B. Ludwig Effet of onventionl nd minimum tillge on physil nd iohemil stiliztion of soil orgni mtter. Biology nd Fertility of Soils 46: Kheyrodin, H., nd H. Antoun Tillge nd mnure effet on soil physil nd hemil properties nd on ron nd nitrogen minerliztion potentils. Interntionl Journl of Nutrition nd Metolism 1:1 8. Kiese, R., B. Hewett, nd K. Butterh-Bhl Sesonl dynmi of gross nitrifition nd N 2 O emission t two tropil rinforest sites in Queenslnd, Austrli. Plnt nd Soil 309: Mhí, J., A. Mrtín, T. Crlls, nd M. Díz-Rviñ Atrzine degrdtion nd enzyme tivities in n griulturl soil under two tillge systems. Siene of the Totl Environment 378: Murugnndm, S., D. W. Isrel, nd W. P. Rorge Nitrogen trnsformtions nd miroil ommunities in soil ggregtes from three tillge systems. Soil Siene Soiety of Ameri Journl 74: Müller, C., R. J. Stevens, nd R. J. Lughlin A 15 N tring model to nlyse N trnsformtions in old grsslnd soil. Soil Biology nd Biohemistry 36: Nnnipieri, P., nd E. Pul The hemil nd funtionl hrteriztion of soil N nd its ioti omponents. Soil Biology nd Biohemistry 41: Nie, J., J. M. Zhou, H. Y. Wng, X. Q. Chen, nd C. W. Du Effet of long-term rie strw return on soil glomlin, ron, nd nitrogen. Pedosphere 17: Olhin, G. P., S. Ogle, S. D. Frey, T. R. Filley, K. Pustin, nd J. Six Residue ron stiliztion in soil ggregtes of no-till nd tillge mngement of drylnd ropping systems. Soil Siene Soiety of Amerin Journl 72: Pikul Jr., J. L., G. Chilom, J. Rie, A. Eynrd, T. E. Shumher, K. Nihols, J. M. F., Johnson, S. Wright, T. C. Cesr, nd M. Ellsury Orgni mtter nd wter stility of field ggregtes ffeted y tillge in South Dkot. Soil Siene Soiety of Ameri Journl 73: Phillips, R. L Denitrifition in ropping systems t su-zero soil tempertures: A review. Agronomy for Sustinle Development 28: Rie, C. W., nd M. S. Smith Nitrifition of fertilizer nd minerlized mmonium in no-till nd plowed soil. Soil Siene Soiety of Ameri Journl 47: Russow, R., O. Spott, nd C. F. Stnge Evlution of nitrte nd mmonium s soures of NO nd N 2 O emissions from lk erth soils (Hpli Chernozem) sed on 15 N field experiments. Soil Biology nd Biohemistry 40: Sánhez, M. L., M. I. Ozores, M. J. López, R. Colle, B. D. Torre, M. A. Grá, nd I. Pérez Soil CO 2 fluxes eneth rley on the entrl Spnish plteu. Agriulturl nd Forest Meteorology 118: Shlesinger, W. H., nd J. A. Andrews Soil respirtion nd the glol ron yle. Biogeohemistry 48:7 20. Ski, U., K. A. Smith, nd D. Fowler Nitrifition nd denitrifition s soures of nitri oxide nd nitrous oxide in sndy lom soil. Soil Biology nd Biohemistry 25: Smith, P Cron sequestrtion in roplnds: The potentil in Europe nd the glol ontext. Europen Journl of Agronomy 20: Stnge, C. F., nd H. U. Neue Mesuring nd modelling sesonl vrition of gross nitrifition rtes in response to long-term fertiliztion. Biogeosienes 6: Su, M. X., K. Kleineidm, nd M. Shloter Influene of different litter qulity on the undne of genes involved in nitrifition nd denitrifition fter freezing nd thwing of n rle soil. Biology nd Fertility of Soils 46:

11 Downloded y [Z. H. Hu] t 06:40 30 Otoer Z. H. Hu et l. Ussiri, A. N. D., nd R. Ll Long-term tillge effets on soil ron storge nd ron dioxide emissions in ontinuous orn ropping system from n Alfisol in Ohio. Soil nd Tillge Reserh 104: Wng, Q. J., Y. H. Bi, H. W. Go, J. He, H. Chen, R. C. Chesney, N. J. Kuhn, nd H. W. Li Soil hemil properties nd miroil iomss fter 16 yers of no-tillge frming on the Loess Plteu, Chin. Geoderm 144: