ORGANIC AMENDMENT TO REDUCE NITROGEN LOSS IN SANDY SOILS

Transcription

1 ORGANIC AMENDMENT TO REDUCE NITROGEN LOSS IN SANDY SOILS By WEN GU A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA

2 2012 Wen Gu 2

3 To ll who nurtured my intellectul curiosity, cdemic interests, nd sense of scholrship throughout my lifetime, mking this milestone possile 3

4 ACKNOWLEDGEMENTS First of ll, I would like to thnk my esteemed dvisor, Dr. Zhenli He, for his expert guidnce nd support. Not only ws he redily ville for me providing comprehensive instructions in the l, ut lso he lwys red nd responded to the drfts of my work in time nd with ptience. His comments re lwys perceptive nd helpful, without which this disserttion would not hve een finished. My thnks go out to my co-dvisor, Dr. Len Q. M nd collegues from Biogeochemistry of Trce Metls group for the hospitlity nd support I hd received during my first two semesters of course studies in Ginesville. I hd enefited lot from Dr. M s insightful nd pertinent suggestions for the reserch group s well s her clss. I would lso like to give my sincere thnks to Drs. Peter J. Stoffell, Ptrick C. Wilson nd Mri L. Silveir for serving on my dvisory committee. I m grteful for their dvice, ssistnce nd encourgement in every step towrds my Mster s degree. I deeply express my pprecition to my collegues in Soil nd Wter Science Lortory: Drs. Yungen Yng, Shengke Tin, Zhigng Li, Suli Li, Ying Guo, Jinghu Fn, Ph.D. students Sntnu Bkshi, Mr. Brin Cin, for providing useful cdemic nd socil ssistnce. We studied nd relxed together. Without their help nd friendship, the successful completion of my Mster degree study is impossile. I hve lwys felt fortunte to e prt of Dr. He s group where I hve lerned, enjoyed nd enefited from temwork. I pprecite the people on the fculty nd stff t Soil nd Wter Science Deprtment s well s Indin River Reserch Center of University of Florid for providing me wonderful environment for oth studying nd living during the two yers. I m prticulrly thnkful to Dr. Peter J. Stoffell, Ms. Lur McKeon, nd Ms. Velm Spencer for their timely nd efficient 4

5 ssistnce nd rrngement in the student dorm. I wnt to lso thnk Mr. Michel Sisk nd Ms. Jckie White for ll their helps with my course registrtion, defense rrngement, etc. Lst ut not lest, I would like to thnk my prents nd ll of my friends for their love nd support. I will cherish ll the hppy moment nd memory. 5

6 TABLE OF CONTENTS ACKNOWLEDGEMENTS...4 LIST OF TABLES...8 LIST OF FIGURES...9 ABSTRACT...11 CHAPTER 1 LITERATURE REVIEW...13 pge Nitrogen nd Plnt Nutrition...13 The Role of Nitrogen in Sustinle Agriculture...14 Soil Nitrogen...19 Nitrogen Trnsformtion nd Avilility in Soil...21 Nitrogen Losses into the Environment...22 Impliction of C/N Rtio in Nitrogen Mngement...26 Conclusions nd Perspectives ORGANIC AMENDMENT EFFECT ON NITROGEN TRANSFORMATION IN SOILS...37 Introduction...37 Mterils nd Methods...39 Soil Collection nd Chrcteriztion...39 Incution Study nd Soil N Dynmics Anlysis...39 Dt Anlysis...40 Results nd Discussion...40 Effects of Orgnic Amendment on Soil ph nd EC...40 Effects on N Dynmics in Soils...41 Conclusion ORGANIC AMENDMENT EFFECTS ON NITROGEN LEACHING...54 Introduction...54 Mterils nd Methods...55 Results nd Discussion...57 Effects of Orgnic Amendment on Soil ph nd EC...57 Effect on N Leching nd Soil N Pool...58 Potentil Effects on Hevy Metls...59 Chrcteriztion of Leched Soil...60 Conclusion

7 4 SUMMARY, CONCLUSIONS AND PERSPECTIVE...73 Summry nd Conclusions...73 Perspective...75 LIST OF REFERENCES...76 BIOGRAPHICAL SKETCH

8 LIST OF TABLES Tle pge 2-1 Generl properties of the two soils nd Hydr-Hume Generl properties of the Hydr-Hume Sttisticl nlysis of KCl extrctle NH 4 -N in Alfisol Sttisticl nlysis of KCl extrctle NO 3 -N in Alfisol Sttisticl nlysis of KCl extrctle NO 3 -N in Spodosol Sttisticl nlysis of NO 3 -N concentrtion nd totl mount of NO 3 -N in lechte from Spodosol Sttisticl nlysis of NH 4 -N concentrtion nd totl minerl N in lechte from Spodosol Sttisticl nlysis of hevy metls in lechte from Spodosol Sttisticl nlysis of NO 3 -N nd totl mount of NO 3 -N in lechte from Alfisol Sttisticl nlysis of NH 4 -N concentrtion nd totl minerl N in lechte from Alfisol Sttisticl nlyses of hevy metls in lechte from Alfisol

9 LIST OF FIGURES Figure pge 2-1 Smpling site Effect of orgnic mendment on Alfisol ph s function of incution time Effect of orgnic mendment on Spodosol ph s function of incution time Effect of orgnic mendment on Alfisol Electricl conductivity (EC) s function of incution time Effect of orgnic mendment on Spodosol electricl conductivity (EC) s function of incution time Effect of orgnic mendment on KCl-extrctle NH 4 -N in Alfisol Effect of orgnic mendment nd fertilizer on KCl-extrctle NH 4 -N in Spodosol Effect of orgnic mendment on KCl-extrctle NO 3 -N in Alfisol Effect of orgnic mendment nd fertilizer on KCl-extrctle NO 3 -N in Spodosol soil Effect of orgnic mendment on KCl-extrctle NH 4 -N in Spodosol Effect of orgnic mendment nd fertilizer on KCl-extrctle NH 4 -N in Spodosol Effect of orgnic mendment on KCl-extrctle NO 3 -N in Spodosol Effect of orgnic mendment nd fertilizer on KCl-extrctle NO 3 -N in Spodosol Column leching setup ph of lechte form Spodosol mended with fertilizer nd different rtes of Hydr- Hume ph of lechte form Alfisol mended with fertilizer nd different rtes of Hydr- Hume Lechte EC form Spodosol in reltion to fertilizer nd different rtes of Hydr- Hume Lechte EC form Alfisol in reltion to fertilizer nd different rtes of Hydr-Hume

10 3-6 Lechte NH 4 -N concentrtion from Spodosol in reltion to different rtes of Hydr- Hume lone Lechte NH 4 -N concentrtion from Spodosol in reltion to fertilizer nd different rtes of Hydr-Hume Lechte NO 3 -N concentrtion from Spodosol in reltion to different rtes of Hydr- Hume lone Lechte NO 3 -N concentrtion from Spodosol in reltion to fertilizer nd different rtes of Hydr-Hume Lechte NH 4 -N concentrtion from Alfisol in reltion to different rtes of Hydr- Hume lone Lechte NH 4 -N concentrtion from Alfisol in reltion to fertilizer nd different rtes of Hydr-Hume Lechte NO 3 -N concentrtion from Alfisol in reltion to different rtes of Hydr- Hume lone Lechte NO 3 -N concentrtion from Alfisol in reltion to fertilizer nd different rtes of Hydr-Hume Soil ph fter leching in reltion to fertilizer nd different rtes of Hydr-Hume Soil EC fter leching in reltion to fertilizer nd different rtes of Hydr-Hume

11 Astrct of Thesis Presented to the Grdute School of the University of Florid in Prtil Fulfillment of the Requirements for the Degree of Mster of Science ORGANIC AMENDMENT TO REDUCE NITROGEN LOSS IN SANDY SOILS Chir: Zhenli He Cochir: Len Q. M Mjor: Soil nd Wter Science By Wen Gu Decemer 2012 Nitrogen (N) is nutrient often ssocited with ccelerted eutrophiction of surfce wter. The extremely low holding cpcity for nutrients nd moisture is the fundmentl prolem of sndy soil in Florid, which cuses losses of nutrients into wterwys. Soil orgnic mendment cn improve soil qulity y incresing soil s holding cpcity for nutrients nd moisture nd is, therefore, promising pproch to reduce lods of nutrients nd toxic metls in surfce runoff wter nd/or lechte. Orgnic mendment cn increse or decrese minerl N in soil, depending on the C/N rtio of the orgnic mterils nd N vilility in the soil. Hydr-Hume is commercil product, which shows the potentil in enhncing soil N vilility or reducing fertilizer N loss. In this study, incution, column leching, nd lortory nlysis were conducted to exmine the effects of Hydr-Hume on trnsformtion dynmics nd leching potentil of minerl N in two representtive soils (Alfisol nd Spodosol) under citrus production in south Florid. The otined results indicted tht Hydr-Hume mendment enhnced ssimiltionof minerl N, when it is pplied to the soil, however, soil orginl C/N rtio lso need to e considered. Hydr-Hume ppliction reduced NO 3 -N leching regrdless of chemicl fertilizer ddition. Significnt reduction in totl NO 3 -N mount could e oserved when Hydr- Hume pplied lone in oth of the soils, ut n ppliction rte of 44.8 kg h -1 is required. If 11

12 fertilizer ws incorported with the tretments, significnt reduction of totl NO 3 -N mounts nd totl minerl N mount could e oserved, ut miniml ppliction rte of 44.8 kg h -1 is required to ccomplish significnt results in Spodosol nd 22.4 kg h -1 in Alfisol. 12

13 CHAPTER 1 LITERATURE REVIEW Nitrogen nd Plnt Nutrition Numerous minerl elements re needed for plnt norml growth nd dequte food nd fier production. Among these elements, Nitrogen (N) is n essentil element for plnt growth nd comprtive lrger mount is required y most griculturl crops thn the other soil-orne elements (Stevenson, 1982). Nitrogen is mjor prt of ll mino cid nd the component of nucleic cid nd chlorophyll. Also, It is essentil for crohydrte use within plnts. Therefore, lmost ll the vitl iologicl processes re relted to N, which is sic constituent of the functionl plsm (protein, nucleic cids). A good supply of N is necessry for norml plnt growth, ut lso uptke of other nutrients (Brdy, 2008). Mny legumes nd some other plnt species cn otin N directly from the tmosphere, ut in griculture system, most N is otined from the soil nd externl sources, such s fertilizers, or through minerliztion process. An optiml supply of N will ring optiml crop yields. Therefore, mintining lnce of N vilility ccording to the needs of the plnt is hot point for sustinle griculture. Plnts respond quickly when supply of N is dequte in the soil. Their leves turn drk green nd the productivity cn e drmticlly stimulted. A deficiency of N in plnts limits the synthesis of proteins nd chlorophyll. It inhiits plnts to ssimilte CO 2 nd synthesize crohydrtes, nd consequently exhiits chlorosis (yellowish or ple green lef colors) nd stunted growth (Zho et l., 2005). Timing of N ppliction is lso importnt. Lte ppliction of N my cuse erly-stge lck of N, which my hve dverse effects on nnul crop yield (Jnsson et l., 1982). It is recognized tht some crops re well dpted to unfvorle conditions, growing improver when soil hs high nutrient levels. Excessive N promotes development of eril orgns 13

14 with reltively poor root growth. The presence of N in excess promotes development of the eril orgns with reltively poor root growth. This increse my cuse excessive vegetle growth nd the risk of lodging. It my lso reduce the plnt s resistnce to hrsh climtic conditions nd to folir diseses (FAO, 1984). To meet the food demnds of growing world popultion, glol use of N fertilizers in intensive griculturl systems hs incresed drmticlly in the lst decdes, especilly for greenhouse vegetle production systems (Ju et l., 2005). Due to the reltively high economic vlue of the higher yields nd difficulties in the precise mngement of nutrient supply, growers tend to use extr lrge mounts of fertilizers in order to otin mximum yield. However, the efficiency of fertilizer N is limited, with often less thn 50% of the pplied N tken up y the crop (Run et l., 1999). Ju et l. (2007) mentioned, only in one of the vegetle production res in Chin, fertilizer N is often pplied t rtes > 1200 kg N h -1 per crop, nd two or three crops re grown ech yer. The huge fertilizer lod nd extremely low crop recoveries of fertilizer nutrients my increse the risk of environmentl pollution of oth ir nd wter nd mrked deteriortion in soil (Wiesler et l., 2001). To improve N efficiency nd chieve the optiml crop yield in griculture, integrted N mngement strtegies, which contin improved fertilizer, soil, nd crop mngement prctices, must e tken into considertion. The Role of Nitrogen in Sustinle Agriculture The glol humn popultion, currently 7.5 illion, is projected to rech 10.5 illion y The vst mjority increse will occur in the developing countries of Asi nd Afric, ccording to United Ntions estimtes. Incresed urniztion nd industriliztion ring rpidly growing popultion, which result in greter food demnds. Meeting the nutrition requirement nd food demnd of the growing popultion hs ecome ig chllenge due to decresed irrigtionl wter supplies nd other environmentl concerns (Singh et l., 2011). Moreover, popultion 14

15 growth nd expnding demnd for griculturl products constntly increse the pressure on lnd resources. The pressure on lnd my cuse lnd degrdtion nd intensifiction of the cultivtion of rle lnds, nd lso expnsion of cultivtion into mrginl res. Mismngement of rle res y frmers nd grzing res y livestock owners is one of the mjor cuses of soil degrdtion (FAO, 2000). Vrious sources suggest tht 5 to 10 million hectres re eing lost nnully to severe degrdtion. If this trend continues, 1.4 to 2.8 percent of totl griculturl, psture, nd forestlnd will hve een lost y 2020 (Scherr nd Ydv, 1996). Losses of N y lnd degrdtion re estimted to rnge from 1 to 100 kg h -1 per yer (White, 1986; Rose nd Dll, 1988), which mkes lnd degrdtion mjor cuse of long-term decline in the fertility of griculturl soils. Lnd degrdtion my lso hve negtive effects on the frm, such s deposition of eroded soil in strems or ehind dms, contmintion of drinking wter y griculturl chemicls, diversion of wter sources from other users y irrigtion, helth prolems cused y wind-eroded soil or loss of hitt, which will ffect the livelihood nd economic welleing nd nutritionl sttus of over illion people (Scherr nd Ydv, 1996). Therefore, it seems sensile to consider lterntive pproches, like sustinle griculture. Continuous cultivtion with inpproprite frming prctices my result in severe depletion of nutrients nd soil orgnic mtter. Heno nd Bnnte (2001) reported tht soils of most countries in North Afric re eing depleted of nutrients t rtes rnging from 20 to 50 kg NPK/h/yer. Ll (2001) reported tht the depletion of soil orgnic mtter in tropicl regions could e s high s 70% s result of cultivtion for 10 yers. Sustinle griculture is vitl in tody s world s it offers the potentil to meet our griculturl needs. A switch from conventionl to sustinle griculture involves more thn just simple sustitutions, such s replcing chemicl fertilizers with green mnure. It ttempts to require more informtion out 15

16 environmentl chrcteristics nd the environmentl impcts of griculturl prctices in order to mke sure the environmentl resources cn e fully utilized nd no hrm ws done to it. The techniques need to e environmentl friendlyto ensure sfe nd helthy griculturl products (Singh et l., 2010; Hue nd Silv, 2000). Erenstein et l. (2012) reported tht sustinle griculturl prctice, such s zero tillge (ZT) prctice, could drsticlly reduce tillge intensity nd loss of nutrients for the whet crop from eight to single trctor, sve 15 16% on opertionl costs nd oost 4% yield increse over verge frmer reported conventionl yields of 4.2 tons h -1 in the rice-whet systems in South Asi. From 1950 s, the concerns of scientists nd consumers out the lrge-scle use of chemicl externl inputs, such s fertilizer N, led to movements tht serched for lterntives to sustinle griculturl prctices. However, the use of N is minly determined y economic incentives such s profitility nd susidies, nd less y environmentl costs (Spiertz, 2009). To mnge nutrients nd productivity of gro-ecosystems, Drinkingwter nd Snpp (2007) proposed n ecosystem-sed pproch, which minimizes N loss nd mintin soil reserves with nutrient inputs equl to hrvested exports. To mintin long-term fertility in sustinle groecosystem, soil orgnic mtter (SOM) is key fctor, which hs gret influences on mny redily mesurle soil functions or processes (Yilmz, 2011). It drives iologicl processes involved in nutrient cycling s reservoir of nutrients nd energy nd lso hs profound influence on soil sic properties, such s ction exchnge cpcity, cheltion of metls nd stiliztion of soil structure. Agriculturl production cnnot e sustined if nutrients removed during cropping re not replenished or if pproprite griculturl prctices re not implemented to mintin or increse soil orgnic mtter. Therefore there is surge of reserch on orgnic frming in recent yers nd it is seen s 16

17 sustinle lterntive to conventionl intensive griculturl systems (Stockdle et l., 2001) Nutrient mngement in orgnic systems is sed on fertility uilding soils to fix tmospheric N, comined with recycling of nutrients y orgnic mterils, such s frmyrd mnure nd crop residues, with only limited inputs of permitted fertilizers (Loes nd Ogrd, 2001). Nitrogen lso plys very importnt role in determining crop yield. Rsmussen et l. (1998) reported tht in the long-term experiments in UK, whet yields with fertilizers exceed those without externl N input y fctor of 2 3. Doermnn nd Cssmn (2002) reported tht grin yields of mize incresed from 3 to 14 t h -1 with n increse in plnt N ccumultion from 50 to 300 kg N h -1 nd rice yields incresed from 2 to 8 t h -1 with n increse in plnt N ccumultion from 25 to 200 kg N h -1. It mens with n incresed mount of fertilizers, especilly N, crop yield will e gretly enhnced. However, more externl N inputs my ring more environmentl impcts. The N inputs re mong the first constituents to e removed y soil erosion ecuse they re concentrted in the surfce soil nd re less dense thn other soil constituents (DeBno nd Conrd, 1976). Before 1960s, N fertilizer ws used t reltively low rte nd crop N uptke ws minly dependent on mnure pplictions, iologicl N fixtion nd indigenous N supply through minerliztion of soil orgnic mtter. Since the erly 1960s, the use of N fertilizers hs drmticlly incresed nd nowdys 30%-80% of N pplied to frmlnd is lost to surfce nd groundwter, nd to the tmosphere (Goulding et l., 2008). Goudrin et l. (2001) reported tht fertilizer N ccounted for 60% of the net primry production in 1990, thus resulting in over-ppliction of fertilizer N from the economic response. Since 1980, the mount of fertilizer N hs exceeded the mount tken up y crops glolly. It mens tht only yield improvement ws considered nd not environmentl sustinility. 17

18 Under the current glol ckground, sustinle food security drws lots of ttrction. Sustinle griculture comines economic profitility, environmentl helth nd ethicl soundness s three min ojects. It focuses on meeting productivity, efficiency nd efficcy ims. Eickhout et l. (2006) explored the role of N in future world food production nd environmentl sustinility, nd concluded tht despite improvements in N-use efficiency of food production systems in developed countries, totl rective N loss would grow strongly to 2030 ecuse of the intensifiction of crop production systems in developing countries. Therefore, there is need in lncing the use of fertilizer N nd the key chllenges re to develop glol cpcity to produce dequte food in sustinle mnner, nd estlish communiction out the risks of N excess in groecosystems nd implement legisltion (Spiertz, 2009). Current knowledge for chieving sustinle crop intensifiction through mesuring oth optiml use of externl inputs nd mke conservtions for nturl resources within n groecosystem is indequte. In order to increse intensifiction nd diversifiction of griculturl production systems, innovtive sustinle technologies, pproprite policies, nd economic incentives will hve to e developed (Keerthisinghe et l., 2003). In the cse of N, there is need to gin refined informtion on N-cycling processes nd to ssess the vlue of the crop, soil or fertilizer mngement prctices designed to improve overll N use efficiency of the groecosystem, with the ultimte gol of enhncing sustinle intensifiction of griculturl production while conserving the nturl resource (Chlk et l., 2002). Spiertz (2009) lso put forwrd two strtegies to meet sustinility gols in food production, with sfe nd profitle use of N: One is developing low-input, high-diversity griculturl systems. Agriculturl system diversity, such s crop choice nd crop rottion, my minimize the risks of yield reduction y iotic nd iotic stress. The other one is developing 18

19 high-input, low-diversity griculturl systems. Some crops with high yield nd high N-response re chosen to chieve mximum productivity per unit of lnd. An optimized N mngement during the whole crop cycle my control N losses. Soil Nitrogen Most of the N in terrestril systems is found in the soil. Normlly, A horizons hve out 0.02 to 0.5% N nd vlue of out 0.15% N in cultivted soils (Brdy, 2008). Nitrogen in soil is lrgely ound to orgnic mtter nd minerl mterils tht protect it from loss ut mke it unville to the plnts. Generlly, only smll mount of N exists in ville minerl forms, such s NO - 3 nd exchngele NH + 4. Therefore, N cycling in soil is closely relted to orgnic mtter turnover. Microorgnisms re responsile for soil N trnsformtions, which ply vitl role in determining the vilility of N for plnt growth nd crop production (Stevenson, 1982; Powlson, 1998). Some studies hve shown pproximtely 1.5 to 3.5% of the orgnic N minerlized in soils nnully (Hue nd Silv, 2000; Wilson nd Jefferies, 1996). After the lnd is first plced under cultivtion, the mount of N decline, nd N removed y hrvested crops must e compensted with n equivlent mount of fixed N into orgnic mtter to form equilirium with the chrcteristics of locl wether, tillge nd cultivted prctice, nd soil types (Stevenson, 1982). Since minerl N is highly moile nd limited in the soil, if it is cnnot e tken up y plnt roots nd microorgnisms, it my e lost through gseous emission, minly y denitrifiction nd voltiliztion, or leching to the groundwter, oth of which my crete environmentl hzrds (Huck, 1990; Jenkinson, 1990). The min method scientists pplied to mintin or restore soil nutrients nd increse crop yields is the ppliction of N fertilizers (Hirel, 2011). Fertilizer N cn gretly improve crop qulity y enhncing the protein content of the grin nd forge crops. Also, some reserches showed the role of pplied fertilizer N in fcilitting crop 19

20 uptke of other essentil nutrients (Whitehed et l., 1986; Pederson et l., 2002; Fgeri et l., 2005). For exmple, the physicl ssocition of NH + 4 with P cn increse the uptke of fertilizer P. Murphy (1978) reported tht the plcement of nhydrous NH 3 with n mmonium phosphte solution is soil my significntly enhnce uptke of the fertilizer P. Moreover, in clcreous soils, fertilizer my nd with Zn nd thus improve Zn uptke y plnts. Tilmn (2002) showed tht with the mount of minerl N fertilizers pplied in soils incresed y 7.4 fold, the overll yield incresed only y 2.4 fold. It mens tht the fertilizer N use efficiency hs declined shrply. It is true tht there is genetic vriility for oth N sorption efficiency nd for N utiliztion efficiency in most of the crops (Hirel et l., 2007). However, the min reson is proly the severely distured N lnce due to the intensifiction of griculturl ctivities nd the ppliction of chemicl fertilizers. Over 50% nd up to 75% of the N pplied to the field is lost y leching into the soil (Hodge et l., 2000; Asghri et l., 2011). With yerly pplictions of N fertilizer, excessive mounts of N re rought into the environment nd hve numer of undesirle impcts on wter, terrestril, nd tmospheric resources (Riudo et l., 2011). Also, chnges in the N cycle ssocited with excessive soil N loding my ring ecologicl impcts, such s chnges in the structure of ecosystems nd iodiversity, nd economic impcts (Mtson, 1998; UNEP, 2004). Similrly, the use of N fertilizer my lso ffect humn helth oth in positive nd in negtive wys, depending on the rtes of N fertilizer used in the ecosystem. Crop yield my e gretly incresed y pplying high rtes of N fertilizer, while negtive helth effects my occur in direct (pollution of ir nd wter) nd indirect (ecologicl feedck to disese) wys (INI, 2004). 20

21 Nitrogen Trnsformtion nd Avilility in Soil Nitrogen is the element tht controls most of the iologicl ctivity in soil. The movement of N etween the lnd, wter, nd tmosphere defines the cycling of N on glol scle. Soil lso hs n internl N cycle where N is converted from one form to nother (Rosewell, 1976). Minerl soils in the temperte regions of the world contin etween 0.06 to 0.3% N nd pproximtely 90% of the N is in orgnic forms (Mtthews, 1992). Inorgnic forms exist primrily s mmonium (NH + 4 ) nd nitrte (NO - 3 ). Once in the minerl form, N is esily trnsported etween ir, wter nd soils. The internl N cycle in soils is constntly chnging due to iologicl, chemicl nd physicl processes. The rte t which N ecomes ville is determined y the complexity nd stility of orgnic mtter nd y microil ctivity. It my occur in dys or, if the N is in very stle form, it my tke yers. Microorgnism cnnot metolize elementl N (N 2 ), which mens N ecomes iologiclly ctive when it is fixed or ound, such s incorporting into mmonium (NH + 4 ) nd nitrte (NO 3 ). Fixed N flows through the food we (plnt niml humns/predtors). This fixtion process distinguishes the N cycle from the cron (C) cycle. From glol environmentl point of view, there is serious concern out the excessive growing fixed-n. Agriculture ccounts the lrgest frction (some 86%) of the totl humn-relesed fixed N (Jordn nd Weller, 1996). Nitrogen fixed y humn ctivity now exceeds the mount y ll terrestril nturl processes comined. Blnce studies hve reported tht the wys of N loss from soil due to uptke, leching, erosion, nd denitrifiction re replenished to vrying extents y iologicl N 2 -fixtion processes. When griculture is introduced into these systems, this nutrient cycle is roken nd the norml supply of nutrients for ny griculturl ctivity comes minly from the soil. Additionl nutrients must e supplied s externl inputs to mintin crop growth nd yield. Orgnic wstes, such s humn, niml, nd crop wstes, re used n sources of nutrients dded to the soil. There re mny 21

22 exmples of the disppernce of whole civiliztions due to diminished soil fertility nd productivity. Rivs et l. (2012) studied soil N dynmics fter severe forest fire nd reported tht the inorgnic N concentrtions were typiclly greter or equl to those of control sites in the first yers fter fire (Smithwick et l.; 2005; Turner et l., 2007; Boerner et l., 2009). An increse in net minerl N in forest soil fter fires cn e ttriuted to higher soil ph, N relese from ded roots nd previously inccessile N forms, incresed nion exchnge cpcity nd decresed N immoiliztion due to loss of C inputs fter fire. There were dynmics in the N cycling. A decrese in net N minerliztion would e the result of incresed C/N rtio of the remining soil orgnic mtter (SOM), decrese in SOM quntity nd qulity occurred s result of pyrolysis, nd reclcitrnt chr production or n increse in N immoiliztion due to enhnced microil ctivity nd/or increses in orgnic C nd phosphorus (P) concentrtion. Therefore, chnges in the composition or undnce of microil nd plnt communities re crucil in influencing internl N cycling in soil. Nitrogen Losses into the Environment In modern society, when the nturl orgnic wste dditions cnnot meet the need of crop production, fertilizers nd severl other mterils hve een used s dditionl sources of nutrients, especilly for the N. The significnce of N originting from fertilizer inputs for nnul crop N requirements hs een evluted y growing test crop under unfertilized conditions (Glendining et l., 1996; Bhogl et l., 2000; Sieling et l., 2006). The excessive N lods my cuse n increse of N loss from the soils though denitrifiction (nitrous oxide (N 2 O) emission), voltiliztion, nd leching, etc. It is estimted tht the nthropogenic N 2 O emissions to the tmosphere re out 3 8 Tg N nnully nd griculturl systems imprt lrge portion of nthropogenic emissions (Mosier nd 22

23 Kroeze, 1998). Bouwmn (1996) reported simple liner reltionship to relte the totl nnul direct N 2 O emission (E) from fertilized fields to the N fertilizer pplied (F): E= F. The emission fctor, 1.25± 1% of N fertilizer pplied, given y Bouwmn, hs een dopted y Intergovernmentl Pnel on Climte Chnge (IPCC) s the defult emission fctor to clculte the emission of N 2 O ffected y N fertilizer pplied. This emission fctor mkes the methodology for clculting emissions simple nd trnsprent. However, there re still disdvntges on the lrge uncertinties nd impossiility to distinguish vrious regions, crop type nd wether ptterns (Ruser et l., 2001; Kuikmn et l., 2006). Smith (1998) reported tht in Scotlnd the verge emission fctor ws less thn the defult vlue of 1.25% of the minerl N pplied, nd suggested lower temperture my ccount for this difference. Doie (1999) reported tht the emission fctor differed gretly mong grsslnd, potto, roccoli, nd grin cerel crops. Therefore, IPCC in 2001 suggests tht the direct N 2 O emission from soil my require etter clcultion sed on different regions. Orgnic mendment, s prcticl mnner, hs een widely used for improving soil fertility. The type of mendment is vitl fctor ffecting nitrous oxide emission (Shelp et l., 2003). Aulkh (1991) reported tht the C/N rtio of the orgnic mendments gretly ffect the mount of N 2 O emission, y ffecting minerliztion nd immoiliztion rte of N in soil. Higher C/N rtios (>30) my led to immoiliztion of minerl N nd microorgnisms decompose orgnic residue nd incorporte minerl N into their iomss. A reltive low C/N rtio (<20) in plnt residue shows high minerliztion rte, which NO3 cn e tken up y the plnts. C/N rtios could e good predictor for N 2 O emission. In the erly stge, Bremner nd Blckmer (1981) reported negtive reltionship etween these two fctors. Hung et l. (2004) reported tht the reltionship etween N 2 O emission nd C/N rtio is linerly negtive, with 23

24 correltion coefficient (R 2 ) rnging from to Amendment of orgnic residues my significntly increse the rte of soil respirtion nd develop neroic environment more rpidly, which will trigger more N 2 O emission (Ding et l., 2006). Hung et l. (2004) nd McKenney et l. (1993) reported tht the emission rte of N 2 O decresed significntly y dding whet strw nd sugrcne stlk, s compred with other mterils in cly soils. Also, in sndy cly loms, niml mnure nd slurry generted more N 2 O emission thn minerl N fertilizer (Lughlin, 2001; Khlil et l., 2002). By integrting N immoiliztion dt, Vigil nd Kissel (1991) reported the rek-even point etween net N immoiliztion nd minerliztion of orgnic residues ws t C/N rtio of 41. Therefore, some orgnic mendments, such s + sugrcne stlk nd whet strw, which hve C/N rtio greter thn 41, my stimulte NH 4 immoiliztion nd N 2 O consumption, nd hence reduce N 2 O emission. Senyrm et l. (2012) nd Jhngir et l. (2011) studied the reltionships etween N nd C sources in reducing N 2 O emissions y pot incutions in the l. A microscle for exploring processes tht occur in deep soil horizons ws used in oth of their studies. Additions of different C sources to the soil vi fertiliztion or crop residue incorportion my increse denitrifiction. Senyrm et l. (2009) quntified the increse in denitrifiction nd concluded tht ppliction of orgnic mtter with high lile C content to fertilized griculturl soils my led to denitrifiction-derived N 2 O emissions. Orgnic mendments used s lterntives to minerl N fertilizers my hve contrsting effects on greenhouse gs emissions, depending on soil C/N rtio. Leching nd erosion re nother mjor wy for N loss in terrestril systems, which re estimted to rnge from 1 to 100 kg h -1 yer -1 (Teixeir et l., 2004). Microorgnisms ply n importnt role in improving soil fertility y metolizing N, which cnnot e uptken y plnts 24

25 directly. Once orgnic N is minerlized nd converted into NH + 4 nd susequently into NO 3, it cn e lost vi leching. The minerl forms of N re very solule nd cn e esily leched into surfce run-off nd groundwter, especilly nitrte (NO - 3 ) nd ure (CO(NH 2 ) 2 ) (Redhimn, 2000; Umr nd Iql, 2007)). However, the process of iologicl conversion is time-consuming nd the movement of NH + 4 in the soil is limited y inding to the ction exchnge complex (CEC) of cly prticles nd soil orgnic mtter. Inpproprite N fertilizer ppliction nd mngement, which exceed the need of crop production, my trigger lrge N leching losses. During leching, the losses of minerl N re often ccentuted y n undnce of precipittion comined with low evpotrnspirtion losses, which enhnce wter sturtion, leding to susurfce or surfce wter flow, especilly in fllow period (Legg, 1982). Leching loss of N from orgnic mteril depends minly on two fctors. The first is the net mount of orgnic N tht is minerlized nd converted into NO 3. Secondly, once the orgnic N is nitrified to NO 3, sufficient wter hs to e present to llow downwrd movement (Legg, 1982). However, if there is too much wter, the soil ecomes wterlogged nd NO 3 will e lost y denitrifiction. Soil texture is n importnt property tht determines how much NO 3 is lost y leching or denitrifiction. A cly soil with hevy texture hs lower hydrulic conductivity thn lighter, sndy soil. Therefore, in hevy textured soil, NO 3 is more susceptile to denitrifiction, wheres in sndy soil, leching is more likely to e the min mechnism of NO 3 loss. The leched nitrte from griculturl lnds is considerle nd contmintes groundwter, rendering it unfit for humn consumption. The increse of N in surfce wter will hve incresed iologicl productivity nd rings out eutrophiction, which generte undesirle chnges 25

26 including prolifertion of lge nd qutic mcrophytes, dissolved oxygen depletion, nd decrese in wter clrity (Conley et l., 2009). While severl rel nd potentil helth nd environmentl impcts of N exist, griculture nd environmentl prctices hve mjor effects only on those impcts which involve excessive nitrte in drinking wter, eutrophiction, nd perhps on O 3 depletion (Mhvi et l., 2005; Ju et l., 2007). Few studies did intelligent risk ssessment nlyses of these impcts, especilly when humn helth s well s socil gols nd vlues re involved. The growing worldwide demnds for food will involve continued increse in the use of fixed N in griculture, most of which must come from fertilizers. However, the gret willing of mking etter world with environmentl sfety tell us the importnce in mnging N oth in griculture nd environmentl qulity (Jmes et l., 2011; Stevenson, 1982). Impliction of C/N Rtio in Nitrogen Mngement The key prolem in mnging N for griculture is to chieve the lnce etween N supply nd crop demnd without excess or deficiency (Cssmn et l., 2002). A definition of nutrient mngement cn e reported t USDA s Nturl Resources Conservtion Service (NRCS) prctice stndrds: mnging the mount, source, plcement, form, nd timing of the ppliction of plnt nutrients to the soil (USDA, NRCS, 2006). Severl scientists studied N-use efficiency (NUE, lwys ssessed y C/N rtio) s n indictor to check the mngement of N in griculture. They define NUE of cropping system s the proportion of ll N inputs tht re removed in hrvested crop iomss, contined in recycled crop residues, nd incorported into soil orgnic mtter nd inorgnic N pools. The excessive N is lost from the cropping system nd thus contriutes to the rective N lod to the environment. (Hussin et l., 1996; Timsin et l., 2001; Zheng et l., 2007; Gju et l., 2011). 26

27 Since Clvert (2004) presented the ide of proportionlity etween C nd N, C/N rtios hve een considered n importnt soil chrcteristic. The C/N rtio of the orgnic mteril dded to the soil influences the rte of decomposition of orgnic mtter nd this results in the minerliztion or immoiliztion of soil N. If the dded orgnic mteril contins more N in proportion to C, then N is relesed into the soil from the decomposing orgnic mteril. On the other hnd, if the orgnic mteril hs less mount of N in reltion to the C, then the microorgnisms will utilize the soil N for further decomposition nd the soil N will e immoilized nd ecome unville to plnt. The soil C/N rtio is n importnt soil fertility indictor due to the close reltionships etween soil orgnic C nd totl N. Generlly, the C/N rtio of the surfce soil flls within nrrow rnges, usully out 10 to 12 for cultivted, griculturlly soils of temperte regions. However, there re mny fctors which ffect soil C/N rtio, such s climte (Miller et l., 2004), soil conditions (Diekow et l., 2005; Glntini et l., 2004; Ouédrogo et l., 2006; Ymshit et l., 2006), vegettion types (Frnzlueers et l., 2000; Puget nd Ll, 2005), nd griculturl mngements (Run et l., 1998; Dll et l., 2011; Ling et l., 2011). Boerg (2009) stted tht the C/N rtio of n orgnism in soil reflects how much C, which microorgnisms requires for iomss production, in reltion to N. For plnts, C cn e used s energy source nd therey lost s cron dioxide. To produce iomss nd lnce the need, the C/N rtio of the sustrte must e higher thn tht of the microorgnism nd the C/N rtio of the new orgnism will e lower thn the sustrte. Moreover, N is essentil to produce the protein rich microil cells. Inorgnic N is immoilized into cteril cell when the metolized orgnic sustrte hs high C/N rtio (Azim et l., 2008; Kirky et l., 2011). The C/N rtios of microil orgnisms re reltive constnt nd the rnge of fungi nd cteri is in the rnge

28 nd 5-18, respectively (Chpin et l., 2002; Rousk, 2009). For generl soil, microil iomss my vry with the fungl/cteril rtio, while rnge of 10:1 to 12:1 is recommended (Griffin, 1972). Therefore, when pplying N fertilizers or orgnic mendments, such rtio rnge cn provide relile sis with which to determine the extent of ville C nd the stilizing nutrients nd to consider implictions for mngement strtegies to optimize retention of stle ville N in soils. Nitrogen minerliztion depends not only N concentrtion of the sustrte, ut lso the decomposility (Jnssen, 1996). Although plnts cn only tke up the inorgnic forms (NH 4 nd NO 3 ), it my lso return orgnic N compounds to the soil in litter fll. Vegettion therefore influences N minerliztion nd nitrifiction through competition with microes for nutrients nd through litter qulity nd quntity (Vitousek et l., 1982). The rek down of orgnic residues y microes is dependent upon the C/N rtio. Hoormn nd Islm (2010) conducted study on compring two seprte feed sources, young tender lflf plnt nd ot or whet strw. Young lflf plnt hs more crude protein, mino cids, nd lower C/N rtio, which mke it much esier for microe to digest. However, ot nd whet strw hs more lignin, less crude protein, nd less sugrs in the stlk nd high C/N rtio. It needs more time nd N to rek down the high cron source nd e decomposed y microes. Therefore, reltive low N content or high C/N rtio is ssocited with slow soil orgnic mtter decy nd generlly, immture or young plnts hve higher N content, lower C/N rtios, nd fster soil orgnic mtter decy (Lewis nd Ppvizs, 1974). As well for composting, the initil C/N rtio is one of the most importnt fctors (Michel et l., 1996). A C/N rtio less thn 20 llows the orgnic mterils to decompose quickly while C/N rtio greter thn 20 requires dditionl N nd slows down decomposition. If considerle 28

29 mount of C is in the form of lignin or other resistnt mterils, the ctul C/N rtio could e lrger thn 20. Generlly, initil C/N rtios of re considered idel for composting (Kumr et l., 2010). If high C sed mteril with low N content is pplied to the soil, the microes will tie up soil N, though it will e eventully relesed. Recently some reserchers hve successfully conducted composting t lower initil C/N rtios from (Hung et l., 2004; Zhu, 2007; Ogunwnde et l., 2008; Kumr et l., 2010). Composting t lower initil C/N rtios cn increse the mount of mnure treted, ut cn lso increse the loss of N s mmoni gs. As the soil orgnic mtter decomposes, the C/N rtio of most plnt residues tends to decrese due to the gseous loss of CO 2. Therefore, the percentge of N in the residul SOM rises s decomposition progresses. The C/N rtio influences the two min decomposing groups, cteri nd fungi, in soils. Bcteri re the first microes to digest newly input orgnic plnt nd niml residues in the soil. Bcteri hve high N content in their cells nd re generlly less efficient t converting orgnic C to new cells. The reltive importnce of decomposition y fungi is tht it cn help decrese the ppliction of N fertilizer (vn Groenigen et l., 2007), while orgnic mtter with high C/N rtio is elieved to stimulte the fungl contriution to decomposition (Henriksen nd Brelnd, 1999; Thiet et l., 2006). For most of the soil, the typicl C/N rtio is round 10, which mens the N is ville to the plnts. The 10:1 C/N rtio of most soils reflects n equilirium vlue ssocited with most soil microes (Bcteri 3:1 to 10:1, Fungi 10:1 C/N rtio). The C/N rtio theory lso pplied in mny griculturl prctices in N mngement, such s cover crops, crop rottion, orgnic mendments, etc. Mny crop production prctices hve the potentil to crete dverse environmentl impcts with respect to N. Due to the intensified crop mngement, such s greter inputs of N fertilizers (Tilmn et l., 2002; Erismn et l., 2008), 29

30 the glol cerel production douled in the pst 40 yers. However, not ll of the pplied N cn e tken up y plnts. When the nturl cpcity of system to cycle N is exceeded in given loclity, the excessive N my e ccumulted in the ground or surfce wters nd lrge mounts of NH 3 or N 2 O my e lost to the tmosphere. The sources of N re diverse. Usully, exogenous N is from the residues of plnt, niml origin nd fertilizers. Techniques re estlished for minimizing N losses nd mximizing N efficiency, including efficient griculturl mngement, innovtive pplictions of griculturl technology, regultions limiting fertilizer pplictions, nd possile even chnges in fundmentl ptterns of lnd use nd crop production (Stevenson, 1982). In generl, prctices which decrese soil erosion nd surfce runoff will lso reduce the mount of N lost from croplnds y these routes. As nutrient mngement tool, the use of cover crops in cropping systems is n importnt strtegy. Cover crops, lso clled green mnure, cn e defined s close-growing crops tht provide soil cover, nd soil improvement etween periods of norml crop production (SSSA, 1997). They re not grown for mrket purpose nd re well suited for conservtion griculture. Growing cover crops in rottion cn reduce erosion through greter levels of soil cover s well s improve soil fertility nd suppress weeds (Flower, 2011). Cover crops cn e leguminous or nonleguminous. Legume cover crops fix tmospheric N into form plnts nd microorgnisms cn use nd thus they re used s source of N (Smith et l., 1987). Non-legume species recycle existing soil N nd cn reduce the risk of excess N leching into groundwter (Meisinger, 1991). There is interest in growing leguminous cover crops, such s red clover (Trifolium prtense L.) nd hiry vetch (Vici villos L.), prticulrly on erodile soils (Goss et l., 1995). These leguminous cover crops pply one more potentil on N fixtion through iologicl pthwys, which cn enefit in reducing the need of N fertilizer for 30

31 succeeding crops (Singh et l., 2004). Nonleguminous cover crop cn ccumulte inorgnic soil N nd hold it s n orgnic form, which cn reduce the minerl N leched from the soil nd leve the soil re. Cover crops cn reduce the potentil for percoltion y extrcting wter from the soil, reducing the potentil for percoltion nd consequent leching (Chpot et l., 1990). The holding N will e relesed fter decomposition of the cover crops. Blck ot (ven strigos Schre.) is widely used s cerel cover crop due to its rpid growth, high iomss production in southern Brzil nd some re in USA. As cerel, it hs high C/N rtio, which leds to slower decomposition rte nd hence possile immoiliztion of soil N following some cerel cover crops (Flower, 2011). Rye (S. cerele L.), cerel, hd gret potentil on ccumulting the residul inorgnic N fter corn hrvest (McCrcken et l., 1994). In ddition to fixing N, severl studies reported tht cover crop could reduce the potentil for nitrte leching from the frm fields (Owens, 1990; Brndi-Dohrn et l., 1997; Stver nd Brinsfield, 1998). Meisinger et l. (1991) conducted study on the impcts of cover crop on nitrte leching nd showed tht cover crops reduced oth the mss of N leched nd NO 3 concentrtion of lechte y 20 to 80% re compred with no cover crop control. Frncis et l. (1998), Shepherd (1999), nd Rsse et l. (2000) reported tht incorporting nonleguminous cover crop in cropping system hs reduced nitrte leching since the cover crop cn reduce wter percoltion nd lso effectively use of nitrte. Cover crops re sometimes plnted fter the principl crop hs een removed to control erosion. Reduction in soil erosion y cover crops is ssocited with incresing in soil orgnic mtter content, which improve soil wter infiltrtion nd holding cpcity. However, there re still some possile disdvntges of cover crop. If cover crop hs very high C/N rtio, it my crete N deficiency for the succeeding crop if excessive N is immoilized nd not relesed in 31

32 timely mnner (Vyn et l., 1999). Moreover, dverse wether often prevents plnting or growth of the cover crop. Crop rottion is prctice, which cn reduce the requirement of N fertilizer. Crop rottion is to plnt different crops on the sme field in successive yers nd usully, the cropping sequences chnge with specilized frming. For exmple, corn-soyen is common rottion group. Soyen cn scvenge residul fertilizer N from the corn crop. John et l. (1975) estimte tht out 40% residul N is removed y soyen. A recent study y Hons (2005) reported tht the 60% increse in lint yield of unfertilized cotton under rottion ws ttriuted to incresed soil orgnic mtter (SOM), totl N, residul nitrte N, nd wter content. Reddy et l.. (2006) lso reported tht the improved cotton growth in rottion with corn ws ttriuted to increse SOM. The sequence of crop rottion is very crucil. Root exudtes from plnts cuse chnge in microil community composition nd iomss nd my depend on plnt species-specific differences in the qulity of resources (e.g. cron) input (Ldygin nd Hedlund, 2010). Plnts tht hve high C/N rtio my increse N immoiliztion nd use up the residul N, which my decrese the yield of next crop. Orgnic mendments, including frmyrd mnures, slurries, sewge sludge, green wstes nd composts, cn increse soil fertility nd qulity to improve crop productivity nd yields (Lupwyi et l., 2005; Fgeri, 2007). Orgnic mendments cn improve the physicl properties of the soil, such s wter-retention cpcity, ulk density nd soil structure. Moreover, the ppliction of orgnic mendments increses soil nutrients, which cn reduce the need for inorgnic fertilizers (Bellmy et l., 1995; Burgos et l., 1996; Brker, 1997). Severl types of orgnic mendments hve een used for improving crop production. Steffen et l. (1995) discussed comprtive tomto yields of conventionl griculture system nd 32

33 n ecologiclly oriented system, which emphsized the uilding up of orgnic mendments. The ltter system hd greter soil wter holding cpcity nd shrply reduced irrigtion requirements. Moreover, the yield of NO.1 fruit ws 55%-60% greter thn the other one. We nd Biggs (1988) exmined the effects of dding humte s orgnic mendment on the growth of citrus. Trees treted with humte exhiited higher wter uptke nd produced more vigorous growth flushes. Foley et l. (2002) studied the pper mill residue pplied s n orgnic mendment to increse vegettion production. Pper mills wste re the residues comining the primry residues from pper mking process with the secondry wstewter tretment sludge nd hve C/N rtio less thn 20:1. It ws pplied in the Centrl Snds region of Wisconsin incresed the wter holding cpcity nd plnt-ville wter y 33%-80%. The utiliztion of orgnic wstes s mendments hd n efficient nd low cost-effective method of disposl these products. Shrifi et l. (2008) compred the field with or without history of orgnic mendment (Solid eef (Bos turus) mnure) in potto (Solnum tuerosum L.) production. The results showed tht historiclly mended soil hd 35% higher vlues of potentilly minerl N nd 8% higher proportion of minerl N prtitioned to the stle minerl N pool. The long-term ddition of mendments results in importnt chnges in ctive nd stle soil orgnic-c nd -N frctions tht cn influence soil N dynmics. Single pplictions of orgnic mendments contriute smll mount to minerlized N in the susequent yer, the comined contriutions of orgnic N from repeted pplictions cn led to sustntil increse in soil N minerliztion potentil (Eghll et l.., 2004; Flvel nd Murphy, 2006; Mllory nd Griffin, 2007). The incresed soil N minerliztion potentil cn led to higher soil N supply nd susequently reduce the need for fertilizer N. 33

34 Orgnic mendments my lso ffect crop yield through disese suppression. In some cses, orgnic mendment my relese toxic compounds to directly inhiit the pthogens, such s isothiocyntes relesed from degrdtion of rssicceous mteril (Lzzeri nd Mnici, 2001), or increse microil iomss nd ctivity to suppress disese (Biley nd Lzrovits, 2003). Ayongw et l. (2011) studied the orgnic mendment impct on host-prsite dynmics of sorghum icolor nd strig hermonthic nd high qulity mendment will hve negtive impct on S.hermonthic severity nd incidence. C/N rtio descries the orgnic mtter qulity; where-in high-qulity orgnic mtter hs low C/N rtio nd low-qulity orgnic mtter high C/N rtio. Some orgnic wstes tht re rich in N cn relese lrge mounts of minerl N through minerliztion nd improve fertilizer efficiency. When minerl N exceeds the mount needed to fill the gp etween crop uptke needs nd the supply from theses sources, Excessive N my e lost y leching nd denitrifiction to the environment. Therefore, the chnge of N dynmics fter pplying orgnic wstes need to e recorded to ccess effective use of the mteril, minimizing the losses of nitrte in lechtes nd voiding negtive environmentl effects tht it my cuse in groundwter. Burgos et l. (2006) compred 3 orgnic mterils, municipl solid wste compost, non-composted pper mill sludge, nd groforestry compost on the N dynmic of sndy soil. All of these three mendments hd different immoiliztion N periods followed y positive minerliztion. Due to the different C/N rtios, the first mendment hd higher nitrteleching rte. Nevertheless, the nitrte losses represented low mount compred with the totl N dded to soil. Rdersm nd Smit (2010) evluted the effect of pper pulp s orgnic mendments on the N loss from fodder rdish nd found tht dding pper pulp led to strong decrese in denitrifiction nd N leching. 34

35 Conclusions nd Perspectives Nitrogen is n essentil mcronutrient for plnt growth. A deficiency of N my cuse symptoms in plnt leves nd stunt plnt growth, while n dequte supply of N in the soil gretly promotes rpid plnt growth nd crop yield. Nitrogen undergoes wide vriety of trnsformtions in soil, most of which involve the orgnic frctions. An internl N cycle exists in soil prt from the overll cycle of N in nture. Even if N gins nd losses re equl, the N cycle is not sttic. Continuous turnover of N occurs through minerliztion nd immoiliztion. Soils vry gretly in their N contents. Nitrogen content of the soil decline gretly during continued cultivtion. Humn ctivities, prticulrly fertilizer N use, my enhnce iologicl N fixtion nd increse mss flow of fixed N. Excessive ccumultions of N my ring dverse effects from the glol environmentl point of view. Therefore, griculturl prctices in the future will focus more on conserving energy nd minimizing dverse environmentl effects rising from the use of N fertilizers. Approprite N mngement nd fertilizer ppliction should e concerned so s to protect N from leching nd denitrifiction. Conventionl N fertilizer will continue to e used ut in efficient method, nd new fertilizers will e developed to chieve specific relese rte with ctive uptke y the plnts. Nitrogen in orgnic mterils is grdully minerlized fter pplied to the soil, nd prt of tht plnt ville N is tken up y crops, immoilized in the SOM pool, or lost in gseous form or through leching. Relese of sustntil mount of N from medium to low qulity orgnic resources often continues eyond growth seson, potentilly resulting in significnt residul effects. Mny techniques, such s erosion control, improved irrigtion, incresed use of legume crops, cover crops, nd orgnic mendments, cn e pplied to improve the efficiency of N use. 35

36 Their effective utiliztion involves ppliction of systems nlysis pproches to frming, nd lso lters iologicl ctivity y chnging C/N rtio in the soils. More studies re needed to identify effective mendment to soils in order to reduce N loss, nd other techniques will e developed s the socil nd economic pressure for efficient N mngement increses. While severl rel nd potentil helth nd environmentl impcts of N exist, griculture nd environmentl prctices hve mjor effects only on those impcts which involve excess nitrte in drinking wter, eutrophiction, nd perhps on O 3 depletion (Mhvi et l., 2005; Ju et l., 2007). Seldom reserches indicted intelligent risk ssessment nlyses of these impcts, especilly when humn helth nd socil gols nd vlues re involved. However, the growing worldwide demnds for food will involve continued increse in the use of fixed N in griculture. Most of this increse must come from fertilizer. Moreover, the gret willing of mking etter world with environmentl sfety tell us the importnce in mnging N oth in griculture nd environmentl qulity (Jmes et l., 2011, Stevenson, 1982). 36

37 CHAPTER 2 ORGANIC AMENDMENT EFFECT ON NITROGEN TRANSFORMATION IN SOILS Introduction Nitrogen (N) is mjor nutrient element for citrus production. In United Sttes, out 75% of the citrus production comes from Florid nd out 28% of Florid citrus crege is on sndy Entisols long the centrl Florid ridge (Mttos et l., 2003). In sndy soils, ppliction of N in excess of tree requirements, indequte plcement nd timing, or irrigtion scheduling my result in leching of nitrte (NO 3 - ) elow the root zone (Alv nd Tucker, 1999). For citrus growth, the minerliztion of N from soil orgnic mtter, crop residues, composts, nd niml mnure contriute significntly to the soil minerl-n reserve. The ppliction of orgnic mendments increses soil nutrients, thus reducing the need for inorgnic fertilizers (Bellmy et l ; Bker, 1997). Moreover, the use of orgnic mendment is common prctice to improve soil conditions nd physicl properties, such s wter retention cpcity, ulk density nd soil structure (Entry et l., 1997). For environmentl mngement of N from orgnic mendment, fctors nd processes tht ffect the extent nd rte of conversion of orgnic N to plnt ville N or loss to the environment should e ccounted for (He et l., 2000). Plnt ville N is defined s the sum of the minerl N, minly s initil nitrte nitrogen (NO 3 -N) nd mmonium nitrogen (NH 4 -N) content in soil, plus the orgnic N minerlized (Gilmour nd Skinner, 1999). During the minerliztion process, soil microorgnisms trnsform orgnic N to inorgnic forms (NO 3 -N nd NH 4 -N). At the sme time, process of immoiliztion of inorgnic N tkes plce with the synthesis of proteins y microorgnisms (Brdy, 1990). This N dynmic system hs een descried s minerliztion-immoiliztion turnover (Jnsson nd Persson, 1982). This turnover cn e used to estimte net minerliztion rte or net immoiliztion rte under 37

38 different soil conditions or types. Better description nd knowledge on N dynmics cn provide more efficient use of orgnic nd inorgnic fertilizers nd minimize the N losses. Different chrcteristics of the orgnic mterils, soil texture nd properties, environmentl fctors, cn influence the rte of N minerliztion in soils (Sims, 1995). The C/N rtio of the orgnic mtter is inversely proportionl to the net N minerliztion (Appel nd Mengel, 1990). The optimum C/N rtio hs een reported to e etween 15 nd 40 (Crer et l., 2005). For the influence of soil texture, Scott et l. (1996) suggested tht smll pores protect orgnic mtter from microil ttck wheres lrge pores fcilitte N minerliztion. The soil microil iomss is nother importnt component of the soil orgnic mtter tht regultes the trnsformtion nd storge of nutrients (Mrtens, 1995). K 2 SO 4 -extrctle orgnic C incresed fter soil fumigtion with chloroform (CHCl 3 ) suggested tht procedure developed for evlution of iomss C could e used to mesure the dynmics of N in soils (Sott et l., 2007). The orgnic mendment used in this study is Hydr-Hume, commercil product from Helen chemicl compny. We nd Biggs (1988) studied the effects of humte-mended soils on the growth of citrus. Humte, humic cid, implies these sustnces re cidic, while they ctully re colloidl nd ehve like clys in soil. Humte cn e source of inorgnic nutrients tht re held y exchnge mtrices nd hs fundmentl effect on wter holding cpcity. However, the effect of this new commercil product to the N dynmics in soil is still unknown. The min im of this study is to investigte how Hydr-Hume ffects N dynmics nd determine the decomposition nd nutrient relese kinetics fter the orgnic mendment is pplied to different soils. An incution experiment ws conducted to estimte the N minerliztion. 38

39 Mterils nd Methods Soil Collection nd Chrcteriztion Two soils (one Alfisol nd one Spodosol) were collected from representtive commercil citrus groves in the Indin River re, south Florid. They were selected sed on soil properties. For ech loction triplicte smples were rndomly collected t 0-15 cm depth, with 3 soil cores eing comined to mke composite smple. After removing plnt mteril nd stones, the soil ws dried nd then sieved (<2 mm). Generl chrcteristics of the study sites re presented in Tle 2-1 nd Figure 2-1. The soil smples were ir-dried, ground, nd pssed through 2-mm sieve prior to physicl nd chemicl nlyses. Soil ph (1:1 soil: wter rtio) nd electricl conductivity (1:2 soil: wter rtio) were mesured in deionized wter using ph/ion/conductivity meter (Denver Instrument, CO). Totl soil cron (C) ws determined y comustion using C/N nlyzer (Vrio MAX CN Mcro Elementl Anlyzer; Elementl Anlysensystem GmH, Hnu, Germny). Incution Study nd Soil N Dynmics Anlysis Portions of soil smple (ech 500g oven-dry sis) were weighed into Ziplock plstic gs ( cm, 3.74 L cpcity). The pellet orgnic mendment ws ground to pss 1-mm sieve efore it ws mixed into the soil. The ppliction rtes of orgnic mendment were: 0, 112, 224, 448, 560 kg h -1 soil, respectively. The mixtures were incuted t 25 C in fter its moisture ws djusted to 70% of its field-wter cpcity. Wter losses were compensted y the ddition of distilled wter during the experiment. At the intervls of 0, 7, 14, 21 nd 28 d, susmples were tken from the incution gs nd nlyzed for ph, electricl conductivity (EC), soil ville N nd microil iomss. For ech tretment, there were three replictions nd the experiment ws followed completely rndomized design, in order to reduce the other influences. 39

40 Soil ph ws mesured in slurry with deionized wter nd 1 M KCl solution t solid: solution rtio of 1:1 using ph/ion/conductivity meter (ph/ Conductivity Meter, Model 220, Denver Instrument, Denver, Co). Electricl conductivity ws mesured in slurry with deionized wter t solid: wter rtio of 1:2 using the sme ph/ec meter. Extrctle NH 4 -N nd NO 3 -N ws determined y shking 5 g ir-dried smple in 25 ml 2 M KCl for 1 h. Concentrtions of NH 4 -N nd NO 3 -N in the filtrte were nlyzed with N/P Discrete Auto-nlyzer (EsyChem, Syste Scientific LLC, Ok Brook, IL). The net N minerlized due to the pplied orgnic mendment ws clculted y the difference etween inorgnic N in ech tretment nd the control soil. Dt Anlysis All dt were nlyzed using SAS progrm (version 8.2, SAS Institute, 2004). Differences in the soils with different orgnic mendment pplictions were tested y mens of one-wy nlysis of vrince (ANOVA). Significnt sttisticl differences of the men vlues of the dependent vriles etween tretments were estlished nlysed to Tukey s test (P<0.05). Results nd Discussion Effects of Orgnic Amendment on Soil ph nd EC The Alfisol is clcreous nd contined slightly less ville N thn the Spodosol (Tle 2-1). The Spodosol is cidic in nture, ut the ph ws rised y liming to close eing neutrl. Both soils re very sndy, with more thn 90% snd, nd hd low orgnic mtter (<1% orgnic C). Appliction of orgnic mendment slightly incresed soil ph initilly due to the relese of lkline sustnces from decomposition of the product (Butterly et l., 2010; Xu et l., 2006). The soil ph decresed with the incution time, proly due to relese of orgnic cids with further decomposition of the orgnic mtter (Fig. 2-2, Fig. 2-3). In ddition, C nd Mg from the orgnic mendment cn replce hydrogen ion (H + ) on the soil exchnge complex, thus 40

41 decresing soil solution ph. However, even t the highest ppliction, soil ph ws out 7.3 to 7.5, which is suitle for most crops. Fertilizers contining NH + 4 cn induce soil cidifiction due to nitrifiction of NH + 4 to NO - 3, which produces H + (Chien et l., 2010). Therefore, for the tretments with chemicl fertilizer, ph decresed more thn those receiving Hydr-Hume lone. The ph chnges in Spodosol hd similr trends. The sndy soils hd low EC (<500 μs/cm) ecuse of its low holding cpcity. Orgnic mendment ddition didn t hve significnt influence on soil EC vlues (Figs.2-4 nd 2-5). The soil EC vlues gretly incresed with ddition of fertilizer, ecuse of the incresed mounts of minerl ions. Even t the highest ppliction rte, the EC vlues of the mended soil were still elow 800 μs/cm, which is criticl level for most crop growth. Therefore, ppliction of Hydr-Hume t the rtes <560 kg h -1 should not hve ny significnt negtive impct on crop growth sed onsoil ph nd EC. The EC chnges in Spodosol hd similr trends. Effects on N Dynmics in Soils In the first two weeks, ppliction of orgnic mendment slightly incresed KCl extrctle NH 4 -N in the Alfisol (Fig. 6). Compred with other orgnic mterils, Hydr-Hume hd reltive smll N content (1.31%), thus, no significnt difference ws oserved mong the different tretments. The increse in NH 4 -N is proly ttriuted to the minerliztion of orgnic mendment nd relese of NH 4 -N from decomposition of orgnic mtter. The concentrtion of NH 4 -N in the third week decresed mrkedly initilly nd continued to decrese with time to lmost zero for ll the tretments. This ehvior hs een reported in eroic incution experiments (Snchez et l., 1997; Mdrid et l., 2001; Burgos et l., 2005). The decrese in NH 4 -N ws generlly ccompnied y corresponding increse in NO 3 -N, indicting tht the NH 4 -N relesed from the orgnic mendment minerliztion ws nitrified into the NO 3-41

42 N (He et l., 2000), s ws shown in Figures 2-6 nd 2-7. Nitrte contents in the tretments tended to increse until the end of incution period. The difference in originl C/N rtio etween the two soils ffected the minerliztion rtes of orgnic mendment in the soils. The C/N rtio of Spodosol is 13.58, which is elow the criticl level for net minerliztion process, while the C/N rtio for Hydr-Hume is (greter thn 30), which my induce net immoiliztion of minerl N in soil. Therefore, in the first two weeks, ppliction of orgnic mendment in Spodosol slightly decresed KCl extrctle NH 4 -N (Fig. 7). With the incution time, ppliction of orgnic mendment slightly incresed NH 4 -N content, due to the minerliztion of orgnic mteril nd relese of NH 4 -N from decomposition of orgnic mtter. The generl trend of NH 4 -N chnge in Spodosol is similr to tht in Alfisol. The orgnic mendment ppered to hve miniml effect on NO 3 -N, s there ws no difference in NO 3 -N concentrtion etween the mended soil nd the control (without mendment) when it ws mesured on the first dy (mesured immeditely fter eing mixed). For Alfisol, tretments with only Hydr-Hume tended to decrese NO 3 -N content in the first two weeks t n ppliction rte of 224 kg h -1 nd ove, ecuse of net immoiliztion induced y ddition of Hydr-Hume (Fig. 8). However, when the soil ws mended with fertilizer nd Hydr-Hume, the dditionl minerl N from fertilizer my promote minerliztion, thus offsetting the effects of orgnic mendment, while the control still hd the highest NO 3 -N contents, indicting net immoiliztion during the incution period (Fig. 9). The difference of soil C/N rtio itself my hve impcts on N dynmics in soils. For Spodosol, ppliction of Hydr-Hume only mrkedly decrese NO 3 -N contents, while when mended with Hydr-Hume 42

43 together with chemicl fertilizer, net minerliztion process occurred. Sttisticl nlyses re listed in Tles 2-2 nd 2-3. Conclusion Appliction of Hydr-Hume, n orgnic mendment with C/N rtio round 42.13, induced immoiliztion when pplied lone in oth of the test soils. For Alfisol, the immoiliztion process only occurred in the first two weeks with the ppliction rtes of Hydr- Hume of 224 kg h -1 or ove. Soil originl properties hve n effect on N dynmics. The difference of C/N rtios in the two soils determined the different N dynmic trends when fertilizer nd orgnic mendment pplied together. The N dynmics in Alfisol, which hd the C/N rtio round 22, showed net immoiliztion, while in Spodosol, there ws net minerliztion curve insted. 43

44 Figure 2-1. Smpling site 44

45 HH rte (kg h -1 ): Without fertilizer With fertilizer Figure 2-2. Effect of orgnic mendment on Alfisol ph s function of incution time Without fertilizer HH rte (kg h -1 ): With fertilizer Figure 2-3. Effect of orgnic mendment on Spodosol ph s function of incution time 45

46 Without fertilizer HH rte (kg h -1 ): With fertilizer Figure 2-4. Effect of orgnic mendment on Alfisol Electricl conductivity (EC) s function of incution time Without fertilizer HH rte (kg h -1 ): With fertilizer Figure 2-5. Effect of orgnic mendment on Spodosol electricl conductivity (EC) s function of incution time 46

47 HH rte (kg h -1 ): Figure 2-6. Effect of orgnic mendment on KCl-extrctle NH 4 -N in Alfisol HH rte (kg h -1 ): Figure 2-7. Effect of orgnic mendment nd fertilizer on KCl-extrctle NH 4 -N in Spodosol 47

48 HH rte (kg h -1 ): Figure 2-8. Effect of orgnic mendment on KCl-extrctle NO 3 -N in Alfisol HH rte (kg h -1 ): Figure 2-9. Effect of orgnic mendment nd fertilizer on KCl-extrctle NO 3 -N in Spodosol soil. 48

49 HH rte (kg h -1 ): Figure Effect of orgnic mendment on KCl-extrctle NH 4 -N in Spodosol HH rte (kg h -1 ): Figure Effect of orgnic mendment nd fertilizer on KCl-extrctle NH 4 -N in Spodosol 49

50 HH rte (kg h -1 ): Figure Effect of orgnic mendment on KCl-extrctle NO 3 -N in Spodosol Figure Effect of orgnic mendment nd fertilizer on KCl-extrctle NO 3 -N in Spodosol 50

51 Tle 2-1. Generl properties of the two soils nd Hydr-Hume Properties/ Alfisol (Sndy,siliceous,hyperthermic,Arenic Soil type Glossqulf) Spodosol (Sndy,siliceous, Hyperthermic, Alfic Alquods) Cropping history Citrus Citrus Soil texture (g/kg) Snd 908, Silt 42.8, cly 9.6 Snd 902,silt 53,cly 45 ph (H 2 0) Electricl conductivity (μs/cm) Orgnic C (g/kg) Totl N (g/kg) C/N rtio Tle 2-2. Generl properties of the Hydr-Hume Properties ph EC N% C% C/N rtio Hydr-Hume

52 Tle 2-3. Sttisticl nlysis of KCl extrctle NH 4 -N in Alfisol KCl extrctle NH 4 -N (mg kg -1 ) in Alfisol HH rte (kg h -1 ) Smpling time (Dy) Without fertilizer With fertilizer c 0.30c 0.29 c *Mens followed y different letters within the sme row indicte significnce level t P<0.05 y the Duncn multi-rnge test. Tle 2-4. Sttisticl nlysis of KCl extrctle NO 3 -N in Alfisol KCl extrctle NO 3 -N in Alfisol HH rte (kg h -1 ) Smpling time (Dy) Without fertilizer With fertilizer *Mens followed y different letters within the sme row indicte significnce level t P<0.05 y the Duncn multi-rnge test. 52

53 Tle 2-5. Sttisticl nlysis of KCl extrctle NO 3 -N in Spodosol KCl extrctle NO 3 -N in Spodosol Without fertilizer With fertilizer HH rte (kg h -1 ) Smplin g time (Dy) c *Mens followed y different letters within the sme row indicte significnce level t P<0.05 y the Duncn multi-rnge test. 53

54 CHAPTER 3 ORGANIC AMENDMENT EFFECTS ON NITROGEN LEACHING Introduction Nitrogen (N) is nutrient often ssocited with ccelerted eutrophiction of surfce wters. It is estimted tht ech yer, more thn 1,000,000 kg N is trnsported to the St. Lucie Estury (SLE) (St. Lucie River Issue Tem Interim Report, 1998) nd the resultnt incresed nutrient lods hve een suspected to cuse declining wter qulity nd decresed grss coverge of the SLE nd Indin River Lgoon (IRL). In South Florid, high temperture nd the sndy nture of soils provide fvorle conditions for rpid minerliztion of orgnic mterils. As soils in this re hve corse texture (snd content often >90%) nd reltive low nutrient retention cpcity, citrus trees cultivted on these soils receive high rtes of fertilizer ppliction, which could increse the potentil risk of nitrte pollution to groundwter (He et l., 1999). Mrtin et l. (1994) reported tht light-textured soils nd intensive production of crops under irrigted conditions could led to considerle nitrte losses y leching. Soil mendments cn improve soil qulity y neutrlizing soil cidity nd incresing soil s holding cpcity for nutrients nd moisture nd is, therefore, very promising pproch to reduce lods of nutrients nd metls in surfce runoff. Environmentl mngement of N from orgnic mendment requires n understnding of the fctors nd processes tht influence the extent nd rte of conversion of orgnic N to forms plnt ville N or loss to the environment (He et l., 2000). In Chpter 2, it mentioned tht the influence of soil texture on N minerliztion is relted to cly content (Brelnd nd Hnsen, 1996). Smll pore spces protect orgnic mtter from microil ttck wheres lrge pores fcilitte N minerliztion. Moreover, other soil 54

55 chrcteristics, such s hevy metl content nd slinity, my lso ffect orgnic mteril decomposition nd N minerliztion. For soil qulity, microil iomss is n importnt indictor (Elliott et l., 1996). Orgnic C from the orgnic mteril my enhnce the growth of microorgnism, thus incresing microil iomss. In Florid, mny soils re extremely sndy with low dsorption cpcity for ions; therefore, microil iomss cn e sensitive indictor to the chnge of N dynmics in soils. The mjor ojectives of this study were to 1) investigte the effect of orgnic mendment on N leching in soils, 2) evlute the effect of orgnic mendment on N vilility in soil nd 3) ssess potentil environmentl risk of hevy metls from the soil mended with Hydr-Hume. Mterils nd Methods The tested orgnic mendment is Hydr-Hume, provided y Helen chemicl Compny, commercil product showing potentil for improving citrus growth in South Florid. However, its effectiveness for reducing fertilizer N loss is not well documented. The soils used in this leching study were collected from representtive commercil citrus grove (citrus) nd vegetle frm (vegetle). One is Alfisol nd the other is Spodosol, representing two mjor soil types for citrus nd vegetle production in the Indin River re. The relevnt properties of the tested soils re listed in Tle 2-1. The orgnic mendment ws ground to pss 1-mm sieve efore it ws mixed into the soil. Orgnic mendment ws pplied t the rtes: 0, 22.4, 44.8, 89.6, 112 kg h -1 soil, respectively. Fertilizer ws pplied t rte of 168 N kg h -1 (N-P 2 O 5 -K 2 O= ). The soil smples receiving no orgnic mendment or inorgnic fertilizer were used s the control. Plexigls leching columns (30.5cm long, 6.6cm inner dimeter), with severl 5mm dimeter holes t the ottom were used (Fig. 1). Aout 1.5 kg soil ws pcked into ech column to the 55

56 ulk density of pproximtely 1.45 mg cm -3 with mendment mixed in the top of the soil column. There re three replictions for ech tretment. The soil columns were sturted with deionized wter for three dys to llow soil compct nturlly nd equilirium of chemicl nd iologicl rections prior to leching. Leching ws conducted t 1, 3, 7, 14, 28, 42 dy, 302 ml of deionized wter eing leched for ech column per leching event, which is sed on hlf yer s rinfll in South Florid. The deionized wter ws pplied using peristltic pump nd the lechtes were then collected from ech leching event nd nlyzed for ph, electricl conductivity (EC), NH 4 -N, NO 3 -N nd metls. At the end of leching, the soils were removed from the column nd susmples were tken fter through mixture, ir-dried, nd mesured for ph, EC, ville N, Mehlich III extrctle metls nd microil iomss. Lechte ph nd EC were mesured using ph/ion/conductivity meter (ph. Conductivity Meter, Model 220, Denver Instrument, Denver, Co). Aville N (NH 4 -N, NO 3 -N) ws nlyzed using N/P Discrete Autonlyzer (EsyChem, Syste Scientific LLC, Ok Brook, IL). Aville metls were determined using n inductively coupled plsm opticl emission spectrometry (ICP-OES, Ultim, JY Hori, Edison, NJ). Electricl conductivity nd ph of soils fter leching were mesured in slurry with deionized wter t soil: wter rtio of 1:1 nd 1:2, respectively, using ph/ion/conductivity meter. Aville N (NH 4 -N, NO 3 -N) ws determined y shking 2.5 g ir-dried smple in 25 ml 2M KCl for 1h nd the concentrtions of NH 4 -N nd NO 3 -N in the filtrte were nlyzed with N/P Discrete Autonlyzer. Aville metls were determined y extrcting the smples with Mehlich III solution (Mehlich, 1984), nd mesuring the metl concentrtions using the ICPAES, following EPA method (EPA, 1998). 56

57 Results nd Discussion Effects of Orgnic Amendment on Soil ph nd EC Incorportion with chemicl fertilizer decresed lechte ph for oth soils, result from the nitrifiction of dded NH 4 -N (Fig. 3-2). Orgnic mendment generlly incresed lechte ph of the Spodosol for the first three leching events, s compred with the control (Fig. 3-2), wheres the difference diminished nd ll lechte ph tended to pproch 7.4 with incresing leching events. The decrese in lechte ph y soil mendment with incresing leching events ws ttriuted to orgnic cids relesed from the decomposition of the orgnic mtter during the leching process (Fig. 3-2). In ddition, C nd Mg from the orgnic mendment cn replce H + on the soil exchnge complex, nd thus decresing soil lechte ph. However, reltively stle lechte ph with leching times ws oserved in the Alfisol ecuse of its clcreous nture. With incresing orgnic mendment rtes, ph of Spodosol incresed, wheres tht of Alfisol slightly decresed fter six leching events (Fig. 3-3), proly due to their different mechnisms ffecting soil ph. Low EC vlues (<500 μs/cm) of lechtes from Spodosol were mesured due to its low holding cpcity nd low slts (Fig. 3-4). The EC of lechtes from Alfisol ws higher s compred to the Spodosol, indicting higher slts contined in the Alfisol (Fig. 3-5). However, there s no pprent difference etween the control nd tretments with orgnic mendment only. Appliction of chemicl fertilizer incresed lechte EC in oth soils (Figs. 3-4 nd 3-5). Oviously, fertilizer contriuted to EC or slt concentrtion in the mended soils. In the first two leching events, lechte from oth soils mended with Hydr-Hume nd fertilizer hd lower EC thn the controls, implying tht less minerl ions ws leched from the soils mended with fertilizer nd orgnic mendment. This ehvior proly resulted from the retention of slts y 57

58 the orgnic mterils, which greed with the results otined in the incution experiments in which processes of nitrte immoiliztion were oserved. Effect on N Leching nd Soil N Pool The volume of leched wter ws very similr nd independent of the tretments. However, the concentrtion of nitrte in the lechte vried depending on the tretments. Appliction of orgnic mendment tended to increse NH 4 -N concentrtion in lechtes, indicting tht minerliztion of orgnic mteril in the mendment my hve contriuted to soil NH 4 -N, which is sujected to leching. Lechte NH 4 -N concentrtions decresed drsticlly in oth soils in the first four leching events nd reched lmost zero fter the sixth leching event (Figs. 3-6, 3-10). The decresed concentrtion of NH 4 -N in lechtes with time or leching events my e relted to depletion of NH 4 -N ecuse of nitrifiction to NO 3 -N nd microil incorportion into orgnic frctions. Lower NH 4 -N concentrtions were oserved in lechte from the Alfisol thn the Spodosol, proly due to lower ville N nd orgnic mtter in the former thn in the ltter (Tle 2-1). Similrly, the totl mount of NH 4 -N recovered in lechtes ws much less for the Alfisol thn the Spodosol, while sme trend nd conclusion cn e drwn from Alfisol. Nitrte leching from soils mended with orgnic mteril depends on the nture of mteril, the pplied dose, the time of ppliction, the quntity of wter pplied s well s the type of soil (Burgos et l., 2006). Compred with the control, ppliction of orgnic mendments drsticlly decresed NO 3 -N concentrtion in lechtes in the first leching event (Fig. 3-8). The mechnisms of NO 3 -N leching reduction y orgnic mendment is likely relted to the enhnced microil trnsformtion of NO 3 -N into orgnic N such s microil iomss N, with the incresed input of orgnic C. Lechte NO 3 -N concentrtions decresed rpidly with incresing leching events nd were elow 10 mg L -1 regrdless of tretments. Since most of 58

59 NO 3 -N in the soils ws leched in the first two leching events, ppliction of orgnic mendment ppered to e effective in reducing NO 3 -N in sndy soils (Fig. 3-8). A significnt difference in the totl mount of NO 3 -N from the six leching events occurred etween the control nd the tretments mended with Hydr-Hume, when the ppliction rte of Hydr- Hume reched 44.8 or ove (Tle 3-1). When fertilizer ws incorported, NO 3 -N contents incresed t the eginning, ut decresed in the susequent leching events, prticulrly for the soil mended with Hydr-Hume, s compred with the control, indicting the potentil of orgnic mteril in reducing NO 3 -N leching in soils (Fig. 3-9). An ppliction rte of 44.8 kg h -1 or ove is required for Hydr-Hume to ccomplish significnt reduction in NO 3 -N leching from the soils (Tle 3-2). In ddition, totl minerl N (NO 3 -N nd NH 4 -N) ws clculted to understnd the N pool in the mended soils. No significnt difference in totl mount of minerl N ws oserved etween the control nd tretments mended with Hydr- Hume only, wheres significnt reduction of totl minerl N in lechte ws otined for the fertilized soils when the ppliction rte of Hydr-Hume reched 44.8 kg h -1 in the Spodosol nd 22.4 kg h -1 in the Alfisol. In generl, orgnic mendment ws effective in reducing N leching in sndy soils when it ws pplied t 44.8 kg h -1 in Spodosol nd 22.4 kg h -1 in Alfisol with fertilizer. Significnt reduction in totl NO 3 -N mount ws oserved when orgnic mendment ws pplied only t the ppliction rte of 44.8 kg h -1 or ove. Moreover, lechtes from the Alfisol hd lower NO 3 - N concentrtion thn from the Spodosol (Tles 3-4 nd 3-5). Potentil Effects on Hevy Metls Trce metls, such s Cu, Cd, Co, Cr, Ni nd P, re usully present t very low concentrtions in soils, ut re toxic to plnts nd soil microorgnisms if t high concentrtion. Controlling the input of toxicnts is crucil for sustinle griculture. Therefore, criticl 59

60 evlution for concentrtions nd potentil toxicnts in orgnic mendment ws crried nd sttisticl nlyses were clculted etween control nd the tretments. The mounts of extrctle hevy metls (Cd, Co, Cr, Ni, P, Zn) were not ffected y the mendment, minly ecuse of their extremely low concentrtions (Tles 3-3, 3-6). The ppliction of orgnic mendment does not increse iovilility of hevy metls in soil or trnsport of these elements from soil to the environment. Chrcteriztion of Leched Soil With incresing orgnic mendment rtes, ph of Spodosol mended with Hydr-Hume lone decresed slightly, ut incresed slightly for the fertilized soil (Fig. 3-14). However, the chnges were smll (within 0.2 ph units), indicting tht this orgnic mteril hs limited influence on soil ph. Compred with lechtes, soil EC fter the leching ws much lower (<200 μs cm -1 ), lthough it hd different trends with or without fertilizer (Fig. 3-15). The difference etween tretments nrrowed grdully with incresing leching events (Figs nd 3-15). No significnt difference in trce metls occurred etween tretments, indicting tht there ws miniml influence on the trnsport of hevy metls from the orgnic mteril or fertilizer to the environment. Conclusion In this chpter, column leching ws conducted to exmine the effects of Hydr-Hume on the trnsformtion dynmics nd leching potentil of minerl N in the Alfisol nd Spodosol. The otined results indicte tht significnt reduction in totl NO 3 -N mount cn e otined when Hydr-Hume pplied lone in oth of the soils, ut miniml ppliction rte of 44.8 kg h -1 is required. If fertilizer is incorported with orgnic mendment, significnt reduction of totl NO 3 -N mount nd totl minerl N mount cn e chieved t miniml ppliction rte of 60

61 44.8 kg h -1 for the Spodosol nd 22.4 kg h -1 for the Alfisol soil. The influence of orgnic mendment on the leching of hevy metls from the soils ppers to e insignificnt. 61

62 Figure 3-1. Column leching setup 62