William A. Lakel, III

Transcription

1 Slsh Mulching nd Incorportion s Mechnicl Site Preprtion for Pine Plnttion Estblishment nd Subsequent Effects on Soil Moisture nd Site Hydrology Willim A. Lkel, III Thesis submitted to the fculty of the Virgini Polytechnic Institute nd Stte University in prtil fulfillment of the requirements for the degree of MASTER OF SCIENCE in Forestry Approved: W. Michel Aust, Chir Sheprd M. Zedker Richrd G. Oderwld August 24, 2000 Blcksburg, Virgini Keywords: wetlnd forestry, site preprtion, forest hydrology, mulching, wter nutrients, pocosins, wet flts, pine plnttions, silviculture Copyright 2000, Willim A. Lkel III

2 Slsh Mulching nd Incorportion s Mechnicl Site Preprtion for Pine Plnttion Estblishment nd Subsequent Effects on Soil Moisture nd Site Hydrology Willim A. Lkel III (ABSTRACT) Over one million hectres of pocosins nd wet flts in the southestern costl plin re intensively mnged for the production of loblolly pine (Pinus ted) plnttions. These mngement ctivities my hve dverse effects on soil physicl properties, site hydrology, nd overll site productivity. Substntil quntities of wood residues re often left on these sites by timber hrvesting opertions, nd it ws hypothesized tht the incorportion of this slsh into the soil could improve the soil physicl properties nd site hydrology. One orgnic pocosin site nd one minerl wet flt site were chosen post-hrvest for tretment. The wet flt study ws orgnized s n incomplete block design hving four blocks nd six tretments: (i) conventionl bedding, (ii) strip surfce mulching with bedding, (iii) strip surfce mulching with tillge nd bedding, (iv) brodcst mulch without bedding, (v) brodcst mulch with bedding, nd (vi) flt plnted control. The pocosin study ws orgnized s rndomized complete block design with four blocks nd four tretments. The tretments re identicl to those of the wet flt site without the brodcst mulch tretments (iv nd v). Soil physicl property dt ws nlyzed pre- nd post-tretment, while posttretment site hydrology nd soil wter chemistry dt ws nlyzed periodiclly for one yer. Seedling survivl nd height dt were nlyzed fter one growing seson. The tretments hd little effect on soil physicl properties, site hydrology, soil wter nutrients, or seedling survivl on the wet flt study site. Bedding in generl significntly incresed tree height growth, but mulching hd no significnt effects. The tretments hd little effect on soil physicl properties on the pocosin study site except for soil mcroporosity, which ws significntly incresed by bedding. Site hydrology nd soil wter nutrients were not significntly ffected by the tretments, but seedling survivl nd height growth were significntly incresed by bedding. Mulching hd no significnt effects on ny of the prmeters studied.

3 ACKNOWLEDGMENTS I would like to express my pprecition to my dvisor nd committee chirmn, Dr. W. Michel Aust, for his constnt guidnce nd ssistnce with both the cdemic nd reserch spects of my grdute progrm. I m grteful to Dr. Aust nd Dr. Jmes Burger for their instrumentl roles in my understnding of forest soils nd their importnt reltionship to forest mngement nd productivity. I wish to express my thnks to the members of my dvisory committee, Dr. Sheprd M. Zedker nd Dr. Richrd G. Oderwld, for their willingness to ssist me throughout my undergrdute nd grdute progrms t Virgini Tech. I lso wnt to thnk Dvid Mitchem for his mny hours of work ssisting me in the forest soils lb, nd Jody Smiley of Environmentl Engineering for her ssistnce in nlyzing soil wter smples. I lso wnt to thnk my work study students, Renzo Rocchegini nd Mrk Myers, for their mny hours in the lb nd the field collecting dt. Specil thnks go out to my fellow grdute students Angie Cummings, Msto Miw, Andy Scott, Tony Lister, nd Bronson Bullock for their ssistnce with vriety of issues regrding my reserch. I m lso very pprecitive of the dministrtive efforts of Sue Snow, Nncy Chpmn, nd Kthie Hollndsworth, ll of which mde my grdute progrm much esier to hndle. Most importntly, I wnt to thnk immensely my wife Holly Lkel for her unlimited understnding, ptience, nd support throughout my studies t Virgini Tech. I cnnot sy enough bout her willingness to put her life on hold nd wit for me to finlly complete this project. Without the funding nd technicl support of both the USDA Forest Service nd Weyerheuser Compny, this project nd my Mster s progrm would not hve been possible. iii

4 TABLE OF CONTENTS Pge ACKNOWLEDGMENTS...iii LIST OF TABLES...vi LIST OF FIGURES...viii INTRODUCTION...1 LITERATURE REVIEW...4 Forested Wetlnds Suitble for Pine Plnttions: Wet Flts nd Pocosins...4 Limiting Fctors for Pine Mngement...6 Silviculturl Mnipultions of Wet Sites -- Dringe...6 Ditching...7 Bedding...7 Fertiliztion...8 Chemicl Weed Control...8 Thinning...9 Forest Hrvesting Systems...9 Hrvesting Impcts on Site Qulity...11 Soil Physicl Properties...11 Soil Orgnic Mtter...12 Soil Orgnic Mtter Losses nd Silviculturl Activities...13 Hrvesting nd Site Preprtion Impct Ameliortion Techniques...14 Dringe s n Ameliortive Technique...14 Bedding s n Ameliortive Technique...15 Mulching s n Ameliortive Technique...16 Tillge s n Ameliortive Technique...16 Fertiliztion s n Ameliortive Technique...17 METHODS AND MATERIALS...18 Site Descriptions...18 Lyout nd Generl Sttisticl Design...20 Instlltion of Field Instruments...23 Smpling...25 iv

5 Pge Soil Properties nd Chrcteriztion...25 Intct Soil Cores...25 Loose Bulk Soil Smples...26 Periodic Repeted Mesurements...26 Wter Nutrients nd Crbon...26 Soil Volumetric Moisture Percentge...27 Depth of Iron Oxidtion...28 Elevtion of Wter Tble...29 Depth to Wter Tble...29 Seedling Height nd Survivl...30 Dt Anlysis...30 RESULTS AND DISCUSSION: WET FLAT SITE...33 Pre-Tretment...33 Post-Tretment...36 Periodic Repeted Mesurements -- Wet Flt Site...38 Groundwter Chemistry...38 Site Hydrologic Fctors...42 First-Yer Seedling Height nd Survivl...46 RESULTS AND DISCUSSION: POCOSIN SITE...48 Intct Soil Cores nd Bulk Soil Smples...48 Pre-Tretment...48 Post-Tretment...51 Periodic Repeted Mesurements...52 Groundwter Chemistry...52 Site Hydrologic Fctors -- On-Bed Dt...56 First-Yer Seedling Height nd Survivl...60 SUMMARY AND CONCLUSIONS...62 Wet Flt Site...62 Pocosin Site...63 LITERATURE CITED...65 VITA...72 v

6 Tble 1. Tble 2. Tble 3. Tble 4. Tble 5. Tble 6. Tble 7. Tble 8. Tble 9. LIST OF TABLES Pge Generl model used for the nlysis of vrince procedure for the site preprtion study on the wet flt site ner Wshington, North Crolin...31 Generl model used for the nlysis of vrince procedure for the site preprtion study on the pocosin site ner Wshington, North Crolin...31 Models used to nlyze soil wter chemistry nd soil moisture percentge dt for the site preprtion study on the pocosin site ner Wshington, North Crolin...31 Models used to nlyze soil wter chemistry nd soil moisture percentge dt for the site preprtion study on the wet flt site ner Wshington, North Crolin...32 Prtil nlysis of vrince informtion for the wet flt site pre- nd posttretment intct soil core nd bulk soil smple dt...34 Tretment effect lest squre mens by horizon for the wet flt site pre- nd posttretment intct soil core nd bulk soil smple dt...35 Prtil nlysis of vrince informtion for the wet flt site post-tretment, onbed soil wter chemistry dt including mmonium, nitrte, phosphte, nd totl orgnic crbon...39 Tretment effect lest squres mens nd ssocited stndrd error vlues for the wet flt site post-tretment, on-bed soil wter chemistry dt...40 Prtil nlysis of vrince informtion for the wet flt site post-tretment, onbed site hydrology dt including soil volumetric moisture, depth of iron oxidtion, wter tble elevtion, nd wter tble depth...43 Tble 10. Tretment effect lest squre mens nd ssocited stndrd error vlues for the wet flt site post-tretment, site hydrology dt including soil volumetric moisture, depth of iron oxidtion, wter tble elevtion, nd wter tble depth...44 Tble 11. Tretment effect lest squre mens nd ssocited stndrd error vlues for the wet flt site post-tretment seedling height nd survivl dt...46 Tble 12. Prtil nlysis of vrince informtion for the pocosin site pre- nd posttretment intct soil core nd bulk soil smple dt...48 Tble 13. Tretment effect lest squre mens by horizon for the pocosin site pre- nd posttretment intct soil core nd bulk soil smple dt...50 vi

7 Pge Tble 14. Prtil nlysis of vrince informtion for the pocosin site post-tretment onbed soil wter chemistry dt including mmonium, nitrte, phosphte, nd totl orgnic crbon...51 Tble 15. Tretment effect lest squre mens nd ssocited stndrd error vlues for the pocosin site post-tretment, on-bed soil wter chemistry dt...54 Tble 16. Prtil nlysis of vrince informtion for the pocosin site post-tretment, onbed site hydrology dt including soil volumetric moisture, depth of iron oxidtion, wter tble elevtion, nd wter tble depth...57 Tble 17. Tretment effect lest squre mens nd ssocited stndrd error vlues for the pocosin site post-tretment, site hydrology dt including soil volumetric moisture, depth of iron oxidtion, wter tble elevtion, nd wter tble depth...58 Tble 18. Tretment effect lest squre mens nd ssocited stndrd error vlues for the pocosin site post-tretment seedling height nd survivl dt...60 vii

8 LIST OF FIGURES Pge Figure 1. Root growth window chrt...12 Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Mp of the generl physiogrphic provinces of the southern United Sttes nd generl loction of the study sites mrked with str...18 Lyout of the tretment plots nd blocks on the wet flt site...21 Lyout of the tretment plots nd blocks on the pocosin site...22 The rtio method used to determine the soil volumetric moisture percentge of ech soil horizon on ech site for the site preprtion study ner Wshington, North Crolin...28 Wet flt site micro- nd totl porosity lest squre mens nd stndrd error brs for the on-bed Ap horizon dt sets...37 Wet flt site post-tretment bulk density nd soil orgnic crbon lest squre mens nd stndrd error brs for the on-bed Ap horizon dt sets...38 Wet flt site post-tretment, one-yer verge wter nutrient concentrtion ls mens pooled cross ll tretments...41 Wet flt site soil wter nutrient (ppm) nd TOC (pp10,000) concentrtions pooled cross ll horizons by tretment...42 Figure 10. Wet flt site post-tretment iron oxidtion depth nd wter tble depth ls mens...45 Figure 11. Wet flt site yer one seedling height nd survivl ls mens...47 Figure 12. Pocosin site mcroporosity nd bulk density ls men vlues for the pocosin site post-tretment, on-bed dt...52 Figure 13. Pocosin site reltive nutrient ion concentrtions in soil wter by horizon (pooled cross ll tretments) nd nutrient type...55 Figure 14. Column chrt showing the mmonium ion concentrtions in soil wter from ech smpled soil horizon pooled cross ll tretments...55 Figure 15. Pocosin site nutrient ion concentrtion lsmens pooled cross ll horizons by tretment nd nutrient ion type...56 viii

9 Pge Figure 16. Site hydrology prmeter ls mens by tretment for the pocosin site...59 Figure 17. Pocosin site seedling height nd survivl fter one growing seson by tretment...61 ix

10 INTRODUCTION Forest products compnies nd non-industril privte lndowners in the estern Crolins nd Virgini mnge 5.3 million cres (2.1 million h) of wetlnd forests. Loblolly pine (Pinus ted L.) occurs on bout 32% of this crege, while lowlnd hrdwoods occupy bout 55%. Approximtely one-hlf of ll pine crege is intensively mnged s plnttions, nd intensive mngement typiclly includes short-rottion hrvests, site preprtion, competition control, fertiliztion, nd thinning. The mjority of these wetlnds re clssified s minerl wet flts or orgnic pocosins (Brown, 1997). Forest products compnies hve cquired these lnds for mngement ctivities becuse vst creges of undeveloped timberlnd were vilble t low costs, the climte is suitble for highly productive forests, nd wetlnds re not generlly suitble for urbn development or griculture. In 1972, the federl government strengthened the Federl Wter Pollution Control Act nd required tht permit be issued to ny lndowner who wishes to dischrge dredge nd fill mterils into nvigble wters nd ssocited wetlnds. Norml frming nd forestry ctivities were exempted from the permit process by section 404 of the 1977 Clen Wter Act, provided tht: (1) the ctivity is not conversion of wetlnd to n uplnd; (2) the ctivity is prt of n ongoing opertion; (3) the ctivity hs not lin idle so long tht hydrologic opertions re necessry; (4) the ctivity does not contin ny toxic pollutnts; nd (5) the ctivity uses norml silviculturl opertions tht comply with certin BMP s (Aust, 1994). The Environmentl Protection Agency (EPA) creted the Office of Wetlnd Protection in 1986 to implement policy tht would gurntee no net loss of the ntion s wetlnds in the future (Andrews, 1993; Siegl nd Hines, 1990). The intensive mngement required to mximize wood production on these lnds often includes extensive ditching nd mechnicl nd chemicl site preprtion to estblish plnttions. Clercutting with ground-bsed systems is commonly used to hrvest timber. Due to the wet conditions tht occur on these sites for much of the yer, ground- bsed rubber-tired equipment opertions cn hve significnt impcts on residul soil nd site qulity. Soil compction nd rutting, combined with site orgnic mtter disturbnces, cn 1

11 led to long- nd short-term reductions in site productivity (Aust et l., 1993; Kozlowski, 1986; Miw, 1999). Soil compction nd rutting decreses gs nd wter movement in the soil profile, which decreses root growth nd survivl. Orgnic mtter disturbnce under sufficiently oxygented conditions my led to incresed decomposition rtes nd subsequent losses of ssocited soil nutrients to leching nd voltiliztion (Aust, 1994; Burger, 1990; Kozlowski, 1986). Subsequent incorportion of slsh residue on these wet (lesser oxygented) sites might decrese decomposition rtes by reducing erted conditions within the soil profile while simultneously enhncing the orgnic mtter nd soil physicl chrcteristics of compcted nd rutted soils. Conventionl timber hrvests cn leve behind significnt mounts of slsh tht usully re left in plce, burned, or moved mechniclly from the site. The gols of this study re to determine if post-hrvest slsh residue cn be mulched nd incorported onto or into the soil profile by vrious tretment methods to meliorte the previously discussed negtive soil/site impcts following wet wether hrvesting opertions. This type of orgnic mtter mngement could replce or ugment current methods nd subsequently reduce mngement impcts nd costs. The incorportion of mulched slsh onto or into the soil profile might lso enhnce inherent soil nd site qulity. This study ws collective effort by the USDA Forest Service, Weyerheuser Compny, nd Virgini Polytechnic Institute nd Stte University. Weyerheuser provided lnd nd bsic tretment instlltion, while the Forest Service provided funding nd ugmented tretment instlltions. The Forest Service concentrted on the evlution of site crbon blnce nd soil physics issues, while Weyerheuser Compny ws responsible for quntifying timber growth nd yield. Tretments were instlled on two wetlnd sites, one orgnic pocosin nd one minerl wet flt belonging to Weyerheuser Compny ner Wshington, North Crolin. Virgini Tech personnel evluted the effects of slsh incorportion on site hydrology, soil wter chrcteristics, nd ssocited soil physicl properties. Mjor concerns included the effects of mulching tretments on soil wter movement, wter tble levels, soil redox 2

12 potentils, soil moisture quntity, soil moisture nutrient concentrtions, nd first-yer seedling survivl nd growth. The generl null hypotheses tested were: Orgnic mtter incorportion did not ffect site hydrology. Orgnic mtter incorportion did not ffect soil wter chrcteristics. Orgnic mtter incorportion did not ffect ssocited soil physicl properties. 3

13 LITERATURE REVIEW Forested Wetlnds Suitble for Pine Plnttions: Wet Flts nd Pocosins Totl plustrine wetlnd crege in North Crolin ws pproximtely 4.7 million cres in 1992 (USDA Ntionl Resources Inventory Dt), nd pproximtely 4.5 million cres (96%) were forested (Sheprd et l., 1998). Minerl wet flts (2.6 million cres or 1.1 million h) nd orgnic pocosins (1.6 million cres or 0.6 million h) re the two mjor forested wetlnd types in estern North Crolin (Cubbge nd Flther, 1993). Minerl wet flts occur in brod interstrem terrces nd re clssified by the USDI Fish nd Wildlife Service Ntionl Wetlnd Inventory * s: System: Plustrine wetlnds Subsystem: None Clss: Forested Wetlnds Subclsses: needle-leved evergreen nd brod-leved deciduous Wter regime: sturted, semi-permnently, intermittently, or sesonlly flooded Wter chemistry: fresh, cidic Soils: minerl *Adpted from Hrms et l., (1998). The minerl soils were formed from mrine nd lluvil deposits of the Quternry, Tertiry, nd Cretceous periods, nd resulting soil orders include lfisols, entisols, inceptisols, spodosols, nd ultisols. In most cses the soil orders re quults, which chrcteristiclly hve cly subsurfce (rgillic) horizon with low (less thn 50%) bse sturtion. Other soil suborders commonly encountered re quents, quepts, nd quods (Allen nd Cmpbell, 1988). These sites re generlly somewht poorly to very poorly drined nd re reltively fertile compred to orgnic soils of this region. Wet flts re often sturted or inundted for brief periods during nd fter hevy rinfll events becuse of the perching effect of the rgillic horizon, combined with very slight relief. Wet flts receive no lluvil inputs of nutrients nd wter. Precipittion is the mjor wter input, while strem nd surfce runoff combined with evpotrnspirtion re the min outputs (Hrms et l., 1998). Wet pine flts (minerl soils) re less often sturted thn pocosins nd hve more frequent nturl fires, therefore they re usully dominted by loblolly pine, with ssocited pond pine (P. serotin) nd longlef pine (P. plustris), while wet hrdwood flts re dominted by 4

14 swmp lurel ok (Quercus lurifoli), wter ok (Q. nigr), willow ok (Q. phellos), sweetgum (Liquidmbr styrciflu), nd red mple (Acer rubrum). In mny cses, minerl wet flts exhibit forest species compositions including pines nd hrdwoods. Wet flts re generlly slightly drier thn pocosins due to their slightly more elevted lnd type nd re more productive due to superior soil nutrient sttus (Hrms et l., 1998). Orgnic pocosins, which re ombrotrophic bogs, re locted in brod interstrem terrces with little or no nturl dringe nd re clssified by the Ntionl Wetlnd Inventory s: System: Plustrine wetlnds Clss: Forested Wetlnds Subclsses: needle-leved evergreen nd brod-leved decidous, Wter regime: sturted, semi-permnently, intermittently, or sesonlly flooded Wter Chemistry: fresh, cidic Soils: orgnic Pocosins developed fter the Wisconsin ice ge s result of rising se levels nd sediment deposition on brod flts tht creted lrge inlnd res of shllow wter. Vegettion growth nd deposition of resultnt orgnic mteril in these flooded res for pproximtely 10,000 yers hve formed orgnic soils clled pets (fibrists) or mucks (sprists), depending on the type of vegettive prent mteril nd the degree of decomposition. In most cses, undisturbed pocosin soils re clssified s medisprists. In some cses, the soils re minerl with shllow orgnic lyer t the surfce. These soils re often poorly to very poorly drined nd re generlly nutrient-deficient nd cidic. Common soil series include Dre (Typic Medisprists) nd Ponzer (Terric Medisprists). Precipittion is the min wter input, while evpotrnspirtion ccounts for nerly ll wter output during the dry growing seson. Strem outflow ccounts for smll mount of wter output during winters nd very wet periods in summer (Shritz nd Greshm, 1998). Ntive pocosin vegettion vries with pet depth to minerl soil. Pocosins with deep pet lyers (3 to 16 feet) re clled low or short pocosins becuse the vegettion community is dominted by short shrubby species such s fetterbush (Lyoni lucid), titi (Cyrill rcemiflor), greenbrir (Smilx spp.) nd severl species of by (Mgnoli or Perse spp.). The sturted deep pet lyers often prohibit plnt roots from reching minerl soil nd 5

15 ssocited nutrients nd prohibit the estblishment of tree communities. Pocosins with shllower lyers of pet (< 5 feet) llow some tree roots to rech minerl soil during periods of drought. This llows some tree species such s pond pine nd severl species of by tht re dpted to sturted condition, low nutrient sttus, nd occsionl intense fires to survive. The shrub species mentioned for the low pocosin dominte the high pocosin s well (Shritz nd Greshm, 1998). Limiting Fctors for Pine Mngement Fltwoods sites, including pocosins nd wet flts, generlly hve nerobic conditions for t lest portion of the growing seson. The lck of topogrphic relief, low elevtions nd/or depressionl topogrphy, nd poor internl dringe cn cuse poor soil ertion, nutritionl limittions, nd reduced productivity for desirble species such s loblolly pine (Hrms et l., 1998; Miw et l., 1998). Industril ctivities on southern wetlnds re further restricted during the winter months, when tree dormncy nd cool tempertures gretly reduce evpotrnspirtion wter losses from sites (Mitsch nd Gosselink, 1993). Hevy equipment trffic is gretly hmpered on most wetlnds by high wter tbles nd wet soils. High wter tbles lso ffect the species nd productivity of wetlnd sites. Mny wet flts nd pocosins must be drined extensively to mke crop production possible. Pine seedling survivl on wetlnds in estern North Crolin is gretly dependent upon rtificil site dringe nd bedding prior to plnting. Low nturl soil fertility nd intense competition from weed herbceous nd tree species re lso impediments to crop tree growth on mny southern wetlnd sites (Allen nd Cmpbell, 1988). Due to the problems ssocited with poor dringe, vriety of silviculturl opertions hve been modified to enhnce the survivl nd growth of desirble species. Silviculturl Mnipultions of Wet Sites -- Dringe Forested wetlnd sites in estern North Crolin, owned by industril nd nonindustril privte lndowners, re often mnged ccording to the limittions tht ffect pine plnttion estblishment nd growth. The mjor limittion for pine mngement is the generlly high wter tble nd resulting wet soil conditions. Therefore, mny sites re rtificilly drined 6

16 through n extensive network of ditches. These ditches re usully constructed with mechnized trcked excvtor, nd fill from the ditches is used to construct forest ccess rods. Primry nd secondry ditches re locted long the system of rods, while tertiry ditches re locted cross the sites t prllel intervls of pproximtely 5 chins (101 m). Ditching Ditching is intended to lower the overll site wter tble level, thereby incresing soil gs exchnge, effective rooting volume, nd orgnic mtter decomposition nd subsequent nutrient minerliztion (Wells nd Crutchfield, 1974). Andrews (1993) noted tht reserch generlly hs shown tht ditching increses long-term growth of southern pine species on wet sites. (Mki, 1955, 1968, 1971; Miller nd Mki, 1957; Pruitt, 1947). Wlker et l. (1961) found tht increses in wter tble depth of 10 to 20 cm produced significnt results (Andrews, 1993). Terry nd Hughes (1975) noted tree growth increses from 80 to 1300 percent on drined sites versus djcent undrined sites (Andrews, 1993). Kelting (1999) found tht pproximtely 45 cm of erted soil is necessry for optiml erly survivl nd growth of loblolly pine grown on wet flts. Bedding Bedding my be used lone or in conjunction with ditching to elevte tree seedlings erly rooting environment bove the ground surfce. This cretes fvorble rooting environment for pine seedlings tht is drined nd erted sufficiently to promote erly seedling survivl (Allen nd Cmpbell, 1988). "Bedding hs been the most widely used site preprtion method in poorly drined res of the southest (Hines nd Hines, 1978; McKee nd Shoulders, 1974; Shoulders nd Terry, 1978; Terry nd Hughes, 1975)" (Andrews, 1993). Dringe lone cn be responsible for up to 25-foot (7.6-meter) increse in tree height fter 50 yers (Klwitter nd Young, 1965), while bedding following dringe cn be responsible for n dditionl 1-meter (3.3-foot) growth dvntge in the first five yers (Allen nd Cmpbell, 1988), possibly leding to shortened rottions. Andrews (1993) noted tht bedding increses survivl nd growth on wet sites, but tht individul tree growth dvntge over non-bedded sites decreses with time (Hines et l., 1975; Lennrtz nd McMinn, 1973), nd overll, bedding my not increse tree height t the end of rottion. However, the 7

17 enhnced erly survivl cused by bedding hs been shown to increse volume yields by 33% even though individul tree growth differences my not be significnt (Andrews, 1993). Fertiliztion A very low level of vilble phosphorus is common limittion for tree growth on wet soils in the lower costl plin. Phosphorus fertiliztion (dimmonium phosphte) is the most common opertionl solution, nd the fertilizer is generlly pplied to the beds just prior to seedling plnting. Pritchett nd Comerford (1982) found tht the effects of phosphorus fertiliztion on loblolly pine growth on poorly drined soils re lrge nd long-term (Allen nd Cmpbell, 1988). Phosphorus fertiliztion cn increse site index by more thn 4 meters (13.1 ft) t ge 25 (Allen nd Cmpbell, 1988). Tippett (1992) noted the reserch results of McCrthy nd Dvey (1976) nd Pritchett nd Comeford (1982), which showed incresed growth of loblolly pine plnttions on fertilized wet sites of estern North Crolin. Stnd growth increses (dimeter, bsl re, nd height) were mesured from yer 1 to yer 20 in severl studies. Phosphorus fertiliztion incresed tree growth on wet sites nd offered some potentil s replcement for bedding on some sites. Long-term growth responses to phosphorus fertiliztion were more pprent on wet sites nd less pronounced on well-drined sites (Tippet, 1992). Chemicl Weed Control Herbicides re generlly pplied to recently plnted sites during the first few growing sesons to control herbceous species tht compete with plnted seedlings for light, moisture, nd nutrients. Control of herbceous weeds cn increse seedling survivl by s much s 30% nd volume growth by s much s 100% (USDA, 1997). Oust (sulfometuron methyl, E.I. Dupont de Nemours & Co., Inc., Wilmington, Delwre), Velpr L (hexzinone, E.I. Dupont de Nemours & Co., Inc., Wilmington, Delwre), Accord (glyphoste, Monsnto Compny, St. Louis, Missouri), Post (sethoxydim, BASF Corp., Chemicls Division, Prsippny, New Jersey), nd Fusilde (fluzifop-p-butyl, ICI Americs Inc., Wilmington, Delwre) re ll common chemicls used for herbceous control. Herbceous relese chemicls re often pplied in bnds with bckpck spryers so 8

18 s to control the plcement of chemicl nd void indvertent exposure of the crop trees to herbicides. Herbicides re lso used to control hrdwood competition fter plnting s well s just prior to stnd closure. These re most often erilly pplied by helicopters or skidders to ensure dequte nd even ppliction of chemicl. Relese ppliction timing nd frequency re bsed on the type nd mount of competing vegettion. Accord, Velpr, Weedone (2-4-DP, Rhone-Poulenc Ag. Compny, Reserch Tringle Prk, North Crolin), Grlon (Triclopyr-mine, Dow Agriculturl Chemicls, Midlnd Michign), nd Arsenl re ll commonly used hrdwood relese chemicls. Appliction methods depend gretly on stnd chrcteristics, but eril sprying nd bckpck sprying re the most common ppliction methods. Thinning Depending on lndowner objectives, southern pine plnttions my be commercilly thinned prior to ge 20 to remove less vigorous trees from the stnd. These thinned stems re removed from the stnd nd mrketed s pulpwood or chip-n-sw products (USDA, 1997). Thinning encourges growth of the higher-qulity trees tht re left behind nd cptures volume tht would otherwise be lost to competition-induced mortlity (Smith, 1986). Stnds re usully thinned to bsl re of bout 70 ft 2 /cre (2.6 m 2 /h). The pine stnds re generlly hrvested t the end of the rottion t pproximtely yers (Smith, 1986; USDA, 1997). Forest Hrvesting Systems Severl ground-bsed timber hrvesting systems re currently used on wet sites in the southestern costl plin. The most conventionl hrvesting system in the southest for lmost ll types of forest lnd in the piedmont or costl plin involves rubber-tired fellerbuncher nd grpple skidders to fell nd trnsport timber out of the woods. This system is used for thinnings s well s finl hrvests t the end of rottion. This system is very costeffective compred to other hrvesting systems, nd production cn be djusted with equipment dditions nd removls from the system. A system of one feller-buncher nd two grpple skidders cn produce 700 to 900 tons of wood per week. The reltively low cost of 9

19 opertion nd verstility of this system mke it the most widely utilized system in the southest for timber hrvesting (Shffer, 1994). Cut-to-length systems involving mechnicl hrvesters nd forwrders re used infrequently. This sophisticted nd expensive system ws recently introduced into the southern United Sttes s n environmentlly friendly lterntive to more conventionl systems due to significntly less stnd nd forest floor disturbnce. This system involves mechnized rubber-tired hrvester nd forwrder to trnsport wood to the deck. The hrvester processes hrvested stems in the woods nd deposits severed limbs in front of the forwrder, which then trvels over them. This mt of limbs reduces the impct of the equipment trffic on the soil nd tree roots. This system is currently being used on very limited scle for first nd second thinnings in pine plnttions. This type of system is ble to produce 400 to 600 tons per week of pulpwood per set of equipment (one hrvester nd forwrder) (Shffer, 1994). Wetlnd hrvesting hs historiclly been difficult due to the inbility of loggers to operte the hevy equipment required on very wet sites. Concerns bout the environmentl impcts of wetlnd logging on residul stnds hve lso incresed the difficulty of wetlnd logging. The rubber-tired skidder is the most utilized piece of hevy equipment for wetlnd logging in the southest (Aust, 1994). In mny cses, dul tires or extr-wide high flottion tires re used to minimize soil nd wter impcts on very wet sites. An excvtor-bsed shovel logger is often used to move felled timber from the stump to the logging deck on very wet sites in order to minimize ground disturbnce (Stokes nd Schilling, 1997). Helicopter nd cble logging systems re lso utilized on very limited scle to remove high-qulity timber from very wet sites with low site impct potentil. Both of these systems re bsed on the trnsporttion of felled logs to the log deck with miniml ground contct. The helicopter system involves tethering logs to hovering helicopter tht trnsports the logs erilly to the deck. The cble system involves the use of n erected tower, power winch, pulleys, nd cbles to move logs cross the site to the deck while minimizing contct with the ground (Aust, 1994; Stokes nd Schilling, 1997). 10

20 Hrvesting Impcts on Site Qulity Soil Physicl Properties Ground-bsed forest hrvesting systems require repeted psses by hevy trcked or rubbertired mchinery. The hevy mchinery cn hve significnt impcts on soil physicl nd chemicl chrcteristics (Aust, 1994). Equipment trffic disturbnce severity is lrgely controlled by soil volumetric moisture percentge t the time of trffic. Trffic impcts on dry soils re usully miniml, while impcts on moist to wet soils re often significnt (Grecen nd Snds, 1980). Scheerer (1994) reviewed studies of conventionl hrvesting opertions nd found tht they trfficked 17 to 48 percent of wet flt sites (Aust et l., 1993; Dickerson, 1976; Htchell et l., 1970; Willis, 1971). Moist soils (t or bove the plstic limit) re wet enough to disply plstic properties when under n pplied force. Therefore, moist soils cn be molded nd compcted by hevy equipment trffic s the soil ctully flows (Grecen nd Snds, 1980). Compction increses soil bulk density nd often decreses soil mcroporosity. Soils tht re wet (t or bove the liquid limit) will often disply liquid properties nd will be rutted nd churned by hevy equipment trffic (Grecen nd Snds, 1980; Bodmn nd Rubin, 1948). Equipment tires or trcks sink into the ground s result of sttic forces, nd tires or trcks spin when shering forces exceed soil strength. Soil displced from under tires or trcks moves upwrd nd forms rut. Hevily rutted nd churned soils re referred to s puddled soils (Burger et l., 1988). Rutting nd puddling of soils in skid trils hve been found to lter lterl subsurfce wter flow cross hrvested sites, thereby impeding soil dringe (Aust, 1994; Miw et l. 1998). Compction decreses mcroporosity (Childs et l. 1989); therefore, compction cuses decresed ir nd wter movement, infiltrtion, nd percoltion expressed s hydrulic conductivity into the soil profile (Burger, 1990). Decresed rinfll infiltrtion my led to incresed surfce runoff nd incresed erosion of soil nd soil nutrients (Brdy, 1990). Decresed soil ertion my cuse reducing conditions within the soil profile tht cn cuse ph chnge towrd neutrlity nd cn ffect soil nutrient vilbility (Aust, 1994; Ponnmperum, 1972). Compction my lso cuse lter increses in soil strength under dry 11

21 soil conditions nd decrese soil strength under wet conditions (Burger, 1990; Burger et l., 199; Grcen nd Snds, 1980). These effects on soil strength hve serious implictions for tree root growth. Overll, soil compction cn hve very significnt effects on the bility of tree roots to grow, respire, nd collect nutrients from the soil profile. Tree root growth is restricted primrily by excessive soil strength resulting from soil compction. Compcted soils become too strong for roots to penetrte t higher wter contents, nd ertion in compcted soils is limiting t lower soil moistures, restricting the soil wter content rnge t which roots cn grow (Figure 1). This root growth window is bounded by soil conditions of indequte ertion nd excessive soil strength. The rnge of wter contents cceptble for root growth decreses s compction nd bulk density increses (Childs et l., 1989) (Figure 1). From n opertionl perspective, this implies tht excessively rutted sites hve reduced periods when they re wet enough to llow root growth, nd they hve incresed periods where excessive wter hinders opertions such s site preprtion. Bulk Density (g/cm 3 ) Excessive Strength Root Growth Window Indequte Aertion Soil Wter Content (m 3 /m 3 ) Figure 1. Root growth window chrt (dpted from Childs et l., 1989). Soil Orgnic Mtter Soil orgnic mtter is centrl to mny nturl soil processes tht re essentil for tree growth. Orgnic mtter in soils cts s slow relese source of nutrients tht stores nd cycles nitrogen, phosphorus, nd sulfur (Wrring nd Schlesinger, 1985). Orgnic mtter is lso 12

22 importnt for the cretion nd mintennce of soil mcroporosity nd, s result, is importnt to reducing soil bulk density. Additions of orgnic mtter to soils generlly improve dringe of the soil profile with incresed ertion, dequte ertion over greter rnge of moisture contents, incresed microbil ctivity, nd esier plnt root penetrtion. Soil orgnic mtter lso improves soil structure, soil wter holding cpcity (Childs et l., 1989), soil ction exchnge cpcity, nd soil ph buffering cpcity (Khnn nd Ulrich, 1984). Soil Orgnic Mtter Losses nd Silviculturl Activities Soil orgnic mtter cn be gretly ffected by silviculturl prctices used in pine plnttion forestry. Removl of the forest cnopy llows sunlight to rech the ground directly nd t greter intensity. This cuses n increse in soil temperture tht encourges microbil decomposition of soil orgnic mtter. Nutrients from this process my then be lost through surfce nd groundwter movement if the plnt nd tree uptke on site re not sufficient to cpture nd incorporte these nutrients into new biomss (Ellert nd Gregorich, 1995). Lrge dditions of slsh to the forest floor during hrvesting my enhnce these effects. Site preprtion methods such s root rking, slsh piling, nd windrowing concentrte orgnic mtter into smll res on the site nd thus deprive the mjority of crop trees of nutrients relesed by the decomposition of this mteril. Whole-tree hrvesting methods remove tree tops nd brnches from the site, which cn result in significnt loss of nutrients. Site preprtion burning cn lso result in the loss of nutrients from the site (McColl nd Powers, 1984). Loss of this orgnic mtter nd ssocited plnt nutrients my led to long- nd short- term soil productivity declines (Nmbir, 1996). Under unsturted conditions, the incresed decomposition of buried orgnic mtter nd ny pplied fertilizers will relese nutrients into the soil nd remining soil moisture. Phosphte levels in soil moisture will likely be low (0.002 to ppm) due to the tendency of phosphte to be dsorbed by cly minerls nd incorported into secondry compounds with iron nd luminum (Tisdle et l., 1985). Verry (1972) reported phosphte in groundwter vlues from minerl nd orgnic soils in Minnesot tht verged 0.12 ppm prior to clercutting nd 0.17 ppm fter clercutting. 13

23 Ammonium ctions relesed into the soil by orgnic mtter decomposition will likely exist t esily detectble levels in soil moisture, especilly under sturted conditions. Verry (1972) reported mmonium in groundwter vlues from minerl nd orgnic soils in Minnesot tht verged 0.35 ppm prior to clercutting nd 0.55 ppm fter clercutting. Ammonium ctions in the presence of oxygen re converted to nitrte nions in bedded soils during unsturted conditions (Wring nd Schlesinger, 1985). These ions (nitrte) might be bundnt in soil moisture becuse they re not ttrcted to the negtively chrged soil ction exchnge complex. Under sturted nd very cidic conditions, mmonium will not be redily converted to nitrte (Tisdle et l., 1985), nd soil moisture smples might hve lower levels of nitrte s result. Verry (1972) reported nitrte in groundwter vlues from minerl nd orgnic soils in Minnesot tht verged 0.31 ppm prior to clercutting nd 0.16 ppm fter clercutting. Verry stted tht the reduction in nitrte fter hrvest is not typicl nd ws probbly due to the cold climte nd subsequent slow orgnic mtter brekdown in Minnesot. Hrvesting nd Site Preprtion Impct Ameliortion Techniques Recently hrvested forested wetlnds re often mechniclly site-prepred in n effort to meliorte the hrvesting process nd to enhnce site conditions tht my limit pine plnttion estblishment. Dringe s n Ameliortive Technique Cmpbell nd Hughes (1991) summrized the results of their wetlnd dringe reserch. Dringe of wetlnd sites is often used to lower verge wter tbles nd increse the periods when soils re not sturted (Hughes et l., 1990). Dringe is ccomplished by digging complex system of secondry nd tertiry ditches tht drin into primry ditches. Dringe is usully responsible for n 800 to 1300 percent tree growth response (Rlston, 1965) nd 3- to 5-meter increse in site index (bse ge 25) tht is mintined through 35-yer rottion (Terry nd Hughes, 1975). "During wet sesons, plnttions with free dringe often hve wter tbles 30 cm to 60 cm lower, with less fluctution, thn undrined pocosin" (Cmpbell 14

24 nd Hughes, 1991). Dringe my not ctully serve s n meliortive prctice for hrvesting disturbnces, but dringe or wter mngement cn be used to lower wter tbles prior to hrvest. This prctice cn minimize hrvest disturbnces by s much s 90 percent (Miw, 1999). Bedding s n Ameliortive Technique Bedding of wetlnd sites is process tht involves either lrge crwler trctor or lrge skidder pulling mechnicl plow (Svnnh triling 6 disc bedding plow, Georgi). The bedding plow pulls soil nd orgnic mtter upwrd nd forms it into long, elevted continuous strip. The surfces of these beds re generlly 0.5 to 1 foot higher thn the surrounding soil surfce. The bedding plow lso cretes ditch on ech side of the beds pproximtely 1 foot (0.30 m) wide nd 1 foot (0.30 m) deep. The plow is pulled cross the site to crete system of prllel beds t spcing tht is dictted by plnting density requirements (USDA, 1997). Bedding is n effective tretment for reversing the soil compction cused by hevy equipment trffic during timber hrvesting (Aust et l., 1998; Belli et l., 1993). The bedding plow breks up compcted soil into smller ggregtes, thereby decresing soil bulk density while incresing soil mcroporosity, ertion, nd dringe (Allen nd Cmpbell, 1988; Morris nd Lowery, 1988). As result, soil volumetric moisture will generlly be less in the bed thn in the off-bed res. The ssocited improvements in ertion nd root volume exploittion re importnt to seedling survivl in forested wetlnds. Bedding gng bldes pile soil onto the previous soil surfce nd my ctully leve lyer of compcted soil underneth the bed. This compcted lyer my eventully inhibit root growth below the bed (USDA, 1997). Bedding lso increses effective seedling rooting volume by rising the soil surfce frther bove the wter tble nd concentrtes orgnic mtter nd ssocited nutrients ner seedling roots in the bed (Attiwill et l., 1985). Bedding lso prtilly controls erly development of competing woody vegettion on the beds by destroying previously estblished vegettion (Willims, 1988). Bedding with nd without mulching my lso increse the decomposition of incorported orgnic mtter nd subsequent relese of soil nutrients within the bed by incresing exposure of orgnic mtter to soil microbes (Wring 15

25 nd Schlesinger, 1985). Overll, bedding increses the volume nd qulity of the erly seedling rooting environment (Allen nd Cmpbell, 1988). Scheerer (1994) noted tht bedding "ppers to be n indispensble site preprtion tretment becuse it increses erly survivl of pine seedlings nd eventul stnd volume." Mulching s n Ameliortive Technique Mulching of orgnic mtter prior to bedding will increse the surfce re of given mss of slsh nd might lso increse decomposition nd nutrient relese by further incresing exposure of orgnic mtter to microbes. Due to poor ertion nd low ssocited oxygen levels in sturted soils, incorportion of this orgnic mtter might preserve it ginst decomposition under sturted conditions within the bed. These sturted soil conditions will not likely exist in beds for extended periods of time, especilly during the growing seson when evpotrnspirtion is high. Incorported orgnic mtter dditions might benefit rutted nd compcted soils by mixing in the soil profile nd consequently lowering the soil bulk density while incresing soil mcroporosity. These chnges in soil physicl properties will improve soil ertion nd increse suitble rooting volume within the soil profile. The "root growth window" of these mended soils might be enhnced, s discussed previously (Figure 1) (Childs et l., 1989; Wrring nd Schlesinger, 1985). Orgnic mtter incorportion nd decomposition might lso elevte totl orgnic crbon levels in soil moisture in the beds. Totl orgnic crbon concentrtions vry widely in forest soil solutions nd generlly rnge from 5 to 50 ppm in A horizons, 3 to 10 ppm in B horizons, nd 1 to 5 ppm in C horizons (Herbert nd Bertsch, 1995). Mulhollnd (1981) found TOC concentrtions to verge 2.5 ppm in the surfce wter of n estern North Crolin swmp-strem ecosystem. Tillge s n Ameliortive Technique Tilling mechniclly mixes minerl soil nd surfce orgnic mtter with rotry tiller or disc hrrow. Tillge breks orgnic mtter into smll pieces nd incorportes it into the soil 16

26 profile (Dickerson, 1976; Willims, 1988). The effects of tillge on soil physicl nd chemicl properties re very similr to those discussed previously for bedding under unsturted conditions (i.e., decreses bulk density, increses mcroporosity, ertion, wter infiltrtion nd movement, nd suitble rooting volume). Tillge lone in wetlnds does not increse the elevtion or volume of the rooting environment (USDA, 1997), nd orgnic mtter decomposition nd ssocited nutrient evolution nd movement my not occur s with bedding. Aust et l. (1998) found tht tillge of skid trils without bedding or fertiliztion ctully decresed loblolly pine survivl nd growth compred to non-treted skid tril on wet flt sites in South Crolin. Tilling n re prior to bedding my result in effects on soil physicl nd chemicl properties tht re very similr to those of bedding lone. This combintion, however, will ensure tht compcted soil will not be buried beneth the bed nd possibly inhibit root growth below the bed. This combintion will lso brek orgnic mtter into smller pieces nd possibly distribute it more uniformly within the bed. The smller orgnic mtter pieces will be more esily decomposed under unsturted conditions nd my led to greter nutrient nd crbon concentrtions in soil moisture s well s incresed crbon dioxide evolution. Fertiliztion s n Ameliortive Technique Scheerer (1994) noted tht fertiliztion is less expensive thn bedding or tilling (by %) nd cn llevite tree nutrition problems tht re often cused by the soil physicl property dmge done by forest hrvesting (Allen nd Cmpbell, 1988; Hrt et l., 1985). Fertiliztion mkes nutrients more vilble to tree root systems tht re growth- prohibited by poor soil physicl conditions. Nitrogen (DAP nd UREA) nd phosphorus (DAP - dimmonium phosphte) re the most commonly pplied nutrients t vrious rtes on loblolly pine plnttions in the southest. Severl reserchers hve noted significnt height growth nd survivl gins in loblolly plnttions tht hd DAP pplictions t or ner the time of plnting (Pritchett nd Comerford, 1982; Wilhite nd McKee, 1986). Nitrogen is often pplied to loblolly pine plnttions t intervls of 5 to 15 yers to enhnce the inherent productivity of site. 17

27 METHODS AND MATERIALS Site Descriptions The study sites were in the lower costl plin, ner Wshington in Beufort County, North Crolin (ltitude 37 o 27 37, longitude 77 o ) on Weyerheuser Compny lnds (Figure 2). The Pmlico River flows west to est through the center of Beufort County, nd the generl elevtion of the county is bout 25 feet (7.6 m) bove men se level. Figure 2. Mp of the generl physiogrphic provinces of the southern United Sttes nd generl loction of the study sites mrked with str (Miw, 1999). The verge dily mximum temperture in Jnury is 55 o F (13 o C) nd the verge dily minimum temperture is 34 o F (1 o C). The verge dily mximum temperture in July is 87 o F (31 o C) nd the verge dily minimum temperture is 70 o F (21 o C). Totl nnul precipittion is pproximtely 53 inches (134.6 cm), with 55% flling in April through September (USDA Nturl Resources Conservtion Service, 1995). 18

28 The two sites were pocosin site with modertely deep orgnic surfce horizon (histic epipedon) nd wet flt site hving sndy lom horizon (ochric epipedon) over cly (rgillic) subsurfce horizon (USDA Soil Conservtion Service, 1997b). The pocosin site is n Umbric Plequult (Pntego Lom) nd the wet flt is n Aeric Plequult (Lenoir Lom) (USDA, Nturl Resources Conservtion Service, 1995). The wet flt site ws most recently hrvested in Jnury The trees were hrvested with conventionl swhed feller-buncher nd rubber-tired skidder opertion. A whole-tree chipper ws used on site to chip hrdwoods into fuel chips prior to trnsporttion. This stnd ws estblished in 1970 by mens of nturl regenertion. On this site, pproximtely 5.6 cunits/cre (45.5 m 3 /h) of loblolly pine were removed s roundwood for vrious product uses. Approximtely 12.0 cunits/cre (83.9 m 3 /h) of wood from vrious hrdwood species were removed s chips for energy fiber uses. Common hrdwood species included sweetgum, red mple, wter ok, yellow-poplr (Liriodendron tulipifer), nd blck gum (Nyss sylvtic). The loblolly pine site index t bse ge 25 yers ws pproximtely ft ( m). The pocosin site ws most recently hrvested in Jnury nd August The trees were hrvested with conventionl swhed feller-buncher nd rubber-tired skidder opertion. A whole-tree chipper ws used on site to chip hrdwoods into fuel chips prior to trnsporttion. This stnd ws regenerted in 1963 with direct seeding of loblolly pine. On this site, pproximtely 19.2 cunits/cre (134.3 m 3 /h) of loblolly pine were removed s roundwood for vrious product uses. Approximtely 0.5 cunits/cre (3.5 m 3 /h) of wood from vrious hrdwood species were removed s chips for pulp nd energy fiber uses. Common hrdwood species included red mple nd wter ok. These two sites were intensively mnged for the production of loblolly pine swtimber. This mngement includes rtificil dringe (ditching), mechnicl nd chemicl site preprtion, weed competition control, nd pest control with two commercil thinnings before finl hrvest t ge 35 to 40 yers. Instlltion of tretments ws overseen by the 19

29 USDA Forest Service nd Weyerheuser Compny. Due to the gret differences between sites, ech ws considered to be n independent experiment. Lyout nd Generl Sttisticl Design Ech tretment plot mesured 132 ft (40.2 m) on ech side nd included 0.4 cres (0.16 h). The center of ech tretment plot served s the center of single 1/50 cre (1/124 h) circulr mesurement plot. All mesurements (pre- nd post-tretment) were tken in this mesurement plot. A 33-ft (10.1-m) buffer of lnd (post-hrvest condition) ws left between ll blocks nd tretment plots (Figures 3 nd 4). A hnd compss nd 50-foot tpe were used to instll these plots. Bed-lines were positioned nd mrked beginning 12 feet inside the tretment plot boundry nd locted every 18 feet therefter, for totl of 7 beds per plot. All bedding tretments were performed long these estblished loctions. The tretments re described below. Tretment 1 (conventionl). The conventionl tretment consisted of conventionl site preprtion methods for the North Crolin costl plin. These methods included trctor-mounted (Cterpillr D8) V-sher blde to push slsh nd debris wy from the bed-lines, followed by bedding with trctor-mounted Svnnh plow. Tretment 2 (mulch/bed). The strip-surfce mulch with bedding tretment consisted of strip-surfce mulching of slsh nd stumps long the bedline followed by trditionl bedding. A trctor-mounted Ryco hydr stumper mulching hed ws used to perform the mulching tsks. This mulching hed ws used to mulch ll slsh nd stumps in 6.5- ft (2.0-m) wide strip long the left nd right side of the bed line. The resulting mulched strip ws 13 feet (4.0 m) wide, centered on the bed lines, nd ws then incorported into the beds by the plow. Tretment 3 (mulch/till/bed). The strip mulch with tillge nd bedding tretment consisted of the exct mnipultions described for Tretment 2, except tht the Ryco TM mulching hed ws set to till the soil to soil depth of 4 inches (10.2 cm) prior to bedding. 20