! ! SPATIAL!AND!TEMPORAL!NITROGEN!SYNCHRONY!IN!RIDGE!TILLAGE!SYSTEMS!AS!COMPARED!TO! CHISEL!PLOW!SYSTEMS! ! By! ! Daniel!Kane! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! A!THESIS! ! Submitted!to! Michigan!State!University! in!partial!fulfillment!of!the!requirements! for!the!degree!of! ! Crop!and!Soil!Sciences!–!Master!of!Science! ! 2013 ABSTRACT! ! SPATIAL!AND!TEMPORAL!NITROGEN!SYNCHRONY!IN!RIDGE!TILLAGE!SYSTEMS!AS!COMPARED!TO! CHISEL!PLOW!SYSTEMS! ! By! Daniel!Kane! ! Ridge!tillage!(RT)!is!a!Precision!Zonal!Management!(PZM)!system,!most!commonly!used! in!cornTsoybean!rotations,!that!creates!raised!beds!for!planting!through!the!repeated!relocation! of!soil!and!residues!from!between!rows.!Several!studies!have!found!that!with!longTterm! management,!the!ridge!and!furrow!spaces!develop!distinct!biological!and!physical!profiles.!The! creation!of!these!zones!has!important!implications!for!nitrogen!(N)!availability!in!RT!systems.! ! To!examine!how!RT!might!alter!patterns!of!N!distribution!and!mineralization,!we! conducted!experiments!in!a!tillage!study!fully!replicated!at!two!sites!in!Urbana,!Illinois!(IL)!and! Mason,!Michigan!(MI).!Over!the!2012!growing!season,!fine!resolution!soil!monitoring!was!done! in!zeroTfertilizer!subTplots!for!inorganic!N,!potentially!mineralizable!N,!particulate!organic! matter,!ion!exchange!N,!and!plant!N!status.!Consistent!with!previous!research,!we!found!that! RT!increased!labile!N!pools,!as!well!as!in!situ!measurements!of!N!mineralization!by!ion! exchange!resins!in!the!ridge!positions!relative!to!the!furrow.!As!well,!mean!cumulative!NO3! adsorption!summed!across!all!positions,!depths,!and!sampling!points!was!greater!in!RT! treatments!than!in!CP!treatments.!Higher!per!plant!yields!and!total!plant!and!grain!N! concentrations!also!indicated!that!the!effect!of!RT!on!soil!N!pools!may!have!increased!N!uptake! in!RT!plants!relative!to!CP!plants.!Results!were!consistent!with!RT!having!the!potential!to!create! distinct!soil!functional!zones!with!the!potential!to!improve!spatial!N!synchrony. ! Copyright!by! DANIEL!KANE! 2013! ! ! ! ACKNOWLEDGEMENTS! ! ! I!would!like!to!thank!my!advisor,!Dr.!Sieg!Snapp,!for!taking!me!on!as!a!M.S.!student,! guiding!me!through!the!process!of!developing!a!research!project!and!executing!it,!and!for! having!such!great!confidence!in!me.!I’ve!learned!a!great!deal!under!your!tutelage!and!your! confidence!in!me!has!helped!me!complete!the!thesis!process.!I’d!also!like!to!thank!my! committee!members,!Dr.!Dan!Brainard!and!Dr.!Stuart!Grandy,!for!providing!feedback!and!new! ideas!as!I!developed!my!project!and!began!producing!data,!as!well!as!Dr.!Adam!Davis,!who! allowed!me!access!to!the!site!at!University!of!Illinois.!! ! I!also!owe!a!great!deal!of!thanks!to!a!number!of!lab!employees!and!fellow!students!for! their!help!with!fieldwork,!ideas,!and!support.!In!particular,!I’d!like!to!thank!Rich!Price,!for!his! help!with!fieldwork!and!excellent!management!of!the!field!site;!Sowmya!Surapur,!for!her!help! in!completing!nitrogen!analyses;!Steve!Culman,!for!his!help!understanding!and!refining!nitrogen! analysis!methods!and!ideas;!and!Mark!Freeman,!for!his!help!with!all!manner!of!analyses.! Thanks!also!go!to!Jodie!Schonfelder,!Rita!House,!Linda!Colon,!and!the!rest!of!the!CSS! administration!for!their!help!in!navigating!the!MSU!bureaucracy.!! ! I’d!like!to!thank!my!mother,!father,!brother,!and!sister,!as!well!as!my!future!inTlaws!for! their!love!and!support,!and!for!keeping!me!grounded!throughout!this!process.!Finally,!I’d!like!to! thank!my!fiancée,!Emily!May.!Without!your!love!and!support,!this!degree!would!have!been! infinitely!harder.! ! ! iv! ! TABLE!OF!CONTENTS! ! LIST!OF!TABLES! ! LIST!OF!FIGURES! ! LIST!OF!ABBREVIATIONS! ! INTRODUCTION:! Ecosystem!services!in!agriculture:! ReTcoupling!strategies,!risk,!and!N!synchrony:!! Precision!Zonal!Management!(PZM):! Ridge!tillage:! Objectives:! ! CHAPTER!ONE! Spatial!patterns!of!labile!nitrogen!in!ridge!tillage!systems!with!and!without! cover!crop!as!compared!to!chisel!plow! Abstract:! 1.1.!Introduction:!! 1.2.!Objectives:! 1.3.!Methods:! !!!!!!1.3.1.!Site!description:! !!!!!!1.3.2.!Experimental!design:! !!!!!!1.3.3.!Soil!sampling:! !!!!!!1.3.4.!Inorganic!N!and!potentially!mineralizable!N:! !!!!!!1.3.5.!Plate!method:! !!!!!!1.3.6.!Particulate!organic!matter:! !!!!!!1.3.7.!Data!analysis:! 1.4.!Results:! !!!!!!1.4.1.!2012!weather:! !!!!!!1.4.2.!Nitrate:! !!!!!!1.4.3.!Ammonium:! !!!!!!1.4.4.!Potentially!mineralizable!nitrogen:! !!!!!!1.4.5.!Particulate!organic!matter:! 1.5.!Discussion:!! 1.6.!Conclusions:!! ! CHAPTER!TWO! Spatial!and!temporal!dynamics!of!nitrogen!(N)!availability!in!ridge!tillage! systems!and!effects!on!plant!N!uptake! Abstract:! v! vii! ! x! ! xii! ! ! 1! 4! 5! 6! 9! ! ! ! 10! 10! 11! 14! 14! 14! 14! 15! 16! 16! 18! 18! 19! 19! 20! 21! 22! 23! 24! 28! ! ! ! 55! 55! ! 2.1.!Introduction:!! 2.2.!Objectives:! 2.3.!Methods:!! !!!!!!!2.3.1.!Ion!exchange!resins:! !!!!!!!2.3.2.!SPAD:! !!!!!!!2.3.3.!Biomass,!yield,!and!tissue!C:N:! !!!!!!!2.3.4.!Gravimetric!water!content:!! !!!!!!!2.3.5.!Data!analysis:! 2.4!Results:!! !!!!!!!2.4.1.!2012!weather:! !!!!!!!2.4.2.!Ion!resin!strips!nitrate:! !!!!!!!2.4.3.!Ion!resin!strip!ammonium:! !!!!!!!2.4.4.!SPAD:! !!!!!!!2.4.5.!Yield!and!biomass:! !!!!!!!2.4.6.!Tissue!N:! !!!!!!!2.4.7.!Gravimetric!water!content:! 2.5!Discussion:! 2.6!Conclusions:!! ! REFERENCES!! ! ! ! vi! 56! 58! 59! 59! 60! 61! 61! 62! 62! 62! 63! 64! 64! 65! 65! 66! 67! 72! ! 95! ! LIST!OF!TABLES! ! Tables!1.1.a!and!1.1.b:!ThirtyTyear!climate!averages!! ! ! ! ! !!!!!!!!29! Table!1.2:!2012!management!tables!!! ! ! ! ! ! ! !!!!!!!!29! Tables!1.3.a!and!1.3.b:!2012!weather!data! ! ! ! ! ! ! !!!!!!!!30! Table!1.4:!Mean!soil!NO3!combined!across!depths!for!Soil!Sampling!1! !! ! !!!!!!!!34! Table!1.5:!Results!for!ANOVAs!on!NO3!data!from!Soil!Sampling!1! ! ! ! !!!!!!!!34! Table!1.6:!Mean!soil!NO3!combined!across!depths!for!Soil!Sampling!2! ! ! !!!!!!!!36! Table!1.7:!Results!for!ANOVAs!on!NO3!data!from!Soil!Sampling!2! ! ! ! !!!!!!!!36! Table!1.8:!Mean!soil!NO3!combined!across!depths!for!Soil!Sampling!3! ! ! !!!!!!!!37! Table!1.9:!Results!for!ANOVA!on!NO3!data!from!Soil!Sampling!3! ! ! !!!!!!!!38! Table!1.10:!Mean!soil!NH4!combined!across!depths!for!Soil!Sampling!1! ! ! !!!!!!!!40! Table!1.11:!Results!for!ANOVAs!on!NH4!data!from!Soil!Sampling!1! ! ! !!! !!!!!!!!40! Table!1.12:!Mean!soil!NH4!combined!across!depths!for!Soil!Sampling!2! ! ! !!!!!!!!42! Table!1.13:!Results!for!ANOVAs!on!NH4!data!from!Soil!Sampling!2! ! ! ! !!!!!!!!42! Table!1.14:!Mean!soil!NH4!combined!across!depths!for!Soil!Sampling!3! ! ! !!!!!!!!43! Table!1.15:!Results!for!ANOVA!on!NH4!data!from!Soil!Sampling!3! ! ! ! !!!!!!!!44! Table!1.16:!Results!for!ANOVAs!on!PMN!data!from!Soil!Sampling!1!! ! ! !!!!!!!!46! Table!1.17:!Mean!soil!PMN!combined!across!depths!for!Soil!Sampling!2! ! ! !!!!!!!!48! Table!1.18:!Results!for!ANOVAs!on!PMN!data!from!Soil!Sampling!2!! ! ! !!!!!!!!48! Table!1.19:!Mean!soil!PMN!combined!across!depths!for!Soil!Sampling!3! !!! ! !!!!!!!!49! Table!1.20:!Results!for!ANOVA!on!PMN!data!from!Soil!Sampling!3! ! ! ! !!!!!!!!50! vii! ! ! Tables!1.21.a!and!1.21.b:!Results!for!ANOVAs!on!POMTC!data!from!Soil!Sampling!2! !!!!!!!!52! Tables!1.22.a!and!1.21.b:!Results!for!ANOVAs!on!POMTN!data!from!Soil!Sampling!2! !!!!!!!!54! Table!2.1:!2012!management!tables! ! ! ! ! ! ! !!! !!!!!!!!73! ! ! ! ! !!!!!!!!73! Table!2.3:!EndTofTseason!cumulative!NO3!adsorbed!by!ion!strips! ! ! ! !!!!!!!!75! Table!2.4:!Results!for!ANOVA!on!cumulative!ion!strip!NO3!data! ! ! !!!!!!!!75! Table!2.5:!Results!for!repeated!measures!ANOVA!on!ion!NO3!adsorption!rate!data! !!!!!!!!77! Table!2.6:!EndTofTseason!cumulative!NH4!adsorbed!by!ion!strips! ! ! ! !!!!!!!!79! Table!2.7:!Results!for!ANOVA!on!cumulative!ion!strip!NH4!data! ! ! !!!!!!!!79! Table!2.8:!Results!for!repeated!measures!ANOVA!on!ion!NH4!adsorption!rate!data! !!!!!!!!81! Table!2.9:!Chlorophyll!content!(SPAD!units)!at!V6,!V12,!VT,!and!R2!! ! ! !!!!!!!!83! Table!2.10:!Results!for!repeated!measures!ANOVA!on!SPAD!data! ! ! ! !!!!!!!!83! Table!2.11:!Corn!yield!of!zeroTfertilizer!plots!measured!on!an!areal!basis! ! ! !!!!!!!!84! Table!2.12:!Results!of!ANOVA!on!yield!data!measured!on!an!areal!basis! ! ! !!!!!!!!84! Table!2.13:!Corn!yield!of!zeroTfertilizer!plots!measured!on!a!per!plant!basis! ! !!!!!!!!85! Table!2.14:!Results!of!ANOVA!on!yield!data!measured!on!a!per!plant!basis!! !! !!!!!!!!85! Table!2.15:!Per!plant!biomass!of!zeroTfertilizer!plots!! ! ! ! ! !!!!!!!!86! Table!2.16:!Results!of!ANOVA!on!per!plant!biomass!data! ! ! ! ! !!!!!!!!86! Table!2.17:!Total!tissue!N!concentration!of!plants!in!zeroTfertilizer!plots! ! ! !!!!!!!!87! Table!2.18:!Results!of!ANOVA!on!total!tissue!N!concentration!data!! ! ! !!!!!!!!87! Table!2.19:!Grain!tissue!N!concentration!of!plants!in!zeroTfertilizer!plots! ! ! !!!!!!!!88! Table!2.20:!Results!of!ANOVA!on!grain!tissue!N!concentration!data!! !!!! !!!!!!!!88! Table!2.2:!Dates!of!ion!strip!sampling!periods!in!2012! viii! ! ! ! ! Table!2.21:!Results!of!ANOVA!on!soil!GWC!data!from!Soil!Sampling!1! ! ! !!!!!!!!90! Table!2.22:!Results!of!ANOVA!on!soil!GWC!data!from!Soil!Sampling!2! ! ! !!!!!!!!92! Table!2.23:!Results!of!ANOVA!on!soil!GWC!data!from!Soil!Sampling!3! ! ! !!!!!!!!94! ! ! ! ! ! ! ix! ! LIST!OF!FIGURES! ! Figs.!1.1.a!and!1.1.b:!Mean!daily!soil!VWC!at!0T5!cm!depth!!! ! ! ! !!!!!!!!31! Figs.!1.2.a!and!1.2.b:!Mean!daily!soil!temperature!at!0T5!cm!depth!! ! ! !!!!!!!!32! Figs.!1.3.a!and!1.3.b:!Soil!NO3!combined!across!depths!for!Soil!Sampling!1!! ! !!!!!!!!33! Figs.!1.4.a!and!1.4.b:!Soil!NO3!combined!across!depths!for!Soil!Sampling!2!! ! !!!!!!!!35! Fig.!1.5:!Soil!NO3!combined!across!depths!for!Soil!Sampling!3! ! ! !!!!!!!!37! Figs.!1.6.a!and!1.6.b:!Soil!NH4!combined!across!depths!for!Soil!Sampling!1!! ! !!!!!!!!39! Figs.!1.7.a!and!1.7.b:!Soil!NH4!combined!across!depths!for!Soil!Sampling!2!! ! !!!!!!!!41! Fig.!1.8:!Soil!NH4!combined!across!depths!for!Soil!Sampling!3! ! ! ! !!!!!!!!43! Figs.!1.9.a!and!1.9.b:!Boxplots!of!soil!PMN!for!Soil!Sampling!1! ! ! ! !!!!!!!!45! Figs.!1.10.a!and!1.10.b:!Soil!PMN!combined!across!depths!for!Soil!Sampling!2! ! !!!!!!!!47! Fig.!1.11:!Soil!PMN!combined!across!depths!for!Soil!Sampling!3! ! ! ! !!!!!!!!49! Figs.!1.12.a!and!1.12.b:!Boxplots!of!POMTC!for!Soil!Sampling!2! ! ! ! !!!!!!!!51! Figs.!1.13.a!and!1.13.b:!Boxplots!of!POMTN!for!Soil!Sampling!2! ! ! ! !!!!!!!!53! Fig.!2.1:!Cumulative!NO3!adsorbed!by!ion!strips!throughout!2012!growing!season!! !!!!!!!!74! Fig.!2.2:!NO3!adsorption!rates!by!ion!strips!throughout!2012!growing!season! ! !!!!!!!!76! Fig.!2.3:!Cumulative!NH4!adsorbed!by!ion!strips!throughout!2012!growing!season!! !!!!!!!!78! Fig.!2.4:!NH4!adsorption!rates!by!ion!strips!throughout!2012!growing!season! !! !!!!!!!!80! Fig.!2.5:!Chlorophyll!content!(SPAD!units)!at!V6,!V12,!VT,!and!R2! ! !! !!!!!!!!82! Fig.!2.6:!Boxplots!of!yield!in!zeroTfertilizer!plots!measured!on!an!areal!basis! ! !!!!!!!!84! Fig.!2.7:!Boxplots!of!yield!in!zeroTfertilizer!plots!measured!on!a!per!plant!basis! ! !!!!!!!!85! x! ! ! ! Fig.!2.8:!Boxplots!of!per!plant!biomass!in!zeroTfertilizer!plots!! ! !!!!!!!!86! Fig.!2.9:!Boxplots!of!total!tissue!N!concentration!of!plants!in!zeroTfertilizer!plots! ! !!!!!!!!87! Fig.!2.10:!Boxplots!of!grain!tissue!N!concentration!of!plants!in!zeroTfertilizer!plots!! !!!!!!!!88! Figs.!2.11.a!and!2.11.b:!Boxplots!of!soil!GWC!data!from!Soil!Sampling!1! ! ! !!!!!!!!89! Figs.!2.12.a!and!2.12.b:!Boxplots!of!soil!GWC!data!from!Soil!Sampling!2! ! ! !!!!!!!!91! Fig.!2.13:!Boxplots!of!soil!GWC!data!from!Soil!Sampling!3! ! ! !!!!!!!!! !!!!!!!!93! ! ! ! ! ! xi! ! ! ! ! LIST!OF!ABBREVIATIONS! ! PZM:!Precision!Zonal!Management! RT:!Ridge!tillage! ! CP:!Chisel!plow! ! CPTfallow:!Chisel!plow!with!winter!fallow! ! CPTrye:!Chisel!plow!with!winter!rye!cover!crop! ! RTTfallow:!Ridge!tillage!with!winter!fallow! ! RTTrye:!Ridge!tillage!with!winter!rye!cover! ! C:!Carbon! ! N:!Nitrogen! ! NO3:!Nitrate! ! NH4:!Ammonium! ! POM:!Particulate!Organic!Matter! ! POMTN:!Particulate!Organic!Matter!Nitrogen! ! POMTC:!Particulate!Organic!Matter!Carbon! ! GWC:!Gravimetric!Water!Content! ! VWC:!Volumetric!water!content! ! ! ! xii! ! INTRODUCTION:! Ecosystem!services!in!agriculture:! ! Agroecosystems!are!primarily!managed!for!provisioning!ecosystem!services!–!the! production!of!food,!fiber,!and!fuel!for!human!and!animal!consumption.!While!major!gains!in! global!agricultural!productivity!have!generally!been!a!boon,!the!pursuit!of!everTincreasing! production!goals!has!resulted!in!a!number!of!simultaneous,!unintended!ecosystem!disservices.! Synthetic!fertilizers!have!vastly!increased!the!productive!capacity!of!agriculture!in!the!past! century!by!providing!farmers!with!a!cheap!and!abundant!source!of!soluble!nitrogen!(N)!for!crop! growth,!replacing!nitrogenTfixing!legumes!and!existing!soil!N!pools!as!primary!sources!of! fertility!(Robertson!and!Vitousek!2009).!But!despite!its!benefits!to!productivity,!the!use!of!N! fertilizer!in!current!practice!comes!at!a!variety!of!wellTdocumented!external!costs.!Nitrate! leaching!to!groundwater!can!lead!to!eutrophication!in!inland!fresh!water!and!hypoxia!in!coastal! marine!waters,!severely!compromising!the!integrity!of!aquatic!ecosystems!(Robertson!and! Vitousek!2009).!Recent!research!has!also!determined!that!high!N!application!rates!often!result! in!higher!rates!of!denitrification!that!lead!to!greater!emissions!of!N2O,!a!potent!greenhouse!gas! (Hoben!et!al.!2011).!Though!accurate!estimates!are!difficult!to!make,!it’s!possible!only!47%!of! fertilizer!N!applied!to!agricultural!fields!makes!its!way!into!crop!plants,!while!the!rest!is!lost!to! the!environment!(Galloway!and!Cowling!2002).!! ! Similarly,!decades!of!extensive!tillage!and!disadoption!of!practices!such!as!summer! fallow!and!crop!rotation!have!led!to!major!declines!in!soil!carbon!(C)!stocks!and!a!concomitant! loss!of!soil!quality.!Globally,!soils!are!an!important!terrestrial!C!sink.!Lal!(2004)!estimates!that! the!conversion!of!soils!to!agricultural!production!accounts!for!as!much!as!50!–!66%!of!the!loss! 1! ! of!stored!C!from!terrestrial!ecosystems.!The!mechanism!for!soil!C!loss!by!tillage!is!well! understood,!as!the!mechanical!action!of!tillage!destroys!soil!aggregates!that!protect!organic! matter!from!microbes!and!decomposition!(Six!et!al.!1998!and!2004).!Janzen!et!al.!(1998)!and! Grandy!and!Robertson!(2006)!both!found!that!tillage!of!previously!uncultivated!soils!can! severely!reduce!soil!C!due!to!the!destruction!of!aggregates.!As!inputs!to!soil!C!stocks!are! outpaced!by!tillageTinduced!losses!to!respiration,!agricultural!soils!lose!their!capacity!to!act!as! sinks!(Schlesinger!and!Andrews!2000).!This!loss!of!soils!as!a!C!sink!has!important!implications! for!global!climate!change!(Lal!2004),!but!from!an!agronomic!perspective!the!loss!of!soil!C!should! also!be!alarming!to!farmers.!Soil!C!plays!a!crucial!role!in!creating!and!maintaining!adequate!soil! structure,!acting!as!a!substrate!for!soil!microbia!that!produce!compounds!that!cement! aggregates!(Bronick!and!Lal!2004,!Reeves!1997).!Plus,!it!is!a!useful!source!of!nutrients!for!crops,! particularly!N,!that!should!be!considered!as!an!alternative!or!a!complement!to!the!use!of! synthetic!fertilizers!(Janzen!2006,!Drinkwater!and!Snapp!2007).!! ! A!growing!interest!among!scientists!and!producers!in!mitigating!these!disservices!onT farm!has!led!to!a!proliferation!of!technologies,!management!strategies,!and!research.!Some!of! these!strategies!tend!to!place!costs!on!growers!through!increased!seed,!labor,!and!equipment! costs,!but!they!often!have!the!added!incentive!of!enhancing!other!ecosystem!services,! particularly!those!related!to!increasing!soil!organic!matter.!One!example!of!an!onTfarm!strategy! is!the!use!of!winter!cereal!cover!crops,!which!has!been!widely!demonstrated!to!reduce!N! leaching!while!increasing!soil!organic!matter!(Snapp!et!al.!2005).!Similarly,!a!review!of!research! on!leguminous!cover!crops!by!Tonitto!et!al.!(2006)!found!that!their!nitrogen!fixation!potential! could!displace!a!significant!amount!of!the!recommended!fertilizer!in!some!cases.!LongTterm!use! 2! ! of!cover!crops!and!increased!rotational!complexity!have!been!demonstrated!to!both!mitigate! disservices!from!agriculture,!stabilize!and!improve!yields,!and!increase!soil!quality!(Davis!et!al.! 2012).! ! Similarly,!years!of!research!on!conservation!tillage!systems!have!shown!that!reducing! disturbance!can!increase!soil!C!pools!while!also!protecting!beneficial!soil!microbes!(Reeves! 1997).!By!reducing!disturbance,!conservation!tillage!systems!encourage!the!physical!protection! of!organic!matter!in!microaggregates!(Balesdent!et!al.!2000,!Six!et!al.!1998!and!2004).!This! protection!enhances!soil!stability!(Bronick!and!Lal!2004),!reducing!erosion!and!concomitant! pollution!(Phillips!et!al.!1980).!Several!studies!of!noTtill!and!conservation!tillage!systems!have! also!found!that!they!are!capable!of!increasing!nutrient!availability!at!surface!depths!(Varvel!and! Wilhelm!2011,!Tebrugge!and!During!1999,!Doran!1994,!Yang!and!Wander!1999).!Reductions!in! disturbance!also!protect!soil!microbial!communities,!particularly!fungal!communities!by! preventing!the!destruction!of!fungal!hyphae!(Helgason!et!al.!2009,!Frey!et!al.!1999).!Protecting! microbial!communities!can!improve!the!capacity!of!plants!to!obtain!nutrients!from!soils!as! fungal!colonization!of!roots!increases!(Jansa!et!al.!2003),!fungi!translocate!nutrients!to!surface! soils!(Frey!et!al.!1999),!and!overall!rates!of!N!cycling!can!be!enhanced!(Muruganandam!et!al.! 2010).!A!longTterm!study!of!conservation!tillage!systems!at!the!Kellogg!Biological!Station!also! found!that!these!systems!can!be!economically!viable,!as!yield!averages!and!variability!is! comparable!to!more!conventional!tillage!schemes!(Smith!et!al.!2007).!! ! With!their!focus!on!capturing!or!fixing!N!in!organic!forms!through!the!use!of!cover!crops! and!protecting!existing!soil!organic!matter!pools!by!reducing!disturbance,!these!strategies!are! often!characterized!by!soil!scientists!and!agroecologists!as!a!reTcoupling!of!C!and!N!cycles.! 3! ! Nitrogen!associated!with!organic!matter!is!generally!less!mobile!and!reactive!than!nitrate,! giving!these!pools!a!longer!mean!residence!time!in!soils!and!reducing!the!possibility!of!loss! through!leaching!or!denitrification!(Drinkwater!and!Snapp!2007).!At!the!same!time,!increased! organic!matter!provides!its!numerous,!wellTdocumented!benefits!to!soil!structure!and!microbial! communities.!Approaches!such!as!these!have!powerful!potential!and!are!essential!in!lowTinput! systems!such!as!organic!operations,!but!they!can!also!entail!some!risks!that!should!be!carefully! considered.!! ReTcoupling!strategies,!risk!and!N!synchrony:! ! Organic!matter!nitrogen!must!be!converted!into!plant!available!forms!via!microbiallyT mediated!processes!before!plant!uptake!is!possible.!These!processes!are!strongly!influenced!by! a!number!of!soil!conditions,!including!temperature!and!moisture!(Zak!et!al.!1999,!Miller!and! Johnson!1964),!and!the!ratio!of!C!to!N!in!SOM!at!a!given!time!(Robertson!and!Vitousek!2009).!In! systems!with!high!residue!inputs,!microbes!metabolizing!the!carbon!in!residues!will!uptake! mineral!N!reducing!its!availability!to!crop!plants!–!a!process!known!as!N!immobilization.! Incorporation!of!cover!crops!results!in!a!particularly!strong!immobilization!effect!early!in!the! season!that!can!dissipate!but!does!reduce!N!availability!in!the!early!season!(McSwiney!et!al.! 2010).!Rice!and!Smith!(1984)!and!Lupwayi!et!al.!(2006)!also!found!that!noTtill!systems!had! increased!rates!of!N!immobilization!in!surface!soils!as!residues!accumulate!there.!Similarly,! Smith!et!al.!(2007)!found!in!the!study!at!Kellogg!Biological!Station!that!contrary!to!the!findings! of!Davis!et!al.!(2012),!exclusive!reliance!on!cover!crops!introduced!yield!variability!across! several!years,!despite!other!soil!enhancements.!Relying!on!organic!nitrogen!pools!could!entail! opportunity!costs!for!growers!as!crop!demand!for!N!and!its!mineralization!from!organic!matter,! 4! ! which!is!highly!dependent!upon!conditions!at!the!time,!are!not!always!well!synchronized.!If!N! deficits!in!the!soil!occur!at!a!time!when!plant!demand!for!N!is!high,!plant!growth!can!be! affected,!impacting!yields.!Synchronizing!these!processes!of!supply!and!demand!are!essential!to! ensuring!the!efficacy!of!conservation!strategies.!! Precision!Zonal!Management!(PZM):! ! Arguably,!some!conservation!strategies!promote!the!enhancement!of!longTterm! regulating!services!to!the!detriment!of!services!that!support!shortTterm!production!goals,!such! as!timely!nutrient!turnover.!In!his!2006!review,!Janzen!argues!that!the!recent!interest!in! conservation!tillage!strategies!has!overshadowed!the!benefits!of!utilizing!soil!C!resources! through!tillage,!which!generally!enhances!conditions!for!nutrient!turnover!by!increasing! aeration,!soil!temperature,!and!releasing!physically!protected!SOM!from!aggregates.!Although! his!argument!is!valid,!a!widespread!return!to!more!extensive,!conventional!tillage!strategies! without!a!simultaneous!reTadoption!of!rotational!complexity!or!fallow!periods!would!only!mean! a!return!to!previous!patterns!of!soil!degradation.!But!given!recent!advancements!in!agricultural! technology,!such!as!GPS!guidance!systems,!it!may!be!possible!to!achieve!adequate!regulating! and!provisioning!ecosystem!services!in!the!same!field!using!a!strategy!of!Precision!Zonal! Management!(PZM).!! ! PZM!is!a!management!approach!centered!on!strategic!tillage!and!residue!management.! Conceptually,!these!systems!strike!an!optimal!balance!between!regulating!and!provisioning! ecosystem!services!by!creating!zones!with!different!soil!biological!and!physical!characteristics.!! Typically,!there!is!a!planting!zone,!managed!to!optimize!nitrogen!turnover!and!soil!physical! 5! ! conditions!for!crop!growth,!and!an!adjacent!zone!of!protected!soil,!managed!to!increase!soil! organic!matter!pools!and!reduce!water!and!nutrient!losses!(Overstreet!and!Hoyt!2008).!The!! most!prominent!examples!of!PZM!systems!in!current!use!are!stripTtill!and!ridge!till.!Although! neither!is!a!new!technology,!their!ability!to!create!zones!in!the!row/interTrow!space!and!the! implications!for!both!production!and!ecosystem!services!make!them!an!interesting!alternative! to!more!popular!conservation!tillage!strategies!like!noTtill.!In!this!study,!we!focused!on!ridge! tillage!in!the!cornTsoybean!system.! Ridge!tillage:! ! Historically,!ridge!tillage!(RT)!has!been!used!in!the!smallholder!farmer!context,!with! ridges!being!made!by!hand!to!concentrate!soil!and!improve!root!growth!(Lal!1990).!At!an! agronomic!scale,!RT!involves!creating!permanent!raised!beds!for!planting!and!is!primarily!used! in!cornTsoybean!rotations,!although!analogous!systems!with!nonTpermanent!ridges!are!used!in! the!production!of!cotton!and!potatoes.!Before!planting,!the!ridge!crest!is!either!minimally! disturbed!to!create!a!seedbed!or!left!undisturbed.!Ridges!are!then!rebuilt!every!season!using!a! ridge!cultivator!that!moves!soil!from!the!furrow!onto!the!ridge!when!plants!are!at!a!sufficient! growth!stage!to!withstand!disturbance,!typically!around!V6!in!corn.!In!terms!of!production,!RT! is!comparable!to!other!conservation!tillage!schemes!overall!(Pikul!et!al.!2001)!but!may!enhance! production!in!systems!with!heavy,!poorlyTdrained!soils!(Cox!et!al.!1990).!In!recent!years!RT!has! been!disadopted!in!some!locations!as!noTtill!has!increased!in!popularity!and!efficacy,!but!it!was! a!popular!conservation!tillage!scheme!in!the!1980’s!and!early!1990’s!and!was!the!focus!of!a!fair! amount!of!research!then.!! 6! ! ! Important!field!research!on!RT!includes!several!longTterm!tillage!studies!that!investigate! RT!effects!on!soil!properties!as!compared!to!other!conservation!and!conventional!disturbance! tillage!practices!such!as!chisel!or!moldboard!plough.!In!three!separate!experiments!on!three! different!soil!types!RT!was!found!to!support!gains!in!soil!C!and!N!relative!to!conventional!tillage,! though!slightly!less!in!magnitude!than!noTtill!practices!(Zibiliske!et!al.!2002,!Varvel!and!Wilhelm! 2010,!and!Shi!et!al.!2012).!These!increases!are!likely!due!to!increases!in!aggregation!and! microbial!activity/biomass!brought!about!by!reduced!disturbance!(Zhang!et!al.!2012!and!2013).! With!higher!levels!of!soil!C,!RT!also!provides!some!of!the!same!soil!physical!and!microbial! benefits!as!noTtill!and!other!conservation!tillage!systems.!Zibilske!and!Bradford!(2007)!found! that!RT!increased!waterTholding!capacity!of!soils,!while!Miller!et!al.!(1995)!found!it!increased! fungal!colonization!of!roots!and!Neave!and!Fox!(1998)!found!it!increased!spring!invertebrate! populations!relative!to!conventional!tillage!by!moldboard!plow.!! A!key!difference!that!RT!offers!from!noTtill!and!other!types!of!conservation!tillage!is!in! its!alteration!of!the!threeTdimensional!structure!of!soil!by!the!repeated!translocation!of!soil! from!the!furrow!space!to!the!ridge.!The!creation!of!ridges!is!thought!to!have!pronounced! effects!on!soil!physical!characteristics!and!organic!matter!pools,!leading!to!the!creation!of!zones! in!RT!systems.!Although!there!is!a!limited!amount!of!research!on!what!characterizes!these! hypothesized!zones,!a!handful!of!studies!have!demonstrated!clear!soil!physical!and!biochemical! differences!between!the!ridge!and!furrow!spaces!in!RT!systems! ! Among!the!most!touted!benefits!of!RT!are!its!unique!effect!on!soil!water!distribution!in! the!row/interTrow!space!and!the!creation!of!temperature!gradients.!Chen!et!al.!(2011)! demonstrated!in!a!simulated!laboratory!experiment!that!water!preferentially!flows!to!furrows! 7! ! but!is!then!horizontally!distributed!by!the!negative!water!potential!of!the!ridge.!Similar!results! were!seen!in!the!field!by!Waddell!and!Weil!(1996).!This!pattern!leaves!the!ridge!space!dry!and! warm!but!not!droughty,!providing!optimal!conditions!for!planting!(Stone!et!al.!1990).!Combined! with!the!increased!waterTholding!capacity!of!protected!soil!in!the!furrow,!RT!is!a!moisture! conservative!system!that!can!still!avoid!issues!of!waterlogging!in!poorly!drained!soils!(Cox!et!al.! 1990).!This!moisture!gradient!can!also!have!a!unique!effect!on!roots,!drawing!their!growth!into! soil!beneath!the!furrow!space!(Kovar!et!al.!1992)!where!they!can!access!soil!moisture!and! nutrients.! ! The!repeated!movement!of!soil!and!residues!from!the!furrow!to!the!ridge!could!also! have!strong!effects!on!the!spatial!distribution!of!soil!C!and!N,!creating!gradients!across!the! row/interTrow!space.!Despite!multiple!studies!characterizing!longTterm!changes!in!these!pools! overall!in!RT!systems,!there!is!limited!research!on!whether!or!not!the!ridge!and!furrow!develop! unique!soil!biological!profiles.!The!strongest!evidence!for!zones!with!unique!chemical!profiles! was!found!by!Shi!et!al.!(2012),!who!sampled!soils!from!several!positions!across!the!row/interT row!space!of!a!longTterm!ridge!tillage!field!and!found!that!soil!C!and!N!were!higher!in!the!ridge! relative!to!the!furrow.!A!number!of!more!shortTterm!studies!have!found!functional!differences! between!zones,!including!differences!in!CO2!respiration!(Liebig!et!al.!1995,!Müller!et!al.!2009a)! and!soil!inorganic!N!concentrations!(Müller!et!al.!2009b).!! ! Given!evidence!for!zonation!of!both!soil!physical!and!chemical!properties,!as!well!as! results!from!several!longTterm!studies!demonstrating!its!carbon!sequestration!capacity,!RT!has! potential!as!a!PZM!system!that!can!balance!both!longTterm!regulating!ecosystem!services,!such! as!carbon!sequestration,!and!more!shortTterm!services,!such!as!N!mineralization,!that!support! 8! ! production!goals.!Detailed!studies!of!N!turnover!and!availability!to!support!crop!growth!have! not!been!studied!in!RT,!particulalrly!at!a!fine!scale!of!resolution.!Interaction!of!tillage!and!cover! crop!presence!is!expected!to!influence!N!dynamics,!as!temporary!immobilization!from!cover! crop!residues!has!been!shown!to!have!marked!effects!on!inorganic!N!status!in!corn!(McSwiney! et!al.,!2010).!Perhaps!surprisingly,!Eadie!et!al.!(1992)!demonstrated!that!rye!cover!had!no!effect! on!yield!in!RT!systems,!but!we!found!no!studies!examining!how!withinTseason!N!dynamics! might!change!in!RT!systems!when!a!cover!is!introduced.!Further!research!into!characterizing! ridge!and!furrow!zones,!as!well!as!understanding!how!those!zones!may!impact!withinTseason! nitrogen!dynamics!will!be!important!to!understanding!RT!potential!alone!or!combined!with! winter!cover!to!support!high!grain!yield!and!efficient!use!of!N.!! Objectives:! ! We!focused!this!study!on!withinTseason!N!dynamics!of!RT!systems!as!compared!to!chisel! plow!(CP)!systems.!In!addition,!we!investigated!interaction!of!tillage!systems!with!cover!crop! versus!fallow!management!over!the!winter.!More!specifically,!we!sought!to:! 1.) Characterize!how!the!process!of!reTridging!redistributes!residues,!organic! matter,!and!associated!nutrients!in!the!row/interTrow!space.!! 2.) Examine!how!RT!might!mitigate!the!effects!of!early!season!N!immobilization,! especially!where!a!winter!cover!crop!is!used.!! 3.) Verify!if!possible!effects!on!N!pools,!both!spatial!and!temporal,!affect!patterns!of! N!availability!in!situ,!and!examine!how!those!patterns!may!be!influenced!by!soil!physical! characteristics.!! 4.) Quantify!plant!N!uptake!in!all!experimental!treatments.!! 9! ! CHAPTER!ONE! Spatial!patterns!of!labile!nitrogen!in!ridge!tillage!systems!with!and!without!cover!crop!as! compared!to!chisel!plow! Abstract:! ! Ridge!tillage!(RT)!has!been!shown!to!increase!soil!carbon!(C)!and!(N)!at!surface!depths! over!long!periods!of!time!by!reducing!disturbance!in!a!manner!similar!to!other!conservation! tillage!systems!(Zibiliske!et!al.!2002,!Varvel!and!Wilhelm!2010).!The!repeated!movement!of! residues!and!soil!organic!matter!from!the!furrow!to!the!ridge!space!also!results!in!elevated! levels!of!C!in!the!ridge!space!relative!to!the!furrow!(Shi!et!al.!2012),!creating!soil!functional! zones!across!the!row/interTrow!space.!The!creation!of!these!zones!and!the!rebuilding!of!them! every!season!may!have!important!implications!for!spatial!and!temporal!patterns!in!N!pools,! especially!in!systems!that!employ!winter!cover!crops.!Several!studies!have!found!that!RT! systems!exhibit!higher!levels!of!microbial!respiration!and!inorganic!N!levels!in!the!ridge!position! at!different!points!in!the!season!(Clay!et!al.!1995,!Müller!et!al.!2009a!and!2009b,!Liebig!1995).!! ! To!test!how!RT!may!alter!the!spatial!distribution!of!N!pools!of!different!turnover!times,! we!sampled!a!tillage!study!fully!replicated!at!two!sites!in!Urbana,!Illinois!(IL)!and!Mason,! Michigan!(MI)!that!included!chisel!plow!(CP)!and!ridge!tillage!treatments!both!with!and!without! rye!winter!cover!crop!and!planted!to!corn!(Zea!mays)!in!the!2012!growing!season.!Sampling!was! conducted!at!fine!spatial!resolution!to!better!characterize!gradients!across!the!row/interTrow! space.!Differences!in!spatial!patterns!of!N!pools!were!not!seen!during!the!early!season!(10!d! after!planting).!But!following!reTridging,!potentially!mineralizable!nitrogen!(PMN)!and! particulate!organic!matter!carbon!and!nitrogen!(POMTC!and!POMTN)!were!both!increased!in!the! 10! ! ridge!position!of!RT!treatments!while!values!decreased!in!the!furrow.!Similar!spatial! redistribution!of!N!was!not!seen!for!CP!treatments.!This!result!is!consistent!with!previous! studies!and!is!strong!evidence!for!RT’s!utility!as!a!Precision!Zonal!Management!system!(PZM)! that!has!the!potential!to!improve!spatial!N!synchrony!in!agricultural!systems.!! 1.1.!Introduction:!! ! Ridge!tillage!(RT)!is!a!Precision!Zonal!Management!(PZM)!scheme!that!is!unique!in!how! it!manages!residues,!leaving!them!on!the!surface!in!the!furrow!during!the!spring,!then! concentrating!and!incorporating!them!in!the!ridge!space!at!reTridging.!This!spatially!explicit! method!of!management!has!been!shown!to!create!zones!in!soil!C!and!N!pools,!with!higher! levels!of!C!and!N!in!the!ridge!space!than!in!the!furrow!(Shi!et!al.!2012).!The!creation!of!these! zones!and!their!reTestablishment!every!year!has!important!implications!for!both!spatial!and! temporal!N!synchrony!and!the!distribution!of!N!pools!of!varying!turnover!rates!across!the! row/interTrow!space.!Concentrating!residues!to!the!inTrow!space!after!a!period!of! decomposition!in!the!furrow!may!make!their!associated!nutrients!more!available!to!plants,! especially!since!the!reTridging!process!has!been!shown!to!both!increase!microbial!activity! (Grigera!et!al.!2007)!and!nodal!root!growth!(Thomas!and!Kaspar!1995!and!1997)!in!the!ridge.! Additionally,!since!the!reTridging!process!occurs!when!corn!is!at!the!V6!growth!stage,!just!as!it!is! beginning!exponential!growth,!increases!in!N!mineralization!due!to!the!reTridging!process!could! improve!temporal!N!synchrony.!! A!handful!of!studies!have!investigated!differences!in!functional!signals!of!microbial! turnover!of!residues.!Liebig!et!al.!(1993!and!1995)!demonstrated!differences!in!a!variety!of!soil! physical!measurements!between!ridge!and!furrow!spaces!and!that!greater!porosity!in!the!ridge! 11! ! space!led!to!higher!rates!of!CO2!respiration.!Similarly,!Clay!et!al.!(1995)!and!Müller!et!al.!(2009a! and!2009b)!demonstrated!that!labile!C!and!N!and!associated!respiration!tends!to!be!higher!in! the!ridge!space!at!different!points!in!the!growing!season.!Finally,!Zebarth!and!Milburn!(2003)! found!that!after!hilling!in!a!zeroTfertilizer!potato!system,!a!system!analogous!to!RT!in!cornT soybean,!NO3!was!increased!in!the!hill.!These!studies!suggest!that!these!zones!do!indeed! exhibit!functional!differences!and!that!the!ridge!zone!is!characterized!by!higher!levels!of! microbial!activity!and!SOM!turnover.!! Given!this!evidence,!we!sought!to!investigate!the!effects!of!zonation!on!N!synchrony! both!temporally!and!spatially.!In!particular,!we!were!interested!in!the!possible!interactions!of! RT!with!the!use!of!winter!cover!crops.!In!some!systems,!rye!cover!has!been!shown!to!cause!net! N!immobilization,!especially!in!the!early!season,!suppressing!plant!growth!(Rosecrance!et!al.! 2000,!Burger!and!Jackson!2003,!Hu!et!al.!1997).!Although!systems!may!eventually!recover!from! this!immobilization!as!residues!are!decomposed,!resulting!in!net!N!mineralization!(McSwiney!et! al.!2010),!it!poses!a!risk!to!which!many!growers!are!averse.!Similar!problems!are!possible!with! previous!corn!residue!(Rice!and!Smith!1984),!so!a!similar!effect!would!be!advantageous!in!cases! where!corn!residue!inputs!are!high.!Given!the!way!RT!manages!residues,!it!could!have!the! potential!to!mitigate!immobilization!problems!by!relocating!the!site!of!immobilization!away! from!plants!into!the!furrow.!! Using!a!spatially!resolute!sampling!design!we!took!soil!cores!from!multiple!positions! across!the!row/interTrow!space!from!field!sites!in!IL!and!MI!at!points!throughout!the!growing! season!that!correlated!with!points!of!high!N!uptake!in!plants!and!important!management! 12! ! events.!Soil!samples!were!then!analyzed!for!inorganic!nitrogen!(NO3!and!NH4),!potentially! mineralizable!nitrogen!(PMN),!and!particulate!organic!matter!carbon!and!nitrogen!(POMTC!and! POMTN).!! While!conventional!soil!extractions!for!inorganic!forms!of!N!are!informative,!inorganic! pools!are!highly!ephemeral!and!soil!samples!can!only!provide!a!snapshot!of!soil!N!levels!at!the! time!of!sampling.!PMN!and!POM!measurements!provide!a!more!integrated!assessment!of!soil! N,!quantifying!what!may!not!be!available!at!the!time!of!sampling!but!could!be!available!soon! thereafter.!Gregorich!et!al.!(1994)!suggest!that!PMN!represents!a!labile!pool!of!organic!N!that! can!readily!supply!N!to!crops!and!is!a!good!indicator!of!shortTterm!fertility.!Similarly,!POM!is!a! collection!of!pools!of!organic!matter!at!various!levels!of!decomposition,!typically!distinguished! or!fractionated!by!size!or!density,!that!have!been!wellTassociated!with!labile!pools!of!organic! nitrogen!(Hassink!1995,!Wander!and!Bidart!2000).!An!analysis!of!POM!fractions!can!provide! insight!into!the!capacity!of!a!soil!for!organic!matter!turnover!and!associated!N!mineralization.! An!increase!in!both!PMN!and!POM!would!suggest!improvements!in!nutrient!cycling/availability,! and!these!measures!may!help!shed!light!on!CTN!linkages!in!study!systems.! We!hypothesized!that!RT!would!improve!temporal!N!synchrony!by!delaying!turnover!in! the!early!season!when!plant!demand!is!low!and!increasing!it!when!corn!enters!the!exponential! growth!phase!and!demand!is!highest.!We!also!hypothesized!that!RT!would!improve!spatial!N! synchrony!by!relocating!labile!forms!of!N!from!the!furrow!space!to!within!rows!through!reT ridging,!increasing!inorganic!N,!PMN,!and!POMTN!in!the!crop!row.!Finally,!we!hypothesized!that! the!site!of!earlyTseason!N!immobilization!would!be!relocated!to!the!furrow!space!from!the!ridge! 13! ! in!RT!treatments,!mitigating!some!of!the!early!season!N!immobilization!problems!associated! with!the!use!of!cover!crops!and!high!amounts!of!residues.!! 1.2.!Objectives:! 1.) Characterize!differences!in!both!inorganic!and!labile!organic!soil!N!pools!across! experimental!treatments!and!different!row/interTrow!positions!at!important!points! throughout!the!growing!season.! 2.) Characterize!differences!in!POMTC!pools!across!experimental!treatments!and!different! row/interTrow!positions!for!surface!soils!just!after!reTridging.!! 1.3.!Methods:! 1.3.1!Site!description:! The!study!was!conducted!at!two!sites!participating!in!a!longTterm,!multiTuniversity! tillage!experiment,!one!in!Mason,!MI!owned!by!Michigan!State!University!and!the!other!in! Champaign,!IL!owned!by!the!University!of!Illinois!ChampaignTUrbana.!Hereafter!the!sites!will!be! referred!to!using!the!abbreviations!for!either!state:!IL!and!MI.!The!IL!site!is!dominated!by! Drummer!silty!clay/loam!(mesic!Typic!Endoaquoll)!with!3T3.5%!OM!and!pH!of!6.4,!while!the!MI! site!is!dominated!by!Marlette!sandy!loam!soils!(mesic!Oxyaquic!Glossudalf)!with!1T2%!OM!and! pH!of!6.2.!The!thirtyTyear!average!growing!season!(MayTOctober)!precipitation!at!IL!is!61.59!cm,! while!in!MI!it!is!48.02!cm!(Table!1.1).!!Summer!daytime!temperatures!have!historically!ranged! from!20!–!25!C!at!both!sites!with!periodic!highs!near!30!C.!! 1.3.2.!Experimental!design:! Sites!were!established!in!2011!and!had!previously!been!planted!to!field!crops!(corn,! soybean,!and!wheat).!The!experimental!setup!is!a!cornTsoybean!rotation!with!sampling! 14! ! conducted!only!in!plots!in!the!corn!phase!of!the!rotation.!The!experimental!design!is!a! randomized!complete!block!design!with!four!blocks!and!one!splitTplot!factor.!The!whole!plot! factor!is!tillage!and!consists!of!two!levels,!chisel!plow!and!ridge!tillage.!The!subTplot!factor!is! cover!crop!and!also!consists!of!two!levels,!winter!rye!cover!and!winter!fallow.!Plots!at!MI!are! sized!30!x!30!ft!with!30!x!10!ft!zero!fertilizer!subTplots,!and!plots!at!IL!20!x!100!ft!with!20!x!40!ft! zero!fertilizer!subTplots.!Zero!fertilizer!subTplots!were!established!to!allow!for!monitoring!of! plant!N!uptake!in!the!absence!of!fertilization.!We!chose!to!conduct!a!subTstudy!in!these!zero! fertilizer!subplots!because!they!allow!us!to!examine!N!turnover!from!organic!matter!exclusively.!! 1.3.3.!Soil!sampling:! We!collected!soil!samples!at!a!series!of!time!points!that!coincided!with!important!crop! growth!stages!and!field!operations!(Table!1.2).!Soil!sampling!I!was!conducted!at!both!sites!as! plants!were!emerging!(~2!weeks!after!planting)!to!document!early!season!conditions.!Soil! sampling!II!was!conducted!at!both!sites!~10!d!after!the!reTridging!operation!was!conducted!in! the!ridge!till!plots.!Around!the!time!of!this!operation,!corn!plants!in!both!treatments!had! achieved!growth!stage!V6!and!were!entering!the!exponential!growth!stage,!when!nitrogen! demand!is!highest.!Soil!sampling!III!was!conducted!at!just!the!Mason!site!when!the!corn!was!at! the!grainTfilling!stage!R3.!! To!gain!a!better!understanding!of!the!spatial!distribution!of!nitrogen!and!the!spatial! differences!in!turnover!in!each!system,!we!chose!a!sampling!approach!with!high!degree!of! spatial!resolution!.!Soil!cores!were!taken!at!three!different!positions!in!the!rowTinterrow!space:! inTrow/ridge!(ridge);!7.5!in!from!the!row!(shoulder);!and!15!in!from!the!row!(furrow).!Five!cores! were!taken!at!each!position!to!a!depth!of!20!cm!and!divided!into!three!depth!increments:!0T5,! 15! ! 5T10,!and!10T20!cm.!Depth!increments!were!composited!across!the!five!cores,!sieved!to!6!mm! while!still!fieldTmoist,!and!stored!at!4!C!until!analysis.!! 1.3.4.!Inorganic!nitrogen!and!potentially!mineralizable!nitrogen!(PMN):! Soil!moisture!was!determined!gravimetrically!(subsamples!were!weighed!fresh,!oven! dried!to!no!change!in!weight,!and!weighed!to!calculate!percent!moisture),!and!NH4!and!NO3,! were!extracted!from!another!subsample!using!a!1M!KCl!solution.!For!each!subsample,!10!g!+/T! 0.1!g!of!fresh!soil!was!weighed!into!a!50!mL!centrifuge!tube,!mixed!with!40!mL!1M!KCl,!and! shaken!at!240!rpm!on!an!orbital!shaker!for!1!hour.!After!samples!had!settled,!15!mL!of!KCl! extractant!was!then!filtered!from!each!sample!into!scintillation!vials!through!Whatman!#42! qualitative!filter!paper!to!remove!soil.!Extracts!were!then!analyzed!for!both!NH4!and!NO3! concentrations!by!the!procedure!described!in!section!1.3.5.!!! At!the!same!time,!a!duplicate!set!of!50!mL!centrifuge!tubes!containing!10!g!+/T!0.1!g!soil! from!each!sample!was!prepared!for!a!potentially!mineralizable!nitrogen!(PMN)!assay!as! described!in!Waring!and!Bremmer!(1964).!These!samples!were!mixed!with!10!mL!water!and! allowed!to!incubate!for!7!days!at!30!C.!After!incubation,!samples!were!extracted!by!the!same! process!as!the!samples!described!above!but!using!30!mL!1.33!M!KCl!to!achieve!the!same! molarity.!Extracts!were!then!analyzed!for!NH4!only!since!the!anaerobic!condition!created! during!the!incubation!inhibits!nitrification,!meaning!nitrogen!turnover!from!SOM!effectively! stops!after!mineralization! 1.3.5.!Plate!method:! 16! ! To!measure!the!concentrations!of!NO3!and!NH4!of!extracts,!we!used!the!method! described!in!Doane!and!Horwath!(2003).!This!method!employs!colorimetric!reagents,!different! reagents!for!either!NO3!or!NH4,!that!are!combined!with!extracts!on!a!96Twell!microplate.!Once! the!reaction!was!complete,!plates!were!read!on!a!MultiTSkan!Ascent!96Twell!plate!reader!(MTX! Lab!Systems,!Inc.)!for!absorbance!values!at!630!nm!for!NH4!and!540!nm!for!NO3.!Standard! curves!were!created!on!each!plate!using!standards!of!known!parts!per!million!values.!Slope!and! intercept!terms!of!the!standard!curves!were!then!used!to!convert!absorbance!values!to! concentrations.!! Since!extracts!came!from!samples!taken!at!several!time!points!and!positions,! concentrations!of!both!NO3!and!NH4!varied!greatly.!To!account!for!variability,!the!ratio!of! reagent!to!sample/standard!can!be!adjusted!to!fit!the!range!of!concentrations!of!a!given!set!of! samples.!Combining!a!high!volume!of!sample!with!a!low!volume!of!reagent!is!useful!for!samples! in!the!lower!concentration!range,!while!the!opposite!is!useful!for!samples!of!higher!N! concentrations.!To!understand!the!upper!and!lower!limits!of!sensitivity!for!a!number!of! dilutions!(ratio!of!sample!to!reagent),!we!ran!several!different!dilutions!with!broad!standard! curves!(i.e.,!0.1!ppm!–!70!ppm).!The!values!between!which!these!standard!curves!remained! linear!represented!the!range!in!which!we!considered!the!dilution!to!be!accurate.!!! All!samples!were!first!analyzed!in!duplicate!for!NH4!and!NO3!using!a!“midTrange”! dilution!that!encompassed!most!likely!values.!After!initial!analysis,!samples!for!which!values! were!out!of!the!range!of!the!dilution!or!for!which!duplicate!error!was!greater!than!10%!were! 17! ! reTanalyzed!using!a!more!appropriate!dilution.!Concentrations!were!then!converted!from!ppm! T1 to!mg!kg!soil .! 1.3.6.!Particulate!organic!matter:! We!used!a!size!fractionation!POM!method!modified!from!Cambardella!and!Elliot!(1993)! on!soil!samples!from!the!0T5!cm!depth!increment!taken!in!Soil!Sampling!II.!Unground!soil! samples!were!first!dried!in!a!forcedTair!oven!at!30!C!and!10!g!+/T!0.1!g!was!weighed!into!a!50!mL! centrifuge!tube.!Samples!were!mixed!with!30!mL!of!a!5%!aqueous!solution!of!sodiumT hexametaphosphate!and!shaken!at!120!rpm!on!a!reciprocal!shaker!for!4T6!hours!to!disperse!all! particulate!matter!in!the!samples.!Shaken!samples!were!poured!onto!a!pair!of!stacked!sieves! with!mesh!sizes!of!213!μm!and!53!μm.!Distilled!water!was!used!to!gently!wash!samples!through! the!sieves,!capturing!particulate!matter!≥!213!μm!on!the!first!sieve!and!particulate!matter!of! 53T213!μm!on!the!second.!Particulates!collected!on!the!sieves!were!transferred!to!aluminum! weighing!dishes!and!dried!in!a!forcedTair!oven!at!55!C!for!24!h,!weighed,!and!pulverized!in!a! ShatterBox®!(SPEX®!SamplePrep®)!until!homogenized.!Particulate!organic!matter!C!and!N! determinations!were!made!by!dry!combustion!of!the!samples,!using!a!CarloTErba!NA!1500!CNS! (CarloTErba,!Milan,!Italy).! 1.3.7.!Data!analysis:! For!analysis,!data!were!treated!as!having!one!main!plot!factor,!tillage,!and!three!split! plot!factors,!cover,!position,!and!depth.!Although!position!and!depth!cannot!be!considered!as! treatments,!we!chose!to!analyze!them!as!fixed,!splitTplot!factors!since!we!were!specifically! interested!in!their!possible!effects!on!data.!Site!was!either!included!as!a!random!factor!or!data! were!separated!by!site!and!analyzed!separately!according!to!the!following!procedure.! 18! ! For!Soil!Sampling!1!and!Soil!Sampling!2,!data!from!both!sites!were!initially!combined!for! analysis!by!a!mixed!effects!model!ANOVA.!Initial!analysis!was!performed!with!tillage,!cover,! position,!and!depth!as!fixed!factors,!as!well!as!site!to!determine!if!site!had!a!significant!effect!(α! =!0.05)!on!results.!If!site!had!a!significant!effect,!or!a!significant!interaction!with!a!treatment! effect!of!interest,!data!from!either!site!was!separated!and!reTanalyzed!with!tillage,!cover,! position,!and!depth!as!fixed!factors.!If!site!did!not!have!a!significant!effect!or!interaction!with!a! treatment!effect!of!interest,!it!was!changed!to!a!random!factor,!while!tillage,!cover,!position,! and!depth!remained!fixed.!Since!soils!were!collected!only!at!MI!for!Soil!Sampling!3,!data!were! analyzed!with!tillage,!cover,!position,!and!depth!as!fixed!factors.! 1.4!Results:! 1.4.1.!2012!Weather:! The!2012!growing!season!was!exceptionally!hot!and!dry!across!the!American!Midwest.! At!the!IL!site,!total!precipitation!in!the!months!of!May,!June,!and!July!was!22.63!cm!below!the! thirtyTyear!average,!and!mean!daily!maximum!temperatures!were!above!the!historical!averages! from!May!to!August!(Table!1.3.a).!At!MI,!total!precipitation!from!June!to!August!was!9.43!cm! below!thirtyTyear!averages,!and!mean!daily!maximum!temperatures!above!historical!averages! 3 3 from!May!to!September!(Table!1.3.b).!Soil!volumetric!water!content!(cm !H2O!per!soil!cm )!at! both!sites!dropped!considerably!in!the!month!of!June!as!very!few!rain!events!occurred!(Figures! 1.3.a!and!1.3.b).!At!MI,!a!series!of!rain!events!briefly!increased!VWC,!but!given!the!sandy! texture!of!the!soil!onTsite,!VWC!dropped!again!quickly.!At!IL,!VWC!remained!low!throughout!the! month!of!July!except!after!one!rain!event!towards!the!middle!of!the!month.!As!a!result!of!low! rainfall!and!high!air!temperatures,!soil!temperatures!(C)!increased!rapidly!at!both!sites!during! 19! ! the!month!of!June!to!reach!a!peak!above!30!C!at!the!beginning!of!July,!declining!thereafter! (Figs.!1.4.a!and!1.4.b).!!! 1.4.2.!Nitrate:! Soil!NO3!values!tended!to!be!highest!in!the!0T5!cm!depth!and!were!generally! constrained!to!similar!ranges!at!either!site!for!each!sample!round,!with!the!exception!of!Soil! Sampling!1!at!MI,!for!which!values!were!much!higher!than!at!IL!(Table!1.4).!But,!spatial!patterns! of!distribution!varied!across!sample!rounds.!Initial!analysis!of!Soil!Sampling!1!data!from!both! sites!revealed!a!strong!effect!of!site!(p!=!0.02),!so!Soil!Sampling!1!data!was!then!separated!by! site!and!reanalyzed.!!At!IL,!there!were!strong!main!effects!of!tillage,!cover,!position,!and!depth! (p!