d Soil Qu Agronomic and age and Tilla Ames, Iowa

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1 Agronomic nd A d Soil Qu ulity Trends T O Over Fivve Yerss of Diffferent Till ge nd d Croppiing Systtems crross Iow w Mhdi Al-Kissi, Associtte Professoor Sooil Mngeement/Envvironment Deprtmeent of Agroonomy Iow Sttte Univerrsity Am mes, Iow Brd Onel, Reserch Associte Soil Mngement Deprtment of Agronomy Iow Stte University Ames, Iow December, 21

2 Tble of Contents Acknowledgment... iii Executive Summry... 1 Introduction... 2 Site Selection nd Methods... 4 Site Selection... 4 Experimentl Design... 7 Mterils nd Methods... 8 Results nd Discussion Dt Presenttion nd Anlysis: Sttewide Trends or Chnges in Agronomic nd Soil Qulity Indictors Over Five Yers Summry of Sttewide Agronomic nd Soil Qulity Indictors Trends Regionl Trends or Chnges in Agronomic nd Soil Qulity Indictors Region 1 Northwest Iow Plins Summry of Agronomic nd Soil Qulity Trends for Region 1: Region 2 Des Moines Lobe Summry of Agronomic nd Soil Qulity Trends for Region 2:... 5 Region 3 Northest Iown Region Summry of Agronomic nd Soil Qulity Trends for Region 3: Region 4 Southern Iow Drift Plin Summry of Agronomic nd Soil Qulity Trends for Region 4: Literture Cited ii

3 Acknowledgment This report is one component of the Iow Lerning Frm project tht ws estblished in 25. This gronomic report is n effort of mny individuls over the pst 5 yers including frmers who offered sites where reserch ws conducted cross the stte, Extension Field specilists who prticipted nd helped in conducting field trils nd collecting dt, reserch ssocites who helped in mnging this reserch nd demonstrtion projects, mny undergrdute students who helped in dt collection nd smple processing, nd mny other griculture professionls nd collegues ssocited with the Iow Lerning Frm. This effort would not be possible without the funding from the Iow Deprtment of Agriculture nd Lnd Stewrdship, Iow Deprtment of Nturl Resources, nd Nturl Resources Conservtion Service-U.S Deprtment of Agriculture. The prtnership nd collbortion with Iow Frm Bureu nd Iow Soil Conservtion Districts ws invluble in implementing this project ide. This document is intended for public use nd outrech. Any reproduction must credit uthors nd sources. iii

4 Executive Summry The Iow Lerning Frm ws estblished with the gol of promoting conservtion prctices through field demonstrtions nd outrech ctivities tht improve soil nd wter qulity in Iow. This project included field demonstrtions on coopertors fields tht included conservtion mngement prctices, where gronomic nd soil qulity monitoring lso took plce. Coopertor sites were estblished cross four mjor soil regions of Iow in order to chieve the gols of this project. This included 32 sites cross the stte; selected sites were chosen from ech region for yerly monitoring of soil nd gronomic properties. Agronomic nd soil prmeters monitored included: grin yield, surfce residue, fll corn stlk nitrte, soil orgnic mtter, bulk density, compction, ph, microbil biomss crbon, ggregte stbility, nd wter infiltrtion. Representtive sites from different soil nd climte conditions were used to mke interprettions bout ech region s response to different mngement prctices. The min objectives of the gronomic component of this project focused on: 1) Monitor chnges in soil qulity nd productivity under different tillge nd cropping systems over 5 yer period, 2) Document regionl nd sttewide chnges nd trends in soil qulity using set of gronomic nd soil qulity prmeters, nd 3) Develop regionl nd stte wide recommendtions for tillge nd cropping systems tht re effective in sustining soil qulity nd productivity. Sttewide nd regionl results indicte cler differences between tillge prctices for corn yields, while differences in soyben yields re less pronounced. A loss of corn yield is ssocited with no-tillge for ll regions, lthough the extent of yield loss vries by region nd depends on specific site conditions. Reduced tillge prctices offer cler dvntge over conventionl tillge in the mount of residue left on the field, wter infiltrtion rtes, nd mount of stble mcroggregtes. The results demonstrted the slow chnge in soil orgnic mtter (increse or decrese) under no-till or conventionl tillge over the 5 yer period. Soil compction of no-tillge sites decresed slightly over time for individul sites, but the sttewide verge revels no differences between tillge systems. Regionl results show no cler difference between tillge systems for soil ph, bulk density, orgnic mtter, or microbil biomss crbon for ny of the four soil regions. Observtion of these soil properties for longer thn 5 yers would be necessry to observe significnt chnges s documented by pst studies. The doption of no-tillge offers cler dvntges to soil nd environmentl qulity over conventionl tillge, regrdless of region. No-tillge nd reduced tillge offer benefits in the form of erosion control nd improved soil qulity, including: reduced soil compction, higher wter retention nd flood control, incresed surfce residue, nd stbility of soil orgnic mtter. However, decresed yields ssocited with no-tillge my not mke it prcticl for some sites. Corn yield decreses in no-till re especilly pronounced in poorly drined soils. The Adoption of conservtion tillge prctices such s strip-tillge, re vlid lterntive to no-tillge in poorly drined res where yield loss is concern. Conservtion tillge produces corn nd soyben yields equivlent to conventionl tillge, but still provides some of the environmentl nd soil qulity benefits of no-tillge. Al-Kisi nd Onel, 21 1

5 Introduction The Iow Lerning Frm (ILF) ws estblished in 25 s wy of promoting eduction nd communiction bout griculturl prctices in Iow. This is sttewide inititive involving producers, government gencies, conservtionists, nd ILF collbortors. The overll gol of the ILF project is to demonstrte nd promote conservtion mngement systems with emphsis on conservtion tillge, cropping systems, nd nutrient mngement cross Iow. Demonstrtion nd evlution of different mngement prctices t coopertor sites is essentil to mking recommendtions on prctices nd educting the public bout mngement options. These findings will help to relte individul frm-level decisions to their impct on soil nd wter qulity, nd provide recommendtions on mngement prctices. The doption of no-tillge nd conservtion tillge prctices hs been incresing over the pst few decdes, especilly in response to stte nd federl progrms encourging reduced tillge. Environmentl concerns such s erosion control nd wter qulity, s well s concerns over long-term soil qulity drive the rgument for doption of reduced tillge prctices. However, there re lso concerns tht reduced tillge will result in loss of yield nd economic returns, especilly in corn. No-tillge produces higher mount of surfce residue, resulting in greter soil wter retention nd lower soil temperture. These conditions my cuse dely in corn emergence nd slow down erly seson growth of corn. Slow corn growth due to no-tillge is most pronounced in poorly drined soils where conditions re lredy cool nd wet, while yield loss due to no-tillge is generlly miniml in well-drined soils (Kpust et l., 1996; Kww-Mensh nd Al-Kisi, 26). Yield losses ssocited with no-till re not only cused by dringe conditions, but cn lso be mplified by mono-cropping system or cooler climte. Although loss of corn yield is often reported due to no-tillge, some studies hve indicted tht no-tillge will produce the sme economic returns even with loss of yield (Al-Kisi nd Yin, 24). There re vlid rguments both for nd ginst the doption of reduced tillge prctices, but evidence from pst studies is often conflicting nd does not consider regionl nd site specific conditions such s the effect of climte nd soil properties on yield performnce. A key component of mking sound recommendtions on mngement prctices involves collection of field dt nd ssessment of the impct of tillge systems nd crop rottions on soil nd gronomic properties. Coopertor sites were estblished in loctions cross Iow to chieve this gol; this includes 32 sites in four mjor soil regions in Iow. Representtive sites from different soil nd climte conditions llow for interprettions bout ech region s response to different mngement prctices. This report will focus on presenting soil nd gronomic trends over the pst five yers nd will highlight differences due to tillge prctices (no-till, conservtion, or conventionl), crop rottions (corn-soyben, corn-corn, or corn-corn-soyben), climte, nd vrition in soil properties. Al-Kisi nd Onel, 21 2

6 The min objectives of the gronomic component of this project focused on: 1. Monitor chnges in soil qulity nd productivity under different tillge nd cropping systems over 5 yer period. 2. Document regionl nd sttewide chnges nd trends in soil qulity using set of gronomic nd soil qulity prmeters. 3. Develop regionl nd stte wide recommendtions for tillge nd cropping systems tht re effective in sustining soil qulity nd productivity. Results from the five yer study will be presented seprtely for ech soil nd gronomic prmeter. Soil qulity nd gronomic dt will be presented both t sttewide level nd lso for ech individul region. An verge vlue of three replictions is presented for ech prmeter; this vlue is used to compre trends between tillge prctices. A sttisticl pproch is lso used to compre the significnce of differences between mngement prctices over the five yer period. Al-Kisi nd Onel, 21 3

7 Site Selection nd Methods Site Selection Field sites were initilly estblished in five regions cross Iow to evlute chnges in soil qulity due to differing tillge prctices, crop rottions, nd conservtion prctices. The regions were chosen bsed on mjor differences in soil type cross the stte. The even distribution of field sites cross the stte is intended to cpture ny differences in soil qulity due to soil nd climtic conditions. The number of regions used in this report ws reduced to four, including: (1) Northwest Iow Plins, (2) Des Moines Lobe, (3) Northest Iown Surfce, nd (4) the Southern Iow Drift Plin (Figure 1). The Loess Hills nd Southern Iow Drift Plin regions were combined due to the miniml mount of dt for the Loess Hills region nd the similr soil types found within the loess derived regions. The specific loction of Iow Lerning Frm coopertor sites re shown in Figure 2. Iow Lerning Frm coopertor sites Al-Kisi nd Onel, 21 4

8 Figure 1. Mjor soil regions of Iow in which field sites were estblished. The four regions include (1) Northwest Iow Plins, (2) Des Moines Lobe, (3) Northest Iown Surfce, nd (4) the Southern Iow Drift Plin. Al-Kisi nd Onel, 21 5

9 Figure 2. Specific loction of Iow Lerning Frm coopertor sites. The color of ech loction indictes the mount of detiled field mesurements tht were collected. Al-Kisi nd Onel, 21 6

10 Experimentl Design A replicted block design ws used to monitor chnges in soil properties nd other prmeters due to different mngement prctices for ech field site. An exmple of plot lyout showing typicl replicted tillge tretments is shown in Figure 3. The plot rrngement, number nd type of tretments, nd size of ech repliction vry gretly between sites in different regions. This vrition in plot lyout is prtilly due to differences in equipment nd the willingness of coopertors to dopt multiple mngement prctices, but is lso due to the lrge number of tillge nd cropping systems tht were evluted. A summry of mngement prctices nd crop rottions tht were evluted s prt of this study re shown in Tble 1. No-till repliction 1 X No-till repliction 2 X No-till repliction 3 X Conventionl till repliction 1 X Conventionl till repliction 2 X Conventionl till repliction 3 X Figure 3. Exmple of plot mp with three replictions of ech tillge tretment. The X represents typicl loction for yerly soil smpling nd infiltrtion mesurements. Al-Kisi nd Onel, 21 7

11 Tble 1. Trgeted conservtion tillge prctices nd crop rottions for evlution. Tillge Systems No-tillge Conservtion Tillge (Strip-tillge, 1-pss field cultivtion, miniml tillge) Conventionl Tillge (Disc or chisel plow, V-rip, field cultivted, deep or subsoil tillge) Cropping Systems Corn-soyben Corn-corn-soyben Continuous corn Mterils nd Methods Field mesurements were tken yerly on mny of the 32 Iow Lerning Frm coopertor sites cross the stte. Mesurements collected from the sites were used to compre the effects of mngement prctices on soil qulity nd gronomic productivity. Fifteen of these sites were consistently smpled during the five yer period, but mny of these sites hve prtil dt due to chnges in coopertors or mngement prctices. Six sites were smpled in detil for the full five yers of the study. Soil smples nd infiltrtion mesurements were collected from centrl loction within ech plot to void ny confounding fctors from neighboring plots or the edge of the field. Chnges in soil qulity due to mngement prctices were monitored over the five yer durtion of the project using stndrd set of gronomic nd soil qulity prmeters. Agronomic prmeters include yield, residue count, nd stlk nitrte. Soil qulity prmeters include: orgnic mtter content, soil bulk density, soil compction, ph, microbil biomss crbon, infiltrtion rte, nd ggregte stbility. The methods used to nlyze gronomic nd soil prmeters will be discussed for ech prmeter. Residue Cover The mount of surfce residue for ech plot ws mesured using line trnsect method where beds were spced every six inches for totl length of 5 feet. The percentge of residue on the plot ws determined by counting the number of beds under which there ws t lest 1/8 inch of corn or soyben residue. The number of beds with residue is esily converted to percentge since there re 1 totl beds on the line. Corn Stlk Nitrte Corn stlk nitrte ws mesured in the fll by determining NO 3 -N concentrtion from dried nd ground corn stlks. Fifteen 8 inch segments of corn stlk were collected between 6 to 14 inches bove ground level; the collected stlks were then plced in pper bg for drying. Al-Kisi nd Onel, 21 8

12 Corn stlks were oven-dried t 6 C for 8 hours nd were then ground with crbon steel pulverizer (Blckmer nd Mllrino, 1996). Stlk NO 3 -N concentrtions were determined using the 2M potssium chloride extrction method (Mulvney, 1996) using Lcht Quickchem FAI+8 nlyzer. Orgnic Mtter Content Soil smples for orgnic mtter determintion were collected for the top six inches of ech repliction nd tretment. Soil smples were ir dried, ground, nd stored t room temperture. Totl crbon nd nitrogen concentrtions were determined by dry combustion using Leco Truspec CN nlyzer. One qurter grm of ir dried soil ws used to determine both totl crbon nd nitrogen percentge. The soil crbon percentge ws converted to orgnic mtter percent using the following eqution tht ws developed through regression nlysis: Orgnic Mtter %= -.2*Totl Crbon % (TC)^3-.2^TC^ *TC Bulk Density Bulk density ws determined by collecting soil cores to stndrd depth using soil probe with known dimeter. Cores with dimeter of.7 inches were collected for depths of -6 nd 6-12 inches; the volume of the core ws then determined using these dimensions. The soil ws dried overnight t 15 C to determine soil moisture content for clculting bulk density on n oven dry weight. The oven dry weight of the soil ws then divided by the volume of the soil cores to obtin the bulk density vlue. Soil Compction Soil compction ws mesured using Rimik CP2 cone penetrometer (see picture below). The penetrometer utomticlly logs mesurements of soil resistnce in increments of one inch s the cone is pushed to depth of 24 inches. All plots were mesured t soil moisture field cpcity to eliminte soil moisture effect on penetrtion resistnce vlues due to differing moisture content. The penetrometer records resistnce vlue in kilopscls; this vlue ws converted to n index for ese of presenttion. The compction index rnges from to 1, with the highest compction vlue t 1. Index vlues were clculted by dividing ech resistnce vlue by the highest observed vlue for ech site nd for ech yer. Al-Kisi nd Onel, 21 9

13 Rimik CP2 cone penetrometer Soil ph Soil ph ws determined using 1:1 mixture of wter nd soil. Ten grms of ir dried soil ws mesured nd n equl mount of wter ws dded. The soil ph of the smples ws mesured fter one hlf hour using n Accumet AR15 ph meter. The mixture ws stirred immeditely fter dding wter, left sitting for 3 minutes, nd stirred gin immeditely before reding the ph. Microbil Biomss Crbon Soil smples for microbil biomss crbon nlysis were collected erly in the spring from selected sites by using golf course hole cutter to collect soil from the top 6 inches. The collected soil smples were processed immeditely to minimize ny chnges in microbil biomss crbon or were stored in cooler until the next vilble time for processing. Smples were extrcted within one week to observe microbil ctivity tht closely mtches field conditions. Soil smples were first sieved through four mm sieve. Twenty grms of soil ws mesured out for live microbil extrction, twenty grms for ded microbil extrction, nd ten grms to determine the soil moisture content. Ded microbil biomss smples were treted overnight with chloroform in vcuum chmber. An extrction solution of 1 ml of.5 M potssium sulfte ws used to extrct both the live nd ded microbil biomss from soil smples. The extrctnts were then filtered through Whtmn 42 filter pper. The mount of dissolved crbon in ech smple ws determined using n Elementr TOC nlyzer. The crbon Al-Kisi nd Onel, 21 1

14 concentrtion ws djusted ccording to the moisture content of the soil nd clculted on dry bsis. The mount of crbon mesured in the live smple ws subtrcted from the crbon in the ded smple to determine the microbil biomss crbon. Infiltrtion Rte The infiltrtion rte of ech plot ws determined with Cornell sprinkle infiltrometer (see picture below). A metl ring ws pushed into the ground until the runoff hose on the ring ws even with the soil surfce. The infiltrometer ws then plced on top of the metl ring. The sprinkler system dispenses wter t known inflow rte (IN) on the soil surfce within the ring; this rte is clculted by subtrcting the finl wter height (H2) from the initil height (H1) nd dividing by time (T). The pplied wter simultes the effect of hevy rinstorm. Wter ws dded to the soil until runoff (R) ws observed coming out of the ring. Once runoff begn, the mount of wter running off ws collected nd mesured every three minutes. The runoff mount ws recorded for minimum of 3 minutes or until the runoff rte levels off for t lest three redings. The infiltrtion (IR) rte cn be clculted by subtrcting the mount of runoff from the totl mount of wter being dispensed for ech three minute intervl. The verge rte of wter dispensed during the infiltrtion reding ws determined with the following eqution: IN (inch/min) = (H 1 -H 2 )/T [1] The infiltrtion rte for ech three minute intervl ws determined using the following eqution: IR (inch/min) = IN-R [2] Cornell sprinkle infiltrometer Al-Kisi nd Onel, 21 11

15 Aggregte Stbility Wet ggregte stbility ws mesured for the top 6 inches of soil from selected plots using method modified from Kemper et l. (1985). A golf course hole cutter ws used to collect ggregte smples. Soil smples were broken down by pplying light pressure to breks between lrge ggregtes; severely compcted portions were discrded. Once the smple ws broken down s fr s possible by hnd, the soil ws pssed through n 8 mm sieve. The portion of the smple tht pssed through the sieve ws ir dried for 2 dys nd subsmple of 1 g ws weighed out fter spreding the smple nd collecting the subsmple rndomly. The 1 g soil smple ws spryed with wter until moist, mking sure to cover ll surfces. The soil ws then trnsferred to the top of nest of sieves, including the following sizes from top to bottom: 4 mm, 2 mm, 1 mm,.5 mm,.25 mm, nd.53 mm. The mount of soil tht pssed through the.53 mm sieve (<.53 mm frction) ws lso clculted by subtrction from the mount retined on the other sieves. The smple ws submerged in column of wter for 5 minutes t 9 rpm to brek the smples; the stble ggregtes for ech size remin on the surfce of the sieves. The remining ggregtes on ech sieve were wshed into plstic continers to weigh the mount of soil remining. The weight of ggregtes for ech size frction ws clculted s percentge of the initil 1 g soil smple. Aggregte Stbility Shker Al-Kisi nd Onel, 21 12

16 Results nd Discussion Dt Presenttion nd Anlysis: Agronomic nd soil qulity prmeters were monitored over five yer period to determine if there were ny chnges due to differences in mngement prctices. Sttewide trends in soil qulity nd gronomic productivity will first be discussed. Six prmeters will be discussed t the sttewide level, including: 1) corn nd soyben yields, 2) residue cover, 3) orgnic mtter content, 4) soil compction, 5) infiltrtion, nd 6) ggregte stbility. These properties were chosen for discussion of the overll sttewide trends or chnges in soil qulity becuse they re the most responsive indictors to short term effects of tillge nd cropping systems on soil qulity. The relevnce of ech prmeter nd the trends ssocited with ech of the six sttewide prmeters will be discussed in detil. Trends ssocited with ech of the four mjor soil regions of Iow will lso be discussed fter the sttewide trends. Ech region will be discussed seprtely using the dt from detiled reserch sites within ech region. Soil nd gronomic prmeters will be discussed for ech soil region, including: 1) corn nd soyben yields, 2) residue cover, 3) fll corn stlk nitrte, 4) soil orgnic mtter content, 5) bulk density, 6) soil compction, 7) soil ph, 8) microbil biomss crbon, nd 9) infiltrtion rte. Anlysis of vrince using the generl liner procedure nd lest significnt difference of.5 ws used to compre significnce of difference between tretments. Seprtion of mens in figures re presented with letter, indicting significnt sttisticl difference in results if the letters re different. Al-Kisi nd Onel, 21 13

17 Sttewide Trends or Chnges in Agronomic nd Soil Qulity Indictors Over Five Yers Grin Yield Agronomic yields re one of the most obvious indictors in response to chnges in soil mngement, nd re lso mjor concern when producers re deciding whether to switch to different tillge prctices. Adoption of no-tillge nd conservtion tillge systems hs been promoted in recent yers becuse of their benefits to soil helth nd environmentl qulity. However, yield losses ssocited with reduced tillge continue to be concern, especilly in notill corn (Al-Kisi nd Yin, 24). Sttewide corn yields for coopertor sites re shown in Tble 2; soyben yields re presented in Tble 3. Yield differences between tillge prctices re summrized for ech region in the right column of Tble 2 nd 3. Yield performnce is presented s percentge of no-till over conventionl or conservtion tillge nd conservtion over conventionl tillge for ech region. If yield percentge is below 1% tht mens no-till or conservtion tillge ws lower thn conventionl tillge. For exmple, the verge corn yield of no-till in Region 1 is 84% of the conventionlly tilled tretment, while no-till yields re 11% of conservtion tillge plots (Tble 2). Al-Kisi nd Onel, 21 14

18 Tble 2. Multi-yer corn yields listed by coopertor nd tillge tretment. Listed yields re n verge of the three mesured replictes from ech tretment. Averge Corn Yield (bu/c) Coopertor Tretment Averge Yield Percentge* Cly Co. Growers No-tillge Region 4 Region 3 Region 2 Region 1 Conventionl Crew No-tillge Conservtion Mnthe No-tillge Conservtion Ronsiek No-tillge Conservtion No-tillge Eklund Conservtion Conventionl Hoffmn No-tillge Conventionl Mson No-tillge Conservtion No-tillge Pierce Conservtion Conventionl Smeltzer (Est) No-tillge Conservtion Smeltzer (West) No-tillge Conventionl Hunter No-tillge Conventionl Jensen No-tillge Conventionl Moore 1 No-tillge Conservtion Moore 2 No-tillge Conservtion Conservtion Vske Conventionl Conventionl + Mnure Cviness No-tillge Conservtion Kielkopf No-tillge Conservtion No-tillge/Conv. 84% No-tillge/Conserv. 11% No-tillge/Conv. 97% No-tillge/Conserv. 98% Conserv./Conv. 13% No-tillge/Conv. 97% No-tillge/Conserv. 1% Conserv./Conv. 15% No-tillge/Conv. 92% No-tillge/Conserv. 99% Nolte No-tillge Conventionl *No-till or conservtion tillge yield ws clculted s percentge of conservtion or conventionl tillge bsed on the verge yield over ll yers for ech region. Al-Kisi nd Onel, 21 15

19 Tble 3. Multi-yer soyben yields listed by coopertor nd tillge tretment. Listed yields re n verge of the three mesured replictes from ech tretment. Region 4 Region 3 Region 2 Region 1 Averge Soyben Yield (bu/c) Coopertor Tretment Cly Co. Growers No-tillge Conventionl Mnthe No-tillge Conservtion Ronsiek No-tillge Conservtion No-tillge Eklund Conservtion Conventionl Hoffmn No-tillge Conventionl Mson No-tillge Conservtion Smeltzer (Est) No-tillge Conservtion Smeltzer (West) No-tillge Conventionl Hunter No-tillge Conventionl Jensen No-tillge Conventionl Moore 1 No-tillge Conservtion Moore 2 No-tillge Conservtion Conservtion Vske Conventionl Conventionl + Mnure Cviness No-tillge Conservtion Kielkopf No-tillge Conservtion Nolte No-tillge Conventionl Averge Yield Percentge* No-tillge/Conv. 92% No-tillge/Conserv. 98% No-tillge/Conv. 96% No-tillge/Conserv. 1% Conserv./Conv. 13% No-tillge/Conv. 15% No-tillge/Conserv. 1% Conserv./Conv. 12% No-tillge/Conv. 97% No-tillge/Conserv. 96% *No-till or conservtion tillge yield ws clculted s percentge of conservtion or conventionl tillge bsed on the verge yield over ll yers for ech region. Al-Kisi nd Onel, 21 16

20 Over 5 yers, verge corn yields for ll four regions were lower in no-tillge plots compred to conventionlly tilled plots, with yield verges rnging from 84-97% of conventionlly tilled tretments. On the other hnd, verge corn yields for no-tillge plots were similr to conservtion tillge yields, where the percentge of yield performnce rnges from 98-11%. Corn yields were higher for conservtion tillge plots thn conventionlly tilled plots for Regions 2 nd 3, where yields were 13% nd 15%, respectively. Soyben yield comprisons between no-tillge nd conventionlly tilled plots vry gretly, with rnge of 92-15% between the four regions. Averge soyben yields were similr between no-tillge nd conservtion tillge plots, with percentge rnge of 96-1% for the four regions. Soyben yields in conservtion tillge plots were higher thn conventionlly tilled plots. A percentge difference of 13% nd 12% were observed for Regions 2 nd 3, respectively. Sttewide corn nd soyben yield trends re summrized below, in Tble 4. A comprison of yields bsed on tillge prctice is presented both s percentge difference nd s the verge difference between yield vlues. The verge sttewide corn yield of no-tillge plots is 95% of conventionlly tilled plots, no-tillge is 99% of conservtion tillge, nd conservtion tillge is 14% of conventionlly tilled plots. The verge sttewide soyben yield of no-tillge plots is 98% of conventionlly tilled plots, no-tillge is 99% of conservtion tillge, nd conservtion tillge is 12% of conventionlly tilled plots. The differences in sttewide yield re lso shown s difference of yield in bushels per cre. Corn yields in no-tillge plots re n verge of 1.1 bushels less thn conventionlly tilled plots, no-tillge plots re n verge of 1.6 bushels less thn conservtion tillge plots, nd conservtion tillge plots re n verge of 6.3 bushels higher thn conventionlly tilled plots. Sttewide soyben yields vry less thn corn yields, with no-tillge verge yields 1.6 bushels less thn conventionlly tilled plots, no-tillge plots re n verge of 1.3 bushels less thn conservtion tillge plots, nd conservtion tillge plots re n verge of 1.4 bushels higher thn conventionlly tilled plots. There ppers to be loss of yield ssocited with no-till corn regrdless of region, lthough vritions in the conditions of ech site determine the extent of yield loss. A loss of soyben yield in no-till plots is lso observed in 3 out of 4 regions, but this loss is less pronounced thn in corn. The sttewide yield results showing some loss of yield due to notillge is consistent with pst studies nd demonstrtes tht yield response is ffected by tillge, but lso depends on moisture conditions nd soil properties (Al-Kisi nd Yin, 24). Al-Kisi nd Onel, 21 17

21 Tble 4. Sttewide corn nd soyben yield trends by tillge prctice. Vribility in yields between tillge prctices re displyed s percentge nd s the verge difference in bushels/cre. Corn Yield (%) Soybens Yield (%) Reltive Yield No-tillge/Conventionl Tillge x 1 95% 98% No-tillge/Conservtion Tillge x 1 99% 99% Conservtion Tillge/Conventionl Tillge x 1 14% 12% bu/cre Averge Difference in Yield No-tillge - Conventionl Tillge No-tillge - Conservtion Tillge Conservtion Tillge - Conventionl Tillge Residue Cover It is known tht n incresed mount of plnt residue on the soil surfce cn minimize the mount of soil erosion nd reduce wter runoff. Soil physicl, chemicl, nd biologicl properties cn lso improve due to reduced tillge nd retention of residue on the soil surfce (Gilley et l., 1986; Krlen et l., 1994). Averge sttewide corn surfce residue percents for ech tillge prctice re presented in Figure 4. Averge sttewide soyben residue percents re presented in Figure 5. These mesurements were tken fter plnting, which is the pproprite time to determine residue cover. Corn residue cover is significntly higher in no-tillge plots compred to other tillge prctices (Figure 4). There is no significnt difference in corn residue cover between conservtion nd conventionl tillge plots. The no-tillge verge corn residue is the highest t 79%, followed by conservtion tillge t 55%, nd conventionlly tilled plots hve the lowest verge t 5%. The lck of significnt differences between residue cover percentges between conservtion tillge nd conventionl tillge cn be ttributed to the ccurcy of the trnsect method of determining residue cover nd potentil humn error in using this method. Soyben residue cover is significntly different between ll tillge prctices (Figure 5). The verge soyben residue cover is highest in no-till plots t 64%, followed by conservtion tillge t 41%, nd conventionlly tilled plots hve the lowest verge t 32%. It is obvious, regrdless of the loction in the stte, tht residue cover is highly ffected by the type of tillge system tht ws used. Al-Kisi nd Onel, 21 18

22 Surfce Residue % Surfce Corn Residue - Sttewide Averge b No-tillge b Conservtion Tillge Conventionl Tillge Figure 4. Sttewide verge corn residue percent by tillge prctice. Vlues reflect the mount of corn residue observed the following spring fter corn ws grown. Tretments with the sme letter re not significntly different. 1 Surfce Soyben Residue - Sttewide Averge 9 8 Surfce Residue % b c No-tillge Conservtion Tillge Conventionl Tillge 2 1 Figure 5. Sttewide verge soyben residue percent by tillge prctice. Vlues reflect the mount of soyben residue observed the following spring fter soybens were grown. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 19

23 Orgnic Mtter Soil orgnic mtter plys severl importnt roles in mintining soil qulity, including: promoting plnt root growth, ertion, incresing crop production, nd wter retention. Also, proper mngement of soils cn result in sequestrtion of CO 2 nd reduction of greenhouse gses. It is known tht conservtion tillge prctices will increse the mount of crbon nd orgnic mtter content in soil over the long-term, but short-term impcts of tillge on orgnic mtter re not s well understood (Al-Kisi et l., 25). The short-term chnges in orgnic mtter due to tillge prctice will be discussed for ech of the four regions of Iow, including trends for five yers or less. Averge orgnic mtter trends for sites within ech of the four regions of Iow re shown in Figure 6. There is no significnt difference in orgnic mtter percent between tillge prctices, except for 28 in north-centrl Iow, where conservtion tillge is significntly higher thn no-tillge or conventionl tillge. The higher conservtion tillge vlue in 28 my indicte slight trend upwrd in conservtion tillge orgnic mtter, but is likely due to the vribility of soil properties in the north-centrl region of Iow nd the inconsistency of soil smpling on lrge scle fields. The rnge in soil orgnic mtter vries gretly by region. The northwest region rnges from bout %, north centrl from bout %, northest from bout , nd southern Iow rnges from bout %. These differences between regions reflect the diverse conditions tht ffect the ccumultion of orgnic mtter, including: soil prent mteril, climte, topogrphy, dringe conditions, nd soil texture. The results presented in Figure 6 demonstrte commonly expected slow chnges in orgnic mtter due to short-term monitoring. Generlly, chnge in orgnic mtter is very slow process where increses with conservtion tillge nd no-till cn be very smll, but stbility of such systems cn protect soil orgnic mtter for the long-term. Also, the percentge of crbon loss with conventionl tillge my pper to not be significnt, but this trend is expected in orgnic rich Iow soils. The loss of orgnic mtter cn pper to be very slow since the beginning orgnic mtter content is very high (Al-Kisi et l., 25). These trends reflect high field nd sesonl vribility, which is confounded by smpling errors nd short-term monitoring. Al-Kisi nd Onel, 21 2

24 Soil Orgnic Mtter - Region 1 Orgnic Mtter - Region 2 Orgnic Mtter % No-tillge Conventionl Tillge Orgnic Mtter % b No-tillge Conservtion Tillge Conventionl Tillge Yer Yer Orgnic Mtter - Region 3 Orgnic Mtter - Region 4 Orgnic Mtter % Yer No-tillge Conventionl Tillge Orgnic Mtter % Yer No-tillge Conservtion Tillge Figure 6. Trends in soil orgnic mtter percent by tillge tretment of four mjor soil regions cross Iow. Tretments with the sme letter re not significntly different. Soil Compction Compction levels re n importnt indictor of soil qulity. High soil compction contributes to loss of soil pore spce, reduced wter infiltrtion, nd inhibited root growth. Most compction in fields is the result of frm mchinery trffic, especilly on soils ner field cpcity. Deep tillge cn be used s temporry solution to brek up compcted lyer, but long-term pln to reduce trffic or chnge tillge prctices is more likely to provide permnent decrese in compction. Reduced tillge prctices re expected to result in lower compction levels over time s trffic on the field is reduced nd soil pores nd structure re llowed to form (Vrs et l., 1997, Hnn nd Al-Kisi, 29). Averge compction vlues to depth of 12 inches for four sites cross Iow re shown in Figure 7. Compction vlues re similr between tillge systems for ll four regions nd cross multiple yers. In 28, compction in no-tillge is significntly higher thn conventionl tillge in the north-centrl region. In 29, compction of conventionl tillge plots is significntly higher thn no-tillge in southern Iow. There re no significnt differences for ny of the other yers. The gretest difference in compction between tillge tretments is observed in north centrl Iow. However, these differences re explined by the distnt loctions of the no-till nd conventionl tillge plots from one nother, nd the resulting soil vribility. The results indicte Al-Kisi nd Onel, 21 21

25 very little chnge in soil compction due to tillge system over five yer period. We expect lower compction levels in no-tillge s field trffic is reduced, but five yers is too short of time to observe significnt chnges. The ssumption of using conventionl tillge to reduce soil compction is lso not supported by these findings s shown in Fig. 7, where soil compction of tilled plots in the top 12 inches ws not significntly different from tht for no-till. The use of conventionl tillge cn in the long-term crete less productive soil environment, destroying soil structure nd leding to deeper soil compction below the tillge zone. The results show two importnt fctors ffecting soil compction: yerly vribility nd the effect of soil moisture on compction. Proper soil moisture while mesuring soil compction is criticl when compring compction results; soil compction should be mesured t field cpcity. Vritions in soil moisture between plots my explin the lck of differences between tillge systems. Compction Index Northwest Iow Yer No Tillge Conventionl Tillge Compction Index North Centrl b Yer No-tillge Conventionl Tillge Northest Iow Southern Iow Compction Index No-tillge Conventionl Tillge Compction Index b No-tillge Conventionl Tillge Yer Yer Figure 7. Averge soil compction by tillge for four sites cross Iow. Vlues re n verge of compction indexes to depth of 12 inches. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 22

26 Infiltrtion Rindrop impct on bre soil cn cuse compction nd formtion of surfce sel tht reduces wter infiltrtion rtes. An incresed mount of residue on the soil surfce hs been shown to reduce the effects of rindrop impct, mintining soil structure nd higher infiltrtion rte (Gilley et l., 1986). Direct compction cused by field trffic lso leds to loss of soil structure resulting in decresed infiltrtion rtes. It is expected tht reduced tillge prctices will result in higher infiltrtion rtes both by decresing compction from field trffic nd incresing the mount of residue left on the soil surfce (Hnn nd Al-Kisi, 29). Sttewide infiltrtion rtes by tillge tretment re shown in Figure 8. No-tillge plots hve significntly higher infiltrtion rte thn conventionlly tilled nd conservtion tillge plots. The no-tillge verge infiltrtion rte is the highest t.67 inches/min, followed by conservtion tillge t.45 inches/min, nd conventionlly tilled plots hve the lowest verge t.44 inches/min. The results show the highest infiltrtion rtes re in no-tillge plots, s expected..8.7 Infiltrtion Rte - Sttewide Averge Infiltrtion Rte (inches/min) b b No-tillge Conservtion Tillge Conventionl Tillge.1 Figure 8. Sttewide verge infiltrtion rte by tillge prctice. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 23

27 Aggregte Stbility The mount of soil orgnic mtter nd vilbility of nutrients for plnt growth re both closely relted to soil ggregte formtion nd stbility. Soil disturbnces, such s conventionl tillge prctices, cuse mcroggregtes to brek down nd ultimtely my result in loss of soil orgnic mtter. Pst studies hve shown preferentil ccumultion of C nd N in mcroggregtes nd lter formtion of microggregtes. Thus, destruction of mcroggregtes due to tillge leds to slower microggregte formtion nd overll loss of orgnic mtter (Hussin et l., 1999; Six et l., 1999). Aggregte stbility dt for four sites cross Iow re shown in Figure 9. The percent of stble ggregtes for ech site re displyed by tillge nd re split into 4 mm nd 2 mm sizes, highlighting the chnges in mcroggregtes due to tillge. The mount of 4 mm ggregtes is gretest in no-till plots for ll four sites; conventionl tillge rnges from 32-72% lower thn no-tillge. Strip tillge is 13% lower thn no-tillge t the 4 mm size for north centrl site 1. Aggregtes t the 2 mm size re generlly higher in no-till compred to conventionl tillge; conventionl tillge rnges from 19-33% lower thn no-tillge for three of the sites shown. The first north centrl site hs bout 6% more 2 mm ggregtes in conventionl tillge thn in no-tillge, while conservtion tillge is bout 52% higher thn notillge. This lower mount of 2 mm ggregtes in no-tillge t this site my be due to the lrge proportion of ggregtes t the 4 mm size, resulting in fewer ggregtes of smller sizes. This dt shows cler reltionship between tillge tretment nd the presence of stble mcroggregtes. No-tillge mintins the highest percent of ggregtes, especilly t the 4 mm size, while ny disturbnce due to conservtion or conventionl tillge reduces the mount of mcroggregtes. Al-Kisi nd Onel, 21 24

28 North Centrl - Site 1 North Centrl - Site 2 Aggregte % % -32% +52% +6% No-tillge Conservtion Tillge Conventionl Tillge Aggregte % % -24% No-tillge Conventionl Tillge 4 mm 2 mm 4 mm 2 mm Aggregte Size Aggregte Size Northest Iow Southern Iow Aggregte % % -19% No-tillge Conventionl Tillge Aggregte % % -33% No-tillge Conventionl Tillge 4 mm 2 mm 4 mm 2 mm Aggregte Size Aggregte Size Figure 9. Soil ggregte stbility of 4 mm nd 2 mm sizes for four sites cross Iow; ggregtes sizes re compred between tillge prctices for 27. Percentge differences in ggregtes by tillge tretment were clculted using the ggregte content from no-tillge s bseline. Summry of Sttewide Agronomic nd Soil Qulity Indictors Trends Corn Yield No-till corn yield for ll 4 regions rnged from 84-97% of conventionl yields. Loss of yield in no-till is more pronounced in certin regions (Region 1), but lso depends on specific site conditions. The five yer trend shows little difference in corn yield between conservtion nd notillge for ny region, while conservtion tillge is slightly higher thn conventionl tillge for Region 2 nd Region 3. Al-Kisi nd Onel, 21 25

29 Soyben Yield Soyben yields show less differences compred to corn between no-tillge nd conventionl tillge, with no-tillge yields of 92-15% of conventionl tillge. There is little difference in soyben yield between conservtion nd no-tillge for ny region, while conservtion tillge is slightly higher thn conventionl tillge for Region 2 nd Region 3. Yield nd Crop Rottion The results show tht comprison between rottions within the sme site nd sme yer re necessry to drw ny conclusions bout yield results due to rottion. A cler trend for understnding the effect of crop rottion on gronomic performnce is not vilble becuse of lck of consistent crop rottions t ech site for long-term comprison within ech region. The results show tht yield differences between yers cnnot be clerly linked to rottion, but re likely due to combintion of fctors, including: precipittion, soil wter holding cpcity, temperture, plnting dte, seed hybrid, nd yerly vribility. Residue Cover No-tillge results in t lest 2% more surfce residue thn conservtion or conventionl tillge whether corn or soyben residue is present. The presence of soyben residue mplifies this difference, with no-till hving bout 3% more residue thn conventionl tillge. Orgnic Mtter nd Aggregte Stbility There is no cler difference in soil orgnic mtter due to tillge prctice for ny of the 4 regions, s is expected for study of five yers or less. The findings of this study show tht chnges in soil orgnic mtter re very insignificnt in the short-term. Also, the results show tht there is high sptil nd temporl vribility due to lrge scle grid used in mesuring soil orgnic crbon. Al-Kisi nd Onel, 21 26

30 Aggregte stbility of mcroggregtes is higher in no-tillge or reduced tillge for the 4 sites observed. Higher ggregte content indictes more stble environment for orgnic mtter ccumultion nd could result in long-term increse in soil orgnic mtter. Soil Compction There is no cler difference in soil compction due to tillge tretment for ny of the four regions. The ssumption tht conventionl tillge is more effective t reducing surfce compction thn no-tillge is not supported by these results. Wter Infiltrtion No-till plots hve higher infiltrtion rte thn conventionlly tilled plots due to higher mount of residue nd lower compction levels. Infiltrtion rtes for conservtion tillge nd conventionl tillge re not significntly different. Results indicte tht soil surfce disturbnce with conventionl or conservtion tillge cn contribute to reduction of infiltrtion rte due to destruction of soil surfce ggregtes nd potentil surfce seling. Potentil Impliction of Agronomic nd Soil Qulity Chnges No-tillge nd reduced tillge offer benefits in the form of erosion control nd improved soil qulity, including: reduced soil compction, higher wter retention nd flood control, incresed surfce residue, nd stbility of soil orgnic mtter. Adoption of no-tillge in soybens is recommended for ll regions of Iow; no-tillge in corn is recommended for well-drined soils. Conservtion tillge yields re competitive with no-tillge nd conventionl tillge for both corn nd soybens. Adoption of reduced tillge prctices is recommended when notillge is not prcticl. Al-Kisi nd Onel, 21 27

31 Regionl Trends or Chnges in Agronomic nd Soil Qulity Indictors Region 1 Northwest Iow Plins Region 1 consists of the northwestern portion of the stte, or the lndscpe region known s the Northwest Iow Plins. This is gently rolling lndform with well developed strem systems, resulting in generlly well drined soils. The entire region is underlin by deposit of pre-illinoin glcil till, which is exposed t the surfce in some res of the western prt of the region. The estern prt of the region ws lter covered by Wisconsinn ge glcil till; this ws prt of glcil dvnce occurring prior to dvnces tht resulted in formtion of the Des Moines Lobe. Loess ws lter deposited cross the entire region, covering the older pre-illinoin nd Wisconsinn glcil tills nd smoothing the surfce s loess filled in vlleys. Loess deposits re nerly continuous cross the region, with the thickest deposits in the southwest nd thinning to the northest. Precipittion cross the stte decreses from southest to northwest, resulting in the driest conditions being found in the Northwest Iow Plins. Men nnul precipittion mounts for this region re less thn 25 inches (Prior, 1991). Trend of Agronomic Indictors Yield Yields were recorded yerly for corn-soyben rottion in Region 1 (Figure 1). There is little difference in soyben yields, but corn yields vry over time nd between tillge tretments. The verge soyben yield for conventionlly tilled plots is significntly higher thn no-tillge yield in 26, but there is no significnt difference in 28. Averge corn yield is Al-Kisi nd Onel, 21 28

32 significntly higher in conventionl plots compred to no-tillge plots for both 27 nd 29, mounting to yield dvntge of bout 3 bu/cre in conventionlly tilled corn. Soyben yields re expected to be bout the sme between tillge prctices, lthough poorly drined soils under no-till re more likely to see yield loss thn well drined soils (Yin nd Al-Kisi, 24). The poorly drined soils of this site explin why soyben yields of no-till plots re lower thn conventionl in 26 nd 28, lthough this is more pronounced in 26. The lower no-till corn yield in 27 nd 29 is consistent with pst studies conducted in northwest Iow. Al-Kisi nd Yin (24) lso found significntly lower corn yields in no-tillge compred to conventionlly tilled plots in similr corn-soyben rottion. Reduced corn yield for no-tillge is most pronounced in poorly drined soils, res with cooler growing seson, nd continuous corn rottion (Al-Kisi nd Yin, 24). The increse in corn yield between 27 nd 29 cn be explined by chnges in wether conditions between yers, but lso by plnting dte nd corn stlk nitrte vlues. Plnting ws erlier in 29 (April 23) compred to 27 (My 2); n erlier plnting dte could increse corn yields. Also, fll corn stlk nitrte vlues indicte tht nitrogen vilbility in 27 could hve limited yield. Stlk nitrte vlues were in the mrginl rnge for 27 t n verge of bout 6 ppm, while 29 vlues were in the excessive rnge with n verge of 22 ppm. Yield - Region 1 Yield (bu/c) b b b No-tillge Conventionl Tillge. 26 (Soybens) 27 (Corn) 28 (Soybens) 29 (Corn) Yer/Rottion Figure 1. Corn nd soyben yields by tillge prctice for site 1 locted in Region 1. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 29

33 Residue Cover The mount of residue cover for no-till nd conventionl till plots for Region 1 re presented in Figure 11. Residue vlues for no-tillge plots re significntly higher for ll four yers of observtion, rnging from 71-85% in no-till plots, while conventionl till plots rnge from 25-5%. The mount of residue for no-till plots is t lest 3% higher thn conventionl plots for ll yers. There ppers to be little difference in residue cover in no-till plots due to lternting residue of corn nd soybens. However, residue cover in conventionlly tilled plots is clerly lower in yers when soyben residue is present, with vlues t lest 1% less thn yers when corn residue is present. Surfce Residue - Region 1 Surfce Residue % b b b b No-tillge Conventionl Tillge 26 (Corn) 27 (Soyben) 28 (Corn) 29 (Soyben) Yer Figure 11. Percentge of surfce residue by tillge prctice observed t site 1 in Region 1. The type of residue left on the field from the previous crop is listed for ech yer. Tretments with the sme letter re not significntly different. Fll Stlk Nitrte The fll corn stlk nitrte level is useful indictor of the nitrogen vilbility to corn plnts. An indequte mount of N will result in low fll stlk nitrte vlue, s the plnt removes N from the stlk nd other prts of the plnts for grin filling ner the end of the seson. However, high concentrtion of nitrte in the stlk my trnslte to n excess mount of N in the soil, indicting luxury N use by the plnt. In this cse, lower mount of fertilizer cn be Al-Kisi nd Onel, 21 3

34 used to ttin optiml yields in the future. The concentrtion of fll corn stlk nitrte (NO 3 -N) ws mesured for ll plots in Region 1 for yers in which corn ws grown. The reported corn yield is shown s function of the fll stlk nitrte concentrtion in Figure 12. Stlk nitrte concentrtion ctegory is indicted in Figure 12 by dshed lines. Low or mrginl stlk nitrte vlues re generlly ssocited with lower corn yields, indicting limittion in corn growth due to low nitrogen vilbility. High corn yields re generlly ssocited with high stlk nitrte vlues, but yields level off s the nitrte level reches the excessive rnge. The stlk nitrte test is vluble tool for djusting fertiliztion rtes ccording to nitrte nd yield levels. Producers my be ble to sve money on fertilizer ppliction by reducing rtes on fields in the excessive rnge (>2 ppm), while still mintining high yields. Also, nitrte vlues in the low or optiml rnge indicte tht n incresed ppliction of fertilizer could result in higher yields (Blckmer nd Mllrino, 1996). 25 Corn Yield s Function of Fll Stlk Nitrte - Region 1 2 Yield (bu/c) L M O E y = x.362 R² = Fll Stlk Nitrte (ppm) Figure 12. Corn yields s function of fll stlk nitrte vlues for ll mesured sites in Region 1. Dshed lines indicte stlk nitrte ctegory: L= Low (<25), M = Mrginl (25-7), O = Optiml (7-2), nd E = Excess (>2). Al-Kisi nd Onel, 21 31

35 Soil Qulity Prmeters Orgnic Mtter Soil orgnic mtter percentges for different tillge systems for Region 1 re presented in Figure 13. Orgnic mtter percentge for no-tillge plots rnge from %, while conventionlly tilled plots rnge from %. There is no significnt difference in soil orgnic mtter due to tillge for ny of the four yers. The orgnic mtter percentge for both tillge prctices chnges slightly between yers, but the vlues remin reltively constnt t bout %. Long-term implementtion of conservtion tillge prctices is expected to increse soil orgnic crbon, resulting in higher orgnic mtter content. Pst studies report smll increse or no chnge in the first 2-5 yers of conservtion tillge, while greter increse occurs between 5-1 yers (Frnzluebbers nd Arshd, 1996; Al-Kisi et l., 25). The dt for Region 1 supports the ide tht chnge in tillge prctice results in little or no chnge in orgnic mtter for the first 5 yers. A significnt difference between tillge tretments would most likely be observed if this study ws continued for severl more yers, llowing orgnic mtter to ccumulte in no-till plots, especilly in rich orgnic mtter soils. Soil Orgnic Mtter - Region Orgnic Mtter % No-tillge Conventionl Tillge Yer Figure 13. Soil orgnic mtter percent by tillge prctice observed t site 1 in Region 1. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 32

36 Bulk Density Soil bulk density vlues for Region 1 re shown in Figure 14. No-till bulk density vlues rnge from g/cm 3, while conventionlly tilled plots rnge from g/cm 3. There is some difference in bulk density between yers, but there is no significnt difference observed in bulk density between tillge tretments within ech yer. The lck of significnt differences in bulk density between tillge prctices is consistent with pst studies. Hussin et l. (1998) lso found no significnt difference between no-till nd conventionl tillge fter 8 yers t site in southern Illinois. The differences in bulk density vlues between yers cn be ttributed to sptil vribility, soil moisture content, time of yer, nd repetbility of smpling loction. Bulk Density - Region 1 Bulk Density (g/cm3) No-tillge Conventionl Tillge Yer Figure 14. Soil bulk density by tillge prctice observed t site 1 in Region 1. Tretments with the sme letter re not significntly different. Soil Compction Compction index vlues by tillge prctice in Region 1 re presented for 27 nd 29 (Figure 15). Compction vlues for 27 re higher in conventionlly tilled plots for lmost ll depths, except for the 9-12 inch depth where no-till nd conventionlly tilled vlues re lmost the sme. The compction vlues for 29 re similr to 27, but the no-till nd conventionlly tilled vlues re closer to one nother ner the soil surfce. Conventionlly tilled plots hve Al-Kisi nd Onel, 21 33

37 lower compction vlue thn no-till from 3 to 9 inches, but consistently hve higher compction vlue below depth of 9 inches. Compction index vlues for the no-tillge plots pper to decrese slightly in the top few inches over the two yer period observed. A slight decrese in the top 9 inches of conventionlly tilled plots my indicte temporry reduction in compction due to tillge, but the compcted lyer is pushed deeper in the soil profile over the two yer period. Reduced tillge prctices re expected to result in lower compction levels over time, s trffic on the field is reduced nd soil pores nd structure re llowed to form (Vrs et l., 1997, Hnn nd Al-Kisi, 29). Compction Index by Tillge - 27 Compction Index Depth (inches) No-tillge Conventionl Tillge 24 Compction Index by Tillge - 29 Depth (inches) No-tillge Conventionl Tillge 24 Figure 15. Compction index by tillge prctice to depth of 24 inches. Observtions from 27 nd 29, including site 1 in Region 1. Al-Kisi nd Onel, 21 34

38 Soil ph Soil ph vlues for Region 1 re shown in Figure 16. The ph vlues between tillge prctices re not significntly different for ny of the yers shown. No-tillge ph vlues rnge from , while conventionlly tilled vlues rnge from These results re consistent with the study by Hussin et l. (1999) in which ph ws still not significntly different between no-tillge nd conventionl tillge fter eight yers. The results lso show tht ph vribility cross yers ws not significnt. This reflects the nture of ph s chemicl indictor, indicting tht ny chnge in ph is long-term process. Chemicl chnges re especilly slow in high orgnic mtter soils due to the high buffer cpcity of such soils. 8 Soil ph - Region ph 4 No-tillge 3 Conventionl Tillge Yer Figure 16. Soil ph by tillge prctice for site 1 in Region 1. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 35

39 Microbil Biomss Crbon Microbil biomss crbon vlues by yer for Region 1 re shown in Figure 17. Microbil biomss crbon is biologicl indictor tht mesures the helth of soil nd the effect of tillge nd cropping systems on the soil environment. No-tillge verge microbil biomss crbon vlues rnge from µg C/g soil, while conventionlly tilled vlues rnge from µg C/g soil. There is no significnt difference in microbil biomss crbon between tillge tretments for ny of the three yers shown. No-tillge soils re expected to hve significntly higher microbil biomss crbon thn conventionlly tilled soils over time, but only in the top three inches (Dorn, 1987). The results shown in Figure 17 re to depth of six inches; cler increse in no-till microbil biomss my be more pprent if three inch smple hd been tested. Also, microbil biomss crbon is long-term indictor nd the chnge cn be very slow with chnging tillge or cropping systems. 6 Microbil Biomss Crbon - Region 1 Microbil Biomss (µg C/g soil) No-tillge Conventionl Till Yer Figure 17. Microbil biomss crbon by tillge prctice for site 1 in Region 1. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 36

40 Infiltrtion Rte Infiltrtion rtes for Region 1 re shown in Figure 18. The verge infiltrtion rte for no-tillge plots is t lest.2 inches/hour higher thn conventionlly tilled plots for ll three yers; conventionl tillge infiltrtion rtes rnge from 26-46% lower thn no-tillge rtes. Infiltrtion rtes re sensitive to chnges in tillge nd cropping systems s it depends on stbility of soil structure. It is known tht conventionlly tilled fields re susceptible to compction nd reduction of infiltrtion due to loss of mcropores (Ankeny et l., 199; Ankeny et l. 1995). The results of this study support the ide tht infiltrtion rtes will decrese in conventionlly tilled plots..12 Infiltrtion Rte - Region 1 Infiltrtion Rte (inches/min) % -26% -38% No-tillge Conventionl Tillge Yer Figure 18. Averge infiltrtion rte by tillge prctice for site 1 in Region 1. Percentge differences in infiltrtion rte by tillge tretment were clculted using the infiltrtion rte from no-tillge s bseline. Al-Kisi nd Onel, 21 37

41 Summry of Agronomic nd Soil Qulity Trends for Region 1: No-till results in 14-19% decrese in corn yield compred to conventionl tillge. Almost 1% decrese is observed in soyben yield in no-tillge compred to conventionl tillge; this is only loss of 4-6 bu/cre. However, this is higher thn wht ws reported by other studies. Surfce residue for no-till is t lest 3% higher thn conventionl tillge whether corn or soyben residue is present. Soil orgnic mtter content, bulk density, ph, nd microbil biomss crbon re not significntly ffected by tillge over period of five yers or less. Compction levels generlly decrese in no-till plots over time; tilled soils remin constnt t the surfce but increse t depth s the compcted lyer is pushed deeper. Infiltrtion rtes re 26-46% lower in conventionlly tilled plots when compred with notillge. Al-Kisi nd Onel, 21 38

42 Region 2 Des Moines Lobe Region 2 encompsses the north-centrl re of the stte, or the lndscpe region known s the Des Moines Lobe. The most recent episode of glcition occurred in this re, leving deposits of Wisconsinn ge glcil till tht hve remined reltively undisturbed by erosion over time. Glcil till remins t the surfce in this re of the stte; older glcil till nd loess deposits were buried by the Wisconsinn glcil dvnce. This region is generlly flt nd poorly drined due to the uniform deposition of glcil till. However, locl vribility in glcil deposits resulted in microtopogrphy, llowing for the formtion of wetlnds nd lkes in lower elevtions. Poor dringe conditions nd slow decy of orgnic mtter hs resulted in drk, orgnic rich soils in this region (Prior, 1991). Agronomic Prmeters Yield Yields were recorded yerly for corn-soyben nd corn-corn-soyben rottions in Region 2 (Figure 19). There is no significnt difference in corn yield between no-till nd conservtion tillge plots for 25. In 26, significnt difference in soyben yields is observed between ll tillge prctices. In 27, verge corn yields for conservtion nd conventionl tillge re both significntly higher thn no-till, lthough there is no significnt difference between the two tilled tretments. In 28, no significnt difference in corn yields is observed. In 29, conservtion nd conventionl tillge soyben yields re both significntly higher thn tht of no-tillge; there is no difference between the tilled tretments. Soyben yields re expected to be bout the sme between tillge prctices, lthough poorly drined soils under no-till re more likely to see yield loss thn well drined soils (Yin nd Al-Kisi, 24). The poorly drined soils of this site explin why soyben yields of no-till Al-Kisi nd Onel, 21 39

43 plots re lower thn conventionl or conservtion tillge in 26 nd 29. The lower no-till corn yield in 25 nd 27 is consistent with pst studies conducted on similr site in northcentrl Iow (Licht nd Al-Kisi, 25). However, Licht nd Al-Kisi found no significnt dvntge in corn yield of conservtion tillge over no-tillge, s is shown for 27. Reduced corn yield for no-tillge is most pronounced in poorly drined soils, res with cooler growing seson, nd continuous corn rottion (Al-Kisi nd Yin, 24). Generlly, decrese in corn yield is observed for ll tillge prctices for second yer corn in corn-cornsoyben rottion (Al-Kisi nd Yin, 24; Al-Kisi nd Onel, 21). The increse of ll corn yields in 28, nd no-till hving the highest yield re not consistent with pst studies. However, chnges in yield between yers re not only due to rottion, but cn be explined by vriety of environmentl fctors. Sttewide corn yields in 28 were one of the highest in Iow s history, explining why n increse in yield for continuous corn is observed. Although cool nd wet spring resulted in slow plnting nd growth, lte silking in corn nd idel lte seson wether conditions resulted in high corn yields for 28 (Elmore nd Abendroth, 28). Yield - Region 2 Yield (bu/c) b c b b b b No-tillge Conservtion Tillge Conventionl Tillge 25 (Corn) 26 (Soybens) 27 (Corn) 28 (Corn) 29 (Soybens) Yer/Rottion Figure 19. Corn nd soyben yields by tillge prctice for site 1 locted in Region 2. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 4

44 Residue Cover Residue cover observed for Region 2 is presented in Figure 2. Residue vlues for notillge plots rnge from 65-89%, conservtion tillge vlues rnge from 17-7%, nd conventionl tillge rnges from 15-65%, respectively for both corn nd soyben residues nd cross ll yers. There is no significnt difference in residue between no-tillge nd conservtion tillge for 25. However, no-tillge is significntly higher thn both conservtion nd conventionl tillge for The no-tillge residue vlue is t lest 2% higher thn tht of conventionlly tilled plots for ll yers where corn residue is present nd s much s 55% higher when soyben residue is present. No-tillge vlues re t lest 15% higher thn conservtion tillge between 26 nd 29 when corn residue is present, nd s much s 5% higher when soyben residue is present. These results indicte tht no-tillge mintins high level of surfce residue regrdless of which crop ws grown the yer before, while conservtion nd conventionl tillge plots re consistently lower nd more vrible due to mixing of residue into the soil. These differences in residue cover will hve n impliction on controlling soil erosion nd type of tillge tht should be used, especilly with frgile residue such s soyben. Surfce Residue - Region 2 Surfce Residue % b c b b b c b c No-tillge Conservtion Tillge Conventionl Tillge 1 25 (Soyben) 26 (Corn) 27 (Soyben) 28 (Corn) 29 (Corn) Yer Figure 2. Percentge of surfce residue by tillge prctice observed t site 1 in Region 2. The type of residue left on the field from the previous crop is listed for ech yer. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 41

45 Fll Stlk Nitrte The fll corn stlk nitrte level is useful indictor of the nitrogen vilbility to corn plnts. An indequte mount of N will result in low fll stlk nitrte vlue, s the plnt removes N from the stlk nd other prts of the plnts for grin filling ner the end of the seson. However, high concentrtion of nitrte in the stlk my trnslte to n excess mount of N in the soil, indicting luxury N use by the plnt. The concentrtion of fll corn stlk nitrte (NO 3 - N) ws mesured for ll plots in Region 2 for yers in which corn ws grown. The reported corn yield is shown s function of the fll stlk nitrte concentrtion in Figure 21. Stlk nitrte concentrtion ctegory is indicted in Figure 21 by dshed lines. Low or mrginl stlk nitrte vlues re generlly ssocited with lower corn yields, indicting limittion in corn growth due to low nitrogen vilbility. High corn yields re generlly ssocited with high stlk nitrte vlues, but yields level off s the nitrte level reches the excessive rnge (>2 ppm). The stlk nitrte test is vluble tool for djusting fertiliztion rtes ccording to nitrte nd yield levels. Producers my be ble to sve money on fertilizer ppliction by reducing rtes on fields in the excessive rnge (>2 ppm), while still mintining high yields. Also, nitrte vlues in the low or optiml rnge indicte tht n incresed ppliction of fertilizer could result in higher yields (Blckmer nd Mllrino, 1996). 25 Corn Yield s Function of Fll Stlk Nitrte - Region 2 Yield (bu/c) L M O y = x.514 R² = E Fll Stlk Nitrte (ppm) Figure 21. Corn yields s function of fll stlk nitrte vlues for ll mesured sites in Region 2. Dshed lines indicte stlk nitrte ctegory: L= Low (<25), M = Mrginl (25-7), O = Optiml (7-2), nd E = Excess (>2). Al-Kisi nd Onel, 21 42

46 Soil Qulity Prmeters Orgnic Mtter Soil orgnic mtter percentges for different tillge systems for Region 2 re presented in Figure 22. Orgnic mtter for no-tillge plots rnges from %, conservtion tillge rnges from %, nd conventionl rnges from %. There is no significnt difference in orgnic mtter vlues between ny of the tillge prctices, except in 28 where conservtion tillge is significntly higher thn no-tillge nd conventionl tillge, which cn be ttributed to smpling vribility. There is some vrition in orgnic mtter both between tillge prctices nd between yers. These differences my be explined by the highly vrible soil conditions nd microtopogrphy of the Des Moines Lobe region. Poorly drined conditions in depressions nd presence of crbontes leds to irregulr brekdown of humus into orgnic mtter, nd could explin the vribility within ech plot (Cmbrdell et l., 1994; Schetzl nd Anderson, 25). Long-term implementtion of conservtion tillge prctices is expected to increse soil orgnic crbon, resulting in higher orgnic mtter content. Pst studies report smll increse or no chnge in the first 2-5 yers of conservtion tillge, while greter increse occurs between 5-1 yers (Frnzluebbers nd Arshd, 1996; Al-Kisi et l., 25). The dt for Region 2 supports the ide tht chnge in tillge prctice results in little or no chnge in orgnic mtter for the first 5 yers. A significnt difference between tillge tretments would most likely be observed if this study ws continued for severl more yers, llowing orgnic mtter to ccumulte in no-till plots. Al-Kisi nd Onel, 21 43

47 8. Orgnic Mtter - Region 2 Orgnic Mtter % b No-tillge Conservtion Tillge Conventionl Tillge Yer Figure 22. Soil orgnic mtter percent by tillge prctice observed t site 1 in Region 2. Tretments with the sme letter re not significntly different. Bulk Density Soil bulk density vlues re shown for Region 2 in Figure 23. There is no significnt difference in bulk density between tillge prctices for ny of the five yers. Bulk density vlues remin constnt t bout 1.2 g/cm 3 for ll yers, except for 26 where ll tillge prctices hve vlue of round.9 g/cm 3. This lower vlue in 26 is most likely due to difference in smpling technique for tht yer s opposed to n ctul decrese in bulk density. The lck of significnt differences in bulk density between tillge prctices is consistent with pst studies. Hussin et l. (1998) lso found no significnt difference between no-till nd conventionl tillge fter 8 yers t site in southern Illinois. Al-Kisi nd Onel, 21 44

48 Bulk Density - Region Bulk Density (g/cm3) No-tillge Conservtion Tillge Conventionl Tillge Yer Figure 23. Soil bulk density by tillge prctice observed t site 1 in Region 2. Tretments with the sme letter re not significntly different. Soil Compction Compction index vlues by tillge prctice in Region 2 re presented for 27 nd 29 (Figure 24). Conventionlly tilled plots hve lower compction vlue t ll depths compred to no-tillge for 27. Compction vlues ner the surfce re similr between no-tillge nd conventionl tillge for 29, but no-tillge vlues re slightly higher thn conventionl tillge to depth of 1 inches. No-tillge plots consistently hve lower compction vlue t lower depths thn conventionl tillge in 29. These results indicte decrese in compction levels ner the surfce for no-tillge, while conventionl plots remin the sme. The compction index for conventionl plots gretly increses below depth of 6 inches over the two yer period, while no-tillge vlues decrese. The low compction vlues in the top 6 inches of conventionlly tilled plots is most likely due to incresed porosity from tillge, but the index vlues t depth increse becuse the compcted lyer is pushed deeper in the soil profile over the two yer period. Reduced tillge prctices re expected to result in lower compction levels over time s trffic on the field is reduced nd soil pores nd structure re llowed to form (Vrs et l., 1997; Hnn nd Al-Kisi, 29). Al-Kisi nd Onel, 21 45

49 Compction Index by Tillge - 27 Compction Index Depth (Inches) No-tillge Conventionl Tillge 24 Compction Index by Tillge Depth (Inches) 12 No-tillge Conventionl Tillge Figure 24. Compction index by tillge prctice to depth of 24 inches. Observtions from 27 nd 29, including site 1 in Region 2. Al-Kisi nd Onel, 21 46

50 Soil ph Soil ph vlues for Region 2 re shown in Figure 25. No-tillge ph vlues rnge from , conservtion vlues rnge from , nd conventionlly tilled plots rnge from No-tillge nd conservtion tillge ph is significntly higher thn conventionl till between 26 nd 28, but ll tretments re significntly different from one nother in 29. There is no significnt difference between no-till nd conservtion till for 25. The vrition in ph vlues for conservtion tillge nd conventionl tillge could be explined by the sptil vribility within the plots, nd the uniformity of N fertilizer ppliction nd other mendments (Cmbrdell et l., 1994, Hussin et l., 1999). The ph of no-till plots ppers to decrese stedily over the 5 yer period. This decrese is most likely result of nitrifiction of N fertilizers, ccumultion of fertilizer on the soil surfce, nd minerliztion of plnt residue (Blevins et l., 1983; Dick 1983) Soil ph - Region 2 8 ph b b b b c No-tillge Conservtion Tillge Conventionl Tillge Yer Figure 25. Soil ph by tillge prctice for site 1 in Region 2. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 47

51 Microbil Biomss Crbon Microbil biomss crbon vlues by yer for Region 2 re shown in Figure 26. Microbil biomss crbon is biologicl indictor tht mesures the helth of soil nd the effect of tillge nd cropping systems on the soil environment. No-tillge verge microbil biomss crbon vlues rnge from µg C/g soil, conservtion tillge rnges from µg C/g soil, while conventionlly tilled vlues rnge from µg C/g soil. Conservtion tillge is significntly higher thn both other tretments for 27 nd 28 while there is no difference between no-till nd conventionl tillge plots. No-tillge soils re expected to hve significntly higher microbil biomss crbon content thn conventionlly tilled soils over time, but only in the top three inches. The results shown in Figure 26 re to depth of six inches; cler increse in no-till microbil biomss crbon my be more pprent if three inch smple ws tested. It is uncler why microbil biomss of conservtion tillge plots re higher thn notillge, lthough this could be due to combintion of fvorble conditions for microbil ctivity including soil C nd N, wter content t depth, nd distribution of residue on the soil surfce (Dorn 1987). 6 Microbil Biomss Crbon - Region 2 Microbil Biomss (µg C/g soil) b b b No-tillge Conservtion Tillge Conventionl Tillge Yer Figure 26. Microbil biomss by tillge prctice for site 1 in Region 2. Tretments with the sme letter re not significntly different. Al-Kisi nd Onel, 21 48

52 Infiltrtion Rte Infiltrtion rtes for Region 2 re shown in Figure 27. A high mount of vribility in infiltrtion mesurements is observed due to sptil vribility nd vritions in smpling techniques. However, no-tillge infiltrtion rtes re consistently higher thn conventionl tillge nd conservtion tillge. No-tillge vlues re t lest.2 inches/hour higher thn other tretments for ll four yers. Conventionl tillge infiltrtion rnges from 57-84% lower thn no-tillge while conservtion tillge infiltrtion rnges from 25-6% lower. Infiltrtion rtes re sensitive to chnges in tillge nd cropping systems s it depends on stbility of soil structure. It is well known tht conventionlly tilled fields re susceptible to compction nd reduction of infiltrtion due to loss of mcropores (Ankeny et l., 199; Ankeny et l. 1995). The results of this study support the ide tht infiltrtion rtes will decrese in conventionlly tilled plots..12 Infiltrtion Rte - Region 2 Infiltrtion Rte (inches/min) % -84% -57% -6% -52% -7% No-tillge Conservtion Tillge Conventionl Tillge Yer Figure 27. Averge infiltrtion rte by tillge prctice for site 1 in Region 2. Percentge differences in infiltrtion rte by tillge tretment were clculted using the infiltrtion rte from no-tillge s bseline. Al-Kisi nd Onel, 21 49

53 Summry of Agronomic nd Soil Qulity Trends for Region 2: No-till corn yield is 6-1% lower thn conventionl nd conservtion tillge, except in 27 where no-till is 4% higher thn either. Conservtion tillge corn yield is 1-2% higher thn conventionl. No-till soyben yield is 8-15% lower thn conventionl till nd 1-19% lower thn conservtion tillge. Conservtion tillge is 1-4% higher thn conventionl tillge. Surfce residue for no-till is t lest 2% higher thn conventionl tillge for ll yers, nd s much s 55% higher when soyben residue is present. Residue for conservtion tillge is generlly higher thn conventionl tillge nd lower thn no-tillge, but vries by yer. Surfce compction decreses with 2 yers of no-till. Conventionlly tilled soils remin constnt t the surfce but increse t depth s the compcted lyer is pushed deeper. Soil ph stedily decreses in no-till plots due to minerliztion nd nitrifiction of fertilizers t the surfce. Conservtion nd conventionl ph vlues re unpredictble becuse of the sptil vribility of crbontes nd N ppliction. Soil orgnic mtter nd bulk density re not significntly ffected by tillge over period of five yers or less. Microbil biomss crbon for conservtion tillge is significntly higher thn conventionl nd no-till in 28, nd higher thn no-till in 27. The mount of C nd N, mixing of residue, nd the moisture content in the soil re ll responsible for the higher microbil biomss crbon vlue. Differences in infiltrtion rte re highly vrible for ll tillge prctices, but no-tillge is consistently higher thn conservtion nd conventionl tillge for ll yers. Infiltrtion rtes re 57-84% lower in conventionlly tilled plots when compred with no-tillge; infiltrtion is 25-6% lower in conservtion tillge plots when compred to no-tillge. Al-Kisi nd Onel, 21 5

54 Region 3 Northest Iown Region Region 3 consists of the northestern prt of the stte, or the lndscpe region known s the Northest Iown Region. This lndscpe is chrcterized by slight inclines nd rolling hills. Well developed strem systems llow for well drined soils throughout much of the region, lthough scttered res of wetlnds nd poorly drined soils do occur. This region ws lst covered by glciers over hlf million yers go during the pre-illinoin dvnce. The pre- Illinoin glcil till remined exposed to wethering for hundreds of thousnds of yers resulting in widespred erosion nd formtion of strem systems. Loess ws deposited in this region prior to the formtion of the Des Moines Lobe, lthough current lyers of loess re thin nd inconsistent due to ccelerted erosion during the Wisconsinn glcitions. The estern portion of this region, known s the Pleozoic Plteu, ws never completely covered by glciers lthough ptches of pre-illinoin till re found in some res. Thin soils of glcil till nd highly wethered loess nd shllow contct with bedrock chrcterize this lndscpe (Prior, 1991). The results for Region 3 will focus on the western portion of the Northest Region, considering tht no ILF coopertor sites were locted on the Pleozoic Plteu. Agronomic Prmeters Yield Yields were recorded yerly for corn-corn-soyben rottion in Region 3 (Figure 28). There is no significnt difference in corn or soyben yields between conservtion tillge, conventionl tillge, or conventionl tillge with mnure for ny of the four yers shown. A sttisticl comprison is unvilble for 26 due to the lck of multiple dt points. A significnt decrese in soyben yield due to reduced tillge is not expected in this re due to the well drined soils of northest Iow (Yin nd Al-Kisi, 24). The lck of significnt differences in corn yields between conservtion nd conventionl tillge for 25, 26, nd 28 re consistent with the results of pst study conducted in northest Iow (Licht nd Al- Al-Kisi nd Onel, 21 51