Breeding and management of tropical corn for use in multiple cropping systems in Florida

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Breeding and management of tropical corn for use in multiple cropping systems in Florida
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vii, 286 leaves : ill. ; 29 cm.
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Lang, Timothy A., 1957-
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Thesis:
Thesis (Ph. D.)--University of Florida, 1994.
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Includes bibliographical references (leaves 266-285).
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by Timothy A. Lang.
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Vita.

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BREEDING


AND


MANAGEMENT OF TROPICAL
CROPPING SYSTEMS IN


CORN FOR
FLORIDA


USE


IN MULTIPLE


TIMOTHY


LANG


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


---------- ---


-- -------















ACKNOWLEDGEMENTS


thank


the


following


people


their


assistance


provided


me during


doctorate


years.


major


professor,


Dr. Raymond


Gallaher,


has been


unfailing


his


support


of both


me and


work


patience,


guidance,


and


contributions

appreciated.


while c

Special


conducting


thanks


this research

to Dr. David


are


much


Wright,


. Ben


Whitty,


on the


ass


. Fred


committee


instance


Rhoads,


and


of Steve


and


reviewing


Linda


. Jerry


this


Brett


Sartain


manuscript


Lindo


serving


The


-Terhaar


conducting


statistical


analyses


is appreciated.


. Ken


Quesenberry


has


provided


valuabi


advice


and


guidance


concerning


academic


hurdle


hoops.


The


cooperation


conducting


laboratory


James


anal


Chichester


yses


and


field


Howard


work


Palmer


much


appreciated.


In addition


Walter


Davis


thanked


help


harvesting


crops


and


collecting


soil


samples


Green


Acres.


The


folks


the


soil


testing


laboratory


Wallace


building


, Lamar,


Chuck,


Beverly,


Jim


Austin,


Shirley,


Pam, and


Jim


are


appreciated


tolerating









Fellow


students,


Ron


(Riker)


Rice,


Mike


(Wayne)


Austin,


Bisoondat


(Mac)


Macoon,


Greg


(BP)


McDonald,


Paul


(Wesley)


Lilly,


Brian


(Briney)


Smith


were


important


colleague


supporters


Serge


(Papa


Doc)


Edme


appreciated


his


island


wit


and


laughter


while


helping


conduct


field


work.


financial


support,


a Catholic


education,


and


trying


instill


some


Christianity


thank


my parents,


Charles


Mary.


additional


financial


and


emotional


support


thank


siblings


their


spouses,


Jenny


and


Tom,


Gigi


and


Fred


, Mimi


Bill,


Deede


and


Brian,


Vince


and


Mary


, Patty


Bruce,


and


Chris


Paula,


and


one


single


brother,


Charles.


Finally,


spiritual,


emotional,


and


financial


support,


thank


wife,


Nancy.

















TABLE


ACKNOWLEDGEMENTS


ABSTRACT


OF CONTENTS


* . S * vi

S . * * vi


CHAPTERS


INTRODUCTION


LITERATURE


REVIEW


Nitrogen


Plant
Yiel
Maize
Fert
Breedi
Perf
Tropic
Tillag
Prop
Tillag
Liming
Prop
Liming
Potass


Fertilizatio


Tissu
d
and S


Mineral


Sorghum
orghum


ilization
ng Tropic
ormance
al Maize


e Ef
erti
e Ef
Eff
erti
Eff
ium


Potassium
Growth


fects
es .
fects
ects
es .
ects
Ferti
Ferti


al


n and Maize Yield
Concentration and


Yield

Maize


Responses


Sfor
for


Improved


Performance Studies .
on Soil Chemical and


* .
on
on


Mai
Soil


Maiz
zatio
zatio


ze Growth
Physical

e Growth
n and Soit
n Effects


S


Maize


Nitrogen
* . 11


. 1
* . 1


Phy


sical


* S S S S S S 5 2


and


Chemical


* . 2 2

1 Fertility . 4
on Maize


2


S~ ~ ~ S S S S S S S S S S S 45


RESPONSES
NITROGEN


OF TROPICAL MAIZE
FERTILIZATION .


AND


SORGHUM


S S S SS S S 5 51


Introdu
Material
Results
Discuss
Summary


action . . 5
Is and Methods . . . 5

ion . . . . 10
S . . . .* 10
* * * -L


DEVELOPMENT OF


TROPICAL


MAIZE


HYBRIDS


FOR


USE










OPTIMAL PLANT SPACING FOR LATE
TROPICAL MAIZE PRODUCTION


SEASON


Introduction
Materials an
Results and


d Methods
Discussion


* .
* ~ .
*~ S S


SOIL AND CROP RESPONSES TO
LIME AND POTASSIUM RATES
DOUBLE CROP SYSTEM .


TILLAGE PRACTICE
IN A WHEAT-MAIZE


AND


Introduction
Materials an
Results and


d Methods
Discussion]


S S S S
S~~ S S S S S S
S S S S


SUMMARY


AND


CONCLUSIONS


REFERENCES


BIOGRAPHICAL


SKETCH
















Abstract


the


of Disse


Univer


sity


Requirements


rotation


of Florida


Presented


in Partial


Degree


of Doctor


the


Graduate


Fulfillment


of Phil


School


the


osophy


BREEDING


AND


MANAGEMENT


IN MULTIPLE


CROPPING


OF TROPICAL


SYSTEMS


MAIZE


FOR


USE


IN FLORIDA


Timothy


August


. Lang

1994


Chairman:


Major


Raymond


Department


. Gallaher


: Agronomy


Tropical


maize


Zea


a silage


crop


which


potential


meeting


feed


needs


Florida.


Information


management


practi


ces


is needed


so that


tropical


maize


can


produced

adapted


efficiently

to Florida's


Development


subtropical


tropical


environment


mai


should


hybrids

increase


production.


An experiment


was


conducted


1990


and


1991


near


Gainesville,


to determine


nutrient


removal


and


yield


responses


tropical


maize


grain


and


silage


sorghum


(Sorghum


bicolor


Moench),


to N application


13.4


20.2


g N m-2)


Under


N supply


conditions


, silage


sorghum


produced


more


dry


matter


(DM)


than


tropical


maize


silage


, but


removal


of N and


were


similar


the


two


maYs









and


N and


P removal


under


N supply


were


similar


tropical


maize


and


grain


sorghum.


Under


better


N management


mai


produced


more


grain


removed


more


N and


A second


study


tested


tropical


maize


hybrids


whose


parents


were


inbred


lines


tropical


origin


, but


were


self-


pollinated


and


selected


Florida.


Single-cross


tropical


maize


hybrids


were


developed


which


produced


as well


commercial


temperate


hybrids


the


spring


season


grain


ha-)


A third


experiment


(1989


and


1990)


studied


the


response


tropical


maize


grain


and


DM yie


to equidi


stant


plant


spacing


under


late


-season


conditions.


Predicted


maximum


yields


were


1989


and


1990


Optimum


plant


spacings


were


predicted


DM at 0


spacing


in 1989


m spacing


1990


Maximum


grain


yields


were


predicted


at 228


g grain


1989


and


grain


1990.


A final


yr study


was


conducted


to investigate


effects


liming


rate


, and


dolomiti


lime


ha' )


had


on res


idual


K fertili


zation


134,


201,


K ha-' )


under


no-tillage


(NT)


conventional


tillage


(CT)


practi


ces


in a tropical


mai


ze-


wheat


double


response


to K


crop

was


stem.


quadratic


No-tillage


1989;


maize


maiz


grain y

e grain


field

yield















CHAPTER


INTRODUCTION


In Florida


tropical maize


Zea


mays L.)


has


shown


promise as a high


value


silage crop


Temperate maize


produces high


silage


grain


yields when


planted


early


spring


, but


unadapted


temperature,


disease,


insect pressures which


confront maize


that


is planted


late spring


maize,


which may


early

or ma


summer.

y not b


Adapting


)e photoperiod


lowland


tropical


sensitive,


to the


subtropical


conditions


of Florida


may


allow producers


plant maize silage crops


in the


late


spring


or early


summer.


Research


on the management


tropical


maize grown


alternative growing


seasons


will


help


identify


optimal


production


practices.


Sorghum


[Sorghum bicolor


(Moench)]


is another valuable


silage crop


that


is adapted


late


sowing


conditions.


High


rainfall


events


in summer


Florida cause

Practices need


leaching

to be i


loss


of both N


identified


which


and K fertilizers.

limit fertilizer


losses and maximize


nutrient availability


and


uptake.


Late


sown


tropical


maize has


been reported


to require


higher plant


populations than


spring


sown


tropical











late


season


environment


is needed.


Planting


techniques


which


increase


plant


populations


improve


plant


-to-plant


spacings


need


to be evaluated


Tillage


practice


affects


soil


productivity


No-tillage


with

depth


in-row


subsoiling


disrupting


has


plow


been


pans


reported


, yet


retaining


increase


the


rooting


benefits


a surface


mulch


(Box


and


Langdale


, 1984)


Late


spring


planted


tropical


maize


subject


to periods


of drought


stre


SS.


Evaluation


of K fertility


and


liming


under


no-


tillage


conventional


tillage


will


ass


developing


extension


recommendations


fertili


zation


tropical


maize


under


tillage


stems.


For


Univer


these


sity


reasons


of Florida


four s

s Green


tudi


Acres


were


conducted


Agronomy


Research


the

Farm.


The


first


concerns


tropical


maize


(grain


and


silage),


sorghum


grain,


sorghum


silage


eld


respon


ses


to N


fertili


zer


the


irrigated


May


planting


condition.


The


second

maize


study

hybrids


attempts

adapted


to develop,

to Florida.


produce,


The


and


third


test


study


tropical

was


conducted


identify


tropical


maize


response


to equidistant


plant


spacing


test


a single


m row


treatment


vs.


an alternating


m double-row


treatment.


The


last


study


attempts


to add


ress


effects


tillage
















CHAPTER


LITERATURE REVIEW


Nitrogen


Fertilization


and Maize


Yield


Efficient


use


of N


fertilizer


by maize


influenced by


time and number


of N


applications,


hybrid,


and N


source


application rates.

Typic Argiudoll re


Russelle


ported


(1983)


highest rates


of N


in a Nebraskan

accumulation


were between


12-leaf


silking


growth


stages.


Some


uptake of


fertilizer


N was delayed


when N


application was


delayed.


Accumulation


of N


during


grain


fill


was


reported.


Moll


et al.


(1982)


reported


that at


N supply,


differences


in N


use


efficiency were due


to harvest


index,


but at high N

efficiency.


supply


differences were due


Eight hybrids


varying


to uptake


N efficiency were


tested


their


field


experiment.


Tsai


et al.


(1984)


reported


that


three


hybrids


responded


differently to


levels


Indiana


on a


Typic


Haplaquoll.


Differences


were


due


to ability to


uptake


N after midsilk


, rate


duration


of grain fill,

Edwards


and rate o

and Barber


f grain

(1976)


sink


synthesis


reported


(zein)


influx of N












found that most maize hybrids


accumulate


70 to 75%


their


N by silking


stage.


Gardner


et al.


(1990)


utilized


elite


hybrids


environments


test


for yield


response


to N


rate.


Maize hybrid responded


to N similarly when averaged


across


environments


, however


responses


were not


predictable.


They


concluded


that


farmers


should manage N


fertilization


a similar manner


hybrids.


Placement and source


of N


affect maize


yield.


Reeves


and Touchton


(1986)


reported


subsoiling


in row with


inter-


row placement


of N


five


weeks


after planting produced


highest


yields


on Typic and Plinthic


Paleudults.


Use of N


inhibitors did not affect


Ids.


Touchton


and Hargrove


(1982)


conducted a


yr mai


study


Georgia


on a


Typic


Paleudult and reported amm

than urea-ammonium nitrate


onium nitrate


solution,


was


which


more efficient

was more


efficient


than


urea


Ferguson


et al.


(1991)


observed N


inhibitor reduced


yields


when applied


side-dressed


with N


V6 stage.


Gascho et al.


(1984


experiments


in Georgia


on a


Plinthic


did not


Paleudult


reported


provide better


scheduled,


nutrition


than


sprinkler-applied N


conventionally


applied,


side-dressed


uptake from banded


vs.


They proposed


sprinkler


timing


broadcast


or better


were reasons











irrigation water


input


efficiency


from program


fertilization,


conventional


and a


fertilization


rainfed conditions


no yield


increase


under


in yield


irrigated


difference


program


conditions.


between


program and


conventional


fertilization methods


was


observed.


In a


later


study


Rhoads


and Manning


(1986)


found


that higher


N rates


are needed


on a


Grossarenic


Paleudult


compared


to a


Typic


Paleudult,


late


season


uptake


of N did


compensate


for early


season deficiency.


Determining


optimal


fertilization


rates


from plant


tissue and


soil


samples


has been


investigated.


El-Hout and


Blackmer


(1990)


sampled


soil


from


farms


Iowa


to determine


that 20 to


25 mg


N-NO3 kg-'


pre-plant soil


test


was optimal.


the study


over fertilization


farms


of maize


Iowa


following


higher


alfalfa.


levels due


Binford


(1990)


developed


a stalk NO,


test


after


black-layer to


determine N


supply to


crop.


Response of


stalk NO3


to N


application


was


identified


linear-plateau.


Magdoff


(1991)


suggested


practices


in maize


production


to reduce N


pollution:


sidedressing


soil


nitrate


pre-sidedress


test,


animal


crops as


green manures


traps,


applications,


season


rotations,


stalk NO3


cover


test.


Cerrato and Blackmer


(1990)


from


site-years











square root.


All models


had R2s


that


were high


0.90)


but


the quadratic model


tended


indicate optimal


N rates that


were too


high.


The quadratic-plateau


model


reportedly


best


described


yield responses.


Bock and


model


Sikora


include an


(1990


effi


modified


ciency


the quadratic-plateau


index developed by Capurro


and Voss


(1981).


The modified quadratic-plateau model


improved


predictions


economically


optimum N


rates.


Grimm et


(1987)


tested


polynomial


water plus


crop


response models


against


a Von


Liebig model


and


found


Von


Liebig model


performed


very well


for wheat


, maize,


cotton,


maize silage


, and sugar


beets


(Beta


vulqaris


Grain N


concentrations


have


also


been


used


to measure


plant N


status.


Pierre et


(1977a)


investigated


the


use


of grain N


concentration


to diagnose


N suffi


ciency


in maize.


Moisture stress,


nutrients


plant


had no effect


percent grain N


population,


on a quadratic


relationship.


Pierre


fertility


relative

et al. (1


of other


yield


977b)


utilizing data


from


various


N rate experiments


predicted N


sufficiency


and requirements


from N


concentration


grain.


They


determined


for maize grain


.52%


N critical


value


using data


from


Iowa.


follow up study


(Russell


and Pierre


1980


was


shown


that


differences











concentration


increased


optimal N


increased with N


as grain N


availability


rate,


concentration


grain N


and relative


increased.


concentration


yield

or near


was


reliable


indicator


of N


status


of maize.


Feil


et al.


(1990)


conducted


field


studies


with


tropi


maize


cultivars and


found no


relationship


between


grain


yield


grain


nutrient


concentration


and K).


They


applied


40 kg


N ha-'


their


experiments,


which may


explain


that


no relationship


between grain N


yield was


observed.


Plant


Tissue Mineral


Concentration


and Maize


Yield


Early research


Walker


et al.


(1971)


utilized


polynomial


regression


to describe


relationship


between


crop nutrient


concentrations and maize


yield.


Yields


nutrient concentrations


ear


leaf


samples


were categorized


into


two groups:


less


than


and more


than


bushels


acre


Multiple regression


accounted


variability


of yield


bu A-'


, and


variability


bu A-'


Using polynomial


regression


they


observed


that


the P


x Fe


interaction


was


only


factor


common


to both groups.


They


concluded


that


concentration


interactions


need


investigating.


Research


Walker


Peck


(1972)


determined


that


m tall


maize


plant n


utrient











plant


parts.


In a similar


study


Walker


and


Peck


(1974)


reported


early


growth


stage


plant


nutrient


content


was


better p

at early


redictor

tassel


of yield

nutrient


than n

content


utrient


was


concentrations,


equal


and


to concentration


predicting


yield.


A negative


correlation


between


concentration


was


observed


different


plant


parts


also


, a negative


correlation


was


noted


between


concentration


of K and


leaves


but


stalks.


Maize


plant


nutrient


concentration


content


partially


subject


to genetic


control.


Baligar


and


Barber


(1979)


conducted


studi


with


Florida


maize


genotypes


(inbreds


crosses)


Indiana


maize


genotypes


reported


the


Florida


lines


had


higher


values


Ca and


, and


lower


than


Indiana


lines.


The


of Mg


P for


Florida


cultivars


were


higher


than


Indiana


lines


indicating


they


were


less able


to uptake


and


P at low


concentrations.


In addition


of Ca


were


greater


for Fl

that m

uptake


orida

aize


cultivars.


hybrids


(Gallaher


Research


differ


and


Jellum


ers


effi


, 1976a,


from


ciency


Georgia

of Ca, Mg


1976b).


reported


and


Hybrids


that


were


efficient


in Ca and


uptake


were


ess


efficient


in K


uptake.


They


concluded


that


it should


be possible


to breed


hybrids


adapted


infertil


soil











system compares


nutrient


ratios


in plant


tissue


to a


published norms


to calculate


nutrient


indices


each


nutrient.


Nutrient


indi


ces


which


are


farthest


from zero,


either negative


or positive


, are


those


which


are most


imbalanced


plant.


CNL method


uses


published


nutrient concentrations of


diagnostic


plant


parts


sampled at


specific growth stages


to determine normal


sufficiency


ranges


fall


outside


each nutrient.


Nutrient


the range are determined


concentrations which


to be either deficient


or excessive.


Sumner


(1990)


advised


that


DRIS


system


is better


than CNL due


to less dependence


on age


plant


tissue


DRIS,


however,


both are


useful.


Hallmark


et al.


(1987)


compared DRIS and


CNL methods


diagnosing


soybean


nutrient


status,


included


nutrient


concentration


calculating


DRIS


mndi


ces.


They


found DRIS was


better than


CNL at detecting


P deficiencies


, but


DRIS predicted at


least one


limiting


nutrient


each


time


it assessed


a sample.


Inclusion


of concentration


DRIS


indices


(M-DRIS)


reduced


insufficiency


diagnoses


they


noted


that P


was generally misdiagnosed


DRIS.


Elwali


Gascho


(1988)


conducted


field


experiments on


Plinthic


Paleudults


in Georgia


with


maize


to compare DRIS











supplemental


fertilizer guided


both


CNL and


DRIS.


Walworth and Sumner


, (1987)


reported


that


DRIS


Ca and Mg


norms were


(1981)


lower


investigate


in Southeastern U

ed S requirements


S maize t

of maize


issue.

using


Sumner

DRIS


foliar analysis.


Walworth


(1988)


generated


DRIS


norms


maize


from a


small


data


base


10 observations


field-


grown maize


that


yielded more


than


Norms derived


from the small


location-specific database were


better


predicting


fertilizer


needs


than


norms


from a


broad


worldwide database.


High N


fertilization rates


affect


nutrient


concentrations


of other


elements


maize


other


crops.


Woodruff


et al.


(1987)


noted


that high rates


of N,


and


high


plant


populations


required


application


of B to


produce


high maize


grain


yields


South


Carolina


on a Plinthic


Paleudult.


Yield response


to B occurred


only


the highest


K rate

the Mg


(317


content


K ha') .


Schwartz


of silage ma


Kafikafi


wheat


(1978)


at high N,


studied


and K


rates.


Maize


silage


fertilized


with


N ha-'


no K


fertilizer


contained


64 kg


Maize


silage


fertilized


with


N ha-'


K ha'


contained


39 kg Mg


Magnesium and


Ca uptake


were


functions


of N uptake


in maize.


Brawand and Hossner


reported


that N


rate


increased











Maize and


Sorqhum


Yield Responses


to Nitrogen


Fertilization


Maize and sorghum


(Sorghum bicolor


Moench)


respond


differently to


N fertilization.


observed grain sorghum


to be more


Olson et al.

productive


(1986)

than maize


under


conditions


availability,


and maize more


economic at higher


N rates.


Hibberd


and Hall


(1990)


conducted a


study


sites


with


five


varieties of


maize and


five of


sorghum.


Maize


yields were highest


with


kg N ha-'


, and sorghum yields


highest


with


120


to 180


N ha-'


Peterson


and Varvel


(1989a)


studies


in Nebraska


on a


Typic Argiudoll


reported


maize grown


rotation


required


less


fertilizer


than


continuous


maize


for maximum


yield,


continuous grain


sorghum DM and


grain


yields


showed greater response


to N fertilizer


than


sorghum


rotation


(Peterson and Varvel,


1989b).


Muchow


(1988c)


observed


maize and


sorghum yield


differences were due


in part


to different


rates


of N


accumulation and


extent


of mobilization


pre-anthesis


and N.


Nitrogen supply


greater


effect


on duration


grain


fill


in maize


than


sorghum.


Rate


Increase


harvest


index was greater,


biomass


production was


less,


and duration


of grain


fill


shorter


sorghum


than


in maize.


Grain


yields


two crops


were


similar


N rates;











Muchow


(1988a)


found


leaf


area


development


of sorghum more


responsive


vegetative


Muchow


to N


than maize.


period


(1988b)


plant


reported


Sorghum


population;


increased


maize did not.


that maximum radiation


use


efficiency was


higher


maize


than


sorghum.


Muchow


(1990)


found


grain


sorghum N


uptake


during


grain


fill


unresponsive


to N


application


was


small


relative


total N uptake.


was more


Mobilization


significant.


of pre-anthesis


Variability


the grain


in biomass accounted


variance


in grain


yield.


Variability


total N


uptake accounted


variance


grain N


accumulation.


Breeding Tropical Maize


Improved


Performance


Francis


et al.


(1969)


noted


that


photoperiod


insensitive


lines


of mai


could be


crossed


with


sensitive


lines


to produce genotypes with


wide


adaptability.


Investigation


into


physiological


basis


limiting tropical


maize


yield by


Yamaguchi


(1974a


found


that


small


number


kernels


and short


leaf


duration


limited


yield


tropical


maize.


The senescence


leaves


after


silking was


rapid and


growth duration short


under


high


temperatures.


In addition


high grain


yield


was


attributable


to more


kernels


per unit












increasing


ear size and


reducing


barrenness


at high


plant


density.


Muleba


et al.


(1981)


suggested


that


tropical


maize


breeders


should


emphasis


weak


apical


dominance


in breeding


high grain


yield and high


density tolerance.


Improvement


tropical


maize


for use


US breeding


programs


decreased


involved


photoperiod


selection


sensitivity.


for reduced


Research


plant height and


on tropical


maize germplasm has


shown


that


in general,


photoperiod


sensitive,


ability


is prone


(Goodman,


1988)


lodging


, and has


Johnson et


poor


al. (1986)


combining


utilizing


recurrent


selection


to reduce


plant height


in a tropical


maize


population


reported


a reduction


in height


.4% per


cycle.


Selection


height


reduced


total


lodging


, reduced


barrenness,


earlier


flowering,


fewer


leaves


per plant.


Optimum


plant


density


increased


as well


as yield.


Selection


for reduced height


little effect


on effective


filling period


or kernel


weight.


Selection


for yield


tropical


maize


populations


has


been


conducted.


response


Iglesias


to selection


and H

yield


allauer


,nr'


(1989) reported

tropical maize


population,


advances


were


made


with


tropical


maize


populations.


population


was observed,


No improvement


because


in the


one cycle


1~00


tropical


of selection


was











flints with


US dents


varying


degrees


developed


populations with


, 75,


Argentine


flint.


The


flint population


was


reported most


suitable


developing


high-yielding


hybrids.


Albrecht and Dudley


(1987)


crossed


a South African


Composite and


US maize


belt dent


to produce


100%


exotic germplasm.


Lack


adaptiveness


the African


material


determined


that


backcrossing with


maize


belt


dent


would allow


inclusion


favorable


alleles


into


germplasm before


selfing.


Dudley


parent


with


(1984a)


stated


that


favorable all


backcrossing


eles


would


the one


advantageous


before selecting


or selfing.


Several


techniques


have


been


proposed


improve


inbred


line development


process.


Dudley


(1988)


evaluated


tropical maize


populations


their potential


as sources of


favorable alleles


improve


a temperate hybrid.


Only


one


population had


significant


frequency


of unfavorable


alleles


for root


lodging.


None


populations


had


favorable alleles


stalk


lodging resistance.


Dudley


(1988)


also developed


a method


identifying


populations


with


useful


alleles


inbred


line development


, a modified


method of


identifying useful


inbred


lines


(Dudley,


1987)











populations containing


favorable


alleles


present


elite germplasm


(1984c)


Brewbaker


et al.


(1991


tested


inbred


lines


tropical


origin


reported


good resistance


seven


virus


diseases


Best resistance


to a


particular virus


came


from


lines originating


from where


virus was


endemic.


Tropcial


maize has


been reported


to have


resistance


to many


foliar diseases


ear


feeding


insects


(Brewbaker


et al.,


1989)


The degree


of resistance


to ear


feeding


insects


ze has


been


shown


to be correlated with husk


number


(Brewbaker


and Kim,


1979)


Pandey


et al.


(1991)


improved


tropical


maize


populations


full-sib selection.


They utilized


families


from different


populations


to create


new


cultivars,


hybrid


combinations,


inbred


lines.


Open-pollinated


cultivars


derived


from


improved


populations


undergoing recurrent


selection


were more


stable


yielded better than


cultivars


developed


from


original


populations.


Tropical


Maize


Performance


Studies


Early research


into double


cropping


of maize


southeastern


USA noted


potential


tropical


hybrids


silage production


when


planted


second


crop


(Widstrom











the


risk


crop


failure


when


producing


a second


crop


silage


maize.


Research


tropics


Talleyrand


(1975)


noted


that


among


the


maize


cultivars


'Pioneer


X306


'Pioneer


X306B


and


'Funk


s G745W


' studied


yield


response


180


, Pioneer


affected


X306


yielded


southern


leaf


grain


blight


was


(Helminthosporium


not


mavdi


and


had


tight


thick


husks which


protected


against


earworms


(Spodoptera


fruqiperda)


They


later


observed


malze


yield


respond


to N


fertilizer


under


irrigated


and


unirrrigated


conditions


on two


Oxisol


and


two


Ulti


sols


Puerto


southern


Rico


leaf


(Talleyrand


blight


et al


reportedly


, 1976)


reduced


Earworms


yields.


Badillo


-Feliciano


et al. (1979)


tested


seven


mai


cultivars


Puerto


Rico


on an Oxisol


fertilized


at 67


and


N ha-'


Although


postplant


applied


N resulted


increase


were


in grain


no differences


yield


compared


between


to all


two


N preplant,


N rates


there


there


were


differences


in cultivar


yields


Thiraporn


et al. (1987)


measured


Six


tropical


maize


cultivars


responses


to N rates


of 0


, 40


, and


80 kg


N ha-'


Two


cultivars


had


little


grain


yield


res


ponse


to N rate


, two


had


intermediate


response,


and


two


needed


high


to yield


well.


The


two


responding


to N











increasing the


number


of kernels


per plant


from


to 40 kg N


, and kernel


weight


from


to 80 kg


N ha'


Brun


and Dudley


(1989)


tested


lines


that had been


crossed with


an Argentine


flint and


USA


dent


inbred


testers


for yield response


fertilizer


N rates.


Yield


response


to N rate was not affected by percent


dent


germplasm.


Id means


of dent


tester


crosses


were higher


than means


flint


tester.


They


recommended


using


higher


levels when


selecting


tropical


hybrids.


Tillace


Effects


on Soil


Chemical


and Physical


Properties


Continuous


no-tillage


(NT)


maize


Zea


mays


production


changes


soil


s chemical


and


physical


properties.


On a


Typic


Paleudult


soil


Kentucky


after


yr continuous


vs.


conventional


tillage


(CT)


maize


production,


Blevins


et al.


(1983)


reported rapid


acidification


the soil


surface,


lower


amounts of


exchangeable


at all


soil


depths,


and K accumulations


the


found


0 to


5 cm soil


to be


layer with NT.


lower with NT


than


Soil


After


exchangeable Mg was


continuous


wheat


(Triticum aestivum L.)


-soybean


(Glycine max L.)


rotation on


a Typic


Hapludult


Georgia


Hargrove


et al.


(1982)


reported


that,


, Mn,


Zn accumulated











have


been


released


through


mineral


weathering


the


soil.


Evangelou


et al. (1986)


studied


and


K adsorption


a Typic


Paleudult


Kentucky


as influenced


tillage


practice.


They


reported


a greater


affinity


than


the


NT soil.


Less


affinity


and


NT soil


than


CT soil


was


observed


even


though


organic


carbon


(OC)


content


was


higher


buffer


NT soil.


capacity


the


There

NT soil


was

eve


no increase

n though OC


in potential


content


increased


compared


the


CT soil


Evangelou


and


Blevins


(1988)


from


a Kentucky


tillage


study


conducted


on a Typic


Paleudalf


reported


that


NT soil


had


highest


quantity


labile


K in


the


to 0.05 and


0.05


to 0.10 m soil


depths.


The


higher


K in


the


NT soil


was


attributed


increased


organic


matter


(OM)


which


has


a high


number


of affinity


sites


In another


Kentucky


tillage


study,


Karathanasi


and


Well


(1990)


reported


to 3


fold


increases


in exchangeable


soluble


K for


the


surface


horizon


(Ap).


Increases


were


correlated


with


accumulations.


Adsorption


of K appeared


to be favored


over


Ca and


as OM


increased


a maximum


value,


beyond


which


additional


OM had


no effect


on K adsorption.


They


concluded


that


loessal


soils


under


ess


fertilizer


may











initially


had


higher


extractable


cation


concentrations,


the


second


year


study


, the


NT soil


surpassed


the


CT soil


in extractable


nutrients,


even


though


nutrient


uptake


crops


was


similar


the


two


tillage


systems.


Shuman


Hargrove


(1985)


studied


the


to 0.022


m soil


depth


from


minimum


tillage


(MT)


systems


after


yr and

forms


reported

(plant un


Mn and


available)


Fe shifted


into


from


organic


residual


or oxide


or exchangeable


forms


(plant


available)


under


Phosphorus,


and


were


highest


NT soil


treatments.


No-tillage


practice


often


is associated


with


Increases


OC content


near


the


soil


surface.


Dick


(1983)


reported


that


after


Ochraqualf


of continuous


Typic


, MT


Fragiudalf


, and


Ohio,


on a Mollic


NT soil


accumulated


to 0


to 0.075


Organic


m soil


m soil


P concentrations


depth


depth


were


also


the


the


Ochraqualf


Fragiudalf


higher


soil


soil.


in NT soil


Fragiudalf.


Crop


rotation


grown


under


NT practice


has


been


shown


to influence


rate


of OC accumulation


(Havlin


et al.,


1990) .

residue


They


reported


producing


that


crops,


rotations


such


as maiz


that

e and


included

sorghum,


high

resulted


greater


OC accumulations.


The


study


also


found


that


soil


OC accumulation


was


proportional


to clay


content.











practice did not


influence


net N,


S mineralization


below the


cm soil


depth.


The


to 2.5


cm soil


depth


under


NT accumulated more N03-N,


SO4-S,


PO4-P than did


cultivated soil.


on a


A 10


Typic Cryoboralf


had higher C and N


yr tillage


Arshad


contents


than


study


et al.


conducted


(1990)


CT soil


Ontario


showed NT soil


No-tillage


soil


was also higher


in aliphatic


C and


lower


in aromatic C


compounds


than


CT soil.


Their results


indicated NT


produced quantitative


qualitative


improvements


in soil


A 17


yr study


of NT


CT practice


under maize


cultivation on


a Hapludalf


soil


Balesdent


et al.


(1990)


reported


lower mineralization rates


soil


OC with NT than


A study


tillage


practice


effects on a


Hapludalf


soil


after


yr by


Richter


et al.


1990


in Michigan


reported


that


soil


OC cycled


two di


stinct


pools:


rapid


cycling


plant-dominated


pool,


slowly


cycling


resistant


c pool


bound


to clay mineral


surfaces.


southern


USA higher temperatures


increase


rates


of OC mineralization


and affect


rate


of OC accumulation.


Hargrove


et al.


(198


reported


no differences


in OC


0 to 0.075


.075


to 0.15


m soil


depths


between NT


and


soils cropped


five


years


to a wheat-soybean rotation.











m soil


depth


(43%


more


N and


more


OM in


NT soil


than


soil)


Evangelou


and


Blevins


(1988)


in a tillage


study


NT and


CT for


reported


that


although


OC did


accumulate


the


soil


surface


with


, the


the


soil


determined


BaCl


2 displacement


was


not


different


than


the


lower


OC containing


CT soil.


The


BaCd2


extractant


does


not


remove


organically


bound


A study


of effects


tillage


practice,


or CT,


on soil


property


in the


0.02 m soil


depth


Shuman


Hargrove


(1985)


showed


increased


soil


OC for


NT soil


The


CEC


the


NT soil


was


significantly


different


from


that


the


CT soil,


however


the


method


of determining


CEC


was


not


reported.


Tillage


practice


affects


soil


physical


properties.


Campbell

Southeast


et al. (1974)

ern Coastal I


density


stated


'lains


hori


that


are


zon


Typic


Paleudults


characterized


aris


from


high


their


the

bulk


particle


size


stribution


and


particle


arrangement


Chi


selling


depth


cm disrupted


the


E horizon,


reduced


root


impedance,


Tillage


mechanical


and


increased


affects


soil


impedance.


infiltration

temperature,


Gallaher


(1977)


and


rooting


water re

reported


depth.


tention,


that


and

rye


(Secale


cereal


-summer


crop


rotations


Georgia


on a


Typic


Paleudult


, rye


mulch


treated


soil


had


greater


water











less dense


surface


soil


increased


soil


water


content


with NT vs.


Temperatures


were


lower


in NT


and were


reported t

temperature

systems.


be beneficial


is a problem for


Continuous


South


second


NT without


where high soil


crops


subsoiling


in a double crop

may cause hardpan


formation


in some


soils


(Radc


life


et al.,


1988).


The depth


pan


formation


their


study


varied


from


to 20


below the soil


surface.


Bulk


density measurements at


this


depth


were


1.60


NT soil


1.40


Mg m2


for the


soil.


They reported


increased


infiltration


rates


soil


concluded


that


in summer


rain


events


infiltration


crusting.


in CT soil


Busscher


was


et al.


limited


1988)


soil


studied


surface


effects


three subsoiling


implements


on soil


strength


on a


Typic


Paleudult


in South


Carolina.


They


concluded


that regardless


implement


used,


subsoiling was


effective


disrupting


root restricting


layer.


Tillaqe


Effects


on Maize


Growth


No-tillage maize


production has


been


advocated


as a


practice


that


will


reduce


soil


erosion,


decrease


tillage


expenses,


provide


equal


or higher yields


than


conventional


tillage


production.


Continuous


NT has


been











has been


investigated


(Hargrove,


1985;


Anderson,


1987;


MacKay


et al.,


1987).


Maize grown


under


NT has


been shown


to have equal


or better nutrient


status


than


conventional


tillage maize


(Hargrove


, 1985).


Grain


yields of


NT maize


when averaged


over the


irrigated study were greater


than


CT grain


yields.


No evidence


was


found


that


would


require deeper placement


of nutrients


improved


uptake by


maize.


Two


important macro-nutrients


in maize


production,


and K


, accumulate


in the


soil


surface


under


NT practice.


MacKay


et al.


(1987)


reported


NT maize


P and


K uptake of


total


P and


total


K from


cm soil


depth


, and


total K


from


CT maize


the same


uptake


soil


to be


depth.


total


Accumulation


P and


of nutrients


in the soil


surface


in a MT maize system


influenced root


growth and distribution


increased root


weight


(Anderson,


1987).


Minimum tillage


cm depth


compared


conventional


tillage


Under


non-irrigated


conditions


where


risk


of drought


high


, the


practice


subsoiling


beneath


the row to disrupt

access to subsoil


root re

moisture


stricting


layers


increased


yields


allow roots

(Box and


Langdale,


1984).


Maize grain


to soil


yield


differences.


response


to subsoiling


Anderson


Cassel


variable


(1984)











deeper soils


less


response


was


reported.


Yield response


subsoiling was


experiment


less evident


when drought was


not as


second


year


pronounced.


their


Busscher et


(1988)


reported


similar


findings and


concluded


that


soil


strength determined


yield


response


to subsoiling.


Mechanical


disruption


root


restricting


layers or


management


of water


content


plow


layer


above


the


restriction were


proposed methods


overcome


yield


reductions caused by


high


soil


strength.


Soil

determine


texture and


plant


structure


yield response


horizon


to subsoiling.


also


Sandy


soils


are most


prone


to forming


root


restricting


layers


(Sene et


al.


, 1985)


Other


factors


such


land


sca


pe position and


depth


to the


B horizon have


been


shown


influence maize


yield response


to subsoiling


(Simmons et


al.,


1989)


Grain


yields


from deep


tillage


were


greater


than disking


alone.


They


concluded


that deep


tillage


is obviously


better


than disking


on sandy


Coastal


Plains


soils.


No-tillage may


retard


development


the


maize


plant


temperate regions


lowering


soil


temperatures


early


growing


season


(Al-Darby


and Lowery,


1986) .


However


in dry


years the higher water


content


of NT soil


caused


significant


crop yield


increases


(Gallaher,


1977;


Al-Darby


and Lowery,












left on t

water and


he surface directly


temperature,


affected


the changes


although mulch


in soil


surface was


cited as a


possible


problem


volatilization of


surface-


applied


fertilizers.


Poor plant


stand


establishment


the


NT system is another


factor which may


cause


yie


reductions.


Plant density


been


reported


to be


lower


under NT conditions


(Anderson


Cassel,


1984),


final


yields were equal


or better


the


experiment.


No correlation


was


found between


final


yield


and plant density,


was


concluded


that


selection


ze hybrid


genotypes


specific


NT conditions would


be necessary


for the


upper


Atlantic Coast.


A study


conducted


Iowa


which


tested


commercial


hybrids


under


NT and


systems


CT for


provided


yr, reported


information


hybrid


useful


performance


selecting


in CT


hybrids


conservation


tillage


systems


(Newhouse and


Crosbie,


1986).


Limincr


Effects


on Soil


Physical


Chemical


Properties


Liming


acid


soils


with


CaCO3 generally


reduces


exchangeable Al


and Mn


, and


increases


soil


and


Ca and/or


micronutrients


except Mo


become


ess


soluble as pH


increased;


the effects


liming


on soil


P and Mg


are












and Thomas,


1984).


A 0.33


M LaCl3


solution


was determined


to best estimate


lime requirement


amount


on organic


soils


that


is used


and NT soils


in predicting


with high OC


accumulations


complexes was not


surface


proven,


horizon.


however.


Plant


was


uptake of


inferred


Al-OC


that a


considerable amount


associated


with


extractable with KCl


does


react


with


lime.


The effect of


liming


on soi


P and


plant


P uptake


complicated by the confounding


effects


on root growth


enhanced soil


confounding


Ca and Mg


effects


have


availability


caused by


liming.


to contradicting reports


as to


the relationship


between


liming


and P


availability.


Most


researchers agree


P-lime


interaction


soil


associated with


active


soil


(Sumner


and


Farina,


1986).


Toxic


levels of


restrict


root


growth;


improved root


growth


to decreased Al


caused


liming


directly


affects


P uptake by plants.


Also


P availability may


be precipitated


soluble Al


salt


at pH


values


below


(Sumner


Farina,


1986)


Liming


influences


P solubility


soil.


Most studies


have


investigated Al


fixation


soil


(Sumner


Farina,


1986).


thought


that


P-lime


interactions are most


pronounced


at soil


values


below


5.0.












sesquioxide content.


Uptake


labelled


fertilizer was


highest by


(Avena


sativa


maize


in soils with


high sesquioxide content


regard


ess


lime


rate.


Friesen


et al.


Nigerian


(1980)


studied


Ultisols


lime-P-Zn


and reported


that


interaction


in two


the concentration


of P


in soil


solution decreased


initially with


lime application,


then


increased


to soil


Harrison


and Adams


(1987)


observed


their


field


study that


solution P


increased up


to pH


5.8


with


liming


then decreased


as pH


increased.


They


suggested


formation


of hydroxyapatite


at pH above


as the cause


decreased soil


Schwab


(1989)


studied


the Mn-P


relationship


in an


acid


soil


concluded


for soils with


above


hydroxyapatite


controlled


PC4;


at more


acidic


soil


and Al-


phosphates


controlled


solubility.


Lins


Cox


(1988


concluded


from greenhouse and


experiments


conducted


four


Brazilian


Oxisols


that Mehlich


soil


was


unaffected


changes


in soil


maize


plant and


ear


leaf


concentrations decreased


soil


increased.


Critical


levels


increased


as soil


increased.


Liming


can affect


retention


of other


cations


soil.


Khomvali


on retention


Blue


of K


three


(1977)


Florida


studied


soils


effects


(Ultisol,


lime


Spodosol,











increased


Ca and


Liebhardt


with


reduced

(1981)


liming,


competition


K retention.


reported


adsorption


In contrast


increases


Sparks


in exchangeable


sites


and

K with


liming


on a Typic


Hapludult


from


Delaware.


They


ascribed


observed


increase


in soil


to the


increase


CEC


from


liming.


Micronutrient


availability


, especially


Mn and


are


affected


soil


Junus


and


Cox


(1987)


reported


from


greenhouse


study


that


Mehlich


extractable


Zn decreased


with


increased


soil


on only


one


of eight


soil


studied,


but


Zn concentration


in soyb


ean


plants


grown


on all


soil


decreased


with


increased


soil


A polynomial


regression


equation


relating


soil


CEC,


soil


was


used


predict


maize


ear


leaf


Zn concentration.


Boswell


et al


(1989)


utilized


Mehlich


extractabl


Zn and


soil


predict


maize


shoot


and


ear


leaf


Zn concentrations


over


wide


(1984)


ess


range


of soil


observed


than


silking


that


soybean.


was


determined


and


soil


Critical


to be


soil


level


Mn critical


Mn value


mg kg-'


Mascagni


value


in maize


They


maize


ear


Cox


was


leaf


utilized


soil


Mehlich


extractabl


Mn to calculate


soil


critical


values.


Sumner


et al. (1978)


rev


iewed


results


from


various


lime











by decreased soil


exchangeable Mg.


Decreased


exchangeable


Mg was


thought


to occur


as a result


fixation by


silica


and aluminous


chlorites which


are


found


in many


highly


weathered soil


That


addition


fertilizer


P has


been


reported


to offset


the negative effects


of overliming


plant


yield


thought


to result


from displacement


of Mg


fixed by


silica


or aluminous


chlorite.


Farina


et al.


in a greenhouse


experiment


further


studied


effects


of soil


on soil


adsorption.


Salt


extractable Mg


decreased


as soil


increased,


but Mehlich


extractable


remained unchanged


with


increased


soil


They


concluded


that


exchangeable Mg


was weakly


decrease


held by


aluminum hydroxides


in salt extractable Mg


as evidenced by a


acid


extractable Mg.


Plant


uptake


of Mg


decreased


at both


high


values


and was


ascribed


Rhoads


(1989)


to competitive


conducted


effects


field


between Al


experiments


and Mg.

two


locations


elemental


reported no


Florida


S on Mehlich


effect


studying


effects


extractable


lime


lime


, Ca,


on extractable


and Mg.


Mehlich


soil


test K


was


lower


treated


plots


with


similar


trends


for Ca and Mg.


Application


of dolomitic


lime


increased


Mehlich


Ca and Mg


soil


test


values.


Maximum Mehlich












available


[(CaH2PO4)2-extractable]


subsoils often can


supply


adequate


to plants


root


growth


impeded


due


to compaction or toxic


elements


or Mn).


Soil


texture affects


depth


and rate


liming


action.


Messick


et al.


(1984)


studied seven acidic soils


from


Virginia


for Ca


and Mg movement


from


surface


applied


dolomitic


limestone


found


that


and Mg movement and


depth


of neutralization


decreased


with


soil


clay


content.


Magnesium movement


was


greater


than


on all


soils


neutralization


acidity


accompany


or Mg


movement.


They


concluded


that


cations


moved


as neutral


salts or that


soil


change


was


unmeasurable.


Differences


liming material


composition also


influences


liming


action


soil.


Ritchey


et al.


(1980)


studied


leaching through


columns


filled


with


an Oxisol


from Brazil


and


and reported


increased pH


that


subsoil


Ca S O4


depths.


reduced Al


saturation


Improved root


growth


was


proposed


to result


from


increased


Ca concentration


subsoil,


increased


to sorption


and


release


of OH


Fe oxides.


They


also


reported


marked K

material.


and Mg

Pavan


leaching

et al.


with

(1984


use


in a


CaSO4


similar


liming


greenhouse


experiment


studied the


movement


of Ca, Mg,


and Al


in a











decreasing Mg


concentration.


Calcium sulfate


produced


increased


decreased Mg


concentrations


throughout


the


column and


affect


soil


They


concluded


that


best remedy


add a


soils with


combination


toxi


of dolomitic


Al concentrations


lime


was


gypsum.


The method


lime application affects


soil


properties


and subsequent


crop


yield response.


Fernandez


and Blue


(1984)


in a


greenhouse


experiment


utili


zing


surface


application


lime materials


on two


Florida


soils


(Typic


Quartzipsamment and Typic


Paleudult)


reported


that


lime


was


more efficient


the quartzipsamment


in reducing


subsoil


exchangeable Al;


gypsum was


more


efficient


the


fine


textured Paleudult


decrease


in reducing


in exchangeable Al


subsoil Al.


subsoil


A similar


horizon


Ultisol


from Puerto


Rico


surface


application


lime was


reported by


Perez-Escolar


Lugo-Lopes


(1978) .


Haby


(1979)


acidity more


observed


rapidly


that


than


calcitic


dolomitic


limestone


limestone.


neutralized


They


soil


also


reported


calcitic


maize grain;


limestone


dolomitic


increased


limestone


concentration


increased Mg


concentration


in maize


leaves.


Gonzalez


et al.


(1979)


reported


incorporation


saturation


T CaCO3 ha-'


to 5%


from


to a depth


on an Oxisol


30 cm reduced


from Brazil.











Yield reductions due


to overliming


soils has


been


investigated.


Grove


Sumner


(1985)


studied


lime


induced


stress


in maize


in a


study using


a Typic


Paleudult


from


Georgia.


tissue Mg

reduced t


They


found


level


that


and shoot


he deleterious


lime decreased


DM yield.


effects


extractable Mg


Application of


of overliming.


Magnesium,


Zn were


implicated


nutritional


stress associated


with


overliming.


They


concluded


that


best


way to


minimize


risk


of overliming


lime


to eliminate


toxic


levels


of Mn and Al.


Many methods are


used


to determine


lime


requirement


(LR)


of soil.


The


underlying


principle


is to determine


the


amount


of CaCO3


needed


to neutralize


acidity


soil


achieve a


desired


change.


The Adams-Evans method has


been reported


low CEC


to be


soils of


most


commonly


Southeastern


USA


used method


(Adams


for the


and Evans,


1962).


based


on the


relationship


between


soil


water


pH to


base


unsaturation


of Ultisols,


change


buffer mixture


to predict


lime


requirement.


able


predict


small


lime


requirements


that


are often


found


very


low CEC


soils


(McLean,


1982) .


Basic


determining


Cation Saturation Ratio


LR was developed


is used


BCSR)


approach


north











BSCR approach


often overpredicts


lime


requirements thereby


inducing Mn deficiency,


especially


on sandy


Coastal


Plain


soils


(Liebhardt,


1981)


In a greenhouse


study


by McLean


Carbonell


there


was


no response


by German millet


(Setaria


italica)


to changes


in Ca:Mg


saturation


ratios,


alfalfa


(Medicaqo sativa)


responded


increased


ratios,


presumably


as a


result


of changes


in pH


from 5.4


to 6


to 10%


saturation


was


recommended


for most


crops


to 15%


saturation


grass


forages.


From greenhouse


study results,


Eckert


and McLean


(1981


reported


that


cation


balance


in the


soil


was


unimportant,


except


at extremely


wide cation ratios where


defic


iency


of one element


was


caused by


excess


another.


field


study


McLean


et al.


(1983)


reportedly


found


no validity to


BSCR approach


determine


lime


requirement.


They


also


investigated


Single Limiting


Nutrient


Approach


(SLAN)


applying


lime


and K and


concluded


that


emphasis


should


be placed


providing


sufficient


but not


excessive


levels


of Ca,


, and


that


attaining


a nonexistent


favorable


BCSR


worth


the effort.


The neutralization


exchangeable Al


the soil


has


been


proposed


as an effective


method


determining


lime


requirements,


especially


tropical


soils


(Pearson,


1975).











soils,


and salt


of soil


was


a better


indicator


of maize


response


reported


lime


that


than


four


soil


water pH.


Ultisols


Kamprath


from North


(1970)


Carolina


lime


requirements


based


on exchangeable Al


extracted with neutral


1 N KCl


was a


realistic


approach


neutralizing


exchangeable Al


reducing


saturation


ECEC.


In a


study


of 28


sites


Western


Great


Plains


of Canada


(Hoyt and Nyborg,


1987)


reported


the


yield


four


crops


after


liming


correlated


well


with


soil


0.02


M CaCl,


extractable Al,


with


extractable Mn.


Liminq


Effects


on Maize


Growth


Hanson


and noted


synthesis,


(1984)


reviewed


required


and


the

cel


calmodulin.


functions

1 wall in


cium


of Ca


tegrity


uptake and


in plants

, enzyme


translocation


by plants


is apoplastic


passive;


transfer


into


the


xylem


is active.


Von Marschner


Richter


(1979)


studied maize


root


uptake


from


solution


utilizing


labelled


Roots


were


unable


Ca-free


translocate


solution root


to growing


tips died


within


root

days,


tip.

even


Under

though


other parts of


root


system were


supplied


with adequate


Howard


and Adams


(1965)


reported


that


root


growth


of cotton


(Gossypium hirsutum


was


dependent


upon


percent












(1971)


reported Loblolly pine


(Pinus


taeda


tap


root


elongation was


inhibited when


soil


solution


Ca saturation


was


below


10 percent.


Liming


acid soils


results


improved root growth


presumably


to decreased


levels


toxic


elements,


Mn, and Fe,

Peech (1946)


and/or i

studied


increased


levels


effects


of Ca

lime


and Mg.


Fried and


gypsum on root


growth


various crops


that poor root growth


the greenhouse.


is not


necessarily


They reported


low Ca


supply


but may


be due


toxic


levels


of Mn,


Gammon


(1958)


used


sweet


clover


(Melilotus


alba


pot


experiments


to study


root


penetration


on an acidic


Leon


fine


sand after


Sodium and K


amending with NaCO3,


carbonates


KC03,


allow


CaSO4,


CaCO3.


root growth


into


subsoils,


CaSO4


root


growth


was


less


than


CaCO3 root


growth.


Relative quantity


of Ca


was


reportedly more


important


than


in root


development.


Better


root


growth


application


of CaCO3


was


thought


lower


of CaSO4


amended soil.


Robertson


et al.


studied


crop


responses to dolomitic


lime


four


north


Florida


soil


series.


They


concluded


that


variable


responses


crops


liming,


yield


response


may


be a result


the


effects of


increased


and Mg


levels


on other


nutritional











liming above soil


pH 5.0 was unusual.


One


time application


t ha-'


calcite was no more effective


than


t ha'


for extending the


Adams and Mo

acid subsoils of


length


(1983)


time of


studied


the Southeastern


elevated


soil


cotton root growth


USA


that were


into


limed with


CaSO4,


MgO,


and


Ca(OH),.


Untreated Bt horizons


showed Al


toxicity


deficiency


symptoms,


symptoms,


untreated E,


a few


, BE horizons


Bt horizons


showed


showed both Al


toxicity and


Ca deficiency


symptoms.


Calcium deficiency


occurred when soil


solution


Ca activity was


less


than


0.27


mM and


Ca saturation


less


than


17 percent.


Aluminum


toxicity range was uncertain due


to probable chelation of


by OM in some horizons.


Adams


and Hathcock


(1984)


studied


cotton taproot growth


into subsoil horizons of


woodlands and


cultivated fields that were


untreated


or amended with


CaSO4,


MgO,


or Ca(OH)


2. Soil


class


was


found


ass


predicting Ca


deficiency


or Al


toxicity.


No Ca


deficient


horizon


from cultivated


fields was observed.


No Al


toxic


horizon


from woodlands was


observed.


Differences


chemical methods


to discriminate between


inorganic


Al and


Ca forms


(plant available)


organic Al


Ca forms


(plant


unavailable)


are needed.


Greenhouse studies have shown


that crop growth











was


greater


than


or soil


solution


was


greater


than


0.40


meq


Juo


and


Ballaux


(1977)


conducted


a greenhouse


study


with


a Nigerian


Ulti


and


observed


mai


yield


response

5.5 to 6


to liming


which


Maximum


corresponde


yields

d to 3


occurred

.5 t hal'


at soil

lime


application.


Yields


reportedly


decreased


lime


rates


increase


ed soil


above


Zakaria


et al. (1977)


conducted


a gre


enhouse


study


of soybean


growth


in a spodic


horizon


with


saturation


of 71%


They


reported


optimum


soybean


growth


occurred


when


CaCO3


was


applied


to neutral


150%


the


-extractable


Al which


corresponded


Al saturation.


increased.


They


Sartain


observed


Kamprath


nodulation


(1975)


increased


conducted


greenhouse


experiment


that


studied


soybean


growth


response


to liming


a soil


at pH


Al saturation.


Liming


promoted


growth


larger


number


of small


diameter


lateral


roots.


Nodulation


(nodule


number)


increased


with


liming


and


was


highly


correlated


with


Ca concentration


primary


root.


Aluminum


inhibits


mai


root


elongation


affecting


root


cap


growth


(Bennet


Breen


, 1989)


Some


variation


tolerance


maize


to Al


in soil


genotypes


solution


inbred


lines


has

have


been

been


reported

studied


among

for












tolerance


increased


P concentration


in solution


increased.


Magnavaca


(198


concluded


that


aluminum


tolerance


in maize


was due


to additive gene


effects.


Dominance


effects


accounted


less


than half


variation


caused by

inherited


additive

trait.


effects,


breeding


indicating

tolerant


a quantitatively

to susceptible maize


populations


Magnavaca


et al.


(1987c)


found


introgressing


Brazilian germplasm


tolerance


into


to Al,


concentrations


Nebraska


Brazilian


in roots


than Nebraska


populations


germplasm had


population.


increased


lower


Rhue and


Grogan


(1976)


devised


a screening


technique


tolerance


in maize.


Factors


reported


affect


toxicity


nutrient


solution


included


concentration,


composition.


later


study


(Rhue


Grogan,


1977)


they


observed


that


increased


Ca concentration


in solution


decreased Al


toxicity


symptoms


in maize


roots.


Genotypes


were


found


to differ


in root


growth


response


to Ca


concentration.


Interestingly


they


reported


magnesium was


effective


as Ca


in protecting


maize


roots


from Al


damage.


Maize appears


to be relatively


tolerable


soil


long


as exchangeable Al


low.


Abruna


et al.


(1974)


studied


response


of maize


to acidity


field


experiments on


five


Ultisols


three


Oxisols


of Puerto












increased base


saturation,


other


nutrients


were


affected by


liming.


Maize


yields


increased


with


liming up


to pH 5.2,


which


corresponded


to no exchangeable Al


and a


base


saturation


70%.


McKenzie


et al.


(1988)


observed no


negative effects


on maize


yield


in a


Zambian


Ultisol


when


limed with


t ha-'


lime.


Composition


the


liming material


was not


given.


could


Reportedly


be assumed


that


soil


increased


dolomite


was


with


lime


lime rate


source.


Soil


site was


relatively


exchangeable Al


which


may


explain why there


lime rates.


Liebhardt


was


no depression


(1979


reported


yield


from


the high


field


experiments


on Typic


Paleudult


Delaware


that maize


yield


was


lower


at pH


than


5.7.


Yield


maize


was


negatively


correlated


to soil


higher


soil Mg.


Ratio


of nonexchangeable Mg:Ca


cmol


basis


was


unfavorable


for plant growth.


Magnesium


saturation


of CEC greater than


33% was


reportedly


high


for maize on


CEC soils


cmol


kg-')


leaf


At higher


tissue


was


lime

the


rates


deficiency


t ha- )

range.


Mn concentration


Leaf


concentration


also decreased


with


liming.


Bouldin


and Puerto

uptake of


(1979)


Rico

water,


conducted


found


which


field


subsoil


limited


cro


experiments


acidity

p yields


Brazil


reduced root

He recommended











studied


responses of


the southeastern

Three general re


USA and


sponse


three


Puerto


patterns


crops


Rico

were


liming


acid soils of


in a greenhouse


reported:


study.


increased


yield to


to 6.0


no change


yield


with


additional


increase,


no response


to liming,


and


increased


yield to


6.0


yield


decrease


with additional


increase.

conducted


Lathwell


Ultisolh


(1979

s and


reviewed


Oxisols


field

Puert


liming

o Rico,


experiments

Brazil,


Ghana,


Peru.


Crop


response


was


to neutralization


exchangeable Al


some


instances


elimination


of Mn


toxicity.


Soils with


ECEC required


less


lime


crop


yield response.


Aluminum


saturation ranged


from


60 to 90%.


On Ghanaian


Ultisols


with


ECEC


little exchangeable


crop


response


liming


was


modest.


Ultisols


of Puerto


Rico with high


exchangeable


Brazilian soils with


ECEC


had high


and high


lime


requirements.


exchangeable Al


had


the greatest


yield


response


liming.


One way that


liming


affects


plant


nutrient


uptake


changing t

Reduced Mg


he availability


availability


nutrients


thought


to reduce


the

crop


soil.

yields


when


liming with


containing


liming


material


Aparicio-Tejo and Boyer


(1983


conducted


greenhouse


studies


with maize


nd reported Mg


differences


plant did not












differences


in tissue Mg


concentration


are


needed before


yield responses


are


observed.


Kayode


(1984)


studied


effects


of MgSO4


application


maize grown


on Nigerian


Ultisols and Alfisols.


Optimum rate


of Mg was


20 kg


ha- ;


maize responded


concentrations


to applied Mg with


of N,


increased


decreased


plant


plant


concentration.


Magnesium was


thought


to act


as carrier


plants.


Friesen


et al.


(1980)


studied


lime-P-Zn


interaction


in greenhouse


experiments


on two


Nigerian


Ultisol


lime-P


interaction


on maize


growth


was


significant;


increased P uptake was


primarily


increased


root


exploration


available


soil


Overliming


depressed


yields


only when


was


not


applied.


Plants did


respond


to gypsum treatments


indicating


toxicity was


primary


growth


limiting


factor.


Maize growth


declined


when Al


saturation


was greater


than


the CEC.


Jones


(1978)


from


studies


in Hawaii


reported


that


applied


decreased Mn


and Al


concentrations


in maize


tomato


(Lycopersicum


esculentum


plants


in soil;


application


was


thought


immobilize


Mn and Al


or on


plant roots.


source


their


experiment


was


CaPO4,


which


could have alleviated Mn


or Al problems.


et al.











to 5.5


and decreased Mn


pH range of


to 5.7.


Liming did not change


solution


Ca until


soil


pH reached


and above.


Khomvali


and Blue


(1977)


conducted


greenhouse


experiments


involving K2CO3 applications


to soils


(Ultisol


Spodosol,


and Entisol


from Florida)


that had been


limed with


CaCO3 or dolomitic


lime.


soils applied K2CO3


increased K and decreased


Ca and Mg


concentrations


in all


crops.

crops,


Liming with

and dolomitic


CaCO3 decreased M

lime decreased


Ig concentration

Ca concentration


in all

in all


crops.


However,


and K


concentrations


crops were within suffi


ciency ranges.


Potassium Fertilization and


Soil


Fertility


Sparks


(1987)


in a review of


soil K


discusses


four


forms occurring


in soil


.4.


soil


solution K,


exchangeable


fixed K,


structural K.


Soil


solution K


available


to plants,


is dynamic,


is determined by


equilibria


and kinetic reactions with


other


forms of


soil K.


Exchangeable K


held by negative charges


on OM and


clay.


Fixed K


that


nonexchangeablee)

is not bonded cov


of soil mineral


particles.


distinct


from structural


ralently within crystal


Nonexchangeable or


structures


fixed K i












exchangeable K


total K


is taken


soils


up by


in mineral


plant


form


roots.


(98%


The bulk


bound and


soil


solution and


exchangeable


forms).


Yuan


et al.


(1976)


conducted


K composition


studies


Rhodic,


a Plinthic,


a Psammentic


Paleudult


from


Florida


to investigate


lack


crop


response


to K fertilization.


Soils were


in exchangeable and


nonexchangeable K,


high


depth.


fraction,

fraction.


total


Greater


and no

The r


(1500


to 2800


than


ha-)


total


K-bearing


remaining


minerals


was


was


were


present


each


15 cm soil


feldspars


found


in micaceou


silt


clay

s mineral


forms.


Martin and Sparks


(1985)


studied


release


of K


from Hapludults


nonexchangeable


in Delaware.


important


They


reported


in these


that


soils


supplying


to plant


roots.


concentration


of K


soil


solution


was


found


affect


release


rate


of nonexchangeable K.


the soil


solution K


concentrations


were


high


then


nonexchangeable


K release


rates


were


low.


Soils


high


kaolinite and


small


charge


quantities


vermiculite


montmorillonite


nonexchangeable


micas


contained


contained


Soils


copious


very


with


amounts


nonexchangeable


conducted K


release


mineral

studies


Parker


of sandy


et al.


Hapludults


(1989)


Delaware











Greater


than


total


was


mineral


form,


as K-


feldspars


in the


sand


fraction


Exchangeable


and


nonexchangeable


were


and


of comparable


magnitude.


They


concluded


that


sand


fractions


are


significant


sources


of plant


available


Sadusky


et al. (1987)


from


another


Delaware


study


with


an Arenic


Hapludult


and


two


Typic


Hapludults


form


reported


K-feldspars


high t

Release


otal


in the


of K from


soils


as mineral


feldspars


appeared


to be a surface


controlled


reaction.


They


utili


saturated


resin


0.01 M oxali


acid


to determine


release


rates


Parker


et al.


(1989)


further


studi


Delaware


with


maize


grown


under


intensive


management


found


grain


yield


to 14 Mg


ha-')


was


affected


K rate.


Mehlich


I extractabi


K ranged


from


to 194


the


start


zero


K plots


and


decreased


29 to 45%


the


end


third


growing


season.


Low


crop


removal


of K in


grain,


adequate


buffer


in soil,


and


adequate


subsoil


were


reasons


given


Uribe


for

Cox


K rate

(1988)


affecting


utilized


CEC


maize


and


grain


humi


yie


matter


from


soil


from


North


Carolina


and


two


from


the


Peruvian


Amazon


to develop


soil


K availability


indi


ces


Soil


were


grouped


according


to buffer


power:


soils with


buffer


power, i.e


. humi


matter


>1.9% and


CEC<4


.6 cmol


, and











Cox and


into soil


Uribe


K dynamics


(1992a)


conducted


in tropical


further


soils.


They


investigations

conducted


experiments


sites


in the


Peruvian Amazon


under


maize-maize-soybean rotation


on a


loam soil


sandy


loam


soil


(Typic


Paleudults).


They


reported


that


increased K


rates can be


applied


on finer


textured


soils due


less


risk


leaching.


sandy


loam


soil


increased with


depth;


in the


loam soil


increase


in K with


depth


was


observed.


same


study,


Uribe


1992b)


determined


soil


critical


exchangeable)


K ha


loam and


90 kg


K ha-'


on sandy


loam


for maize.


Maize ear


leaf


test


flowering


determined


a critical


concentration


13 gK kg-'


A linear-plateau


model


describing


ear


leaf K


concentration


and relative


yield


was


fitted


to experimental


data.


Other


researchers


have


reported


critical


ear


leaf K


concentrations


gK kgI'


Tyner,


1946


optimum


ear


leaf


concentration


15 gK kgl


(Moss


al.,


1965).


Potassium


Fertilization


Effects


on Maize Growth


Hsaio and


plants.


synthesizes


Lauchli


required


stomatal


1985

for


opening


reviewed


osmotic

g, and


role of


adjustment,


important


protein


solute


expanding


cells


(expansive


growth


very


sensitive


to K











nutrient


required


the


large


st amount


plants


metabolic


functions


growth.


Investigations


maize


response


K fertili


zation


the


midwest


have


reported


inconsistent


effects


of K


fertili


zation


on yield.


Rehm


et al.


(1981)


reported


maize


yield


response


to added


K after


yr study


from


Nebraska.


The


soil


contained


low


exchangeable


K in


subsoil


medium


Nonexchangeable


amounts


K from


illite


surface


was


to 15


thought


cm depth


to provide


Rehm


et al.


(1983)


a similar


experiment


Nebraska


found


P concentration


in 40


cm maize


plants


increased


with


K rate.


Rehm


et al.


(1984)


studied


soil


test


K in


the


Nebraska


Sandhills


region


and


found


soil


test


K values


increased


linearly


years


with


rat


of K application


Addition


K did


increase


yields


soil


control


pre


-study


was


considered


medium.


Application


of K


increased


soil


test


to 120


cm soil


depth


after


Rehm


Sorenson


(1985)


conducted


yr study


on a Typic


Ustipsamment


and


application


of K


or Mg,


reported


no effect


on yield


throughout


with


K rate


the study

Yearly


Soil

fertili


test

zer


K again in

application


creased


33 k


linearly

g K ha'


maintained


soil


test


values -


assium


concentration


maize


whole


plant


ear


leaves


increased


linearly


with












Research


from Tennessee


Georgia


shown


that


critical


K concentration


in maize


ear


leaf


is dependent upon


rainfall


, temperature,


fertilization rate


(Gallaher


al.,


1972) .


In another


study


Gallaher


et al.


(1975)


yr maize


yield


responded


to 2


k ha'


yr yield


responded up


K ha-'


56 kg


They


K ha'l


, and


determined


yr yield responded


critical


K concentration


range


in the ear


leaf


86 days


after planting


to 44


cmol kg


Ritchey


(1979


reviewed


several


fertilization


experiments


from


tropics


reported


leaching


of K


occurred with


300


K ha-'


as KCl


on a dark


latosol.


Using


soil


critical


level


that


value of


soil


K below which


yield will


increase


with addition


of K fertilizer)


determined a


critical


level


mg kg'


(Mehlich


maize on a


dark red Lat


oso


Brazil.


Critical


level


maize


on a


Peruvian


Typic


Paleudult


was


determined


to be


The critical


level


of K


increased


as other


exchangeable cations


increased


soil.


He concluded


that


soil Mg


or Ca


level


are


low,


K fertilizer


can


reduce


yields,


and when


soil


s low,


chlorides


in KC1


fertilizer will


exacerbate


S deficiency.


Kayode


(1986


reported


V


from


maize yie


trials on











K and decreased


Ca and Mg


concentrations


in ear


leaves


micronutrients element


concentrations


increased with K application.


(Cu,


Yield was


positively


correlated


with


ear


leaf


N concentrations.


Research


on the


response


crops


to K


fertilization


Florida


has emphasized Mehlich


soil


test


values


crop


yield responses.


Blue


(1970


conducted


field studies on a


Leon


fine sand


ryegrass


(Lolium


applying


perenne


at different


-bahiagrass


rates


(Paspalum notatum


pasture.


He reported


no difference


among


K application


rates


forage


(content).


K concentration


Application


of K


or total


fall


K uptake


to a clover-grass


pasture


was


deemed


adequate


summer


season bahiagrass


growth.


Rhoads


et al.


(1990


conducted


field


experiments


with


snap


beans


(Phaseolus


vulqaris


on a Typic


Kandiudult


in North


Florida


reported


yield


response


soil


test K


was


linear


both


years


experiment.


Tissue


K concentration


responded


linearly to


soil


test


K in


curvilinearly


experiment.


Rhoads


Hanlon


(1990)


interpreted


results


previous


snapbean


experiment


using


Fisher


s LSD means


separation


procedure,


separated


Mehlich


soil


test


K into


medium, and


high


ranges.












For either


extractant,


little


yield


response


to added K


fertilizer was


observed,


even


though


soil


tested


soil


mg kg-'


for Mehlich


III,


respectively)


for the


cm depth.


Hochmuth


et al.


(1988)


determined


from


experiments


with


mulched


peppers


(Capsicum


annum L.)


that


revised


fertilizer


K recommendations


based


on Mehlich


soil


test are


needed.


their


study


increasing


K rate


increased K


concentrations


of plant


study was


fruit


conducted


tissues,


on four


did not


Florida


affect


spodosols


yield.


where


The


three of


soils


tested


very


soil


mg kg )


one


soil medium


mg K kg' ).


zero


K rate


was


able


be utilized because


research


was


conducted


farmers


fields.


lowest K


treatments


70 kg


K ha- )


tissue K


concentration


was


suffi


cient.


They


concluded


that soil


test


interpretations


should


lowered


levels


similar to


agronomic crops.


Rhoads


(1985)


conducted


field


experiments


with


irrigated mai


on a Typic


Paleudult


reported


response of


soil


test


to fertilizer


was


linear.


Grain


yield response


to K fertilization


was


significant


the experiment,


response


fertilizer


was


linear


when


it occurred.


Grain


yield


was


positively


related












was


calculated


using


Cate-Nelson


procedure


(Cate and


Nelson,


1971).
















CHAPTER


RESPONSES OF TROPICAL MAIZE AND


SORGHUM TO NITROGEN


FERTILIZATION


Introduction


Maize


(Zea


sorghum


[Sorghum


bicolor


(L.)


Moench]


are


two


important


cereal


crops


grown


silage and


grain


regard


southeastern


to planting


USA.


date allows


Their


them


flexibility with


into numerous


multiple cropping


systems


(Gallaher,


1977).


the coarse-


textured,


well-drained


soils


northern


Florida


summer


grain and


silage


loss of


yields


N by


of cereal


leaching


crops


(Rhoads


are


et al.,


often

1978;


reduced

Rhoads


and Manning,


1986).


Multiple


applications


of N


fertilizer


in reduced


amounts


have


been


shown


improve


use


efficiency


such


conditions


(Rhoads


and Manning,


1986;


Gascho et al.,


1984).


Tropical


maize


shown


potential


as a silage crop


southeastern


(Johnson,


1991;


Wright


Prichard,


1988).


Grain


yield


response


tropical


maize


to N


application has


been


reported


to be


(Lilly,


1991) .


Poor


mays











be due


growing


to genetic


conditions,


limitations


or other


ear


factors


sink,


(Thiraporn,


unfavorable


1978).


Silage


systems


which


are


capable of


capturing


and


removing la

feed are of


rge quantities


interest


of N and


to animal


P and


produce quality


industry workers


(Johnson et


al.,


1991).


Maize


sorghum are


high-yielding


crops


which are


utilized


animal


waste


recycling


systems


capture nutrients


fertilization


of maize


provide

and so


valuable


rghum


feed.

known


Nitrogen


increase


uptake and


removal


other


plant nutrients


(Hons et al.,


1986;


Hibberd


and Hall,


1990) .


Various


models


have


been


utilized


Sikora,


to describe


1990;


plant response


Cerrato


to N


Blackmer,


fertilization


1990a;


(Bock


Gardner


al..,


1990) .


Determining


nutrient


yield


responses of


maize and sorghum to


applied


N will


assist


researchers


developing


efficient management


practices


for maize-based


and sorghum-based


cropping


systems.


objectives


to determine

tropical mai

to determine

tropical mai


this


study


nutrient


ze grown

nutrient

ze grown


are


removal

as silage

removal

as grain


sorghum and


crops,


sorghum and


crops,


to determine


crop differences


in nutrient status












Materials


and Methods


This


2-yr year


field


study


was


conducted


1990


1991


the Green


Acres


Agronomy


Research


Farm near


Gainesville


, Florida.


soil


site


was


an Arredondo


loamy


sand to


sand


(sandy


, siliceous,


thermic,


Grossarenic


Paleudult)(Soil


Survey


Staff,


1984)


The


site had


a history


continuous


no-tillage


(Secale


cereale


followed by


soybean


(Glycine


max


Merr.).


Rye


planted


fall


1989


was


harvested


10 May


1990.


The maize


variety


'Pioneer


X304C


' was


planted


both


as a grain and


silage crop along with


the grain sorghum variety


'Asgrow


Chaparral'


the silage


sorghum variety


'DeKalb


FS25E'


20 May


1990


18 May


1991.


Crops


were


no-tillage


planted


0.76


m rows


into


stubble


viable


seed


for maize


000


viable


seed


sorghum.


Nitrogen


(NH4NO3)


was


band


applied


on the soil


surface


beside


row


four rates,


13.4,


g Nm-2


1990


was


applied


one


week


after


planting


five weeks


after


planting.


1991


was


applied


in three


equal


portions,


one


week


after


planting,


five weeks


after planting,


seven


weeks after planting.


Fertilizer


at 0-45-90


(N-P-K)


and KMAG


(K,SO4: MgSO4)












mixture of


metolachlor


[2-chloro-N-(2-ethyl-6-methylpheyl)-


N-(2-methoxy-l1-methylethyl) acetamide]


1.68


a.i.


and atrazine


([6-chloro-N-ethyl-n'-(1-methylethyl)-1,3,5-


triazine-2,4-diamine]


1.68


. ha


was


applied


maize


plots at


planting.


An atrazine


a.i.


ha )


crop oil


mixture was applied


to sorghum


plots when


plants


were


four


leaf


stage.


Methomyl


(S-methyl-N-


[(methylcarbamoyl)


oxy]


was


applied


once


to control


fall


armyworm


(Spodoptera


fruqiperda)


Carbofuran


,3-Dihydro-


,2-dimethyl-7-benzofuranyl


methylcarbamate)


a.i.


was


banded


row at


planting


to control


soilborne


insect and nematode


pests.


Overhead


sprinkler


irrigation


.5 cm per


event


was


delivered


plots


as required.


Maize


ear


leaf


samples


from


eight


plants


per plot


were


collected at


early


Hiking


stage.


Sorghum


leaf


samples


from


eight


plants


below the


flag


per plot


leaf


were


at early


collected


bloom


from


stage.


third


Harvest


leaf


grain and


silage


yields were collected


from


center


rows


three


meters


long


from


each


plot


a harvest


area


per plot


4.6 m.


Grain


yields


were


harvested


at physiological


maturity.


Silage


whole


plant


yields


were


taken


approximately


matter.


Leaf,


whole


plant,


and


grain


samples were digested


analysis


using


an aluminum block












concentrations


determined


leaf,


from solutions


whole


plant,


prepared


grain were


dry-ashing


1.0 g plant


samples


at 500


six


hours,


followed with


dissolution by


mL of


concentrated


, and


brought


mL final


solution


volume.


Mineral


solutions


were


analyzed


P by


colorimetry


, K by


flame


emiss


spectrophotometry,


and


Mn and


Zn by


atomic


absorption


spectrophotometry.


Plant


nutrient


removal


grain and


silage


was


calculated


by multiplying


concentration


plant


tissue


respective


tissue's


oven dry mass.


inherent


parameters,


differences


the experiment


in measured


was analyzed


as tw


yield

o separate


split-plot experiments.


Experiments


were arranged


split-plot design


with


five


replications.


The


first


compared


silage


crop


(maize


or sorghum)


as the mainplot


variable and N


rate


subplot


variable.


second


experiment


compared


grain


crop


sorghum)


as the


mainplot


variable


and N


rate


as the


subplot


variable.


Subplot


size


was


four


m rows


wide


m long.


Statistical


anal


yses


were


conducted


on a personal


computer


using the general


linear models


procedure


(SAS,


1987)


Results











may have been


partially


responsible


for yearly variation


(Fig.


3.1) .


Single degree


freedom


orthogonal


contrasts


were performed


test


linear,


quadratic,


cubic


responses


to N rate,


when N


rate


was


significant.


addition


orthogonal


contrasts were


performed


test


individual


crop


response


variables


to N rate


when a


significant


crop


x N


rate


interaction


was


observed.


Analyses of


variance


orthogonal


contrasts


are reported


for the


forage experiment


(Tables


for the


grain


experiment


(Tables


.5).


Regression


equation


intercepts,


coeffi


clients,


and R2 values


are


presented


for the


silage


experiment


(Table


3.6)


and


for the


grain


experiment


(Table


.7) .


Plant


responses


to N rate are


presented


graphic


form with


linear


regression


equations


included.


Values


regression


equations


replicated


data


points


are


presented


along with r2 values


for mean data


points


given


in parentheses,


since


number


of observations


in a regression model


affects


the calculated


r2 values


(Cornell


and Berger


, 1987).


Silaqe


Experiment


Whole


plant


maize


sorghum


silage dry


matter


(DM)


yields


responded


differently


to applied


in 1990 as







57

C







0) 0)




C; H
00 3






Ca
z Fe
ap(a\
oz\
0t
P1a'
i i + pa'
ams
____ H
d0




__ 4 Vr


rr z



C u-I
O (a


(a
E ______
0P _______ 0
______ C ~:









58

Table 3.1. Analyses of variance for forage maize and forage
sorghum dry matter yield and plant N, P, K, Ca, and Mg
contents for 1990 and 1991.

1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Foraqe dry matter vield


Crop
Error


N Rate (N)
N linear (lin)
N quad (qua)
N cubic (cub)


.1696
.1150

.3818
.8198
.2160
.1095


0.0026


.0001
.0001
.0148
.0739


0.2131
0.1154


.7516
.2093
.0409
.0046


0.2459


.0001
.0001
.5101
.8244


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error b


0.6713
0.0001
0.0001
0.9650
0.3763
0.4586
0.6666
0.0915


16.9


Forage N


17.2


content


.619
.588


Error


0.2028


54.2132
12.3971


0.0243


linear
quadratic
cubic


CxN
Error


.5735
.3692
.1487
.2028


1.9356


.0001
.0001
.0170
.3031


.1774
.0858


.0464
.6945
.4284
.0162


8.7370


0001
0001
1907
2569


0.1979
5.2006


19.3


16.8












Table


3.1.


--continued


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Foraqe P content


C
Error (a)


.1194
.3844


N
N linear
N quadratic
N cubic


.7325
.3827
.5175
.2972


0.0218


.0044
.0032
.0566
.1421


7.7000
0.4926


.7313
.9234
.4347
.8359


0.0168


.5698
.3615
.5294
.3849


C xN
Error


3
b 24


.0839
.1290


0.5905


0.4728
1.0671


0.7244


20.2


27.1


Forage K content


C
Error


1
a 4


0.0081


2644
3067


0.0711


linear
quadratic
cubic


26.8869
61.9495
11.5025
7.2086


.0006
.0002
.0737
.1518


.7659
.3708
.2924
.6344


.0005
.0001
.8750
.7102


C xN
Error


3
b 24


.3043
.2893


0.2127


.3953
.5623


0.6510


26.3


25.2











Table


3.1.


--continued


1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Foraqce Ca


content


C
Error


.0726
.9197


linear
quadratic
cubic


.7463
.8074
.3734
.0580


0.0054


.0001
.0001
.1555
.0211


1.4341
1.5283


.3150
.6706
.1968
.0762


0.3876


.0001
.0001
.5905
.7372


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error b


17.5


Foraqe Ma


18.6


content


C
Error


.7003
.4135


0.0040


0.0956
0.5239


0.6912


N
N linear
N quadratic
N cubic


.0001
.0001
.0885
.0912


3724
0122
0040
1011


.0001
.0001
.9266
.6455


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum


A











Table 3.2. Analyses of
sorghum whole plant N,
1990 and 1991.


variance for forage maize and forage
P, K, Ca, and Mg concentrations for


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Whole plant N


concentration


Crop
Error


Nitrogen (N
N linear
N quadratic
N cubic


.9662
.1035

.5918
.6056
.0921
.0776


C x N
Error


.1986
.4740


0.0001


.3143
.0781
.6632
.6893


0.7410


18.4144
0.8038


.3865
.7131
.8515
.5948


1.1719
0.5351


0.0087


.0001
.0001
.0299
.0971


0.1154


12.0


Whole


plant P concentration


C
Error


1088
0948


N
N linear
N quadratic
N cubic


.6205
.5834
.2250
.0531


0.0028


.0001
.0001
.0006
.4193


.9241
.1256


.8711
.1014
.1368
.3749


0.0534


.0001
.0001
.3059
.0962


CxN
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error b


2440
1383
1250


14.2


15.3












Table


3.2.


--continued.


1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Whole plant K concentration


C
Error a


.2683
.7077


N
N linear
N quadratic
N cubic


.8833
.7361
.8673
.0465


C xN
Error


.746
.822


0.0445


.0001
.0001
.3146
.8140


0.4519


12.0340
0.9490


.2399
.8487
.6604
.2105


.9600
.6918


0.0236


.0103
.0025
.3383
.1984


0.2706


13.6


Whole nlant


10.8


Ca concentration


C
Error a


0081
1384


N
N linear
N quadratic
N cubic


.1296
.1722
.1651
.0515


CxN
Error


.1493
.0795


0.8205


.2086
.1540
.1625
.4287


0.1601


1.9669
0.2283


.2888
.7576
.0970
.0117

.1513
.0910


0.0426


0.0425
0.0081
0.3122
0.7231

0.2017


12.3


12.1











Table


3.2.


--continued.


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Whole


olant Ma


concentration


0.0336
0.0121


Error


0.1714


0.5017
0.0814


0.0681


N
N linear (lin)
N quad (qua)
N cubic (cub)


.3866
.9828
.1768
.0002


.0001
.0001
.0185
.9196


.2177
.5366
.0722
.0444


.0073
.0017
.2070
.3195


CxN
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error b


10.6











ble 3.3. Analyses of var
sorghum grain dry matter,
1990 and 1991.


'iance of
N, P, K,


grain maize and
Ca, and Mg con


grain
tents


1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Grain dry matter


Crop
Error


0.0009
0.0147


Nitrogen (N)
N linear (lin)
N quad (qua)
N cubic (cub)


.1388
.4131
.0030
.0002


0.8171


.0001
.0001
.3517
.7825


0.6890
0.0467


.3448
.0324
.0000
.0018


0.0185


.0001
.0001
.9384
.6738


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


24.6

Grain N


24.0


content


C
Error A


5654
9516


N
N linear
N quadratic
N cubic


.6081
.4962
.1690
.0128


0.3155


.0001
.0001
.6391
.8971


.0551
.8998


.6693
.0751
.8555
.0017


0.1012


.0001
.0001
.5666
.9793


x N
lin maize
lin sorghum
qua maize


4 -~ a-~~a a -- -- - -


Ta


C
N
N
N
IT











Table


3.3.


--continued.


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Grain P content


C
Error


.0032
.1722


N
N linear
N quadratic
N cubic


.2680
.8032
.0008
.0000


0.8975


.0001
.0001
.9002
.9652


1.2852
0.1439


.5390
.5772
.0330
.0068


0.0404


.0001
.0001
.6559
.8391


CxN
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


33.9


25.6


Grain K content


C
Error


1
A 4


0.3973


12.199
0.328


0.0037


N
N linear
N quadratic
N cubic


.1268
.3617
.0164
.0025


.0001
.0001
.6554
.8609


.8887
.6611
.0050
.0000


.0001
.0001
.8882
.9944


x N
lin maize
lin sorghum
qua maize
qua sorghum
cub maize


C
N
N
N
N
N












Table 3.3.


--continued.


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Grain Ca


content


C
Error


N
N linear
N quadratic
N cubic


.01755
.00038

.0045
.0138
.0000
.0000


0.0025


.0001
.0001
.7960
.9210


0.3323
0.0028


.0419
.1211
.0020
.0025


0.0004


.0001
.0001
.2146
.1693


CxN
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


43.2


Grain Mca


26.0


content


C
Error


0.1359
0.0283


N
N linear
N quadratic
N cubic


.2014
.6039
.0000
.0003


C xN
Error B
CV (%)


.0042
.0083
.2


.0939
.0240


.0001
.0001
.9371
.8478


0.6793


.3431
.0134


.7662
.2823
.0127
.0037


.0258
.0227
.3


0.0073


.0001
.0001
.4620
.6886


0.3548











Table 3.4.
concentrate
grain sorg


Analyses of variance of N, P,
ions in diagnostic leaves of
hum for 1990 and 1991.


K, Ca, and Mg
grain maize and


1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Leaf N


concentration


.2202
.7146


Nitrogen (N)
N linear (lin)
N quad (qua)
N cubic (cub)


C xN
Error B


.6049
.9784
.0222
.8140


.8749
.4692


0.0092


.0001
.0001
.0089
.1380


0.7865


0.8010
2.7716


.0700
.1128
.7210
.3762


.1243
.5877


0.0016


0.0001
0.0001
0.1389
0.2331


0.2855


Leaf P concentration


C
Error


1.6933
0.1636


N linear
N quadratic
N cubic


.6046
.4219
.2231
.1687


0.0324


.0001
.0001
.0001
.1838


11.0145
0.1397


.8565
.7214
.3571
.4910


0.0009


.0001
.0007
.0013
.1110


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


fl a.*


.002
.000
.752
.032
.008
.359
.172


Crop
Error











Table 3.4.


--continued.


1990 1991
Source df
Mean Square Pr>F Mean Square Pr>F


Leaf K concentration


C
Error A


N
N linear
N quadratic
N cubic


.0322
.1528

.7509
.4620
.7822
.0084


0.3213


.3593
.3424
.1324
.9419


.5622
.7916

.1995
.7820
.7562
.0604


0.0439


0006
0002
1075
1612


C x N
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


Leaf


8.4195
3.9569
0.1156
1.3005
1.4580
2.9241
0.1024
0.9856


Ca concentration


C
Error


5.8675
1.3344


0.1040


0.8732
0.2539


0.1373


N
N linear
N quadratic
N cubic


.0001
.0001
.3158
.2780


CxN
Error


0.4859


.9818
.8257
.0050
.1147


.2904
.1898


0.0001
0.0001
0.8717
0.4446


0.2324


14.2


12.4












Table


3.4.


--continued.


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Leaf Mac


concentration


C
Error


.2146
.4592


N
N linear
N quadratic
N cubic


C xN
Error B
CV (%)


1.1190
3.2844
0.0330
0.0394


0.0499
0.0966
14.8


0.5318


.0001
.0001
.5640
.5287


0.6743


.0694
.1350


.6729
.6817
.3204
.0165


.0913
.0782
.9


0.0036


.0005
.0001
.0543
.6497


0.3427












Table


3.5.


Analyses of


concentrations


variance of N,


in grain of


grain mai


P, K, Ca, and Mg
ze and grain sorghum


1990 and


1991


1990


Source


1991


Mean Square


Pr>F


Mean Square


Pr>F


Grain N


concentration


Crop
Error


Nitrogen
N linear
N quad (
N cubic


4.1602
1.1552


.7342
.4640


(lin)
qua)
(cub)


10.5062
1.2024


0.1306


.0152
.0108


0.0425
0.4701


5.9240
0.8771


4.9256
14.4722
0.0160


.2888


0.0002


0.0239
0.0028
0.9128
0.6426


C x N
Error


.3322


.9286
.3071


2.2882


0.2463


11.5


Grain P concentration


Error


0.0255
0.2833


0.7791


25.9854
0.1376


0.0002


0.1931


0.4245


.1345


.5645


C xN
Error


.1281
.1997


0.5957


.0187
.1936


0.9609


16.2


Grain K


11.0


concentration


.8748


Error


0.2903


0.0691


.2463


0.3097
0.1280


0.1133


0.1948


0.7744


nl -- -*- -, -












Table


3.5. --continued.


1990


1991


Source


Mean Square


Pr>F


Mean Square


Pr>F


Grain


Ca concentration


C
Error


0.3204
0.0107


N
N linear
N quadratic
N cubic


.0027
.0069
.0002
.0000


0.0055


.4369
.1344
.7716
.5689


4.8441
0.0603


.0859
.1997
.0144
.0438


0.0009


.0033
.0010
.3241
.0923


CxN
N lin maize
N lin sorghum
N qua maize
N qua sorghum
N cub maize
N cub sorghum
Error B


0.07
0.00
0.37
0.00
0.02
0.00
0.08
0.01


32.4

Grain Mo


27.5


concentration


C
Error


1
A 4


2.9484
0.1561


0.0122


24.3672
0.0405


0.0001


0.0337


0.5026


0.0709


0.1437


CxN
Error
CV (%)


3
B 24


0.0098
0.0418
17.6


0.8710


0.0361
0.0358
10.3


0.4064


























































'00
4C0


sI~
1.4
0


*r4


U,)

s.~ow


( Ur~
16r01


OO


O0


O0


OO


OO


O O


rl O





















UI)
Ie~.4t
) Low
k0

0 Q
5f~a4

0'


0


O0


n o








CN


O0


0'10


O0


U O0


0


NO


'.00





















C')
C


'U e
NH4J








a)


*r4d
r CI-











a)
*r4

Cs)
4-I



C-


010
d'


r4 \O


0


OO


O0


O0


O0


0


r I







N


rI O


m o


cu 0


n o


co o
















rz4


U,
C





lC1
Nk4Jc
0V


O0


OO


0 0


0


NO





ca


CO


a0 o


NO


CO o


cDOo


N O













a)



.1-4


UI)
C







ire


0


O0


O0


O0


O0


0


rI O


ri O


CM1 0


NuO







0X













a)




r34


I/i
C

S0)

'U

r4,-44J


O0


0


O0


O0







e-


O0


r40O







ra


O0


NO


O0


NO


0


r-40


i-bO

























































0)
rev

4J0
(4-I
S- I
5.40
0u


01



Irz


U,




S0)


r~4J

i ra


ma.'


O0


O0


OO


O0


NO


O0


O0


no


0


O0


SwO


0


I-I







0'


v P3 *


II I I

















*rler4
Fz4


I',I



0

e~r44j
I .g rU


O0


O0


O0


O0


0


nO


no


NO


O 0


O0


O0


II F













a)
ski
cog
*rIar


Cu
C
eq'W
owa
0



'U
i re


nH ~


NH


O0


0


rindl


O0


O0


O0


O0


0


O0








6


O0


O0


no


(rIO







0'


n o













01
0

rF:


00)
0

" rr (U




i re




Sd


nfl(


0


flr


O0


O0


O0


0


O0


O0


O0


CO


0


I i













0)


I-I


GI
C
ekq.4(
$owQ


r~r4E


nfl~
o cO


0


O0


in (N
in in
or-
0 0

0 0







N
E


O0


O0


O 0


O 0


O0


O0


OO


O0


O0


NO


0


NC O


II I I













a)


Ca
*r4.,rj


(I,
C
rqI


0 Q
r r44


N 0'0C


ni-


O0


0


O0


O0


O0


r- 0


r- O


(.10




































RATE


(g/m


2)


Fig.


3.2.


Forage maize


and sorghum above ground dry matter


1990


1991.


parentheses equal r2


S=sorghum,


(Vertical be
of equation


F=forages combined,


irs=SE,


numbers


using means,


90=1990,


C=corn,


91=1991)











sorghum forage DM response was cubic.


In 1991


silage DM was


affected by


N rate only.


Both


crops


responded


to added N


with


the same


linear


function.


Nitrogen


content was affected by N


rate only


1990


and crop and N rate


1991


(Fig.


3.3a).


In 1990


N content


response


to N rate was


a quadratic


function.


1991


content


responded


linearly to added N.


Maize had a higher


use efficiency than sorghum as


indicated by


larger


intercept


than sorghum.


1990 whole


plant N


concentration was


affected by


crop effect


only;


maize had higher whole


plant N


concentration


than sorghum


(Fig.


3.3b).


In 1991


whole


plant


N concentration was affected


crop and N


rate;


crop x


N rate


interaction was


concentration


1991


significant.


responded


to N rate


Whole

in a


plant N

quadratic


relationship.


Maize had higher whole plant N


concentration


than sorghum


1991.


1990


P content was


affected


crop and N


rate.


Phosphorus content response


to N rate best


fit a quadratic


function


(Fig.


3.4a) .


Although P


content response


to N rate


was quadratic,


sorghum removed more P than maize due


to a


larger


intercept.


In 1991


under


improved N


supply


conditions


P content


was


affected


crop effect


only;


maize

















































RATE


(g/m


Fig. 3.3.
and b) cc
bars=SE,
means, NS
rnmhi n_ -


Whole plant
concentration
numbers in


forage mai
for 1990 a
parentheses


;=not significant,


Qn=ilQQ


cJ1=qQ1


and sorghum a)


d 1991.
equal r2


C=corn,


N content


(Vertical
of equation using


S=sorghum,


F=forages


"2)



















































RATE


(g/m


Fig. 3.4.
and b)
bars=SE
means,


Whole plant
concentration
. numbers in


forage maize


1990


and


parentheses


NS=not significant,


and sorghum P a)


1991.


equal


C=corn,


content


(Vertical
of equation using


S=sorghum,


90=1990,


91=1991)


2)


9











concentration

maize and a 1


to N


inear


rate


in 1990 was a quadratic


function for sorghum


(Fig.


function


3.4b).


Whole


plant P concentrations


both


crops declined with


increase


in N


rate.


In 1991


crop and N


rate affected whole


plant P concentration;


linear rate


concentrations declined


both maize and sorghum.


the same


Maize whole plant P


concentration was higher than sorghum across


N rate.


Potassium content was


affected by


crop and


N rate


1990.


Both maize and sorghum K


content


increased at


the


same


positive rate


to added N


(Fig.


3.5a).


Sorghum removed


more K


than maize


1990


indicated by a


larger


intercept.


Potassium


content was affected by


N rate only


1991.


Response of K


content


to added N was


linear;


each


g N m'2 applied an additional


0.16


K m-2 was harvested


the crop.


Whole


plant K


concentration


1990


and


1991


responded


to both


crop and N


rate


(Fig.


3.5b)


1990


sorghum had


higher whole


across N


plant K


rates.


concentration


than maize when averaged


Both maize and sorghum whole


plant K


concentrations decreased at similar


rates


(0.12


g K kg-'


each additional


N m-2


added).


1991


maize had higher


whole


plant K concentration


than sorghum when averaged


across


N rates.


This may


have


been due


to less rainfall

















































RATE


(g/m


Fig. 3.5.
and b)
bars=SE


Whole plant
concentration
, numbers in


U


using means,


90=1990.


C=corn,


91 -91


forage maize
for 1990 and


parentheses
S=sorghum,


and sorghum K a)


1991.


equal r2


content


(Vertical
of equation


F=forages combined,


2)











concentration


1991


than


1990


which


indicated


smaller


regressioncoefficients


1991.


Calcium


content


1990


was


affected


a crop


x N rate


interaction


(Fig


.6a) .


Maize


Ca content


responded


linearly


to added


sorghum


Ca content


response


was


cubic.


Harvested


1991


was


affected


N rate


only;


response


to added


was


linear.


Whole


plant


Ca concentration


was


unaffected


crop,


rate


, or the


crop


x N rate


interaction


in 1990


(Fig


.6b).


1991


whole


plant


Ca concentration


was


affected


crop


N rate.


Sorghum


had


higher


whole


plant


Ca concentration


than


maize


when


averaged


across


N rates.


Both


maize


and


sorghum


whole


plant


Ca concentrations


responded


linearly


added


Magnesium


content


was


affected


the


crop


x N rate


interaction


1990


(Fig


7a) .


Maize


and


sorghum


content


responded


linearly


to added


sorghum


content


response


was


greater


than


maize


as evidenced


a larger


regression


coefficient.


In 1991


content


was


affected


N rate


only.


The


contrast


linear


response


of Mg


content


to N rate


was


significant.


Whole


plant


concentration


was


affected


the


crop


N rate


interaction


1990


(Fig


7b) .


1990 maize


whole


maize


1990
















































RATE


(g/m


Fig. 3.6. Whole plant forage mai
a) content and b) concentration
(Vertical bars=SE numbers in pa


ze and
for 19
renthes


sorghum
90 and
es equa


Ca
1991.
1 r2


2)



































C90-2.20-.075N+.002N^2
S90-1.85-.036N+.01N'2


C91-1.98-.015N
S91-2.21-.015N


r"2-.14
r2-.19


ra2m.73
r^2-.27


(.98)
(.79)


(.69)
(.93)


N

N


- 1

*O


RATE


(g/m


Fig.
a)


3.7.


Whole


plant


content and b)


forage maize


concentration


and sorghum Mg


1onA


~nri


L l tJL r sis*s a tt


1


991 -


__ D
*0 C


C


^2)











affected


crop


N rate.


The


linear


contrast


of whole


plant


concentration


response


to N rate


was


significant.


Grain


Experiment


Grain


yield


1990


was


affected


N rate


only;


response


to added


was


linear


(Fig.


.8) .


In 1991


the


crop


x N rate


interaction


affected


grain


yields.


Both


maize


sorghum


grain


yield


responded


linearly


added


Maize


grain


yield


response


was


greater


than


sorghum


response


grain


increase


per


additional


N m-2


maize


VS.


g grain


increase


per


additional


N m-2


sorghum).


Grain


N content


1990


was


affected


N rate


only;


response


to added


was


linear


(Fig.


.9a)


In 1991


grain


content


was


affected


the


crop


x N rate


interaction.


Grain


N content


of both


crops


responded


linearly


to added


Maize


grain


N content


response


was


greater


than


sorghum


grain


N content.


Grain


N concentration


shown


Figure


.9b.


Grain


concentration


1990


was


affected


N rate


only;


grain


concentration


response


to N rate


was


quadratic.


In 1991


grain


N concentration


was


affected


crop


and


N rate.


Sorghum


grain


N concentration


was


higher


than


maize


grain


concentration.


Both


crop


grain


N concentrations


responded