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I NTERPF.L11JI ONSH I PS BETHEDI PERFOR�M·ICE OF
DIRECT DRILLED SEEDS) SOIL �1ICRO-E�·lVIPONMENT
AND DRILLING EQUIP�ENT
A thesis presented in partial fulfilment of the requirements for the degree
of
Doctor of Philosophy at
Massey University Palmerston North
by
Moha�nad Ashraf Choudhary
1979
L IST OF TABLES L IST OF F I GURES LIST OF PLATES ABSTRACT
TABLE OF CONTENTS
CHAPTER 1:
I N TR O D UCTIO N AN D LITER AT U R E R EV I E W1 . 1 General introduction
1 . 2 Interaction between soil, seed and ambient
conditions in tilled soils
1.2.1 Soil and seed moisture requirements
PAGE
1 1 2
for seed germination 2
1.2.2 The mechanism of soil moisture availability to seeds
1.2.3 The importance of seed-soil contact 1.2.4 The soil-root interface
1 .2 . 5 The interaction betw en soil and ambient envi.ronment
1.2.6 Soil mechanical impedence to seedling 1.2.7 Soil aerat ion
1.3 Interaction between soi l , s ed, ambient conditions
3
4
5
6 7
8
and d irect drilling coulter designs in untilled soils 10
1 . 4 Specific research objective� 13
1. 5 'the experimental programme 1 4
CHAPTER 2:
MEASUR EMENT OF THE EF FECTS OF SOIL-MACH I NE I N TERA CTI ONS I N UNDISTURB E D BLO C KS 1 52. 1 General objectives 1 5
2 . 2 Discussion of mater ials and experimental techniques
used
2 . 2 . 1 Tillage bin technique 2.2.2 Coulter types: Selection
2 . 2 . 3 Initial soil moisture content
2 . 2 . 4 Ambient condit ions
2 . 2 . 5 Seed-soil content and cover
2 . 2 . 6 Design parameters of press ing devices
2.2 . 7 Des ign of penetromet�r, and measurement of
1 6 1 6 1 6 2 2 2 3 24 26
soil 111echanical resil!itance 30 '1.. 2. 8 Desigrl of penetrometgr assembly, and nH.'!thods of
operation 31
PAGE
2 . 2 . 9 I n-groove so i l mo i s t ur e m e as u r eme nt me t ho d s 3 5
a . P sy ch r o me t ers 35
b . Gyp s um b locks 3 7
c . Gyp s um b eads 39
d . Gla s s f ibre f i l t er paper 39
e . Th e rmo -grav ime t r ic m e t hod 41
2 . 2 . 10 Des ig n of a so i l core s am p l er a nd s amp l ing
p r o c ed ur e 4 1
2 . 2 . 1 1 I n-groove so i l t emp era t ur e measurem e nt 42 2 . 2 . 12 Des c r i ptio n o f c l i ma t e rooms 42 2 . 2 . 1 3 C l ima t i c co nd i t io ns d ur ing exper ime n t s 4 3 2 . 2 . 14 Mea s u r eme nt o f seed a nd s eed l i ng p er f ormance 4 3
2 . 2 . 1 5 Exp e r ime nt a l d e s i g n 4 4
2 . 2 . 1 6 Da t a a naly s is 4 6
2 . 3 Exp e ri me nt 1 : I nterac t io ns be twee n d irect dr i l l i ng co ul te r d es i g ns , s eed a nd d ry s o i l u nder con t ro l l ed c l ima t i c co nd i t i o ns
2 . 3 . 1 Exp e r ime nt 1 ( a ) : P r e s sure app l i ed over the cove r ed grooves
Ob j ec t i ves
Re s ul ts a nd d i s cu s s i o n
2 . 3 . 2 Exp er ime nt 1 ( b ) : P r e s s u r e app l ied d i r ec t l y ove r t h e seeds b e f o r e cov er ing
Ob j e c t i ves
Res u l ts a nd d i scu s s io n
2 . 4 Exper ime nt 2: I nterac t io ns b e tween d i rect d r i l l i ng cou l ter d es i g ns , seed a nd we t so i l u nder con t rol l ed c l ima t i c co nd i t i o ns
2 . 4 . 1 Exp er ime nt 2 ( a ) : P r e s s u r e a p p l i ed over t h e cov e r ed grooves
Obj ec t ives
Re s u l t s a nd d i s c us s i o n
2 . 4 . 2 Expe r ime nt 2 ( b ) : P r e s sure app l i ed d irec t l y over the s e e d s b e f o r e cover i ng
Obj ec t iv e s Res u l t s D i s c u s s i o n
2 . 5 S ummary o f r e s u l t s a nd concl u s ions o f exper ime n t s ( la & b ; 2a & b )
48
48 48 48
6 5 6 5 6 5
78
78 78 78
89 89 89 89 98
CHAPTER 3: PAGE
S T U DY O F LIM I T I NG F A C TO R S C AU S I NG S E E D L I NG E M E RGE NC E F A I L U R E I N S MA L L U N D I S T U R B E D T URF B L OCK S
3 . 1 I n t roduc t io n
3 . 2 Ma t e r i a l s and me thods
3 . 3 Exper iment 3 ( P i lo t Exper iment )
The e ffec t s of cou l ter des i gn , cover i ng and p r e s s i ng t e c h n i q ues on s eed l i ng eme rgence and s eed f a t e
Ob j ec t iv e s
Resu l t s and d i s c u s s i on
3 . 4 Exp er imen t 4 : The e f f e c t s o f coul t er des igns and p r e s s ing and cove r i ng t e chniques o n s e ed l i ng emergence
3 . 4 . 1 Experimen t 4 ( a) : Cou l t e r d e s igns and s el ec ted press i ng and cover i ng technique Obj e c t ives
1 1 8 1 1 8 1 1 8
1 1 9 1 1 9 1 20
1 20
1W 1 20
Resu l t s and d i s c uss i o n 1 2 1
3 . 4 . 2 Exper iment 4 ( b ) : P romi s i ng s el e c ted c o u l t e r
d e s i g n s and p r e s s i ng a n d covering t ec h n i qu e s 1 2 7
Ob j ec t i ves 1 2 7
Resul t s D i s c u s s i o n
3 . 5 Con c l u s ions and r e s ea r c h pr i or i t ies
0Hr�R 4:
STUDY OF TH E GE RMINATION OF �ffiEAT S EEDS UNDER CONTROLLE D CONDI TIONS4 . 1 I n t roduc t i on
4 . 2 Ma t e r i a l s and me thods
D e t ermi na t ion o f whea t s eed mo i s ture ab s o r p t i o n i s o t h erms
Exper imen t a l me thods i s o th e rms Exper imen t a l me t hods
1 28 1 28 1 3 1
1 3 2 1 32 1 3 2
1 3 2 1 3 2 1 3 3
Experimen tal pro c edure 1 34
4 . 3 Exper iment 5 : The d e t e rm i na t i o n o f equi l i b r i um
mo is ture abso r pt i o n i s o therms o f karamu whea t 1 34
Ob j e c t ives 134
Resul t s and d i s c u s s ion 1 35
PAGE
S T U DY O F TH E I N - GROOVE M I C R O - ENV I R O N M E N T A T
T H E S EE D -SOIL I N TERF A C E 1 40
5 . 1 Me tho d s and meas urement o f mo is t u r e po t en t i a l a t the seed-s o i l inter f a c e
5 . 1 . 1 I n t r od u c t ion
5 . 1 . 2 Des c r i p t io n of t h e rmo - el e c t r i c d ew po i n t hygrome t e r
5 . 1 . 3 Des i gn o f a n in-groove a i r sam pl e r 5 . 1 . 4 Hum i d i ty m easu r ement pro c e d u r e 5 . 1 . 5 Exp e r i me n ta l d e s ign
1 4 0 1 4 0
1 4 2 1 4 2 1 4 2 1 4 3
5 . 1 . 6 D a t a analy s i s 1 4 6
5 . 2 Exp e r iment 6 ( a ) : The e f f e c t s o f c l ima t i c cond i t i ons , cou l t e r d e s i g n and cov e r i ng techniq ues on i n- groove vapour mo i s ture drying ra t e s
Objec t iv e s
Resu l ts and d js c u s s i on
5 . 3 Exp e r i men t 6 ( b ) : Co r r e l a tions b e tween in-groove vapou r mo is t u re po t entia l and s e e d l i ng eme r gence
1 48 1 48 1 48
as f unc t ion o f coul t e r des i gn and cover ing techniq ues 1 5 5
Ob j ec t ives 1 5 5
Res u l t s and d i s c u s s i o n 1 5 5
5 . 4 S ummar y o f r e s u l t s and conc l u s ions o f expe r iments ( 6a & b )
CH_I)_PTER 6:
F I E L D E X P ER I MENTS6 . 1 Exper iment 7 : Compa r i sons of cou l t e r p e r f o rmance und e r a range o f clima t i c and so i l cond i tio ns 6 . 1 .1 Ob j ec t i ves
6 . 1 . 2 Exp e r i men t a l d e s i gn 6 . 1.3 Me thod s a nd ma t e r i a l s
Amb i ent co nd i t i o ns
S o i l mo i s t u re mea s urement
S eed l i ng eme r g ence and s e e d f a t e counts
1 70
1 7 3
1 7 3 1 7 3 1 7 3 1 7 4 1 74 1 7 4 1 7 5
6 . 1 . 4 Re su l t s and d i scuss ion 1 7 5
( a ) S eed l i ng emerge nc e and seed f a t e counts 1 7 5 ( b ) Ef f ects o f ins e c t s and o ther p e s t s
on s eed l ing eme r gence
(c) Ef f e c t s of h e rb i c id es on seed l ing emergence
185
186
PP.GE
6 . 2 Exp e r iment 8 : As ses smen t o f the effec ts of p r e-
d r i l l i ng herb i c ides o n whea t s eed l i ng es tab li shment 188 6 . 2 . 1 I n troduc t ion
6 . 2 . 2 Exper imen t a l objec t i ves 6 . 2 . 3 Exp e r imen t a l d e s i gn 6 . 2 . 4 Results and d i s c u s s ion
CHAPTER 7:
S U M M A RY AND DI S CU S S I ONCHAPTER 8:
BI B LIOGRAPHY A C KNOWLEDGEMEN T S A P P EN DICE S188 189 189 1 9 0
1 94
204 2 1 1 2 1 2
LIST OF Tt�BLES
PAGE
1. The e f f e c t s o f cou l t e r ty p e , app l i ed , so i l pressu r e over t h e covered grooves a nd r e l a t i ve humid i ty levels on
see d l i ng eme rgence a nd t!te s eed fa te o f d ir e c t d r i l l e d whe a t seeds in a d ry so i l
2. The e f f e c ts of d i rec t d rilling cou l t e r types, pr essure app l i c a t i on over cov e red gr ooves , a nd r e l a t ive hum i d i ty regimes on so i l impedenc e in a d ry s o i l
3 . The ef f e c t s o f coul ter Ly p e , rela t i ve humid i ty reg imes and pressures app l i ed over the cov e r ed gro oves on the in-groove so i l t empera t u res at con t r o l l ed d ay/ n i gh t t empe ra t u r e Of 22/lsoc
4. The e f fe c ts o f coulter t y p es and r e l a t i v e humid i t y
regimes on t h e i n-groove d ay- t i me tempera t u r e a t c o n t r o l l ed
49
58
63
day-time t emp era t u re of 22°C ( interactions) 64
5. Th e ef fec ts o f co ul t er type, a p p lied p ressu r e over u ncovered seeds , and relative humid i ty l ev e l s , o n
s e e d l ing eme r ge nc e and seed fa t e o f d i rec t d r i l led whea t in a d ry so i l
6. The e ffec ts o f couller ty pes and t h e r e l a t ive humid i t y r e g imes on d a y 18 d r y ma t t er y i e l d s o f d i r e c t d r i l l ed
66
whe a t 70
7. The ef fec ts o f cou l ter ty pe , and r e l a t iv e humid i ty reg imes on the in-groove s oi l mo i s t u r e con t e n t s
8. The e f f ec t s o f coul t e r t y p e s and re l a t ive h umid i ty reg imes on t h e in-groove so i l t emp er a t ure a t con t r o l led amb i e n t t emp e r a t ure of 22°C/18°C d ay / nigh t
9. The ef f e c t s o f co u l t e r typ e , app l i ed so i l p ressu r e over the covered grooves and relative humi d i ty l ev e l s o n seed l ing emergenc e a nd the seed f a t e o f d i rec t d r i l l ed whe a t seed i n an a d eq u a t e so il moi s t u r e reg ime
10. The i n t e rac t i o ns o f coul t e r t y pes and a p p l i ed
72
74
79
p r e ssu res o n se ed l i n g eme rgenc e o f d ir e c t d r i l l ed whea t 82 11. The e f fe c ts o f c oul t er t y p es and r e l a t ive humid i ty
levels on h e rbage d r y ma t ter y i e l d a t day 18 83
1 2 . The e f fec t s o f re l a t i ve hum id i t y reg imes and t ime o n
in-groove so i l mo i s tu re contents ( o f a l l coul te r t y p es) 86
PAGE
13. The effects of coult�r type and relative humid i ty r eg imes on in-groove s o i l temperatures following d i rec t
d r i l l i ng
1 4 . The effects of couller tyre, Llrplied soi l pressure over uncove r ed grooves a nd rela tiv e hum i d i ty l evel s o n
seedling emergence and tile seed fate o f the d ir e c t d r i l led
wheat seeds in an adequate s oil moisture regime . 15. Th e effec t s o f relative humLdity regimes and t ime o n
t h e i n-groove s o i l moisture content.
16. The effects of inilial soil moisture l ev els , app l i e d p r e s s ure pos i t ions, coul t ur t yre s a n d r e l a tive hum i d i t y
86
90
95
regimes o n the seed fate of direct drilled whea t . 99 17. The effects of in itial soil moisture levles, coulter types,
and relative humidity regimes on seedling eme rgence p e r c e n t ( i n t erac t ions) .
18. The effects o f initial soil moisture levels, pos i t io n
of applied pressures, rel<Jtive humidity regimes, cou l t e r types, and pressure inte ns ities o n p e r c en t unge rm i n a ted
101
s e ed s (interactions). 103
19(a) The effects of iniriul soil moisture l ev e l s , pos i t i o n o f applied pres sures, rela t iv e hum i d i ty r egimes a n d c o u l t e r t y p e s on t h e "germinated bur un emerged " seeds
( in t e r ac t ion s ) 106
19(b) The e f f ec t s of coulter type, i n i t i a l so i l mo is t u r e l e vel s , applied pressure positions, r e l a t ive hum i d i ty
regimes <Jnd pressure intensities on t h e p e rcen tage "ge rmin- ated but unemergcd" seL'ds ( i.nterDctions) 108 20. Th e effects of coulte r type, initial soi l mo is ture l ev e l s
and pos i t i o n of appli�d pressures on unemerged seed l i ngs; as a perc�ntage of germina ted seeds ( in t er a c t ions) .
21. The e f fec t s of seed drill i ng and cov e r ing techni q ue s o n t h e s eedl ing emergence and fate o f d i re c t d r i l l ed whea t seeds
22. The effects of groove formati on and s e ed cover ing t e c h n i ques on seedling emergence.
111
122
129
23 . Equ i l ib r ium ab s o r p t ion i s o t h e rms o f kar amu whe a t at 20°C in N a C l sal t s o l u t ions ( l iq u id imb i b i t io n ) 24 . T h e e f f ec t s o f c oult er d e s ig n a nd cov e r i ng tec h n i q u e s
and t im e on the s o i l in-groove rela t iv e hum id i t y l ev e l s a t con t r o l led ambient r . h . o f 60%
2 5 . The ef f e c t s o f s e l e c ted cou l t er d es igns and cov e r i ng t e c h n i q u e s on t h e in-groove s o i l d r y i ng ra t es i n ( r . h . %/
d a y ) .
2 6 . Th e ef fec t s o f s e l ec t ed d i rect d r i l l i ng cou l ter types and c o v er ing techni�ues on seed l i ng emer g ence a nd s eed f a t e ( a t the terminal day 18 )
2 7 . The e f f ec t s of amb i e n t conditions on the m a t r i x so i l mo i s t u r e c o n t e n t of turf b locks measur ed a t ( 0-4 5 mm d e p t h )
28 . Th e e f fec t s of coul ter t y pes and cover i ng t echniques o n i n-groove r . h . at controlled amb ient c o nd i t ions o f 60% a nd 20°C t em p era ture
29 The e f f e c t s of se l ec t ed co ul t e r d esi gn and cover ing m e t hod s o n t h e in-gr oove soil d r y i ng r a t e s
30 . Es t imat ed t - s t a t i s t i cs for d i f fer enc e s amo n g s t p a i r s o f b o's ,
�
1 's and G2's from t h e c urves o fD I AGE
1 36
1 4 6
1 5 2
1 56
1 5 9
1 60
164
vapour mo is t u r e drying rates in s ix cou l t er t r ea tmen t s 1 6 5 3 1 . The e f f ec t s o f d i rec t d r il l i ng cou l t e r t y p e s on
s e e d l ing emergence o f d i rect d r i l l ed whea t ( counts as at exper imen t t ermination day 21) f rom 1 2 d r i l l ing d a t e s
32. The e f f ec t s of t ime o n s o il mo i s t u re % measu red at 0-4 5 mm d e p t h
3 3 . Es t imat ed t -s t a t i s t i cs f o r d i f fer ences amongs t p a i r s of
£a's ,
�
1 's a nd £2's from the c u rves o f s eed l ing emerg e nc e as a f f e c ted by coul t e r type34. The e f f ec t s of i nsec ts and p e s t s o n the seed l i ng eme rg e n c e p e r c e n t age in t hree c o u l t e r types
3 5 . The e f f ec ts of type and t he t i me of a pp l i c a t ion o f p r e-d r i l l ing herb i c id es and c o u l ter types o n seed l i ng emergenc e o f t h e d i r e c t d r i l l ed whea t
36. The e f f ec t s o f t y pes of p r e-d r i l l i ng h er b i c ides and t h e i r t ime o f a p p l icat ion on the d ry ma t t e r of whea t s eed l ing s ( 1 0 week o l d )
1 76
1 78
184
186
191
193
LIST Ot- FIGl:�ES
1 . G enera l p l a n o f t i l l age b i ns i n a n exp e r im e n t a l s e t u p .
2. ( a , b ) The e f f ec t s o f direc t d r i l l i ng cou l ter t yp e and r el a t iv e h umi d i ty reg i m e s on t h e p e r c e n t age r a t e o f wh e a t s eedl i ng emergence f rom a dry s o i l
( pr e s s u r e over covered s e ed )
3 . ( a , b ) The e f f ec t s o f d i r ec t d r i l l i ng coul t e r types o n i n-groove l iq u id s o i l moisture co n ten t i n a d ry s o i l ( pr e s s u r e over cov e r ed s eed )
4 . Typ i c a l p e n e t r a t ion f o r c e a nd the e nergy expended ( ar ea u nd e r c u rv e s ) ob ta i ned by the "me chani ca l seed l i ng"
i n t h r ee ty p es o f c o u l t e r groov e s .
5 . ( a , b ) The e f f ec t s o f direct dr il l i ng cou l t e r t y p e a nd r e l a t ive humid i ty regimes on the pe rcen tage r a t e o f whe a t s e e d l ing emergence f rom a d ry s o i l ( pr e s s u r e o v e r uncov e r ed seed).
6 . ( a , b ) The e f f ec t s o f d i r ect dr i ll i ng coul ter t y p e and r e l a t ive hum i d i ty regimes on i n-groove l i q u i d so i l mo is t u r e c o n tent in a d ry s o i l ( p r es su r e over uncove r ed s eed ) ,
7 . ( a , b ) The e f f ec ts o f direct d r i l l i ng coul t e r t ypes and r e l a t ive humid i t y regjmes on the p e r c en t age r a t e o f s ee d l ing emergence o f wheat i n a n ad equ a t e s o i l mo i s t u r e l ev e l ( p r es s u re over cover ed s e e d )
8 . The e f f e c t s o f direct d r i l l i ng cou l t er types and r el a t ive humi d i ty regimes on in-groove l i qu i d s o i l mo i s t u r e co n t ent i n a n ad e q ua te s o i l mo i s t u r e l ev e l
( pr e s s u r e over covered s e e d ) .
9 ( a , b ) The e f f e c t s o f d i r e c t d r i l l i ng coul ter type and r e l a t ive humid i ty reg i me s o n the percen tage r a t e o f ·seed l i ng emergence o f w hea t i n an adequa t e so i l mo i s t ur e l e v e l . ( p r e s s u r e over u nc overed s e e d ) 1 0 . The e f f e c t s o f d i r ec t d r i l l ing cou l t er type and
r e l a t iv e hum id i ty regimes on in-groove l i qu i d s o i l mo i s tu re c o n tent i n a n ad equa t e s o i l mo i s t u r e l ev e l
( pr es s u r e over uncov e r ed s e ed ) .
1 1 . The e f fec t s o f i n i t i a l s o i l mo i s tur e , cou l t e r
t y p e s a nd a p p l i ed pres s u r e s i n a h i gh r e l a t iv e humi d i ty r egime on t h e s eed fate of d i re c t d r i l l ed whe a t
PAGE
4 7
5 1
5 6
6 1
68
7 3
8 1
85
9 1
9 3
1 1 4
PAGE
1 2 . The e f f ec t s o f ambie n t cond it i o n s and t ime o n s o i l mo i s t u r e c o n t en t .
1 3 . Equ i l i b r i um mo i s t u r e va pour imb ib i t io n i s o therms o f
1 24
karamu wheet a t 20°C . 1 3 7
l4 ( a ) The e f f e c t s o f coul t e r d es ig ns a nd cover ing techn i q u e s , a nd t ime o n the i n-groove rela t ive h umid i t y a t 60%
c o n t ro l l ed amb i e n t r e l a t ive humi d i t y .
l4 ( b ) The e f f e c t s o f coul t e r d e s i g ns a nd cover i ng t ech ni qu e s o n in-g roove s o i l mo i s t u r e d r y i ng r a tes a t 6 0 % c o n t r o l l ed amb i e n t r el a t ive hum i d i t y ( r egr e s s i o n curves) .
15 . The e f fe c t s o f coul ter design a nd cov e r i ng t echniq ues , and t ime o n the i n-groove r el a t ive h umid i ty at 6 0%
c o n t ro l led amb i ent re l a t i v e humid i ty .
1 6 . The e f f ec t s o f c o u l t e r types and c ov e r i ng techniques o n in-groove r el a t iv e humidit y at co n t ro l l ed amb i ent r e l a t ive humid i t y of 60% (regr e s s i o n curves ) .
17. Co r rela t i o n c u rv e o f (s eedl i ng eme r g e nc e + sub-su r f ac e s e e d l ing s u rv i val) v s i n-g roove r el a t ive h umid i t y l o s s r a te .
1 8 . The e f f e c t s o f coulter t ypes, under c hang i ng f ie l d mo i s t u r e c o nd i t ious, o n seed ling emer gence counts .
1 5 1
1 5 3
1 58
1 6 2
1 6 8
1 8 3
LIST 01 PU1TES
l ( a) Tur f b lo c k ex trac t io n proced ure; connec t io n o f t i ll ag e b in to tur f cu t t er .
l ( b ) Tur f b lo c k ex t rac t i o n procedure; i n i t ia t i o n of tur f cu t te r and b i n t ravel i n to so i l .
1 ( c ) Tur f b l o c k ex t r ac t io n proced u re; t i l l age b in a t f u l l dep t h .
2 ( a ) The o r i g i na l pos i t i o n o f d ep th c o n t r o l whe e l s i n rela t io n t o the c o u l ter a s s emb l y ( no t e t h e d is tance
1 7
1 7
1 8
ahead o f h o e coul t er ) . 20
2 ( b ) The mod i f i ed pos i t io n of the d e p th co n tr o l wheel s ( no te t he c l o s e n e s s to the hoe cou l t er . Thi s p l a t e a l s o
i l l us tra t e s t h e hoe coul ter a s s emb l y . 20 2 ( c ) Rear v i ew o f the ch i s e l coul ter a s s emb ly w i th the mod-
i f ied pos i t io n of th e dep t h c o n t r o l whee l s . 2 1 2 ( d ) Rear v iew o f the t rip l e d i sc a s s emb l y wi th the mod i f i e d
pos i t io n o f t h e d e p t h con trol whe e l s . 2 1 3 ( a ) The p r e s s whe e l a s s emb ly for the c hi s e l coul ter; f o r
apply i ng p r e s s ure ove r t h e covered s eeds a f ter b a r h ar rowing
3 ( b ) The press sk i d f o r the ch i s e l coul t e r to d i r ec t l y press t h e s ee d s i n to t h e groove b a s e b e f o r e bar
28a
harrowing . 28a
4 ( a) The press wheel as sem b l y for t he hoe coul t e r to appl y pressure o v e r covered s eeds after b a r harrow i ng . 4 ( b ) The pres s wheel a s s emb ly for the hoe c o u l ter to
d irec t l y p r e s s the seed i n to t h e groove base
28a
b e f ore bar harrow i np, . 28b
S ( a ) The pres s whee l a s s embly for t h e t r i pl e d i s c cou l ter to app l y p r es sure over covered s e e d s a f ter b ar
harrow i ng . 28b
S ( b ) The press wheel a s s emb l y for the t r i p l e d i sc cou l t e r t o d i re c t l y p r e s s t h e seed i n to the g roove b a s e b ef o r e
bar harrow i ng . 28b
6 ( a ) R i gh t : The "mecha n i cal s eed l i ng" p e ne t rome ter to measu r e s o i l imped ence above t h e seed . Le f t : A 4 mm d iame ter rod to press holes t h rough the so i l b l o c k f rom
benea th to the s eed l evel befo re measur i ng the s o i l
imped en c e w i th the "mechanica l s e e d l ing" . 3 3
6 ( b ) The "mechani c a l s eed l i ng" pene trom e t er d r ive
mech a n i sm , a l ignment a s s emb l y ( el e c t ro -magne t i c ) and i nd u c t ive d i s p l a c eme nt transducer and proving r i ng u n i t .
7 . S o i l mo i s ture po ten t ia l meas urement s e ns o r s :
(A) Psychrom e t e r ( 38 mm l o ng x 6 . 4 mm d ia - "Wes cor") ( B ) Gyp s um b lock ( 15 . 0 mm l o ng x 1 5 . 0 mm d ia . )
( C ) Gyps um b lo c k ( 1 5 . 0 mm l o ng x 7 . 5 mm d ia . ) ( D) Gyp s um b l o ck ( 15 . 0 mm long x 6 . 0 mm d ia . ) 8 . Core sampler ( 1 5 . 0 nun l o ng x 7 . 5 mm d i a . )
9 . G e ne ral v i ew of soi l turf b l o ck i n a c l im a t e room ( d ay 17).
1 0 ( a ) Ty p i c a l d irec t d r i l Jed whe a t seed l i ng emergence pa t tern i n i n i t i a l l y d ry soil (d ay 1 7 ) ; sown wi t h
PAGE
3 3
4 0 4 0
5 2
c h i s e l cou l t er . 52
l O( b ) T y p i c a l d i rec t d r illed v.1h e a t seed l ing emergence pa t te r n i n i n i t i a l l y d ry s o i l ( day 1 7 ) ; sown wi th h o e cou l t e r . 5 3 1 0 ( c ) Ty p i cal d i rec t d r i ll e d whea t seed l i ng emergence p a t t er n
i n i n i t ia l l y d ry sojl (day 1 7 ) ; s own w i t h tr ip l e d i sc
c o u l ter . 5 3
1 1 . Typ i c al d ir e c t d ri l l ed whea t seed l ing emergenc e
p a t t e rn i n i n i t i a l l y ad equa t e s o i l mo i s t u r e ( day 1 7 ) ; I n the l ow r e l a t ive humid i ty regime w i th ( a)
c h i s e l cou l ter ( b ) hoe coul t e r ( c ) t r i p l e d isc c o u l ter ; i n the h i gh r e l a t ive h um id i ty r e g ime w i th the ( d) ch i s e l coul ter ( e ) hoe coul ter ( f ) t r i p l e d i sc cou l ter
1 2 . Typ i cal seed l i ng eme rgence p a t tern in i n i t ia l l y d ry s o i l o n d ay 1 7 ; 1 2 ( a ) Gene r a l v i ew o f smal l und i s turbed s o i l b l o cks in a c l ima t e room; 12 ( b ) The hand-d r aw n kni f e cu t grooves wi thout cover and p r e s sure ( no te no s e ed germina t i o n/ eme rgenc e .
1 2 ( c ) The t r i p l e d i sc coul ter g roove w i thou t cover and p res s ur e ( no t e no s e ed g e rm i nat ion/ emergence) .
1 2 ( d ) The hand-d rawn kn i f e c u t g roove w i t h 70 kPa pres sure d ir e c t l y over s eed .
1 2 ( e ) the t r i p l e d i sc co u l t e r groove \vi th 70 kPa p re s sur e d i r e c t l v over s eed .
1 2 ( f ) bo th the hand-d rawn k n i f e cu t and t r i p l e d is c c o u l ter groove s cove r ed w i t h cl ear po l y thene .
9 6
9 7
1 2 5
1 26
PAGE
12(g) The "germina ted b u t unemerged " s eeds f rom a triple
d isc cou l ter groove in ini tially dry so i l . 1 39 1 3 ( a) Typ i ca l seed fa te o f seeds grown i n NaCl soluti o ns ;
( 1 ) d is t i l led wa t e r ( 2) 0 . 2 5 Mol . ( 3) 0 . 5 Mol .
(4) 1 . 0 Mol ( 5) 2 . 0 Mol (6 ) concen tra ted s a l t solu tion . 1 39 1 3 ( b ) A the rmo-elec t r ic h ygrome t e r in a c t io n to measure
14
i n-groove soil r e l at ive humid i ty .
A "Dun c a n 7 30 mul t i s eeder" d r ill equipped w i th ; l ef t , t r i p l e d i sc ; centre, hoe; r i gh t , chisel cou l ter assemb l i es for fie l d d r i l l ing .
1 5 . Typ ica l whea t seedling emergence pa t tern i n;
( a ) p l o ts where paraq ua t + d i c amba were used as
p r edr ill ing herbic i d es (b) headlands wh ere no spray was used (no te more vigorous seed l i ng emergen c e ) .
1 4 5
1 4 5
187
ABSTRACT
S tand es tabl ishmen t of crops by di�ec t dr i l l ing i s a f unc t io n o f seed germ i na tion and seed l i ng emergence e f f i cacy a n d their i n ter
a c ti ons wi th th e so i l physical micro-e nvironmen t c�ea ted by d ir e c t dri l l c o u l t ers .
Experiments conuucted i n two contrasting contr o l l ed c l ima tes us ing 0.5 tonne und isturbed tu�f blocks sugges ted tha t the three cou l ter
types compared (v i z . an expe�imental chisel coul ter , a �e and a tr i p l e d is c coul ter) perfo�med significantly differently, in terms o f whea t
seedling emergence, when the seed was d ir ec t dr i lled into a f i ne
s andy loam soil. Overall the chisel coul ter promo ted h ighes t s eed l i n g emergence ( 63 . 5%) followed by the h o e coul ter ( 50 . 6%) a n d t h e triple d i sc coul te� (27.0%) . When the initia l so i l moi s ture po tent i a l was clos e to pe�manent wilting point, seedl i ng emergence coun t s b e tween these three cou l ters were highly signi f icant w i th the d i f f erence b e tween the chi sel and tr i pl e d i sc coul t ers b eing almo s t s ix- f o ld .
Whe n the ini t i a l so i l moisture l evel was adequa te , s eed l i ng emergence coun ts from the triple d i sc g�uoves, were st il l s igni f icantly lower than
f rom the ch isel and hoe coulters which thems elves p er formed equally .
When the contro lled relative hum i d i ty was i ncreased from 60%
t o 90%, seed l ing emergence inc�eased but th is d i f f erenc e was s igni f i c a n t o n ly at a l ower leve l of probabili ty o f P = 0 . 1 0 .
App l ica tion o f pressures (using press wheels) up to 70 kPa o v er the covered seeds after bar harrow ing had no s i gn i f icant e f fec t o n seed l i ng emergence at either the l ow or ad equa te ini t ial s o i l moi s tur e l ev e l s . When similar p�essures were appl i ed d irec tly over the uncovered s eeds , s eedl ing emergenc e significantly increased to 60% in the hoe c o u l ter g�ooves and to 2 8% in the triple d isc coul ter grooves
c ompared to the unpressed seeds. No s igni f icant increase was observed from the ch i sel co ulter groove as a resul t o f these pressur es because i t had already promoted a high seedling emergenc e coun t o f 5 8% .
Fur ther experiments, using small und i s turbed tur f b locks , to e xamine more closely the poor performance o f the tri p l e d i sc c oul ter ,
indicated that smearing had not been the mai n cause o f seed l i ng
emergence f a i l ure . When the triple d i sc coul ter grooves were mod i f ied
u s i ng comb ina t io ns o f pressure appl ica t ions and s eed covering t e chniques , seed l i ng emergence was s i g n i ficantly improved . I t a p peared tha t thi s improv ement in s eedl i ng emergence was a func t i on o f a mod i f ied s o i l physi c a l m i cro-environment a t the seed-soi l i nter
f ac e . Based on these res u l ts two hy po theses were evolved . The f ir s t hypo th es is s ugges ted that the tran s f er o f l iq u i d soil moi s ture t o the s ee d for germina tion (and perhaps away f rom the u npro tec ted seedl i ng a f t e r germina t ion but pd o r to emergenc e ) could b e al tered by the shape o f the seed groove and placement and covering of the seed . Thi s was d e
s c r ibed as " s o i l moi st u r e dif fusion "
The second hypothesjs suggested that af te r the germina tion , s ub terr
a ne a n seed l i ng s u rviva l depended o n the ava ilabil i ty o f vapour phase mois ture which was aJso a f u n c tion of the groove shap e and cove r i ng med i um . T h i s was d escr i bed as "soil m o i s t ure cap t iv i ty" .
A thermo-electri c dew point hygrome ter was used to mea sure the
i n-groove vapour moisture potential with i n the d r i l l ed grooves in th e large r t u r f blocks , in a con trolled env i ro nment . Signi f icant and re peatable d i f ferences i n the drying r a tes o f the grooves c rea ted
by th e th r ee coulter types were measured and promi sed to a t l eas t par t ly expl ain the und e r I y i ng causes of th eir ab i l i t i es ( o r lack of a bi l i ties in some cases ) to p romo te see d l i ng emergence . Comb ined counts of seedl ing eme rgence and sub-surface seed l ing s u rviva l were modera tely c or r e l a ted (r = 0 . 7 1 ) with the cor responding ra tes o f loss o f i n-groove s oi l vapour mo i s ture .
I t appeared f rom the d a ta that the impor tan t design charac ter i s t i c s f o r d irec t d r i l l ing coul te r s were tha t they mus t have the abi li ty to b o th exploi t the l imi ted supp l y of s u b-sur face l iquid mo is ture for g e rmina tion and also to retain so i l mo is ture i n the vapour f o rm for s eed l ing emergence and / o r survival . The la t te r f unc tion appeared to b e a ided by the c rea tion o f m i n i mum sur face sha t tering and main tenance o f a h i gh inc idence of surf ace mulch in the f o rm of sod or o rgani c ma t ter .
F i e l d experimen ts s u gges ted that when the only measured soi l mo i s tu r e d a t a ava ilab l e w a s a t o r prior to d r i l l i ng , the present
s ta te o f knowledge would no t permi t a c cura te s eedl ing emergence da ta to
be predicted fo r any given cou l ter and covering technique . I f however , soil mo is ture data was ava ilable for the period b e tween d r il ling and seedl ing emergence, reasonable predic tions of seedling emer gence could be mad e, given the characteri s tics of the cou l ter typ es and coveri ng techniques used . Examp les of ma thema tical models were c ons truc ted for each of the three coulter types used , to pred i c t s eedl ing emergence as a func tion of these soil moi s ture da ta .
The field experimen t s also conf irmed tha t higher seed ling emergence counts could be expec ted when the chis el c oulter was used in dry soils c omp ared wi th the hoe or triple disc coul ters . During a typical
s p ring-summer-au tuntn per iod in the Manawa tu , when whe a t s eed was d i re c t
d r i l l ed at for tnigh tly interva ls in to a "Tokomaru s i l t loam soil";
from 1 6% of the dr illings the chisel coul ter promo ted s ignif�cantly higher seedl ing emergence counts than e i ther the hoe or triple dis c c oulters .
