I� U NDIS T U RBED SO I L BLOCKS 2 1 GENERAL OBJ ECTIVES

The p e r f o nna n c e o f L l 1 r e e c o u J L e r d es i g n s a nd cov e r i ng techniq ues w e r e tes t ed in terms o f L I J ei r a b J .I i ty t o p r omote whea t s eed l ing

emer genc e . Th i s techn i q u e u t i l .i zed J a r g e ( 0 . 5 tonne) und i s turbed t u r f b l o c ks wh i c h w e r e p l ac ed i n c.: u n t r o l l eJ c l ima t e r o oms for 2 to 3

weeks a f t e r d r i l l ing . M ea s u r emen t s i nc l ud ed s eed g e rm i na t ion and s e ed l i ng emer gence c o u n t s , s u i l moi st ure c o n t e n t s , temp e ra ture in t h e d i r ec t d r i l l ing g ro o v e s a nd t he mec hanical imped e n c e to

s eedli ng eme r g e n c e .

The mai n a i ms o f L I J L' S e ex p e r i rue 1 J t s w e r e f o u r fo l d :

(a) To c omp a r e the p e r f o rma nc e o f t l t r- e e c o u .l t e r a s s emb l i e s i n t h e i r

ab i l i t i e s t o form s u i t a b l e s e e d b ed s f o r s eed g e rm i na t i o n and s eed l i ng emergenc e .

( b )

T o assess t h e ef f ec ts o f ini tial g e n e r a l ma t r i x so i l mo is ture

l evel at t h e t im e o f d r il J i ng , o n s eed germ i na t ion and seedling emer

g

en c e.

( c ) To s tudy the i n t e r a c t i o n s o f l n j t i a l i n-groove so i l mo i stu r e co n t e n t s w i t h so i .1 p h y s i c a l f a c t o r s .

( d ) To d e t ermi n e the e f f e c L s o f amb i e n t rel a tive humid i ty on so i l mo i s t u r e s ta tus , wh i c h mi ght i n turn af fec t the seed performanc e .

( e) To exam i n e the ro l e o f d i f f e r e n t m e thod s of c ov e r i ng and

press i ng the seed a f t e r J r i l l i ng , in an a t temp t to i so la t e the e f f e c t � of s e e d - s o i l c o n t a c t on so i l mo i s t u r e d i f f u s i o n and abso rp t .i o n by the i m b i b i n g and g e rm i na t ing s eed .

1 6 .

2 . 2 D I S CUS S iON OF MAT E R I A L S AN D E X P E H l M ENTAL TECH N I Q U ES US ED

T h e u_{se o f s o i l b J ns l s no t new i n the sc ein tific} s t ud ies o f s o i l - p l a n t-ma c hi ne re l a t i o n s . S c i e n t i s t s n nd engi neers have used d i s turbed s o i l s ampl e 8 and / o r a r t i f i c i a l _l y p a c k ed b i n s to s tu d y s o i l phys i ca l

b eh a v i o u r , s o i l ma c h i ue w e c l w n j c s a n d s o i l - p l an t in terac t i o n s ( 6 3 , 6 4 , 6 5 ) . Variab_{le amb i en t cond i t i o ns h a v e ma d (· i t necess ary} to _{use such t e ch n i q ues} ma i n l y i ndoo rs, a n d e v e n i n c o n t r o l l c·d c l ima t i c cond i U ons , i n o r d e r t o

ac_cur_ate l_y f o rmu l a t e _{q u a l i l w t i v � a nJ CJ U i:l tl t i ta t i v e i n t e r a c t i ons .}

By d e f i n i t i o n , it i s c l L·a r J y lH:!C' l· s s a r y t o u s e u n d i s t u r b ed s o i J s a m p l e s , r e p r e s e n t a t i v e u l i c l d C • l n d i t: L o n s , i n d i r e c t drilli_{ng studies} u s i ng s u ch techni q u e s . Th e i m po r t a nc e o f using a t i l l age b i n t ec hn i q u e i n direc t d r i l l i ng s t u d i e s i s ::> t t p po r t ed b y the _{f a c t tha t f u n d ame n t a l} s o i l p h y s i c a l param ters a nd L h t:d r i n t e r a c t i o n s with c o u l t e r d e s i g ns a nd amb i e n t c o nd i t i o ns hn v e no t h <.! e n w e l l ttnde rstood a nd inter pr eted u s i ng f i e l d s tud i e !:' . ( 6 6 ) B a k e r exp l <:t i t l t:J d tnv c l l a n i z e d t e c h n i q u e f o r ex t r a c t i ng " u nd i s t t t r b e d " t u r t b l o ck s f rom t h e f i e l d a nJ o u t l i n ed t h e Tne r i t s o f their u s e i n laborato_{ry t}i_{JJ age s t u d i <.: s . T n L i t e ! ' r e s e n t s t u d y , use was mad e o f t h e s e} s o i l b i ns to i nv e s t i ga t e c r i t i c a l l y t h e i n t e r a c t i o ns of so i l phys i ca l f ac tors , amb i e nt c o nd i t i o n s il t td d i r e c t d r i l l i ng t e c h n i q u e s . Und i s tu r b ed t u r f b locks (mea s u r i ng I . 8 m l o 1 1 g , h60 mm w i d e a nd 200 mm deep) w e r e

ex t racted f rom a "Ma nawa t u t i n e s a n d y l o am" soi l , and a tool t e s t i ng a p p a r a t u s ( l oc . c i t ) w a s etn pluyed t o o p e r a t e t h e chosen d i r e c t d r i l-li n g t o o l s _{i n t l t e � e s o i l b l o c k s . T h e me t h o d o f p r e- d r i l l i n g treatment anJ} s to rage o f these b i ns u nd e r r a i n c a n Ll p i es a nd dr illing ( Baker) ( 6 7 ) was f o l l owed w i t h only m i no r v a r LH i u n s . Th e m e t h o d o f _{ex t r a c t i ng t h e s e soi l} b l o c k s j s s hown and summa r i sL·d i n p 1 a l e s ( 1 . a , b , c ) .

2 . 2 . 2 Cou J t e r

The r e a r e a va r i e t y o f e f f e c U v e direct _{d r i l l i ng c}o_{ult ers ava i l ab l e} ( 6 7 )

c o mme r c i a l l y and e x p e r i rnen t i.l l l y . T h e s e i nclude co u l t e r a s s �.::mb l i e s w i t h ch i s e l s , d i s c s , s w e t· p s <t nd ro t il r y s t r L p t i l l er s . I n o r d e r to c om p a r e c o u l t e r d es i g ns , wh i ch p r o v i d ed c o tl t r a s t i ng a ctions i n t h e s o i l s , _{t h e}

f o l l ow i ng p e r f o rma n c e c r i t e r i a w e r e a d o p ted w i t h r es p e c t t o t h e g ro o v e s cr eated.

P la t e . l ( c) Turf b lock ex trac t ion procedure ;

(a) M i n imUJn shat ter l ng a n J a "V" o r " U " s h a p ed g r o o v e .

( b ) A s ha t t e r ed " V " o r " U " s h a p e d g ruuve \v i t h c o ns i d e r a b l e l oo s e s o i l a v a i l a b l e .

( c ) S u b s u r f ac e sha t t e r i n g o f s o i I w i t h m i n imum surface d is turbanc e . W i th these b road c r i t e r i a i n m l t H I i t was c o n s i d e r ed that the f o l l ow i ng t h r e e c o u J L L ! r t y p L: s p r u v i d t• d s u i t a b l e examples of the

t y p e s o f grooves to be c o t n p <J r t!d .

1 . Tri ple D i s c C o u l t e r

The t r 1 p l e disc c o t t I l l't w a s a c umm e r c lal l y availab le cou l t e r a s s emb l y * . l t c o ns i s l l'd o l a l i a r v e r t i ca l pre-d isc o f 2 5 0 mm d i ame t e r f o ] l owed b y two I I il l d i s c s n n g l ed towards e a c h o t h er a t

B !J p r o x l rn a t e l y I 0 d e g r e L: s i t H ' l t t d , • d a n g I e a nd t o u c h i ng n e a r t h e bo t t om ( 6B) .

T h e g r u o v e w a s c r ea t ecl w i t h i.l c om p r· ·ssive ac t i o n a nd usua l l y t h e r e was

0 _{( 6 9 )}

l i t t l e l o o s e s o i l av a i l a l l l l' i n L i t e: s e ed e n v l r o nm t! n t . A n exatn r l e o f t l t i s c o u l L cr i s s ho w n i 1 1 p l d l l' ( 2d ) .

2 . Hoe C uu 1 t e r

The hoe c u u l t e r· u s c·d \,/ i t S :.J C Ollllllc o t c i a ] l y av a i l a b l e c o t t l t e r as :::; emlJ J y * . l t cons isted o f a f ] a l v e r t i c a l l l r Lo-c l i s c fol lowed b y a na r row " V " s h d p ed h o e cou l t e r . T l t i s g a v e souw s h a t t e r i n g e f f e c t , pa r t i c u J a r l y J n d r i e r a nti f i rm s o i l s , h u t t e nd e d L n p t t l l u p l umps o f so i l a nd t u r f , c r ea t 1 ng su i J J 1 L• a r t h e r u\v o A n exam p l e o f t h i s c o u l t e r

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