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1 . BACKGROUND INF ORMATION

l a . BACKGROUND INFORMATION OF STYLOSANTHES HAMATA CV . VERANO AND MACROPTILIUM ATROPURPUREUM CV . S I RATRO

S ty l o s anthes , wh i le i t i s only a sma l l genu s c ompr i s ing about 30 s pec ie s , provides more pa s ture cul tivars than any other trop i c a l genus and is a l s o u s e ful over a much wider range o f tro p i cal cond i tions than many other genera.

S ty losanthes c ontains two mark e d ly d i f fe rent p la n t forms , annua l s and perenn i a l s ( Burt e t a l., 19 8 0) .

The m a i n cen tre o f dis tribu t i on o f S tylosanthes i s from 3 0 °N t o 3 0 °S in the trop i c s and sub tropics o f South and Cen tra l America . With in this area species are found

in a very w i d e range o f c l ima tes and geograph i c l o c a t i on s . A number o f we l l adapted cul t ivar s have been s e l ec ted f rom this col l e c t ion inc luding S. hamata, S. scabra and s. humi lis for drier ho tter r egions , and S. guianensis for wetter and more subtrop i c a l cond i t i on s ( Burt et a l . � 1 9 8 0 ) .

hamata cv . Verano

Verano s tyle , sometimes known as Carr ibbean S ty l � origina ted i n the i s land s o f the We s t I ndies a n d the ad j acent coa s tal regions of the North and South Amer ican contine n t s . The original c o l l e c t ion was made in Vene zue l a by Mr Tom Atk ins on o f the NSW Department o f Agr i c u l ture .

Verano s tyle i s a herbaceous , i nde terminate perenn i a l with a s em i - erect hab i t and a branching pattern whi c h i s

of ten d i ch o tomous , with l eave s t r i fo l i ate . The i n f l ores cence is an ob long spike with 8 -1 4 f lorets on a long s tem . The

s eeds are medium to d ark brown in colour and 2 . 0 - 2 . 5 mm l on g . I t also has a superior competit ive abi l i ty wi th n a t ive grasses and weed s and grows we l l wi th companion grasses ( Skerman , 19 7 7 ) . Burt e t a Z . ( 19 8 0 ) men tioned tha t the grow th hab i t o f S ty losanthes i s mark e d ly di f feren t f rom tropical pa s ture l egumes in o th er genera . The growing

poi nts o f Sty Zosanthes s pp . a re o f ten c lo s e to the ground , th is ch arac ter i s t i c tending to con fer tolerance to gra z i ng . S. hamata can be d i s t inguished from other access ions o f th i s s p ecies b y i t s more pro fuse branch ing , s l ender s tems and sma l l er leave s . I t has a l so been s hown to per s i s t i n o ther tropical reg ions wh ich have a pronounced dry season , such a s the nor th -e a s t of Tha i l and . It has a h i gh s e ed produ c t ion capa c i ty for a perenn i a l l egume, but may behave as an annual p l a n t in very dry areas (Humphreys , 19 7 4 ) .

Wi laipon and Humphreys ( 19 8 1) found that i n Tha i l an d S . hamata cv . Verano produced h igh s e ed y i elds even unde r g r a z i ng . Tor s s e l l e t aZ . ( 19 6 8 ) have mentioned tha t the

abi l i ty o f Town svi l l e lucerne - a s imi lar but annual s p e c i e s o f Sty Zosanthes - to continue exp l o r i ng a greater d ep th o f soil enab l e s i t t o grow and comp l e te i ts l i f e cyc l e even

i f the we t sea s on i s vir tua lly over . However , the importance o f drought re s i s tan c e through root pene tra tion below 1 5 0 cm

soi l depth and so i l water ava i l ab i l i ty at that depth requires further s tudy .

The int roduc t i on of Sty Zosanthes species from South Amer ica into Aus tra l i a i l lus trated the impor tance of p l a n t introduc tion i n improving p a s ture and beef produc tion .

It i s sugge s ted tha t bee f produc t i on in Tha i l and woul d a l s o bene f i t from a s imi lar introduc t ion programme ( Topark - Ngarm , 19 7 6 ) .

cv . S i ratro

Th e spec i es i s native to many countr ies o f Cen t r a l and Sou th Amer ica and has proved to be one of th e mos t produc tive

and adaptab l e trop ical l egumes in many o ther c oun tries such as South-ea s t As i a and the P a c i fic I s l ands . The cul tivar S i ra tro was bred by Or E . M . Hutton , by cro s s i ng two Mexican introductions o f M. atropurpurewn Vl2 . C P I S 1 6 8 7 7 and 16 9 7 9 and was r e l e ased i n 1 9 6 0 . S iratro i s a deep-rooting peren n i a l with trail ing , s l i gh t ly hairy s terns wh ich root readi l y at the node s . Le aves are tr i fo l iate , dark green and s l ightly ha iry on the uppe r sur face and s i lvery and very h a i ry on the lower surface . F l owe ring s ta l k s 1 0 - 2 5 cm

in l e ngth carry c l u s ters o f 6 - 1 2 , o f ten paired , f l owers which are deep purp l e or almos t bl ack in col our . Pod s are narrow , cy l indrical , sharp pointed about 7-9 cm long and con tain 1 2 - 1 3 ovo id but f l a ttened, brown to b l ack seeds . Pods s h a t ter read i l y when r i pe but h i gh s eed y i e ld can be ob tai n ed . S i ra tro is sui ted to sub trop ical and trop i ca l cl imates with an annua l r a i n f a l l o f 7 5 0 - 1 7 5 0 cm and wi l l

wi th s tand high summe r tempe ratures . I t also has a high l eve l o f d rought re s i s tance even under s teady gra z ing pre s s ure . S i r atro can be grown on an extreme ly wide range o f soi l s from l igh t textured sandy s o i l s t o h eavy c l ay s . Seed

germina t i on i s usually above 7 0 % w i th a per c en tage o f h ard seeds wh ich c an remain viable in the s o i l for f ive years or more . S i ra tro s eed should be s own wi th companion g r a s s e s and c an a l s o be sod -s eeded i n to nat ive pas ture s ( Skerrnan , 1 9 7 7 ) . I ts v igorous s e ed l i ngs nodu l a te freely and e s tab l i sh read i ly even i n gra zed s i tua tions . The twi n i n g s terns o f S i ra tro enab le i t to c ompete wi th a s s oci ated gras s e s and weeds under leniently gra zed management sys t ems . Unde r s u c h si t ua tions cons iderab l e vege tat ive spread b y both s to l ons and rh i z omes c an oc cur . However S i ra tro cannot

withs tand repea ted heavy d e fol i a t i on s ( Jones and Jone s , 1 9 7 8 } . Hopk inson ( 1 9 7 7 ) men t ioned that ma ny Aus tra l i an farme r s

f ound S i ratro t o b e a poor pasture legume but a vigorous s eed c rop . The succ e s s o f Sira tro s eed production depends on where b e s t to grow the s eed crop and how best to harve s t

i t ( Hopkinson , 1 9 7 7 ) . C l imate has been a cri t i cal prob l em for s eed produ c t ion . Imr ie ( 197 3 ) and Wh i teman ( 1 9 7 4 )

found tha t p l ants f a i l e d to flower i n a 1 6 hour photope r iod but that photope r i ods b e l ow 12 hours has tened f l ower i ng .

For seed produc tion o f both Verano s tylo and S i ra tro , Hare and Waranyuwa t ( 1 9 8 0 ) found tha t in Thai land , S ty lo per forms we l l on the free drai ning up l and sandy loam s o i l s that retain the ir mo is ture we l l i n to the dry season .

s. hamata has only a moderate to lerance to s a l i n i ty and genera l l y , s a l i ne so i l should be avoided . S i ratro on the other hand e s tab l i shes we l l on a wide range o f soi l s and can a l s o to lera te modera tely sal ine c ond i t i on s but does not tole rate f l ooding or water logging . He avy soi l s w i l l cause S i ra tro t o produce too much vegeta tive growth rather th an reproduc tive grow th .

l b . BACKGROUND INFO RMAT ION ON F I ELD EXPERIMENTAL S I TE

North-eas tern Tha i l and , d e s i gna ted as the Kor a t P ia teau , i s descr ibed as a gently undu l a t ing , saucer- shaped p l a teau , t i l ted to the south- e a s t and l imi ted on th e north and the e a s t by the Mekong River . Four main l eve ls of s e d imen ta t i on are recog n i s ed i n the area . The s e l eve ls are the a l l uvi a l p l a ins o f the r ivers and creeks , and three ma in s tream terraces ( low terrac e , middle terrace and h i gh terrace ) . The experimen ts were s i ted on the h igh terrace . Th e s ur face area o f th is h igh terrace forma t i on is mos tly compos ed of l o amy sand ; wh i l e deeper down the s o i l is more c l ayey , and generally regarded as a sandy c lay loam . S o i l s o f the s e s ed iments a r e red y e l low la tos o l s ( Moorman e t a l ., 1 9 6 4 ) .

The f i e l d expe r imen ts were conduc ted a t Khon Kaen Unive r s i ty in the NE region of Tha i land in Khon Kaen province , s i tu ated on a free draining up land sandy loam s o i l of the Ya sothon s eries . Th e topsoil (A . hor i zon )

con s i s ts o f approx imate ly 1 2 cm o f dark redd i s h-brown l o amy sand . I t has a weak coarse crumb s truc ture w i th a s o f t con s i s te ncy . The topso i l provides a sandy mu l c h l ayer which reduces the rate of mo i s ture l o s s durin g the dry seaso n . The s ubso i l can re tain moi s ture eve n in the dry season wi th very l i ttle runo f f . Th i s subsoil , wh ich is up to 1 2 0 cm i n depth , is very uni form and oftens conta ins many pore s . I t provides a l arge s torage capac i ty o f s o i l mois ture . F i e l d c apac i ty i s reached throughout the pro f i le

in the we t season al lowing s o i l mois ture leve l s h igher than wou l d be expec ted in the dry s eason ( Ey les , Personal

communication . Based on S o i l Survey Reports o f Land Deve l opment i n Th a i l and No . 5 1 , 1 9 6 6 ) .

Mongko l s awat and Kat awet in, (1979) � s tudied mois ture dis tribu tion i n th e Yas o tho n soil s e r i e s under rain fed cond i ti ons at d i f ferent depths and re corded the leve l s of mo i s ture content tha t con tr ibute to the y i e ld of crops p l anted during the dry per iod . They found tha t p l ants tha t s urvived during thi s per iod of planting had to b e those with deep root sys tems o r which exh ib i ted drough t to l erance . They a l s o found that s o i l moi s ture d i s tribut ion in the

2 5 -6 0 cm zone was gen er a l ly h i gher and les s var i ab l e th an i n the upper so i l layer . The period in wh i ch the moi s ture was ava i l ab l e in th i s l ower zone was from Apr i l to l a te Oc tobe r . On ly plants w i th deep root sys tems could util i s e moi s ture in the se zone s .

Khan Kaen i s a trop i c a l savanah with a marked seasona l d i s tributi on o f rainfal l . Mo re than 8 5 % o f the rain f a l l s i n the s i x mon ths from mid-Apr i l to mid-Oc tober . There are four d i s tinc t s easons controlled by the nor th- south movemen t o f th e i n te r tropical Conve rgence Zone . The we t season occurs from May to September . Heavy rains wh i ch occur from July

to Au gu st sub s equently decrease . The me an maximum temperature is 3 2 °C wh i l e the mean minimum temperature is 2 3 °C . Re l a tive humidi ty i s gen eral ly h i gh at about 7 5 - 8 0 % . The s econd

season is during October which is the tra n s itional per i od o f the we t season to the d ry season resul t i ng in a decreased rain f a l l , wi th a mean max imum tempera ture of 3 1°C , a minimum

o f 2 1°C and a RH o f about 7 5 % . The thi rd season i s the cool s eason s tarting f rom November to February w i th a mean maximum temperature o f 2 9 °C and mean minimum of 1 6 °C , RH about 7 5 % . The four th s e ason is the hot season occurring during March and Apr i l wi th a mean max imum temperature of 3 5 °C . The lowe s t r e l a t ive humid i ty o f the year is in March at 6 5 % ( Van den Ee larr t , 1 9 7 3 } .

At Khon Kaen during January to Jun e sunshine duration range s from 7� to 8� hour s per day . C loudy wea ther during July to September reduces sunsh i ne hour s to about 4 �- 5 . From October to De cember sunshine dura tion incre a s e s again to about 6 - 8 hours per day ( Vorasoot and Ti enro j , 1 9 7 9 } .

Pan evaporation r a te varies accor d i ng to the sunsh ine hours in each season or each month wi th an average o f

4 - 4 . 5 mm/day d uring the months from August t o January . Evapotranspira t ion r a te i s about 3 mm per day in the dry s ea s on (Vorasoot and T { enroj , 1 979 )