pH OPTIMA FOR CROP GROWTH

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Plant and Soil 54, 339-357 1980) Ms. 4115

p H O P T I M F O R C R O P G R O W T HR E SU L T S O F A FL O W I N G SO L U T I O N C U L T U R E E X PE R I M E N T

WITH SIX SPECIESby A. K. M. S. ISLAM, D. G. EDWARDS and C. J. ASHER

Department of Agriculture University of QueenslandSt. Lucia Queensland 4067 Australia

KEY WORDSCalcium Cassava Chemical composition Control of sol uti onp H Copper Flowingsolution culture French bean Ginger Hydrogen ion injury Magnesium MaizeManganese Nitrogen Opti mum pH range pH Plant growth Root weight ratioTomato Wheat

SUMMARYGinger, cassava, maize, wheat, french bean and tomato were grown for periods up to six weeks incontinuously flowing nutrient solutions at seven constant pH values ranging from 3.3 to 8.5. Allspecies achievedmaximum or near-maximum growth in the pH range 5.5 to 6.5. However, there weresubstantial differences n the ability of species to grow outside this range. Ginger and cassava were themost tolerant species to low solution pH, while ginger and tomato were the only species to show noyield depression at the highest solution pH. Roots of all species at pH 3.3 and some species at pH 4.0exhibited symptoms of hydrogen ion injury. In addition, the concentrations of magnesium n the topsof all six species, of nitrogen in the tops of tomato and cassava, and of manganese in the tops of maizeat these pH values were inadequate for optimal growth. Growth depression at high solution pH wasassociated with iron deficiency n maize and wheat and with nitrogen and/or copper deficiency ncassava.The relevance of the present results to crop growth under field conditions is discussed. The complexinterplay of plant and soil characteristics militates against precise definition of an optimum pH rangefor the growth of a particular crop unless the soil is also specified.

INTRODUCTIONSoil pH is an i mp or ta nt factor affecting the growth of crops an d pastures, an d thedi st ri bu ti on of na ti ve p la nt specie s 15,21,34, 52, 54, 58,64 Often the effects of pH arecompl ex a nd it is difficult to separate direct effects of excess hydr oge n or hydro xylions from indirect effects associated with changes in the solubility of variousbiologically imp ort an t minera l e lements.

Solu tion cult ure exper iment s offer a mea ns of studyi ng direct effects of pH onplant growth in the absence of large changes in other root env iro nme nt para-meters. However precise control of solution pH and nutr ient ion conc entra tionsis difficult to achieve using con vent iona l solution culture methods. The magni-

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t u d e o f t h i s p r o b l e m i s i l lu s t r a t e d b y t h e w e l l - k n o w n s t u d y o f A r n o n a n dJ o h n s o n a w h o h a d t o e m p l o y l a r g e v o l u m e s o f w e l l s t i r r e d n u t r i e n t s o l u t i o n ( 10t o 2 01 p l a n t - 1), p l u s c o n t i n u o u s s l o w a d d i t i o n o f a c i d o r a l k a l i t o e a c h c u l t u r ev e s se l a n d t w i c e d a i l y c h e c k s o f s o l u t i o n p H t o c o n t r o l p H t o w i t h i n _ 0 .2 u n i ts .M o d e r n f l o w i n g c u l t u r e t e c h n i q u e s 5, 7 ,13 a r e i d e a l l y s u i t e d t o m e e t i n g t h e t w i np r o b l e m s o f p r e c i s e p H c o n t r o l a n d t h e m a i n t e n a n c e o f a d e q u a t e n u t r i e n tc o n c e n t r a t i o n s a t a l l p H l e ve l s , b u t d o n o t a p p e a r t o h a v e b e e n u s e d f o r t h isp u r p o s e u p t il l n o w * .

I n t h e p r e s e n t s t u d y , g i n g e r Z i n g i b e r o f f i c i n a l e R o s c o e ) a n d f iv e o t h e r s p e c i e sw e r e g r o w n i n c o n t i n u o u s l y f l o w i n g n u t r i e n t s o l u t i o n s m a i n t a i n e d a t c o n s t a n tp H v a l u e s r a n g i n g f r o m 3 .3 t o 8.5 . T h e s t u d y w a s c o n c e r n e d p r i m a r i l y w i t he s t a b l i s h i n g t h e o p t i m u m p H r a n g e f o r g i n g e r , b u t o t h e r s p e c i e s w e r e i n c l u d e d t of a c i l i t a te c o m p a r i s o n s w i t h e a r l i e r s t u d ie s a n d t o p r o v i d e , a m o r e a d e q u a t e b a s i sf o r g e n e r a l i z a t i o n s c o n c e r n i n g e f f ec t s o f p H o n p l a n t g r o w t h .

M A T E R IA L S A N D M E T H O D S

P r o p a g a t i o n , s e l e c t io n o f s p e c i e sGin ger rh izo m e pieces weighing 10-15 g were germ inated in pe at m oss fo l lowing success ive pretreat-men ts with water a t 51~ for 10 minutes , benlate , and 1000 ppm ethrel as described elsewhere 26.Other species included were cassava Manihot esculenta Cran tz , cv . N ina) , tomato Lycopersiconesculentum cv. Gro sse Lisse), f rench bean Phaseo lus vulgaris cv. Redland Pioneer) , wheat Triticumaestivum cv . G a tcher ) , and maize Zea mays cv . N K 195). Wi th the excep t ion o f tom ato , the minera lnutr i t io n of a ll of these species had been the subject of o ther f lowing cul ture s tudies with in theD ep ar tme n t o f A gr icu l tu re a t the U n iver s i ty o f Q ueens land . T om ato w as inc luded to a l low acom par iso n of , the resul ts with those obta ined for that species by Arn on a nd Jo hns on 3.Cass ava p lants we re ra ised f rom s tem t ip cut t ings in a mis t prop aga t ion c ham ber as descr ibed byF o r n o et al? ~ Th e rem aining fo ur species were ra ised f rom seed. In each case the seed was surfacesterilized for 1 m inu te in 0.1 HgC1z solut ion , r insed thoroug hly in deionized water , then soak ed inaerated deionized wa ter for e i ther two hou rs ( tom ato , f rench bean) o r 12 hou rs (wheat, m aize) . Th epar t ia l ly imbibed seeds were then germinated between mois t paper towels in an incubator a t 25~Th e seeds were t ransfer red to the n utr ient so lu t ions when the radicles were 5 to 10m m long.Pro pag at ion of individua l species was com m ence d at d i ffering t imes so that a l l species would be readyfo r tr ans p lan t ing a t ap p rox ima te ly the s am e t ime .

F l o w i n g c u l t u r e e q u i p m e n tThe f low ing cu l tu re equ ipm en t u s ed in the p res en t s tudy i s o f the con t inuous ly r ec i r cu la t ing types imilar in pr inciple to tha t descr ibed by A sher et al. 7.A br ie f des c r ip t ion o f the equ ipm en t w as g iven byEdw ards and A s her 13 and a m ore de ta i l ed des c r ip t ion by A s her and Edw ards s.* N~teaddedinpr~j~.Sincethispaperwasaccepted~rpub~icati~nthef~wingreferencehasc~met~theauth~rs~attention: M oritsugu, M. and Kawasaki, T. 1979 A new system of autom atic pH regulation in solution culture.Bet. Oha ra Inst. landw. Biol. 17, 171-178.


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PH OPTIMA FOR GROWTH OF SIX CROP SPECIES 341

De tails o f treatments, ex perimen tal designThe composition of the basal nutrient solution was as follows aM): Ca 250, K 250, N as nitrate ) 250,S 260-560, P 15, Mg 10, Na 40-63, Fe as sequestrene 138 ~20, Si 10. CI 5, B 3, Zn 0.5, Mn 0.25, Cu 0.1,Co 0.04, and Mo 0.02. The temperature of the nutrient solutions was maintained at 25 __+1 ~For the first five days after transplanting the nutrient solution in all flowing culture units wasmaintained at pH 6.0 + 0.1 and the plants were lightly shaded to aid establishment. The pH was thenadjusted with 0.25 M H2SO 4 or 0.5 M Na OH to values of 3.3, 4.0, 4.8, 5.5, 6.5, 7.5 or 8.5. Thereafter thepH was held approximately constant by the automatic pH control equipment incorporated in eachflowing culture unit. A Rikadenki multi-channel chart recorder Rikadenki Kogyo Co. Ltd. ModelPBR-I 2) recorded the pH in each unit at one minute intervals as a check on the short term stability ofpH control. Long term stability was assessed on the basis of twice daily pH meter readings over the sixweek experimental period.Within each of the seven flowing culture units there were 18 replicate cultures of ginger, and eightreplicates of each of the o ther species. The possible role of iron deficiency as a factor limiting growth athigh solution pH values was assessed by spraying half the replicates of all species at each pH with 0.5per cent w/v) ferrous sulphate solution three times per week.To ensure an adequate supply of all essential elements the nutrient solutions were completelyrenewed at weekly intervals. In addi tion, solution nitrogen and phosphorus concentrat ions werechecked every 3 to 4 days and adjusted as necessary. Nitrate concentrations were measured with anOrion Model 404 Specific Ion Meter and solution phosphorus analyses were conducted using themethod of Taras et a l 63

Harvestin9, chemical analysisImmediately prior to imposing the pH treatments, a thinning harvest was conducted leaving oneplant per pot of all species except wheat which was thinned to four plants per pot. Initial weights ofroots and tops of each species at the time of imposing the pH treatments were obtained from thisthinning harvest.

The differing absolute growth rates among the species and the need to avoid shading by the fastergrowing species resulted in the harvest of plants after treatment periods ranging from two weekstomato, french bean) to six weeks ginger). The remaining three species were harvested after fourweeks.At each harvest, the roots were separated from the tops, rinsed free of nutrient solution and blotteddry. Fresh and dry weights of tops and roots were then obtained, a 70~ forced draft oven being usedto dry all plant samples. Selected samples of plant tops which had not been sprayed with ferroussulphate were ground in a cast iron laboratory hammer mill and subjected to multi-element analysisby direct reading emission spectroscopy using a briquetting technique as described by Johns on andSimons 3~.

RESULTS

a) Control o f solution pHB o t h s h o r t t e rm a n d l o n g t e rm s t a b i li t y o fp H i n t h e s e ve n t r e a t m e n t s w e re fo u n dto be h igh ly sa t i s fac to ry . A s tudy o f char t reco rd in gs shows tha t very few o f themor e tha n 1400 obse rva t ions per un i t du r i ng a 24 hour per i od l ay mor e t han 0 .1


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~ Illllll

I I ~ 0 I I I I0 8 0 0 1 2 0 0 1 2 0 0 0 2 / 0 0 0 / 0 0 0 8 0 0T I M E O F O A Y h r s )

Fig. 1. Variation in solution pH of sevenflowingculture units over a represen tative 24 hour periodduring the exp eriment. The thickness of each line represents the range o f values recorded.

p H u n i ts a b o v e o r b e l o w t h e m e a n F ig . 1 ). T h e m e a n p H v a l u e s a n d t h e ir 95 p e rc e n t c o n f i d e n c e l im i t s c a l c u l a te d f r o m t h e t w i c e d a i ly p H m e a s u r e m e n t s o v e r t h es ix w e e k e x p e r i m e n t a l p e r i o d w e r e a s f o l l o w s : 3 .3 + 0 .0 1 , 4 .0 + 0 . 01 , 4. 8 + 0 .0 1,5.5 + 0.01 , 6.5 _ 0.02 , 7.5 + 0.0 3, an d 8.5 +__ 0.02 .

b) Ef fect o f solution p H on plant growthS o l u t i o n p H h a d l a r g e ef fe c ts o n g r o w t h o f a l l s ix s p e c ie s F i g. 2). G i n g e r w a s t h em o s t t o l e r a n t s p e c ie s t o e x t r e m e s o l u t i o n a c i d i t y a c h i e v i n g a m e a n r e l a ti v e y ie l do f 4 4 .5 p e r c e n t a t p H 3 .3 . C a s s a v a w a s t h e n e x t m o s t t o l e r a n t s p e c i e s a t th i s p H ,f o l lo w e d b y t o m a t o , f r e n c h b e a n , w h e a t a n d m a i z e . T h e l a tt e r t w o s p e c ie sa c h i e v e d o n l y 1 2 a n d 8 p e r c e n t o f m a x i m u m y ie ld r e s p e c ti v e ly a t t h is p H . A t p H3 .3 a n d a l s o 4. 0 t o m a t o s h o w e d s y m p t o m s s im i l a r to m i l d n i t r o g e n d e f i c ie n c y 61,w h i le m a i z e a n d w h e a t s h o w e d s y m p t o m s s u g g e s ti v e o f m a g n e s i u m d e f ic i en c y 61.

M o s t s p e ci e s r e a c h e d o r c l o se l y a p p r o a c h e d m a x i m u m y i el d a t p H 5 .5 a n d n os ig n i fi c an t p o s i t iv e g r o w t h r e s p o n s e s t o i n c r e as i n g p H w e r e o b s e r v e d a b o v e th i sp H v a l u e .

I n c r e a s i n g t h e p H f r o m 5 .5 to 8 .5 h a d n o s i g n if i ca n t e ff e ct o n t h e g r o w t h o fg i n g e r o r t o m a t o b u t d e p r e s s e d t h e g r o w t h o f a ll o t h e r s p ec ie s. I n m a i z e a n dw h e a t t h e g r o w t h r e d u c t i o n i n t h e u n s p r a y e d s e ri es w a s a c c o m p a n i e d b y th ed e v e l o p m e n t o f i r o n d e f i c ie n c y c h l o r o s i s 61. S p r a y i n g w i t h f e r r o u s s u l p h a t es ig n i fi c an t ly r e d u c e d t h e g r o w t h d e p r e s s i o n i n m a i z e a n d r e d u c e d t h e i n te n s i ty o fi r o n c h l o r o s i s i n b o t h s p e c i e s . I n w h e a t , h o w e v e r , t h e i r o n s p r a y i n g a l s o c a u s e ds o m e l e a f i n ju r y . T h e g r o w t h o f w h e a t w a s s i g n if ic a n tl y r e d u c e d b y t h e s p r a y


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t r e a t m e n t a t p H 4 .8 a n d 5 .5 a n d t h e e f f ec t iv e n e s s o f s p r a y i n g i n r e d u c i n g g r o w t hd e p r e s s i o n a t h i g h e r p H v a l u e s w a s s u b s t a n t i a l l y l es s t h a n i n m a i z e F i g . 2 ).S p r a y i n g w i th f e r r o u s s u l p h a t e a l s o c a u s e d s o m e l e a f i n j u ry a n d g r o w t h d e p r e s-s i o n i n f r e n c h b e a n F i g. 2 ). I n c a s sa v a , a s u b s t a n t i a l g r o w t h d e p r e s s i o n o c c u r r e da t p H 8 .5 in b o t h s p r a y e d a n d u n s p r a y e d p l a n t s b u t n o s y m p t o m s o f i r o nd e f ic i en c y o r o f a n y o t h e r m i c r o n u t r i e n t d e f ic i en c y w e r e o b s e r v e d . S p r a y i n g w i t hf e r r o u s su l p h a t e d i d n o t i m p r o v e g r o w t h o f c a s s a v a i n th e h i g h e r p H t r e a tm e n t s .

c ) Root in jury a t low pHD a m a g i n g e ff ec ts o f l o w s o l u t i o n p H o n r o o t g r o w t h w e r e o b s er v e d i n a l l s p e c ie sa t p H 3 .3 , a n d i n s o m e s p e c i e s a t p H 4 .0 . A t p H 3 .3 , r o o t s w e re s h o r t , t h i c k e n e d ,c o m p a r a t i v e l y fe w i n n u m b e r , a n d d i s c o l o u r e d b r o w n o r d u l l g re y . L a t e r a l r o o tg r o w t h w a s s e v e r e l y i n h i b i t e d i n a ll sp e c ie s . A t p H 4 .0 , r o o t g r o w t h a p p e a r e dh e a l t h y i n g in g e r , c a s s a v a a n d m a i z e . B y c o n t r a s t , a t p H 4 .0 , r o o t s o f f r e n c h b e a na n d w h e a t e x h i b i te d n e c r o t i c r o o t t ip s a n d s h o r t l a t er a ls . T h e r o o t s o f f r e n ch b e a nw e r e d i s c o l o u r e d g r e y w h il e t h o s e o f w h e a t a n d t o m a t o w e r e b r o w n . I n t o m a t o , a tt h i s p H , h e a l t h y r o o t g r o w t h o c c u r r e d o n l y i n t h e m o i s t a i r g a p a b o v e t h en u t r i e n t s o l u t i o n .T h e r e l a t i v e l y c o a r s e , d i s c o l o u r e d r o o t s p r e s e n t i n a l l s p e ci e s a t l o w p Hc o n t r a s t e d m a r k e d l y w i t h t h e f in e , l ig h t c o l o u r e d , p r o f u s el y b r a n c h e d a n d s y m p -t o m - f r e e r o o t s p r e s e n t a t p H 4 .8 a n d a b o v e .

d) E f f ec t s o f so lu tion pH on root we ight ra t ioE f f e ct s o f t h e i r o n s p r a y i n g t r e a t m e n t o n r o o t w e i g h t r a t i o w e r e n o t s i g n if i c a n t a tP = 0 .0 5 i n 3 9 o f t h e 42 s p e ci e s p H t r e a t m e n t c o m b i n a t i o n s s t u d i e d . H e n c e , i tw a s c o n s i d e r e d l e g it im a t e t o p o o l t h a t d a t a f o r s p r a y e d a n d u n s p r a y e d p l a n t s.T h e r e w e r e l a rg e e f f ec ts o f s o l u t i o n p H o n t h e r o o t w e i g h t r a t i o o f a l l s p ec ie s. I ne a c h c a se , r o o t a n d t o p g r o ~ v th w a s p o o r a t p H 3 .3 . H o w e v e r , as t h e s o l u t i o n p Hw a s r a i s e d f ro m 3 . 3 t o 4 . 0 , t h e ro o t w e i g h t r a t i o i n c r e a s e d s h a rp l y i n c a s s a v a ,t o m a t o a n d g i n g e r a s a r e s u lt o f t h e g r e a t e r r e sp o n s e i n r o o t g r o w t h t h a n s h o o tg r o w t h t o t h e i n c r e a s e i n p H F i g . 3 ). B y c o n t r a s t , th e r o o t w e i g h t r a t i o r e m a i n e du n c h a n g e d i n f r e n c h b e a n a n d f ell r a p i d l y in w h e a t a n d m a i z e a s t h e s o l u ti o n p Hw a s i n c r e a s e d f r o m 3 .3 t o 4 .0 . T h i s r e d u c t i o n i n r o o t w e i g h t r a t i o w a s e n t i r e l y d u et o i n c r e a s e d t o p g r o w t h a t p H 4 .0 . R a i s i n g t h e p H f r o m 4 . 0 t o 4 .8 i n c r e a s e d th er o o t w e i g h t r a t i o o f a ll s pe c i es e x c e p t g in g e r , a g a i n i n d i c a t i n g a g r e a t e r r e s p o n s ei n r o o t g r o w t h t h a n t o p g r o w t h t o i n cr e a s e i n so l u t i o n p H . T h e r o o t w e i g h t r a t i o so f c a ss a v a, t o m a t o a n d g i n g e r d e c r e a s e d w h i l e t h o s e o f m a i ze a n d w h e a t i n-


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pH OF NUTRIENT SOLUTI ONFig. 3. Ef fec tof solution pH on root weight ratio of six crop species grown in flowing culture.(Means of 18 replications for ginger and eight replications for othe r species; means followed by thesame le t ter are not s ta t is t ical ly different a t P = 0 .05) . The roo t weight ra t ios of p lants p r ior toim pos ition of treatm ents were: ginger not determined, cassava 0.20, tom ato 0.14, french bean 0.11,whea t 0.37, maize 0.50.

c r e a s e d s i g n i f i c a n t l y a s t h e s o l u t i o n p H w a s r a i s e d f r o m 4 .8 t o 5 .5 . T h e r o o tw e i g h t r a t i o o f m a i z e c o n t i n u e d t o i n c r e a se , b u t t h a t o f t h e o t h e r s p e c i e s s h o w e dl i t t l e c h a n g e o v e r t h e p H r a n g e 5 .5 t o 7 .5 . T h e r o o t w e i g h t r a t i o o f a l l s p e c i e si n c r e a s e d s i g n i f i c a n t l y w i t h f u r t h e r i n c r e a s e in p H t o 8 .5 . A l t h o u g h e f f ec ts o f p Ho n r o o t w e i g h t r a t i o d i f fe r e d s u b s t a n t i a l l y a m o n g s p e ci e s, n o c l e a r d i f fe r e n c e w a se v i d e n t b e t w e e n m o n o c o t y l e d o n s a s a g r o u p a n d d i c o t y l e d o n s ( F ig . 3 ).

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PH OPTIM FOR GROWT H OF SIX CROP SPECIES 3 4 7

e m e r g e d . F u r t h e r r e s e a r c h i s n e e d e d t o e x p l a i n t h e s e r e s p o n s e s . D i f f e r e n c e s i nr o o t w e i g h t r a t io p r i o r t o i m p o s i t i o n o f t h e p H t r e a t m e n t s ( Fi g. 3 ) a n d s u b -s e q u e n t e f fe c ts o f t h e se t r e a t m e n t s o n b o t h r o o t a n d t o p g r o w t h m a y b e in v o l v e d .

e) Chem ical composition o f plant topsA n a l y s is o f w h o l e t o p s o f u n s p r a y e d p l a n t s f r o m s e l ec te d t r e a t m e n t s s h o w e d t h a tp H h a d v e r y l a rg e e f fe c ts o n c h e m i c a l c o m p o s i t i o n ( T a b l e 1 ). I n c r e a s i n g s o l u t i o np H f r o m 3 .3 t o 5 .5 s t r o n g l y i n c re a s e d t h e c o n c e n t r a t i o n s o f p o t a s s i u m , c a l c iu ma n d m a g n e s i u m i n th e t o p s o f al l s p e c ie s . A f u r t h e r i n c r e a s e i n s o l u t i o n p H t o 8 .5r e s u l t e d i n i n c r e a s e d m a g n e s i u m c o n c e n t r a t i o n s i n a ll s p e c ie s , i n c r e a s e d c a l c i u mc o n c e n t r a t i o n s in f re n c h b e a n a n d m a i z e , a n d a n i n c r e a se in p o t a s s i u m c o n -c e n t r a t i o n i n to m a t o . N i t r o g e n c o n c e n t r a t i o n s in t h e t o p s o f a ll sp e c ie s e x c e p tg i n g e r i n c r e a s e d a s t h e s o l u t i o n p H w a s r a i s e d f r o m 3 . 3 t o 5 . 5 . T h e n i t r o g e nc o n c e n t r a t i o n i n c a s s a v a a n d w h e a t w a s s t r o n g l y d e c r e a s e d a n d t h a t i n t o m a t oi n c r e a se d a s th e s o l u t i o n p H w a s f u r th e r i n c r e a se d t o 8 .5. P h o s p h o r u s c o n -c e n t r a t i o n s g e n e r a l l y i n c r e a s e d w i th i n c r e a s e in s o l u t i o n p H f r o m 3 .3 to 5 .5 , t h e nd e c l i n e d a s t h e s o l u t i o n p H w a s i n c r e a s e d t o 8 . 5 . S u l p h u r c o n c e n t r a t i o n s w e r el es s i n t h e t o p s o f a ll s p e c ie s e x c e p t c a s s a v a a t p H 4 .0 t h a n a t p H 3 .3 , a n d e i t h e ri n c r e a s e d o r s h o w e d l i t t l e c h a n g e a s t h e p H w a s r a i s e d t o 5 . 5 a n d 8 . 5 .

M a n g a n e s e a n d z in c c o n c e n t r a t i o n s in t h e t o p s o f a ll sp e c ie s i n c r ea s e d w i thi n c r e a s i n g s o l u t i o n p H f r o m 3 . 3 t o 8 . 5 . C o p p e r c o n c e n t r a t i o n s d e c r e a s e d i ng i n g e r a n d m a i z e a n d i n c r e a s e d in w h e a t a s t h e s o l u ti o n p H w a s in c r ea s e d . I r o nc o n c e n t r a t i o n s w e r e m a x i m a l in w h e a t a t p H 3 .3 a n d in a ll o th e r s p e ci es a t p H 4 .0a n d w e r e s t r o n g l y d e p r e s s e d b y f u r t h e r i n c r e a s e i n s o l u t i o n p H i n a l l s p e c i e se x c e p t t o m a t o . B o r o n c o n c e n t r a t i o n s w e r e li tt le a f fe c te d b y s o l u t io n p H f r o m 3 .3t o 8.5 , w h i le m o l y b d e n u m c o n c e n t r a t i o n s i n c r e a se d a s th e s o l u t io n p H w a s r a is e df r o m 3 .3 to 5 .5 , a n d t h e n d e c l i n e d i n m o s t s p e c i e s a s t h e p H w a s f u r t h e r r a i s e d t o8.5.

DISCUSSION

a) Apparent sensitivity o f plants to variation in pHO n t h e b a si s o f c a r e fu l ly c o n d u c t e d s o l u t io n c u l t u r e e x p e r i m e n t s w i t h t o m a t o ,l et tu c e a n d B e r m u d a g r as s, A r n o n a n d J o h n s o n 3 c o n c l u d e d :

W i t h i n a r e l a t i v e l y w i d e r a n g e o f p H b e t w e e n 4 a n d 8 , f l u c t u a t i o n s i n t h eh y d r o g e n i on c o n c e n t r a t i o n a r e to l e r a te d b y p l a n t s p r o v i d e d a n a d e q u a t es u p p l y o f a ll n u t r i e n t e l e m e n t s i s m a i n t a i n e d .


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348 A . K . M . S . I S L A M D . G . E D W A R D S A N D C . J . A S H E R

T h e i r p a p e r , w h i c h h a s b e e n w i d e l y q u o t e d i n t h e l i t e r a t u r e , o f t e n h a s b e e ni n t e r p r e t e d t o m e a n t h a t a n y m a j o r e f fe ct s o f p H o n p l a n t g r o w t h b e t w e e n p H 4a n d 8 a r e l i k el y t o b e i n d i r e c t e ff e ct s a s s o c i a t e d w i t h p H d e p e n d e n t c h a n g e s i n t h es o l u b i li t y o f m i c r o n u t r i e n t s o r o t h e r b i o l o g i c a l l y i m p o r t a n t e l e m e n t s i n th e s o il .S o m e s u p p o r t f o r th e c o n c l u s i o n s o f A r n o n a n d J o h n s o n 3 c o m e s f r o m s t u d ie s o nt h e n u t r i t i o n o f n o n - n o d u l a t e d l e g u m e s in w h i c h l it tl e o r n o g r o w t h d e p r e s s i o no c c u r r e d i n s o l u t i o n c u l t u r e s o r s a n d c u l t u r e s a t p H v a l u e s a s l o w a s 4 . 5 ( a n ds o m e t i m e s 4 . 0 ) p r o v i d e d t h e p l a n t s w e r e a d e q u a t e l y s u p p l i e d w i t h c a l c i u m ,m i n e ra l n i t r o g e n a n d o t h e r e s s e n t i a l e l e m e n t s ~ '3 9 4 7.

H o w e v e r , a c a r ef u l e x a m i n a t i o n o f t h e d a t a o f A r n o n a n d J o h n s o n ( Re f. 3 ,T a b l e 2 ) sh o w s t h a t a t p H 4 o n l y B e r m u d a g r as s g r e w w e ll ; t h e y i el ds o f t o m a t oa n d l e t t u c e w e r e r e d u c e d t o l e ss t h a n 3 5 p e r c e n t o f m a x i m u m . A g a i n a t p H 8 , t h eg r o w t h o f t h e t h r e e s p e ci es st u d i e d w a s r e d u c e d t o b e t w e e n 5 8 p e r c e n t ( t o m a t o )a n d 6 9 p e r c e n t ( B e r m u d a g r a s s) o f m a x i m u m . I n t h e p r e s e n t s t u d y a l so , y i e ld s o fa ll si x s p e ci e s w e r e m a r k e d l y r e d u c e d a t p H 4 , r a n g i n g f r o m 1 4 p e r c e n t o fm a x i m u m f o r m a i z e t o 6 2 p e r c e n t f o r c a s s a v a ( m e a n o f s p r a y e d a n d u n s p r a y e dt r e a t m e n t s ) . S i m i la r l y , s u b s t a n t i a l y i e l d r e d u c t i o n s o c c u r r e d i n t h e r e g i o n o f p H 8i n c a s s a v a , w h e a t a n d m a i z e (F i g . 2 ) .

S i n c e i n b o t h s t u d i es a c o n s c i o u s e f fo r t w a s m a d e t o m a i n t a i n ' a n a d e q u a t es u p p l y o f a ll n u t r i e n t e l e m e n t s ' w e m u s t c o n c l u d e t h a t e i t h e r p l a n t s a r e r a t h e rm o r e s e n si ti v e t o e x t r e m e s o f p H t h a n h a s b e e n p r e v io u s l y s u p p o s e d , o r t h a t t h ep r o b l e m s o f m a i n t a i n i n g a n a d e q u a t e n u t r i e n t s u p p l y a t lo w o r h i g h p H v a lu e sh a v e n o t b e e n f u l ly o v e r c o m e .

b ) I n j u r y b y H + o r O H - i on sS h o r t t e r m s tu d i es h a v e s h o w n t h a t a t l o w p H , i o n t r a n s p o r t m a y b e i m p a i r e d ,e s p e c ia l l y a t l o w c a l c i u m c o n c e n t r a t i o n s 2~, a n d t h a t s u f fi c ie n t m e m b r a n e d a -m a g e m a y o c c u r t o a l l o w t h e l o s s o f p r e v i o u s l y a b s o r b e d s o l u t e s 2 9 4 5. L o n g e rt e r m s t u d i e s o n s e v e ra l p l a n t s p e c i e s 3,2,~. 5 7 .6 2 h a v e s h o w n t h a t p r o l o n g e de x p o s u r e o f r o o t s t o l o w p H l e ad s t o s u p p r e s s i o n o f l a te r a l r o o t d e v e l o p m e n t a n d ,i n e x t r e m e c a se s , t o d e a t h o f t h e r o o t t i ps . I n t h e p r e s e n t s t u d y , a ll s p ec i es s h o w e dt h e se s y m p t o m s a t p H 3.3 , a n d f r e n ch b e a n , w h e a t a n d t o m a t o s h o w e d t h e m a tpH 4 .0 .

L e s s is k n o w n a b o u t t h e e ff ec ts o f O H - i o n s t h a n o f H + io n s o n p l a n t g r o w t h ,b u t d i r e c tl y in j u r i o u s e ff ec ts w i t h i n t h e r a n g e o f p H v a l u e s n o r m a l l y e n c o u n t e r e di n so i ls s e em u n l i k e l y . T h u s e v e n a t p H 8 .5 , t h e h i g h e s t p H s t u d i e d i n t h e p r e s e n te x p e r i m e n t , t h e O H - i o n c o n c e n t r a t i o n w o u l d h a v e b e e n o n l y 3 .2 /a M . T h i s v a l u em a y b e c o m p a r e d w i th H + i o n c o n c e n t r a t i o n s o f 1 0 0 /a M ( p H 4 ) t o 5 0 0 / a M ( p H3 . 3 ) a s s o c i a t e d w i t h v i s i b l e r o o t i n j u ry i n t h e p r e s e n t s t u d y .


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P H O P T I M A F O R G R O W T H O F S IX C R O P S PE C IE S 349

c ) E f [ e c t s o f p H o n i on u p t a k eS e v e r al sh o r t t e r m s tu d i es h a v e s h o w n l a rg e e ff ec ts o f p H o n t h e r a t e o f u p t a k e o fv a r i o u s c a t i o n s . T h u s , R a s h i d et al . 51 s h o w e d t h a t r e d u c i n g t h e p H o f t h e t es ts o l u t i o n f r o m 5 .5 t o 4 .5 d e c r e a s e d z i n c a b s o r p t i o n r a t e s b y f a c t o r s o f 1 0 0 0 a n d1 0 0 00 in t h e r i c e c u l t i v a r s IR - 6 a n d B a s m a t i - 3 7 0 r e s p e c ti v e l y . I n a n o t h e r s t u d y ,d e c r e a s i n g t h e s o l u t i o n p H f r o m 5 .0 t o 3 . 0 r e d u c e d z i n c a b s o r p t i o n b y a f a c t o r o fa b o u t 1 00 in w h e a t s e e d l i n g s 1 ~ S i m i l a r l y , l a r g e d e c r e a s e s i n t h e r a t e o f a b s o r -p t i o n o f m a n g a n e s e 9 4 3 5 3, c a l c i u m 4 2 , m a g n e s i u m 4 , 3 7,4 .4 ,4 6, p o t a s s i u m 2 8 a n dc o p p e r 9 w i t h d e c r e a s in g p H h a v e b e e n r e p o r t e d .I n t h e p r e s e n t s t u d y , t is s u e c o n c e n t r a t i o n s o f a ll e ss e n t ia l e l e m e n t s f o r w h i c hw e a n a l y s e d w e r e a d e q u a t e f o r h e a l th y g r o w t h a t p H 5 .5 ( T a b l e 1 ) 6 1 5 3 2 4 0H o w e v e r , t h e m a g n e s i u m c o n c e n t r a t i o n s i n th e t o p s o f a ll si x s p e ci e s a t p H 3 .3a n d 4 .0 ( 0 . 0 3 - 0 . 1 6 ~ ) w e r e s u f fi c ie n t ly l o w t o b e e i t h e r d e f i c ie n t o r m a r g i n a l l yl im it in g for pl an t g ro w th 6,19, 2o, 30, 33, 60, 6 5 6 6 . M a n g a n e s e c o n c e n t r a t i o n s in t h et o p s o f m a i z e a t p H 3 .3 a n d 4 .0 ( 1 2 a n d 1 4 p g . g - ~ r e s p e c t iv e l y ) w e r e a l s o i n t h er a n g e c o n s i d e r e d t o b e in a d e q u a t e f o r h e a l th y g r o w t h 3 2 3 6 . I n a l l s p e c i e s e x c e p tg i ng e r, n i tr o g e n c o n c e n t r a t i o n s i n t h e t o p s d e c r e a s e d w i th d e c r e a s i n g p H o v e rt h e r a n g e 5 .5 t o 3 .3 ( T a b l e 1 ) a n d i n t o m a t o t h e c o n c e n t r a t i o n s a t p H 3 .3 a n d 4 . 0(1 .2 a n d 1 . 3 ~ r e s p e c t iv e l y ) w e r e c l e a r ly in t h e d e f i c i e n t r a n g e . N i t r o g e n c o n -c e n t r a t i o n s i n c a s s a v a t o p s a t p H 3 .3 a n d 4 . 0 (2 .3 a n d 2 . 6 ~ r e s p e c t iv e l y ) w e r e a ls ow e l l b e l o w t h e c r it i ca l n i t r o g e n c o n c e n t r a t i o n o f 5 .1 ~o i n t h e f o u r t h a n d f if th fu l lye x p a n d e d l ea v e s o f c v. L l a n e r a 18 a n d t h e n o r m a l n i t r o g e n c o n c e n t r a t i o n s r a n g -i n g f r o m 4 .5 t o 6 .5 ~o i n y o u n g f u l l y - o p e n e d l e a v e s ~1. N o s a t i s f a c to r y e x p l a n a t i o nc a n b e g i v e n fo r t h e d e c l i n e i n p l a n t n i t r o g e n c o n c e n t r a t i o n s a t l o w p H . B a s s io n i 8r e p o r t e d t h a t n i t r a t e u p t a k e b y e x c i s e d b a r l e y r o o t s w a s l es s a t p H 4 t h a n a t p H 6 .H o w e v e r , th i s r e s u l t is s o m e w h a t s u s p e c t a s t h e t e s t s o l u t i o n s a p p a r e n t l y d i d n o tc o n t a i n c a l c i u m . In m o r e r e c e n t w o r k , R a o a n d R a i n s 50 r e p o r t e d h i g h e r r a t e s o fn i t r a t e a b s o r p t i o n i n sh o r t - t e r m u p t a k e e x p e r i m e n t s w i t h b a r l e y r o o t s a t p H 4 .0t h a n a t p H 5 .7 o r 8 .5 . S i m i l a rl y , i n a fl o w i n g s o l u t i o n c u l t u r e e x p e r i m e n t , F o r n o 16f o u n d t h a t m e a n r a t e s o f n i t r o g e n u p t a k e (a s n i t r at e ) p e r u n i t r o o t w e i g h t w e r ee i t h e r h i g h e r a t p H 4 . 4 t h a n a t p H 6 . 8 ( c a s s a v a c v . M A u s 3 , c o t t o n ) o ra p p r o x i m a t e l y t h e s a m e ( c a s s a v a c v s N i n a , C e i b a ) .

C a l c i u m c o n c e n t r a t i o n s i n m a i z e a t p H 3 . 3 a n d 4 . 0 ( 0 . 3 9 a n d 0 . 3 7 ~ r e -s p e c ti v e ly ) w e r e b el o w t h e c o n c e n t r a t i o n n o r m a l l y c o n s i d e r e d a d e q u a t e f o rh e a l t h y g r o w t h (0 .5 ~o )1 5; h o w e v e r , L o n e r a g a n a n d S n o w b a l l 4 ~ o b t a i n e d m a x -i m u m y i el d o f y o u n g m a i z e p l a n t s i n fl o w i n g s o l u ti o n c u l t u r e w h e n t h e c a l c iu mc o n c e n t r a t i o n i n th e t o p s w a s o n l y 0 . 1 2 ~ . I n t h e s a m e e x p e r i m e n t , to ma ~to a n dt h e w h e a t c u lt iv a rs G a b o a n d W o n g o o n d y a c h ie v e d m a x i m u m y ie ld w it h ca l-


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3 5 0 A . K . M . S . I S L A M D . G . E D W A R D S A N D C . J. A S H E R

c i u m c o n c e n t r a t i o n s i n t h e p l a n t t o p s o f 1 .2 9 ~o, 0 . 15 ~o a n d 0 .3 2 ~o r e s p e c t i v e l y 40 .T h e s e c a l c i u m c o n c e n t r a t i o n s a r e w e ll b e l o w t h o s e o b t a i n e d i n th e t o p s o f t o m a t oa n d w h e a t c v. G a t c h e r i n t h e p r e s e n t e x p e r i m e n t a t p H 3 .3 a n d 4 .0 . I t w o u l d t h u sa p p e a r t h a t c a l c iu m w a s n o t g r o w t h - l i m i ti n g f o r m a i z e, t o m a t o , w h e a t o r p r o b -a b l y fo r a n y o t h e r s p e c i es a t a n y s o l u t i o n p H i n t h e p r e s e n t e x p e r i m e n t .

I n c r e a s i n g t h e s o l u t i o n p H f r o m 5 . 5 t o 8 . 5 c a u s e d s u b s t a n t i a l r e d u c t i o n s i nn i t r o g e n c o n c e n t r a t i o n s in s h o o t s o f c a s s av a a n d w h e a t , a n d s m a l le r r e d u c ti o n si n m a i z e , f r e n c h b e a n a n d g i n g e r ( T a b l e 1). D e c r e a s e s i n r a t e o f p h o s p h a t ea b s o r p t i o n w i t h i n c r e a si n g p H a r e w e l l d o c u m e n t e d 2 2 2 3 a n d A r n o n a n dJ o h n s o n 3 c o n s i d e r e d t h a t p h o s p h o r u s d e f ic i e nc y c o n t r i b u t e d t o t h e p o o r g r o w t ho f t h e i r p l a n t s a t t h e h i g h e r p H v a l ue s . H o w e v e r , in t h e p r e s e n t e x p e r i m e n t , t is s u ep h o s p h o r u s c o n c e n t r a t i o n s w e r e i n a l l c a s e s a d e q u a t e a t p H 8 . 5 .

P o o r i r o n n u t r i t i o n d e p r e s s e d th e g r o w t h o f m a i z e a n d w h e a t a t p H 7 .5 a n d 8 .5 ,d e s p it e t h e u se o f F e E D D H A ( s eq u e s tr e n e t 3 8 ) a s a n i r o n s o u r ce . T h i s c o m -p o u n d is r e p o r t e d t o b e s t ab l e o v e r t h e p H r a n g e 4 to 9 4 8 b u t w a s n o t e n t i r e l ys a t is f a ct o ry u n d e r t h e c o n d i t i o n s o f o u r e x p e r i m e n t , p a r ti c u l a rl y a t t h e h i g h e r p Hv a l u e s. I n t h is c o n n e c t i o n , L i n d s a y a n d H a l v o r s o n 38 h a v e r e p o r t e d t h a t i nn u t r i e n t s o l u t i o n s a b s o r p t i o n o f i r o n b y t h e p l a n t r o o t s l e a v es fr e e c h e l a t i n g a g e n ti n s o l u t i o n w h i c h t h e n c o m p e t e s w i th t h e p l a n t r o o t s f o r t h e f er r ic i o n s r e m a i n i n gi n s o lu t i o n . Ir o n c o n c e n t r a t i o n s i n t h e t o p s o f t o m a t o , g i n g e r a n d f re n c h b e a nw h i c h s h o w e d l i tt le y i e ld d e p r e s s i o n a t p H 8 .5 w e r e h i g h e r t h a n t h o s e i n c a s s av a ,m a i z e a n d w h e a t i n w h i c h y i e l d s w e r e s e v e r e ly d e p r e s s e d ( F ig . 2, T a b l e 1). In fact ,t h e i r o n c o n c e n t r a t i o n i n t h e t o p s o f m a i z e g r o w n a t p H 8 .5 ( 8 5 / t g . g - 1 ) i s i n t h er a n g e t h a t h a s b e e n c o n s i d e r e d d e f i ci e n t fo r t h i s s p e c i es 3 s, a n o b s e r v a t i o nc o n f i r m e d b y t h e d e v e l o p m e n t o f s e ve r e s y m p t o m s o f ir o n c h l o ro s i s ( cf.S p r ag u e 6 1 ). I t w o u l d a p p e a r t h a t t o m a t o , g i n g e r a n d f re n c h b e a n w e r e m o r ee f fi c ie n t t h a n t h e o t h e r t h r e e s p e ci e s i n o b t a i n i n g t h e i r i ro n r e q u i r e m e n t s f r o m t h en u t r i e n t s o l u t i o n a t p H 8 . 5 .T o m a t o w a s c o m m o n t o b o t h t h e p re s e n t s t u d y an d t h a t o f A r n o n a n dJ o h n s o n 3 a n d h e n c e p r o v i d e s t h e m o s t s a t is f a c to r y b as is f o r c o m p a r i s o n o f t h er e s u lt s o b t a i n e d i n t h e t w o s t ud i e s. A b o v e p H 7 g r o w t h i n t h e p r e s e n t s t u d y w a ss u p e r i o r to t h a t i n A r n o n a n d J o h n s o n s s t ud y , p r e s u m a b l y b e c a u s e o f t h e b e tt e rc o n t r o l o f p h o s p h o r u s n u t r i t i o n a c h i e v e d u n d e r f l o w in g c u l tu r e c o n d i ti o n s .H o w e v e r , o v e r t h e p H r a n g e 4 to 6 .5 b e t t e r g r o w t h w a s o b t a i n e d i n A r n o n a n dJ o h n s o n s s t u d y ( F ig . 4), p a rt l y b e c au s e o f i n a d e q u a t e n i t ro g e n a n d m a g n e s i u mu p t a k e a t l o w e r p H v a l ue s i n t h e p r e se n t s tu d y . A r n o n a n d J o h n s o n a t t r ib u t e dm u c h o f t h e i r g r o w t h r e d u c t i o n b e l o w p H 5 t o i n a d e q u a t e c a l c iu m a b s o r p t i o n . I na s u b s i d ia r y e x p e r i m e n t w i t h l e tt u c e a n d t o m a t o t h e y s h o w e d t h a t r ai si n g t h ei n i t i a l c a l c i u m c o n c e n t r a t i o n i n t h e n u t r i e n t s o l u t i o n f r o m 2 0 0 0 t o 7 0 0 0 / z M


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P O P T I M A F O R G R O W T H O F S IX C R O P S PE C IE S 351

i n c r e a s e d y i e l d s a t b o t h p H 4 a n d 5 , w h e r e a s l o w e r i n g t h e i n i t i a l c a l c i u mc o n c e n t r a t i o n s t o 5 0 0 ~ M l o w e r e d p l a n t y i e ld s . F u r t h e r e v i d e n c e o f t h e in -t e r a c t i o n b e tw e e n e f fe c ts o f l o w p H a n d c a l c iu m c o n c e n t r a t i o n c o m e s f r o ms t u d i e s i n le g u m e n u t r i t i o n . T h u s , M u n n s 47 s h o w e d t h a t l u c e r n e p l a n t s s u p p l i e dw i t h c o m b i n e d n i t r o g e n g r e w e q u a l l y w e l l a t p H 4 a n d 5 w i t h a c a l c i u mc o n c e n t r a t i o n o f 5 0 0 0 ~ M , b u t t h a t g r o w t h w a s p o o r e r a t p H 4 w h e n lo w e rc a l c iu m c o n c e n t r a t i o n s w e r e u se d . C a l c i u m d e f ic i en c y s y m p t o m s w e r e n o t o b s e r-v e d i n t h e l u c e r n e t o p s a t p H 4 w h e n p l a n t s w e r e g r o w n a t t h e l o w e s t s o l u t i o nc a l c iu m c o n c e n t r a t i o n u s e d 1 0 0 0 / tM ) . A n d r e w i s h o w e d t h a t t h e g r o w t h o f s ixt e m p e r a t e p a s t u r e l e g u m e s p l u s t h e t r o p i c a l l e g u m e s Glyc ine w ight i i a n d Des-modium unc inatum s u p p l i e d w i t h i n o r g a n i c n i t r o g e n w a s m o r e s e v e r e ly r e -s tr ic t e d a t p H 4 w h e n c a lc i u m w a s s u p p li e d a t 1 2 5 p M t h a n a t 2 0 0 0 p M . At t h i sp H , D. uncina tum M acropt i l iurn lathyroides l u c e r n e a n d G. wight i i d i s p l a y e dc a l c iu m d e f i c ie n c y s y m p t o m s w i th c a l c i u m c o n c e n t r a t i o n s i n t h e p l a n t t o p s o f0 .1 3 , 0 .1 5 , 0 .1 6 , a n d 0 .2 1 ~o r e s p e c t i v e l y 2. T h e o t h e r s p e c i e s wh i c h s h o w e d y i e l dr e d u c t i o n s a t lo w c a lc i u m 1 25 p M ) a t p H 4 h a d s o m e w h a t h i g h e r c o n c e n t r a t i o n si n th e p l a n t t o p s a n d d i d n o t e x h i bi t a n y c a l ci u m d e f i ci e n cy s y m p t o m s . L o n e -r a g a n et al. 41 d e t e r m i n e d t h e s o l u t i o n c a l c i u m c o n c e n t r a t i o n s n e c e s s a r y f o rm a x i m a l g r o w t h o f 3 0 g ra s se s , ce r e al s , h e r b s a n d l e g u m e s i n f l o w i n g c u l t u r es o l u t io n s a t p H 5 .7 . W h e a t c v . G a b o a n d m a i z e a c h i e v e d m a x i m a l g r o w t h a t as o l u t i o n c a l c i u m c o n c e n t r a t i o n o f l O p M w h i l e w h e a t c v . W o n g o o n d y a n dt o m a t o a c h i e v e d m a x i m a l g r o w t h a t 1 0 0 p M c a lc i u m . In t h e p r e s e n t st u d y , ac o n s t a n t c a lc i u m c o n c e n t r a t i o n o f 2 5 0 /~ M w a s m a i n t a i n e d t h r o u g h o u t t h e

o o

~ c

p OF NU /RIENT SOLUTIONF i g . 4 . E f f ec t s o f s o l u t i o n p H o n g r o w t h o f t o m a t o :

O O D a t a f r o m A r n o n a n d J o h n s o n 3.O O D a t a f r o m c u r r e n t e x p e r im e n t .


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e x p e r i m e n t a t a l l s o l u t i o n p H v a l u e s . T h e f a i l u r e t o o b s e r v e a n y c a l c i u md e f ic i en c y i n t h e p l a n t t o p s a n d t h e a d e q u a t e c a l c i u m c o n c e n t r a t i o n i n t h e p l a n tt o p s , e v e n a t p H 3 . 3 a n d 4 . 0 , i n d i c a t e t h e r e w a s n o d i r e c t c a l c i u m l i m i t a t i o n o np l a n t g r o w t h . H o w e v e r , t h e p o s s ib i li ty e x is ts t h a t b e t t e r g r o w t h o f a t l e a st s o m es p e ci es m a y h a v e o c c u r r e d a t l o w p H in t h e p r e s e n t e x p e r i m e n t i f a h i g h e rs o l u t io n c a l c i u m c o n c e n t r a t i o n h a d b e e n s e le c te d . P r o t e c t i o n o f p l a n t t i s su e sa g a i n s t h y d r o g e n i o n i n j u ry b y a n e l e v a t e d c a l c iu m c o n c e n t r a t i o n 2 8,4 5 p r o v i d e st h e m o s t l i k e l y e x p l a n a t i o n f o r su c h a n e f fe c t.

T h e a b o v e o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e v i e w t h a t i f s u f fi c ie n t a t t e n t i o nis g i v e n to t h e f o r m u l a t i o n o f n u t r i e n t s o l u t io n s a t l o w a n d h i g h p H v a lu e s ,v i g o r o u s p la n t g r o w t h m a y b e o b ta i n e d o v e r a r a th e r b r o a d r a n g e i n p H .H o w e v e r , a s f a r a s t h e a u t h o r s a r e a w a r e , n o o n e h a s y e t s u c c e e d e d i n d e -m o n s t r a t i n g a n o p t i m u m r a n g e a s w i de a s t h e 4 p H u n it s p r o p o s e d b y A r n o n a n dJ o h n s o n 3.

d ) R e l e v a n c e t o p l a n t g r o w t h i n t h e f i e l dL a r g e d i ff e r en c e s w e r e o b s e r v e d i n t h e a b i l i t y o f t h e s ix c r o p s p e c i es u s e d i n t h ep r e s e n t s t u d y t o g r o w a t l o w p H v a lu e s . T h u s a t p H 3 .3 a n d 4 . 0 s p e ci e s r a n k e d i nt h e f o l l o w i n g o r d e r o f r e l a t iv e y i e ld : g i n g e r > c a s s a v a > t o m a t o > f r e n c h b e a n> w h e a t > m a i z e F i g . 2 ). T h e s e re s u l t s a r e i n g o o d a g r e e m e n t w i t h t h o s eo b t a i n e d i n a r e c e n t f ie ld s t u d y i n w h i c h t h e a b i l i ty o f s p e c ie s to g r o w i n a h ig h l ya c i d o x i s o l w i t h 0 o r 0.5 t o n n e s l i m e p e r h e c t a r e r a n k e d i n th e o r d e r c a s s a v a >b e a n s > m a i z e C I A T ) 12. T h e b e h a v i o u r o f g i n g e r a l s o a c c o r d s w e l l w i t h fi el de x p e r i e n c e . I n r e c e n t f i e l d s t u d i e s , I s l a m et a l . 27 o b t a i n e d r h i z o m e y ie ld s /> 9 0 ~o f m a x i m u m a t c o m p a r a t i v e l y l o w p H v a l u e s o n a m a j o r i t y o f s oils . T h u s , o f e i g hts o il s e x a m i n e d , o p t i m u m y ie ld s w e r e o b t a i n e d o n f o u r at s o il p H v a l u e s m e a -s u r e d i n 1 : 2 s o i l/ 0 .0 1 M C a C l a ) r a n g i n g f r o m 4 .3 t o 4 .6 , a n d i n a f u r t h e r t h r e e a tp H v a l u e s r a n g i n g f r o m 5.0 t o 5 .2 . T h e p H r e q u i r e d f o r 9 0~ o o f m a x i m u m y ie ld int h e r e m a i n i n g s o i l w a s 6 . 4 .

T h e w i d e r a n g e o f o p t i m u m s oil p H v a lu e s o b s e rv e d b y I s la m et a l . 27 f o r t h es a m e c r o p o n d i f f e re n t s o il s p H 4 .3 t o 6 .4 ) c a l ls i n t o q u e s t i o n t h e c o n c e p t o f a no p t i m u m p H f o r t h e g r o w t h o f a p a r t ic u l a r c r o p . I n t h e f ie ld , r e s p o n s e t o v a r y i n gp H w i ll b e i n fl u e n c e d n o t o n l y b y s u s c e p t i b i li t y o f t h e c r o p t o h y d r o g e n i o n i n j u r ya t lo w p H a n d t o v a r i o u s d e f i ci e n c ie s a t lo w a n d h i g h p H d i s c u s s e d in c ) a b o v e ,b u t a l s o b y la r g e p H d e p e n d e n t c h a n g e s i n th e s o l u b il it y o f a l u m i n i u m , p h o s -p h o r u s , m a n g a n e s e , i ro n , zi nc , c o p p e r a n d m o l y b d e n u m . S u s c e p t ib i li ty t o a d v e r s ee ff ec ts o f h i g h c o n c e n t r a t i o n s o f s o l u bl e a l u m i n i u m o r m a n g a n e s e p r e s e n t i ns o m e s o il s a t lo w p H is a l so l ik e ly t o b e a m a j o r f a c t o r d e t e r m i n i n g t h e o p t i m u m


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PH OPTIM FOR GROWTH OF SIX CROP SPECIES 353

p H . I n s o m e s oils , e ff ec ts o f p H o n t h e r a t io o f a m m o n i u m t o n i t r a t e -n i t r o g e nm a y b e i m p o r t a n t a ls o . H e n c e a c o m b i n a t i o n o f s o il a n d c r o p c h a r a c t e r i s ti c s w illd e t e r m i n e t h e o p t i m u m p H a t a n y p a r t i c u l a r s i t e .

A f u r t h e r d if fi cu l ty in c h a r a c t e r i z i n g t h e o p t i m u m p H f o r g r o w t h o f a p a r t ic -u l a r c r o p c o n c e r n s t h e m e a s u r e m e n t o f s o il p H . D i f fe r e n t m e t h o d s o f m e a s u r e -m e n t o f t e n y i e l d m a r k e d l y d i f f e r e n t p H v a l u e s f o r t h e s a m e s o i l . H o w e v e r , ac o n s e n s u s a p p e a r s t o b e e m e r g i n g t h a t t h e m e a s u r e m e n t o f s o il p H i n a d il u tee l e c t r o l y t e s u c h a s 0.0 1 M C a C 12 s o l u t i o n p r o v i d e s t h e b e s t i n d e x o f t h e c o n -c e n t r a t i o n o f h y d r o g e n i o n s p r e s e n t i n t h e s o i l4 9 55, 5 6 6 7 . S o i l p H v a l u e s m e a -s u r e d i n 0 .0 1 M C a C I 2 a r e o f t e n 0.5 t o 1 .0 p H u n i t s l o w e r t h a n v a l u e s m e a s u r e d a tt h e s a m e s o i l / s o l u t i o n r a t i o i n w a t e r 67. U n f o r t u n a t e l y , a w i d e v a r i e t y o f p Hm e a s u r e m e n t s a r e c u r r e n t l y i n u s e a n d i t o f t e n h a p p e n s t h a t t h e m e t h o d o fm e a s u r e m e n t i s n o t s p e ci fi ed p r ec i s el y w h e n c r o p r e s p o n s e d a t a a r e r e p o r t e d .

R e c e n t r e s e a r c h o n t h e l i m i n g o f c a s s a v a s o il s m a y s e r v e t o il l u s t ra t e t h ep r o b l e m s in a r r i v in g a t a n o p t i m u m s o il p H f o r t h e g r o w t h o f a p a r t ic u l a r c r o p .S p a i n e t a l 5 8 f o u n d t h a t m o s t o f t h e 1 38 c a s s a v a c u l ti v a r s g r o w n o n a h ig h l y a c ido x i so l in C o l o m b i a r e a c h e d m a x i m u m y i el d s a t a l o w r a t e o f l im i n g ( 0.5 t . h a - 1 )c o r r e s p o n d i n g w i t h a p H (1 : 1 s o i l / w a t e r s u s p e n s i o n ) o f 4 .4 . R a i s i n g t h e p Hf u r t h e r t o 4 .7 o r 5.3 c a u s e d m o d e r a t e t o s e v e r e y i e ld d e p r e s s i o n t h r o u g h t h ei n d u c t i o n o f z in c d e fi ci en c y . E d w a r d s a n d K a n g 1 4 o b t a i n e d s o m e w h a t s i m i l a rr e s u l t s o n t h e l im e r e q u i r e m e n t s o f t w o c a s s a v a c u l t i v a r s o n a h i g h l y a c i d u l ti s o li n N i g e r i a . I n t h i s c a s e , t h e o p t i m u m p H (1 : 1 s o i l / w a t e r s u s p e n s i o n ) w a s i n t h er a n g e 4 . 6 t o 5 . 1 . H i g h e r l i m i n g r a t e s r e d u c e d y i e l d s d r a s t i c a l l y d u e t o z i n cd e f ic i e n c y , w i t h t u b e r y i e ld s r e d u c e d t o z e r o a t a n a p p l i c a t i o n r a t e (5 t . h a - 1 )c o r r e s p o n d i n g w i t h a so il p H o f a p p r o x i m a t e l y 7 .0 . T h e r a n g e o f p H v a l u e sc o r r e s p o n d i n g w i t h m a x i m u m y i e l d i n t h e s e t w o s t u d i e s ( 4 .4 t o 5 .1 ) f al ls o u t s i d et h e o p t i m u m r a n g e f o u n d f o r c a s s a v a o f 5 .5 t o 6 .5 i n t h e p r e s e n t s t u d y ( F ig . 2).S in c e t h e m e a s u r e d p H v a l u e s o f t h e C o l o m b i a n o x i so l a n d t h e N i g e r i a n u l ti so lw e r e b o t h a b o v e t h e z er o p o i n t o f c h a r g e , t h e d i s c r e p a n c y b e t w e e n t h e o p t i m u mp H r a n g e s w o u l d h a v e b e e n e v e n w i d e r h a d t h e so il p H s b e e n m e a s u r e d i n ad i lu t e e le c t r o ly t e in s t e a d o f i n w a te r . M o r e r e c e n t w o r k o n t h e C o l o m b i a n o x i so lh a s s h o w n t h a t w h e n a d e q u a t e a m o u n t s o f z in c a n d o t h e r m i c r o n u t r i e n ts w e r ei n c lu d e d i n th e f e rt il iz e r m i x t u r e , c a s s a v a s h o w e d a m a r k e d p o s i t iv e g r o w t hr e s p o n s e f r o m 0 . 5 t o 2 t o n n e s l i m e p e r h e c t a r e a n d a s m a l l e r p o s i t i v e g r o w t hr e s p o n s e u p t o 6 t o n n e s l i m e p e r h e c t a re a t w h i c h r a t e t h e s o il p H h a d i n c r e as e dt o 5 .3 25 . N o i n f o r m a t i o n i s a v a i l a b l e o n t h e e ff e ct o f s u p p l y i n g z i n c o n t h e p Ho p t i m u m i n t h e N i g e r i a n s o il s t u d ie d b y E d w a r d s a n d K a n g 14.T h e f o r e g o i n g c o n s i d e r a t i o n s l e ad u s t o t h e c o n c l u s i o n t h a t w h i le it a p p e a r sp o s s i b l e t o r a n k c r o p s i n t e r m s o f th e i r s e n s i t i v it y t o e x t r e m e s o f s o il p H , i t is


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3 5 4 A. K . M. S . IS LAM, D. G . EDW AR D S AN D C . J . AS HER

e x t r e m e l y d i f f i c u l t t o d e f in e p r e c i s e l y t h e o p t i m u m p H r a n g e f o r t h e g r o w t h o f ap a r t i c u l a r c r o p . E v e n i n c a r e f u l ly c o n d u c t e d s o l u t i o n c u l t u r e e x p e r i m e n t s i t i sd i f f i cu l t t o e n s u r e o p t i m u m l e ve l s o f s u p p l y o f a l l e s s e n t i a l e l e m e n t s a t a l l p Hv a l u e s . I n so i l s , e f f e ct s o f p H o n n u t r i e n t s o l u b i l i t y f u r t h e r c o m p l i c a t e t h es i t u a t i o n . H e n c e p u b l i s h e d v a l u e s f o r t h e o p t i m u m p H o f a c r o p m a y h a v e r a t h e rl i m i t e d a p p l i c a b i l i t y o u t s i d e t h e p a r t i c u l a r s e t o f c o n d i t i o n s u n d e r w h i c h t h e yw e r e d e t e r m i n e d .

A C K N O W L E D G E M E N T SGra t e fu l a c know l e dge m e n t is ma de t o t he R e se rve B a nk o f Aus t ra l i a fo r supp or t o f A .K.M.S . I s l a m i nt h e f o r m o f a R u r a l C r e d i ts D e v e l o p m e n t F u n d r e s e ar c h g r a n t . T h a n k s a r e a ls o d u e t o B u d e r i mG i n g e r G r o w e r s C o o p e r a t i v e , B u d e ri m , Q u e e n s l a n d f o r t h e s u p p l y o f p l a n t i n g m a t e ri a l, to M r . G .Ke rve n , Mr . H . Mi ghe l l a nd Mrs . J . Me rc e r fo r t e c hn i c a l a s s i s t a nc e , a nd t o Mr . B . Ke nyon fo ra s s is t an c e w i t h t h e p r e p a r a t i o n o f t h e m a n u s c r i p t. S p e c ia l t h a n k s a r e d u e t o M r . A . D . J o h n s o n ,C S I R O C u n n i n g h a m L a b o r a t o r y , S t . L u ci a, Q u e e n s l a n d f o r r u n n i n g m u l t i - el e m e n t a n a ly s e s o f p l a n ts a mpl e s f rom se l e ct e d pH t r e a t me n t s .R e c e i ved 12 Jun e 1979 . R e v i se d Augus t 1979

R E F E R E N C E S1 An dre w , C . S . 1976 Ef fe c t o f c a l c i um, pH a nd n i t roge n on t he g row t h a nd c he m i c a l c om-pos i t i on o f some t rop i c a l a nd t e mp e ra t u re pa s t u re l e gume s. 1. N odu l a t i on a nd g row t h . Aus t . J .

Agric . Res . 27 , 611-623.2 And re w, C . S , a nd Johnso n , A . D . 1976 Ef fe ct o f c a l c i um, pH a nd n i troge n on t he g row t h a ndc he mi c a l c ompos i t i on o f some t rop i c a l a nd t e mpe ra t e pa s t u re l e gume s . 11 . C he mi c a l c om-pos i t i on ( c a l c i um, n i t roge n , po t a s s i um, ma gne s i um, sod i um a nd phosphorus ) . Aus t . J . Agr i c .Res . 27 , 625-636.3 Ar non , D . 1. a nd Johnso n , C . M. 1942 In f l ue nc e o f hyd r oge n ion c onc e n t ra t i o n on the g row t ho f h i ghe r p l a n t s und e r c on t ro l l e d c on d i t i ons . P l a n t P hys i o l . 17, 525 -539 .

4 Ar non , D . 1 ., F ra t z ke , W . E . a nd Joh nso n , C . M. 1942 Hy drog e n i on c on c e n t ra t i on i n r e l a t i ont o a bso rp t i on o f i no rga n i c nu t r i e n t s by h i ghe r p l a n t s . P l a n t P hys i o l . 17 , 515 -524 .5 A s h e r , C . J . a n d E d w a r d s , D . G . 1 9 7 8 R e l e v a n c e o f d i l u t e s o l u t i o n c u l t u r e s t ud i e s t o p r o b l e m sof low fe r t i l i ty t rop ica l so i l s , n M i ne ra l Nu t r i t i on o f Le gume s i n t rop i c a l a nd su b t rop i c a l S o il s.Eds . C . S . Andre w a nd E . J . Ka mpra t h pp . 131 -152 . C S IR O, Me l bourne , Aus t ra l i a .6 Ashe r , C . J . a nd Le e , M .T . 197 5 Di a gn os i s a nd c o r re c t i on o f nu t r i t i o na l d i so rde r s i n g i nge r .D e p a r t m e n t o f A g r i c u l t u r e, U n i v e r s i ty o f Q u e e n s l a n d , B r i s ba n e , A u s t r a li a .

7 Ashe r , C . J . , Oz a n ne , P . G . a nd Lo ne ra g a n , J . F . 1965 A me t h od fo r c on t ro l l i ng t he i on i ce nv i ron m e n t o f p l a n t roo t s . S o i l Sc i. 100 , 149 -156 .8 B a s s i on i , N . H . 1971 Te m pe ra t u re a nd pH i n t e ra c t i on i n n i t r a t e up t a ke . P l a n t a nd S o i l 35 ,445~ ,48 .9 B ow e n , J . E . 196 9 Ab so rp t i on o f c oppe r , z i nc a nd m a nga n e se by suga rc a n e l e a f t is sue. P l a n tPhys io l . 44 , 255-261.10 C ha udry , F . M. a nd Lo ne ra g a n , J. F . 1972 Z i nc a bso rp t i o n by wh e a t s e e d li ngs . I I . In -h i b i t i on by hyd ro ge n i ons a n d by m i c ron u t r i e n t c a t i ons . S o i l S c i. S oc . Am . P roc . 36 , 327 -331 .11 C IA T, C a l i , C o l om bi a An nu . R e p . (1974) .


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12 CIAT, Cali, Colombia Annu. Rep. 1977).13 Edwards, D. G. and Asher, C.J. 1974 The significance of solution flow rate in flowing cultureexperiments. Plant and Soil 41, 161-175.14 Edwards, D. G. and Kang, B.T. 1978 Tolerance of cassava M a n i h o t e s c u l e n t a C r a n t z ) to highsoil acidity. Field Crops Res. I, 337-346.15 Epstein, E. 1972 Mineral Nutrition of Plants: Principles and Perspectives, John Wiley andSons, Inc., New York, 412 p.16 Forno. D. A. 1977 The mineral nutrition of cassava M a n i h o t e s c u l e n t a Crantz) with parti-cular reference to nitrogen. Doctoral Thesis, University of Queensland, Brisbane, Australia.

17 Forno, D. A., Asher, C. J. and Edwards, D. G. 1976 Mist propagation of cassava tip cuttingsfor nutritional studies: effects of substrate calcium concentration, tempera ture and shading.Trop. Agric. Trinidad 53, 47 55.18 Fox, R. H., Talleyrand, H. and Scott, T. W. 1975 Effect of nitrogen fertilization on yields andnitrogen content of cassava, Llanera cultivar. J. Agric. Univ. Puerto Rico 59, 115-124.19 Garner, W. W., McMurtrey, J. E., Jr., Bowling, J. R., Jr. and Moss, E. G. 1930 Magnesiumand calcium requirements of the tobacco crop. d. Agric. Res. 40, 145-168.20 Goto , Y., Shigeta, K., Ishihara, T. and Yamamoto, M. 1953 Studies on the magnesium

deficiency of crops. 2. Chemical relations in cases of wheat and rape. Sci. Rep. Shiga Agric. Coll.Shiga Pref., Japan) 5, 15-18.21 Crime, J. P. and Hodgson, J. G. 1969 An investigation of the ecological significance of lime-chlorosis by means of large scale comparative experiments, I n Ecological Aspects of theMineral Nutrition of Plants, Ed. 1. H. Rorison. pp. 67-100, Blackwell Sci. Publ., Oxford andEdinburgh.22 Hagen, C. E. and Hopkins, H.T. 1955 Ionic species in orthophospha te absorption by barley

roots. Plant Physiol. 30, 193-199.23 Hendrix, J. E. 1967 The effect of pH on the uptake and accumulation of phosphat e andsulphate ions by bean plants. Am. J. Bot. 54, 560-564.24 Hoagland, D. R. 1917 The effect of hydrogen and hydroxyl ion concentration on the growthof barley seedlings. Soil Sci. 3, 547-560.25 Howeler, R. H., Cadavid, L. F. and Calvo, F. A. 1977 The interaction of lime with minorelements and phosphorus in cassava production, In Proc. 4th Syrup. Int. Soc. Tropical Root

Crops. Eds. J. Cock, R. Maclntyre and M. Graham pp. 113-117, IDRC, Ottawa, Canada.26 Islam, A. K. M. S., Asher, C. J., Edwards, D. G. and Evenson, J. P. 1978 Germinat ion andearly growth o f ginger. 11. Effects of 2-chloroethylphosphonic acid or e levated temperaturepretreatments. Trop. Agric. Trinidad 55, 127-134.27 lslam, A.K .M. S., Edw ard s, D.G. andAsher, C.J. 1979 The role oflime in commercial gingerproduction in Australia. Fifth Symp. Int. Soc. Tropical Root Crops, Manila, Philippinesin p ress ) .

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plant tissue using a briquet ting technique. Commun. Soil Sci. Plant Anal. 3, 1-9.32 Jones, J. B., Jr. 1972 Plant tissue analysis for micronutrients. In Micronutrients in Agriculture.Eds. J. J. Mortvedt et a l . pp. 319-346. Soil Sci. Soc. Am., Inc., Madison, U.S.A.33 Jones, J. P. 1929 Deficiency of magnesium, the cause of chloros is in corn. J. Agrie. Res. 39,873-892.34 Kamprath, E. J. 1972 Soil acidity and liming. In Soils of the Humid Tropics, 136--149, Nat.Acad. Sci. - Nat. Res. Council Committee on Tropical Soils, Washington, D.C.


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3 5 K a s h i r a d A . a n d M a r s c h n e r H . 1 97 4 I r o n n u t r it i o n o f s u n f l o w e r p l a n t s i n m o n o a n d m i x e dc u l t u r e . P l a n t a n d S o i l 4 1 9 1 - 1 0 1 .3 6 L a b a n a u s k a s C . K . 1 9 66 M a n g a n e s e . In D i a g n o s t i c C r i t e r i a f o r P l a n t s a n d S o i l s . E d . H . D .C h a p m a n p p . 2 6 4 - 2 8 5 U n i v . C a l i f . D i v . A g r i c . S c i.3 7 L e g g e t t J . E . a n d G i l b e r t W . A . 1 9 6 9 M a g n e s i u m u p t a k e b y s o y b e a n s . P l a n t P h y s i o l. 4 4

1182- 1186 .3 8 L i n d s a y W . 1_. a n d H a l v o r s o n A . D . 1 9 7 1 C o m p a r i s o n o f F e E D D H A a s a n ir o n s o u r c e t ~ rn u t r i e n t s o l u t i o n s a n d f o r s o il s. A g r o n . A b s t r . p . 9 2.3 9 L o n e r a g a n J . F . a n d D o w l i n g E . J . 1 95 8 T h e in t e r a c t i o n o f c a l c i u m a n d h y d r o g e n i o n s i n t h e

n o d u l a t i o n o f s u b t e r r a n e a n c l o v e r . A u s t . J. A g r i c . R e s . 9 4 6 4 - 4 7 2 .4 0 L o n e r a g a n J . F . a n d S n o w b a l l K . 1 9 69 C a l c i u m r e q u i r e m e n t s o f p l a n t s . A u s t . J . A g r i c . R e s .

2 0 4 6 5 - 4 7 8 .4 1 L o n e r a g a n J . F . S n o w b a l l K . a n d S i m m o n s W . J . 1 96 8 R e s p o n s e o f p l a n t s t o c a l c iu mc o n c e n t r a t i o n i n s o l u t i o n c u l t u r e . A u s t . J. A g r i c . R e s . 1 9 8 4 5 8 5 7.4 2 M a a s E . V . 1 96 9 C a l c i u m u p t a k e b y e x c i se d m a i z e r o o t s a n d in t e r a c t io n s w i t h a l k al i c a t io n s .

P l a n t P h y s i o l . 4 4 9 8 5 - 9 8 9 .4 3 M a a s E . V . . M o o r e D . P . a n d M a s o n B . J . 1 96 8 M a n g a n e s e a b s o r p t i o n b y e x c i se d b a r l ey

r o o t s . P l a n t P h y s i o l . 4 3 5 2 7 - 5 3 0 .4 4 M a a s E . V . a n d O g a t a G . 1 9 7 1 A b s o r p t i o n o f m a g n e s i u m a n d c h l o r id e b y e x c is e d c o r n r o o t s .

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s t r u c t u r e o f c o r n r o o t t ip s i n d u c e d b y H - i o n . P l a n t P h y s i o l . 4 1 1 7 2 5 -1 7 3 5 .4 6 M o o r e D . P . O v e r s tr e e t R . a n d J a c o b s o n L . 1 9 6 1 U p t a k e o f m a g n e s i u m a n d i ts i n t e r a c ti o nw i t h c a l c i u m i n e x c i s e d b a r l e y r o o t s . P l a n t P h y s i o l . 3 6 2 9 0 - 2 9 5 .

4 7 M u n n s D . N . 1 96 5 S o il a c i d it y a n d g r o w t h o f a le g u m e . I I. R e a c t i o n s o f a l u m i n i u m a n dp h o s p h a t e in so l u t io n a n d e ff ec ts o f a l u m i n iu m p h o s p h a t e c a lc iu m a n d p H o n Medicayosativa L . a n d Trifolium subterraneum L . i n s o l u t i o n c u l t u r e . A u s t . J . A g r i c . R e s . 1 6 7 4 3 - 7 5 5 .4 8 N o r v e l l W . A . 1 97 2 E q u i l i b r i a o f m e t a l c h e l a t e s i n s o i l s o l u t i o n In M i c r o n u t r i e n t s i n A g r i c u l -

t u r e . E d s . J . J . M o r t v e d t et al p p . 1 1 5 - 1 3 8. S o il S c i. S o c . A m . I n c . M a d i s o n U . S . A .4 9 P e e c h M . 1 96 5 H y d r o g e n - i o n - a c t i v i t y In M e t h o d s o f S o i l A n a l y s i s . E d . C . A . B l a c k P a r t 2 .

C h e m i c a l a n d M i c r o b i o l o g ic a l P r o p e r t i e s 9 1 4 - 9 2 6 . M o n o g r a p h N o . 9 A m . S o c . A g r o n .M a d i s o n W i s c o n s i n .5 0 R a o K . P . a n d R a i n s D . W . 1 9 76 N i t r a t e a b s o r p t i o n b y b a r l e y . I . K i n e t i c s a n d e n e r g e ti c s .P l a n t P h y s i o l . 5 7 5 5 - 5 8 .

51 R a s h i d A . C h a u d h r y F . M . a n d S h a r if M . 1 97 6 M i c r o n u t r i e n t a v a i la b i li ty t o c e r e a ls f r o mc a l c a r e o u s s o i ls . 111 . Z i n c a b s o r p t i o n b y r i ce a n d i ts i n h i b i ti o n b y i m p o r t a n t i o n s o f s u b m e r g e ds o i l s . P l a n t a nd S o i l 45 613 623 .5 2 R o b s o n A . D . 1 96 9 S o i l f a c t o r s a f f ec t in g t h e d i s t r ib u t i o n o f a n n u a l Medicayo s pe c i e s . J . A u s t .I n s t . A g r i c . Sc i. 35 154 - 167 .

5 3 R o b s o n A . D . a n d L o n e r a g a n J . F . 1 97 0 S e n s it iv i ty o f a n n u a l Medicago s p e c ie s to m a n -g a n e s e t o x i c i t y a s a f f e c t e d b y c a l c i u m a n d p H A u s t . J . A g r i c . R e s . 2 1 2 2 3 - 2 3 2 .

5 4 R o r i s o n 1. H . 1 96 9 E c o l o g i c a l i n f e r e n c e s f r o m la b o r a t o r y e x p e r i m e n t s o n m i n e r a l n u t r i t i o nIn E c o l o g i c a l A s p e c t s o f t h e M i n e r a l N u t r i t i o n o f P l a n t s . E d . 1 . H . R o r i s o n . p p . 1 5 5 - 1 7 6 .B l a c k w e l l S c i . P u b l . O x f o r d a n d E d i n b u r g h .5 5 S c h o f i e l d R . K . a n d T a y l o r A . W . 1 9 55 T h e m e a s u r e m e n t o f s o i l p H . S o i l S ci. S o c . A m . P r o c .19 164 - 167 .5 6 S m i l ey R . W . a n d C o o k R . J . 1 97 2 U s e a n d ab u s e o f t h e s o il p H m e a s u r e m e n t . P h y t o p a t h . 6 2193- 194 .

5 7 S m i t h P . F . 1 9 7 1 H y d r o g e n io n t o x i c i t y o n c i t ru s . J . A m . S o c . H o r t i c . Sc i. 9 6 4 6 2 - 4 6 3 .5 8 S p a i n J . M . F r a n c i s C . A . H o w e l e r R . H . a n d C a l v o F . 1 9 75 D i f f e r e n t i a l s p e c i e s a n dv a r i e t a l t o l e r a n c e t o s o il a c i d i t y i n t r o p i c a l c r o p s a n d p a s t u r e s . In S o il M a n a g e m e n t i n T r o p i c a l


19/19

P H O P T I M A F O R G R O W T H O F S IX C R O P S P E CI ES 3 5 7

A m e r i c a . E d s . E . B o r n e m i s z a a n d A . A i v a r a d o . p p . 3 0 8 - 3 2 9 . S o i l S c i. D e p t . N . C a r o l i n a S t a t eU n i v e r s i t y R a l e i g h N . C . U . S . A .5 9 S p e a r S . N . A s h e r C . J . a n d E d w a r d s D . G . 1 97 8 R e s p o n s e o f c a s s av a s u n f l o w e r a n d m a i z e

t o p o t a s s i u m c o n c e n t r a t i o n i n s o l u t io n . 1 . G r o w t h a n d p l a n t p o t a s s i u m c o n c e n t r a t i o n . F i e ldC r o ps R e s . l 347 361 .6 0 S p e a r S . N . E d w a r d s D . G . a n d A s h e r C . J . 1 97 8 R e s p o n s e o f c a s s a v a s u n f l o w e r a n d m a i z e

t o p o t a s s i u m c o n c e n t r a t i o n i n s o l u t io n . I l l . I n t e r a c t i o n s b e t w e e n p o t a s s iu m c a l c iu m a n dm a g n e s i u m . F i e l d C r o p s R e s . 1 3 7 5 3 89 .

6 1 S p r a g u e H . B . 1 96 4 E d . H u n g e r S i g n s i n C r o p s 3 r d e d i ti o n . D a v i d M c K a y C o . N e w Y o r k461 p .6 2 S u t t o n C . D . a n d H a l l s w o r t h E . G . 1 95 8 S t u d i es o n t h e n u t r i t io n o f f o r a g e l e g u m e s . I . T h e

t o x i ci ty o f lo w p H a n d h i g h m a n g a n e s e s u p p l y t o l u c e rn e a s a f fe c t e d b y c li m a t ic f a c t o r s a n dc a l c i u m s u p p l y . P l a n t a n d S o i l 9 3 0 5 - 3 1 7 .6 3 T a r a s M . J . G r e e n b e r g A . E . a n d H o a k R . D . 1 9 7 1 S t a n n o u s c h l o r i d e m e t h o d I n S t a n d a r dM e t h o d s f o r t h e E x a m i n a t i o n o f W a s t e W a t e r . E d s . M . J. T a r a s e t a l p p . 5 3 0 - 5 3 2 . A P H AA W W A W P C F W a s h i n g to n U .S . A .

6 4 V a n d e n B e rg h J . P . 1 96 9 D i s t r i b u t i o n o f p a s t u r e p l a n t s i n r e l a ti o n to c h e m i c a l p r o p e r t i e s o ft he s o i l . I n E c o l o g i c a l A s p e c t s o f t h e M i n e r a l N u t r i t i o n o f P l a n ts . E d . I . H . R o r i s o n . p p . 1 1 -2 4 .B l a c k w e ll S c i. P u b l . O x f o r d a n d E d i n b u r g h .

6 5 W a l l a c e A . E l G a z z a r A . a n d S o uf i S . M . 1 96 8 T h e r o l e o f c a l c i u m a s a m i c r o n u t r i e n t a n d i tsr e l a t i o n s h i p t o o t h e r m i c r o n u t r i e n t s . T r a n s . 9 t h I n t . C o n g r . S o i l S c i . A d e l a i d e A u s t r a l i a 2357 366.

6 6 W a l l a c e A . F r o l i c h E . a n d L u n t O . R . 1 96 6 C a l c i u m r e q u i r e m e n t o f h i g h e r p l a n t s . N a t u r eL o n d o n 20 9 6 3 4 .6 7 W h i t e R . E . 1 9 69 O n t h e m e a s u r e m e n t o f s o i l p H . J . A u s t . I n st . A g r i c . S ci. 3 5 3 1 4.

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