A NEW SYSTEM OF AUTOMATIC pH REGULATION IN SOLUTION CULTURE
*
Masumi M O R I T S U G U a n d T o s h i o K A W A S A K I
I n s o l u t i c i n c u l t u r e s ， t h e pH o f n u t r i e n t s o l u t i o n i s an i m p o r t a n t f a c t o r i n p l a n t g r o w t h . Many r e p o r t s ( 1 ‑ 8 ) have been p u b l i s h e d on t h i s problem.
Much c a r e i s r e q u i r e d t o keep t h e pH c o n s t a n t i n s o l u t i o n s o f p l a n t c u l t u r e s . S e v e r a l s y s t e ms have been u s e d : ( i ) a l a r g e volume o f n u t r i e n t s o l u t i o n t o a u n i t o f p l a n t ( 9 ) ， ( i i ) t h e f r e q u e n t a d j u s t m e n t o f s o l u t i o n pH o r t h e f r e q u e n t renewal o f n u t r i e n t s o l u t i o n ( 1 0 ) ， ( i i i ) f 1 0wing s o l u t i o n c u l t u r e s ( 1 1 ‑1 4 ) ， ( i v ) TRIS b u f f e r ( 1 4 ) ， and ( v ) i o n ‑ e x c h a n g e r e s i n s ( 1 5 ) t o keep t h e n u t r i e n t s o l u ‑ t i o n i n c o n s t a n t pH. However ， m a i n t a i n i n g t h e s o l u t i o n pH w i t h i n 1
.0 u n i t i n l o n g ‑ t e r m p l a n t c u l t u r e s i s d i 侃 c u l t ， even with t h e s e s y s t e m s . Although an a u t o m a t i c pH r e g u l a t o r was developed t o m a i n t a i n c o n s t a n t pH ( 1 6 ， 1 7 ) ， t h e a p p a r a t u s was complex and e x p e n s i v e a s i t was combined a pH meter and a u t o m a t l c t l t r a t o r s .
A new system f o r a u t o m a t i c pH r e g u l a t i o n was d e s i g n e d and assembled i n o u r l a b o r a t o r y u s i n g an i n d u s t r i a l pH i n d i c a t i n g c o n t r o l l e r and d u a l t i m i n g s w i t c h e s .
MA TERIALS AND METHODS
The main com 凹 n e n t su s e d i n t h e new a u t o m a t i c pH r e g u l a t o r we 叱 ( i )an i n d u s t r i a l pH i n d i c a t i n g c o n t r o l l e r (Toa De mpa ， HIC‑2) ， ( i i ) a c i r c u l a t i o n pump (Iwaki ， MD‑15 ， magnet pump) ， ( i i i ) d u a l t i m i n g s w i t c h e s (Omron ， TDV 仏 o r u n i t s o f timing s w i t c h e s ， when a wide r a n g e o f time s e t t i n g s i s n e c e s s a r y ) ， ( i v ) i n j e c t i o n pumps t o add a c i d o r a l k a l i n e s o l u t i o n (Mitsumi ， p e r i s t a l t i c m i n i ‑ pump ， o r m i c r o a e r a t i o n pump f o r g o l d f i s h c o n t a i n e r s ) ， ( v ) a r e s e r v o i r f o r n u t r i e n t s o l u t i o n ( a b o u t
231 volume)， and ( v i ) f o u r i n d i v i d u a l c u l t u r e v e s s e l s ( a / 5 0 0 0 凹 t ) .
Corn and cucumber were u s e d i n t e s t c u l t u r e s ， which were c a r r i e d o u t i n t h e summers o f 1 9 7 4 and 1975 i n a g l a s s h o u s e . Table 1 shows t h e c o m p o s i t i o n s o f t h e n u t r i e n t s o l u t i o n s . The n u t r i e n t s o l u t i o n s were renewed once a week ， and t h e i r o n s o u r c e was added every two d a y s . C u l t u r e p o t s were c ∞ l e d by r u n n i n g t a p water i n t h e daytime t o p r e v e n t a r i s e i n temperature i n n u t r i e n t s o l u t i o n .
The o u t p u t v o l t a g e o f t h e pH i n d i c a t i n g c o n t r o I l e r was r e c o r d e d by an a u t o m a t i c r e c o r d e r a t 20 m m p e r h o u r c h a r t s p e e d .
. D a t a p r e s e n t e d i n t h i s p a p e r w e r e p u b l i s h e d i n ] a p a n e s e i n t h e J o u r n a l o f t h e
Sci e n c e o f So a l i n d
M a n u r e . ] a p a n ， V o l .
48， p p
. 243・247(1977).凶 ( N H . ‑ N 5 mM)
KH. P O . K ， s O . ( C ) lNO;‑N 4mM
NH . H
J唱 .
~...・・4‘・ e ・~...寝台・・...ーー..~・ー・・・・包・
F e .
1.0 p p m . Zn 0
.0 5 p p m .
T a b l e 1 .
C o m p o s i t i o n o f n u t r i e n t 回 l u t i o n s
2 . 5 mM
1.0mM 1 . 5 mM
4 . 0 mM
1.0mM C a C l . MgSO.
B
Cu
(NH
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̲̲̲‑̲̲ 2
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̲1
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1.5 mM
( P ) I N O . ‑ N 5 mMl
ー0 . 5 p p m . 0
.0 2 p p m .
(
削
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0 . 5 p p m . 0 . 0 1 p p m . . F e w a s a d d e d e v e r y o t h e r d a y a s c i t r a t e .
RESULTS Outline 01 t h e A P . μ r a t u s
As i n d i c a t e d i n F i g . 1 ， the a p p a r a t u s was assembled by connecting f o u r c u l t u r e p o t s ， a n u t r i e n t s o l u t i o n r e s e r v o i r ， a c i r c u l a t i o n pump. two i n j e c t i o n pumps ， two d u a l timing switches ， e l e c t r o c l e s { f o r pH ， r e f e r e n c e and automatic temperature compen 則 i o n } ， and an i n d u s t r i a l pH i n d i c a t i n g c o n t r o l l e r .
The mechanical sequence o f t h e o p e r a t i o n i s d e s c r i b e d . ( i ) The pH o f t h e n u t r i e n t s o l u t i o n i s measured by a pH e l e c t r o d e . ( i i ) When t h e pH exceeds t h e determined range ， a r e g u l a t i o n s i g n a l i s generated by t h e pH i n d i c a t i n g c o n t r o l ‑ l e r . ( i i i ) The r e g u l a t i o n s i g n a l i s t r a n s p o r t e d t o t h e i n j e c t i o n pump through t h e d u a l t i m i n g s w i t c h . ( i v ) After a p r e
‑w a i t i n g time ( e s t a b ! i shed a s t h e f i r s t s t e p o f t h e d u a l timing s w i t c h ) ， the a c i d o r a l k a l i n e s o l u t i o n i s i n j e c t e d t o t h e r e s e r ‑ v o i r during t h e a d d i t i o n time ( e s t a b l i s h e d a s t h e second s t e p o f t h e d u a l timing s w i t c h ) . ( v ) The a d d i t i o n o f a c i d o r a l k a l i n e s o l u t i o n i s repeated i n t e r m i t t e n t l y u n t i l t h e pH r e t u r n s t o t h e determined pH r a n g e .
The f u n c t i o n o f t h e d u a l timing switch i s t o l i m i t the p r e ‑ w a i t i n g time and a d d i t i o n t i m e . The p r e ・ waitingtime i s s e t t o delay t h e s t a r t o f t h e a d d i t i o n o f a c i d o r a l k a l i n e s o l u t i o n ， j u s t a f t e r t h e i n d i c a t i o n needle o f t h e c o n t r o l l e r momentarily exceeded t h e determined pH r a n g e . The a d d i t i o n time i s s e t t o prevent t h e e x c e s s a d d i t i o n o f a c i d o r a l k a l i n e s o l u t i o n .
When a c i d o r a l k a l i n e s o l u t i o n i s added i n t o t h e r e s e r v o i r ， i t i s i m p o s s i b l e t o mix up uniformly a c i d o r a l k a l i n e s o l u t i o n and n u t r i e n t s o l u t i o n on t h e moment.
Therefore ， i f the r e g u l a t i o n s i g n a l o f t h e c o n t r o l l e r i
sd i r e c t l y t r a n s p o r t e d t o t h e
i n j e c t i o n pump without t h e d u a l timing switch ， and when t h e determined pH
range i s t o o narrow ， hunting phenomenon o c c u r s ， a s shown i n F i g . 2 ・ A. To
Automatic pH Regulation in Solution Cuture 173
Fig. 1. Block diagram of automatic pH re
思
11atorin solution l'ulture. 1. Industrial pH indicating controller 9. Alkali injection pump2. Range determination needle 10. Alkali reservoir
3. Indication needle 11. Nutrient solution reservoir 4. Electrodes. 12. Circulation pump 5. Timing switch (A).. 13. Culture pot 6. Timing switch (B).. 14. Aeration pipe
7. Acid injection pump 15. By.path and stirring flow in nutrient
回
lutionreservoir 8. Acid re日
rvoir• The
肥
arepH. refere即
eand automatic temperature compen岨
tioneledrodes.•• These switches are usually combined as a dual timing switch.
prevent thi~ phenomenon
，
it is necessary to increase the pH range by more than 1.0 at plf near 5.0. This broader pH range is similar to that of Tadano and Tanaka( 1 8 )
who worked with a simple system of automatic pH regulation in solution culture experiments.On the contrary. when the setting of the dual timing switch is appropriate. the sequence of the regulation becomes slow and accurate. as shown in Figs. 2・B and 3. Thus. the sequence is as follows: (i) Just after the regulation signal is generated. the pre.waiting time. which is su
侃
cientfor mixing nutrient solution and the acid or alkaline solution. starts and continues for the time determined as the first step of the dual timing switch. (ii) Acid or alkaline solution is injected during the addition time set as the second step of the dual timing switch. (iii) When the pH of nutrient solution does not return to the determined range. the pre‑waiting time starts again after the addition time. (iv)I .
n this manner. thePractical pH Regulation of Nutrient Solution with the A.
ρμ
ratusCorn plants were cultured in the summer of 1974. Culture solutions were (C) and (D) in Tabl.e 1. Two plants per pot were used in this experiments;
This means that eight seedlings were grown in the apparatus.
Du
ring this culture，
the pH of nutrient solution was recorded continuously by the automatic recorder.intermittent addition of the acid or alkaline solution is continued until the regulation signal is cut off. Accordingly
，
the pH of nutrient solution is regulated in high accuracy.In our apparatus
，
the optimal pre.waiting time was about one minute，
while the addition time should be adjusted according to various concentrations of acid or alkaline solution，
or to the kind of injection pump. It is recommended that the addition time is set for about 0.1 unit of pH shift per single addition.{
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byt h e a p p a r a t u s . The a r r o w i n d i c a t e s t h e t u r n i n g p o i n t i n pH t r a n s i t i o n .
1 7 5
The r e s u l t s o b t a i n e d with a b o u t 2 0 ‑ d a y ‑ o l d p l a n t s a r e shown i n F i g . 4 . The a d d i t i o n o f a c i d o r a l k a l i n e s o l u t i o n was a b o u t 20 times p e r h o u r . The a c c u r a c y o f pH r e g u l a t i o n i n t h i s s o l u t i o n c u l t u r e was w i t h i n 0 . 3 r e g a r d l e s s o f t h e d i r e c t i o n o f pH change which was a f f e c t e d by ammonium o r n i t r a t e i o n 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 . D i f f e r e n c e s p r o b a b l y e x i s t i n pH between c u l t u r e p o t s and r e s e r v o i r ， b e c a u s e pH was r e g u l a t e d i n t h e r e s e r v o i r and p l a n t s were grown i n c u l t u r e p o t s . However. even when p l a n t r o o t s were a lm os t f u l l y grown i n p o t s ， t h e d i f f e r e n c e was o n l y 0 . 1 t o 0 . 2 pH i n t h i s experiment a t a b o u t one l i t e r p e r minute o f f 1 0w r a t e .
I n t h e experiment d e s c r i b e d above ， a micro a e r a t i o n pump f o r g o l d f i s h c o n t a i n e r s was used a s t h e a d d i t i o n pump. I n o t h e r e x p e r i m e n t s . t h e u s e o f a p e r i s t a l t i c pump ， which enabled t h e a c i d o r a l k a l i n e s o l u t i o n t o be i n j e c t e d a t c o n s t a n t r a t e ， improved t h e a c c u r a c y o f pH r e g u l a t i o n by r e d u c i n g t h e pH
varia‑t i o n t o l e s s than 0 . 2 .
A p p l i c a t i o n ofthe Apparatus t o S t u d i e s o n D i f f e r e n t Nitrogen S o u r c e s
The a p p a r a t u s developed i n o u r l a b o r a t o r y was a p p l i e d t o t h e s t u d i e s on t h e e f f e c t s o f ammonium and n i t r a t e n i t r o g e n on p l a n t growth. C u l t u r e s o l u t i o n s used were (A) ， (8) and (D) i n Table
1.The pH o f n u t r i e n t
solutionwas r e g u l a t e d t o 5
.0 th r o u g h o u t t h e experimental p e r i o d . For
comparison with th e c u l t u r e method d e s c r i b e d above ， t h e pH o f t h e n u t r i e n t s o l u t i o n was r e g u l a t e d manually t o 5 . 7 on a l t e r n a t e d a y s . The former was c a l l e d auto‑pH s o l u t i o n c u l t u r e " . and t h e l a t t e r c o n v e n t i o n a l s o l u t i o n c u l t u r e " . The experiment was c a r r i e d o u t f o r a b o u t two weeks with cucumber p l a n t s ， whose growth u s u a l l y d e c r e a s e d by
ammoniumn i t r o g e n i n c o n v e n t i o n a l
solution culture.As shown i n P l a t e 1 ， p l a n t growth was very poor when ammonium n i t r o g e n
a l o n e was s u p p l i e d i n c
onventional so l u t i o n c u l t u r e ， while t h e growth d r a s t i c a l l y
improved i n auto‑pH s o l u t i o n c u l t u r e . The pH o f n u t r i e n t s o l u t i o n changed
s i g n i f i c a n t l y f o r two days i n c o n v e n t i o n a l s o l u t i o n c u l t u r e . In extreme c a s e s ， pH
reached 3 . 3 i n t h e n u t r i e n t s o l u t i o n o f ammonium n i t r o g e n a l o n e ， and 6 . 8 i n t h e
A
B
Plate 1. The effects of nitrogen sources on growth of cucumber plants under different culture method. A. Conventional solution culture. B. Auto.pH
田
lutionculture.nitrate‑type nutrient solution. In conventional solution culture
，
the poor growth of cucumbers in the ammonium‑type nutrient solution might be caused by increased concentrations of hydrogen ions in nutrient solutions.SUMMARY
An automatic pH regulator for solution culture was designed and assembled at low cost
，
using an industrial pH indicating controller and dual timing switches. This apparatus regulated pH highly accurately.The accuracy of pH regulation by only the industrial pH indicating control‑
Automatic pH Regulation in Solution Cuture 177
ler was unreliable
，
as pH varied by more than 1.0
unit near pH5 . 0 .
Whenever the regulation signal was generated
，
the first step of the dual timing switch allowed a pre，
wBiting time for mixing nutrient solution and the acid or alkaline solution， before the addition of acid or alkaline solution. Because of the acid or alkaline solution was apt to be excessive，
the second step of the dual timing switch was set mechanically so as to give about0 . 1
pH change per single addition. Using these two mechanisms，
the accuracy of pH regulation was highly improved，
i. e.，
the pH change of the nutrient solution was within 0.2 in long.term cultures of plants.With this automatic pH regulator
，
cucumber growth in ammonium.type nutrient solution was improved markedly，
and was similar to nitrate nutrition.LITERA TURE CITED
1. Wadleigh. C. H. and Shive. J. W. 1939. Base ∞ntent of corn plants as influenced by pH of sub. slrate and form of nitrogen supply. Soil Sci. 47: 273 ‑285.
2. Fauzy. H.. Overstreet. R. and .Jacobson. L. 1954. The influence of hydrogen ion concentration on cation absorption by barley r
∞
ts. Plant Physiol. 29・234‑237.3. McEvoy. E. T. 1964. The effects of pH and calcium on the uptake of radioph
田
phorusby flue・cured tobacco. Can. J. Plant Sci. 44: 28 ‑3
1 .
4. Andrenko. S. S. and Alekhina. N. D. 1967. Absorption of nitrate and ammonium forms of nitrogen by corn plants with different pH of the nutrient solution. Plant Physiol. (USSR) (English trans
・
lation) 14・108‑112.
5. Chaudhry. F. M. and Loneragan. J. F. 1972. Zinc absorption by wheat seedlings: 11. Inhibit
回
nby hydrogen ions and by micronutrient cations. Soil Sci. Soc. Am. Proc. 36・327‑331.6. Dodge. C. S. and Hiatt. A. J. 1972. Relationship of pH to ion uptake imbalance by varieties of wheat (Trit
釘
umvulg四
re).Agron. J. 64: 476ー481.7. Falade. J. A. 1972. Differentiation between bicarbonate effect and pH effect on cation accumula. tion by barley r∞，t5. Can.
J .
Bot. 50: 1567 ‑1570.8. Rubinstein. B. 1974. Effect of pH and auxin on chloride uptake into Avena coleoptile cells. Plant Physiol. 54: 835 ‑839.
9. Parker. F. W. and Pierre. W. H. 1928. The relation between the ∞ncentration of mineral ele
・
ments
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a四
lturemedium and the absorption and utilization of those elements by plants. Sol i Sci. 25: 337 ‑343.10. Matsumoto. H.. Wakiuchi. N. and Takahashi. E. 1968. Changes of sugar levels in cucumber leaves during ammonium toxicity. Physiol. Plant. 21: 1210 ‑1216.
11. .Johnston. E. S. and H08g1and. D. R. 1929. Minimum potassium level required by tomato plants grown in water cultures. Soil Sci. 27: 89 ‑109.
12. Andrew. C. S. and Pieters. W. H. J. 1962. A continuo
凶
nutrientflow technique for∞
mparat1ve studies in plant nutrition. Al昌
t.J. Agric. Res. 13: 1054 ‑1058.13. Reisenauer. H. M. 1969. A technique for growing plants at controlled levels of all nutrients. Sol i Sci. 108:
お
0.353.14. Tromp. J. 1962. Interactions in the absorption of ammonium. potassium. and
田
diumions by wheat r∞ts. Acta Bot. Neer. 11: 147 ‑192.15. Harper. J. E. and Nicholas. J. C. 1976. Control of nutrient solution pH with an ion exchange system: Effect on田ybeannodulation. Physiol. Plant. 38: 24 ‑28.
16. Asher. C. J.. Ozanne. P. G. and Loneragan. J. F. 1965. A method for controlling the ionic envト
ronment of plant r∞ts. Sol iSci. 1
∞ :
149 ‑156.17. Clement. C. R.. Hopper. M. J.. Canaway. R. J. and Jones. L. H. P. 1974. A system for measuring the uptake of ions by plants from flowing solutions controlled composition. J. Exp. Bot. 25: 81
‑99.
18. Tadano. T. and Tanaka. A. 1976. Comparison of adaptability to ammonium and nitrate among crop plants. (Part 1) Selective absorption between and responses to ammonium and nit悶teof crop plants during early growth stage. ‑Study on the comparative plant nutritionー J.Sc Si.oil Manure. Japan 47: 321 ‑328 (in.Jゅanese).
