Plant and Soil 39, 555-565 (1973) Ms. 2099

C H E M I S T R Y OF S U B M E R G E D SOILS

A N D G R O W T H A N D Y I E L D OF R I C E

I. BENEFITS FROM SUBMERGENCE

by A. ISLAM* and W. ISLAM** Department of Soil Science, University of Dacca, Bangladesh

SUMMARY

Submergence caused a small initial decline followed by a gradual increase in pH values of soil solution. At field capacity too, the pH showed similar trends but the changes were much less pronounced. The redox potential of soil solution decreased sharply and assumed negative value after five weeks of submergence. At field capacity, however, more or less similar values were maintained throughout the growing period of rice plants. Submergence caused an increase in concentration of both water-soluble iron and manga- nese. The concentration of water-soluble phosphorus increased upon sub- mergence, reached maximum and then decreased. The changes in phosphorus concentration at field capacity were irregular. The concentration of nitrate decreased under submerged condition but the case was reverse at field ca- pacity. Submergence resulted in an accumulation of ammoniacal nitrogen. At field capacity also the concentration of ammonical nitrogen increased with time, but the increase was much less pronounced. Submergence caused an increase in the concentration of calcium, magnesium, and potassium in the soil solution. The nitrogen, phosphorus, potassium, calcium, and iron contents of rice plants grown under submerged condition were higher than those in plants grown at field capacity condition.

The plants grew better under submerged condition than at field capacity condition. The yield of grain was better under submerged condition than that at field capacity condition. Better growth and yield was associated with higher uptake of nutrients by rice plants grown under submerged con- dition.

INTRODUCTION

Although rice is almost everywhere grown on submerged land and in the Orient submergence of the land has for centuries been assumed to be a sine-qua-non for successful rice culture, no scien-

* Associate Professor, and ** Lecturer, Department of Soil Science, University of Dacca, Bangladesh.

556 A. ISLAM AND W. ISLAM

tific evidence has been adduced in suppor t of this prac t ice ( P o n n a m p e r u m a is). The evidence is clear t h a t submergence of

the soil is beneficial to rice. But , apa r t f rom the t h r eadba re expla-

na t ion t h a t submergence helps to control weeds, not a single val id reason has been adduced b y workers in the field of rice research for the necessi ty of this prac t ice is. V a n D e G o o r 5, cites some

advan t ages of the prac t ice b u t t hey relate s t r ic t ly to field con- ditions. G r e e n 6, f rom a s t udy of f looded organic soils in Flor ida

also summar ises some of the possible benefi ts of submergence of the soil in rice culture. Bu t these are benefi ts of a long t e rm charac- ter. L i n 7, on the basis of nu t r i en t solution studies, suggested t h a t the beneficial effects of submergence migh t be associated wi th grea ter ava i lab i l i ty of iron. S u b r a h m a n y a n and associates 17,

felt t h a t i t migh t be due to increased ava i lab i l i ty of silica.

Wi th these views in mind, a greenhouse expe r imen t was per-

fo rmed to s t u d y (a) the chemical and phys icoehemica l changes t h a t t ake place in submerged soils and (b) thei r u l t ima te bear ing

on the g rowth and yield of rice.

METHODS AND MATERIALS

Soil samples representing 0-6" depth and differing in pH, texture and chemical properties (Table 1) were collected from different parts of Bang- ladesh, namely Parbata, Dacca (Red soil tract); Kashore, Mymensingh (Brahmaputra Alluvium); Assadpur, Rangpur (Teesta tract); Chanchora, Jessore (Gangetic Alluvium), Bayra Khulna (Coastal saline tract) and Rup- tali, Barisal (Coastal saline tract). A greenhouse experiment was set up in the Department of Soil Science, University of Dacca with a total of 36 glazed silica pots arranged in completely randomized design. Two weeks old seedlings of rice (Oryza sativa variety 'Boro') were transplanted at the rate of 3 plants per pot. Each soil was replicated thrice in both field capacity and submerged conditions. The soils in pots at field capacity received suf- ficient distilled water to bring the soil just to field capacity and every effort was made to keep the moisture content at this level during tile experiment by tile addition of distilled water whenever needed. The soils under sub- merged condition were kept continuously submerged and 2" standing water in these pots was maintained by the daily addition of distilled water. The soil solutions used for analysis were the percolates collected from the bottom of the pots at submergence and the displaced soil solutions from the pots at field capacity, they were collected in the strict absence of air in 500-ml erlenmeyer flasks which have previously been filled with nitrogen. The flasks were then stored in a refrigerator till analysis. The soiI solutions were

BENEFITS FROM SUBMERGENCE IN RICE GROWING

TABLE 1

Texture class and chemical analyses of soil

557

Soils Textvral pH Org. Total ExchangeabIe nutrients class matter phosphor- (in ppm)

% us (ppm) N Ca Mg K

Kashore Loam 7.7 1.9 218.0 85.0 540.0 680.0 50.4 Assadpur Sandy loam 7.4 2.3 388.0 90.0 420.0 750,2 50.9 Chanchora Sandy clay 7.8 1.3 312.0 58.1 570.0 600.2 41.7

loam Bayra Clay loam 7.1 2.9 401.0 120.0 640.0 860.0 60.0 Ruptali Clay loam 6.0 3.0 480.0 135.0 660.3 S60.0 41.6 Parbata Sandy clay 5.5 1.5 412.0 71.8 460.4 387.9 20.0

loam

collected at the in tervals of 0, 1, 3, 5, 9, and 13 weeks f rom the s ta r t of the exper iment and were analysed for the following {a) p H ; (b) redox potent ia l (Eh) ; (c) n i t ra te ni t rogen; (d) a m m o n i u m ni t rogen; (e) phosphorus ; (f) calci- um; (g) magnes ium; (h) potass ium; (i) iron and (j) manganese. The plants were f inal ly harves ted at m a t u r i t y and thei r weights were recorded, The d ry weights of grains produced were also noted. P lan t samples were t h a n analyzed for (a) n i t rogen; (b) phosphorus; (c) calc ium; (d) magnes ium; (e) po tass ium; (f) iron and (j) manganese.

Labora to ry methods adopted for analyt ica l de te rmina t ions are brief ly de- scribed below:

1. S o i l a n a l y s i s . The mechanica l analysis was done by the hyd rome te r me thod according to P i p e r 11. Organic carbon was de termined volume- t r ica l ly by wet oxidat ion me thod as devised by W a l k l e y and B l a c k is Exchangeable calcium, magnes ium and po tass ium were de termined on the normal neutra l a m m o n i u m aceta te leachate of the soil by using f lame photo- meter , p H was de termined by using the Pye p H meter .

2, S o l u t i o n a n a l y s i s . Ni t ra te and a m m o n i u m form of ni t rogen were de termined separa te ly f rom the soil solut ion following the me thod described by P i p e r 11. I ron was es t imated by the me thod of F o r t u n e and M e l l o n 4 Manganese was de termined by the me thod out l ined by W i l l a r d and G r e a t h o u s e 19, and la ter modified by P e e c h 9. Phospha te was analysed by a modif icat ion of the benzene- isobutanol me thod described by M a r t i n and D o r y s. Calcium, magnes ium and potass ium were de termined direct ly f rom the soil solution by using the f lame pho tome te r (sp. 900).

3. P l a n t t i s s u e a n a l y s i s . Ni t rogen in the dried p lan t t issue was de- t e rmined by using the me thod of P i e r c e and H a e n i s c h 10 and la ter modified by P r i n c e 12. Phosphorus conten t in perchloric acid ex t rac t of the dried tissue was measured following the me thod devised by F i s k e and S u b a r r o w a. Calciunl, magnesium, potass ium and iron were es t imated di- rec t ly in the perchloric acid ex t rac t wi th the help of a f lame pho tome te r

5 5 8 A. ISLAM AND W. ISLAM

(sp. 900). M a n g a n e s e w a s d e t e r m i n e d b y t h e m e t h o d of W i l l a r d a n d

G r e a t h o u s e 19 a n d l a t e r m o d i f i e d b y P e e c h 9

RESULTS AND DISCUSSION

The pH of soil solution (Table 2) first registered a slight decrease on submergence and then gradually increased and maintained a stable pH in the range 6.4 to 7.1. The initial decrease of 0.9 to 1.3 units in Ruptali, Bayra, Assadpur and Kashore soils were associ- ated with appreciably high organic matter and low iron content of the soil, while the decrease of 0.6 units in Parbata soil was associ- ated with high iron content. The subsequent increase in pH on submergence was associated with reduction of the soil. The pH of soil solutions collected at field capacity were more or less similar during the growing period of rice. It is evident from the experi- mental data (Table 2) that the redox potential of soil solution de- creased sharply with time of submergence. The redox potential reached the negative value within 5 weeks of submergence. The redox potential of soil solution at field capacity varied from 121 to

TABLE 2

Changes in pH and rcdox potent ial of soil solution at submerged and field capacity condition with t ime

Soils Weeks from s ta r t

0 1 3 5 9 13

Sub. F.C. Sub. F.C. Sub. F.C. Sub. 7F.C. Sub. F,C. Sub. F.C.

pH

Kashore 7,0 7.0 6.2 6.5 5.7 6.8 6.7 6.7 7.1 6.9 7.1 6.8 Assadpur 7,3 7.3 6.4 7.2 6.1 7.2 6.2 7.3 6.4 7.4 6.4 7.3 Chanchora 7.4 7.4 7.1 7.1 6.6 7.0 6.9 7.4 7.2 7.3 7.0 7.3 Bayra 7.2 7.2 7.0 6.9 6.3 7.1 6.5 7.0 6.8 7.1 6.9 7.2 Ruptal i 7.5 7,5 6.8 6.7 6.4 6,7 6.6 6.8 6.7 6.8 6.8 6.9 Parba ta 6.2 6.2 6.0 6.1 5.6 6.3 6.3 6.4 6.6 6.4 6.5 6.4

Redox potential (mv)

Kashore 135 135 85 130 60 128 --20 134 --75 138 --78 140 Assadpur 130 130 75 127 40 130 --20 132 --82 138 --100 135 Chanehora 130 130 65 130 50 131 --25 130 --90 133 --98 138 Bayra 125 125 80 128 50 125 --17 130 --68 131 --80 135 Ruptal i 155 155 9g 155 70 150 --17 152 --72 152 --80 154 Parba ta 125 125 100 121 70 130 --10 129 --65 131 --77 133

B E N E F I T S F R O M S U B M E R G E N C E I N R I C E G R O W I N G 5 5 9

T A B L E 3

Changes in nitrate nitrogen, ammonium nitrogen and phosphorus in soil solution at submerged and field capacity condition with time

Soils Weeks from start

0 1 3 5 9 13

Sub . F.C. Sub . F.C. Sub . F.C. Sub . F.C. Sub . F.C. Sub . F.C.

NOs-N (ppm)

Kashore 0.O 0.0 8.4 3.4 5.2 3.9 3.7 4.2 2.1 6.1 0.0 6.1

Assadpur 0.0 0.0 12.6 1.4 7.4 3.3 5.2 4.6 3.4 8.9 0.8 I0.1

Chanchora 0.0 0.0 7.9 11.1 4.1 16.5 2.7 18.2 1.8 I9 .2 0.0 16.4 Bayra 0.0 0.0 12.0 4.1 8.5 8.0 5.0 10.2 4.0 12.5 0.0 9.5

Ruptali 0.0 0.0 7.0 4.6 5.8 5.0 4.0 5.6 2.9 6.8 1.2 5.0

Parbata 0.0 0.0 19.9 5.4 12.3 17.5 8.2 18.9 6.1 18.9 4.0 16.0

NHa-N (ppm)

Kashore 0.0 0.0 3.5 0.0 3.5 2.0 8.6 4.0 9.9 4.2 9.5 3.4

Assadpur 0.0 0.0 2.4 2.0 4 .2 2.9 7.0 4.9 8.0 4.0 8.0 3.5

Chanchora 0.0 0.0 0.0 2 . 7 3 .2 4.2 5.3 6.0 7.5 6.9 6.0 5.1

Bayra 0.0 0.0 2.1 3.0 4.9 4.9 7.2 5.1 8.9 7.8 7.5 5.6

R u p t a l i 0.0 0.0 0.0 1.1 2.6 3.5 5.9 6.6 11.6 8.3 10.0 6.1

P a r b a f a 0.0 0.0 8.7 4.0 13.0 5.9 18.3 7.5 22.1 7.2 19.9 6.9

P (ppm)

Kashore 0.2 0.2 0.7 2.2 1.8 2.0 2.4 1.9 3 .2 2.2 1.7 0.6

Assadpur 0.9 0.9 1.3 0.6 2.8 1.I 3.3 2.3 5.1 2.4 2.8 1.1 Chanchora 0.5 0.5 2.0 1.7 2.4 2.5 3.4 2.2 4.8 3.0 2.0 3.0

Bayra 0.7 0.7 1.2 0.9 2.1 1.8 3.0 1.0 5.4 1.7 3,2 0.8

Ruptali 0.0 0.0 0.6 1.3 1.5 0.5 4.0 1.0 8.9 1.2 4.1 0.8 Parbata 1.1 1.1 1.8 0.3 3.7 0.8 4.8 0.5 5.7 0.4 3.5 0.3

155 mv and maintained more or less similar values during the growing period of rice.

There was a progressive decrease in nitrate concentration with time from the 2nd week of submergence (Table 3). The rate of de- crease was most marked during the first 5 weeks. The decrease was then rather gradual and finally the solution collected from Kashore, Chanchora and Bayra soils attained a nitrate concentration below the level of detection by distillation method. P o n n a m p e r u m a 13, stated that the rapid loss of nitrate from the submerged soils was undoubtedly due to active denitrification. The nitrate concen- tration under field capacity condition, however, increased with time. The increase was more sharp during the first five weeks in the soils except Kashore, Assadpur, and Bayra soils where the

560 A. ISLAM AND W. ISLAM

increase was more pronounced during the period between 5th and 9th week. The increase in nitrate concentration was probably due to the mineralization of organic matter by micro-organisms. The gradual decline in nitrate concentration after 9 weeks may be attri- buted to the utilization of nitrate nitrogen by the rice plants. Sub- mergence caused an increase in ammonium concentration with time upto 9 weeks, the increase being more pronounced during the first five weeks of submergence (Table 3). The velocity and magnitude of the increase in ammonium concentration varied with different soils. The increase was most marked in the case of solution col- lected from Parbata soil, the peak value being 22.1 ppm. The corresponding values for other soils ranged between 7.5 to 11.6 ppm. The increase in ammonium concentration was due to the fact that the mineralization of organic nitrogen in the soil stopped at the ammonia stage because of the absence of oxygen to carry the process to nitrification. The small decline in ammonium concentration regis- tered after 9 weeks of submergence was attributed to their assimi- lation by the rice plants. The changes in ammonium concentration at field capacity also showed similar trends but the changes were much less pronounced. Phosphorus concentration under submerged condition first increased, reached maximum and then decreased (Table 3). The peak values in all the soils were reached in 9 weeks. The peak values varied with soils probably because of total phos- phorus contents and pH. The increase in solubility of water soluble phosphorus may be attributed to (a) release of phosphorus from organic matter, (b) increase in solubility of calcium phosphates as- sociated with the decrease in pH caused by accumulation of CO2 in the calcareous soils ( P o n n a m p e r u m a 15), (C) reduction of FePO4. 2H20 to the more soluble Fe3(PO4)2.3H20 (E r ik s son 2) and in- crease in solubility of FePO4.2H20 and A1PO4-2H20 caused by the increase in pH accompanying reduction of the acid and strongly acid soils ( P o n n a m p e r u m a 14) and (d) displacement of phosphate from ferric and aluminium phosphates by organic anions. The subsequent decrease in water soluble phosphorus following the peak may be caused by resorption of phosphate on clay and or aluminium hydroxide ( B r o m f i e l d 1) and adsorption, by precipitation and isomorphous replacement reactions, ( P o n n a m p e r u m a 15). Phos- phorus concentrations in percolates collected from soils at field capacity were irregular.

B E N E F I T S FROM SUBMERGENCE IN RICE GROWING 561

As is evident from the experimental data (Table 4) the calcium concentration increased rapidly with time of submergence, reached maxima and then decreased. The velocity and magnitude of the increase in calcium content to reach the peak value varied with different soils. In all cases, however, the peak values were obtained in the 9th week of submergence followed by a gradual decrease in calcium concentration. The increase was very much pronounced in solution collected from Chanchora soil, the maximum concentration being 199.5 ppm. Similar trends were noticeable at field capacity, the changes, however, were not very much pronounced, as com- pared to those under submerged condition. Magnesium concen- tration followed the similar trends as were noticed in case of calcium. But the peak values were reached within 5 weeks from the date of

TABLE 4

Changes in calcium, magnesium and potassium in soil solution at submerged and field capaci ty condition with t ime

Soils Weeks from s ta r t

0 1 3 5 9 13

Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C.

Ca (ppm)

Kashore 18.0 18.0 58.0 Assadpur 0.0 0.0 53.0 Chanchora 6.5 6.5 79.2 Bayra 13.8 13.8 65.0 Ruptal i 3.8 3.8 47.8 Parba ta 0.0 0.0 40.0

Mg (ppr~) Kashore 10.0 10.0 52.8 Assadpur 0.0 0.0 15.8 Chanehora 0.0 0.0 57.9 Bayra 3.0 3.0 50.7 Ruptal i 0.0 0.0 I8.3 Parba ta 0.0 0.0 24.8

K (ppm)

Kashore 9.9 9.9 16.6 Assadpur 15.0 15.0 21.7 Chanehora 2.5 2.5 26.2 Bayra 6.0 6.0 29.9 Ruptal i 5.0 5.0 9.4 Parba ta 0.0 0.0 35.0

44.4 74.5 58.2 95.2 65.7 103.0 75.0 79.0 53.0 11.4 58.0 24.0 59.3 52.5 67.6 62.2 43.9 40.2 47.6 127.6 50.2 154.1 64.5 199.5 80.0 180.8 89.6 53.0 112.4 59.1 122.9 70.7 152.6 78.0 125.5 36.4 19.5 57.2 35.3 62.5 37.7 69.7 55.4 53.5 45.1 9.5 52.4 21.8 65.5 30.3 65.0 57.2 33.2 26.9

42.0 75.0 55.8 109.2 77.0 80.4 44.7 68.0 28.0 16.1 27.1 30.0 38.4 33.7 35.4 25.5 26.6 18.5 26.5 81.0 34.3 109.2 53.1 98.7 45.0 51.0 27.9 31.2 89.1 42.5 120.8 61.6 91.5 28.5 44.3 20.2

3.5 27.1 30.1 48.3 41.9 36.6 31.4 15.5 11.8 2.7 34.5 3.5 75.4 23.3 52.6 18.0 25.0 16.4

13.5 39.9 21.5 72.0 45.0 115. I 78.8 85.0 69.1 18.0 45.2 25.0 79.9 51.2 102.0 84.2 70.0 69.1 18.0 65.0 34.4 108.9 70.1 155.0 112.3 80.0 99.5 21.0 78.0 41.2 124.1 70.1 178.2 124.2 100.0 125.2

9.4 35.2 17.2 76.3 45.0 98.0 67.3 78.0 61.0 25.1 86.5 48.0 145.0 86.5 185.3 135.0 139.0 129.0

562 A. ISLAM AND W. ISLAM

submergence or addition of water to bring the soils to field capacity (Table 4). Potassium concentrations also followed the same trend of increase as those of calcium and magnesium and the peak values were reached in 9 weeks (Table 4).

The average values of iron concentration of the percolates reveal a progressive increase with time of submergence (Table 5). The peak

TABLE 5

Changes in iron and manganese in soil solution at submerged and field capaci ty condition. with t ime

Soils Weeks from s tar t

0 1 3 5 9 13

Sub. F.C, Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C.

Fe (ppm)

Kashore 0.0 0.0 5.1 0.0 23.8 0.0 54.9 0.0 86.2 0.0 110.5 0.0 Assadpur 0.0 0.0 7.5 0.0 36.4 0.0 69.2 0.0 115,2 0.0 144.0 0.0

Chanehora 0.0 0.0 2.0 0.0 15.5 0.0 36.8 0,0 59.0 0.0 81.5 0.0 Bayra 0.0 0.0 5.2 0.0 20.2 0.0 40.1 0,0 68.6 0.0 89.0 0.0 Ruptal i 0.0 0.0 10.2 0.0 31.1 0.0 68.5 0,0 109.5 0.0 135.0 0.0 Parba ta 0.0 0.0 20.9 0.0 45.2 0.0 145.0 2.0 200.0 2.8 234.0 2.8

Mr~ (ppm)

Kashore 0.0 0.0 0.0 0.0 2.0 0.0 2.5 0.0 3.4 0.0 4.0 0.0 Assadpur 0.0 0.0 0.6 0.0 1.3 0.0 2.9 0.0 3.6 0.0 4.5 0.0 Chanchora 0.0 0.0 0.0 0.0 1.0 0.0 1.3 0.8 2.5 2.0 3.2 2.2 Bayra 0.0 0.0 0.0 0.0 0.1 0.0 0.1 0.0 0.5 0.0 0.8 0.0 Ruptal i 0.0 0.0 0.0 0.0 0.4 0.0 1.0 0.0 1.5 0.0 2.1 0.0 Parba ta 0.0 0.0 1.3 0.9 2.2 1.6 4.0 1.8 5.4 2.2 5.5 2.7

values ranged between 81.5 to 234.0 ppm attained on the 13th week, the highest and the lowest being respectively in Parbata and Chan- chora soils. P o n n a m p e r u m a 14 15 attributed this increase in con- centration of water soluble iron to the reduction of ferric hydroxide. Changes in iron contents in percholates at field capacity were only slightly noticeable in Parbata soil. However, in the other soils, percholates failed to extract any amount of detectable iron. The changes in soluble manganese under submerged condition followed the same general pattern as those of iron (Table 5). The increase in manganese concentration was most marked in the solution col- lected from Parbata soil. The peak values ranged between 0.8 ppm to 5.5 ppm. The percolates collected from soils at field capacity

B E N E F I T S FROM SUBMERGENCE IN RICE GROWING 5 6 3

TABLE 6

Average dry weights and grain weights of rice plants grown at submerged and field capaci ty condition

Soils

Dry weights Grain weights of rice plants (g) of rice plants (g)

Sub. F.C. Increase Sub. F.C. Increase in dr. in grain

wt. by wt. by sub- sub-

mergence mergenee

Kashore 2.15 0.93 1.22 0.34 0.34 0.0 a a a a

Rupta l i 3.03 1.82 1.21 0.44 0.21 0.23 a ab ab a

Bayra 5.42 2.22 3.20 0.99 0.14 0.85

b ab ab a Assadpur 5.09 1.49 3,60 1.03 0,28 0.75

b ab b a Parba ta 4.55 3.12 1.43 1.16 0,71 0.45

b b b a Chanehora 4.76 1.05 3.72 1.88 0.36 1.52

b a c a

LSD at 5% 1.73 1.73 1.73 LSD at 1% 0.66 0.66 0.66

Below the values reported in this table are one or more letters. These symbols are ranges of equivalence as defined by D u n c a n . Within columns of these tables numerical values with the same let ters below them are not s ta t is t ica l ly different at the 5% and 1% level.

were extremely low in soluble manganese. The percolates collected from Kashore, Assadpur, Bayra, and Ruptali soils contained manga- nese beyond the traceable amount.

Chemical composition o/ rice plants The nitrogen, phosphorus, potassium, calcium, iron, and manga-

nese contents of rice plants grown on soils kept at submergence were higher than those in plants grown at field capacity (Table 7). These constituents also varied quite considerably with soils at the same moisture level. To relate these variations with nitrogen, phos- phorus, potassium, calcium, magnesium, iron and manganese in soil solutions collected at the end of 3rd week from pots both at sub- mergence and field capacity correlation studies were made following the methods devised by S n e d e c o r is. Significant positive corre-

564 A. ISLAM AND W. ISLAM

TABLE 7

Average nitrogen, phosphorus, potassium, calcium, magnesium, iron and manganese contents of the aerial vegetative portion of the rice plants grown on soils at submerged

and field capacity conditions. (Results expressed in per cent)

Soils N t ' K Ca Mg Fe Mn

Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C. Sub. F.C.

Kashore 1.8 1.0 0.5 0.3 0.5 0.5 0.7 0.7 0.3 0.3 30.1 20.0 4.0 0.5 Assadpur 1.3 1.1 0.5 0.5 0.6 0.6 0.8 0.4 0.3 0.3 22.0 21.6 12.2 1.1 Chanehora 1.6 1.6 0.5 0.4 0.5 0.5 1.2 0.8 0.3 0.3 24.2 20.9 2.1 1.8 Bayra 1.6 1.2 0.3 0.2 0.4 0.2 0.9 0.9 0.3 0.3 23.2 18.7 2.1 1.8 Ruptali 1.5 0.9 0.5 0.2 0.1 0.1 0.8 0.8 0.3 0.3 21.3 10.5 6.4 1.5 Parbata 1.7 1.4 0.3 0.2 0.2 0.1 0.8 0.7 0.3 0.3 23.2 20.5 14.9 12.8

lation at 1% level were obtained between nitrogen and manganese in soil solution and those in plants. Significant positive correlations at 5% level were also obtained in case of calcium and phosphorus of soil solution at both submerged and field capacity condition and those in plants.

Dry weights o/rice plants Growth of rice plants as reflected from dry matter production

and grain yield on soils at submerged condition varied significantly. This was probably associated with variation in nutrients extracted in soil solution. At field capacity growth on parbata soil was only significantly better than growth on Kashore and Chanchora soils. The growth of rice plants, in respect of dry matter production, was better under submerged condition. Significant differences were no- ticed in case of Chanchora, Assadpur and Bayra soils only.

Received November 13, 1972

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