response of rice plants to constant and cyclic submerged soil temperature regimes

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Plant and Soil 34, 493-496 (1971) Ms. 1466 SHORT COMMUNICATION Response of rice plants to constant and cyclic submerged soil temperature regimes Summary An experiment was conducted ill controlled temperature water baths to compare the response of rice plant of variety Taichung (Native) 1 to cyclic soil temperature regime of 32°C/20°C and constant soil temperature regime of 26°C. These temperature regimes are reported to be highly favourable for rice growth and therefore selected for comparison. The plants growing at 32°C/20°C showed some superiority over those growing at 26°C in respect of root growth and tiller development. The grain yield at 32°C/20°C was higher which resulted from larger number of tillers and panicles than at 26°C, although the difference ill other yield character- istics was not appreciable. NPK content of grains, straw and roots did not vary appreciably between 32°C/20°C and 26°C but the total uptake of these nutrients varied because of the difference in total dry matter production. The results suggest that the development of rice plants, particularly in reproductive phase, is practically as good at 26°C as at 32°C/20°C and there seems to be no sufficient ground for generalising the phenomenon of diurnal thermoperiodicity for rice plants. Introduclion Earlier studies 2 3 indicated that rice plant is highly responsive to sub- merged soil temperatures. These studies were made at constant temperatures. Since the temperature variation under natural conditions is of cyclic nature, a comparison of these results with that of the natural condition would not be valid. Recently tile authors 1 conducted studies on the effect of cyclic soil temperature regimes on rice growth and found that 32°C/20°C cycle was most favourable for growth of rice plant. A cyclic soil temperature regime simu- lating the natural pattern would be justified on the ground that it allows a valid comparison of the results with that in the field but it needs clarification whether a diurnal temperature cycle as under natural condition is ideal for the growth of rice plant. In this study, the response of rice plant of variety Taichung (Native) 1 to cyclic temperature of 32°C/20°C and constant temper- ature of 26°C was compared. The constant temperature regime of 26°C was selected for comparison because it is the mean of 32-20°C and is also reported to be a highly favourable temperature for rice growth 4

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Plant and Soil 34, 493-496 (1971) Ms. 1466

SHORT COMMUNICATION

Response of rice plants to constant and cyclic submerged soil temperature reg imes

Summary An experiment was conducted ill controlled temperature water baths to

compare the response of rice plant of variety Taichung (Native) 1 to cyclic soil temperature regime of 32°C/20°C and constant soil temperature regime of 26°C. These temperature regimes are reported to be highly favourable for rice growth and therefore selected for comparison.

The plants growing at 32°C/20°C showed some superiority over those growing at 26°C in respect of root growth and tiller development. The grain yield at 32°C/20°C was higher which resulted from larger number of tillers and panicles than at 26°C, although the difference ill other yield character- istics was not appreciable. N P K content of grains, straw and roots did not vary appreciably between 32°C/20°C and 26°C but the total uptake of these nutrients varied because of the difference in total dry matter production.

The results suggest that the development of rice plants, particularly in reproductive phase, is practically as good at 26°C as at 32°C/20°C and there seems to be no sufficient ground for generalising the phenomenon of diurnal thermoperiodicity for rice plants.

Introduclion Earlier studies 2 3 indicated that rice plant is highly responsive to sub-

merged soil temperatures. These studies were made at constant temperatures. Since the temperature variation under natural conditions is of cyclic nature, a comparison of these results with that of the natural condition would not be valid. Recently tile authors 1 conducted studies on the effect of cyclic soil temperature regimes on rice growth and found that 32°C/20°C cycle was most favourable for growth of rice plant. A cyclic soil temperature regime simu- lating the natural pattern would be justified on the ground that it allows a valid comparison of the results with that in the field but it needs clarification whether a diurnal temperature cycle as under natural condition is ideal for the growth of rice plant. In this study, the response of rice plant of variety Taichung (Native) 1 to cyclic temperature of 32°C/20°C and constant temper- ature of 26°C was compared. The constant temperature regime of 26°C was selected for comparison because it is the mean of 32-20°C and is also reported to be a highly favourable temperature for rice growth 4

494 SHORT COMMUNICATION

Materials and methods

T h e r m a l l y in su la t ed w a t e r b a t h s equ ipped w i t h h e a t i n g an d cooling sys t ems were used for m a i n t a i n i n g t e m p e r a t u r e s . C o n s t a n t t e m p e r a t u r e was es tab- l i shed w i t h t he accuracy of ± 1 °C b y m e a n s of a c o n t a c t t h e r m o m e t e r wh ich was connec t ed to h e a t i n g a n d cooling un i t s t h r o u g h a j u n c t i o n box. Cyclic t e m p e r a t u r e was m a i n t a i n e d b y m e a n s of t i m e r t y p e t h e rmo reg u l a t o r . The ope ra t ion m e c h a n i s m was such t h a t i t a l lowed t h e sys t em to pause for a ce r t a in per iod be tween t he opera t ions . The t ime lag b e t w e e n t h e opera t ions was cont ro l led b y a k n o b set a t a level p r e d e t e r m i n e d b y tr ial . Tile k n o b se t t i ng was per iodica l ly a d j u s t e d so t h a t t h e m a x i m u m t e m p e r a t u r e was a t t a i n e d a t a b o u t 4 p .m. The h e a t i n g s y s t e m was t h e n swi tched off a n d t h e cooling sys t em was s t a r t e d which also ope ra t ed t h r o u g h a t imer . T h e cooling s y s t e m was also connec ted to a c o n t a c t t h e r m o m e t e r set a t t h e m i n i m u m t e m p e r a t u r e level. The m i n i m u m t e m p e r a t u r e was a t t a i n e d a t a b o u t 5 a .m. which r e m a i n e d a lmos t s t e a d y t i l l t h e h e a t i n g s y s t e m was swi tched on a t a b o u t 7 a.m. The cyclic t e m p e r a t u r e was a t t a i n e d w i t h an accuracy of ± 1.5°C.

Rice p l a n t s of a pho to in sens i t i ve Ta iwanese indica var ie ty , T a i c h u n g (Native) 1 were g rown in m e t a l pots . The t e m p e r a t u r e t r e a t m e n t s were im- posed b y p lac ing 4 p o t t e d p l a n t s w i t h one p l a n t pe r p o t in each w a t e r ba th . W a t e r level was m a i n t a i n e d a t a d e p t h of 5 to 7 cm above t h e soil surface. The ave rage aer ia l t e m p e r a t u r e of t he green house va r i ed b e t w e e n 25.2°C to 37.2°C d u r i n g t he per iod of t he expe r imen t .

M e a s u r e m e n t of t i l le r deve lopmen t , g rowth du ra t ion , g ra in yield charac- ter is t ics a n d roo t g rowth was recorded. Chemical ana lys is of grains, s t r a w a n d roots was done for c o n c e n t r a t i o n of n i t rogen , p h o s p h o r u s a n d po tass ium.

Resul ts and discussion

The effects of cyclic a n d c o n s t a n t soil t e m p e r a t u r e regimes on g rowth a n d yield charac te r i s t i c s of rice p l a n t s are p re sen ted in Tab le 1. T h e cyclic soil t e m p e r a t u r e reg ime p roduced more t i l lers t h a n did t h e c o n s t a n t t e m p e r a t u r e regime. Ea r l i e r work b y T s u n o d a a showed t h a t cooler n i g h t t e m p e r a t u r e

TABLE I

Growth and yield characteristics of rice plants growing at 32°C/20°C and 26°C (average values)

32°C/20°C 26°C

Growth duration, days 94.2 93.0 Number of tillers 41,5 37.0 Number of panicles 41.5 36.0 Number of spikelets per panicle 64.6 64.0 Spikelet sterility, % 31.2 29.8 Hundred grain weight, g 1.94 2.0 Grain yield, g 35.78 32.35 Dry weight of roots, g 18.65 16.50 Total dry matter, g 99.41 89.75

SHORT COMMUNICATION 495

favours t i l ler development . His explana t ion was tha t high night t empera tu re increased respirat ion loss and so reduced N A R whereas high day t empera tu re increased N A R by increasing the ra te of photosynthesis . No twi ths tand ing the accelerated katabol ic process dur ing night at 26°C, the ear emergence was not delayed. I t was ra ther has tened by about one day (Table 1). This could happen probably because of the fact t ha t some par t of g rowth is regula ted by auxin like substances which do not enter di rect ly into respi ra tory metabol ism.

The d ry weight of roots was smaller by about 12 per cent at 26°C than at 32°C/20°C. This also tends to ver i fy the previous assumpt ion of increased respirat ion loss dur ing night at 26°C.

The larger root sys tem at 32°C/20°C implies a greater absorpt ion of nutr i - ents and in consequence, sustained a larger top growth. Because of ti le differ- ence in ti le to ta l dry m a t t e r p roduc t ion be tween 32°C/20°C and 26°C, the to ta l up take of nut r ien ts varied, a l though the difference in N P K conten t of grains, s t raw and roots be tween 32°C/20°C and 26°C was no t appreciable (Table 2).

TABLE 2

Concentration and uptake of N, P, and K in rice plants growing at 32°C/20°C and 26°C (average values)

Concentration, % Soil

temperature N P K regimes, °C

Grains Straw Roots Grains Straw Roots Grains Straw Roots

32/20 1.410 0.691 0.462 0.246 0.060 0.046 0.545 2.076 1.989 26 1.405 0.710 0.470 0 . 2 5 0 0.060 0.050 0 . 5 5 0 2.090 1.970

Uptake, mg

N P K

32-20 902.2 124.6 1801.4 26 822.1 113.6 1357.75

The higher grain yield a t 32°C/20°C was ev iden t ly due to a larger number of ti l lers and panicles. The difference in the number of spikelets per panicle, spikelet s ter i l i ty and hundred-gra in weight was not appreciable.

The favourable effects of cyclic t empera tu re regime on t i l ler deve lopment and root growth seem to be media ted th rough the direct effects of lower n ight t empera tu re . No advan tage of lower n ight t empera tu re was, however, ob- served in the reproduc t ive phase of the p lan t deve lopment .

496 SHORT COMMUNICATION

Acknowledgement

This s t u d y was c o n d u c t e d in t h e D e p a r t m e n t of Agr i cu l tu r a l Eng inee r ing , I n d i a n I n s t i t u t e of Technology, K h a r a g p u r (India) .

T. N. GHAUDHARY Punjab Agricultural University, Ludhiana (India)

B. P. CHILDYAL U.P. Agricultural University, Pant Nagar (India)

Received February 24, 1970

Re]erences

1 C h a u d h a r y , T. N. and Gh i ldya l , B. P., Agron. J. 62, 281-285 (1970). 2 M a t s u s h i m a , S., et al., Proe. Crop Sci. Soe. Japan 33, 53-58, 135-140 (1964). 3 T s u n o d a , K., Bull. Nat. Inst. Agr. Sci. 11, 75-174 (1964). 4 Ueki, K., Proc. Crop Sei. Soc. Japan 29, 75-78 (1960).