Plant and Soil 45, 49-56 (1976) Ms. 2769

C A N O P Y A N A L Y S I S ON T H E R E L A T I O N S H I P S

B E T W E E N L E A F A R E A I N D E X A N D P R O D U C -

T I V I T Y IN L O W L A N D RICE, ORYZA SATIVA, L.

by B. VENKATESWARLU, P. KOTESWARA RAO and A. V. RAO

All-India Coordinated Rice Improvement Project Rajendranagar, Hyderabad-500030, India

SUMMARY

Different densities of populations were created under field conditions at two levels of N and canopy analysis was made with variety Sona on different growth parameters governing productivity. The relationships between leaf area index (LAI) and dry matter, grain yield and grain number were quadrat- ic. LAI v s panicle number and grain number v s grain yield relationships were linear. The panicle number and grains per panicle are found to be compensato- ry for one another. The intercepting points of the two appear to be around 400 panicles per square metre with a grain range of 90-100 per panicle.

INTRODUCTION

Though the dwarf rice types of recent origin have exhibited higher yield potential, realisation of the same was involving skilful manage- ment which should be guided by the analysis of a given situation. The components of a situation could be type of soil, environment, variety and management. Since the maj or change was in the variety, it was imperative to know the yield determining factors. The yield is governed by yield components such as panicle number per unit area, grain number per panicle, percentage of maturity and 1000- grain weight. Some correlations were reported between panicle number and yield and more consistently between grain number per unit area and yield 2

The panicle development and grain filling are dependent on the support received from the leaves. Thus LAI decides the level of crop performance in a given situation. The relationship between LAI and

50 B. VENKATESWARLU, P. KOTESWARA RAO AND A. V. RA0

yield turned out to be optimum type in typical tall indicas and ceil- ing type in dwarfs 1. However, information on the intercepting points between panicle number and grains per panicle would be a pre-re- quisite to plan out suitable strategies for exploiting yield potential. Therefore, the present effort is aimed to elucidate the interrelation- ships between LAI and productivity as governed by panicle number and grains per Panicle.

MATERIALS AND METHODS

25-aay old seedlings of Sona were transplanted in 5 × 4 m plots adopting spacings of 102, 202, 302, 502 and 1002 cm. Two levels of fertility - I00 and 200 kg N/ha - were included in the trial. P and K were applied basally at 25 and 40 kg/tla for 100-N plots and 50 and 80 kg/ha for 200-N plots, respective- ly. Fifty per cent of N was applied 15 days after planting and the rest split into two doses of 25% each. The final dose of N was applied around panicle initiation. The present experimental design was aimed to manipulate LAI and tile panicles over a range of levels. The trial was conducted during kharif 1973 and rabi 1974, with 4 replications and laid out on split plot design, with N levels as major plots and spacings as sub plots.

Similar type of study was also conducted on coordinated basis during kha- rif 1973, at Cuttack (Orissa State), Mandya (Karnataka State) and Pat tambi (Kerala State) stations.

LAI was worked out at flowering with automatic leaf area meter, Model AAM-5 of Hayashidenko Co. Ltd., Tokyo. Tile dry matter, panicle number, grain yield, spikelets and grains per manicle were determined by adopting standard methods.

RESULTS AND DISCUSSION

L A I and dry matter

LAI increased with increased density of population during both the seasons (Table 1). The total dry matter per square metre showed a quadratic fit (Fig. 1) when plotted against LAI in both the seasons. Although quadratic equations could be fitted to data from different locations, the dry matter seemed to be increasing with increased LAI. The dry matter production did not differ considerably be- tween the seasons, although the panicle production greatly differed (Fig. 2), thereby suggesting that partitioning of dry matter to panic- les was greater during rabi.

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CANOPY ANALYSIS IN LOWLAND RICE

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51

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5 2 B. VENKATESWARLIJ , P. KOTESWARA RAO AND A. V. RAO

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Khar i f 73 1000

~800 i=r)

_~ 600

"~" 400

• ~ 200 (..,b

/ /

u i I I I I I I I

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Rabi 74

ol 3 166 ( 6 Rabi 74

,," O

/ Leaf area index

Mean

I I I I I ! f . 0,½34;6;;;10,,12 Mean

lOON ~" 200N .....

t t I l t ~ !

o, 23 6 o ; s,o111

Fig. I. Relationships between LAI and total~dry~matter and between LAI and grain yield.

Mean : The curves indicate the mean of four locations for kharif 1973.

L A I and grain yield

The relationship is quadratic (Fig. 1) in both the seasons and at different centres. But the critical LAI for yield differed which was around 4-5 during kharif and 5-6 in rabi (Fig. 1). Yield did not pro- portionately increase in kharif along with LAI particularly at 200-N level suggesting that the cultivar did not respond to LAI changes in yield. But during rabi, higher LAI influenced the yield consider- ably. While the Intern. Rice Research Institute 2 reported pla- teauing in yield with IR 8, Sona returned decreased yields after an optimum LAI which is between 6 and 8 at Hyderabad.

L A I and grain number per square metre

The grain number was falling beyond 4-5 LAI during kharif and 5-6 during rabi at 100N, while at 200-N, the fall in grain number was beyond 6 LAI and during rabi, the relationship was linear.

Grains per panicle is greater during kharif than rabi indicating that higher yield recorded during rabi is mainly due to higher panicle number, since grain number is fairly stable (Table 1).

L A I vs panicle number

Panicle number showed linear relationship with -LAI (Fig. 2)

CANOPY ANALYSIS IN LOWLAND RICE 53

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Fig. 2.

Kharif'73 ~ - - /" .... 100N Means

J 0 1 2 3 4 5 6 7 8 9 1 0 0 1 2 3 4 $ 6 7 8 9 1 0 0 1 2 3 4 5 6 7 B 9 1 0 1 1 1 2

Leaf area index

Kharif '73 Rabi'74

/ jf

Mean

i | J i I ~ r i i i i r i I I ! ~ I I I 2 3 a 5 6 0 I 2 3 4 5 6 " 7 0 J _2 3 4 S b

Panicle number(hundreds per m 2)

Rela t ionsh ips b e t w e e n LAI a n d panic le n u m b e r a n d be tween panic le n u m b e r a n d gra in yield.

M e a n : T he curves i nd i ca t e t h e m a n of four loca t ions for kha r i f 1973.

during both the seasons and at different centres. Apparently, since LAI depends on tillering, it was but natural to get such a relation- ship. Panicle number was much influenced by N-level during kharif rather than during raN. But the influence of spacings was quite contrasting. The increase ill panicle number per square metre from 202 to 102 cm spacing indicates that dependability in panicle number was greater at higher densities of population, particularly beyond 25 hills per square metre (Table 1).

Panicle number vs yield

A quadratic equation was again fitted (Fig. 2) between the two parameters not only in both seasons but at the different locations. The yield is related to panicle number upto 400 during kharif, but during rabi, yield increased upto 500 panicles and later there was a fall beyond which the yield is not necessarily related to panicle num- ber. Across centres, the yield increased even beyond 400-500 pa- nicles per square metre, exhibiting genotype's better expression with favourable environment. The influence of spacings was signi- ficant; closer the spacings higher is the panicle number per square metre.

~ 4 B. V E N K A T E S W A R L U , P. KOTESWARA RAO AND A. V. RAO

Panicle number vs grains per panicle The data of both seasons and different locations showed inverse

relationship between the two factors (Fig. 3). Clearly increased panic-

~'~56 t Kharif'73

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Leaf area index Rabi 74

4"

%

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Mean

i i i i i i i i • • , •

O I 2 3 4 5 6 7 a 9 1 0 1 1 1 2

Mean

• 100N o ooN

• , , . . . . . i t • i

o l 2 3 4 s 6 7 8 9 1 0 . J 2 number ( in h u n d r e d s )

Fig. 3. Relationships between LAI and grain number and between panicle number and grains per panicle.

Mean: The curves indicate the mean of four locations for kharif 1973.

le number was associated with reduced grain 'number and vice versa, indicating the existence of compensatory mechanisms. These find- ings further confirm the earlier I R R I 2 results• The variation in grain number per panicle from 102 to 1002 cm spacings was 92% at 100N and 109% at 200-N level during Kharif (Table 1). Similarly, the values at 100 and 200-N levels were 38 and 36 per cent respectively during rabi. I t clearly suggests that stability in grains per panicle is the key factor for further transformation in rice.

Grain number vs grain yield Since panicle number and grains per panicle compensate for each

other, none of them are an adequate measure of yield• The grain num- ber per unit area which is a product of these two factors seemed to be a dependable or reliable measure o f yield since the relationship between the two is linear (Fig. 4) not only among the seasons but at different locations. Thus these results lend support to the earlier findings of the Intern. Rice Research Institute s

CANOPY ANALYSIS IN LOWLAND RICE 55

Intercepting points o/ panicle number and grain number

The curve (Fig. 4) clearly shows tha t the grain n u m b er 95-100 per panicle in te rcep ted with the panicle n u m b er when the la t te r

I1OO

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0 to 2030405060 70 0 I0 203040 506070 G i a i n n u m b e r I o 3 p e r m 2

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:,, ~ - ' ~ ,25 '5

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x x l O O N o .... o 2 O O N • , l O O N . . . . . * 2OON

Fig. 4. Relationship between grain number per square metre and grain yield per square metre, and Intercepting points between panicle number per square

metre and grain number per panicle. Mean : The curves indicate the mean of four locations for kharii 1973.

Legend: Grains/panicle × × 100 N O - - - O 200 ~"

Panicle no./m ~ • • 100 N • - - -O 200 N

was a round 370-400 per square met re during kharif. Similar rela- t ionship was also observed during rabi except ing for slightly lower grain number at 200-N. These in tercept ing points suggest t ha t the va r i e ty has a l imitat ion of 400 panicles per square met re when the grain number is a round 90-100 per panicle. Cultivars with grea ter panicle number bu t s tabi l i ty wi th the same range of grain n u m b er or vice versa would give higher yields. Therefore , in fu ture variet ies aiming for s tabi l i ty in grains per panicle is highly desirable. Another point of impor tance is to get higher yields o n e has to hold grain number and manipula te panicle number or vice versa as bo th of t hem appear to be flexible or compensa te for each o ther over the ranges obta ined in the present studies. Higher yields therefore ,

56 CANOPY ANALYSIS IN LOWLAND RICE

depend on the finer tuning or manipulation of these two factors. How to achieve them is a mat ter of greater detail involving several parameters of production technology. The approaches desired like the application of nutrients at a proper stage to boost up tiller num- ber and later application of fertilizers at an appropriate stage to enhance grain number holding the panicle number at a given level etc., are under study. Further, information on the genotypic va- riability among the different duration groups is being elucidated.

ACKNOWLEDGEMENTS

T he a u t h o r s are g ra te fu l to Dr. S. V. S. S h a s t r y and Dr. W. H. F r e e m a n , P r o j ec t Coord ina to r a n d J o i n t Coordina tor , respect ive ly , of t h e Al l - Ind ia Coord ina ted Rice I m p r o v e m e n t Pro jec t , H y e r a b a d , for p r o v i d i n g facil i t ies a n d necessa ry help in ca r ry ing ou t t h e s tudies . Gra te fu l t h a n k s are also due to all t h e coopera tors i n v o l v e d in t h e c o n d u c t of th i s t r i a l a t t he o t h e r centres .

Received 28 February 1975

REFERENCES

1 T a n a k a , Akira , Efficiency of respiration I n Rice Breeding. The International Rice Research Institute, Philippines, 483-98 (1972).

2 International Rice Research Institute, Annual Report, p. 17-45 (1968).