P H O T O N I R V A C H A K

J o u r . l n d . S o c o P h o t o - l n t . & R e m o t e sensin~j Vo l . 13 No. 1, 1985

I N F E R R E D L E A F S E N E S C E N C E OF R I C E C R O P A N D ITS R E L A T I O N S H I P W i t H G R A I N Y IE ! D

P.P. N a g e s w a r a Rao ISRO H e a d q u a r t e r s , B a n g a l o r e

M .V . K r i s h n a Rao and R.S. A y y a n g a t N a t i o n a l R e m o t e Sensing A g e n c y , H y d e r a b a d

ABSTRACT

The p o s s i b i l i t y of d e t e c t i n g change in g reen c o v e r of r i ce c rop and i t s r e l a t i o n s h i p w i t h the g ra i n y i e l d was s t u d i e d us ing the s p e c t r a l da ta c o l l e c t e d by an a i r b o r n e s c a n n e r . The spec t t,al da ta in th~ f o rm of d i f f e r e n c e in v e g e t a t i o n i ndex over a 35 day i n t e r v a l , f r o m the t i m e of f l o w e r i n g ~ was obse rved to show good r e l a t i o n s h i p b e t w e e n change of g reen c o v e r (a measure of degree of senescence ) and g ra in y i e l d .

I N T R O D U C T I O N

Lea f senescence is one of the c r i t i c a l p h y s i o l o g i c a l processes t h a t d e t e r m i n e s the l ea f d u r a t i o n . D e v e l o p m e n t a l changes l ead ing to the f o r m a t i o n of g ra ins i n d u c e c o m p e t i t i o r , b e t w e e n the m a t u r e l eaves and the g r o w i n g shoot r e s u l t i n g in senescence . H o w e v e r , the deg ree of senescence depends on the g e n o t y p e and a b n o r m a l c r o p - s o i l - a t m o s p h e r i c c o n d i t i o n s .

One of the o b s e r v a b l e s y m p t o m s of tea f senescence is the se lec - t i v e b reak d o w n of c h l o r o p h y l l s (Sanger , 1971). A m o n g c h l o r o p h y l l s , c h l o r o p h y l l "a" is more r a p i d l y d e s t r o y e d than c h l o r o p h y l l "b" (Woo l - house, 1974). Thus change in c h l o r o p h y l l c o n t e n t of a l ea f d u r i n g the l a t e r s tages of a ce rea l c rop can be t aken as a mebsure to assess the deg ree of s e n e s c e n c e . M a n y i n v e s t i g a t o r s obse rved c lose r e l a t i o n - sh ip b e t w e e n v a r i o u s i n d i c i e s of senescence , name ly~ d e c l i n e in p r o t e i n c o n t e n t , p h o t o s y n t h e t i c ra te and r i bu l ose d i p h o s p h a t e c a r b o x y l a s e p r o t e i n c o n t e n t and i ts a c t i v i t y and the d e c l i n e in c h l o r o p h y l l c o n t e n t ( H a l l et alo, 19787 W i t t e n b a c h e t . a l . , 1980)o

2 P.P. N a g e s w a r a Rao, M.V. K r i s h n a Rao & R.S. A y y a n g a r

Wi th the d e v e l o p m e n t of r e m o t e sens ing t e c h n i q u e s , many i n v e s t i -

g a t o r s have a t t e m p t e d to r e l a t e r e m o t e sens ing da ta w i t h y i e l d i n d i - c a t i n g p a r a m e t e r s l i ke l e a f a rea index~ c a n o p y t e m p e r a t u r e , senescence

r a t e , e tc . fo r e s t i m a t i o n of c rop y ie lds (Bauer, 1975; Idso e t . a l . , 1977, Wiegand e t . a l . , 1979, T u c k e r e t . a l . , 1980, Idso e t . a l . , 1980). N a g a r a i a n e t . a l . (1984) used a vegeta t~ ion i n d e x d i f f e r e n c e t r a n s f o r m a t i o n s i m i l a r to t h a t e m p l o y e d by Ne lson (1983) fo r d e t e c t i o n of w h e a t rust d isease f r o m L a n d s a t d a t a . In the p r e s e n t s tudy , an a t t e m p t is made to

use the t r a n s f o r m e d v e g e t a t i o n i ndex d i f f e r e n c e to i n f e r the deg ree of senescence of r i ce c rop and i ts e f f e c t on g ra i n y i e l d .

M E T H O D O L O G Y

The e x p e r i m e n t was c o n d u c t e d in the M a n d y a d i s t r i c t o f K a r n a - t a k a 5 t a r e w h e r e r i ce c rop is one of the ma jo r i r r i g a t e d crops in the Rab i season. The study a rea c o v e r e d abou t 15 square k i l o m e t e r s h a v i n g n u m e r o u s f i e l d s of v a r i o u s s izes r a n g i n g f r o m 0.8 to 1,0 h e c t a r e . Range of o b s e r v a b l e senescence in t e r m s of c rop g reenness and g r a i n

y i e l d wre o b t a i n e d as a f u n c t i o n of p e r c e n t change in g reen c o v e r per f i e l d . S p e c t r a l da ta we re c o l l e c t e d by an e l e v e n c h a n n e l M o d u l a r

M u l t i s p e c t r a l Scanner on t w o da tes one i m m e d i a t e l y a f t e r the b o o t i n g s tage of r i ce c rop and the o t h e r at the g ra in f i l l i n g s tage , Out of

the t w o red bands a v a i l a b l e in the scanner (0 .620 - 0 .660 um and 0.660 - 0 .700 urn), the s p e c t r a l da ta of 0 .660 - 0 .700 um band w h i c h

is mo re s e n s i t i v e to c h o l o r p h y l l " a " a b s o r p t i o n was u t i l i z e d in the s tudy . The s p e c t r a l da ta of i n f r a r e d band (0 ,770 - 0 .860 urn) was

also i n c l u d e d in the s tudy because Tucke r and M a x w e l l (1976) and A y y a n g a r e t , a l . (1980) have f ound th is s p e c t r a l r e g i o n to be ve ry use fu l fo r v e g e t a t i o n m o n i t o r i n g , The scanner was o p e r a t e d w i t h an i n s t a n t a n e o u s f i e l d of v i e w of 2.5 m i l l i r a d i a n s at an a l t i t u d e of

abou t 1000 m e t e r s above the g r o u n d l e v e l .

f he s p e c t r a l da ta c o l l e c t e d on a h igh d e n s i t y d i g i t a l tape was t r a n s f e r r e d to a c o m p u t e r c o m p a t i b l e tape for f u r t h e r ana lys i s on the m u l t i s p e c t r a i da ta ana l ys i s sys tem ( M - D A S ) . E s t i m a t e d p e r c e n t

g reen cove r f o r m e d the ma in g r o u n d r e f e r e n c e da ta . A f t e r the ana lys i s the s p e c t r a l d a t a ( M - D A S mean coun ts ) of the red (sd R) and i n f r a r e d (sd IR) bands w e r e used in the c a l c u l a t i o n ,of a t r a n s f o r m e d v e g e t a t i o n

i ndex (TV l ) s i m i l a r to t h a t of Rouse e t . a l . (1975):

= 0.5] 1/2 TVI [(sd IR - sd R) / (sd IR + sd R) +

This t r a n s f o r m a t i o n of two a d j a c e n t bands ( red and near i n f r a r e d ) n,nr m,~l izes the s u n - t a r g e t - s e n s o r g e o m e t r y i n d u c e d changes in the

i n f e r r e d L e a f Senescence of R ice Crop )

r e f l e c t e d r a d i a t i o n observed on t w o d i f f e r e n t da tes ( T u c k e r e t . a l . , 1979). The d i f f e r e n c e in TVI f r o m the t i m e of f l o w e r i n g to the end of g ra in f i l l i n g s tages of r i ce c rop ( i .e . Over a t i m e i n t e r v a l of 35 days) was t a k e n as a measu re of change in g reenness , i .e . the degree of senescence .

Gra in y i e l ds we re measu red f r o m a min i~num of six r a n d o m l y s e l e c t e d one square m e t e r s a m p l i n g un i t s in each r i ce f i e l d . F rom these un i t s a l l the pan i c l es were c o l l e c t e d and g ra ins we re s e p a r a t e d i n to u n f i l l e d and f i l l e d g ra ins . M o i s t u r e c o n t e n t of the g ra ins was d e t e r m i n e d and the f i n a l g ra in y i e l d ( m e t r i c tons per h e c t a r e ) was c a l c u l a t e d ( Y o s h i d a eL.e l . , 1976).

R E S U L T S A N D D I S C U S S I O N

Change in g reen c o v e r , s p e c t r a l da ta ( M - D A S mean counts ) , d i f f e r e n c e in TVI and g ra in y i e l d are p r e s e n t e d in T a b l e - I . N e g a t i v e c o r r e l a t i o n was obse rved (F ig . 1) b e t w e e n r i ce crop g ra in y i e l d and the degree of senescence exp ressed in t e r m s of the d i f f e r e n c e in TVI over a ]5 day i n t e r v a l f r o m the t i m e of f l o w e r i n g (r = -0 .96) . The obse rved r e l a t i o n s h i p b e t w e e n the g ra in y i e l d and senescence cou ld be a t t r i b u t e d to the high s e n s i t i v i t y of the red band, used in the s p e c t r a l t r a n s f o r m a t i o n , to the a m o u n t of c h l o r o p h y l l ( B e n d i c t and S w i d l e r , 1761; K n i p l i n g , 1970; Gausman e t . a l . , 1975 and Tucke r , 1979) p resen t in the r i ce c rop du r i ng senescence . The g r e a t e r dec rease in s p e c t r a l r a t i o i n d i c a t e s a g r e a t e r d e c l i n e in c h l o r o p h y l l c o n c e n t r a - t i on end t h e r e f o r e , more canopy senescence .

i t is d e s i r a b l e t h a t most of the c e r e a l c rops r e m a i n g reen fo r l onger t i m e in the l a t e r s tages of t h e i r l i f e c y c l e so t h a t t hey can s y n t h e s i z e and t r a n s l o c a t e the p h o t o s y n t h a t e to the g ra i n . H o w - e v e r , in r e a l i t y t h i s does not happen due to s e v e r a l f a c t o r s . Bes ides g e n e t i c v a r i a b i l i t y , any of the c o n d i t i o n s r e l a t e d to n u t r i t i o n a l a v a i l - a b i l i t y and w a t e r a v a i l a b i l i t y l e a d i n g to crop s t ress can also i m p a i r the p h y s i o l o g i c a l ba l ance and a g g r e v a t e l ea f senescence . This in t u rn may d e p r i v e the crop f r o m a c c u m u l a t i n g s u f f i c i e n t a m o u n t of c a r b o h y d r a t e s w i t h a consequen t r e d u c t i o n in g ra in y i e l d . The o b s e r v a - t i on made in t h i s s t udy , i . e . t the i n v e r s e r e l a t i o n s h i p b e t w e e n sene- scence and the r i ce g ra in y i e l d f u r t h e r s u b s t a n t i a t e the w o r k o! A l l i s o n

t (1964) on w h e a t and m a i z e and A b u - S h a k r a eL.e l . (197B) on soybean n e n o t y p e s w i t h d e l a y e d senescence .

b, P.P. Nageswara Rao, M.V. Kr ishna Rao & R.S. Ayyangar 4

CONCLUSIONS

The re la t i onsh ip observed between spec t ra l data and degree of senescence ind ica tes the p o t e n t i a l use o'f the remote sensing data as one of the ind ices of assessing crop y ie ld . This study using a i rborne scanner data is only the begin ing and more studies are requ i red in th is d i r ec t i on to br ing such studies to opera t iona l leve l using s a t e l l i t e

data.

A C K N O W L E D G E M E N T S

The authors wish t o express the i r deep sense of app rec ia t i on to the D i r e c t o r , NRSA for p rov id ing necessary f a c i l i t i e s . Authors thank the Research F l igh t F a c i l i t i e s of NRSA for col lect ing the spec- t ra l data . The help rendered by Mr. S.S. Budwal and Mr. K. Damodaran dur ing the f i e l d observa t ions is also g r a t e f u l t y acknowledged. Special thanks are due to Or. C.J. Tucker of NASA/Goddard Space F l igh t Cent re , Greenbelt~ Mary land for his encouraging suggest ions.

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6 P.P. Nageswara Rao, M.V. Krishna Rao & R.5. Ayyangar

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