improvine n fertilizer efficiency in asia

8/4/2019 Improvine N Fertilizer Efficiency in Asia

http://slidepdf.com/reader/full/improvine-n-fertilizer-efficiency-in-asia 1/16

10. Improving nitrogen fert i l izer ef f ic iency in lowland rice

in tropical A s ia

SK DE DATTA

International Rice Research Institute, P.O. Box 933, Manila, Philippines

Key words: improved water management, best split, mechanisms of N losses, varietaldifferences in N use efficiency, deep placement, nitrification and urease inhibitors

Abstract. Rice production in Asia must increase 2.2-2.8% annually to keep abreast ofincreasing population. Greater fertilizer use and crop intensification together withvarietal improvement and investment in irrigation will all contribute to increased ricesupply. Because fertilizer and input prices have risen faster than the price of rice,increasing fertilizer N efficiency will be a major challenge for rice researchers and farmers.Greater fertilizer N efficiency may be achieved through improved timing and applicationmethods, and particularly through better incorporation of basal fertilizer N withoutstanding water. Other promising alternative practices are use of N-efficient rice varieties,hand or machine deep placement of urea supergranules, and use of slow release Nfertilizers. Research challenges include development of placement machines for prilledurea and identification of cost-efficient nitrification and urease inhibitors. Under thepresent resource-scarce situation in many Ixopical Asian countries, several comple-mentary practices must be followed to supplement inorganic N sources. Fertilizersupplies and proper price support should be maintained and wherever possible increased,and appropriate fertilizer materials and application methods must be devised to increaseN use efficiency in lowland rice, so that increasing rice requirements are fulfilled.

Introduction

Rice curre ntly represents as muc h as 7 5% of the caloric intake of the 2 billio n

people living in Asia. It is the most imp ort ant food crop in the region where

population densities are highest and overall dietary levels are least adequate.

In the vast m ons oon al areas of tropical Asia, rice gives the highest food-staplecereal yield from a fixed land area of arable land.

In many tropical rice-growing areas, particularly in South and Southeast

Asia, lowland rice culture predominates. Under lowland culture, land is either

prepared wet by pudd ling the field or prepared dry, but water is always held

in the field by bun ds [6].

In Asia, rice prod uct ion has increased an average 2.7% ann uall y - slightly

faster than population growth, but somewhat slower than the growth in

demand [17]. Yield has increased because of the adop tion of mod ern varieties

and associated technol ogy, increased year-rou nd irrigation facilities, and more

fertilizer use.

171

Fertilizer Research 9 (1986) 17 1- 18 6© Martinus Ni]hoff /Dr W. Junk Publishers, Dordreeht - Printed in the Netherlands



172

These spectacular y ie ld increases s ti ll d o no t ref lec t the pote nt ia l tha t

researchers be lieve the te chn olo gy has a t the farm level in t ropica l Asia . There

i s gene ra l ag reement among po l i cy makers and ana lys t s t ha t gove rnment

op t ions to inc rease r ice p rod uc t ion inc lude a com bina t io n o f :

1 . improved wa te r managem ent ,2 . increased pro du ct ivi ty f rom no n-i r r iga ted areas ,

3 . va r i e ta l impro vem ent ,

4 . increased use of fer t i l izer and pest co nt rol , and

5. app ropr ia te ag r icul tura l policies a nd inst i tu t ion s.

As the need fo r h ighe r rice y i e lds and p ro duc t ion becomes more u rgen t ,

and as prices o f energ y-re la ted mater ia ls suc h as fer t i lizers con stan t ly increase ,

effo r ts to increase fer t i lizer N eff ic ienc y in low land rice sh ould inc lude

de ta il ed s tud ie s on fe r ti li ze r nu t r i en t use an d c rop m anagem ent p rac ti ces.

My p a p e r su m m a r iz e s so m e o f t h e c u r re n t k n o wle d g e o n m a n a g e m e n t

prac t ices for imp roving N u se eff ic ien cy in low land r ice soil s.

Nitrogen requirements for rice

Rice plants require as mu ch N as possible a t ear ly and m id- t il le ring to

maximize pan ic l e number . P l an t s a l so need N a t r eproduc t ive and r ipen ing

stages to produce opt imum spikele ts per panic le and percentage f i l led

spikelets.

N requ i rement by the r ice c rop can be a sce r ta ined by : v isual symp tom s o f

the crop, plant analyses, soi l analyses, and yield response with fert i l izer

app l i ca t ion . T he l a st m e tho d i s t he su res t, bu t t he o th e r me thod s can p rov ide

su p p l e m e n t a r y i n f o r m a t i o n .

Nitrogen use e f f i c i ency

Research o n cons t ra ints to high yie ld in farmers ' f ie lds in the Phi l ippines has

shown tha t i nsuf f i c i en t f e r t i l i ze r o r i nappropr i a t e f e r t i l i ze r management

accoun t s fo r on e -ha l f t o two- th i rds o f t he gap be tween , ac tua l and po ten t i a l

r ice yie lds in farm ers ' f ie lds [7] . These yie ld di f ferences were de term ined by

com paring farm er 's fer t i l izer prac t ices wi th th e best avai lable tech no logy ; the

best-split appl ica t ion.

A l t h o u g h t h e h i gh N c o n t e n t a n d l o w p ri ce o f u r e a m a k e it t h e m o s t

pop ular fer t i l izer for t ropica l r ice , i t i s no t a n ideal fer t i lizer for the low land

r ice crop. No single urea fer t il izer or urea fer t i lizer m ana gem ent prac t ice is

sui ted to a l l c rop s i tua t ions because o f d iversi ty o f soil and c l imat ic regimes

un der w hich rice is grown. A l ternat ive s t ra tegies m ust be developed to increase

fer t i l izer e f f ic ienc y in t ro pica l low land r ice .

Effic ienc y o r fertil izer nitrogen util ization

The percentage of N recovery by r ice var ies wi th soi l proper t ies , methods,am ou nt and t iming o f f e r t il i ze r app l i ca tion , and o the r man agem ent p rac ti ces .



173

N f e r ti li z e r r e c o v e r y u s u a l ly i s 3 0 - 5 0 % i n t h e t r o p i c s [ 2 4 ] . P e r c e n t a g e o f N

recov e ry tend s to be h ighe r a t low N app l ica t ion l evel s and wh en N is p laced

deep in so il o r top dres sed a t l a t e r g row th s tages .

N u t i l i z a t io n e f f i c i e n c y f o r g r a in p r o d u c t i o n i n t h e t r o p i c s is a b o u t 5 0 k g

roug h r i ce /kg n i t rogen absorbed , an d i s a lmos t con s tan t rega rd le ss o f r i cey i e l d [ 3 2 ] . N e f f i c i e n c y is a b o u t 2 0 % h i g h e r in t e m p e r a t e r e gi o ns t h a n in

t h e t r o p i c s.

Us ing va lues fo r the rec ove ry pe rcen tage and u t i l i za t ion e f f i c i ency

ob ta in ed fo r the t rop ic s , Yosh ida [32] e s t ima ted fe r t il i ze r N e f f i c iency to be

1 5 - 2 5 k g r i ce / k g a p p li e d N . T h e se v al u es w e r e c o n f i r m e d i n N r e sp o n s e

e x p e r i m e n t s [ 2 4 ] .

T h e p r i m a r y g o a l o f i m p r o v e d N m a n a g e m e n t p r a c t i c e s s h o u l d b e t o

m a x i m i z e N u p t a k e a t cr i ti c a l g r o w t h s ta ge s a n d m i n i m i z e tr a n s f o r m a t i o n

proces ses tha t l ead to los ses o r t em po ra ry losses o f N f ro m so il wa te r sys tems

[12] . I t a lso i s c r i t ica l to ensure tha t N ab sorbed by the p lan t i s used fo r g ra in

p r o d u c t i o n , w h i c h M u r a y a m a [ 2 2 ] c a ll ed product ive e f f ic iency . P r o d u c t i v e

e f f i c i e n c y is t h e a m o u n t o f r ic e p r o d u c e d p e r k i l o g ra m o f n u t r i e n t a p p li e d.

Poor u t i l i za t ion o f N fe r t i l i ze r by r i ce i s though t to be l a rge ly due to N

los ses f ro m the soi l p lan t sys tem. A m m onia vo la t i l iza t ion , den i t r i f i ca t ion ,

run of f , an d l each ing a re ma jo r m echan i sms o f los s [3 ] . Obv ious ly , the na tu re

of the N fe r t i l i ze r, the app l i ca t ion m e tho d , and f i eld - leve l cond i t ions a ll

a f fec t fe r ti l i ze r e f f i c i en cy [26 ] .

Management pract ices for fer t i l i zer n i trogen

Since modern h igh-y ie ld ing r i ce va r ie t i e s were in t roduced in t rop ica l As ia in

the mid-1 960 ' s , r e sea rche rs have sough t to impro-ve fe r t i li ze r N e f f i c ienc y

i n f l o o d e d r ic e c u l t u r e . T h e n e e d f o r i n c re a s ed e f f i c i e n c y h a s b e e n f u r t h e r

emphas ized by recur r ing ene rgy shor tages , a fe r t i l i ze r N shor tage , and r i s ing

pr ices . Fur the rmore , fe r t i l i ze r subs id ie s have been d i s con t inued o r reduced

in seve ra l cou n t r i e s (F igure 1 ) , wh ich m ake h igh ra te s o f fe r t i l i ze r use un l ike ly .

Shortage s , p lus th e hea vy losses o f fer t i l izer N in r ice f ie lds , have enco urag ed

fe r t i l i ze r t echno log i s t s and agronomis t s to deve lop more e f f i c i en t fe r t i l i ze r

m a t e r ia l s a n d m a n a g e m e n t p r a c ti c e s.

Payof fs f rom inves tmen ts in ag r icu l tu ra l re sea rch a re h igh in i r r iga ted

a reas [31] , bu t m os t r i ce fa rme rs st il l depe nd on ra inwa te r to sus ta in the i r

c rops .

High levels of inputs such as fer t i l izers are not used even in i r r iga ted r ice .

Fo r ra in fed a reas , the in pu t l eve ls a re even l es s [29] . Fo r exam ple , cons t ra in t s

r e s e a rc h i n r a i n f e d c o n d i t i o n s i n 1 9 8 1 - 8 3 w e t s e a so n s s h o w e d t h a t 5 7% o f

a 1 .4 t /ha y ie ld gap in 2 Ph i l ipp ine p rov inces is caused by low ra te s and po or

t iming o f fe r ti l i ze r N ap p l i ca t ions by 84 fa rm ers (F igure 2 ) .

Seve ra l a l t e rna tive p rac t i ces have be en eva lua ted a t IRRI a nd e l s ewhere toinc rease N use e f f i c i ency in lowland r i ce [11] . Th ey a re:



174

F e r t il iz e r c o s t ( U S $ ) p a i d b y f a r m e r s5 0 0

4 00

5 0 0

2 0 0

1 0 0

/ . / .#

/ / / 2

[ ] M a r k e tin g c o s t

I ~ C I F p r ic e

~_ .o_

I ~ S u b s i d y

r - ' l F a r m e r

p r i c e ( t o t a lc o s t m i n u s s u b s id y )

i

! i ! i i ! . . . .:i:ii

I : : : i :i i i i i ' ,i : i : i :

, / ~ , / / , - ]

.~ 3 .g

m F -

Figure 1 . Total cost (C IF + marketing cost) , fertil izer sub sidy, and fa rm er price o f

ferti l izer in selected Asian rice grow ing countries. From FA O [ 16 ]

1 . v a r i et a l d i f f e r e n c e s i n N u t i l i z a t i o n e f f i c i e n c y ;

2 . i m p r o v e d t i m i n g o f N a p p l i c a ti o n ;

3 . d e e p p l a c e m e n t o f N fe r t il iz e r ;

4 . c o n t r o l l e d r e le a s e N f e r t il i z e r s ;

5 . u s e o f n i t r i f i c a t i o n a n d u r e a s e i n h i b i to r s ; a n d

6 . c o m p l e m e n t a r y p r a ct ic e s t o i m p r o v e N u s e e f f ic i e n c y .

1 . Farieta l d i f feren ces in n i trogen u t i l i za t ion e ff ic ienc y

S u c c e s s f u l e x p l o i t a t i o n o f v a ri e t a l d i f f e r e n c e s i n a b i l i t y t o u t i l i z e s o f t N i s

i m p o r t a n t b e c a u s e s o i l i s t h e m a j o r N s o u r c e in l o w l a n d r ic e . R e s u l t s f r o m

1 9 7 6 - 1 9 8 2 e x p e r i m e n t s a t f o u r s t a t io n s in t h e P h i li p p in e s s u g g es t t h a t I R 4 2

u s e s s o il a n d f er t il iz e r N m o r e e f f i c i e n t l y t h a n I R 3 6 , t h e m o s t w i d e l y g r o w n

r i c e v a r i e t y i n t h e w o r l d [ 1 1 ] . S u b s e q u e n t r e s e a r c h s h o w e d t h a t u p t o 3 0

d a y s a f t e r t ra n s p la n t in g ( D T ) m e d i u m d u r a t i o n I R 4 2 u s e s s o il N m o r e

e f f i c ie n t l y t h a n I R 9 7 2 9 - 6 7 - 3 , a v e r y e a rl y d u r a t i o n r ic e. A f t e r 3 0 D T , I R 4 2

u t i l i z e s f e r t il iz e r N b e t t e r t h a n I R 9 7 2 9 - 6 7 - 3 ( F i g u r e 3 ) .

I n I R R I - U n i v e r s i t y o f C a l i fo r n i a -D a v i s c o l l a b o r a t i v e r e s e a rc h , 1 5 N - d e p l e t e d

a m m o n i u m s u lf a te w a s us e d in 1 9 8 1 - 8 2 d r y an d w e t s e a s o n f ie ld ex p e r im e n t st o a n a l y z e g r a i n y ie l d a n d N u p t a k e o f s e v e ra l r i ce s . R e s u l t s s u g g e st e d t h a t



175

G r a in y ie l d ( t / h a )8

6

H i g h

4 - - F o r m e r s 'i n p u t s

r i l l 1~ - f f f j

r i J J . ~

r 1 1 7 ~

r l i i ~

r . , - / / . ~F I I I .

r / 1 1 1f J J . f ,

c f J J ,

. . . . ,. . . ." "" "" N ~ l d f g a p l ' 8 t 4 / h a

. . . . .

Figure 2. Average yiel ds with farmers' inputs and hig h inputs and contributions offertil izer, insect control, and w eed control to the y ield gap in rainfed farms in Tarlac,Libmanan , and San Femando in Camarines Sur, Philippines, 19 81 -83 wet seasons

g r a in y i e ld a n d t o t a l N u p t a k e , a n d t o t a l q u a n t i t y o f N u s e d i s r e la t e d t o

g r o w t h d u r a t i o n o f r ic e ( T a b le 1 ) . T h e t o t a l q u a n t i t y o f N u s e d b y t h e r ic e

p l an t i s r e l a t ed t o d u ra t i on g roup . I n 1981 d r y s eason , t he long du ra t i onr i ces abso rb ed m ore t o t a l N b u t l es s f e r t il i ze r N t ha n shor t e r du ra t i on

va r i e t i e s . H ow ever , i n 1981 w e t s eason , t o t a l N up t ake w as h i ghes t i n t he

m e d i u m d u r a t i o n g r o u p . I n 1 9 8 2 d r y s e a so n , s h o r t d u r a t i o n r ic e s a b s o r b e d

l es s N t h a n m e d i u m a n d l o n g d u r a t i o n v a r ie t ie s , w h i c h a b s o r b e d s im i l ar

am ou n t s . I n gene ra l , sho r t du ra t i on r i ce s used mo re f e r t il i ze r N . I n 1983 ,

an add i t i ona l 78 r i ce s w ere eva l ua t ed t o de t e rmi ne cons i s t en t d i f f e r ences

i n N f e r t i l i ze r r e sponse , w i t h t he ob j ec t i ve o f s e l ec t i ng r i ce s t ha t w ou l d

p e r f o r m w e l l w i t h m i n i m u m f e rt il iz e r N .

R esu l t s f r o m 3-yea r t r ia l s sh ow ed s i gn i fi can t d i f f e r ences in f e r ti l ize r N

u t i l iz a t i o n b a s e d o n g r o w t h d u r a t i o n , t il le r in g , a n d p o s s i b l y o t h e r p l a n t

cha rac t e r i s t i c s . P r e l i mi na ry r e su l t s sugges t t ha t shor t s eason va r i e t i e s depend

m o r e o n s u p p l e m e n t a r y f e r ti li z e r N i n t h e d r y s e a s o n t h a n l o n g d u r a t io n

va r i e t i e s [ 1 ] .

2. Improved timing o f N application

Th e t i mi ng o f f e r t i l ize r ap p l i ca t i on va r ie s subs t an t i a ll y . C om m on f ie l d p r ac t i ces

r a n g e f r o m a s i n g l e t r e a t m e n t u n r e l a t e d t o a n y s p e c i f i c c r o p d e v e l o p m e n t

phase t o a s many a s f i ve sp l i t app l i ca t i ons ca r e fu l l y t i med t o max i mi ze

y i e l ds . M any r i ce f a rm er s ap p l y N i n t h r ee sp l it doses - t he f i r s t dose j us tb e f o r e t r a n s p la n t i n g , t h e s e c o n d d o s e a t m a x i m u m t i ll er in g , a n d t h e f i n al



17 6

N u p ta k e ( g / m 2 )

1 0

2

"I.0

0 .5

/i I

- s o / / N //I/ I * - - I R 4 2

i I t ' '

_ J I / / * - - l R 9 7 2 9 - 6 7 - 5

- / / - - f . ~ ~ . ~ ,

, ' /

I I I3 0 D T P I H o r v e s l

G r o w t h s t a g e

Figure 3. Uptake of soil N and fertilizer N (15N-depleted) in IR42 and a n early maturingIR9729-67-3 rice. IRR I, 1982 wet season

dose a t o r j u s t be fo re pan i c l e i n i t i a t i on . Spr i t appf i ca t i on s eeks t o ma i n t a i n

a po o l o f l ab i le N w hi l e m i n i mi z i ng t he r i sks o f mass ive l os ses t h ro ug h

ammoni a vo l a t i l i za t i on , den i t r i f i ca t i on , and l each i ng .

Many f a rmer s i n t r op i ca l A s i a s t i l l app l y f e r t i l i ze r d i r ec t l y i n t o t he f l ood-

w a t e r 1 - 3 w e e k s a f t e r t r a n s p la n t i n g d e s p i t e r e se a r c h t h a t sh o w s t h e b e n e f i t s

o f i m p r o v e d t i m i n g a n d a p p l i c a t i o n m e t h o d s . B r o a d c a s t i n g N f e r t i l i z e r i n t o

f l o o d w a t e r r e s u l t s i n e x t e n s i v e N l o s s e s t o t h e a t m o s p h e r e t h r o u g h s u r f a c e

w a t e r [ 4 ]. F o r e x a m p l e , i n 1 9 8 4 d r y s e as o n w h e n 8 7 k g N / h a a s p r il le d u r e a

( P U ) w a s a p p l ie d u s i n g f a r m e r s ' ti m i n g - o n e - h a l f N a p p l i e d i n t o 5 c m o f

w a t e r 1 0 D T a n d o n e - h a lf t o p d r es s e d in t o 5 c m o f w a t e r a t 1 0 d a y s a f t e r

p a n i cl e in i t i a ti o n ( P I ) - a b o u t 1 8 + 1 4 k g N / h a o f t o t a l N ( u r e a + N H ~ - N )

ended up i n f l ood w a t e r (F i gure 4 ) . W i th r e sea r che r s ' sp l it app l i ca t i on -t w o - t h i r d s b r o a d c a s t a n d i n c o r p o r a t e d w i t h o u t s t a n d i n g w a t e r a n d o n e - t h i r d



Table 1. Grain yield, total N uptake, and fertilizer N uptak e by ricecrop duration. From Broadbent F E and D e Datta SK [ 1 ]

177

Duration Grain yield Total N upta ke Fertilizer N uptake(days) (t/ha) (kg/ha) (kg/ha)

1981 D ry season100 4.6 78 17

110 4.5 87 15

120 4.8 97 11

1981 Wet season

100 3.6 107 9

110 4.0 121 7

120 3.7 105 6

1982 Dry season100 5.6 74 4

105 -115 5.5 90 3

120 -135 5.5 91 4

t o p d r e s s e d i n t o 5 c m o f s ta n d i n g w a t e r a t P I - o n l y a b o u t 6 + 4 k g N / h a

e n d e d u p i n f l o o d w a t e r (F i g u r e 4 ) .

W a t er d e p t h e f f e c t s o n i m p r o v e d t i m i n g o f N a p p l ic a t io n s . I n 1 9 8 4 d r y

s e a s o n w h e n t h e f ir s t d o s e o f a p p l i e d u r e a N w a s b r o a d c a s t i n t o 5 c m o f

s t a n d i n g w a t e r u s i n g r e s e a r c h e r s ' s p l i t , a b o u t 4 k g N H ~ - N / h a e n d e d u p i n

f l o o d w a t e r v e rs u s o n l y 2 k g N H ~ - N N / h a w h e n b a s al N w a s a p p l ie d w i t h o u t

s t an d i n g w a t e r a n d i n c o r p o r a t e d t h o r o u g h l y i n t o p u d d l e d s o il ( F i g u re 5 ) .

B a s al a p p l i c a ti o n o f u r e a w i t h 5 c m s t an d i n g w a t e r r e s u lt e d i n 3 5 k g / h a o f

t o t a l N ( u r e a + N H ~ - N ) i n t h e f l o o d w a t e r v e r s u s 8 k g N / h a w i t h o u t s t an d i n g

w a t e r ( F i g u re 5 ) . G r a i n y i e ld w a s 0. 9 t / h a h i g h e r w i t h i n c o r p o r a t i o n o f a

b a s a l d o s e p r i o r t o p l a n t i n g w i t h o u t s t a n d i n g w a t e r t h a n w i t h u r e a a p p l i -

c a t i o n i n t o s t a n d in g w a t e r a n d i n c o r p o r a t i o n ( T a b l e 2 ) . P r o p e r l y a p p l i e d

r e s e a r c h e r s' s p l i t w i t h b a s a l i n c o r p o r a t i o n w i t h o u t s t an d i n g w a t e r ga v e

s im i l ar y ie l d t o d e e p p o i n t - p l a c e d U S G o r b r o a d c a s t a n d i n c o r p o r a t e d S C U(Tab l e 2 ) .

T h e s e r es u lt s e m p h a s i z e t h e i m p o r t a n c e o f p r o p e r w a t e r m a n a g e m e n t

and basa l f e r t i l i ze r i ncorpora t i on p r i o r t o p l an t i ng i n i nc r eas i ng N use

e f f i c i ency i n l ow l and r i ce . Th i s t echno l ogy i s h i gh l y r e l evan t i n f a rmer s '

f i e lds because i t app ea red t o have no r i sks t o t he f a rmer s . B ased on t h i s

a n d o t h e r I R R I r e s e a r c h , t h e P h i l i p p i n e e x t e n s i o n p r o g r a m Masagana-99,

h a s m o d i f i e d i ts 1 6 - s te p f e r ti li z e r a p p l i c a t io n r e c o m m e n d a t i o n s .

3 . D e e p p l a c e m e n t o r f e r t i li z e r n i tr o g e n

D e e p p l a c e m e n t o f f e r t i l i z e r i n r e d u c e d s o i l h a s b e e n c o n s i d e r e d t h e m o s t

e f f i c i en t me t hod t o i nc r ease f e r t i l i ze r N e f f i c i ency i n l ow l and r i ce [12 ] .



18

16

14

12

10

8

6,

05 5 7

_ Pr/71ed ur ea

8 7 k g N / h a

Researchers'spl i t(2 /5 broadcast andincorporated withou tstanding water + ] / 5broadcast in 5cm water

IP t )

' ~ k ~ I I

Farmers' split (1/2 broadcast Zin5cm water at 10 D T+ I /2broadcast in 5 cm wa ter at10 DAPI)

I I I ,¢

9 11 13 15 2 9

D ays a f t e r t r ansp l an t i ng

1 7 8

Total ure a+ NH4+- N ) f lood~ ] ter N (k g /h a )

PI

L A A / / I

51 55 59 41 4 3

Figure4. Total (ure a + NH ]-N) floodwater N at 13 00 to 140 0 hours as affected bytiming and method of nitrogen application. IRRI, 198 4 dry season. DT = days aftertransplanting, D AP I = days after panicle initiation, P I = panicle initiation

D eep p l acemen t o f N f e r t i l i ze r s i s becomi ng i nc r eas i ng l y r e l evan t s i nce

t h e i n t r o d u c t i o n o f m o d i f i e d u r e a m a t e r ia l s s u ch a s u r e a b r i q u e tt e s , U S G ,

and u r e a marb l e s f o r te s t i ng i n l ow l and r i ce .

C a o e t a l. [ 2 ] r e p o r t e d t h e m o s t r e c e n t re s u l ts o n t h e e f f e c t s o f p l a c e m e n t

me t hods on t he f e r t i l i ze r N r ecove ry and g r a i n y i e l d us i ng l SN - l abe l l ed u r ea

i n f ie ld m i c r o p l o t s . U S G p o i n t p l a c e m e n t a n d u n i f o r m p l a c e m e n t o f P U

gave t he h i ghes t g r a i n y i e ld o f 6 . 4 t / h a i n d ry s eason , suggest ing t ha t bo t h

d e e p p l a c e m e n t m e t h o d s e f f e c t i v e l y i m p r o v e f e r t i l i z e r N e f f i c i e n c y . T h e

h i g h e f f i c i e n c y ( 5 2 k g r o u g h r i c e / k g a p p l i e d N ) w i t h p o i n t p l a c e m e n t w a s

due t o l ow er N f e r t i l ize r l o sses as ev i denced by t he l ow t o t a l N (u r ea +

N H ~ - N ) i n f l o o d w a t e r [ 2 ] .



N H

4 £

&C

2C

L N ( k g / h a )

2 5 4 5

+

T o t a l N ( u r e a + N H 4 - N ) , k g / h a

: ; 0 -

, P r / l l e d u r e a { 5 8 k g / V / h a ) ,

b a s a / , b r o a d c o s l o n d m c o r -

50 p a r o l e d

k , ~ W i thou t wa te r

~ Wi th 5 cm wa te r

~ 2 ~ ~ N o f e r t i l i z e r N

~0 ~ Sampling time (h)

- \ ~ 0 7 0 0 - 0 8 0 0

~ 1 5 0 0 -1400

u

l 2 3 4 5 6

Days af ter fer t i l izer appl icat ion

1 7 9

F i gu r e 5 . F l o o d w a t e r N H ] - N a n d t o ta l N (u re a + N H 4 - N ) a t 0 7 0 0 - 0 8 0 0 h a n d 1 3 0 0 -

1 4 0 0 h a f t e r b r o a d c a s t a n d i n c o r p o r a t i o n o f u re a a t d i f f e r e n t w a t e r d e p t h s . I R R I , 1 9 8 4

d r y s e a s o n

T a b l e 2. E f f e c t s o f w a t e r d e p t h , u r e a s o u r c e , a n d a p p l i c a t i o n m e t h o d a t 8 7 k g N / h a o n

t h e g r a i n y i e ld o f I R 5 8 a . I R R I , 1 9 8 4 d r y s e a s o n

W a t e r d e p t h d u r i n g

U r e a b a s a l f e r t i l i z e r G r a i n y i e l d e

s o u r c e A p p l i c a t i o n m e t h o d b a p p l i c a t i o n ( c m ) ( t /h a )

- N o f e r t i l i z e r n i t r o g e n - 2 . 9 c

S C U B r o a d c a s t a n d i n c o r p o r a t e d 0 6 .6 a

P U R e s e a r c h e r s ' s p l it 0 6 . 4 aP U R e s e a r c h e r s ' s p l i t 5 . 1 5 . 5 b

P U F a r m e r s ' s p li t 0 5 . 4 b

P U F a r m e r s ' s p l i t 5 . 1 5 . 2 b

P U F a r m e r s ' s p l it 1 0 . 0 4 . 7 b

P U F a r m e r s ' s p l it 1 4 .9 5 .1 b

U S G A l l b a s al , h a n d p o i n t - p l a c e m e n t 5 . 2 6 .6 a

a A v o f 4 r e p l i c a ti o n s . S C U = s u l f u r - c o a t e d u r e a , P U = p r i ll e d u r e a , U S G = u r e a s u pe r -

g r a n u l e s , P I = p a n i c l e i n i t i a t i o n

b R e s e a r c h e r s ' s p l it = 2 / 3 b r o a d c a s t a n d i n c o r p o r a t e d a n d 1 /3 t o p d r e s s e d w i t h 5 c m

s t a n d i n g w a t e r a t p a n i c l e i n i t i a t i o n . F a r m e r s ' s p l i t = e q u a l s p l i t - d o s e s a t 1 0 d a y s a f t e r

t r a n s p l a n t i n g a n d a t 1 0 d a y s a f t e r p a n i c l e i n i ti a t i o ne M e a n s f o l l o w e d b y a c o m m o n l e t t e r a r e n o t s i g n if i c a n tl y d i f f e r e n t a t t h e 5 % l ev e l b y

D u n c a n ' s m u l t i p l e r a n g e t e s t



18 0

R e s e a rc h o n U S G d e e p p l a c e m e n t u n d e r t r o p i c al a n d s u b t ro p i c a l c o n -

d i t ions was rev iewed by Juang [20] . In Ta iwan , a t the s ame ra te o f app l ied

N, USG inc reased r i ce y ie lds by an average 20% over PU in a low-y ie ld a rea

such as Ta ichung b u t no t in a h igh-y ie ld a rea such as P in tung .

R e s u l t s f r o m 1 6 f i e l d e x p e r i m e n t s c o n d u c t e d b y t h e I N P U T S p r o j e c tin 8 As ian count r ie s ind ica ted tha t USG t rea tm ents o u ty ie ld ed PU a t the

same ra te of N in 11 o f 16 i r riga ted s i tes [20 ] .

S e v e r a l y e a r s o f a g r o n o m i c d a t a f r o m t h e I n t e r n a t i o n a l N e t w o r k o n

S o i l F e r t i l i t y a n d F e r t i l i z e r E v a l u a t i o n f o r R i c e ( I N S F F E R ) n e t w o r k s h o w

tha t deep p lacem ent i s gene ra l ly mo re e f f i c ien t than the t rad i t iona l

spl i t appl ica t ion o f ure a [4 , 28, 10, 12, 15] . Individual t r ia l resul ts ,

how ever , va ry by s it e and season . T e jeda e t al . [28] de te rm ined the

re la t ionsh ips be tw een the e f f i c iency o f th e d i f fe ren t fe r t il i ze rs and s i te

cha rac te r i s t i c s , us ing da ta f rom 114 INSFFER t r i a l s in 11 count r ie s .

Average e f f ic ienc ies (de f ined a s the inc rem ents in r i ce y ie ld pe r un i t o f N

a p p l i e d ) u p t o 5 6 k g N / h a f o r U S G w a s f o u n d t o b e 2 1 - 2 4 k g r o u g h r i c e / k g

appl ied N.

Eco nom ic ana lys is o f the s ame se t o f t r ia l s showed an average re tu rn o f

U S $ 4 - 7 f o r e v e r y d o l la r s p e n t o n l a b o r f o r U S G a p p l i c a ti o n [ 4 ] . R e c e n t

ana lysi s by F l inn e t a l. [15] o f the 1981 we t s eason IN SF FE R tr i a ls showed

tha t N app l ied a s USG usua l ly was t echn ica l ly more e f f i c ien t than N app l ied

as pr i l led urea , par t icular ly a t low N ra tes . Averaging the data from al l

e x p e r i m e n t s , 2 0 - 3 0 % le ss N o f t h e m o d i f i e d N s o u r ce g av e t h e s am e y i e ld

inc rem ent a s N app l ied a s PU. Separa t ing the d r y season f ro m the we t s easonI N S F F E R t r ia ls d u r in g 1 9 8 1 - 8 2 , t h e a v e ra g e y i e l d i n d r y s e a s on w a s h i g h e r

than in we t s eason a t the s ame N ra te (F igure 6 ). Bo th USG and su l fu r -coa ted

urea (SCU) were equa l ly e f fec t ive and be t te r than p r i l l ed u rea dur ing we t

season , e spec ia lly a t lower N ra te s up to 87 kg N/ha . How ever , a t 116 kg N/h a

all the 3 fo rm s we re s imilar .

To mak e deep p lacem ent re levan t a t the fa rm leve l, i t is c r i ti ca l to dev e lop

a ser ie s o f p lac em ent machines tha t wi ll po in t -p lace PU, .u rea so lu t ion , and

USG. Severa l p lacem ent m achines a re cu r ren t ly be ing deve loped and

eva lua ted fo r th i s purpo se a t IR RI .R e s u l t s f r o m t h e 1 9 8 4 d r y s e a s o n s h o w e d t h a t h a n d d e e p - p l a c e d U S G

produced s ign i f ican t ly h ighe r g ra in y ie ld (ave rage o f 58 and 87kgN/ha)

than machine -p laced N fe r t i l i ze r (Tab le 3 ) . Deep p lacement machines app l ied

b e t w e e n 4 6 a n d 7 2 k g N / h a f o r 5 8 k g N / h a i n t e n d e d r a t e a n d b e t w e e n 7 9 a n d

9 1 k g N / h a f o r 8 7 k g N / h a i n t e n d e d r a te , in d ic a ti ng c o n si d er a bl e r o o m f o r

i m p r o v e m e n t i n t h e a c c u r a c y o f a p p l i c a ti o n r a t e . F e r t i l iz e r N e f f i c i e n c y w a s

g r e a t es t w i t h U S G h a n d p o i n t p l a c e m e n t ( T a b l e 3 ).

4 . C o n t r o l l e d r e l e a s e N f e r t i l i z e r s

SCU is the mo s t w ide ly t e s ted c oa ted fe r t i li ze rs fo r r i ce [4 , 5 , 12] . S tud iessuggest th a t s low-re lease fer t i l izers such as SCU cons ide rably redu ce amm on ia



Grain6.0

5.5

5 0

4.5

4 0

s 5 1

5.C

ield (t /ha )

/ / / 6 . ¢ . - "/ / / . - 2 " _ . "

~ S ~ ~ ' / . . $ / " - - D r y season

f / ; / _ / / / . . . . W et season" / t °

I o Sulfur-coated urea,~ I I broadcast and inco rpora tedrt ~ Urea supergranule, point

placement• Urea best spl it

I 1 I I I0 29 58 87 116 174

Nitrogen a ppl ied (kg /ha)

181

Figure 6. Nitrogen responses of rice with different forms of urea and application rates.

Data are averages on 14 dry and 55 wet season trials. Fifth International Trial onNitrogen Fertilizer Efficiency in Rice, 1981-82 crop seasons. From IRRI [8]

Table 3. Grain yield o f IR58 rice as af fected by hand- and machine-placed fertilizer N.IRRI, 1984 dry season

Urea Applicat ion met hod Grain yieldb Fertilizer efficiency

source a (t/ha) (kg rough rice/kg N)

PUPU

USG

USG

USG

PU

PU

Band placement by spring auger 3.6 d 26

Band placement by oscillating plunger 3.8 cd 28

Po ~t placement by deep plunger 4.6 b 40

Point placement by press wedge 4.2 bc 28

Point placement by hand 5.2 a 46

Researchers' split 4.4 b 34

Farmers' split 3.4 d 21

No fertilizer nitrogen 1.9 e -

apu = prilled urea, USG = urea supergranulesbAy of 4 replications and 2 nitrogen rates. Means followed by a common letter are notsignificantly differen t at the 5% level



1 8 2

v o l a t i l iz a t i o n l o s s es [ 2 1 ] a n d p r o v i d e t h e c r o p a d e q u a t e N n u t r i t i o n t h r o u g h -

o u t t h e g r o w in g s e as o n [ 1 2 ] .

I n t h e i r ri g a te d I N S F F E R t r i al s S C U e f f e c t i v e l y in c r e a s e d g r a i n y i e l d i n

v a r i o u s s o ft s a n d e n v i r o n m e n t s [ 1 0 ] . T h e av e r ag e e c o n o m i c r e s p o n s e , b a s e d

o n 3 0 % e x t r a c o s t o f S C U o v e r o r d i n a r y u re a , s h o w e d a U S $ 6 - 7 r e t u r nf o r e v e r y d o l l a r s p e n t o n S C U . C o m p a r a t i v e a n a l y si s o f N s o u r c e s t e s t e d 1 9 8 1

I N S F F E R w e t s e a s o n tr ia l s re v e a le d t h a t i n m o s t c a s e s , N a p p l i e d a s S C U

w a s t e c h n ic a l l y m o r e e f fi c ie n t t h a n N a p p l i ed a s P U [ 1 5 ] . C u r r e n t I N S F F E R

r e s u l t s c o n f i r m e d t h a t [ 1 8 ] .

I n t h e l a t e s t I R R I e x p e r i m e n t h o w e v e r , S C U d id n o t i n c re a s e g ra i n y i e l d

o v e r t h e i m p r o v e d t i m i n g , b e s t s p l it N a p p l i c a t i o n ( F i g u r e 7 ) .

B e c a u s e o f S C U s l o w - r e le a s e q u a l i t i es , N c o n c e n t r a t i o n i n t h e s o f t a n d

f l o o d w a t e r i s r e s t r ic t e d a t a n y g i v e n t i m e , w h i c h r e d u c e s N lo s se s . F i g u r e 8

s h o w s f l o o d w a t e r N H ~ - N a n d t o t a l N ( u r e a + N H ~ - N ) w e r e lo w w i t h S C U

a n d h a n d d e e p - p l a c e d U S G . H o w e v e r , b a n d p l a c e m e n t w i t h o s c i l l a t i n g

p l u n g e r o f p r i U e d u r e a r e s u l t e d i n r e l a t i v e l y h i g h e r N H ~ - N a n d t o t a l N c o n -

c e n t r a t i o n s i n f l o o d w a t e r ( F i g u r e 8 ) .

Gra in /ield (t/ha) °J7.5

ZO

6.5

6.0

5.5

5 0

45 '

/ Y /

Y J/ / / Urea sourceb-/

/ / / ~ SOU ~ c o r p o r a t e d ,

e I I I58 87 ] 16 174

Nit rogen rate (kg/ha)

Figure 7. Effe ct o f forms, rates, and methods of urea application on grain yield ofirrigated IR58 rice. IRRI, 1984 dry season, aAv of 4 replications. Separation of means

by Duncan's multiple range test at the 5% level, bSC U = sulfur-coated urea, USG = ureasupergranule, PU = prilled urea. eTwo-thirds broadcast and incorporated at planting;one-third topdressed at 5 -7 days before panicle initiation



N H 4 + N [ k g / h e )2 0

67kgN/ha -~7""~7Prilled urea, bond plocernentI (oscillating plunger)with 5 cm waterUrea supergranules, ointplacement

] 87kgN/ho with 5era waterSulfur-caated urea , broadcastandincorporoled without w ater

1.O ~ Nofer t i l izer N

1 2 3

÷T o ta l N [ u r e a + N H 4 - N ] , k g / h a

l 10 r Samp l ing ime (h )

, 0 7 0 0 - 0 8 0 01 3 0 0 1 4 0 0

O ,

4 1 2 3 4Days a f te r fe r t i l i ze r app l i ca t ion

183

Figure 8 . Floodwater NH ~-N and total N (urea + NH~ ) a t 0 700 -080 0h and 1 30 0-1400h as affected by sources of urea, application methods, and water depth. IRRI,1984 dry season

B a s ed o n t h o s e r e s u lt s a n d t h e r e s u l ts s u m m a r i z e d b y S a v a n t a n d D e D a t t a

[ 2 6 ] , t h e b e n e f i t s o f u s in g S C U t o i m p r o v e t h e N u t i l iz a t i o n e f f ic i e n c y i n

l o w l a n d r i c e c a n n o t b e o v e r e m p h a s i z e d . T h e b e n e f i t s o f S C U a r e:

1 . increased fer t i l i zer use ef f ic iency,

2 . r educe d N los ses,

3 . r educe d t o x i c i t y t o r ice seed l ings ,

4 . r e d u c e d a p p l i c a t i o n f r e q u e n c y , a n d

5 . f u l f il l m e n t o f S r e q u i r e m e n t s [ 8 ] .

R esea rch t o i den t i f y a l t e rna t e s l ow , and con t roU ed- r e l ease N f e r t i l i ze r s i s i n

p rogres s .

5 . Use o f n i t r if i ca t ion and urease inh ib i t or s

A mong N f e r t i l i ze r l o s ses , n i t r i f i ca t i on and den i t r i f i ca t i on have t r ad i t i ona l l y

b e e n c o n s i d e r e d t h e m a i n l o s s m e c h a n i s m s . R e c e n t r e s u l t s s u g g e s t t h a t N H 3

vo l a t i l i za t i on l os ses a r e mos t i mpor t an t i f pa r t i a l p r e s su re o f N H 3 i s h i gh i n

f l ood w a t e r , w i nd speed i s h i gh , and t he r i ce c rop i s t oo you ng t o ab so rb

f a s t e r t h a n t h e l os s m e c h a n i s m s [ 1 4 ] .

O n t h e o t h e r h a n d , i n s t u d ie s c o n d u c t e d i n N e w S o u t h W ale s, A u s t r a li a

o n a c l a y s o il w i t h p H 8 .2 S i m p s o n e t al . [ 2 7 ] r e p o r t e d 4 6 % o f a p p l ie d N

w as l os t f r om t he w a t e r - so f t -p lan t sys t em dur ing t he f i r s t 11 days a f t e r

a p p l i c a t i o n . - O n l y 1 1 % w a s v o l a t i l i z e d a s a m m o n i a , d e s p i t e f l o o d w a t e r p H

va l ues up t o pH 10 and s t r ong w i nds . G aseous l os s a s n i t r ous ox i de w as

neg l ig i b le , and s i mi la r t o ea r l i e r r e su l ts [ 4 ] . Leach i ng o f N be yo nd 100 cm

soi l depth was a l so negl ig ib le .

R esu l t s f r om S i m pson e t al. [ 27 ] i nd i ca t e 35% o f t he app l i ed N w as l os t

t h r o u g h d e n i t r i f ic a t i o n o f n i t ri te a n d n i t r a te a f t e r n i t r if i c a t io n o f a m m o n i u m

near t he so il su r f ace . F i na l f e r ti l ize r N r ecove ry by t he c rop w as on l y 17%.

These r e su l t s sugges t r ema i n i ng cha l l enge t o dev e l op m ana gem ent p r ac t i ces

and su i t ab l e n i t r if i ca t i on i nh i b i t o r s t o m i n i mi ze d en i t r i f i ca t i on l os ses and

i mp rove N use e f f i c i ency i n l ow l and r i ce .



1 8 4

Nitri f icat ion inhibi tors . E a r l y r e s u l t s o f e x p e r i m e n t s w i t h n i t r i f i c a t i o n

inh ib i to rs were repor ted by Prasad e t a l . [25] . IRRI re su l t s show tha t app l i -

c a t i o n o f P U w i t h 1 0 o r 1 5% d i c y a n d i a m i d e ( D C D ) d u r i n g t h e f i n a l h a r r o w i n g

p r o d u c e d y i e l d s c o m p a r a b l e t o t h o s e w i t h s p l i t - a p p l i e d P U w i t h o u t D C D i n

l o w l a n d I R 3 6 r i c e [ 1 1 ] . D C D b r e a k d o w n i s h i g h w i t h h i g h t e m p e r a t u r ein the t rop ic s . Resu l t s w i th n i t rapy r in have bee n incons i s t en t in the t rop ic s .

Resea rch shou ld be acce le ra ted to iden t i fy n i t r i f i ca t ion inh ib i to rs fo r the

h i g h te m p e r a t u r e t r o p i c s t h a t a r e b e t t e r t h a n D C D a n d n i t r a p y r i n .

Urease inhibitors. De Dat ta and Craswel l [9] suggested tha t research on

u r e as e i n h i b i t o r s s h o u ld b e c o n d u c t e d . U r e as e in h i b i t o r s c a n r e d u c e a m m o n i a

vo la t i l i za t ion los ses f rom broadcas t u rea app l i ca t ions by de lay ing , and then

r e d u c i n g , t h e b u i l d u p o f a m m o n i u m c o n c e n t r a t i o n i n t h e f l o o d w a t e r [ 3 0 ] .

F ie ld re su l t s a t IRRI [12] and Mal igaya [13] co nf i rm ed the de lay ing ,

r e d u c in g a c t io n . A l t h o u g h p h e n y l p h o s p h o r o d i a m i d a t e ( P P D ) r e t a r d e d u r e a

h y d r o l y s i s, i t d i d n o t i n c re a s e g r ai n y i e l d a n d t o t a l N u p t a k e c o m p a r e d w i t h

a con t ro l w i tho u t u rease inh ib i to rs [ 11 ] . In a rece n t u rease inh ib i to r s tud y ,

f l o o d w a t e r p H w a s u n a f f e c t e d a n d d i s p l a y e d a n o r m a l d i u r n a l p a t t e r n .

Co n t ra ry to ea r li e r f ind ings , ap p ly ing PPD wi th u rea s ign i f i can tly inc reased N

u p t a k e a n d g r a in y i e ld i n a n I R R I e x p e r i m e n t w h e r e u r e a o r u r e a + 1 % P P D

w e r e t o p d r e s s e d 2 6 D T . G r a i n y i el d w a s n o t i n c re a s e d b y a p p l y in g P P D i n a

s imi la r exp e r im en t a t the Maligaya R ice Resea rch and T ra in ing Cen te r in

N u e v a E c ij a , P h i li p p in e s w h e r e u r e a + 1% P P D w e r e a p p l ie d 1 8 D T [ 1 9 ] .

Resea rch shou ld be ca r r i ed ou t to iden t i fy spec i f i c fac to r ( s ) tha t cause PPDto give var iable resul ts in d i f fere nt s i tes .

6. Co m plem entary pract ices to imp rove N use e f f ic iency

S e v e r a l c o m p l e m e n t a r y m a n a g e m e n t p r a c t i c e s c a n m a r k e d l y i n c r e a s e t h e

N fe r t i li ze r e f f ic i ency . The y a re :

1 . p l a n ti n g a t o p t i m u m t i m e t o e x p o s e t h e r i c e c r o p t o m a x i m u m s o l ar

e n e r g y a t t h e r e p r o d u c t i v e a n d r ip e n i n g p e r io d s ,

2 . c lo s e p la n t in g a n d o p t i m u m g e o m e t r y t o m a x i m i z e p a n i cl e p r o d u c t i o n p e r

un i t a rea ,

3 . e a r ly , t h o r o u g h w e e d r e m o v a l t o m a x i m i z e u t i li z a t io n o f w a t e r a n d

n u t r i e n t s b y t h e c r o p ,

4 . repa i ring o f levees to m in imize s eepage ,

5 . tho rou gh pudd l ing an d level ing o f f i e lds to conse rve wa te r and nu t r i en t s ,

6 . use o f s t raw, azo l l a, and o rgan ic and g reen m anure s a s supp lem enta ry N

sources , and

7 . o t h e r g o o d c r o p h u s b a n d r y p r a c t i c e s t o m i n i m i z e c r o p d a m a g e t o p e s t s

a n d o p t i m i z e g r o w t h f o r m a x i m u m n u t r i e n t u s e e f fi c ie n c y .

T h e s e a g r o n o m i c p r a c t i c es a r e m o s t i m p o r t a n t t o f o l l o w u n d e r r es o u rc e -

sca rce s i tua t ions , a s in mos t t rop ica l As ian coun t r i e s , than unde r re source -a b u n d a n t s i tu a t i o n s t h a t e x i s t i n m a n y t e m p e r a t e c o u n t r i e s .



185

In the present fertilizer use-intensive rice production technology, agron-

omists and soil scientists should pay greater atte ntio n to managem ent of the

natural supply of plant nutri ents [23]. Natural nutri ent sources for a rice soil

are m ain ly edaphic cons titu ents , rainwater and irrigation water, the rice

cultur al system per se, rice based c ropping systems, recycling of crop residuesand other organic waste materials and biological N fixation.

Deep tillage and good land preparation promote full and efficient

utilizat ion of the native soil nutrien ts and enhance expensive produ ctio n

inputs such as N fertilizers.

It is apparent that max imu m average 4 to 5 t/ha rice yields can be ob tained

with deep tillage, high fertilizer rates, good irrigation, use of input-responsive

mod ern rices and op tim um crop hus bandr y practices. The research challenge

for increased tropical Asian rice production is not only to maximize rice

yields bu t also to max imize i np ut use efficiency, particul arly N use efficiency,

in lowl and rice.

References

1. Broadbent FE and De Datta SK (1984) Differences in response to nitrogenfertilizer by rice varieties/lines. Agronomy Abstract. 1984 Annual Meetings,American Soc Agron, Las Vegas, Nevada, USA

2. Cao Zhi-Hong, De Datta SK and Fillery IRP (1984) Effect of placement methodson floodwater properties and recovery of applied nitrogen (15N-labeled urea) inwetland rice. Soil Sci Soc Am J 48:197-203

3. Craswell ET and Vlek PLG (1979) Fate of fertilizer nitrogen applied to wetland

rice. In International Rice Research Institute. Nitrogen and rice, 175-192, LosBafios, Laguna, Philippines4. Craswell ET and De Datta SK (1980) Recent developments in research on nitrogen

fertilizers for rice. IRRI Research Paper Series 49, 11 pp5. CraswellET and Vlek PLG (1982) Nitrogen management for submerged rice soils.

In Symposia Papers. II. Vertisols and rice soils of the tropics. Transactions 12thCong Int Soil Sci 3:158-181, 8- 16 February 1982, New Delhi

6. De Datta SK (1981) Principles and practices of rice production. John Wiley & Sons,New York, 618 pp

7. De Datta SK, Garcia FV, Chatter~ee'AKI Abilay WP Jr, Alcantara JM, Cia BS andJereza HC (1979) Biological constraints to farmers' rice yields in three Philippineprovinces. IRRI Paper Series 30, 69 pp

8. De Datta SK, Crasweli ET, Fillery IRP, Calabio JC, and Garcia FV (1981) Altern-ative strategies for increasing fertilizer efficiency in wetland rice soils. Paper pre-sented at the International Rice Research Conference, 27 April-1 May 1981.International Rice Research Institute, Los Bafios, Laguna, Philippines

9. De Datta SK, and Craswell ET (1982) Nitrogen fertility and fertilizer managementin wetland rice soils. In International Rice Research Institute. Rice researchstrategies for the future 283-316

10. De Datta SK, and Gomez KA (1981) Interpretive analysis of the international rialson nitrogen fertilizer efficiency in wetland rice. In Fertilizer International 1-5, TheBritish Sulphur Corp. L t d . , Parnell House, England

11. De Datta SK (1985) Availability and management of nitrogen in lowland rice inrelation to soil characteristics. In International Rice Research Institute. Wetlandsoils, characterization, classification, and utilization, 247-267, Los Bafios, Laguna,

Philippines12. De Datta SK, Fillery IRP and Crasweli ET (1983) Results from recent studies on

nitrogen fertilizer efficiency in wetland rice. Outlook on Agriculture 12:125-134

improvine n fertilizer efficiency in asia

Documents