crop monitoring and forecasting

FOOD AND ACIRICULTURE OROANUTlO#

FA0 PLANT PRODUCT ION AND PROTECTION PAPER

agrometeorological crop monitoring and forecasting

bw m. frbre and g.1. popov

plant production and protection dlvlslon

FOOD AND AORICULTURE ORGANIZATION OF THE UNIT ED NATIONS Rome 1970

T h . d m a q M b r r n n p l o y . d . n d t ) w ~ o f m r r ~ 6 n t M . ~ k n * n o r k n O I y t t u empramdon at rcry aOkrian UI)UZIO.WI 011 th. pm of th. Food md Agricu)hrm Orgmbtfm ol the Unitod N c t h th. kgrl etnw ot .ny country, tmttory, dty or woo u d its euthodtkr, ar ccmamhg the d.&ncuni ol lts f r o m k n oa bounbwi...

Tha copVriOht In this bOOk iO vested in the Food UlCL Agdcdturo w- nintmnoftheUnh.dN8tknr. Theboo&nuvnotkrwwodu;csd.mwhob

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

C H A P T E R I: Importance of c r o p lorecarting bared o n . . . . . . . . . . . . . . . . . . . . . . . . agrometeorological m o n l t o r i n ~ I

C H A P T E R 2 : Summary of the methodr ured lor c r o p torecanting . . . . . 4

C H A P T E R 3 : T h e c r o p forecastin8 method baaed o n a l r o - . . . . . . . meteorological information .................... 8

C H A P T E R 4 : Agronomic concepts of the phy,rically-daflnrd growing searon.........,...............,..,..., . . . . . . 19

. . . . . . . . . . . . . C H A P T E R 5 : R e v i r w of applications and of experienca 2 1

CHAPTER 6: Organization of a c r o p m o n f t o r i n ~ and forecasting myatem bared o n agramrtmorolog1cal i n f o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

C O N C L U S I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

R E F E R E N C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7

A N N E X : A method for the practical appllcatlon o f the penman formula for the ertimation of potentlal evapotranrplration and evaporation from 6

. . . . . . . . . . . . . . . . . . f r e e water surface.....,............ 38

A f t e r t h e d r o u g h t whlch n t r u c k t h e c o u n t r i r w In t h e S r h # l l a n r r r a ! r a n l U 7 l t o 1973 F A 0 8 n J t h e World Food P r o g r r a m e u n d t r t n o k r u y r t @ a a t l c ~ n o n l t o r i n g of r a l n l r l l d u r l n g t h e g r o w i n n r a r r o n 41 t h a t u r e a I n i r r d l r tcr d e t e c t r t a n e a r l y d a t a any r n o m r l i e r i n t h e q u r n t l t y rnd d t a t r i b u t l o n o f r a i n f a l l which m i g h t h a r m f u l l y r f f a c t c r o p @ .

In 1Y7h t h e s t m p l t r r l n f r l l a o n l t o r i n ~ b a r e d nn d e p r r t u r r r r r o n " n o r m a l " r a i n f a l l e v o l v e d i n t o rn r r r a r r m r n t of t h e c u m u l n t l v r w a t e r b a l a n c e of c r o p e and r r h o r t n o t e v r a p r l n t a d r n d w l d r l v d l s t r l h u t r d ( F r e r e and Popov , 1 9 7 6 ) . Ar a r e r u l t of t h l r n o t * t h e Y l l n t P r o d u r t l a n and P r o t e c t i o n D t v l r l o n r e c a l v c d many r e q u c r t e f rom y o v r r n a e n t r f o r Lhr l n t r o d u c t l o n r t n r t i o n a l l e v e l sf t h e mothad d r r l ~ n e d b y t h e Crop t . c o l n ~ r and L t n e t l c R e a u u r c e r U n i t ( A C P E ) . C o n r r q u a n t l y r p r c I f l r n i a r l o n r went t o F - t h l o p l a , A l g r r t r . T a n z r n l r , C h r n r , Togo, N i g a r l r r n d W r i r l r n d many u t h r r c o u n t r l e r , much r e B r n g l a d c r h , I n d o n a r l r , V ~ n r r u e l r and h u d r n , have drmon- # t r a c e d i n t @ r * f i t i n this r g r o a o t e o r o l o g l c r l c t o p m o a i t o r l n g and f o r e e r r t i n l m e t h o d .

T h e p u r p o r t of t h i n p u b l l r a t l o n I a t o p r e s e n t t h e method f in I t now s t a n d s , t o g e t h e r w i t h r o o @ r e a u l t r o b t r f n r d I n r wide rrnfr,# a f s n v l r o n - m t n t n . The e x p e r i e n c e g a i n e d oo f r r r l r a r d y a l l o w r w l a o d a a r r r a m a n t t o hc made o f t h e u u e f u l n c r r o f t h e method i n c o u n t r i e r u h r r e v r t r r n v r l l - a b i l i t y l o t h e main c o n r t r a i n t f o r c t o p p r o d u c t i o n , l i l r r l f i n c l e a r t h a t i n many i n e t a n c e n t h e r p p l i c r t l o n of t h e method w i l l f o s t a r r h r c o l l e c t f a n o f s e t s of flood b i o l o ~ 1 c r l d r t r ( y i e l d and p h a n a l o g y ) w h l c h , when I n t e r - p r e t e d t o g e t h e r w i t h t h e r g r o c l l m r t o l o ~ l c r l d r t r , w i l l p e r m i t t h e p r o g r o r e - i v e o o t a b l i s h m e n t of f u l l y q u n n t l t r t l v r r o d e l r . Thr main a d v r n t r ~ e n l t h e present m e t h o d , h o u ~ v e r , f r t h a t t h e work c a n b e f n l t l r t a d t m m r d l a t r l y b i t h o u t r o p h i s t i c r t e d m a r n r , e v e n i f d e t a i l e d q u r n t l t n t l v c y t r l d d r t r r r r n o t r e a d i l y r v r l l r b l c . .

I H P ( ~ R I A N E E oF CROP F O R E C A S T l N C B A S L D 08 A C M O H E t ~ ( J I I l I . O C I C A L H C r N I T O R I M C

Tha c v u l u t h a n o f r r u p p r n d u c t l o n over t h e p a r t 30 y e a r 8 hrn r h o y p w ~ r l k i n ~ p r a l r a r r In nonc d r v c l o p e d c o u n t r i a r i n the y i t l d e and r l r o I n t b c l l u b v l p r o d u r t l n n , r l t , h t ~ u g h Lhlm l n c r e r r r h r r b a r n c o m p r n r r t e d r o m e u h r t b y 8 r a d u c t i u n of 1 . t i l t l v a t ~ d r r s n r . The r e s u l t o f t h i s p r o g r r r n i r t h a t c (nr r01 p f O d ~ ~ t l l ) n t n d r v r l o y r d r o u n t r l e a hnu nhc~uti o n l r ~ c r r r n ~ over t h e p a r l o d o f r b n u t 5 0 1 .

In d a v r l a p l n g c u u n t r l e a , h o r c v r r , p r o d u c t i o n i n c r e r r r t t r r b r a n much r l o u t t r , u h i l a In mcrwt c o u n t r l e r t h e p o p u l a t i o n !la# lncrcar red d r u a t l r a l l v , dud t o Lmprnvad h y g l c n a and m a d l c r l c a r e . T h l r phanoornon h a s been a g y r r v r t a d b y r h s a t ~ r r t l e n of l r r g a ~ r o u p m of p e o p l e fro. r u r r l r r r r r t o l o v n r , w i t h r c u t r r r p o a d l n ~ c h r n a e i n f e e d i n g h r b l t o , Thin h a r l a d t o r g r r r t e r c a n n u m p t i o n o f p r o d u c t r which h r v r t o be i m p o r t e d , #uch 4 0

w h a r t f l o u r i n t r ~ r p t c r l c o u n t r l e r , l o r e x r r p l a . In r d d i t l o n , fwd p r u d u c t - Ion v r r i r a f r o m y e a r ru y e r r , r a t h e r e I r a l w r y r r a a v s o e n t a f c a p e n a r t i o n f rom r u r y l u r t o d s f i c i t a r c n u . I t r o h r p p e n r t h a t c l i m r t l c v r r b b l l l t y hum n x h i b l t r d roms a x t r a m t p e r i o d r of d r o u l h t o v e r t h e l r r t d e c a d e , some- t l n r r I n r r v c r r l p r u d u c c l o n r r a r v r t t h e r rme t l n e . T h i a h r r a a c e n t u a t c d t h e i m b n l o n c r i n f o o d r u p p l i e r a x l l t l n p b a t w a r n v r r i o u r r e g i o n s of he w o r l d .

I n v l a v o f t h l r r i t u r c l o n , I t h r r become I n c r e r f i l n g l y n r c e a r s r y t o f o r ~ c r e t thr r l r r r n d q u n l i t y o f h a r v e r t r , p r r t i c u l r r l y f o r c e r l r l c r o p a , whlch r r m r l n t h e b r r l c r o u r c e o f f o o d i n a o r t p r r t r of t h e w o r l d . F o r e - c n r t r e r e v e r y i m p o r t r n t t o h e l p t h e p r o d u c i n p c o u n t r i e r t o know i n r d v r n c c t h n r i r a o f t h e h r r v e r t r n d t h e p o r t i o n o f i t which c a n be e x p o r t e d . They a r e r i r o v a r y i m p o t t r n t f o r t h e f o o d - i m p o r t i n g c o u n t r i a r , i n o r d e r

p r e d i c t i n a d v a n c e t h r r i z r o f t h e n r t i o n r l h r r v e r t ; t h e i r e x p o r t a t i o n ~ a p r c f t y , @ r r l t r r n a t i v e l y t h e p o r t i o n of t h e c a u a t r y ' r food c o ~ s u a p t i o n which w i l l h a v e t o be p r o c u r e d f r o m a b r o a d , c a n t h e n be d e t e r m i n e d . The

ramark* a p p l y , o f c o u r s e , t o r m a l l e r a r e r e w i t h i n r g i v e n c o u n t r y ,

P i n a l l y , t t i s a l s o l m p a r t r n t f o r t h e i n t o r n r t i o n a l and d o n o r r g e n c i a r l o know t h e f o o d p r u c u r e m e n t p o s s i b i l i t i e s and r e q u i r e m e n t 8 i n r d v r n c a , r o r 0 t o o r g r n l t c emarRencv f o o d a a o i a t a n c e programmer i n t h e b e s t p o s s i b l e wry, p e r t i c u l r r l y f o r t ho l e a s t d c v e l o p a d c o u n t r i e r who c a n n o t r l w r y r 1 0 b i l l z 4 h r r d c u r r e n c l e a f o r t h e p u r c h a s e o f f o o d , A good e x r m p l e o f t h i n a c t i o n l r t h e emergency meaeureo t r k a n s i n c e 1 9 7 3 by t h e O f f i c e o f S p e c i a l B e l i e f d p l r r t i o n r (OSRO) o f FA0 t o a l l e v i a t e t h e f o o d c r i ~ i s i n t h e d r o u g h t r t r t c k r n t o u n t r i a s of t h e S a h c l i a n r r g i o n . S i n c e t h e n , a c a r e f u l e a r l y 8fiBgS8mant o f t h e ~ D ~ Q C S ~ haa been made i n t h a t a r e a and i n o t h e r a r @ r r n a r c r c n r i t i v a t o d r o u o h t .

?h i8 e f f o r t h r r c e r t a i n l y b d r n I r u l t l u l , ar i t ha# r l l c ~ w r d l m p ~ n d l n l dra#&rou8 # l t u r t l o n a l a r d l n ~ t o t o e d crlrnr t ,o ba d r t r c t e d a t n v r r y s r r l v r t r g s and adequate ns raurea t o be t l k a n v r l l In r d v ~ n c a , I t I r t l r a r , howevrr, t h a t i n the f u t u r e t h l r t r e k o f c r o p t a r e c r a t l n g w l l l l ~ r v a l o b s c a r r i e d out p r f r a r l l y b y t he r o u n t r l o r tblaku1vra and w l l l c o n r t l l u t r r f u n d r r e n t r l p a r t uf ( h a i r n a t i a a r l food r r c u r l t y wchftmr, Thr pu r roa r o f t h l a p u b l i c r t i o n l a thua t o p r r r r n t 4 authod w h i c h , u l t h n u t r e q u l r l n a r o p h l 8 t i c r t a d rranm f o r the i n t e r p r r t r t l a n u[ thr J r t r , w i l l rnrblr a good r r 8 e r r r e n t t a be r r d r o I t he f o r t h c o a t n g h r r v r a t ,

SUMMARY OF Tl!E HCTHODS U B L D FOR CROP ?ORkCASTIMC

2.1 I n t r o d u c t i o n

C r o p r h a v e r l u a y a I t u c t u a t e d f r o m y e a r t o y e a r ; t h i s phanomenon c a n be r r e n i n f i g u r e 1 , v h t c h a h o v a r e r i e o o f f a v o u r r b l e and u n t r v o u r a b l e y a a r r f o r c r a p r , O v r r t h a l a r k d a c r d e r , h o w e v e r , much more e m p h a a i s h r r been p l r c a d on wayr t o L n c r a r a r r g r i c u l t u r r l p r o d u c t i o n t h r o u a h c r o p r a l a c t i o n , t h a u r e of f e r t i l i r a r r a n d improved e g r l c u l t u r a l t e c h n o l o g y , i m p l y i n # r v i d e u a r o f c h e a p e n e r g y .

f t 1, o n l y r a l r t i v e l y r e c a n t l y t h a t r e n e u e d a t t e n t i o n h r r b e a r d o d i c r t a d t o v e r t h e f t n f l u e n c ~ a on c r o p u r o w t h a n d d e v a l o p m r n t , i n p r r t i c u t a r r r r r a a r d b t h a r e l r r l o n r b a t w e e n w e a t h e r r n d y i e l d r . Tho r p p t o a c h a a u a r d ware d l v e r s a a n d r o n a c o n f u r i o n e x i s t 8 i n t h e t r r m l n o l a g y u r a d i n r h a r a t n v a r t i g r t l o n m . A r e c e n t a r t i c l e ( B a l e r , 1 9 7 9 ) h r r t r i e d t o c l a n a l l y the b a s l c t y p e s of c r o p - w a r t h a r m o d e l r r r l o l l o u r :

1 C r o p y r a u t h r i n u l r t l o n m o d e l r

2 . C r o p - w a r t h e r r n a l v r l a m o d e l r

Figurr 1: United S t a t e s ' corn y i e l d 8

A crop 8rovth rtmulrtioa nodel ma) be drfiaed 4r r rlmplltlrd reprrrentrcloa of the pbyrlcrl, chemirsrl and phyrlolo~icrl aechanlrmr underlying plrat prouth ptocerrer. It the brrlc plrat proerrrer - produccloa rod dlrtribution of dry Ratter aad water talrttoar - rte properly uadrrrtood aad modellrd, the rntire rerponre of tha plant to the enviroamrntrl coadltloar can be simulated, Thrrefarr there I8 a o noad to diffrrantirte betuera cAtmrtkc ta&ioar, rincr the rlaulrtlon model itrrlt will ahon the limitlag factore for arouth. In humid climate8 vith low temparrture end rrdietioa levrtr. the modei will generally rhow the grrrtrrt rrrponre of yield8 to increrrer in totr) rrdlrtlon received, la rn arid rnd hat climate it will rhov tho grartert rrrponra to tho dlrtribution and totrl rmount of precipitation.

Vrriour tiar intrrvrlr era be introduced la riaulatlon modelr; for arrmplr, la view of the drily cyclr of many plrnt procerr*r, hourly latrrvalr are mort practical, It ir then rrrumrd that the rrte crlculrted for 8 prrtlculrr moment doer not change rpprecirbly over 8 period of oar hour. It ir porribla to rvrlurte thereby rpecific procerrea ruch rr photo- ryntherir, tranrpirrtfon or rerpirrtion for rn hour rnd than recumulrce the hourly rrtrr over the day and thr daily rrtrr ovrr the @tovin# rranon in order to rrrivr at the totel rrreonrl dry matter production or yield of economic productr. &t the prrrent time, r$mulrtioa progrrmmer murt br ! Irrgardrd morr a8 a 8uidr to rerarreh taco the brhlviour of biologlcrl ryrtear rrthrr than rr r final rolution. Simulrtion can br *or( urrlul "' !if the model account8 for mort rmlrvrnt pheaomrnr and contalnr a o frlre rrrumptionr. Simulrtton providrr ra fnright into crop-werther relrtion- rhipr, erplrinr why roma frctorr ate more importrnt for ylrld than othrrr, a u g ~ r r t r frctorr ltkrly to have rtrtirticrl rigalficrncr rnd providrr the brrir for nrw rxperimeatr on procerrer which rpprrr to be importrnt but are nor yat rufficiently underrtood, Thur, thr rimulrtdon rpprorch doer not rtplrct the rtrtirticrl rpprorcb, but la complrrratrry to it.

A typical exrmple of a dynroic model of plrnt and crop lrowth ir thr elemeatrry crop growth rimulrcor (ELCRQS) dercrlbrd by dm Wit, brouwrr and Penning da Vrier (1971).

rhc WHO Commiarlon for Agriculturrl Meteorology, rt it8 rixth arrrlon, appointed two rapporteur8 (f . P . Hrun, U S A , rad 0 ,D . Sirotrnko, U S I R ) on rimulrtion modellin& in rgrometaorology rnd the reader ir referred to their forthcoming raportr. Sever81 excellent rrvirvr of prprrr rrlevant to model rimulatlon brve rrcrnrly brcore rvrilrble, ruch rr: "Potentirl crop productioa" (edited by Warelag rod Cooper, 19711, "Progrerr in biorrceor- ology; Divirion C, progrerr in plrnt bionrteorolopy" (edited by Smith, 19!5r) r rpecirl irrue of the A ~ r l c u l t u r r l Hrtrorology Journrl entitled "Plant modificrtion for aore rfflcieat water ure" (edited by Stone, 1 1 7 4 ) .

2.3 Crop-vrrtbcr rarlyrir models

Crop-weather raalyria modelr rra drftnrd hrra rr tho product of tuo or more frctorr, each raprerenting tbr (riaplifird) function81 rrlrtionrhip brtvern r p ~ r t f c u l r r plant rerponre (e.g. yield) rad the vrrirtfoar La relected varlablrs rt different plrat drvrloprrntrl phrrer. Thr ovrrrll

elfrctr, r r ewpranrad by !ha numcrfcrl vrluer of the Irctors, modify arch other but #rm n o t rddltlva a r In the crrc of r multl-vrrfrte linear res- rerrlon nqurtion. Suth modelr dn not require r formulatrd hypotheria of the b r r l ~ plant and rnvlronaental process; thus, the laput rrquirrmeotr rra l a ~ r rtrlngant but the ourput iaformatlon 1 1 more deprndent oa the tnput Jrta rnd leer datrilod than In the crrr of riaulrtion aodelr, There- fore, crop-weather rnrlyrir modelr are r pratical rtrearch tool for the rnalynlr o f crop rcnponrrr to vrrther rnd rllmata vrrirtionr when ealy cllrrtolo~lcal data are avrllable, Convrntlonrl rtatlrticrl p r o c e d u r ~ r are urad in ruch aodwla to evrluata the cortficirntr ralating crop rerpoarer t o cllmrtulogical or derived rgrarrteorologlcal data. A convenirat time interval 11 one day, but In prrcricr rhorter or longer prrlodr can rlro be urrd, pruvldrd tho rerponrr chrracterimtlcr of tho crop. do not chanle spprrclrbly ovar ~ h c relsct*d period In relation to thr variable trktg lnto canriderrtion.

A typical r ~ r m p l e of thin rpprorch ir the crop-uoathar rnrlysir madel proporad by Ialrr (1973). the prfmrry o b f ~ c t i v r of thir model ir t a rnalyar the drily contrlbutionr of up to throe relrcted rgrolrteor- olofiicrl vrrlwblrn to the final or rrrronrl yield, althouah othfir crap rarponrrr ruch a# velatrtlvr growth or reproductive drvelopment (progrerr touardr maturity) rra rlro conriderad. Tha crop rerpoare to rr@h of the thrrr input varlsblea 18 rithrr linear (poritive or ne#rttve) 0%' quadratic (concrva or convex). The rntponac chankea ~ r r d u a l l y during the life cycle of aanurl craps a8 r functioa of bioarteorologlcrl rlre (~obortfion, 1968). the rerponrr charrctsrlrticr arr not known and are not pre-decc ined. Inaterd, it in rrrured rhrt r fourth pover pulynomirl, with bio t eteor- o l o ~ i c r l time an indapendrnt vrrirblo, ir rdrqurta for fitting #he dally wrl@ht in# lactorn rraaciated with the daily contribution of ercv vrrirble ta the fin81 yield.

Thu dlclrlon regarding the functionrl ralrtionrhip to br u#*d in'the madel warn bared on the a ~ r u a p t i o n that crop yieldr depend brric!lly on three rgrolnt~orologlcal vrriabler: molar anergy, temperrture r6d 8011 aoirture (gr evrpotranapirrtfon). There three vrrirbler modify arch other on any prrtlculnr dry during the life cycle of a crop and produLe a pomitive or n ~ g r t l v @ effect on tha final yleld.

In thr capiricrl approach, one or sevrrrl varirblar (reprerenting weather u r elimnte, no11 characteristics or a time trend) are reletad to crop raoponsrr ruch re yield. Tha "independentw vrrirbler are often tempsraturr or precipitrtion t e r ~ a or derived rgtometC0rol06icrl vatiabler such rr an index of the atnorpharic aoirture atreme or the soil moiftura r@uirn@. The weiuhting coafficienta in there equrtionr arc by n e e e l 8 i t ~ obtained in rn capir ical manner uring standard rtrtirt ical procedures, ruth 48 multlvarlbale regcornion anrlyair, Thie atatirticrl rpprorcb doer not crtily lard to rn explanation of the cruse and effect relrtionehips, but it 18 a very practical approach for the aarrrement or prediction o f Yleldfi. coafficienta in euch arpirical models and the validity of the e@ti@atca depend to r large extent o n the derign of the model, ar w e 1 4 ar on the rrprarantativenerr o f the input data. If the soil and climate coaditlona and the cropping practices are fairly homogeneous over the area r@Prar@nfed by the iaput drtr, or if soil and prography are properly

urt$hred in t he equa t ionr , then i t #rn be expected t h r t the c n n t f l c t ~ n t a and the e r t i m r t a r have p r r c t i c r l r i a n i t i c r n c a f o r rhr r r r r r rment o t r h t crop cand i t i on r o r p r ed i c t l oa of y l e l d r f o r t he rp*c i f i c r r a r In q u o r t l o n

Ia .leu of i t r r i r p l l c i t ~ , i t l r d i f f i c u l t t o a t t r i b u t e r p r e r l r e place i n t h i n c l r m r i t i c r t i o a t o the method d r r i an rd b y t A O and r r p l r l a r d in chapter 3. I t ernnot br c a l l ed a r l r u l r t i a a aethod beerurr [,ha v r r l r b l e taken i n t o account, r l tbou#h r y n t h e t i c , i r ualqur and brcrurc r h a rvolur l u n o f the c r o p r r f a r r e davelopmeot pherac r r r concernad l a tnkmn r e r ctlarrrnr, f o r a given p l r ca rad crop. On t he o thar hrnd, i t r approrch by auccrarlvm rttpm of 10 dryr a r r a s t h r t i t t r k e q i n t o %ci~eount e l l r r t l c I ,nI lurnear w o r k l n ~ over rho r t per iodr end thur i r not r e t l l y thn n lobr l r a p l r l e r l r t r t i r t i c r l approrch,

Ur f a r l , t he r e fo re , t b r t d e r p i t e i t r #anulnr r l w p l i c i t y t h l r k i n d a t mudrl f r l l r i n t he c r t e l o r y which Briar c r l l r crop-warthcr r n r l y r l r b u d o l ,

T H I CPOP POPICA$II#C HCfHOD RASLU OM A(;ROHETECII1OLOCICAL IIfOPMATlOU

Th* mothod pr r*rn t rad i n c h i * c t ~ a p t c r r her bean d e s i g n e d by t h e C r o p 1 . c 1 v l a ~ and CanM l c R*eaurcar U n i t ol t l i c P l a n t P r o d u c t i o n and P r o t a c t i o n b l v l r l o n of FAU. I t r o r l g 1 n a ) i t y l i e * i n t \ ~ e f i l m u ~ t a n e o u r u s e o f a c t u a l r r l n l r l l d d t a and c l l m r t o l u g l c r l I n l u r r r t . l w n f o r r h a c a l c u l a t t o n o f t h e uakur x r g u l r u a ~ n t n u t c r o p u . 'Il lenc t v n k i u d a o f d a t a a r e c o a b l n a d l o r t b r e r t r b l i r h m d n t o f t h c c r o p w r t r r b n l r n r a .

While b a i n g more p r n r i u c r hat\ rr s l n ~ l r a u s e r s m c n t o f n c t u a l r d n f a l l and Ltn c a m p a r i r o n w i t h "normit!" r a i n f a l l , ttru msthud r e m a i n s # l a p & rnouglh t o b* r n s l l y o p a r r t e d wl t l lou t ~ t n p h l r t l r s t a d e q u i p m e n t . I t r e l l e r Q r mtnlwua r a a u n t o f r r t o r l d u t a dnd ~ n k a r u a e u f r o a e c l t a r t o l o g l c a l N n f o r a - tit i o n u l ~ l c t ~ aby be a r w ~ a h l a d b r f u r a t t ~ c " o p e r u t l a n n l " p h a s e , o u t r i d @ t h a c r o p p i n g r r r r o n . V l n a l l y . t k e m r t t ~ a d f n d c n l g n r d i n ~ u c h r wry t h d i t p r o v i d e r r (irwt q u r l i t a t l v r m u n l t o r i n & a 1 c r o p c o n d i t t u n e . by a u r c q b a i v t trccpa and rllawu thur y r c s p r r a l l o n o f q u a n t i t a t l v e y i e l d a s ~ e a 6 i m e n t n , p r o v i d e d rrnclu~h Lnf u r n a t i o n on aq,r t c u l t u r a l y i e l d s i s a v a i l a b l e f o r t h e r c ~ j i o a u n d e r c o n r l d o r a t l o n , T h s p r e c i s i o n o f t h e s e a s s e s s m e n t e w i l l improve t o d a r d s t h e \ \ o r v e n t t l a t .

Thr method f u b e a r d on a c u m u l a t l v e w a t e r b e l a n c e e e t a b l i e h e d o v e r t h a whulr g r o k t n ~ r e a s o n f o r t h c y l v e n c r o p and e s t a b l i e h e d f o r a u e c e e n i v e p e r i o d # of 10 d r y u . The l a n t d e c a d e s of some m o n t h s w i l l h a v e 8 , 9 o r 11 dryr; o v a p o t r a n r p l r r t i ~ n f i g u r e s w i l l be c a l c u l a t e d a c c o r d i n g l y . Some c o u n t r i r a p r r f a r t u work u t t h wcsk ly p s r i o d a , g e n e r a l l y f o r r e a s o n 8 of o r g a n i x r t l o n o f t h e work . Thin 1 a p o s s i b l e , and FA0 h a s p r e p a r e d weekly forma Ln Chis r s a p e c t . However, t h l a a p p r o a c h p r e s e n t s some d i f f i c u l t i e s f o r r h r i d e n t i f i c r t i o n o f t h e p l a c e o f t h e weak i n t h e month o r f o r t h e f a a p a r t s o n o f crop pin^ n e a t o n e f r o m one y e a r to t h e n e x t . F o r r e a r o n 8 of conv*ni*nca , however , a l l t h e s u h a e q u c n t e x p l a n a t i o n r w i l l r e f e r t o d e c a d e s

The w a t e r b a l a n c e i s t h e d i f f e r e n c e be tween p r e c i p i t a t i o n r e c e i v e d by tba c r o p and t h o water l o s t b y t h e c r o p and t h e s o i l . The w a t e r r e t a i n e d by t h r r o i l nhould wlmo be t a k e n i n t o a c c o u n t i n t h e c a l c u l a t i o n .

Thr c a l c u l a t i o n o f t h e w a t e r b a l a n c e i s c a r r i e d o u t on e p c c i a l f o r a s , r copy o f u h l c h i a reproduced a a f i g u r e 2 , w h i c h r e p r e s e n t s s e v e r a l r x r m p l e r c r l c u l r r e d from re81 vaLudtt anaembled f o r v a r i o u s l o c a t i o n s a n d crop* In t h e S c h e r + ( - n r e * ,

i t W 8 t r t r o bo montionrd t h a t tho method i r l a t r a d e d r a l a l y f o r u t l l i t r t i o n f a dev r lop i a# c o u a c r t r r , v h r r r l a t.iafe4 r ~ r L c u l t u r r t h e # r l n c o a r t r r i a t i r g t n r r r l l y l n a d r q ~ t r t r r v a i l r b l l i t y of wrc t r t o t b r c rop . T h r r r f o r r t h c method d o r r a o t d i r r c t l y i avo lv r tho r e s p a r r t o t a which c o a d l t t o n r t h e growth of t h r c rop . Uoutver, looking c r r aCu l ly r t the ozrmplrr e lcod t n c b r p t r r 5 from c o u a t r i e r wbrrr t h e method h r r bean t r r t o d , i t r p p r r r r t b r t th* t e a p r r r t u r a w i l l l a f a c t i a t e r v e a r l a d i r e c t l y i n 3 vayr i n t he method of c rop u r t a r b r l r a c e r r r r o r o e a t . The a f f e c t of r l r t r r p r r r t u r r w i l l f i t a t be n o t i c r d i n t ha l r a g t b o t tbo growing c y e l r , vh icb i r g e o r r r l l y d i r r c t l y dopandrat on t b r t a r p a r r t u r r . t o r r samplr , i n Co lo rb i r t h e d u r r t l o n of t h e v r t a t r t i v a c y c l e of mr i ra p r r r r r from 150 t o 300 dayr going from r e r l r v r l t o 2500 r l t l t u d r . In t he r r a r w r y , r r p r r i m e a t r mrdr with t he rrmr v r r i r t y of wheat, n 8 i r t r C r r r o r u , sown i n g r e a t l y d i f f e r i n g c o n d i t i o a r , have rhoua groving c y c l e r g o i n v from 74 t o 177 d r y r . Air t a m p r r r t u r r 8180 i n t r r v r n r r d i r e c t l y l a t b e c r l c u l - r r l o a o f potent181 r v r p o t r r n r p i r r t i o a and i n t b l r r r r p r c t i a f l u r n c r r t b r wholr wr ta r b r l a n c r . t i a r l l y , r r t r r m a t r m p r r r t u r r r may br impottrnc i n r o r r c l i r r t i c r o a r r , p r r t i c u l r r l y r r r e g r r d r f r o r t a .

1 .3 ua ctrmr o f tho SII-~OP o f t h r w r f r r bd l l nc r

Thr d i f f a r r n t a t r p r of tho c r l c u l r t i o a of t he cumul r t i v r v r t r r b r l r n c r r r d a t r i l e d h r r rund r r and r r i r r t o t h r rymbolr rhoun on t he c r b c u l r t i o n form i n f i$ure 2 .

3 , J . l Normal p r r c l p l t r t i o n (pH)

Thir symbol r r p r r r r r r t h r norm81 p r a c i p i t r t i o n by dec rd r c&lcwi r t rd from lonn t a r 8 a e r i e r of c l l m r t o l o $ i c r l d a t a f o r tho r t r r i o n c ~ c r r n e d , I f on ly monthly t o t r l r r x t r q they can a r r i l y br broken dawn InCY, decade8 by g r r p b i c r l p r o c r r r r r o r with t he he lp of r mlnlcomputrr ( roe k i g u r r 3 ) . Thir rhowr rn rrrmp9r of ruch r p l l t t i a g mrdr by computrt f o r tY r t r t t o a of Crp Ha l t i on , t l r l t i . I t w i l l b r noted t h a t t h r po in t8 of in$$ex- ion c h r r r c t r r i r t i c af t h r blmodrl d l r t r i b u t i o a of r a i n f a l l r r r pmoothsned by Chr p roce r r . T r b l r 1 rhowr tho o r i t l n r l r v r r r @ r monthly vrlj;ler of r r l n f r l l rad t h e r r r u l t i n g v r l u r r f o r t he r u e c a r r i v r 10 dry p r t i o d r ,

li '

6 2 2 9 18 62 Jan. 3 1 Apri l 30 J u l y 1 3 O c t . 7 4 110 34 90 31 44 13 2 1 9 8 3

3 5 4 6 12 9 8 I r b . 36 May 5 4 i 06

Augurt 1 3 Nov. 106 35 1 4 7 1 7 4 5 20 298 9 1

39 36 2 7 73 Match 33 Junr 30 Sept . 35 Dec. 61

97 33 90 2 4 109 4 7 186 52

Tabtr - I : Vaturr of n o n t h t ~ and 10 day aurrage raiafuZZ tor Cap B o i t i r n R n i t i

o o r m r l p r r c l p i t r t i o a r p p e a r r o n l y r r S a f o r m r t i o r Lo L n d l c a t r t h a " a o t m r l ' d r t r of t h a r t r r t o f t b a r r l a y r a r r o a r e d i t r " n o r m r l n l a o 8 t h . I t r l r o g l v r r a n Idma of t h o d e p r r t u r r of t h e a c t u r l r r l a f a l l f rom t b r " a o r m r l N whoa comprrad w i t h t h r r c t u r i r r o u a t of r r l n f r l l r k o u n on tbr n e x t l i n e .

With r v e r y r h o r t r r l n y r r r r o a , r u c k r a t h a t of M a u r l t r n l r , t h r l r c t t h a t i n 1977 no r a l a hrd t r l l e n by mid-Autur t o v e r t b r p a r t o l t h o c o u n t r y d e d i c a t e d t o c r o p c u k t l v a t l o a l a d i c a t r d t h a t moat p r o b a b l y , d u o t o t b r r h o r t amount of t f m r l r f t , t h r c r o p would n o t m r t u r e , which war i n f a c t v r r t f i a d i n d u e c o u r s r .

r c t u a l p r e c i p i t r t l a n r e p r a r r n t r t h e t o t a l p r a e i p i t a t i o n which f a l l 8 i n r r c h d r c r d a , i . a . from 1 t o 1 0 , f rom 11 t o 20 r a d from 2 1 u n t i l the r a d o f t h e month. Wo a c c o u n t h r r b r a n t a k e n i n c h i @ method o f t h a n o t i o a of " r f t t c t l v e " r r l n l r l l * Howevrr, i t murt be ment ionad t h a t r a i n f a l l i r rounded t o t h e n r r r r r t m l l l i m e t r r , a l l m i n r t i n g r m r l l r h o w r r r w i t h o u t a g r i c u l t u r a l n l $ n l f l c r n c r . At t h r o t h r r e x t r e m e , l r r g r q u r n t i t i e r of r a i n f a l l o a c u r r l n g d u r i n l r dncada p e n e t r a t e l n t o t h e r o i l and a r r u r r t h a r e c h a r g i n g o f t h e r o i l w r t r r n t o t r a a up t o t h b Zave l r e l e c t e d f o r t h e g i v r n o t r t i o n ( e r r p a r a 3 . J V 8 b r l o w ) . Any q u a n t i t y of v r t r r p e n a t r r t i o g i n t o t h e r o i l bepoad t h i r t h r r r h o l d w l l l p r r c o l r t r i n t o t h e d r r p l r y a r r of t h e r o i l r a d b s e l @ i n r t r d f r o m t h a w a t e r b d a n c e . S i n c e r n e r c a r r o f w r t a r w i l l be n o x i o u s t$ t h e c r o p # , a i t h a r t h r o u a h m ~ c h r n i c a l r c t l o n o r t h r o u g h g r a r t e r d i r e r r r E a f e r t - r t i o n , i t Lr p r o p a r r d t o r r d u c r t h e Index f o r t h e d e c r d r ( r a e par. j.3.9 and 3 . 3 . 1 0 ba low) by 3 u n l r o f o r e v e r y 100 am a p p e r r i n g r r t x c a n r wqtar f o r r r S n 8 l a docrdm. T h i s r r r e r r m a n t i r i n l l n e w l t h t h o r r l r t i o n r p b r t w e e n t h e i n d r x and t h e f l n r l y i r l d made i n rome c o u n t r i e @ of t r o p i c r l A f $ i c r . Thr p r r c i p i t r t l o a mearured i r r r rumad t o f a l l on r h o r i t o n t r l r u r f a C e , i g n o r i n g p u r r i b l r l r t e r r l r u n o f f . T h i r r a d u c t i o n of t h e i a d c x r h o u t d be , r p p l l a d t a k i n g I n t o a c c o u n t o t h e r c h r r r c t a r i r t i c r of t h e c r o p and i f r e n v i r o n m r n t , hawevar .

3 . 3 . 3 -bet of d r y s of r a i n f a l l

The o b r a t r r t l o n of t h a number of r a i n y d a y s i n t h e d e c a d e a l l o w s t h e d i r t r i b u t i o n #f t h e r a i n d u r i n g t h e p e r i o d t o be u n d a r r t o o d b e t t e r . For r r a m p l r , t o c r l r a i n f a l l o f , r a y , 150 am which f r l l r i n o n l y 1 o r 2 d r y 8 w i l L i u p l y heavy , i n m f f r c t i v r r a i n @ , p r o b a b l y w i t h rome damage t o c r o p r , w h i l e t h e ram@ q u a n t i t y f a l l i n g o v e r 8 d r y s v o u l d b e more p r o f i t a b l e t o c r o p r . I n t h o mame w r y , n t o t a l r a i n f a l l of 30 am f a l l i n g i n a r i a g l c d r y r a y morn won* d r a u g h t s t r e a r o v e r t h e d e c a d e , p r r t i c u l r r l y i f i n 2 s u c c a r r i v a d r c a d a r 2 ouch r r i n r o c e u r , a t t h e b e g i n n i n g of t h o f i r s t d e c r d a and a t t h t r n d of t h e racond o n e . For t h i r r e a n o n , i f r r i n g l a r a i n y d a y o c c u r 8 d u r i n g t h e d r a r d e i t 8 p r r c i w e d a t e r h o u l d be i n d i c r t a d .

3 . 3 . 4 P o t r n t i e l e v r p o t r r n s p l r a t i ~ (PET)

t h o p o t a a t i r l t v r p o t r r n s p i r r t i o n t a k e n a s r e f e r e n c e in t h i n work i s t h r ~ r r l m u m q u r n t i l r o f w a t e r which may be t v r p o r e t a d by a un i foym c o v e r o f d r a b @ r h a r t l r r r s when t h e w a t e r e u p p l y t o t h e r o i l i r n o t l i a i t e d , r r drt iarb by Panman (1948) . It8 c a l c u l a t i o n i s made a c c o r d i n g t o t h e method darcr ibrd i n annex . T h i r annex r a p r e r e n t s t h e e x p a r l e n c e a c q u i r e d i n FA0 ~ i t b thr P8a.r~ f o r m u l a o v ~ r the p a s t 10 y e a r e , S o n s s l i g h t m o d i f i c r t , i o n 8 , t a r o d u c r d i a the c r k c u l r t i o n of t h e r t r o d y n r m i c t e r m i n v e r y h o t and d r y q l i u t r a , m i l l i n p a a a r r l n o t b e r p p l i c a b l a i n t h i a e x e r c i s e r i a c * it tbavara r a i a f a d c r o p r l rown i n more bumid t n v i r o n a e n t a l c o n d i t i o n r , 4 t + ?.pal a t tho ttar ~4 t h e e r o ~ ~ ~ ' - nn

C l i m r t o l o ~ i c r l rrcordr o f t r rper r tur4 , vrpour prrnrure or r r l r t l v r a i r humldlty, runrhinr durr t loa and r U d rprrd wil l r l l ov tho cr lculrclon of po t r a t l r i evrpotrraaplrr t ioa oa r mnth ty b r r l r . Vrlurr for er th decrdr of tho year wil l tbra br drducrl ~ r r p b l c r l l y or: ochrrr l ra I t i#ura 4). Thlr l r porr lblr brcrure rho v r r l r b l l l t y a t pot rn t la l rv rpa t r rnrp l r i t lon l r much l r r r than thr t of r r l a f r l l rad r l r o brcrure thr d r l l y f luc tur t lonr u i th ln the drcrdr drnprn themrrlver ovar tha 10 day parlod, Uhrn no prra- mrtera a r e a v r l l r b l r for tho Praman crAculrtSon the Thorathwrlte farmulr may be urrd, with precrurioar; aood mrrrurementa @ad6 wlth r Pan A evrpo- rat ion trak rren pre t r r rb ia , hourxrr, Thr vr luer of rviporr t lon louad wlth the A Pro ahould then br ~ u l t t p l i r d by 4 l r c to r of 0 .70-0 .75 l o obtain the valuer of LTP, r t I r r r t for the hut114 nonrhr corrr#pondlna to the e f f r c t i v r lrowlng rrreon of r r l a t r d cropr.

Figure 4 : Monthly and decade valuor of aalaulatod i ~ o t s n t i a l avayutranayiratiul

I t i s r l r o recognized t h r t i t wj11 not be porrible t o c r l cu l r t a potent ial evrpotranspfrr t ion f o r a l l the r t r t iona whrra r r l n l a l t lnfarm- at ion i s avai lable . However, riace evrpotrrnrpirr t ion I r mucn I t # # variable in upace than pracipitrttofi , eaprc t r l ly if cumulated over 10 dry pariodr, the valuer cr lculr ted for r r t a t ion wil l be rpp l ic rb l r In neigh- boutins r t r t i o n r , provided coaditionr of r l t l t u d s , tsnparr tura , r e l r r fv r humidity, runshine rod wind are r im i l r r , r r i 8 8ea r r r l l y the care i n p l r i n r or platsru conditionr. Bowrvcr, the r l t u r t ion i r q u i t e d i f f e r rn t i n mountainour a reas , where tho difference In r l t i t u d r rnd rrpect w i l l generally influence a l l the fac tor r rod will r l ao modify the r a i n f a l l d i r t r i bu t i on .

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l o r t h o r p p l i c r t t o n of t h o r o t b d t o d l f f r r e a t c r a p r , a u i t r b l e a d a p t - a t i o n of t h o c r o p e o o P f i c i o n t r b o u l / bo c r r c l o d o u t r c o o r d i r g t o t h o rbovo p r i n c l p l r o . I t t r r o r l l r o d t h a t f o f t h o o c g r n t t r t l o a c r n t r o l i 8 i n g t h o i a f o r 8 a t i o n f o r c r o p 8 o n i t o r i a g a t git'ovinc t a t , a r t i o n a l &ad L a t r r a a t l a r a l l o v o l r i t may be difficult t o r t t r i b p t r r h e propor c r a p c o r E l i c i r n t t o t g i v o a d r c r d e r i n t h e y e a r . For t h l r r o r r n n i t 11 i a d i r p r n a r b l o t h a t t h o i n v r o t o r y of background d o t & f o r c r a p m o n i t o r i n g l n a l u d o r va ry p r r c i r o i n f o r m a t i o n on t h r v r r i r t y of c r o p r # t o m l a t h e v a r i o u r r t r r r , t h o normal l e n g t h of t h e i r growing c y c l e and t h e i r d a t e a f r a u i n g , l a r r m i - r r l d r r o a r . vhora t h o r h o r t d u r r t l o a of t h e r a i n y r e a r o n c o r d i t i o n r i m p o r r t i v o l y t h o l e n g t h of t h o growing c y c l o of c r o p r , t h e r l t u r t i o a l a ronouhat r i r p l e c t h r p i n more humid r r e r r , wborr r o u i a g of t h o c r o p r may be e p t o r d ovor r l ongor p r r i o d . In t h l r kind of o x a r c i r e , p h a n o l o # i c r l d a t a r r o r r i m p o r t r a t r r a e t e o r o l o g i c r l d a t a .

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3 . 3 . 6 &Cer r epu l remonte of t h o e r o g ( W R )

The d e f i n i t i o n of t h e u r t o r r r q u i r r a e n t r of t h r c r o p i r a r r i v e d r t by m u l t i p l y i n g t h e p o t e n t l a l e v a p o t r r n r p l r a t l o n f o r t h o doc rda by t h o r e r p o c t i v o c r o p c o e f f i c i e n t f o r t h e r a a o decade . Gince p o t r a t i r l r v r p o - t r r n r p i r a t i a n i r c r l c u l a t a d from c l i m a t o l o 8 i e r l v r l u e n and r i a c r t h o c r o p c o e f f i c i a n t i r " p r e - r o t " a c c o r d i n g t o t h e n o r a r l l r n ~ t h of t h o growing p e r i o d , i t i s p o r r i b l r t o c r l c u l a t r r t t h e bog lnn in& o l t h o r e r e o n t h o t o t a l v r t e r r e q u i r e a e n t a of t h e c r o p f o r t h e r a r r o n by r d d l n l t b e r u c c o a r i v o water r e q u i r r m r n t r decade b y decade .

3 . 3 . 7 D i f f e r e n c e between a c t u a l p r r c i p l t a t l o n gnd c r o p water r e q u i r e m r n t r (Pa - V P )

T h i r e x p r e r r o r t h e q u a n t i t y of water r v r f l a b l e t o t h o c r o p r , v l t h o u t t a k i n g i n t o accoun t t h e water s t o r a d i n t h a l o l l , however, which 18 d e a l t w i t h i n p r r r g r r p h 3.3.8. Proa t b l a , Lt can bo r r r n t h a t t h e o f f a c t of a g iven p r c c l p i t s t i o n a r y vary r c c o r d l n p t o t h o c r o p drvttlopment r t a g e .

3 . 3 . 8 Wetrr r e r e r v a r In t h e ( o i l (R6)

T h i r term e x p r e r r e r t h e watar r t o r e d l a t h e r o l l which can r r r d i l y b r ured by t h e c r o p . In o t h e r word@, i t i r t h o w a t e r r e r o r v o botvaon t h e f i e l d c r p r c i t y and t h e permrnrnr w i l t i n g p o i n t .

The amount of w r t e r u r r f u l l y s t o r e d i n t h a r o l l w l l l d rp rnd on :

- t h e d e p t h of t h e r o i l e x p l o f t e d by t h e r o o t r of t h o c r o p ;

- t h e phgr io -chumic r l c h r r c a t e r i r t i c r of t h e r o l l ,

The d e p t h of t h e r o i l exploited by t h e r o o t r h r r t o b r g iven r p r c h l c o n r i d e r o t i o n , L t w i l l depend oc t ho devolopmrnt r t r g o of t h e p l r n t , rho p r e ~ o a c a o f hard p r n r o r a prraam#at r h r l l o v w r t e r f r b l r o r r r r l i a o h o r i z o n , o t c , On t b o c r o p r i d e , It w5.13 a l r o l r r g r l y doprad on t,ho typo of environment i n whicb rho c r o p i r 8rowa. Ra in fed r i c e c u l r i v ~ t a d i n r o u t b errt As ia h r r 8 r h r l l o v ~ 0 0 t i n 8 r y r r r m g o n o r r l l y l i m i t e d t o 8080 20-25 cm. n i l l ~ c grovn i n r emi -a r id r r a a s u y r o o t r t 60-80 C 8 , w h i l e wher t growin8 Ln t h o A r g o n t i n i r a prmpr 8 r y grow r o o t r doua t o 1 8 o t r r . Taking i n t o e c c o u n t t h e p h r r i c r l q u a l i t y of t b a r o l l , r h u morar rn a r o i l a b l o w r t e r e c o r r g o f o r t h e f u l l y davolopod c r o p of r b o u t 30, 60 r a d 1.50 mm of v r t o r t o r p e c t i v e l ~ .

Thr p h y r i c r l c b r r r c t r r i r t i c r of t b r r o l l w i l l r l r o i a f l u e a c r t be u r r a r r r t r n t l o n c r p r e l t y fo r rho rrmr d r p t h of s o i l , t bo p r o p e r t i a s of c l r y a end c o r r r r r rot11 aernn t h a t t h r wotrr r r t a a t i o a of Lbr r o l l b y u n t t r of d rp th will br d i f f r x r a c . A l r y r r of 50 cm of randy r o i l w i l l probably r r c r i n lclrr than 30 u of r v r t l r b l r v r t r r , while t b r r a r e depth of Lorr might r r t r i n up t o 60-80mr .

In r cco rd rnc r with t h r r r s r r k r r a p r e r r r d above on t he c rop d e t r l o p - ment phraar , i t vauld br l o # l c r l 4100 t o modify t b r d r p t b of t h r r o o t l a 8 ryrkaa and t hu r t b r p o t r n t i r l w r t r r r r r a r v r r v r i l r b l r rccord l -g t * t h r dev r lop r rn t r t r a r of tba c rop , In t he p r r r e n r r r t h o d i t h r r been r c c e p t r d , howrvrr, c h r t r l a c e c b r Kc of tho c rop dur lna f t r f i r r t grovln# r t r g a r i r r a l r t l v r l y amr l l r h r v r r e r r v r i l r b l l l t y rhould 8 r n r r r l l y be r u f f l c i r n t and r t c o r d l n a l y r f i r e d r o i l - v r t a r r v r i l r b i l i t y h r r bran u t t l i r r t . * Working on r r m r l l r r r c r l r than tho one normrl ly urrd In t h l r kitC o f r c t l v l t y , one could con r id r r r v r r i r b l r v r t r z r r t a a t i o n c r p r c i r y accord in# t o the warfour dev r lop r rn t a t r g r r of tho p l r n t , Thl r approach rbould , hau rv r r , be br r rd o r r x p e r i a r n t r l r r r u l t r on t b r r oo t l ng d rp th of p l r n t r , w h i c h r r r r r l d o r r v r i l r b l r .

P i t u r r 6 rhowr tho water r r t r a t i o n c r p r c l t i r r r r p r e r r a d i n ma f g r romr c rops and locaEion8 wblch ha*. her* w**d 90 f a r by FAO, There f i #u r? r a r e only r a w p l r r , of cou r r a , rod a rch v r l u r of t h l r vary important f r c f # r v i l l hrva t o br v r rv c r r o f u l l v r r r r r r r d .

F t g u ~ r 8 : fts'samplr of r o i l uatrr r r t rn t lon a a p a o i t 8 for r r l ro t rd ,aropr a ~ d region@

3 . 3 , 9 $ Su CS/D)

~ h i r l i a r i r in t raded t o i a d l c r t r t h r r u r p l u r r r and tho d e f i c i t r (na8a t iva ly marked) r r g r r d i n g t ha w r t r r r t o r r g r c r p r c i t y of t h e r o i l . Su tp lur r a t e r r t o any q u a n t i t y of wrtrr rbovr t he r e l e c t r d wrtrr r e t a n t i a n a . D a f i c i t r r e t r r t o ray water requirements undar t he t r r o I r v e l of t h e v r t r r # toraga capec i t y . From experience i n t h r f i e l d , i t reemr r r c r o a - a b l e t o cona idr r t h a t ray rxce r r of va t e r of morr than 100 mm tor 8 r i n g l r dac rd r w i l l b. r e f l e c t e d i n a raduc t ion of t b r iadex ( r e r p r r r 3.3.10) of 3 u n i t # , Any n r8a t i vo v r lua correrpondin8 t o r d e f i c i t of wrtar i n r e l a t i o n t o t h e wrtrr requirement v i l l 8180 l a f l u r a c e t h e indax ( r e r I * 3.3.1n) .

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a n a . r m m n a r r n - a n o o r r - o r o r r , u o r r r r * * m ~ C P ~ m a * l b ~ r - ~ m * ~ n C * m O * m P m * D . r b - c , * Q l l * * L O m w e m m e w w a o q e a m s m o e

w m r m O O s n C * ~ P W C ( O ~ - m w m e - m ~ o w r o n r g ~ ~ - + . . L C O I J .I * Y ~ ~ Q ~ O I P I C C m r r a ~ c

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r r o 8 o a e w s r a c ~ & - u- o - t a e r m c e a m o o m m t s o - - a r m * o m e m nure . . rc C I U rr o r - u C Q t n - e m - ~ p r m - r r w r r n r O e m - ~ a O t - o Q O r n r .I= w r a m e s o - 1 r m m e m w a - 4 a s o e n - r n ~ r ~ ~ orre n m a r m I r w m o r n * m - s m C a m Z * - n o r ~ n * D O E c r l b o m - c c a m m R O r ( O * O e * O u y m S m r l C O U Q I B- 0 - 1 0 - 7 Q X U C O s w r ( O C I u * a L I ~ U D l r r r * 0 . r a m o a e a Y - t o a s - e c m w s - n ~ m n s c a = r n - m r r - a r w - e m o r r ~ c m

m c r . m ~ n c 1 a m m a * o . r % ~ m o ~ ~ a r # r ~ r c ~ r u m m r o r m a 0 O I O ~ ~ C O I * ~ ~ O * o - - - m U r e *

m o w 0 - a w c D - w a c r l u O w W m l ~ * ~ 8 m r n w o m n o e u r m m m ~ ~ r o r r o r r r m ~ r l u r ~ r r a r r 0 - a e y e E ~ ~ m m ~ a - e n ~ m r o e l r e r Q O e u e a m n - 1 0 a e r r - Y ~ ~ O O O . = - i l ~ a u m - m u - r n o * c:z z . 0 w - - a m m - m e w- r

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m r r m - a ~ P -.+ r r r E O W - 0 - +--*Pa r. a = a f m Z Z - r - r r D I m m m Z m a 1 I ~ C - O * < * 0 0 - a m - w o s m m - Z 3 e n w s r r l C P Q e 7 e o I g) b * r , m

r r r ~ w * m O ~ * r . ~ * - - o e e r s m . - . m - e * m * m ~ ~ r l w m m e m o Q - c o - r r m e n ~ m C - w o - n r r r w a n - - .r ~c - - r ~ a 1 m r w z - 5 * O - S C W m - m . I ) s S r r O ~ m a d - a r w m * m * m C r c P n n r 8 r - 0 s - u c s.c - a a I

~ S ~ C I m O l r ) - - * m n r w s - ~ ~ o m I l u~ ~ - r l r o c ~ ~ ~ - O Y I U n n m r a a. -u e r r s - c a w - ~ r r r - r s - - - r r r e * O E m r * O m O * O ~ Z ~ ~ D - ~ C ~ P I W s m - - - P . c ~ * a s m a * a - * f f u a + -

r r r -nn Q 0 5 3 rn - 1 * 7 * c II 0 U . I O ~ d * ~ * C O m ~ & ~ I L . I ~ -%-**I W f **I f * - - s r s ,

a n r & e o * ~ r m r ) Q m = L m rr rrrr rr m e w r rr s r m c O R r n m 6 U l c l = r b - t - - a * O l l O . - - * X I r r o -r, I a - 0 3 ) P e ( C = I * L I I Q I e W

r W r C Q - m r O l D m e O d C I e Y I Y = d r u t m e r w - m e 1.1 c Q s r e n r - ( a m w r r u s r r ~ c m w pl-u re- w * & s o s m c J W - - L = r r C O rr rn n m - 0 1 ~ r r m s - R L

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lo r t b i r rer ron, the r r t rb l l rbaan t of r f i n r l f o t a t r r t of r k vial4 wt l l probrbly be vary doperdrat i a rrsy cream oa tho water r t r t o r t a t b r p l rnt b u t rbould r l r o trka in to rcceuot a l l t k other c r r r a r . Tblr i r why l o f o r r r t i o a r r oorple t r a0 parrib14 an a l l r rpac t r of crop d r v r l o y r r t is importrot f a r tho rrtrbAlrhma8t @I I 8004 atop ro8i tor ta# r M t o r r c r r t i a # r y r t r r in tbr cara t ry . t b t r l g b r r i s a e r l r o tba fmpartrwa of rr#*lar raporrr prrprrad by t b r r @ t t c u l t o r r l r r t b o r t t f e r ,

l a the d l roc t rpp l ic r t ion of t b r nathod in tba f i r l d , tbe l e q t h of the croppin8 rarroa ra4 i t s l o c r t i o s i n tba t a r t i r wall kaom from l a c r l uroa, Ilowrvrr, i t ray hrpprn tbrt tba method w i l l b r road in r c a a t r r l plrnaio# o f f i c r , whara Liald l i r t r o a i r lafir d i r e c t , a t r t ra#tomal or t n t r r a a t l o a r l 1rvoSr. I t t r i a t r r r r t i o # l a tblr c r r a t o brva r v r i l r b l o romr 8aneralirad i n f o r r r t l o r on crop c r laadr r r . such tr tormrt too, uafor tun1 at017 r t S l l vary incomplata, hrr barn collactad by ?A0 rad publirhad l a h a o r n o 1 Thir publicrt ion producrr irformrtioa on rlr d r t a r of rewin@, f ~ o w a r i n ~ rnd nrcur i ty to r cra of tba a r i a r g r t c u l r u r d crop8 by t a l i v i d u r l country. I t r l a o l i v r r t a f o r r r t i o a by country on g e r , yield rnd production of t b r r r ctopa.

The Srowina period coar idered i a Chi8 p u b l l r r t i o a r a J pravioua onor (TAO, 1978) c o n r i r t r of tho pr r fod v h r r r o l l u r t r r , r e r u l t i n $ mainly !tom r r i a , i r f r e e l y r v r i l a b l e t o t b r c rop . Th i r occu r r vhea tho u r t r r conrumo~ by t b e c rop i r i n equi l ib r ium w i t h r r l n f r l l and water mrored i n t h r r o l l .

The r p p l i c r t i o a of t he method mxplrined i n Chepter f prerupporr r r good k a o w l e d ~ r of t he c h r r n c t e r i r c i c r of t he r e l a y e a r r a n , t i a u r r 7 rhoue t ou r r ch rmr t i c r e p r e r e n t r $ i o n r of v r t e r b r l a a c r r v l t h r v r p o r r r n r - p i r r t i o n o t t he orma order and very d i i f e r r a t q u r n t i t i e r and d l r t r i b u t i o a of r a i n f a l l . Thr f i r r t type , p u r l i f i a d r r n o r a r l , i r tho moot eommol t o r remi-ar id c l i m r t e r vbar r r r i n f r d r g r i c u l t u r a Ir p r a c t i c e d , I n t h i r c a r e , t h t r e pe r iod r c b r r r c t # r i r e t he t r i n y r e r r o a t

r A f i r r t p r r i o d , c a l l e d "prr-humid", du r ing which p r e c i p i t ~ t t o n remr inr lover than P l t g

b ) A r e c o ~ d p r r i o d , c r l l r d "humidn, f o r which average p r a c i p t r r r i o a v r i u r e ramrin h igher than p o t e n t i a l r v a p o t r r n s p i r r t l ~ n ~ A t t he rnd of t h i e pr r iod t he water b r l r n c e i n g e n r r r l l y p o r l t i v a and mome v r t o r ramsin8 e tored i n t h e a o t l i

c ) The t h i r d pe r iod , c a l l & "port-humid", co r r r rpond r w i t h t he r educ t i on rod t he and @f r r l n t r l l . U r t r t r t o r a d i n t h e s o i l w i l l c o a t i a u r t o be ur4d by t he c rop u n t i l i t i r exh ru r t ed , vbich partod i a t b r bee t c r r r e co t r r rpond r t o c rop mr tur icy .

Tho pre-bumid per iod oorreqpondr t o t he roving p r r i o d . Souin# may be c a r r i e d ou t w i t h r a adequate 'ldagrer of c e r t i t u d e when rho p r r c l p i t r t ion f o r r given decade i r g r e e t e r t F n 0.5 PgT. In p t a c t i c r l work, aceord in# t o t A 0 a r p e r i e n c e , r rbrerhold #i 30 ma o t r r i n t r l l i a r r i n g l r decade i r t & k e r 2 In o t h e r very 8rr l ; in 1 r r e r e rown w i t h d r o u g h t - r e r i s t e a t t r o p r , t he p l a n t may be w u a when t k t ! i r r t t r i n e r t r r t , i n o rde r Co t8k1 t he mrx i ro r .dvrntrar of r very r h o t t growin# r e r eoa (75-90 d r y # ) . In tYir cnae , howrver, t b r p r o b a b i l i t y @I r r t r b l i r h i n 8 8 good c rop v i t h t h e f i r r t rov ing i r lower and o f t e n , i t r r p e f l of drought occu r r r l t r r t h e f i r r t r o w i a ~ , rha f a r m e r i m o b l i a r d t~ rov r secoad time a s room r r t b r r r i n r r.lu.8 .

In t b e recond per iod t b e v r t r r needs r r a $ o a r r a l l y covrred r ad wrtrr r e r e r v e r b u i l t up i n t h e r o l l . Ih r metbod d r a c r i b r d i n Cbapt8r 3 r l l o w r t b r r i&o@t$on t o b r monitored u r i n g r c t w l r r ~ n t 8 1 1 vc l#rk t o d e c r o t t h e brrmtal dry rrr l lr r a d r r r e r r t h e i r e f f e c t ob tbr crop .

la the port-brrmld period t h r crop w i l l r rp lo i r the t.u:ni*8 t e i n f e l l rad drew OR cba urtor r8rervrr l a the r o i l ~ m t i l l t r u t u r l t y .

70 rummrrirr thr rbovr eon##rretlaar, t b r t loa t re t ionr 18 crop y l r ld r w i l l drpaad sa t

1. Tho lra8tk of t b r r t t o c t l v r vrgorrt lvr rreron fro8 t b r rowin8 un t i l the rub af the r r i a a ;

1 , Fhr quantity rad the r r#v lc r i ty of thr r r t a fr l l lmg brforr rad r f t r r row la^;

3. tb r rzcrr r ro o t r r l a f r i l dur ia l tho haaid prriod fa re ta t ton t o t b r bulldia# u p of u r t r r r r r r rve r t a the r o i l , on tha psrlCivr r ide , rod ' w i t h rorr wrtrr lo#)lng c porr tb l r crop lod8lag. on the a r# r t ivo a idr i

4. The quenrity a t wrcrr f a l l i n 8 i n tbr port-humid petiad, r r t h i r era iacrrbrr r o w wrtrr t r r r r v r r a t tbr l a r t r t r g r of v r ~ o r r t i o a .

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Thr Cant r r o l A g r l c u t t u r r l l r r r r r c h l a k a b r y ( $ r n r # a l ) hrr r r p r r f - mantrd l o r many yarer v i t b v r r i o u r food 8md c8 rh e ropr . l a p 8 r t l e u l r r , d a l l y r r l n f r i l o b r e r v r t i oa r , r o v l n g r a d h r r v r r t d r t e r and y i r l d r o f $rooad* out rrr r v r i l r b l s l o r r per iod o f 32 y r r r r (1932-1964). t h e method deac r i b rd l a C h r p t r r 3 h r r bran app l ied t o C k l r r e t o f d r t r . The r n r l y r i r of t he r r r u l t ~ rhovr t h r t :

a T h r r r l r no c o r r a 2 r t t a n b r t u r r n t o t a l r r # r o n r l rrlafrll r n d y l r l d a (P!@ur@ 8)1

- t ho Q l r S r l b u t i o n of r a i n 8 o v r r 10 d r y p r r i o d r i r ve r y impor t ra t ;

- Ninimua y i81dr (about 700 (I#/brl.) occur i n b o t h t h e d t i r r t y t l l r (300-400 wm) rod tho w r t c a r t (1200-1300 ma) ;

- Thrra r a t i r n o f d r t r h r v r r r r v r d t o q u e n t l f y t ho n e s a t l v r r t l r c t on t he i n d r x o f r r c r r r i v r r r t n f r l l (a re p r t r u r r p h 3 . 1 . 2 ) ;

- A good c o r r a l r t i o a r x l r r r b e t v r r n t h r l n d r u (rr c a l e u l ~ t e d b C h r p t r r 3 ) r od t h r y l r l d l a kg/hr ( f t 8 u r r 9). I

ta 1978 t h r Vorld ~ * t r o r o l r ~ i r r # OI aa laa t loa o ta r t rd r r a i n t a l l t *obitotin8 r & a r c i r r on @ p i l o t r o r i r 'la 2 countriaa a t Weat Atricr lor tar putporr PI crop !orr~rr tSa&. Tb# mrthodoioay drvrlopad by ?A0 hrr bran a p p t W La Orao, rhich ura tbe a r n t b of tho ~ p r r r t l o n ~ Tba opportuntty v r s taken t o apply thm mathod Po tb@ s r a i o o of Orra, rbara tor4 yirld racordr l o t r i n t r t whrrt wera r v a l l a U r f a r the yarrr 197l l l2 to 1977/78, u i t b the rxcaption of 1912/13 rrd l i lrJl74. Tbr fL#utr 10 rhowr tor r s a r i o r of p ra r r the r r l r t i o a brtwrrn tho i a h o t tbr vrriouo r r r r o r r rod tho y t r l d r abtrlnad. Thr t ab la l a valid to r the r t r t i o a o t Oraa, bouavet, rad w i l l have to ba r o a r l c o l s t r l rccordJn8 t o yiotdr obtrinrd fa arch r t 8 t l o o undar invast lg r t ioa . l o u r r r r , tha r r l r t i o a a x l r t i a 8 batwaea crop ibdrx and yield l r of d i r r t e i a t a r % r t . T h i s r l ao rhour the urr lu lnear of a o l l e c t l r 8 ylald dc t r i n a r y r t a a r t l c wry in the r r r r of tb r r t r t i o a r whera rgromatrorologlcrl infor8r t ion i r r v r l l r b l e .

mu

Piurrr 10: Coaparlron brtwrrn y i r td and Cndra for whrat i n Oran

Tbe axrrpte trken for Bantlrdrsh i r r x t r r r r l y i n t a r r r t i n g brcrurr tbr crop concarard i r r i c r rnd becrurl i t comer from r v r r , t ropical c l i r r t a vhlch ooa doas not expact t o prr rbat droulht c o n s t r r l a t r for crop arowth. Soar i r r e t u l r r i t i a s i a ronrooa rrasoa r i c r (July-lovrrbrr) i n 1978 laducad ur t o r a r l y r r the r ~ r o m r t e o r o l o ~ i e r l iaformrtion r v r l l & b l r , cceordfa# t o the method drrcribad i n Chrpfer 3, The rtudy war r r t r rmrly i a t r r r s t l a # , and brought t o l i l b t tha followia& pointrr

1. Moaroon r r a r a i n Asir often rhov rxcra r iv r r a i n f a l l roouatr ovar tha growing sarroa. flouavar, dry r p e l l r of two or .ore drarder can ocaur in t h r t prrlod and be brrrfoS t o cropr. Ie r h t r p r r t i c u l r r c r ra , dry s p r l l s occsrrad d u r i a l rhm ~ r o v i a g cycle rod th r monsoon r r i a l r l l anlad r a t l y .

1 , Crrr nuat be t r kea i a t h r a r r r t r r t o r t t r i b u t r the c o r r e c t v d u r t o tha u r t r r a t o r r # r c r p r c l t y of t h r r o i l f o r r l i v e n crop. TLlr poin t ir of p r r r l e o l r r iupor t rnca l o t r r i n f r d rice, wbicb bra s vary rhr l iow root ing dopth, not r rceedln# t h r d rp th of t be r o i l wbicb bra barn warkrd, o r rhova tr f i 8 u t r 11. l u t b i r p r r t l c u l a r c a m tho c r i c u i r t i a n of t he u r t r r b r l r n c e , t a k l a l a v r t e r s t o r r e e c r p r c i t y o f 60 am, rr i n t he dry ronea, dor r not ahow any v a t e r r t r e a s t o r t he crop. With 30 ma o f wr t r r a t o r r l e c r p r c l t y , however, t he s c h r a ~ r p p e r r l n l in f l l u r e 12 rrex8ea, #bovia8 water d r l l c i t problem# i n t he r r n t r r l roar of Iangiadoeh, In prac t l c e , r decade wtthaut r a in - f a l l a t t he he l#ht of tho #rowin# @ t a l e v l l l e ruae a t t e r a i n t he c rop ,

pisupc 11 : ~ahrmatia r e p r r ~ e ~ t a t i v a of the diffrronor in rooting d e p t h f~l' tYd dPOP8

P ~ P U F C 10: E i t r a t i o n of t h & ria* arop i n Bangladarh (June t o louumbarl in the ysar 1 O74

Lookina r t tho f i 8 u r r r Jn Lab11 8 , oar cra a l s o r e r t b r t the r o l e whlcb h r r r r p e r i r a c r d t h e a o r t r r r i o o r dror#ht problear, r r d whfcb r r h l b l t r r ere? t r d r r l a f r r l o r t o W, boo # r r r t a l i l r e c * i v d 8 l r r g r r r r r r o a r l raooat o f r r l o f r ~ J o a r LS S~vm~ber tba. tha rv8rr.e r a i n f a l l ~ x p r c e r d dor ia8 t l i r p r r l d . Thtr sbovr t h r groat impertroce of r r i a f r l l d i r t r i b r t i o o ra the r car@ i t# t o t a l rmorat cad t b r i n t r r c r t of the water b r l r n o r m r t h d baled a8 *eek&j or ton d a l l y p r r i o d r , tho wrtrt b r l r w r r d r a w up f o r J r r r o r r am4 l r r r j r n l r m j i l l u r t t r t r the rxtrmr c a r r r obarrrod i n 1970 ir k n r l r drab ( t l#uro 13). In J r r r o r r tIr r o i l u r t r r rr8.rr.r rr8ai1.l r t t b r mrxtwum thxou~bovt tho r r r r a a . lo I r r r j r a g 4 o J . bovrvrr, ma indew of 61 war r n p e r l r a e d , i t marc r l r o br rraarked t b r t 80 r rduc t l ea b r r b r r a a rdc i a t b r c ~ l c o l r t i o n t o tho b r l r r c r for cba rwcrar o f wrtor i a r drccdr , i n view o f t b r f a c t t b a t t b r crop i n v r r t l $ r t r d i r r r i o f r d r i c e .

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5 . 5 Ethiopia

In 1977 r miorion wont t o E th iopia t o r r t r b l i r h r n a t i o n a l ryr t rm of c rop f o r e c a r t i n @ b r r rd on tho method explainad i n Chrp t r r 3 . t h i s mi r r ion o b t r i n r d romr crop y ie ld d a t a f o r t he y r r r r 1 9 7 4 , 1975 and 1916 f o r t he r r @ i o n of Frd i r a t 1700 rn r l t l t u d r . t

Yorkiap with r ~ o r g h u s of 140 d r y r , t he rg romr t ro ro lo f i i c r l d r t l f o r t he co r r r rpond iaa y r r r r u r r r rxrmiaed and led t o tho r a l r t i o a l eapreraed fn f i g u r e 1 4 . Tbr r a id - f a l l and index nuubrr du r i ag rho growin8 r e r r o a wrrr tha t o l l o w i a ~ r

PLaurr 14 : fC#tdr and i n d i o r r for aorghw i n BthiopCa

There f t # u r e r demonstrate again t h a t i n c o a a t r i r s wborr t b r rmoroc of r a i n f a l l i a g on r crop i s r u f t i c i e n t , Lh* v 8 r i r t l e o of tho c u a u l a t i v e water ba lance , f n d f c r t i o e temporary wrtrr r r ~ r r r r r , is g o a e r r l l y more i ~ d i c a t t v e of t h e y i e l d f l ~ c t u s t f o o r of CLa crop.

I a to tmr t i on c o l l e c t a d ia Tolo oa t h r c u n o l r t i v r vator b r l r n c r a end y t a l d r of mr t r e l a r i a # t he r ecen t r a n o r r r r r o a r i n t b r t r f i i oa of L o u h r r r l l oved t he folLowin@ t r b f r (no. 4 ) t o be e a t r b l l r b r d , i l l u r t r r t o d by t l # u r r 15,

Thir t a b l e r l r o rhowr t h r 18 imporr ible t o r r l r t e t he r r r i a f r l l rnd t he c rop y i e ld8 I t i r i n d i r p e a r r b l r t o break t he v r t r r r v r i l r b i l i t y r i t u r t t h e crop for arch r i g n i f i c r n t t o hrvr &n t d e r of t he r e r l w r t r r r r endured by t he crop.

- a )O & (16 ;10 10 # #) t h r Jumlr r r e r i n no r th wart Wepal

r t 2300 r i t i t u d e dur ing t ha 1977-78 croppin( r r a r o a . In €h i e p ~ r t i c u l r t

Clprrr 16: r ( i td# and indiarr c a r e t he water r t o r r l e c r p r c i t y of for naC8r CR Toflo t he r i l t y lor. Se vary hiah &ad r o i l

wel l d r r i a r d , t hu r 8 iv ing r root fn( eyrtem c r p r b l e of e x p l o i t i n 8 romr 225 r of wr te r i n t he f i r s t metre of depth which, from t h e obrervrc ioor

of r o i l mo t r t u r r , 10 e f f r c t i v e l y e x p l ~ i t e d by t he c rop over r a axtrndad ~ r o v i a @ period of 230 dry r . ?or t h i r r e r r o a t he r o i l wrtrr r e se rve t e u i n o d r d r q u r t r u n t i l t l r hrcd&n8, wbrn d roo lh t r t r r t e d t o rodace t he iodrx f i g u r e (t i t u r r 16).

/m I

5.7 Weprl

The c u m u l r t i v ~ wrter b r l a r c e shown t o r Weprl p e r t r i a r t o f i a l d experimentr c a r r i e d out by t b r . U i l 1 Agr i cu l t u r r Development P r o j r c t . The experfmeat war c r r r i c d ou t i n

Another rnprrfmrnt war nrdr with the rear vrrtrry but under l r r i&r t lon and the two field$ weir f e r t i l i r ad . Thr f i r ld under rrinfrd condlrlanr produced 2380 kl/hr rod tho one under l r r i#r t ion 1520 ka/hr, I t 18 iatr<arting to note that the 1000 #r&in weight war 21.5 and 1 2 @rrarer rerprctfvrly.

In the Arlratina Prnpa r rimilar mrthod of cu8ulrtlvr wrtrr brlrncr var u t i l i r rd and i t wrr found t h a t it era lard to a qurnti t r t ivr idrr of thr rrduction of yield tor uhrrt. The principlrr &re the foflowlng,

1. thr b#lmcr i s crrr i rd out i n auccerrlvr 10 day periodr, f a the ramr vry r r rxplriaed i n Cbrptrr 3 .

2 . Thr wrcrt rcored i n the rol l re tbr rovin& data i r 8rnrrrlly ruf f ic l rn t for thr f i r s t s t rser of drvrlognrnt o f vhert; vatrr r t r r r r mry occur only af ter thr t i l le r in8 rtrge.

3 . The crop co r f f i c f r a t r rre simitrr to thore urrd rbovr,

4 . Out of total vr trr ratention of roar 150 mn of water a t f u l l crop . devrlopweat, 100 8. r r r coarldrrrd rradlly rvr f l rb l r to tbr plrnt w i tbo~ t r t td r r .

5. The e r t t rc t ioa of water by the plrat for wrtrt rtorsgr o f l r r r than 50 r raprrrentr r r t r r r r and tbr total number a t drys of r t r r r r i r aceouated for .

4 . t k r i i a a l y i r l d f 8 o b t r f i r r d by r q u r d r r t i a aqurtlon 05 t b r type8

1 bO * b161f + bZf!] 2

I t r tha mumbrr o f dry# of e t t r a a , a# r r p r c r r r d rbova, d u t t n g the d o l e crop a y c l r ,

7 , R o r u l t r bava r h o w t b o t y i e l d t a b u c t i o a r rrr 50 k & / b r par d r y o f r t t e r r i n A r $ o n t i o r and 40 k#/br po t d r y i n C h i l r .

Aa ?A0 p r o j o c t i r p r o r e a t l y r t r r t i na i n T o a r r a i r for the m o a i t o t i n a o f r ~ r o m r t a o r ~ l o $ i c r l c o n d i t i o a r r o d the f o t o c r r t i a ~ o f food c l o p r , p r r t t c u l r r l y @ r i # o , Tho o n r l y r i r 18 borod on 5 7 r t r t l o a r , t o r u b i c h the t r l e c o m u n t c r t i o a r network L r r c h r m r t l t o d i n f i # o t o 1 7 .

T A N Z A N I A

mRmm.am -hlL*r .-. "-a y -.--

PSawlr 17: Sohrna OJ t h e t e Z a a m u n i n 8 ~ 8 8 d for MO R o j a o t on arop m o n f tori%$ i n Tasta~ ia

l r o a t h o r r c r p l r r c i c d r b o v h i t r p p r r r a t b r t tha r r t b o d of t he e a m ~ l a t i v r a a t r r b r l a n c r t a r u 1 t i q $n @1 r # t ~ r a t r o t b l o # i c r l 1 n d r ~ tivcra r tood i a d i c r t i o n of t h a r a t Q I a c t i o a of t ha c rop wrtrt r equ t r a - r a a t r l a t ba 84ny r r r r r of t h a world vhare wrtrt r r p r a r r a t r t h e ~ r l n c o a a t r r i r t f o r c t o p r . D i t r c t t a l a c t o a r v i t h y i e ld bare braa 4amonr t r r t rd .

Thr t a r e a n t a p r r r a n t t h r a a t e a u l t r u r r t o I a r i l i a r i m r t he r e r d a t wi tb t h e r e tbod i t r a l l red t o rhov &ha l r p o r t r r c a of cbr c o r r r c t r d j u r t - @ r a t of t h e v r r i o u r p r t r r e t e r r rad ooaCtIc laa to u t i l l r r l . Mrtrr t a t r n l l o a c a p r e l t y i n t b i r r a a r r i r r vary i r p a r t r n t v r l u e vbich w i l l #rankly i o f l o o a c r tha way tha crop p r r r r r t b rou lh un fa rou rab l r r p a l l r . ?or axmrple, 30 mu of wrtrt t a t a n t l o a c a p r c i t y for t i e r r e r n r t h a t tha p l an t 10 a x t r e r r l y r e n r i t i v a t o rr abo r t 4 par iod r r 7 d r y r v l t b a u t r r l n , u h l l r mbart a tova i n tha h iah mountr iar o! Wrpal, on r r o i l u l t b r vary high v r t a r r e t a a t i o a c r p r e l t y , w i l l ba r b l a t o w l th r t rnd b r t t a t t he a f t a c t e of l o r r r i n t r l l and i t r poor d i r r r l b u t l o a throu8hout t he $rowin& r a r a o a ,

An rdaqu r t a r p p r o c i a t i o a of tbr v r t a r r t r r r r and h r a ~ a of t he probrb la j i a l d of tha c rop can br ob t r i a ad v t t h t b r mrtbod r t r n marly d u e rbrou&h tba v r l u e of tba index.

I t i r r l a o i a p o r t r a t f o r t he r ra r f i@arnt of r crop f o ~ a o r r t i n & r y r t a a t o kaap up t o d r t a ' p h a o o l o # i c r l rnd r c r t i r t i c r l i n fo rmr t l on , ruch r r t ha d a t a of r ov l a8 o t , b e t t o r , t he c o a d i t i o a r requi red by t b r i r r a a r r t o a rk# a o r i o ~ e , rha l e n ~ t h of t he #roving r a r ron f o r thr v r t l o u r crop r p r c i e r and v r r i a t i a r and t h e i r v r r i o u r r r a r r of c u l t l v r t i o n , A t t an t i an murt a l r o ba l i v a a t o tha r r p r e r r n t r t i v a n a r r of t he ma tao ro lo&ic r l r t r t l o n e u r f l i r a d i n thr r p p l i c r t i o a of cbr ra tbod .

ORCAWI~ATIOW O t A CROP HOMITORIHC A I D FORtCASTIlO 818T31 r ~ a t ~ on A C R O W I T ~ O R O ~ O G I C A L IUFORNATIO~

IAO'r rxper ience i n t he f i e l d of crop t o r e c r r t i n # h r r been o t i e n t r d mrinly t ov r rd r develop in^ c o u a t r i r r . Thia chapter v i l l p re reo t t he r e r u l r r of t be axparieaca devaloped pr imar i ly i n Afr ic? .

The ryr tem, r r i t h r r barn propored by t A O , e r a be a t e r t e d u q a 8 t he p r r r r n t i n f r r r t r u c t u r r # rad doer not r equ i r e ray r o p h i r t i c r t a d eq4,ipment. Thr t i t r t r t e p of ruch ryrtem i r t o form r t n r t i o n r l l e v e l r co*ittee c o ~ p r i r i a f i t b r v r r i o u r #overnmratr l r e r v i c r r iavolved i n r # r i c u l t ~ r l production and coverin8 t he f i r l d r r e l a t e d t o t he f a c t o r r i a f luen#ln8 r g r i c u l t u r r l product ioa. Tbi r formal comwitter rhould have an eq#bvrlent r t th8 t a c h n l c r l l e v e l , which would c o n r t i t u t r r n o p a r r t i o n r l vor g.8 group r e r p o n ~ i b l e f o r t he concept ion end t he dry t o dry o p r r r t i o a , f tho ryrtam i n r p r c i f i c r r8 lon r or r t n r t i o n r l l e v r l r , rccordlng t o t h 4 po r r i - b i l i c b a r o f f w e d .

The nuaber of i n r t i t u t i o n r concerned map vary from one count& t o rno tha r , rccszd in8 t o t he o r g r a i t a t i o n r l rcheme a t a r t i o n r l l e v e l cot r g r i c u l t u r r l , ' r e r r r r ch and product ion. For example, i n Tolo r wor&ia8 t roup h r r beau c r e r t ed with t he p r r t i c i p r t i o n of r e p r e r r n t r t i v r r from the toll ow in^ i a r t i t u t i o n r :

1, Hinimtry of Rurr l Development

- $erv ice of Agr i cu l t u r a l S t r t i r t i c r - qe rv i c r of P l r a t P ro t ec t i on

- ~ r t ~ o r o l o ~ i c r l Service

3. H i n t r t r y of Rurr l Lrad Mrnr8ement

- Service a t S o i l Survayr - Serv ice of Lrad Improvemeat

In o the r c o u a t r i a r , rucb r r T rna ra i r rad P r i t i , t he b e r i r of t he ryete. (181) be 8 drvrlopment p r 0 j r c t f i n r aced by e x t e r a r ~ rou rc r r w i t h exper te and equipment provided by ?A0 o r ocher doaor r . The putpom of t he p r o j e c t i r t o e r t r b l i r b p r a t r e r r l v e l y t he kind of committee o r workin8 l roup r e f e r r ed t o above and t o i n t roduc r t he ayrtem In t he couatry.

b . 2 C o n t r i b u t i o n o f t h e r e l r t i v r tmchn ic r l f l e l d r &be o ~ e r r t i o n of t h c r y r t r r

In v i e u o f t h e f a c t t h r t t.he nrmrr of r r r v l c e r o r i n r t i t u t i o a r r n J t h e i r r t r r i b u t i o n r may vary I r a* one c o r n t r y t o r n o t h r r , wr p r r f a r t o r n u r e r r t r t h e con t r tbu t ionm t o t h e r y # t m by t c l chn ic r l f i e l d # , l a r v l n g t h e r t t r i b u t i o n by government r r r v i c r r t o t b r c o u n t r t e r t h r a r e l v m r ,

Agrometeorology is g s n c r r l l y one o f t h e d i v i r l ~ n r o f t h e Wr t lonr l n e t r o r o l o ~ i c r l S e r v i c e . Ar h r r bran r a i d i n C h r p t r r 3 , t h e r y r t r m i r h y b r i d , inrrmuch r r t h e water b r l r n c e I r c r l c u l r t r d I r o n a c t u a l d r c r ( r r i n f r l l ) rnd c l l r r t o l o ~ l c r l h i r t o r i c r l d r t r ( r v r p o t r r n r p i r r t l o n ) . The f l r r t r r k of t h e r @ r o m e r e o r o l o p i c r l r e r v i c r r l l l t h u r br t o c o l l e c t t h e c l i m r t o l o g i c r l d r t r n e c e r r r r y f o r t h e c r l c u l r t t o n of p o t e n t l r l r v r p o - t r r n r p i t r t i o n by t h e Penurn method ( r e r r n n r x ) f o r each month of t h e y e a r , t h e r e v r l u e r b r i n g d iv ided t h r r r r f t r r i n t o d a c r d i c o r ue rk ly v r l u a s ( r e e p r r r 3 . 3 . 6 ) .

The recond t r r k of t h e a g r o m t t e o r o l o ~ l c r l r r r v i c e will be t o d r r e u b l e , i n t h e r h o r t , e r t p o r r i b l e t ime r f t e r t h e end of t h e dec rde (2-4 d r y r ) , i n f o r a r t l o n on cumulat ive r a i n f a l l rnd t h e number of r a i n y d r y s dur ing t h e prevloun decade , t o g e t h e r wi th i n f o r m r t i o n on r r t r a a r r a i n ) c r p r b l r of c a u r i n g drma.ge t o c rop# through l o d g i n g , w r t r r l o p g l n p of t h e r o i l o r f l o o d i n g of e n t l r e r r r r r . The a g r o m m t e o r o l o ~ i c a l r e r v l c a , In c u o p r r r t l u n wi th t h e r p r i c u l c u r a l r e r v f c e r , v l l l r l r o c o l l e c t d a t a on t h r r v r r r g n d r t e r of rowing and t h e l e n g t h of v e g e t r t i v e c y c l e r of t h e mrtn c r o p # under l n v r r t l g r t i o n i n t h e v r r i o u r r e g l n n r .

The main t a r k of t h e n a t i o n a l a e t r o r o l o g l e r l s e r v i c e w i l l br tha u t i l i t r t i o n of t h e n a t i o n r l m t t e o r a l o ~ i c r l nrtwork ( r y n o p t l c rnd r l r o c l l o r t o l o g i c a l , r r f a r r r p o ~ r i b l e ) t o trrnmmit t h a n a c a r r r r y d r tm. The r e l e c t i o n of t h e r t r t l o n r which w i l l c o n t r i b u t e t o t h e ryr tem w i l l i n c l u d r p r i m a r i l y t h e r y n o p t i c r t r t i o n r , which a r e r l r r r d y equipped f o r thm i a a t d i a t e t r a a r m i r r i o n of me teoro log ica l o b r e r v r t l a n r . I t would then be u s e f u l t o complete t h t r b a r i c network wi th " r a t m l S l t e " s t a t l . o n r . There s a t e l l i t e s t a t i o n s should co r t c rpond t o t h a f o l l o v l n p c r l t r r l r :

1. R e p r e r e n t r t i v e of impor tant r g r i c u l t u r r l r e g i a n r ; 2 . B e l i r b l t 8 s f a r r a obae rva t lonn a r e concerned; 3 . Able t o communicrtr d a t a t o 0 "aynop t i cn r t r t l o n w i t h i n

2 d r y s by t e l ephone o r any a t h e r mrrnr of comaun lc r t lnn ( b i c y c l e , c r r , r t c . )

The p u r p o r t of complet ing a b r r t c ryctem by a a t e l l i t r r r r t l o n s In t o reduce t h e e r r o r r a r d e by i n t e r p o l r t l n g r e s u l t # br twren n t r t t o n r ~ In 1 9 1 8 , f o r e x r n p l e , a drought occur red l a r r e p l o n of Upper V o l t r rnd cou ld not be d e t e c t e d . Indeed, t h e r t r t i o n r of Our6adougou, Dori and O t ~ r h f ~ o u y r , r i t u r t e d o u t r i d e t h e r r r r , r e p o r t e d normal c r o p c o n d i t i o n r .

On a n r t i o n r l r c a l e , i t i r of course s r r e n t l r l t h a t , b v r i d e r t h r nr twork of r t r t i o n r p r o v i d i n g cumulative d r t r 2 o r 4 d r y # r f t e r t h e end of t h e drnc.de, r c l o s e watch c o n t i n u r t o be r x r r c l n e d on t h a c l i a r t o Z a ~ i c r l a e t u o r t and t h r t complamentrry d r t r o b t r i a e d from f h r t a r twork b r comprred when rece ived w i t h thoae of the. " r ap id a r c h r n p r n r t u o r k " , A good l l l u r - t r r t i o a of 8 complax o b r e r r r t i o n n r t u o r k i r t b r c of T r a r r a i r (roe Chapter 5 ) ,

A g r o n o m l r t r w l l l h r v r t o d e f i n e a t t h e o n r a t of t h o r y r t r m which w i l l br t h e c r o p r u n d e r i n v a a t i g r t i o n , c o n r i d r r i n # r r r g e n o r r l g u i d r t b r t t h e mothod h r r b r a n d r r i f i n o d p r i m a r i l y f o r a n n u a l c a t a r l c r o p @ , O t h e r r n n u a l c r o p r m i g h t r l a a be u r e d , h o w r v r r , mince t h e r r t h o d , b a r e d on e c o p b y r i o - l o g i e r 1 c h r r r c t r r i r t i c e o f t h o p l a n t , t a o f g e n e r r l r p p l l c r t i o n .

A ~ r o n o m l r t r r h o u l d r l r o r r t r b l i r h t h e p r r c i r r c r o p c r l e n d r r r l o r t h e v r r i o u r r d m l a l r t r r t i v e r a l i o n r r n d f o r t h o v r r l o u r v r r i r t l r r of c r o p r L n v a r t i l r t r d . t h e y w i l l r l r o h r v o t o c a r r y o u t r p r a c i r o r t u d y o f t h e t i m i n k o f t h e p h e n o l o ~ l c r l p h r r e r o f t h a c r o p , 80 88 t o b u i l d c h r a u c c r r a i o n of c r o p c o r ~ f l c l r n t s f o r t h r w h o i r c y c l e of t h r c r o p , I n t h i r r e g r t d , t h e r r r u l t r o f r x p r r i m e a t r c r r r i r d o u t by r 6 r i c u l t u r r l r a r e r r c h l n r t l t u t i o o e mry bo of a r o a t i n t r r r r t f o r t h e r y r t e m and r e p r e r e n t 4 t i v a r o f t b o r r i n r t i t u t i o n r r h o u l d form p a r t o f t h a o p a r r t i o n r l u o r k f n g g r o u p .

6 . 2 , 3 P l r n t p r o t a c t i o n

A l t h a u 8 h t h i r r p o c i r l l t y b r r n o t y r t b o r n m r n t i o m e d , r o r v p r r i r r l of r a y p h r a o r e n r ( p e r t 8 and d i r e r r r r ) which w i l l r f f o c t t h o p r ~ u c t i v i t y of t h e c r o p , o v o r r n d r b o v r t b r f l u c t u r t i o n r o f t h e w r t r r b r l r ) c r , w i l l be of S o t e r r r t t o r t h r m o n i t o r i n g s a d f i n a l f o r r c r r t i n g .

2 4 A t r i c u l t u r r l r t r t i r t i c r

The r o l e o f t h e r e r p e c i r l i r t r v i l l b r t o c o l l r c t r r l i r b l a , : i o f o r m a t i o n on t h r r r r r r c u l t i v r c r d w i t h t h a c r o p r u n d e r i n v m r t i g r t i o n , t h f i i r y i e l d r and t h a i r p r o d u c t i o n . T h i r l n f o r m r t i o n mur t be a r t r b 1 i r h . d b l ; i r d m i n t r t r r t i v e u n i t 8 80 I 8 t o r r t r b l i r h t h e r r l r t i v r r 8 r i c u l t u r r l i m p o r t r n c r i f t h e v e r & o u a r a g l o n r , For r x r m p l r , r h o u l d t h e f o r e c r r t i n g o x e r c i r e ~ d a m o q e t r r t e r c o n p r o m j r r d c r o p i n t v o d i f f e r e n t r r r r r of r c o u n t r y i t i r i q p o r t r n t t o knov t h a t o n e r r r r p r o d u c r r 4 O X o f t h e t o t a l p r o d u c t i o n of t h a " c o u n t t y and t h r o t h e r o n l y 2 X , S t r t i r t i c r l d r t r r r a r l r o v e r y i m p o r t a n t t# e n r u r e t h e

r t v r a r p r c t o f t h r f o r e c r r t by o b t a i n i n g h i a t o r i c r l y i h l d d r t r o f m m p r r i n B t h a n w i t h t h r r r r u l t r of t h e c r o p r a t e r b a l a n c e c a l - c u l r t i o n r ( r e e C h r p t r r 4).

6 . 2 . ) g o 1 1 r c i r a c e

The a o n t r i b u r i o n o f r o i l r c i r n t i r t r i r v e r y i m p o r t a n t i n o r d e r t o r a a a a r t h e p h y r i c o - c h e m i c r t c h a r r c t r r i r t i e r of t h e r o i l s i n t h a r r r r r under i n v r r t i g . t i o n . I t w i l l be of p a r t i c u l a r i n t r r e 8 t t o r r r e r r t h e r o o t i n g d e p t h of c r o p r , e r p r c i r l l y i f t h e r e a r e r e r i o u r r o i l c o n r t r r i a t r 8uch r r a t e r i l r h o r i r o n r , h a r d p r n r , a r c . T h e i r c o n t r i b u t i o n w i l l 8100 be f m p o r t r n t f o r t h e d o t e r a l n r t i o n o f t h e u p t r r r t o r r g a c a p a c i t y o f t h e r o i l i n a r c h r e g i o n u n d e r i n v e r t i p r t i o n , p a r t i c u l r r l y i n t h e h o r i r o n r v h e r e t h e r o o t 8 r c q u i r r m a j o r d r v r l o p a r n t . T h i r d e t r r m i n r t l o n i r most i m p o r t a n t f o r c r o p r c h r r r c t r r i r r d by r r h r l l o v r o o t i n g r y r t e m , r u c h 88 r r i n f ed t i c e .

6.3 The v r r i o u r t r r k r o f t h e u o r k i a r g r o u p

Having c o a r i d e r e d i n t h e p r e c e d i n g p a r a g r a p h t h e v r r i o u r d i r c i p l i a r r i n v o l v e d i n t h e c r o p f o r e e r r t i n 8 r y r t e m , l e t um k a o v r u m m r r i a e t b e v r r i o u r t r 8 k 8 of t h e w o r k i n 8 g r o u p . Thin mroup w i l l brve t o g a t h e r t b e r v r i l a b l a

i n f o t m r t i o n th rou&hou t t h o c r o p ~ r o u l n g marran and p r r p a r r r v r r y 10 d r y @ t h o c u m u l r t i v a ur t r r b r l r n c a r t o r a l l t h e c r o p r r n d t h o r t r t l o n a i a i t t r l l y r e l r c t a d , t a k i n g e r r 8 t o o b t r i n i n t l m r r a y m i m a l n ~ o r d r l r y r d i n f o r m r t i o n , I n t r r d i r c i p l i n r r y d i r c u r r i o o r ahou ld r l r o t a k a p l r c r w l t h t a t h r work ing group i n o r d e r t o improv r t h o r y r t a m d u r i a n i t 8 o p a r r t l a a rr n r u r l r m a a t r r r a c o l l r c t a d , l a p r r t t c u l r r rr coaoerna t h e p h r a o l o r l c r l a t r $ r a d u r i n $ t h e c u r r e a t r a r a o n and o t h r r p h r n o r r s r c r p r b l r a t m o d i f y i n # u n @ x p r c t r d l y t h e f i n a l r r r r a r m r n t .

Tho u o r k i n g group r b o u l d r l r o c o n r i d r r t h e d a r i r r b i l i t y o f p u b l l r h t n g i n t a r i n r a p o r t r a v a l u r t i n g r h r c r o p l t r t u r lor v r r i o u r c r o p # and r r & l a n a r t one o f r a v e r r l p o i n t r o f t h o c r o p p i n 8 r r r r o n . Another i m p o r t a n t t r r h o f t h o v o r k i n g Oroup v i l l ba t h e r e l a c t i o a o f p l o t 8 whr ra c r o p r i t u r t l o a r may ba c o n r i d a r a d r a r v a r r & e and which u t l l b r h r r v e r t e d by r p a c i r l l r t r o f t h e v o r k i a g group o r by t h e f r r m a r r t b a m r a l v r r , undar c l o a r a u p r t - v i r i o n . Tho r a r u l t r of t h e r a p l o t r r i l i b r v a r y i m p o r t r a t Por tLa p h y r i c r l r r r a a a m r n t i n k e / h r r a d f o r t h a " c r l t b r r r i o n " o f chr i a d r x i n t a r m r o f c r o p y i r l d a . T h i a o p a r r t l o n 11 o f oxcrema i r p a r t r n c a r n d r p p r o p r i r t e methodr c o u r a m u r r t e w i t h t h e t i n r l r r a u l t r e x p r c t r d h r v a r o be d r v c l o p r d by t h e r # r i c u l t u r r l f i e l d r t r t i r t i c i r n r ,

The r b o v a c o n a i d r r r t i o n r on t h r o r g r n i r r t i o n o f r r y r c r m o f c r o p f o r e c r a t i a g b r r r d on r g r o m a t r o r o l o g i c r l i a f o r m r t i o n r rr n o t marnt t o c o n r t i t u t a r i l i d r u l a r b u t t r t h r r t o p r o v l d a loma g u t d r a c r d r r t v r d f rom the a x p r r i r n c r r c q u i r r d by FA0 and t h o World X e t a o r o l a g l c r l O r ~ b ~ i 8 1 t i ~ 0 i n c o u n t r i r r what8 much r c t i v i t i a r h r v r been j o i n t l y d r v e l o p r d over t h o p a r t t h r e e y a r r r . FA0 and WHO, vho rrr d r v r l o p i n g r o r r and more J o i n t r c t l v i t i e r i n t h i r r e r p r c t , may u r e f u l l y c o a t r l b u t ~ t o t h e r a t r b l f a h r a n t o f t h e r y s t r m t h r o u g h s h o r t c o n r u l t r n t a ' m i r r l o n r at t h e o n a r t o f t h e r y r t r a and d u r i n g tho r u c c r r r i v r c r a p p l n g a r r I o n a .

The p r r c rd in# c h r p t r r r h rvr r t t r m p t r d t o d r r c r i b r romr of t b r r t p r r - i r n c r galnod by ?A0 i n t h r u r r of r mrthod of c rop a r r r r r m e a t rad f o r r - c a r t l ag brrrd on r ~ r o m r t r o r o l o g l c r l i a formr t Lon. Thr mrthod ha8 born . dr r lgn rd t o r rrmi-rrid c o u o t r l e r ; hovrvr r , e x p r r i r a c e l o h w i d t r a p l c r h r r 1110 d rmo0r t r r t r d t h r occur rancr of harmful d ry r p r l l r vhich may c ru ra r r d u c t l o n r of v r ry lng d r 8 r r r r l a t h r y i e ld of r g r i c u l t u r c l p roducts . I t i r by no mrrnr r r o p h l r t l c r t r d mrthod r ad i t u r r r r r v e r a l work hypo- t h e r r c vhlch mrker l t r o p r r r t l o a q u i t e r imp l r . In r d d i t l o o , r l o t of c r l c u l r t i o n r may br prrformrd b r t o r r t he croppin$ r r r r o a b r g i a r .

T h r mrthod p r r r r n t r d h r r r doer not c laim t o r r p l r c e o the r formi of c r o p a r r r r r m r a t r b r r rd mainly on r t r t i r t i c r l r rmplin8. f n r t e a d , t t c o n r t i t u t r r r u r r f u l complrmrnt t o l t r t t r t l c r l r r m p l l n ~ , r 1 l o v i n g ' ~ r a e a r l y rrrrrmmrnt of t he crop r i t u r t i o a b r r r d on t h r ~~@uI,u of po rq ib l r m o d l f l c r t i o a i n c rap brhrv iour l o rd ing t o product loo l o r r r r . I t #r hoprd t h a t tha i n t roduc t ion of ruch a mrthod in a r t i o a r l crop f o r o c r r t l $ g ryr t rmr w l l l l aprovr t h e i r # r n @ r r l food r l t u r t i o n a r r a r rmen t r .

Crop-urr tbrr r a r l g e i r modelr Rrvlrv and model develop- m a t . f . of Applird Wrtrarolo#y, l X ( 0 t 911-941

MI IR* Y . Mote oo t he trtald01o#~ o f crop-worther nodeln, 1979 Aarlc. M r t r o r o l o ~ y , 201 137-143

CULOt, t, Per roa r l c o r u a i c r t l o n on r r tbod ured i~ Ararat in r . 1979

Report on the r ~ r o e c a l o ~ l c r ) @onor p r o j @ c t l Val 1 , Hetbodololy rad R r r u l t r f o t A f r i c r . World 8011 Rraourc*e Report no, 48, Rome

FRIIRK, N. A a r thad t o r t he p r r o t l c r l a p p l l c r t $ o a of the Penran 1972 f o r r u l r f o r c b r o r t l m r t i o a of p o t e a t i r l r vapo t r rn r -

p l r r t i o n and r v r p o r r t i a n fro* 4 f r e e v r t e r r u t f r r a . I A O , l o r e .

P R E R E , U. rod P O t O V , C.I . 4 pra#rrrme f o r non i to r in8 crop condt t lonr 1976 rnd crop t o r e c r r t i n $ i a t he S r h e l l r n r e# ion , C A O ,

R e ACPltcol.9

FRIRE, W , , RIJKS, J.Q. b R I A , J . Latud l o a ~ r o c l ~ n r c o l 6 ~ t c a d r i r ronr 1975 r n d l n r . Y A O , Roar

P R E R B , H, , RIJKS, J.Q. b R t A , J . I r t u d i o r # r o c l i m r t o l ~ g t c o de l a roar 1978 r n d l n r . WHO, Baaerr

L'IRAT e t l r r i r p l u v i r l . Frcr lmi le 2 . IRAT, 110 rue de l l U n i v a r r i t d , P r r i r

UAWALO, t .B , A g r o c l i r r t i c rurvey of Bragl rdr rh , Brn#lrdarh R i c e 1975 Oeeeatch Inre l rure / IRRI

MATTEI, P. Wheat crop ecoloay r eae r r ch . FA0 l r n r l repor t (roneol 1978

POPOV, C.F. A # r o c l i m ~ t o l o ~ k a l a o a i t o r i n ~ t o r crop l o r r c r r t r in 1978 the Sah r l i r n rope. PAOIWnO t r c h n t c r l confer rnca , Roar

ROBERTSOH, 6 .W, A b i o a e t ~ o r o l o ~ i c r l time r c r l e fo r r c e r e a l crop 1968 Lnvolvinp dry rbd night t e r p e r r r u r r r rad photoperlod,

l o t . J , Biomrtaorologg, 1 2 ( 3 ) : 191-223

IdBfTtl4AU, P. Tscba ic r l repor t bared on t he r c l i v l c i a r of t he 1979 Jumlr Agr l cu l t u r r l P r r r L977~f8 .

YIT. C.T. dr, BROUYtR, 1. b PEX$IUG dc VPLLB, t ,U .T . A dyn~m&c nodel of 1971 plan t rad crop ~ r o w t h . &: P , P . U#rein# and

J .R . Cooper ( E d # . ) P o t r a t i r l crop p r o d u c r i o ~ , 8 c r r r s tudy . Ii.iursanu t d u c a t i o a r l Boohe, London

A WE510P POI Tlt PUACTXCAL C I ~ L X C A T 5 0 1

T M ?-I TORNOLA ?OR T u 88TIWATXoM

91 PO- 8 V & ? O t U A ~ T f O W AID E V A t O ~ T I O C

A IItIYlflCI S W l l A C k

Tbr formula, d r r i f n r d i n 1948 by Crnmru f o r t he a r t i m r t i o n of rvrpo- t r t i om from 1 f r e e water r u r t r c r rOJ of po t an t l a1 e v r p o t r r n r p l r r t i@n from r v r ~ r t r t f v r cover, h r r bran v l d a l y u8ed t h r o u ~ h o v t t he w r l d f o r t ha l r r r JC year. w i t h g e u a r r l l y a r t i a f r c t o t y r e # u l t a . The mathod h48 bean widely r p p l l r d i n ?A0 r c t i v f t l o r r e q u i r f n ~ tkr taoul rd8a of potent i r l a v r p o t r r a r - p l t r t i o a ,

Oar of t he main d i l f l c u l t l e r f o r the u r r r i r not 80 much tha r r t h r r I r r a r number of c l i a r t i c p r r r a e t r r r iavolvrd !a t h e f o r u u l r , aa t he con- p u t r t i o a i t r e i f , p r r t i c u l r r l y I f t h e r e p r r amr t r r r a t e exp r r r r ed i n u n l t r d i f f e r a n t ftom t b o r r o r i g i n a l l y u r rd by P rn r rn . Whrn u r i a l t h e f a r r u l r i t i r r r r r n t i r l r t t h r r t o k r rp t o tho u n i t 8 o r i # i n r l l y used by Pramrn or t o rdcp t t h r rppropr i r t a coave t r iou coef l i c i r a t r ,

l a viaw of t h e r e d i f f i c u l t i e r r f i t r t v r r r i o n of t h i r no te war p r cp r r rd i n 1972. I t fm t o l t t h a t , in @ p i t 8 of tho p r o j r r r r mrdr r i n c r then i n tho r r r r of poekrt and dark min icoapuar r r , i t 10 r r i l l u r r t u l t o havr r v r i l r b l r r r impl r a r thod f 6 r f i e l d c r l c u l r t l o n r of t he Pramrn formula

2 . C o r f f i c i r a t r ured in t he formula

The o r l a i n r l f o r r u l r war dr8i)nrd f o r t h r rnv i ronmra t r l c o a d l t i o a r of r ou th r rn l a & l r n d . Sorr rmr l l m o d i f i c r t i o n r t o t h r o r i @ i n r l f o r n u l r h rvr born in t roducrd t o take f a t o rccount r x p r r l e a c e grcharrd i n ?A0 with t he u r r of t he formula around tho world.

2.1 Tbe c o r f f i c i e n t r r r a l b u r rd fa t he Anlrtrdm lormulr l o r t he r r t i r r t i o a of t he t o t a l r r d i r t i o r from the d r t r o f runrh inr d u r r t i o a a r e o f t e n r u b j r c t t o d i r c u r r i o n . Nr8y t r r t r madl w i t h i n ?A0 p s o j r c t r hrve rhova t b r t t h r r r r e t o of c o r f f i c i r n t r a t law 8ood r e r u l t r t o br ob t r innd f a t he v r r f o u r goner of tho world. l h r r r a r t 8 of c o r l i i c i r a t r a r r r

r b - - 0.18 t 0.55 f o r t h a c ~ l d and t r r p r r r t r Loner

0.25 + 0.45 f o r d ry t t o p i c r l roaor

0.29 + 0.42 f o r huwid t r o p i c a l r on r r

The arp a t t ached , barad on T r r v r r r h r (11571 ahown t h r r r d i f f e t r n t goner* The goner rhown on t he map h w r onfy rn i n d ~ i c r t i v a v r l u e .

2 , 2 Tbe v r l u r r of r a d i r t i o n r t tho Z i m t t of t he rtmorpher! h r ~ a ~ b r r n c r l c ~ 1 . t e d 0. t h e b.#i# of 8o l@r ~ 0 n 8 t 4 n t O! 2.00 C ~ I . C R - ' , S ~ B '.

2 . 3 I r r f m r t i o n r of e v r p o t r r a r p i r r t i o o made i n vary dry anvi roamrnt r , c h r t r c t r r i z o d by 4n.u.l 4v r r r8e minimum t n p e r a t u t e 8 rbova I * C .ad d l f f e r - eneer batween a o a t b l y r ~ a r r r e mrsimum and alnimum t e a p o r r t u r r r of more t h r a 12'C, rhow an undr ra r t i . r t ioa of p o t e a t i ~ l e v r p o t r r n r p i r r t i o n duo in mort c7 .re@ t o tbt r d v r c t i o a of d ry a i r .

Ia ordrr to ramedy t h i s r i tu r t lon , v r r i f i r d i n e r t r n r c l k r t e r , the cor f f i c i ra t r f f rc t i ag thr vind rpeed a t 2 m rbovr the trouad (U) hrr brra ~ o d i f i r d i n tho followin$ wry:

Diffrrrncr betwean mrra Moothly arrn monthly mrxlmom red

R- minimum t rmpera tu t r~ Car t f ic i ra t o f p

Tha t r b l r r VIII rad I X have been divided into six-to rccommodqte the vrriour corff ic lentr for thr cr lculr t ion of rvrpotr rarpi r r t ioa rad avrporrtion.

i:

2.4 Otbrr cor f f i c i rn t r hrvr r l r o bran propored for the r r t i r )J t ioa of the r f t r c t i v r r rd i r t ion . Rarultr of r r r r r rch i n t h l r f i r l d , hobver , are not very coaclurivr, For th ie rereon the coef f i c i rn t r f i r r t p*pored by Brunt have barn mrintrinrd. i%

l e r l i r i n g t h r r r d i f f i c u l t i r r rad rhr irportrncr of tryla6 to b i m p l i f y the c r l c u l r t i r a r involved i n tho Penara toraulr , with p r r t i cu l r r r i f r r rnce to f i r l d proj lc t r vherr r l r b o r r t r cr lculr t iag f r c i l i t i r r are aot o ten readily rv r i l#b l r , two rimplr vorkiag 8h8rt8 hrvo born prepared, r f lowing the c r l cu l r t i#a r to br mrdr r t r p by r t r p , with t h o help of t r b l r r h l i d for r l t i tudar betwren S O O N rad $0'8.

A copy o f the two vorkiag r h r r t r , oar for the computation of po t rn t i r l evrpotrrnrpiration and the othar for the computrtion of the rvrporrtioa of r f r r r wrtrr ru r f rc r , are prr r ra t rd ,

Thr tw r h r r t r d i f f r r from oar raothar i n the f i l u r e rdoptrd for the albedo* t h i r bria$ 2 5 2 f o r the v rgr t r t iv r covrr and only 5X for the v r t r r 8urfrcr. Another d i f f r reace rpprrrr i n the 80-crllrd rerodpnrmic term, whore thr conetrat factor r r roc i r t rd with the vind rpaed i r 1.00 in the e r r r of the vyle t r t ioa , to allow for 8rrrt.r roughnerr of the evrporrtin# ru r t rc r , rad 0.50 i a the care of the evrporatioa of water.

TBr two formulrr for thr computrtioa of potential rvrpotr rarpi r r t ioa and avrporrtion from r free rurfrce of wrtrr now read r r follovr:

* Tho rlbedo rxprrr r r r the percrntr8e of rhort wave incoming r rd l r t ioa ra f l rc t rd by the r o i l covrr or the wrtrr rurfrce.

b) Evrporr t ion of r f r e e v r t e t r u t f acq -

3 . Gxplrnrt ioa of t h r u n l t r o8rd Dn tho farmul&

The trrmr i n t r r v e n i a # in tha lormulre rnd i n the v o r k l n ~ aha r t# a r e defined h r r r u e d ~ r and rxp r r r r rd l a t h r follow in^ unlcr r

E, - e r t i n r t i o n of t h r p o t e n t i r l , v rpo t r r a rp i r r t i on f a r a uivrn pa r l ad , expramred in ma;

go e r t i n r t i o n of the rvepo r r t i oa from r f r r r v r t e r r u r f r c r f o r r given e x ~ r e r r e d i n nm;

po * mean r t no rphe r i c p r e r ru re rxprer red In m l l l j b r r r r t e r r l r v r i ;

p - mean r tmorphr r ic p r e r ru re expr r r red i n n i l l i b r r r r r r func t ion of r l t i t u d r , f o r t he r t r t l o n whet# the e r t i m r t r I8 e r l c u 2 r t ~ : ;

A - r a t e of change w i t h t enpe r r t u r e of the r r t u r r t i o n vrpour p r r r r u r a axprarred in n i l l i b r r r par degree ' C ;

y - the p r ~ c h o n e t r i c c o e f f i c i r n t f o r the prpchometer with fb4,.4d v e n t i l r t 1 o a 0.66;

0.75 and 0.95: f a c t o r # rxprer r ing tho reduct ion i a t he i nca r in@ rho r t wrvr r r d i r t i o h on the r v r p o r r t i n @ r u r f r c r r rnd corrrrpond- i n s r r r p e c t l v e l y re r a r lbado of 0.2) and 0 . F :

RA 8hort wave r r d i r t i o a r a c e i v ~ d 1t t he limit of the r t r o sphe re expr r r red . i n m of evrpor rb le v s t r r (1 an * 5 9 c r l o r i $ f ) and taking f o r t he r o l r r con r t rn t the value of 2.00 ~ r l . c m - ~ ..in ;

r and b c o e f f i c i e a t r f o r the r r t i m r t i o a of t o t a l r r d l r t i o n from the rua rh i a r b u r r t l o a (a re p r t rg r rph 2 . I ) ;

0 . 8ua$hfer d u r r t i o n f o r the period conaldrred in haurr and t en th@;

Y - runrb iae dura t ion s r c r o a o r l c r l l y p o r r l b l r for t he r iven period;

uT14 = Blackbody r a d i r t i o a espramred i n r of evaporrb le water f a r t h e p r e v a i l t ag r i r temperature;

r 4

= r r t u r r t i o n vrpour p r r r r u r r e r p r e r r a d La r i l l i b a r a ;

a d vrpour p r e r r u r r f o r t h r per iod under c o n t i d a t r t i o a exp r r r r ed i a r i l l i b a t r ;

a i r temperature axproroad i n degree# Kelvin where TbK TbC t 273;

Urn l r r r r n wind rperd a t aa r l r v r t i o n of 2 m f o r t h r 8iven period and rxpr ra rad i n mlrec ,

1, When t o t a l r a d i r t i o a mraruremente axp re r r rd i n c r l . ~ r - ~ r d r g ~ ~ a r e a v r i l a b l a , they may be introduced d i r e c t l y i n t b e u o r k i l ~ aha r t La t he block mrrkrd ItC c r l o r i e a .

2. If r l r humidity i e ewpteerrd r r r e l a t i v e h u r i d i t y , t h i r ~ c a n br t r cn r fo raed i s t o a b r of vapour p r e r eu re by multip1,tn' i h e r r t u r r t i o n vrpour p r r r r u r a ( t a b l e VII) f o r t h e 8iven Tea by t h e r r l r t i v r humidity.

Fot errmplo, i f R0 0 7 8 % and Tot 12.4' t a b l e 111 8 iv rb f o r a,

8 Value of 27.08 mbr, ed rill be 0 . 7 8 x 27.08 21.12 4,. *

3 . Th4 d a t a requi red f o r t h r conpu t r t i on r which a r e r a t r r e i n thr c o b r a of boxer oa t h e l e f t - h r a d r i d r of t he form r h o u l , 3 a l l be f a t t he r a r e per iod , a , ~ , t he monthly no to of t he d a i l ~ i v a l u e . Thl f i n a l r r ~ u l t of t h e c r l c u l r t i o o r will then be 8 o r " l o i n d d r y and t h r monthly va lue could be found by r u l t!pl;in( by 21, 29, 30 or 31.

The 10 j i l f r r r a t t r b l r r naca r r r ry for t h r rbovr c o r p u t r t i o a @ a r e a t t a ched . T b ~ i r * n u r b e r r e r e r e f e r r e d t o i n t h e c r l c u l r t i o a workin8 r h r e t r i n iornrn n u n e r r l r betwean b r r c k e t e appear in8 under lone of t he block8 of t he workin8 a h a r t .

2 ) t e a m a , H . L . 1963

Proc. Roy. Joc, A191 p . 1 2 0

Vw8wtrtlon and Wydrolo#y. Coamonwrrlth A l r i c . Burrru

Lr ditarminirar dr l f6vrporrt &on drna i r nature, I W E A C , Bruxollra, $aria S e l r n t i f i q u e Publ, no, 68

Smithroairn Matrarologlcrl Trblrr

Elrnwdtr of Fhyi icrl Caography. McCrrw H i l l

P h p r i ~ r l rnd dynrrtcrl netaorolory Cambtidfia Univarrlty i r r r r

dolrr rrdirtioa oa r horiroatrl rurface rt the lieit of thr

J P n A n J J A s o B D Lrt N 10' 3.81 1 9.41 12,71 15,76 17.12 16,44 14.07 10.85 7.37 4;49 3.22 48' 4 . 3 3 6.60 9.81 13.02 15,88 17.15 16.50 14.29 11.19 7,81 4 i 9 9 3.72 46' 5 7.10 10.21 13.32 16.00 17.19 16.55 14.51 11.53 2 5 ~ $ 6 9 4.27 44' j.30 7.60 10.61 13,65 16,12 17.23 16.60 14.73 11.87 8.69 6$OO 4.70 42' 5.86 8.05 11.00 13,99 16.26 17,26 16.65 14,95 12.20 9 , 1 3 6Q5l 5.19

P

T A B l R 1 b l r - R A ---WC*

T A B L E 11 N

Mart ha t n L r t r . J

S o u t h e r n L r t r . J

D a i l y a v r r r l e month by month o f t h e r r t r o n o m t c r &

p o r r l b l a r u n r h i n a d u r a t i o n i n h o u r 8 and t e n t h @

x 0 . 7 5 for p o t e n t 1.1 # v a y c t r * n n p i r ~ t i o n o f v e 8 r t . l c o v r r

x 0.9) f a r r v a p n r r l l n n f ; o m i r r r w l t e r

/ k 0 . 1 5 t ~ r p u t c ~ i t i a i P v s ~ o t r r n a p f r a t f n n of

v c g r . t i a l c . o l : u r n l a * b ; I ,.,

6 . 9 5 f o r e v a p o r a t : on f r o % f r s r v a t v r

T A B I 1 ! I v

B l r c k b a d y t r d i r t i o n ( g T y b ) r x p r a c a e d ln

srn o f water i n function of 7 ° C

S r t u r a t t o a vapour prC8mure ovrr u a t a t * 4

i n m t l t l b a r r 41 fuact foa o f T ' C - (Saitbmoalao tablr 1931 )

0 . 2 0 . 3 0 . 0 .5 0 . 6 0.7

TABLE V I l I - U

E x p r e r r l o n 0 . 2 6 (1 + 0 . 5 6 U ) where wtnd spard ( U ) i s expresred In u f r e c f a r T - Tn 5 12.C

U 0.0 0.1 0 . 2 0 .3 4 0 .5 0 . 6 0 .7 0 . 0 0 .9

Erprrarlon 0.26 (1 + 0.blU) where wind rperd (U) i s axpressad 14 mlrec for 12'C < TM - T. 5 13'C

Exprrsrtoq 0 . 2 6 ( 1 + O.68U) where wind speed (U) i r e x p r t s r e d i n mlrec f o r 13.C < TM - Tm , - - _

E x p r e ~ s l o n 0 . 2 6 (1 4 0.75U) vbere vind rprrd (US Ia 6xpr#8*9d i n mIrar for 14 .C < t), - tm 5 1 3 ° C

Exprerrion 0 . 2 6 ( 1 + 0 . 8 2 0 ) where wind rpead (U) I r oxprarrad I n . /arc f o r 1 5 ' C e In - 1. $ l b b C

vhero wind f o r 16.C *

e v r ~ o r r t i o n o_k. r f r e e u s t a r r u r f a c e

Expreralon O . Z b (0 .5 + 0.54.U) vhrre v ind rperd ( U ) i s axprearrd i n 8 1 r e c l o t TX - Tms 12'C

0 0.130 0.144 0,158 0.172 0.186 0.200 0.214 0.228 0.242 0.296 1 0,270 0,284 0.298 0.313 0.327 0 .341 0,355 0,369 0.383 0.397 2 0.411 0,425 0,439 0.453 0.467 0.481 0.495 0.509 0.523 0.537 3 0 .511 0,565 0.579 0.593 0.603 0,621 0.635 0.649 0.664 0.678 4 0.692 0 .706 0 ,720 0.734 0.748 0.762 0.776 0.790 0.804 0.818 5 0.832 0.846 0.860 0.874 0,888 0.902 0.916 0,930 0.944 0.958 G 0.972 0.986 1 .000 1.015 1 .029 1.043 1.057 1 ,071 1.085 1.099 1 1.113 1,127 1 .141 1.155 1.169 1.183 1.197 1 .211 1.225 1,239 8 1 . 2 9 3 1.267 1.281 1 .295 1.309 1.323 1.337 1 .351 1.366 1 ,380 9 1 .391 1.408 1,422 1 .436 1.650 1,464 1.478 1 .492 1 .506 1.520

10 1.534 1.548 1 .562 1.576 1 .590 1.604 1 6 1 8 1.632 1.646; 1.660 11 1.674

1

C x p r r r r i o n 0.2b (0.5 + 0 . 6 1 . U ) vhrre v ind rpeed ( U ) i n exprerrcd i q mlsec f o r 12.c c T~ - T, S l3.C !

Expreraion O.2b ( 0 . 5 + 0.68.U) where wind speed (U) i r exprersed i a mlrac f o r 13.C < TH - Tm 5 14'C

gv(~uoratItion free urtrr ,surf o c e

: x p r r r r i o n 0 . 2 6 ( 0 . 5 + 0 . 7 5 . U ) whrtr vind aprod (U) i r oxprorued i n r t l e c f o r l b * C c TH - 7% $ 15*c

:xprerrion 0 . 2 6 (0.5 + 0 . 8 2 . U ) uhere vind r p r e d (U) i r rxprorord i n c /arc f o r l 3 . C 4 T,, - Tm $ 1&*C

, 8 9 . U ) where uind rprrd ( U ) i n exprrarrd i n ninrc f o r 16.C 4 TH - Trn

Table ~ l v l n ~ L,&g i n funct ion o f T'C Y P

and rtandrrd r l r v U i o a L D matram 8b0W Qt ~ C ~ R V me1 1qv91

Trblr ~ I v f a f i k& i n f u n c t i o n of T'C 1 0

p d rtrndtrd ele*rtion !A urtrrr rbsvr 9s )#low r m

I FAO/UNESCO/WMO AGROCLIMATOLOGY SURVEYS

POTENT lAL EVAPOTRANSPIRATION after PENMAN

. . . . . . . . . . . . . . . . . . . . . . . . . . . . ‘ . . . . . . . . . . Country St ot ion Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lot~tuda. Longitude Altihud,

:-;cIp. . t t bJ I

r II.1 t v t

o n - o o r e f i - t

l Y l t l

I Tma n > u* m ~ i t n tlol. v..

I FAOIUNESCOIWMO AGROCLIMATOLOGY SURVEYS

LVIPWAflOM OF A FREE WTER SURFACE at lu OLlYMAN

..................... ................. . . . . . . . . . . . . . . . Country Slotbn Par bd ................. ............. L l i t W . . LongHuda Altltudo, . . , . . . . . . . . . .

FAOI UNESCOIWMO AGROCLIMATOLOGY SURVEYS I POTEN TlAL EVAPOTRANSPlRAT ION oftrr $ENMAN I

Country .I ?!,& ?/ . . Sta l ion . . ROW , . . . . , , W i o d d ' i y ( + ~ 0 ~ /

Lotituda ,1110 $9 d, . Lospit~do . /.tO.q',&. . , . . *It tudr .it m:. , I

n > (za arrr wtth VOtl) vu.

RO/UNESCO/WMO AGROCLIMATOLOGY SURVEYS

EVAPORATION OF A FREE WATER SURFACE aftor PENMArl I