CHAPTER I INTRODUCTION
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INTRODUCTION
The continuous growth of the w orld population re p r e se n ts an a ss o c ia te d increase in demand for food and c lo t h in g too. I t is expected th at there w i l l be 6 b i l l i o n s people in the world in the year 2 0 0 0 . The expected in c rea se i n the demand for w heat, r i c e , m aize, root and tuber crops and other a g r ic u ltu r a l products w i l l be more a ^ .e a s t
80 per cent o f the p re s e n t l e v e l . M aize occupies about 1 1 . 2 per cent of w orld crop-land area and accounts for about 1 6 .1 per cent o f the world crop c a l o r i e s . In g e n e r a l , maize ranks t h ir d a fter w heat and rice among
a l l crops for food-supply to the p eo p le in the w o r ld .
Eastern p art o f In d ia (s u b t r o p ic a l humid r e g i o n ) , a mono-cropped r ic e dominated a re a , gets a high r a i n f a l l d u r in g k h a r if (July-0c t o b e r ), a sh o rt s p e ll of w in t e r r a i n
(November-March) fo llo w e d by hot w in d s , and o c c a s io n a l r a in s d u rin g summer s e a s o n . The s o i l is mostly a l l u v i a l , deep and f e r t i l e and is also h aving s u f f i c i e n t ground w a t e r . High r a i n f a l l and poor d ra in a g e system p ro v id e a s i t u a t i o n fo r grow ing mainly r ic e crop d uring the k h a r i f s e a s o n . Even d uring r a b i season u nd er assured i r r i g a t i o n , r i c e comes forth at f i r s t p r e f e r e n c e . I t is a w e ll known f a c t th a t ric e re q u ir e s more w ate r, has low water use e f f i c i e n c y and can be s u b s titu te d by any other c e r e a l h a v in g le s s water requirem ent d u r in g the ra b i s e a s o n . The area under m aize in t h is p art o f the above m entioned r e g io n is less than one p er c e n t.
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Enhanced i r r ig a t i o n f a c i l i t i e s and a v a i l a b i l i t y of h ig h y ie l d in g v a r ie t ie s of maize made i t s c u l t iv a t io n f e a s i b l e i n the w in te r season, p a r t i c u l a r l y in those re g io n s where th is crop is y et to f i n d a place i n the e x i s t i n g cropping system . However, the survey of e a r l i e r l i t e r a t u r e reveals th at l i t t l e has been done to explore the p o s s i b i l i t i e s of growing maize i n w in t e r season in the humid subtrop ical c o n d it io n s .
In many parts of the world the most important c o n s t r a in t in a g r ic u lt u r a l development is the lim ite d a v a i l a b i l i t y of i r r i g a t i o n w ater, and even i f w ater is a v a i l a b l e i t is not b e in g used e f f i c i e n t l y in crop
p r o d u c t io n . I t is p ro b a b ly f a i r to say t h a t most crops s u f f e r some-times in t h e i r l i f e c y c le , atjleast from sh o rt p e r io d s of water sh o rtag e, even i n l o c a t io n s where r a i n s
are l i m i t i n g not in the t o t a l amount, but from tim ely d i s t r i b u t i o n .
E n vironm entally in d u ced water d e f i c i t s have lo ng been r e c o g n ize d as one o f the c h ie f l im it a t io n s fo r m aize p r o d u c t io n in many a r e a s , Even a m ild drought during the
c r i t i c a l s t a g e (s ) o f crop-growth can d r a s t i c a l l y reduce the s e e d /e a r p ro d u c tio n . The fre q u e n t occurrence o f t h is problem in the semi-arid humid s u b t r o p ic a l re g io n s,
t h e r e f o r e , makes i t l o g i c a l to i n i t i a t e a thorough
i n v e s t i g a t i o n o f the im pact o f w ater d e f i c i t on d i f f e r e n t growth-stages of m a ize .
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I t is an e s t a b l is h e d fact th a t fo r a t t a in in g maximum crop y i e l d s , the s o il m oisture stipply should be adequate throughout the growth p e r i o d . In g e n e r a l/
the ro le of water fo r p la n t growth and development is v e ry w e ll documented. S e n s i t i v i t y o f maize grain developm ent to m oisture stress is r e la t e d to the p h y s io lo g ic a l stage of developm ent. For th is reason the time when moisture stress occures is important in d eterm in in g f i n a l g r a in y i e l d ; hence tim ing o f precep- i t a t i o n or i r r i g a t i o n becomes an im portant economic f a c t o r i n maize p r o d u c tio n . However, w it h regard to the e f f e c t s o f w ater d e f i c i t at s p e c i f i c growth stag es o f m a ize , enough has not been done under s u b tro p ic a l c o n d i t io n s . F u rth er, the a v a ila b le in fo rm atio n is very much d iv erse and deb atab le w ith re sp e c t to the c r i t i c a l s t a g e (s ) of maize to water d e f i c i t .
E v ap o tran sp ira tio n during the l i f e cycle o f the p l a n t is reported to be com paratively low d uring the v e g e t a t i v e stag e, w h ile i t is maximum d u r in g the p e r io d
from t a s s e l l i n g to g r a in f i l l i n g ; hen ce, i t can be r e a s o n a b ly p o stu la te d that the y i e l d and water use
e f f i c i e n c y may be in c r e a s e d through e f f i c i e n t s c h e d u lin g o f i r r i g a t i o n w ith due c o n s id e r a t io n to the seasonal e v a p o r a t iv e demand and crop s u s c e p t i b i l i t y to w ater d e f i c i t during d i f f e r e n t growth s t a g e s . This is
an o ther area o f f e r i n g e x c e l l e n t scope fo r te s t in g the
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above hypothesis and fo r developing s u i t a b l e i r r ig a t i o n s c h e d u le fo r maize„
The p lan t growth and s o i l m oisture d ep le tio n
approaches for sc hed u ling of i r r ig a t i o n have been in vogue i n the p a s t . However, both these approaches have c e r t a in li m i t a t i o n s or these are c o s t l ie r and can not be adopted by the In d ia n farm ers. The recently developed climatol- o g i c a l approach, i . e . , IW /CPE ( I r r i g a t i o n water a p p lie d to cum ulative pan evaporation) seems to be sim pler and has h ig h ex ten sio n v a l u e . T h ere fo re , i n the present i n v e s t i g a t i o n the i r r i g a t i o n s were time-based upon the d i f f e r e n t I W /C P E 'S . I t is also known th a t under l im i t e d w a te r su p ply the n u t r ie n t uptake may decrease as a
consequence o f the reduced p la n t g ro w th .
F e r t i l i z e r is another im portant but c o s t l ie r in p u t w h ich needs s c i e n t i f i c management fo r o b ta in in g maximum p roductio n at minimum c o s t . In g e n e r a l, the n u t r ie n t requirem ent o f d i f f e r e n t crops v a r ie s under d i f f e r e n t s o i l types, c lim a t ic c o n d it io n s , water a v a i l a b i l i t y and other management p r a c t i c e s . The role of n it r o g e n , phosphorus and potassium are w e l l e s t a b lis h e d f o r plant- growth and developm ent. S c i e n t i f i c info rm atio n on the n it r o g e n , phosphorous and p o tash requirem ents f o r w in t e r m aize is a v a il a b le under those r e g io n s where t h is crop i s w e ll adopted. However, v ery l i t t l e inform atio n i s a v a i l a b l e on these asp ects under s u b t r o p ic a l humid r e g io n where this crop i s not g e n e r a lly grow n. Th us,
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e f f o r t s were made in the p resen t in v e s t ig a t i o n to develop s u i t a b l e scheduling of ir r ig a t i o n fo r enhancing the water u se e f f i c i e n c y and also to f in d out the optimum requirem ent o f n u t r ie n t s for maximum g ra in p rod u ctio n in m aize.
A se r ie s of experim ents was p lan n e d and c a r r ie d out w i t h the fo llow in g s p e c i f i c o b je c t iv e s :
1 . To id e n t ify s u it a b le i r r i g a t i o n schedules b ased on pan ev a p o ratio n during d i f f e r e n t growth s t a g e s .
2 . To evaluate the crop response to delayed i r r i g a t i o n during d i f f e r e n t reproductive s t a g e s .
3 . To study the e f f e c t s o f i r r i g a t i o n sc h ed u lin g and f e r t i l i t y le v e ls on water requirem ent, grow th, y i e l d and n u t r ie n t content of m a iz e .
