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IIT Kharagpur
INTRODUCTION
I n I n d i a , rice is the most important food crop grown in an area of 39 m illio n h ectares. Of t h is , about q~ m illio n hect
ares are annually subjected to flooding or water-logging. Most o f this problem area lies i n the low lands of eastern U ttar P radesh, B ih a r , West B engal, O r is s a , Assam, M anipur, Tripura and Kerala s t a t e s , which come w ith in the high r a in f a ll regio n . Even the moderate r a in f a ll zones of coastal Andhra Pradesh and Tam il Nadu are prone to this problem. R ic e , the only crop grown
in the low lying areas during rainy season, o ften suffers due to water-logging or occasional flooding as a result o f un
p redictable heavy rains and drainage congestion. Under such s it u a t io n s , the p ro d u ctiv ity o f the crop is not only low but also u n sta b le.
There is growing concern over the p lig h t o f rice farmers i n the flood-prone and water-logged areas o f I n d i a . I t is recognised that so fa r these regions have not been able to contribute s i g n if i c a n t l y to meet the growing food requirements o f the country. B e s id e s , they have been neglected by modern rice production technology and have received l i t t l e research a t t e n t io n . As a consequence, the av a ila ble technology has remained app licable only -to the problem free medium lands and is found to be inadequate or inappropriate fo r the vast problem a r e a s . The crop i n these regions su ffe r mostly from uncon
tro lle d excess water during the growing p e r io d . By v irtue o f geographical lo ca tio n i t may not be p o ssib le to control w a t e r logging by any engineering methods. T h e r e fo r e , the strategy
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IIT Kharagpur
for improving the crop yield should be aimed at development of agro-technology to escape or endure flooding or water-logging.- To achieve this o b je c t iv e , the major gaps in the a v a ila b le rice technology for low lying areas are necessarily to be id e n t ifie d and effo rts are to be made for a technology that combines high yield p o ten tial with low risk and su its the p rev a ilin g environ
ment .
One of the major causes of poor and unstable y ield of rice i n the low lands is the cu ltivatio n o f t r a d it io n a l, t a l l , low y ie ld in g v a r ie tie s which manage to survive^ under water-logging or flo o d in g . T h e re fo re , for a revolutionary change and ra isin g the lev el of productio n, modern v a r ie tie s o f high y ield po ten tial need to be introduced replacing the tr a d itio n a l v a r ie t ie s .T h e s e improved v a r ie tie s should possess adequate tolerance to deep
standing w ate r. Morevover, the ba sic understanding o f the e ffe c t o f varying depths and durations of submergence on growth and
y ield of rice and mechanism involved in tolerance to submergence is necessary for id e n t if i c a t i o n of suitable types which can to ler ate a wide range o f flooding or water-logging without losing
t h e ir y ie ld p o t e n t i a l i t i e s . With the development of improved high y ie ld p o te n tia l v a r ie t ie s suited to the low la n d s , prospects of ra isin g the lev el of production o f such problem areas have in c r e a s e d . However, very l i t t l e inform ation i s a v a ila b le on the agronomic requirements of these v a r ie t ie s for the r e a l i z a t io n o f th e ir p o te n tia l y ie ld when grown under such conditions of e n v i
ronmental s t r e s s .
The damage o f the crop due to flood v aries considerably w ith years and lo c a t io n . This is m ainly due to v a r ia tio n i n
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the depth o f w ater, time o f occurrence and duration of sub
mergence, time of planting and stage of the crop at which flood occurs. As the depth, of w ater, occurrence and duration of flood depend upon natural fa c to r s, so far very few research e ffo rts have been made to assess the extent of damage caused by them. B u t, for the development o f an appropriate production technology to^ overcome the problems of low land r i c e , a detailed study of the factors associated with the crop damage becomes im perative. Besides th ese, the studies on the e ffe c t of flood at d iffe re n t growth stages o f the crop would eventually help i n id e n t ify in g the c r it ic a l stages susceptible to submergence.
Such inform ations are necessary for proper scheduling of cu l
tural p r a c t ic e s , p a r tic u la r ly seeding or transplanting i n the flood-prone a re a s . By adjusting the date of seeding or p l a n t i n g , i t may become possib le to enable the crop to either escape the flood at the vulnerable stages or withstand it s adverse effectso T h u s , the im p licatio n o f adjustment o f p lanting time is considered to be important for minimising the risk i n c u l t i v a tio n .
One o f the problems of flash-flood and water-logged areas is the poor stand o f the crop. Th is generally happens due to m ortality o f seedlings p a r tic u la r ly at the early stage of the crop growth. Under such s it u a t io n s , aged seedlings at tran splan tin g may have an added advantage of greater submergence tolerance than the seedlings o f normal age o f 25 d a y s. Moreover, the higher number of seedlings transplanted per u nit area does
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compensate to some extent for the poor t ill e r in g which is not very uncommon under deeper depth of standing w ater. A c r it ic a l appraisal o f the above aspects would help i n suggesting agro
nomic measures for m aintaining adequate plant population as one o f the major steps for successful rice c u ltiv a tio n i n the flood-prone or water-logged situ a tio n s .
The t r a d itio n a l v ar ie tie s being poor f e r t i l i z e r respon
s i v e , are usually grown either without f e r t i l i z e r s or with
meagre doses of nitrogen o n ly . Moreover, the recovery o f n it r o gen is very low due to unavoidable losses which increase when applied as single b asal dose at p la n t in g . As y e t, no su itable technique has been developed for increasing the e ffic ie n c y of nitrogenous f e r t i l i z e r s , p a r tic u la r ly when the standing water depth i n the f i e l d is h ig h . With the advent of high y ield
p o te n tia l and f e r t i l i z e r responsive v a r ie tie s fo r the low lands, i t becomes e s s e n tia l to develop appropriate techniques of
f e r t i l i z e r a p p lic a tio n as the recovery of the flood damaged plants has close relationship with so il f e r t i l i z a t i o n . The slow release N f e r t i l i z e r s , which have been developed i n the recent p a s t , hold some promise i n such situations fo r increasin g the production through bette r supply of nitrogen to the p lants and
hence need to be s t u d ie d .
Keeping the above points i n v iew , an in v e s t ig a t io n was planned w ith the follow ing o b jectiv es s
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1 . To id e n t ify the causes of low and unstable y ie ld and to find out the extent of damage caused by flash - flo o ds.
2 . To overcome some of the problems of flood-prone and water-logged areas and to increase the y ie ld of r i c e .
3 . To develop su itable agronomic management p ractices for re a liz in g the yield po ten tial of improved rice v a r ie t ie s .