Agricultural Water Management, 22 ( 1992 ) 335-343 335 © 1992 Elsevier Science Publishers B.V. All rights reserved. 0378-3774 /92 /$05 .00

Water management strategy for increasing monsoon rice production in Bangladesh

M.D. Jahirul Islam and Manoranjan K. Mondal Irrigation and Water Management Division, Bangladesh Rice Research Institute (BRRI), Gazipur,

Bangladesh

(Accepted 9 September 1992 )

ABSTRACT

Islam, M.D.J. and Mondal, M,K_ (1992) Water management strategy for increasing monsoon rice production in Bangladesh. Agrw. Water Manage., 22: 335-343.

Different studies on water management for monsoon (transplanted aman) rice cultivation were conducted at BRRI farm, Gazipur from 1978-1988 to determine its economics and feasibility. It was observed that the necessity and benefit of supplemental irrigation mainly depend on the amount of rainfall and its distribution pattern during the season. The crop suffers from moisture stress when the rainfall ceases by the first week of October. Percent filled grains is seriously affected by moisture stress at the later part of crop growth but other growth parameters remain unaffected because of sufficient rainfall during the crop development stage. Under these circumstances, one timely supplemental ir- rigation of about 60 mm can increase the rice y~eld up to 59% relative to the rainfed condition. Besides that, benefit-cost ratios of 5_3 and I 1.7 (for different devices ) indicated that supplemental irrigation is highly profitable for monsoon rice production. A pond size of about 5% of the total cultivable land area is required to store enough water for one supplemental irrigation, and it is economically viable with a benefit-cost ratio of about 2.4. Moreover, where there is no source of supplemental irrigation, a well-managed 15 cm high level is very effective (91%) in rain water conservation and can reduce yield loss to about 21%.

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

The need to increase rice production is a prerequisite to feed the ever in- creasing population of Bangladesh. In order to meet the increasing food de- mand, it is necessary to produce 20 million tons of food grain by 1992, whereas the present food production is only 17.0 million tons (BBS, 1989). It is a formidable task, but it is possible provided appropriate strategies and policies are followed. Irrigation water management is a key factor in this strategy along with proper utilization of rainfall.

Correspondence to: M.D_ Jahirul Islam, Irrigation and Water Management Division, Bangla- desh Rice Research Insti tute (BRRI) , Gaz ipur 1701, Bangladesh.

336 M.D.J. ISLAM A N D M.K. M O N D A L

Rice covers about 80% of the total ( 10.3 million ha) amount of cultivable land. Among the three distinct rice crops (wet: April-July; monsoon: July- December; dry: December-May), monsoon rice is the most important and is planted to about 54% of total rice area, which contributes about 50% of the total rice production (BBS, 1989 ). Therefore, the overall food position of the country depends mainly on a good harvest of monsoon rice.

During the monsoon, farmers usually cultivated low yielding local rice va- rieties without irrigation even if the farms have access to irrigation facilities. In Bangladesh, it is almost impossible to increase food production by bringing new areas under cultivation due to shortage of land. Therefore, the produc- tion per unit of land should be increased by adopting modern technologies. At present, modern variety (MV) coverage in the monsoon season is only about 21%, whereas in the dry season (December-May) it is about 84% (BBS, 1989). Consequently, there is ample scope to increase MV coverage in the monsoon season. In addition to modern variety, fertilizer and pest manage- ment; efficient water management is very important for increasing produc- tion. As a result, the government has put emphasis on supplemental irrigation so as to fulfill the target of food production by 1992. The objective of this paper is to document the strategy that should be adopted to achieve the target of food production within the stipulated time and its impact on the econom- ics of rice production in Bangladesh.

I M P R O V E M E N T OF WATER M A N A G E M E N T

Rainfall pattern, amount and distribution, its onset and termination, na- ture and intensity of drought all strongly influence the rice production in Bangladesh, because only about 29% of the cultivable land has access to irri- gation facilities (BBS, 1990). Normally rainfall starts by March and reaches a peak in July-August (Fig. 1 ). It is most active from June to October and about 80% of total rainfall occurs during this period. The amount of rainfall that occurs from June to September is basically higher than the amount needed for growing rice. The variation in rainfall from the mean value is quite high, especially during the 'higher-rainfall' months. In October, the crop normally remains at flowering to milking stages which are the most critical stages and the average rainfall of about 150 mm (range: 100-200 mm) is not always sufficient for potential yield of modern rice.

Inadequate rainfall during the critical stages of the transplanted monsoon (July-December) rice, commonly known as T. Aman, largely determines the extent of the annual shortage of food grain. Early recession of the monsoon exposes the crop to drought stress often in the critical reproductive stage, causing a considerable reduction in yield (Zaman, 1986; BRRI, 1984). Therefore, it regularly occurs that supplemental irrigation is needed in Octo- ber to stabilize the monsoon rice production because grain filling and the yields

WATER M A N A G E M E N T STRATEGY FOR INCREASING M O N S O O N RICE P R O D U C T I O N 337

Ramfa.H ( ram] I~o~r~loLI [ ram)

700 700

600

506

~,00

300

200

100

J F M A M J J A S 0 N D

Nolot,on • Average

t Stondord de'~lahon

T i

i

T

I" T

i Bongtadesn

J # M A M J J A S0 N D

500

"500

-.00

-300

2 0 I]

-100

Fig. 1. Rainfall distribution pattern of BRR1 farm, Gazipur (av. of 1975-1989 ) and Bangladesh (av. of 7 locations from 1982-1989).

are seriously affected by water stress. Considering this fact, the water manage- ment strategies that should be followed (according to their suitability) for increasing and stabilizing production in the monsoon season are stated below.

Management of irrigation water At present, only 29% of land has access to some form of irrigation in Bang-

ladesh, and 78% of the irrigated area is used to grow rice only (BBS, 1990). However, most of the rice irrigation facilities (79% of total rice irrigation) are used only in the dry season. The structures and facilities for irrigation remain idle in the monsoon due to lack of knowledge with regard to supple- mental irrigation.

Generally, in irrigated areas where with wet and dry seasons, the first aim is to stabilize production in the wet season, and the second is to meet the demand of water as much as possible in the dry season depending on the sup- ply of available water. However, in Bangladesh all the efforts are diverted to increase production through irrigation in the dry season, and in the wet sea- son (monsoon) irrigation is not considered to be of any importance. An ex- periment at the BRRI farm indicated that in 1978 and 1981 the rice yield was increased by about 57% and 21%, respectively, with two supplemental irri- gations from a nearby deep tubewell (Table 1 ). Even a single supplemental irrigation increased the rice yield up to 59% in 1983. Majumder and Choud-

338 M.D.J. ISLAM AND M.K. MONDAL

TABLE 1

Water requ i rement and yield o f rice cult ivars under supplementa l irrigation and rainfed condi t ion in BRRI farm, Gazipur , m o n s o o n seasons, 1978-1987

Year Variety Supplemental Rainfall Total Yield ( t / h a ) Yield irrigation ( m m ) water increase

( m m ) over N u m b e r A m o u n t Suppl. Rainfed rainfed

( m m ) irri. (%)

1978 BR4 2 100 431 531 3.6** 2.3 56.5 1979 Pa jam 1 60 514 574 3.2* 2.7 18.5 1981 Nizersail 2 100 451 551 2.9* 2.4 20.8 1983 BRI 1 1 60 899 959 4.6** 2.9 58.6 1984 B R I I 1 60 738 798 5.4* 4.9 10.2 1985 BR11 1 60 475 535 5.9* 5.3 11.3 1986 BRI 1 1 60 1270 1330 4.6 ns 4.5 3.2 1987 BRI 1 1 60 1530 1590 4.5 ns 4.4 2.3

*Significant at 5% level than rainfed condit ion. **Significant at 1% level than rainfed condit ion.

hury ( 1981 ) mentioned that one irrigation at the right time can increase the yield more than 2-6 irrigations not at the proper time. Hence the benefit of supplemental irrigation is directly related to the proper time of watering rather than to the number of irrigations. The rice yields from 1978 to 1985 were significantly higher with the use of supplemental irrigation due to a decreased rainfall during the growing season. However, in 1986 and 1987, the rainfall was much higher than in the previous years; yet, supplemental irrigation was provided because there were short periods of drought during the flowering stage of the rice. The yields obtained under supplemental irrigation were not significantly different from rain-fed farms because of a sudden rainfall 2-3 days after the application of irrigation water.

Benefit-cost analyses were performed by the partial budgeting method, where benefits were calculated only for the increased yield due to supplemen- tal irrigation, and the costs were taken as the expenses involved for the deliv- ering of water. The added costs for both deep tubewell and low-lift pump, run either by diesel or by electricity, were increased from 1983 and onward (Ta- ble 2) mainly because of the increased costs of driven energy. The benefit- cost ratio (BCR) of supplemental irrigation is presented in Table 2. The BCR was very high in 1978 and 1983, which means that supplemental irrigation was highly profitable in those years, which was due to the insufficient and uneven distribution of rainfall during the growing season. The BCR was less than 1.0 in 1986 and 1987, which was due to the uniform distribution of rain- fall even at the later stage of crop growth. The overall BCR (2.6 for deep tubewell and 4.8 for low-lift pump ) for the study period indicates that supple-

WATER MANAGEMENT STRATEGY FOR INCREASING MONSOON RICE PRODUCTION 339

TABLE 2

Benefit-cost ratio of supplemental irrigation in monsoon seasons

Year Added Deep Tubewell Low Lift Pump return (Tk/ha)* Added Benefit Added Bencfit

cost cost cost cost (Tk /ha ) ratio (Tk /ha ) ratio

1978 2925 450 6.5 283 10.3 1979 1340 450 3.0 316 4.2 1981 1611 660 2.4 393 4.1 1983 6559 1242 5.3 560 11.7 1984 2345 1767 1.3 736 3.2 1985 2733 1767 1.5 736 3.7 1986 469 1792 0.3 866 0.5 1987 500 1792 0.3 866 0.6

*1 US$ =Tk. 3 0 / = (approx.)_

mental irrigation is profitable in the monsoon season. Therefore, emphasis should be given to utilizing existing irrigation facilities for increasing and sus- taining rice production during the monsoon.

Management of rainwater The onset of the monsoon determines the planting time and the subsequent

temporal distribution of rainfall greatly influences the growth and develop- ment of the crop. The severity of drought depends on the distribution of rain- fall, while the phases of the crop growth are affected by dry periods and not by the total amount of rainfall alone (Sastry, 1976). Among the rainwater management strategies, the following parameters should be considered and applied according to their need and suitability in the monsoon season.

Rainwater harvest by farm pond In a rainfed environment (about 70% of the cultivable area), rainwater

harvesting for increasing and stabilizing the monsoon rice production should get top priority in Bangladesh. In plain land, a suitable pond can be con- structed at one corner of a plot. In hilly areas, a farm reservoir can be made at a suitable place of the catchment. A study in a BRRI farm, with a plot size of 25 X 20 m, a trapezoidal pond of 5 X 5 × 2 m was found to be appropriate for storing enough rainwater for one supplemental irrigation of about 60 mm depth. The pond size was about 5% (2 m deep) of the rice plot and was suf- ficient to conserve rain water for sustaining rice productivity during the mon- soon season. Moya et al. (1988) mentioned that about 7-8% of land (2 m deep) is required to collect direct rainfall and the run-off from the adjoining land, which is an attractive technology in Central Luzon in the Philippines.

340 M.D J. ISLAM AND M.K. MONDAL

The study indicates that in 1983 the rice yield increased by about 59% over rainfed cultivation, which was due to one supplemental irrigation at the boot- ing stage from the pond (Table 1 ). However, yields did not differ signifi- cantly in 1986 and 1987 because of sufficient and uniform distribution of the rainfall throughout the growing season, which fully satisfied the crop's water demand. The average rainfall at the BRRI farm in October was higher than the national average, which was due to the higher rainfall in 1986 and 1987 (Fig. 1 ).

The benefit-cost ratio of pond irrigation was also calculated on the basis of the partial budgeting method like deep tubewell and low-lift pumps. The as- sumptions were the same as before, only the cost of the rice that can be har- vested from the pond area and the interest on the investment for pond exca- vation were added to the costs. The highest BCR was 6.8 in 1983 (Table 3 ), which indicates that a farm pond is highly profitable for the drought years. Like the BCR of deep tubewell and low-lift pump, the BCR of the farm pond was less than 1.0 in 1986 and 1987 because of sufficient rainfall distributed

TABLE 3

Benefit-cost ratio of farm pond for supplemental irrigation, monsoon seasons, 1983-1987

Item 1983 1984 1985 1986 1987

a. Added return ( T k / h a ) increased rice yield due to supplementa l irrigation

b. Reduced cost ( T k / h a )

Added benefits ( a + h )

6384 2112 2772 200 530

6384 2112 2772 200 530

c. Reduced return ( T k / h a ) value of out-put not produced on the ditch area

d. Additional cost ( T k / h a ) interest on investment for ditch making ,~, 15% labour cost for irrigation

Added costs ( c+ d )

Ben~fit-c'ost ralto [ ( u + b ) / ( c + d ) ]

Labour wage ( T k / d a y ) Price of rice I T k / k g ) 1 US $ = T k . 3 0 / = (approx.)

28 54 58 56 58

750 750 750 750 750

160 224 240 180 180

938 1028 1048 986 988

6.8 2,1 2.6 0.2 0.5

20 28 30 30 30 3.8 4.4 4.4 5.0 5.3

WATER MANAGEMENT STRATEGY FOR INCREASING MONSOON RICE PRODUCTION 341

more or less uniformly throughout the growing period of rice. The average BCR values (2.4) indicate that a permanent farm pond is profitable even if there is a drought once every 5 years. Moreover, fish production may help to increase the benefits from the pond. Maintenance and the cleaning of the pond, especially the depth should be done once in every three years so that the re- quired quantity of water can be stored as per design.

There are about 1.3 million ponds in Bangladesh, of which 52% (area ba- sis) are used for fish culture (BBS, 1989). If serious attempts are made, a large number of those ponds could be used as a source of supplemental irri- gation as well as fish culture.

Levee management for rainwater utilization Only a portion of total rainfall can be considered effective in promoting

crop growth, and the remaining portion goes out as surface drainage from the crop field due to lack of proper management practices. Rainfall could be uti- lized more beneficially if it were stored and managed properly.

A study in the BRRI farm with different levee heights indicates that the effectiveness of rainfall was higher (71-100%) with a levee height of 15 cm when compared to 7.5 cm (55-100%) and no levee at all (37-92%) treat- ments (Table 4 ). A similar finding was also reported by Bhuiyan et al. ( 1979 )

TABLE 4

Rainfall effectiveness and yield of rice cultivars under different heights of levee managemenl in mon- soon seasons, BRRI farm, Gazipur

Treatment 1979 1980 1981 1988

RF¢ Yield RF~ Yield RFe Yield RFe Yield (%) ( t /ha) (%) ( t /ha) (%) ( t /ha) (%) ( t /ha)

TI =0 cm levee 92 4.3** 68 3.5** 37 5.7** 59 3_9** T2=7_5 cm levee 100 5.2 80 4.6 55 8.0 91 4_6 T3= 15 cm levee 100 5.2 94 5.8 71 7.9 100 4_4 T4= 15 cm levee 95 5.5 82 6.3 71 8.6 98 4 7

with 0 .5 -7 .5 cm continuous standing water

LSD Value at 5% level 0.5 0.6 0.8 0 4 LSD Value at 1% level 0.7 0.8 1.1 0.6

**Significant at 1% level. *Significant at 5% level. RF e, effective rainfall. Note: Rainfall was measured by tru-check rain gauge. Runoff ( i f any) , collected in a constructed ditch, was also measured the following day. From this data "effective rainfall' was determined, taking into consideration the evaporation, seepage and percolation values.

342 M.D.J. ISLAM AND M.K. MONDAL

who reported that significant differences in the amounts of effective rainfall were found among spillway heights of 2, 5 and 12 cm. Each successive in- crease of 2 cm spillway height reduced the mean stress day by about 50%.

The yield difference between 15 cm levee height with continuous standing water (T4) and without levee (T1) plots was more than 1 ton (Table 4), and this was statistically significant. There was no significant yield difference be- tween 15 cm levee without standing water (T3) and with continuous stand- ing water having the same levee height (T4) plots; but yield differences be- tween no levee (TI ) and 15 cm levee (T3)plots were highly significant in all years (Table 4). In 1980, the yields of rice under 15 cm levee (T3) and 15 cm levee with continuous standing water (T4) plots were significantly differ- ent from those obtained in 7.5 cm high levee (T2) plots meaning that if the amount and frequency of rainfall are low from mid-September to mid-Octo- ber, then 7.5 cm high levees are not enough to stabilize rice production. Therefore, it can be concluded that well managed 15 cm high levees could help to conserve sufficient amounts of rainwater (91%), which can be bene- ficially used by plants, particularly during short drought periods for obtaining the potential yield (saved about 21% yield) of monsoon rice.

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

The following conclusions and recommendations can be drawn from the studies: 1. If rainfall continues up to November with adequate amounts, there is no need of supplemental irrigation even in the case of late transplanting. How- ever, if it ceases in the first week of October, late transplanted monsoon rice will suffer from drought and the yield will be reduced. This situation can be overcome by:

(a) transplanting monsoon rice in time so that it can be harvested by late October. (b) cultivating short-duration, early maturing varieties which may be less affected by moisture stress at the later part of crop growth.

2. The grain yield of monsoon rice can be increased by up to 59% by one timely supplemental irrigation of about 60 mm depth, if there is a short drought at the critical stages of crop growth. 3. Approximately 5% area of total cultivable land is required for a farm pond (2 m deep) to store enough water for one supplemental irrigation. A perma- nent farm pond for supplemental irrigation is profitable even if there is a drought only once every 5 years. 4. 15 cm high levees can reduce yield loss to a large extent (21% ) where there is no source of supplemental irrigation in monsoon season.

WATER MANAGEMENT STRATEGY FOR INCREASING MONSOON RICE PRODUCTION 343

REFERENCES

Bangladesh Bureau of Statistics (BBS) (1989) Statistical year book of Bangladesh. Dhaka, Bangladesh.

Bangladesh Bureau of Statistics (BBS) (1990) Statistical year book of Bangladesh. Dhaka, Bangladesh.

Bangladesh Rice Research Institute (BRRI) (1984) Annual internal review report for 1983. Agricultural engineering division, BRRI, Gazipur, Bangladesh, 74 pp.

Bhuiyan, S.I., Wickham, T.H., Sen, L.N. and Cablayan, D. (1979) Influence of water-related factors on land preparation, cropping intensity and yield of rainfed lowland rice in Central Luzon, Philippines_ In: Rainfed lowland rice, 1RRI, Phihppines, 231 pp.

Majumder, D.K. and Choudhury, R. ( 1981 ) Nitrogen response to irrigation. Indian Agricult. 25, 241-247.

Moya, T.B., de la Vina, W C. and Bhuiyan, S.I. (1988) The potential of farm reservoir use in increasing productivity in rainfed areas. Philippines J. Crop Sci. 1 l, 125-132.

Sastr~', P_S.N_ (1976) Climate and rice. In: Proceedings of the Symposium on Climate and Rice. IRRI, Philippines.

Zaman, S.M.H. (1986) Current status and prospects for rainfed foodgrain production in Bang- ladesh. BRRI, Gazipur, Bangladesh.