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Characterization of Rainfed Rice Growing Environment in Bangladesh Based on Relative Water Supply

Md.Shahjahan Kabir
SSO
Agricultural Statistics Division, BRRI, Gazipur

DR. D.N.R. Paul
CSO and Head
Agricultural Statistics Division, BRRI, Gazipur

Abstract/ Executive Summary:

Water is the basic requirement for any plant to grow and it is very much applicable to the water loving crops like rice. Despite of adequate availability of other inputs and presence of most favourable environment, rice cannot be grown without water either applied through external sources such as rainfall, irrigation or from soil reserve. The productivity of rice in a geographical area depends on the ability of the soil to supply water to rice plants. Relative water supply (RWS), an index of water supplying ability of the soil to rice plants was, therefore, used to characterize the rainfed rice environment. RWS values were computed for the month of October using the estimated nearly assured rainfall (minimum monthly rainfall at 90% probability level) only for those weather stations (Both of BMD and BWDB) for which records were available on monthly ET values. Then RWS was interpolated for whole of Bangladesh. ARCView Spatial Analyst Version 3.2 was used to construct the surface of RWS and following classification was used to define the rainfed T. Aman rice growing environments.

Keywords: Characterization, Rainfeed rice, Evapotranspiration and Relative water supply

Location: All district of Bangladesh

Start Date: 01-07-2004

End Date: 30-06-2005

Program Area: Socio-economic and Policy

Commodity: Rice

Objectives:

To construct map of rainfed rice growing environment of Bangladesh.

Methodology:

Water availability during the crop growth season was determined by using the concept of relative water supply (RWS), which is defined as the ratio of water supply to water demand by the crop. RWS is a pure number and is used as an index of water availability. An RWS value greater than 1 indicates that the water supply is abundant, whereas an RWS value less than 1 indicates a drought.Daily ET (Evapotranspiration) values at each location were summed up to obtain monthly ET values of that location. Rainfall at all interpolated points (created through krigging) falling within a district boundary was averaged to represent the rainfall for that district. This was due to the obvious reason that the observed rainfall would not represent the whole district as it was recorded at a particular rainfall station located within the district. Seepage and percolation was estimated for different land type and soil texture classes. These estimates of rainfall, ET, S and P were then used to compute RWS. The RWS values were calculated for the crop season (July-October) and that for grain filling period (October) of T.Aman rice. The correlation analysis was performed for the greater districts for which evapotranspiration and long term data on yield of rice was available. The results indicated significant correlation between Yield and RWS in October in most of the districts but only few districts yield had significant correlation with RWS for the entire growing period of T. Aman rice.

Source of Information: BRRI Annual Report 2005-06

Article Link (Online Journal):

Funding Source:

1. Government

Budget: 200000

Total Budget (Tk.) : 200000

Achievement/Findings:

The resulting map indicates that droughts occur in the month of October in more than half of the country from the central to the north-west and south-west part except Bogra and parts of its surrounding districts indicating least to less favourable for rainfed T. Aman cultivation. Almost entire of Noakahli and some areas of Sylhet region are also characterized by least to less favourable environment for growing rainfed T. Aman due to October drought. Water deficit is about 70% - 80% in the least favourable area 60%-70% in the less favourable area in the month of October. These areas may require a considerable amount of supplemental irrigation in October for growing rainfed Aman rice. The rest of the country falls under favourable to most favourable for rainfed T. Aman cultivation. In the favourable environment, water deficit may be about 50% to 60% in the month of October. Bogra, B. Baria, Bhola, Chittagong, Cox’s Bazar and Bandarban districts are characterized by most favourable environment for rainfed T. Aman where water deficit remains below 20%. Characterizing the rainfed T. Aman environment based on RWS in the month of October can be used as a decision making tool for planning rainfed rice cultivation in Bangladesh. If the expected rainfall in October is inadequate to meet the water demand of the crop in a certain area, the farmers may be advised to be equipped with supplemental irrigation facilities.

Knowledge Management: Report/Proceedings