Trends of Water Requirements of Major Crops and Cropping Patterns in Bogura and Rajshahi Districts of Bangladesh

Reliable past trends of water requirements of individual crops and cropping patterns at local level, although crucially important for irrigation forecast and agricultural planning, are yet inadequate for the water-scarce Barind region of Bangladesh. This study, therefore, determined water requirements and their trends of eight major crops (aus, aman, boro, vegetables, mustard, sugarcane, wheat and potato) and six cropping patterns (aus–aman–boro, aus–aman–potato, aman–potato–fallow, vegetables–aman, aman–mustard–fallow and aus–fallow–wheat) of Bogura and Rajshahi districts of the Barind region. Water requirements were determined from crop, soil and weather data for the period 1985–2013 by using Soil-Water Balance via CropWat (SWBcropwat) model. Trends of rainfall, crop evapotranspiration (ETc) and irrigation requirement (IR) were determined with MAKESENS statistical tool. Monthly total rainfall revealed increasing trend in January, August and October but decreasing trend in the other months, with significant (p≤0.05) trend in July in Bogura. Monthly total ETc decreased except in July and September, with significant trend in October–April/May. Seasonal ETc for the crops decreased significantly except for aman rice and sugarcane in Bogura and for aman rice in Rajshahi. ETc also decreased for the cropping patterns except for aman–mustard–fallow in Rajshahi. While effective rainfall (ER) for the crops and cropping patterns decreased only minimally, IR decreased significantly for boro, potato and vegetables in Bogura and for mustard and vegetables in Rajshahi. IR decreased for all cropping patterns, with significant trend for aus– aman–potato, aman–potato–fallow and vegetables–aman patterns. In response to changing cropping area, total volume of ETc increased gradually from 1985 to 2005 in Bogura and from 1985 to 2010 in Rajshahi for boro rice, but it decreased until 2005 before increasing for aus rice in both districts. After the year 2000, total volume of ETc decreased for wheat but increased for potato, indicating a shift from wheat to potato cultivation. Due to contrasting trends of ER and ETc and self-motivated shift in crop-choice, continuous adjustment of irrigation-based crop planning is necessary. The results of this study can guide future investigation for all other crops and cropping patterns to help planning agriculture of the study areas by choosing appropriate crops and cropping patterns based on available water resources.