The feasibility of high yielding aus-aman-rabi cropping systems in the polders of the low salinity coastal zone of Bangladesh

Abstract

Cropping intensity and agricultural productivity in the polders of the coastal zone of Bangladesh are much lower than that of most of the country. The main reasons for this are waterlogging, the late harvest (December/January) of the rainy season rice crop (known as ‘aman’), and the lack of readily accessible fresh water during the dry season in the polders. Waterlogging prevents the production of high yielding and earlier maturing rainy season rice varieties (HYV aman), and of high yielding/value rabi (dry season) crops such as maize and sunflower. However, gravity drainage of excess water from the polders is physically feasible. Furthermore, the rivers surrounding the polders in the central coastal zone (Barisal Division) contain large volumes of fresh river water throughout the year. Research was therefore undertaken to evaluate, under good water management, the feasibility of intensifying to high yielding rice-rice-rabi cropping systems in the low salinity central coastal zone. A replicated cropping system experiment was conducted for two years at Patuakhali using a short duration modern ‘aus’ variety (aus is the name of the rice crop grown during the early rainy season) (BRRI dhan65), a medium duration modern aman variety (BRRI dhan44), and high yielding/value rabi crops. The cropping systems included four aus sowing dates (20 March, 5 and 20 April, 5 May) which resulted in four aman and four rabi sowing dates. Two rabi crops were compared within each sowing date (maize – Pacific 984, sunflower – Hysun 33). Annual cropping system rice equivalent yield (REY) ranged from 13.7 to 20.0 t/ha. All systems were profitable with 100% of labour purchased, although benefit cost ratios (BCR) were not always >3, suggesting low attractiveness to farmers. However, most polder farms are small, with 30–60% of labour provided by the family. With 75% or less of labour purchased (the rest provided by family), all cropping systems were financially attractive, even with a 10% decline in grain price. Rabi crop yield was the main determinant of total system REY and profitability, both of which declined as sowing date of the rabi crops was delayed beyond 15 December. Optimisation of sowing date of the rabi crops should therefore be the first consideration in cropping system intensification for the low salinity coastal zone. The optimum sowing date of both the maize and sunflower was mid-December. For adequate "turn around" time between all crops, for the varieties used in this study, the aus crop should be sown in mid-April and the aman crop in mid-August. This research shows that, with good water management, it is possible to implement highly productive and profitable aus-aman-rabi cropping systems in the low salinity coastal zone of Bangladesh.