Raw data PhD thesis:The feasibility of high yielding aus-aman-rabi cropping systems in the polders of the low salinity coastal zone of Bangladesh

The cropping intensity and productivity of the coastal zone of Bangladesh is much lower than that of most of the country, despite enormous investment in the construction of polders to protect the lands from tidal flooding and saline water intrusion. In the coastal zone, farmers typically grow a single crop of rice (aman) during the rainy season using low yielding, photoperiod sensitive local varieties, followed by a low yielding pulse or sesame crop. Much of the cultivable land remains fallow for 3-7 months each year. The main reasons for the low productivity in the polders are waterlogging as a result of high rainfall and poor drainage during the rainy season, the late rice harvest (December/January), and the lack of readily available fresh water during the dry season. The waterlogging prevents the production of high yielding and earlier maturing aman varieties (HYV aman). The late harvest of the local aman varieties and saturated soil prevent the cultivation of high yielding rabi crops such as maize and sunflower, and delay establishment of traditional rabi crops such as mungbean and sesame, which are thus often damaged or destroyed by pre-monsoon rains and cyclones. However, by draining excess water at low tide during and at the end of the rainy season, it should be possible to grow modern HYV rice varieties and establish high yielding rabi crops at the optimum time. Furthermore, the south central coastal zone (Barisal division) is supplied by large volumes of fresh river water throughout the year. Therefore, the research undertaken in this thesis was designed to evaluate, under good water management, the feasibility of intensifying to high yielding aus-aman-rabi cropping systems in the low salinity coastal zone. A replicated cropping system experiment was conducted for two years at Patuakhali using a short duration modern aus variety (BRRI dhan65), a medium duration modern aman variety (BRRI dhan44), and high yielding/value rabi crops. Performance of the systems was compared for 4 aus sowing dates (20 March, 5 and 20 April, 5 May), 2 rabi crop species (maize – Pacific984, sunflower – Hysun33) and 2 mulch treatments (0, 5 t/ha of rice straw during the rabi crops). The longest total system in-field crop duration was about 330 d. This allowed for an average turn-around time between crops of about 10 d. Annual cropping system rice equivalent yield (REY) ranged from 13.7-20.0 t/ha. The highest REY was for systems with early (20 March and 5 April) aus sowings, at 17-20 t/ha with maize, and 16-20 t/ha with sunflower (2 to 5 times that of current farmer practice). Rabi crop yield was the main determinant of trends in total system rice equivalent yield, which declined as establishment date of the rabi crops was delayed beyond 15 December. All cropping systems were profitable in terms of gross margin, net return and benefit-cost ratio. The most profitable system (with 5 April aus sowing and maize) had a gross margin of Tk. 101,000 per ha, net return Tk. 73,000 per ha and BCR 1.29. While maximum yield and profitability occurred with the first 2 aus sowings, these systems had the shortest turnaround time. Early aus sowing advanced the sowing of all crops and thus reduced the risk of rabi crop damage by pre-monsoon rainfall and cyclones. This work 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.