Abstract
Rice-fallow and rice-rice are major cropping systems in the salt affected region of the Ganges Delta covering West Bengal, India and Bangladesh. The dry season rice (Boro) is grown mostly by irrigation from ground water in this water scarce region. Boro encounters soil and water salinity, air temperature fluctuations and intense evaporative demand. We studied six sowing dates (1 October, 15 October, 1 November, 15 November, 1 December and 15 December) and three varieties (WGL 20471, Bidhan 2 and IET 4786) of rice to find an interacting effect on yield and water productivity. Soil and water salinity varied during the growing period with lower soil salinity during the month of November (2.20–2.53 dS m−1) and higher soil salinity towards the end of the growing season (4.30–5.23 dS m−1). The mean field water salinity was higher (1.78 dS m−1) during the Boro 2017–18 compared to that (1.65 dS m−1) during 2016–17, as about 49 mm rainfall was received in the month of March 2017. Sowing dates significantly affected the yield of Boro rice. Earliest sowing on 1 October is not feasible as it significantly reduced the grain and straw yields. Sowing of nursery up to 1 of November was found to be the best possible option, and it should not be delayed up to 15 December. The rice variety IET 4786 was found to be susceptible to salinity with the lowest grain yield 2.65–2.98 t ha−1, compared to Bidhan 2 (3.41–5.95 t ha−1) and WGL 20471 (3.40–5.81 t ha−1). Both irrigation and economic water productivity of Boro were affected by sowing dates and variety. Rice variety IET 4786 required less irrigation water (1320 mm) than the other two varieties (1350 mm). Higher (>0.5 kg m−3) irrigation water productivity of Boro can be achieved by selecting salt tolerant varieties (WGL 20471 and Bidhan 2) and optimum sowing window of 1–15 November.
Highlights
Rice (Oryza sativa L.) is the predominant field crop in the coastal areas of India and Bangladesh during the major cropping seasons of monsoon (Kharif/Aman) and post monsoon/dry season (Boro)
The Boro rice crop was exposed to different air temperature regimes during vegetative and reproductive stages due to the different sowing dates
During the subsequent four sowing dates, mild temperature regimes prevailed, while the extreme late sowing date of 15 December exposed the rice crop to highest temperature regimes of the growing period prevailing in the month of May (Max. temp. 34.9–36.6 ◦C)
Summary
Rice (Oryza sativa L.) is the predominant field crop in the coastal areas of India and Bangladesh during the major cropping seasons of monsoon (Kharif/Aman) and post monsoon/dry season (Boro). Boro rice is one of the cropping options for the dry season, provided sufficient irrigations are assured. This is a cost-intensive crop, requiring specific management strategies to tackle soil and water salinity. The optimum sowing date is important for three major reasons [6] It ensures that vegetative growth occurs during a period of satisfactory temperatures and high levels of solar radiation/sunshine hours. Rice seeded before the window of optimum dates usually has a slow germination and emergence, poor stand establishment, soil borne seedling diseases under cold condition, as well as being prone to damage by birds (parrots, pigeon, sparrow, munia etc.) during sowing time and damage by rodents and birds upon earliest maturity, when adjacent fields have not flowered. Finding an optimum sowing window for Boro in coastal region is the foremost important requirement
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