Analysis of Assured Rainfall for Crop Planning under Rainfed Condition in Drought-Prone Tract of Bihar

Abstract

The agroclimatic zone III-B (part of south Bihar alluvial plains) of Bihar is considered as the dry region of the state, where rainfall is the limiting factor for successful raising of rainfed crops. It is, therefore, logical that agricultural planning needs to be drawn up based on the climatic potential of the area. For this purpose, the minimum assured weekly rainfall at different probability levels viz. 25, 50 and 75% has been computed for all 11 districts of the agroclimatic zone by employing weekly historical rainfall data for 30 to 55 years. Accumulated assured rainfall (AAR) calculated over 23 to 41 standard meteorological weeks (SMW)[4 June-7 October] and the GIS map revealed that long duration crops (≥ 16 weeks) could be grown at potential rate in 5 out of 10 years. Considering 20 mm rainfall events in a week, the rainfall sufficiency prevailed for 8 to 11 weeks at 75% probability level. At 50% probability, sowing week with 20 mm threshold rainfall varied from 24 to 26 SMW (11 June-1 July) and ending week extended from 38 to 39 SMW (17-30 September) across various districts. Gaya district recorded the highest water availability period of 16 weeks as against the lowest of 13 weeks in Arwal district. Six districts had water availability period of 14 weeks during which at least 20 mm of rainfall per week is assumed at 50% probability level. The duration of crop period and cropping plan have been suggested based on the probability of assured rainfall. Intercropping of pigeon pea (Cajanus cajan) with maize (zea mays) and sequential cropping of short-duration rice (Oryza sativa) followed by chickpea (Cicer arietinum)/lentil (Lens culinaris) could be the most efficient cropping systems in the drought-prone region of Bihar state.