Evaluation of onset, cessation and length of rainy season for sustainable rainfed crop production in Bihar

Abstract

An agroclimatic study based on forward and backward rainfall accumulation criteria was conducted to determine the onset, cessation and length of rainy season at 50 and 75% probability levels for all 38 districts of Bihar. The results revealed that the districts under Zone IIIB (Part of south Bihar alluvial plains) recorded the shortest length of rainy season and the longest in Zone II (North east alluvial plains). The earliest sowing of rainfed crops based on 75 mm forward accumulated rainfall could be done in the districts under Zone II and delayed sowing in Zone IIIB. The length of safe growing period for rainfed transplanted rice calculated based on 200 mm forward and 50 mm backward accumulated rainfall criteria was found to prevail for 13-17 weeks in Zone I (North west alluvial plains), 14-19 weeks in Zone II, 13 to 15 weeks in Zone IIIA (part of south Bihar alluvial plains) and 11 to 13 weeks in the districts under Zone IIIB at 50 per cent probability level, which indicated that early maturing rice varieties (Prabhat, Turanta) could be successfully grown under rainfed condition in the districts under Zone IIIB in 50 out 100 years. At 75 per cent probability level (i.e., 75 out 100 years), the length of rice growing season appeared to be too low to grow even such short duration rice in this Zone. In the districts under Zone I and Zone IIIA, short to medium duration rice varieties (Dhanlaxmi, Richhariya, Saroj, Rajendra Bhagwati, Rajendra Suwasni, Prabhat, Rajshree) could be considered for growing under rainfed condition. Zone II appeared to be the most productive in terms of longest duration of water availability.