An agroclimatic approach for identifying sowing window and production potential of rainfed kharif maize in different districts of Bihar

Abstract

Thermal and moisture regimes are the important agroclimatic factors governing time of sowing of a crop. In rainfed agro-ecosystem, identification of sowing window is an essential prerequisite for farmers to plan sowing of their crops at appropriate times for achieving higher yield. In this paper, sowing windows for rainfed kharif maize, which is an important crop in Bihar, contributing significantly to its economy, have been identified based on probabilistic assured weekly total rainfall for 36 districts spread over 4 agroclimatic zones of Bihar state. The concept of moisture availability index (MAI), the ratio of weekly total assured rainfall to potential evapotranspiration (PET), postulated by Hargreaves (1974) and adopted by Sarker and Biswas (1986), has been employed as an index of water availability for evaluation of potential productivity. Results revealed that at 30 to 50 per cent probability levels, sowing windows of all the 13 districts under Zone I prevail during 21 to 27 SMWs, during 18 to 24 SMWs in 7 districts under Zone II, 22 to 26 SMWs in 5 districts under Zone IIIA and 23 to 27 SMWs in 11 districts under Zone IIIB. The earliest commencement of sowing week (18 SMW) occurs in Zone II followed by Zone I (21 SMW), Zone IIIA (22 SMW) and Zone IIIB (23 SMW). In terms of the longer length of growing period and higher values of MAI at all probability levels, the Zone II (North east alluvial plains) is adjudged as the most potential zone for cultivation of rainfed kharif maize followed by Zone I (North west alluvial plains), and Zone IIIA and Zone IIIB both under South Bihar alluvial plains zone in Bihar. Thus the determination of sowing windows and quantification of MAI values during growing season are useful agronomic criteria for cultivation of rainfed kharif maize in Bihar State.