Bioclimatic agro-ecosystem of India has been divided into 20 agro-ecological regions for judicious crop planning. Among these ecosystems rice is mainly grown in agroecological regions falling under subhumid to humidlperhumid ecosystems with low productivity. The cause of low productivity in principal rice growing ecosystems as revealed by the investigations of World Bank as well as International Rice Research Institute (IRRI), is reported to be the lack of understanding on rice agro-climatic characteristics and rice land hydrology. The present paper discusses the different classification criteria used to classify rice growing environment while developing suitable classification criteria under Indian conditions, adopting Rice Aridity Index (RAI) based criteria where, RAI is defined as the ratio between rice water requirement (ETR) and the precipitation (P). The principal rice growing environment of eastern India has been classified into 5 distinct rice agro-climatic zones and 22 sub-zones. Further it is found that though, rice is cultivated in entire ecoregions, ecologically the rice subhumid and rice humid ecosystems are most suitable for intensive rice cultivation. Cultivating rice in rice perhumid and rice arid zones involves risk of different degree due to varying moisture stress. It is, therefore, suggested that the area not suitable for optimum rice production should be used for alternative agriculture.
Agroecosystem, classification, rice aridity index
