AGRICULTURA TROPICA ET SUBTROPICA VOL. 39(3) 2006 QUANTIFICATION AND PRIORITIZATION OF CONSTRAINTS CAUSING YIELD LOSS IN RICE (Oryza sativa) IN INDIA SHANMUGAM T.R., SENDHIL R., THIRUMALVALAVAN V. Abstract The present study was carried out in Tamil Nadu State of India to quantify and prioritize the constraints causing yield loss in rice. Data were collected from 120 scientists across various disciplines working on rice. Priorities were arrived then by comparing the relative yield losses caused by constraints and ranking them. The total loss in Tamil Nadu was 2.73 million tonnes accounting for about 39 per cent of production. Leaf folder emerged as the major constraint in the study area. The present study attempted to prioritize those constraints by bringing them under the purview of research aimed to eliminate their ill effects on rice yield. Key words: Quantification; Prioritization; Rice and Constraints. INTRODUCTION Rice is the staple food of more than 60 per cent of the world's population especially for the people in South- East Asia. Among the rice growing countries, India has the largest area under rice crop and ranks second in production next to China. It occupies about 23.3 per cent of gross cropped area of the country and plays a vital role in the national food grain supply. Rice alone contributes 43 per cent of total food grain production and 46 per cent of total cereal production of the country. The average rice productivity in India was 3049.60 kg/ha (2004), which is 23.83 per cent below the world’s average productivity of 4003.80 kg/ha during the same year. Rice productivity in the country fluctuates significantly from region to region due to various factors such as pest and diseases, soil type, soil fertility, rainfall pattern, flood, drought, water logging and climatic conditions. India, with its current population would be the most populous country in the world by 2030. Apparently, rice production does not keep pace with the burgeoning population at a growth rate of 1.93 per cent per annum and has come to stagnation in recent years. With almost no hope for increasing the area under rice production, only way out for production increment is to increase the productivity of rice lands in future. The approach should be to identify the constraints that operate to keep rice yields significantly below their potential maximum and find the yield gap. Yield gap is not identical for all environments. It is explained by a number of constraints - pests, diseases and management and decomposed into two parts viz., Yield gap I and Yield gap II. Yield gap I is the difference between an experimental station’s maximum yield and an on-farm experiment’s maximum yield. This yield gap arises from differences in environment, which cannot be managed in the farmer’s field. Yield gap II was the primary concern of present study, because, it is the difference between actual farm yield and yield attained in on-farm experiments. This gap reflects the presence of significant constraints. In a study conducted by Tamil Nadu Agricultural University in Tamil Nadu state, the average yield (5.16 tonnes/ha) realized by farmers during Kharif season was below the average potential yield (5.68 tonnes/ha) resulting in an yield gap of 10.13 per cent. Likewise, the gap was estimated to be 12.83 per cent during Rabi season (C.Ramasamy et al., 1997). Occupying the extreme south of the Indian peninsula, Tamil Nadu is an agrarian state having 18.73 lakh hectares under paddy. The state contributes about 5 per cent of total rice production in the country with an average productivity of only 2702 kg/ha (2004-05). The present study would identify and quantify the rice productivity constraints responsible for yield gap of rice in the state of Tamil Nadu in India. Constraint analysis as conceived in the present study identifies pests, diseases and mismanagement factors impeding higher farm yield. MATERIALS AND METHODS In order to develop location specific constraint solving rice production technologies that are ecologically, economically and culturally sustainable, it becomes mandatory to identify specific farming situations with reference to different agro-climatic zones existing in Tamil Nadu. The variations may be observed in terms of soil structure, texture, soil depth, soil reaction, drainage, land shape and variations in moisture regime linked with rainfall and irrigation. For the present study, the agro-climatic zones that have been delineated under National Agricultural Research Program were adopted as study zones within the state (Appendix I). Further, we had to resort to this classification; because regional rice research is organized on the basis of agro-climatic zones and research resource allocation are zone-based. All the zones except high altitude zone possess a favourable environment for rice production. Though 194