1 VARIATIONS IN THE YIELD OF COCONUTS, AS INFLUENCED BY THE PATTERN OF RAINFALL AND DURATION OF DRYSPELL Jacob Mathew, Amarnath C.H., Vijaya Kumar K, Mohamed Yusuf and Balakrishnan T K. 1 ABSTRACT Study of the variations in the yield of coconuts in the West Coast of India, in relation to the pattern of rainfall and duration of dryspell revealed that the yield obtained in any year is not directly related with the total rainfall received in the same year or in the preceeding years. Summer rains were having positive correlation with the yield in the succeeding year. About 60% of the variations in the annual yield were due to the changes in the duration of dryspell in the preceeding two years. INTRODUCTION Weather factors are known to influence crop production, especially under rainfed conditions. In the west coast of India, coconut is grown mostly as a rainfed crop. During the past five decades, many attempts have been made in India, Sri Lanka and Malaysia, to study the relationship between weather factors and yield of coconuts (Patel and Anandan 1936, Abeywardena 1968 and 1983, Balasubramaniam 1956, Lakshmanachar 1963, Marar and Pandalai 1957, Prasada Rao 1984 and 1986, Pankajakshan Nair 1985 and Vijaya Kumar et al 1986). The studies have highlighted the influence of pattem of rainfall, the quantity of precipitation, usefulness of sununer rains and the harmful effects of excess rains received during monsoon period, on yield. The usefulness of relative humidity, sunshine hours, drought index, etc., in predicting the yield was also brought out by some of these studies. In tWs paper, an attempt has been made to study the fluctuations in the annual yield of coconuts, in relation to the pattern of rainfall and duration of dryspell in the preceedings two years. MATERIALS AND METHODS The annual yield data of 187 palms in Block E of Central Plantation Crops Research Institute, Kasaragod, located in the west coast of India, for the period 1961 to 1984 were considered in this study. The palms were about 40 - 45 years age in 1961 and were growing under rainfed condition, receiving the recommended doses of fertilizers. Weekly and monthly data on rainfall (mm) and number of rainy days (with not less than 2.5 mm rain) for the period 1958 to 1984 were coflected from the agro-meteorology Observatory of the Institute and were considered as four seasons, viz. June to August (S. W. monsoon period), September to November (N. E. monsoon period), December to February (Winter) and March to May (Summer). Pearson's coefficient of correlation were worked out between the annual yield of coconuts and the weather factors, both annual (January to December) and seasonal, considering lag periods upto three years. Usefulness of these weather variables for selected periods, in explaining the variations in the annual yield of coconuts, was also examined, using multiple regression models. RESULTS AND DISCUSSION At Kasaragod, the average annual rainfall is nearly 3,500 mm, spread over about 115 days. During the period under consideration it ranged from a lowest of 2,499 in 1964 to a highest of 5,703 mm in 1961. The number of rainy days varied from 90 in 1979 to 1945 in 1961 (Table I). The mean annual vield per pahn during this period was 64 nuts, the range being 50 nuts in 1965 to 79 nuts in 1 Central Plantation Crops Research Institute, Kasaragod-670 124, Kerala, India.