EFFECTS OF BIMONTHLY RAINFALL ON COCONUT YIELD IN THE LOW COUNTRY INTERMEDIATE ZONE (IL,) OF SRI LANKA

Abstract

Coconut yields in Sri Lanka show considerable fluctuation between years mainly due tovariation in the distributions of major climatic parameters such as rainfall, solar radiation andrelative humidity. The effect of current weather is usually reflected on the yields of the followingyear. However, the degree of. influence of these variables on coconut yield is yet unknown. Anattempt was made to study the influence of intensity and distribution of rainfall in two-monthlysub-periods of the previous year on nut yield at Ratmalagara Estate in the Low Country DryIntermediate Zone (75% annual rainfall probability > 1500) of Sri Lanka. Rainfall during January/February was found to be the most influential factor on the subsequent years total yield and theyield increased with increasing rainfall. The rainfall during March/April had a similar effect wherearound 400 mm was found to be sufficient. The high intensity of rainfall during May/Augustadversely affected the crop, where amount in excess of 450 mm was not utilized to increase theyield. The impact of rain during July/August was minimal. High rainfall during September/October and November/December had a depressing effect on yield, and this was very significantwith respect to the November/December rainfall. A multiple regression model with R = 89% wasdeveloped using a combination of some parameters of bimonthly rainfall which would be usefulin determining the potential yield and to explain yield fluctuation between years to a certaindegree.