Abstract:The final yield of coconut (Cocos nucifera L.) is determined by early fruit set. Thus understanding the factors controlling fruit set including climate change is of importance for assessing the yield and its accurate prediction. This study assessed the survival pattern of female flowers produced in different months of the year, the effects of climate factors during early phase of flowering and the competition for assimilates from previously formed fruits on the fruit set of newly opening inflorescences in a 25 -26 year-old coconut plantation in the Intermediate Zone (IL 1a ) of Sri Lanka over a period of three years. The rate of fruit survival since the onset of flowering to maturity varied with the month of inflorescence opening. Abortion of fruits after three months from inflorescence opening was negligible. The optimum (T opt-in vitro ) and maximum (T max-in vitro ) temperatures for in vitro pollen germination were 28 ºC and 39.7 ºC, respectively. The fruit set of an inflorescence/s opened in a given month (number of set fruits palm -1 month -1 ) was negatively correlated with the total reproductive dry matter requirement of the palm (TDMR) of the month of inflorescence/s opening (first month), and the number of high temperature days (T max ≥ 33 ºC) during the first three months of inflorescence opening, whilst it was positively correlated with the number of female flowers produced in the inflorescence. There was a highly significant correlation between the monthly fruit set (at three month stage) and the corresponding harvested fruit yield palm -1 month -1. The lag period between flowering (opening of the female phase) and fruit maturing was eleven months.

Two field experiments were conducted in gravelly soils (Andigama series) in Sri Lanka to investigate the effect of different mulches and cover crops, utilized to conserve soil moisture, on water status, gas exchange and related soil parameters of coconut palms {Cocos nucifera L. var typica).The results revealed that mulching only the manure circle was not effective in improving the palm water status, gas exchange and soil water status during dry periods in Andigama soil series (gravelly soils). The mulches tested were coconut husks, coir dust, straw, black polythene and dried coconut fronds. The palms were equally sensitive to soil water depletion and responded to the water deficit by increasing the stomatal resistance irrespective of the mulch treatment. When the manure circle was mulched with dried coconut fronds, and the rest of the land was also mulched with a five cm thick layer of coir dust, the palms showed an improved gas exchange ability than palms growing in bare land or with cover crops during the dry period.