Measuring Light Interception and the Efficiency of Light Utilization by the Coconut Palm (Cocos nucifera)

Abstract

A mobile sampling method was used to measure the amount of photosynthetically active radiation (PAR) transmitted through the canopies of coconut palms in two long term field trials. PAR transmissions were measured at approximately monthly intervals for one year. Fractional interception of light was found to vary considerably between months, and to be associated with frond shedding caused by dry season water stress. Palms receiving potassium fertilizer intercepted more light and replaced leaf area lost during the dry season more rapidly than those receiving no potassium. Palms planted at a higher density intercepted more light and carried more fronds per palm, but intercepted less light per frond than those planted at a lower density. The ratio of moles of carbohydrate yield to moles of intercepted PAR quanta was calculated for six plots of hybrid palms, giving a dimensionless light efficiency index (LEI) comparable to harvest index. Mean LEI for all plots was 1.275 X 10~4 and was found to increase with increased light interception, results suggesting that there is a basal level of light interception below which no yield is produced. The potential for using LEI in agronomic experimentation on sole cropping and multicropping and as a criterion for genetic selection of coconut palms is discussed. Interceptacion de la luzporparte del coco RESUMENSe utilizo un metodo de muestreo movil para medir el grado de radiation fotosinteticamente activa (RFA) transmitida a traves de bovedas de cocoteros en dos ensayos de campo a largo plazo. La transmision de RFA fue medida a intervalos aproximadamente mensuales durante un ano. Se observo que la interceptacion fraccional de la luz varia considerablemente de un mes a otro, y que esta relacionada con el cambio de hojas producido por la falta de agua ocasionada por la estacion seca. Los cocoteros que recibieron fertilizante con potasio interceptaron mayor cantidad de luz y reemplazaron la superficie de hoja perdida durante la estacion seca con mayor rapidez que los cocoteros que no recibieron potasio. Los cocoteros plantados con mayor densidad interceptaron mayor cantidad de luz y presentaron mayor cantidad de hojas por cocotero, pero interceptaron menor cantidad de luz que los cocoteros plantados con menor densidad. Se calculo la relation entre los moles de hidrato de carbono producido y los moles de la cantidad de RFA interceptada para seis parcelas de cocoteros hibridos, obteniendo un indice de eficiencia luminosa (IEL) sin dimension comparable al indice de cosecha. El IEL medio para todas las parcelas fue de 1,275 X 10~4, y, segiin se observo, se increment^ con el incremento en la interceptacion de la luz, razon por la cual los resultados sugieren que existe un nivel basico de interceptacion de luz por debajo del cual no se produce rendimiento. Se discute el potencial de uso del IEL para la experimentation agricola con cultivos simples o multiples, y como criterio para la selection genetica de cocoteros. tPresent address 41 Horsford Road, Brixton, London SW2 5EP.

THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF COCONUT (Cocos nucifera): A REVIEW

“…Based on these measurements, Moss (1992) was able to demonstrate a close linear relationship between yield of copra (and the whole fruit) and cumulative light interception ( n = 6; r 2 = 90%). As the line(s) did not pass through the origin, this suggested that there was a minimum level of light interception below which no yield is produced.…”

“…So although young palms in a plantation cover the ground, well older palms do not. Using a mobile sampling method in Thailand, Moss (1992) measured the amount of photosynthetically active radiation intercepted by the leaf canopy at monthly intervals throughout one year. Seasonal reductions in the amount of light intercepted were related to water stress, its most immediate effect being to increase the rate of frond shedding and to slow the production of new fronds.…”

Measuring Coconut Palm Dry Matter Production

“…These concepts have not been applied to the coconut palm (Cocos nucifera L.), though Moss (1992) studied the ratio of copra yield to canopy light interception, which is effectively the product of e and P. To estimate total dry matter production for coconut requires measurement of the dry weight of the nuts and also of vegetative dry matter production. The dry weight of copra, the main product, is routinely measured or estimated in the majority of coconut experiments.…”