The effects of artificial shading on some growth characteristics of arabica and robusta coffee seedlings. I. The effects of shading on dry weight, leaf area and derived growth data.
In experiments at Kabanyolo, Uganda, in which radiation incomes were measured and growth analysis was employed, seedlings of both robusta and arabica coffee, grown in sand culture at controlled high levels of nutrition, attained maximum dry weight at a moderate level of shade because net assimilation rate was not maximal in full daylight. Increasing shade increased specific leaf area relatively little, robusta being somewhat more plastic in this respect than arabica. In full daylight the leaf margins of both robusta and arabica seedlings became yellow, and on robusta leaves some interveinal chlorosis developed also. High levels of solar radiation appear to decrease the net photosynthetic capacity of both arabica and robusta coffee leaves. A review of literature showed that, although similar effects of high light intensity on coffee have been reported by most earlier workers, some have found that growth is most rapid in full daylight. However, since information on such factors as the absolute amounts of solar radiation and the nutritional status and water relations of the plants in earlier experiments is often incomplete, critical comparisons cannot readily be made.-Makerere Univ. Coll., Kampala, Uganda.