Light availability to the understorey annual crops in an agroforestry system.

Abstract

Light availability was determined in rows of upland rice cv. UPLRi-7 and mung beans cv. Pag-asa 7 grown under trees of Gliricidia sepium, Acacia auriculiformis and A. mangium in an experiment at the Central Luzon State University College of Agriculture farm in the Philippines during Aug. to Dec. 1991. The trees were planted at spacings of 2 × 3 m and pruned 3 times during the experimental year or left unpruned. Rice was sown in rows in alleys between 10-month-old trees and mung beans were sown in furrows immediately after harvest of rice. The mean reduction of light incidence on rice and mung bean rows was low (3-10%) in the pruned alleys, but it was severe (53-59%) in the unpruned alleys. Across the alleys mean light availability on crop rows decreased as they approached the tree rows. The rate of decrease was greater in unpruned than in pruned alleys. The percentage incident radiation was highest under G. sepium. Rice and mung bean yields decreased linearly with reduced light incidence. For every 1% decrease in relative light incidence, rice yields decreased by 47 kg/ha and mung bean yields decreased by 10 kg/ha. Mung bean yields decreased more in pruned conditions (13 kg/ha) than in unpruned conditions (9 kg/ha), probably because of a less favourable canopy microclimate under drought stress during the dry season (Nov.- May).