Due to the presence of sufficient sunlight in the inter
row, intercrops requiring full sunlight can be grown up
to the fourth year after establishment of rubber
(immature rubber) under conventional spacing systems
(eg. 8.1 m · 2.4 m) (Pathiratna and Perera
2003b). Interference from rubber roots is also low in
the inter row at this stage (Pathiratna and Perera
2003a). Under these spacing systems, closure of rubber
canopies takes place in about five years, leading to
the reduction of light transmitted into the inter row
space to levels lower than 20% (Pathiratna and Perera
2003b; Pathiratna and Perera 2006; Pathiratna et al.
2004). The rubber roots can also invade the whole inter
row space in 4–5 years under standard spacing systems
(Pathiratna and Perera 2003a).