Root competition for phosphorus between coconut, multipurpose trees and Kacholam (Kaempferia galanga L.) in Kerala, India

The magnitude of root competition 17 year-old coconut palms suffer from three year-old inter-planted multipurpose trees, Vateria indica L., Ailanthus triphysa (Dennst.) Alston. or Grevillea robusta A. Cunn. and kacholam (Kaempferia galanga L.), a herbaceous medicinal plant, was evaluated based on the extent of absorption of applied P-32 by the palms in sole and mixed crop situations. The multipurpose tree (MPT) species were grown under two planting geometries (single row and double row). The hypothesis that, when grown together, widespread root proliferation of coconut and multipurpose trees occurs in the well-fertilised kacholam beds was tested by root excavation. Interplanted MPTs substantially altered absorption of P-32 by coconut. Both Ailanthus and Vateria exerted a modest depressing effect, while Grevillea enhanced P-32 uptake by coconut. Single rows of MPTs also favoured P-32 recovery by coconut, presumably because of the increased root densities in the subsoil. Ailanthus, Vateria and Grevillea absorbed substantial P-32. Overall, high P-32 absorption in the coconut-Grevillea plots indicates complementary root-level interactions between these species. P-32 absorption by MPTs was generally higher closer to the trees owing to the greater root concentration of the MPTs, which in turn suggests possible root interference between MPTs and coconut. Hence selection of tree species with low root competitiveness and/or trees with complementary root interaction is of strategic importance in agroforestry. Kacholam showed substantial P-32 content in its foliage. This P-32 appears to have been translocated by coconut into the kacholam beds where new coconut roots were abundant.