Sj. George et al., ROOT COMPETITION FOR PHOSPHORUS BETWEEN THE TREE AND HERBACEOUS COMPONENTS OF SILVOPASTORAL SYSTEMS IN KERALA, INDIA, Plant and soil, 179(2), 1996, pp. 189-196
Root competition in polyculture systems involving combinations of four
tree species and four grass species was evaluated based on P-32 recov
ery by each species in mixed and sole crop situations. The tree specie
s were: Leucaena leucocephala, Casuarina equisetifolia, Acacia auricul
iformis and Ailanthus triphysa, and the grass species were: Pennisetum
purpureum (hybrid napier), Brachiaria ruziziensis (congo signal), Pan
icum maximum (guinea grass) and Zea mexicana (teosinte). Four lateral
distance (25 and 50 cm) and depth (15 and 50 cm) treatments were inclu
ded in the study to characterize the relative fine root distribution o
f trees. Absorption of P-32 was monitored through radioassay of leaves
. Regardless of the species, P-32 uptake from 50 cm soil depth was low
er than that of 15 cm depth. Absorption of P-32 from 50 cm lateral dis
tance was also less than that of 25 cm distance in Acacia and Casuarin
a. Grass species in sole crop situations absorbed more P-32 than in mi
xed systems. None of the grass species when grown in association with
tree components affected the absorption of P-32 by trees. An grass spe
cies exerted a complementary effect on P-32 absorption by Casuarina. L
eucaena also benefited in the same way when grown in association with
congo signal and/or teosinte. Of the tree species, Acacia and Leucaena
adversely affected the P-32 uptake by grass species.