Root competition for phosphorus between the tree and herbaceous components of silvopastoral systems in Kerala, India

Abstract

Root competition for phosphorus between the tree and herbaceous components of silvopastoral systems in Kerala, IndiaS u m a n Jacob G e o r g e I , B. M o h a n K u m a r 1, RA. W a h i d z and N.V. K a m a l a m z Abstract Root competition in polyculture systems involving combinations of four tree species and four grass species was evaluated based on 32p recovery by each species in mixed and sole crop situations. The tree species were: Leucaena leucocephala, Casuarina equisetifolia, Acacia auriculiformis and Ailanthus triphysa, and the grass species were: Pennisetum purpureum (hybrid napier), Brachiaria ruziziensis (congo signal), Panicum maximum (guinea grass) and Zea mexicana (teosinte). Four lateral distance (25 and 50 cm) and depth (15 and 50 cm) treatments were included in the study to characterize the relative fine root distribution of trees. Absorption of 32p was monitored through radioassay of leaves. Regardless of the species, 32p uptake from 50 cm soil depth was lower than that of 15 cm depth. Absorption of 32p from 50 cm lateral distance was also less than that of 25 cm distance in Acacia and Casuarina. Grass species in sole crop situations absorbed more 3Zp than in mixed systems. None of the grass species when grown in association with tree components affected the absorption of 32p by trees. All grass species exerted a complementary effect on 32p absorption by Casuarina. Leucaena 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 32p uptake by grass species.

Root distribution pattern of the wild jack tree (Artocarpus hirsutus Lamk.) as studied by 32P soil injection method

“…Regarding vertical distribution of roots, root activity percentages for depths of 30, 60 and 90 cm were 49, 32.7 and 18.3%. A higher root activity in the surface soil layer compared to lower depths observed in the present study is similar to that of Wahid et al (1989b) for cashew (Anacardium occidentale) at Vellanikkara, India and George et al (1996) for four multipurpose tree species (Casuarina equisetifolia, Leucaena leucocephala, Acacia auriculiformis and Ailanthus triphysa) in another experiment at the same location.…”

“…The study was conducted using a field experiment initiated in June 1985, involving wild jack tree and eight other fast growing multipurpose trees at the Livestock Research Station, Thiruvazhamkunnu, Kerala, India (see Jamaludheen and Kumar (1997) for a list of all species involved, and George et al (1996) for a description of the climatological factors of the locality). The soil of the experimental site is of lateritic origin (Oxisol), with a pH of 6.7.…”

“…This approach has proved to be an efficient method for obtaining root distribution data (Nye and Tinker, 1977;Vose, 1980) and has been used by many previous workers in plantation and other agricultural crops (IAEA, 1975;Wahid et al, 1989a;Wahid et al, 1989b). George et al (1996) used it for characterising root competition in intercropping systems involving multipurpose trees.…”

“…Wahid et al (1989a) also observed that as much as 73% of the total root activity in cacao (Theobroma cacao) was confined to a lateral distance of 100 cm. Similarly, George et al (1996) found that in five-year-old Acacia auriculiformis and Casuarina equisetifolia trees at the same site, much of the root activity was concentrated within a radius of 50 cm. Most of the studied tree roots thus exhibit a similar lateral distribution pattern.…”

Can productivity and post-pruning growth of Jatropha curcas in silvopastoral systems be regulated by manipulating tree spacing/arrangement without changing tree density?

“…Some methods of minimising effects of interspecific BG competition on productivity of Jatropha in agroforestry have been suggested, namely: clearing competing understory crops within 0.6 m distance from the trees [40], using spatial separation of resource use [42] and planting less competitive understory crops [17,43].…”