Leucocephala Trees Research Articles

ALEUCAENA LEUCOCEPHALA—BASED INDIGENOUS FALLOW SYSTEM IN CENTRAL PHILIPPINES: THE NAALAD SYSTEM

ABSTRACT The Naalad system is an indigenous agroforestry practice developed by farmers more than 100 years ago in a small village in central Philippines. This study is the first attempt to scientifically document and evaluate the system. Six farm parcels at different stages of fallow and cultivation were selected as case studies. Farmers' practices were documented through interviews and record keeping. Soil samples were collected and selected chemical properties and bulk density were analyzed. Carbon (C) storage and sequestration were estimated by converting existing biomass data to C content. Results showed that there are two modifications in the Naalad system compared with common shifting cultivation systems in the Philippines. First, Leucaena leucocephala trees are planted in the fallow fields to shorten the fallow period to 5–6 years. The fallow field is also used as a source of fodder for cattle. Second, branches of Leucaena are used in the cultivated fields to serve as a fascine-like structure calle...

Growth and yield of sorghum or cowpea in an agrisilviculture system in semiarid India

This study was conducted near Hyderabad, India during 1991–1994 to quantify the effects of shoot pruning, fertilization, and root barriers around Leucaena leucocephala trees on intercropped sorghum(Sorghum bicolor) or cowpea (Vigna unguiculata) crop production under rainfed conditions. Crop plants grown with pruned trees attained higher dry matter and leaf area index than did those with unpruned trees. Two-year mean grain yields of sorghum with no root barriers were76% and 39% of pure crop yield (1553 kg ha–1)for pruned and unpruned trees, respectively. Corresponding values for cowpea were 49% and 26% of pure crop yield (1075 kgha–1). Sorghum or cowpea intercropped with trees responded to fertilizer application more strongly than did their respective pure crops, suggesting an increased need for fertilizer application in this agrisilviculture system over that currently used for pure crops. Impact of root barriers was small on either crop. Irrespective of root barriers, a high response to tree pruning suggested above ground competition for light dominated tree/crop interactions in this agrisilviculture system.

Recycling of the naturally-occurring 15N In an established stand of Leucaena leucocephala

The natural 15N abundance method was used to trace the sources of N in a stand of Leucaena leucocephala and its understorey species. Changes in the δ 15 N of various above-ground parts of the L. leucocephala trees and understorey vegetation were monitored for 6 yr. The resulting data provide the first direct evidence of internal N cycling between a N 2-fixing tree and non-N 2-fixing understorey species within an agro-ecosystem. The δ 15N of all tree parts and understorey vegetation decreased with time. One year after the plantation was established, the non-N 2-fixing understorey species exhibited a significant enrichment in 15N relative to the L. leucocephala. At 4 and 6 yr after planting, however, the δ 15N value of the understorey vegetation had decreased significantly and was nearly identical to that of the L. leucocephala. The decline in δ 15N values of the understorey species was attributed to net N-mineralization of plant parts shed by L. leucocephala, and to root exudation and decay. That is, a portion of the N 2 fixed during the early stages of tree growth was made available to the understorey species through the decomposition and subsequent incorporation into the available soil-N pool of the abscissed L. leucocephala parts. This indicates that there was a tight coupling between N 2 fixation and the availability of net mineralized N. The natural 15N abundance method appears to provide a suitable means by which the fate of fixed-N in a forest ecosystem can be monitored, provided the difference between the initial (δ 15N value of the N 2-fixing and non-N 2-fixing (reference) species is of sufficient magnitude. The rate of change in the δ 15N value of the understorey species can provide valuable insights into the intensity of net N-mineralization and N-cycling.

Observations of Some Tree Root Systems in Agroforestry Intercrop Situations, and their Graphical Representation

SummaryRoot systems of unpruned Cassia siamea and Leucaena leucocephala trees and regularly pruned hedges of C. siamea, L. leucocephala and Gliricidia sepium were examined in a semi-arid area in Kenya. Trenches were dug across rows of trees or hedges, soil profiles washed, and different sized roots counted in small 5 × 5 cm grids fully covering both faces of the trench. The roots were displayed using two computer software programmes written for this purpose: a spline technique that displays smoothed root densities in different shades; and a random dot method which displays roots as dots, using any specified scale. The fine roots of four-and-a-half-year-old C. siamea penetrated the soil to meet with rocks at depths between 0.60 and 2.0 m, and spread laterally to 9 m, traversing adjacent crop plots. Roots of eight-year-old L. leucocephala covered an extensive soil volume and included a greater density of fine roots than C. siamea at comparable distances. Above-ground pruning restricted the roots of hedges to a depth of 1.5 m, although roots of different hedges spaced 5 m apart intermingled freely in the alley space. L. leucocephala roots filled the alley very densely while those of G. sepium were sparse, particularly in the middle of the alley. Rooting density of C. siamea was intermediate. The dot method is more precise when rooting densities are low but when densities are high the splining method appears to be more visually helpful. These graphical methods greatly facilitate overall comparisons of sections of tree root systems, but quantification of root densities at different distances away from trees is still needed to understand more precisely the competitive effects of trees and associated crops.Systemas de raices de los árboles

Diseases ofLeucaenaspecies

Abstract Diseases caused by fungi, bacteria, a possible virus and nematodes have been recorded on Leucaena leucocephala and at least seven other Leucaena species throughout the tropics. Most diseases are caused by fungi and include leaf spots, gummosis, pod rots, root and collar rots, stem cankers, anthracnoses, damping‐off, rusts and shoot and twig blights. The most important diseases are considered to be Camptomeris leaf spot (CLS) (Camptomeris leucaenae) gummosis and various root and pod rots. Although not a lethal disease, CLS can cause serious forage dry matter and quality losses. Gummosis is regarded as the most important disease of L. leucocephala in India and Sri Lanka, but further work is urgently required on its pathology and economic importance. Root rots caused by Ganoderma species, Fusarium species, Pseudolagar‐obasidium leguminicola and Pirex subvinosum kill L. leucocephala trees throughout Asia and Australia. Pod rots caused by Fusarium species are of major concern not only because of their...