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The objective of the study was to determine the apparent digestibility and nutrient composition of Leucaena leucocephala leaf meal (LLM) inclusion in Black Australorp and Potchefstroom Koekoek diets. Tender and mature leaves were separately harvested from 10 individual trees and stored separately for chemical analyses. The leaves were air-dried in a well-ventilated laboratory to constant weight and milled to pass through a 1-mm sieve. A mixture of tender and mature leaves was also collected to produce a bulk leaf meal. The four iso-nitrogenous dietary treatments were 0 (control), 2.5, 5.0 and 7.5% of LLM, respectively. The apparent digestibility of two chicken breeds was also evaluated. The dry matter (DM), neutral detergent fibre (NDF), ether extract (EE), cellulose and hemicellulose of the samples did not differ between tender and mature leaves. Tender leaves had higher (P P L. leucocephala leaf meal affect (P L. leucocephala increase. Both tender and mature L. leucocephala leaves have a potential nutritional value that can be used in feedstuff and can be used as a protein supplement for Black Australorp and Potchefstroom Koekoek chicken breeds.

Management options to improve phosphorus (P) availability in the West African savanna include the application of organic residues, separately or with inorganic fertilizers. The quality and quantity of organic resources affect their contribution to nutrient availability. The quality of residues influences decomposition and nutrient release in the short term but its importance in the long term is unclear. A greenhouse study with six different soils assessed the residual effect of contrasting organic residues (maize stover, farmyard manure, Senna siamea, Mucuna pruriens, Leucaena leucocephala, Gliricidia sepium, Pueraria phaseoloides, and Lablab purpureus) and triple superphosphate (TSP) on maize growth during four cropping cycles of 7 weeks. For the first cropping, the average shoot dry matter yield (DMY), 14 g pot–1 obtained with residues of carbon to phosphorus (C:P) ratio ≤200, was similar to the TSP treatment and higher than the yield obtained with maize stover (C:P ratio = 396). From the second cropping, the shoot DMY of the maize stover treatment (15 g pot–1) was higher than those of the other treatments. Both high- and low-quality residues had similar effects on the cumulative DMY. Cumulative shoot P accumulation in the maize stover treatment (53 mg pot–1) was significantly higher than in the control (30 mg pot–1) and similar to those from high-quality residue treatments. Significant interaction (P < 0.05) between soil and organic resource for DMY occurred only during the first two croppings. This indicates that the effects of soil type and residue quality on nutrient availability dwindle with time.

Plant residues offer a viable alternative to the costly and non-readily available commercial lime in addressing the constraint of soil acidity among the rural smallholders. The liming potential of the residues, attributable to excess cations over inorganic anions, exists in either available or non-available forms. This study investigates cation flux and its effect on pH and plant residue alkalinity of four plant residues, maize (Zea mays), soya beans (Glycine max), Leucaena (Leucaena leucocephala) and Gliricidia (Gliricidia sepium), upon incubation for 100 days with and without application of lime in an acidic Zambian Ferralsol. Initial characterization of base cation content ranged from 239 to 879 (Ca2+), 188 to 458 (Mg2+) and 298 to 477 mmolc kg–1 plant material (K+). Of these, 26–60, 62–92 and 76–96% in that order were water soluble. On incubation, up to 70% Ca2+ and at least 80% Mg2+ and K+ added in the residues were initially present eventually increasing to 84 and 95%, respectively. Potential alkalinity values were 373 (maize), 1264 (soya beans), 794 (Leucaena) and 1024 (Gliricidia) mmolc kg–1. Of these, between 42 (Gliricidia) and 52% (Leucaena) constituted available alkalinity. Exchangeable aluminium was absent or appeared in insignificantly very low amounts towards the end of the incubation, while base cations were fixed. There was initial dependence of pH on both total cation concentration and residue alkalinity, but this relationship was later lost, suggesting incomplete activation of the non-available fraction of the potential alkalinity. Nitrogen mineralization affected both cation flux and residue alkalinity. This study highlights the importance of residues on amelioration of major cation deficiencies and aluminium phytotoxicity.

There is potential for smallholder farmers in Zimbabwe to use locally available plant resources to improve soil fertility and crop production. The challenge is to identify species with high nutrient concentrations and large amounts of above-ground biomass. Such a potential species is Ipomoea stenosiphon (Hall) A. Meeuse, a plant species indigenous to Zimbabwe, Malawi, Mozambique and Zambia, and it is currently being used by farmers in Zimbabwe. The aim of this study was to determine its productivity and variation in shoot nutrient concentrations on different soil types, its N mineralisation potential and effect on maize productivity. Ipomoea stenosiphon grown on clayey soils had significantly higher shoot macronutrient concentrations than when grown on sandy soils (N 43 vs. 11 g kg–1 soil, P 4.6 vs. 2.5 g kg–1 soil, K 4 vs. 1.5%). Laboratory incubation of I. stenosiphon shoot biomass showed greater (P < 0.05) N mineralisation than did many other agroforestry species, although it was inferior to Leucaena leucocephala and Acacia angustissima because of their higher N content of 3.2 and 3.03%, respectively, compared to 2.3% for I. stenosiphon. Field evaluation as an organic nutrient source in semi-arid areas of Zimbabwe showed an increase in maize grain yields of 111 and 161% at two study sites after applying I. stenosiphon biomass at 75 kg N ha–1. These yields showed an average N fertiliser (ammonium nitrate) equivalency of 83%. The study showed the high capacity for acquisition of soil nutrients in I. stenosiphon biomass, with corresponding high levels of mineralisation and crop production.

Declining crop productivity is a major challenge facing smallholder farmers in central highlands of Kenya. This decline is caused by continuous cultivation of soils without adequate addition of external inputs in form of manures and fertilizers. With this background, an on-station trial was initiated at Embu in 1992 to evaluate the feasibility of using two leguminous shrubs; Calliandra calothyrsus and Leucaena leucocephala for improving food production. In 2000, an off-station farmers’ participatory trial aimed at offering farmers soil enhancing technologies for replenishing soil fertility was established in Meru South District. The results from the Embu on-station trial indicate that, over the 11 years of study, calliandra and leucaena biomass transfer with half recommended rate of inorganic fertilizer treatments gave the best average maize grain yields of 3.3 Mg ha-1. Treatment where calliandra was alley cropped with maize but the prunings removed recorded the lowest maize yield of 1.2 Mg ha-1. Treatments with calliandra and leucana biomass transfer had similar yields but treatments that were alley cropped with leucaena did better than those that were alley cropped with calliandra. On the other hand, results from the off-station trial in Meru South indicate that, on average, across the seven seasons, sole tithonia gave the highest maize grain yield followed closely by tithonia with half recommended rate of inorganic fertilizer with 6.4 and 6.3 Mg ha-1 respectively. Control gave the lowest yield of 2.2 Mg ha-1 across the seasons. On average, integration of organic an inorganic sources of nutrients gave higher yields compared to all the other treatments.

To supplement high costs of inorganic fertilizers, smallholder farmers in the tropics are likely to increase the use of appropriate plant residues as an alternative source of plant nutrients especially nitrogen (N) and phosphorus (P). To maximize benefit accrued from these materials, synchronizing nutrient release patterns of the materials with crop’s nutrient requirements need to be understood. Consequently, this study was undertaken to: (1) evaluate the effect of plant residues on mineralization and N-release patterns, (2) evaluate the N release patterns of mixtures of low and high quality organic materials and synchrony with maize uptake. Incubation studies were established for 12 weeks using six selected plant residues: which included Leucaena leucocephala,Croton macrostachyus,Calliandra calothyrsus,Tithonia diversifolia,Sorghum bicolor and rice (Oryza sativa) husks.Soil samples were taken at 2 weeks interval for ammonium nitrogen (NH4 +-N) and nitrate nitrogen ( NO3 --N) determination.

In the present times, when tissue culture techniques are reckoned as prerequisites for studies on genetic transformation, it is encouraging to note that a few important leguminous tree species such as Dalbergia, Robinia, Sesbania, Bauhinia, Cassia, Cercis, Parkinsonia, Tamarindus, Acacia, Albizzia, Paras er ianthus, Prosopis and Leucaena can be mass propagated in vitro. Despite their utility as timber, pulp wood, firewood, forage, avenue trees and soil fertility enrichment, further improvement in their quality attributes is desirable through genetic transformation. However, since tree legumes are recalcitrant to genetic transformation, quality improvement programme for these tree legumes through tissue culture and genetic transformation is still in its preliminary stage of development. The present review gives a comprehensive account of the studies conducted so far on the regeneration and transformation of various tree legumes. Though in vitro regeneration for many tree legumes has been achieved, the genetic transformation has been achieved only in Robinia pseudoacacia, Acacia mangium and Leucaena leucocephala. A detailed protocol for plant regeneration and transformation of Leucaena leucocephala is presented here.

1.-The rhizobial populations associated with the 3 legume species tested were very divergent. 2.- Some of the rhizobial groups were common for the 3 legume species and others are unique for each of the hosts. 3.-Nodulation on S. herbacea in flooded soils is a unique feature for R. huautlense and flooding is a factor affecting rhizobial diversity associate with this plant.

No nitrogen fixing tree (NFT) species has so far been studied as extensively as soybeans, alfalfa, clover or beans. There are two main reasons for this statement: the economic potential of the single NFT species is much lower and, second, trees are in general much more difficult to study than annual plants. By the „Nitrogen Fixing Tree Association“ 50 species have been selected with special economic or ecological importance (Brewbaker, 1990). Robinia pseudoacacia, Casuarina equiseti/olia, Alnus rubra, Leucaena leucocephala, Sesbania sesban and Acacia tortilis are pronounced examples. Robinia pseudoacacia has been selected as a model tree legume, as a fast growing hardwood tree, capable to form symbioses with Rhizobium loti (Mesorhizobium sp.) and with arbuscular mycorrhizas producing leaves with a high protein content resistant to several stresses, with very high net photosynthesis rates, a very plastic root system and a high genetic variation (Hanover, 1990) (Table 1).

A study was conducted in and around Chandigarh, India to analyse the vegetation under the monoculture plantations of exotic (Eucalyptus tereticornis, E. citriodora, Populus deltoides and Leucaena leucocephala) and indigenous (Albizia lebbeck, Dalbergia sissoo and Acacia nilotica) tree species. Exotic plantations were observed to harbour less number of plant types compared to indigenous ones. In addition, but their density and biomass were also drastically reduced. Likewise, the indices of diversity, evenness and richness were also comparatively less under exotic plantations indicating the homogeneity and thus instability of the vegetation under them. Further, the soil collected beneath these exotic plantations was found to be rich in phytotoxic allelochemicals as indicated by their bioefficacy against Phaseolus aureus — a test plant.

In our search for different determinants responsible for host specificity, we are analysing the broad host range strain Rhizobium sp. BR816 isolated from the nodules of a tropical tree, Leucaena lencocephala. pBRF2, a 24 kb clone from the megaplasmids cosmid bank of R. sp. BR816 confers host range extension of the narrow hostrange bean symbionts Rhizobium etli CE3 and CNPAF512 to Leucaena leucocephala. Deletion and sequence analysis of this clone revealed open reading frames of which the putative products show homology with the NodO protein of R. leguminosamm bv. viciae and the GroESL in Rhizobium meliloti. Similar to the role of certain chaperonins in R. meliloti and Bradyrhizobium japonicum (Fischer et al 1993, Ogawa, Long 1996) the GroESL homologue in R. sp. BR816 appears to have a function in the symbiotic nitrogen fixation. While nodO alone is sufficient for the Nod+ phenotype of R. etli on Leucaena, the full length pBRF2 clone containing groESL is required for the Fix+ phenotype on Leucaena (van Rhijn et al 1996). A similar hostrange extension has been demonstrated for Azorhizobium caulinodans ORS571. This strain normally nodulates L. leucocephala with a very low efficiency and the resulting nodules do not fix nitrogen. A nodS mutant of ORS571 does not show any nodulation on Leucaena (Waelkens et al 1995). Interestingly, introduction of the full length pBRF2 clone into this mutant strain resulted in the formation of nitrogen fixing nodules on L. leucocephala while the mutant containing nodO alone formed merely non-fixing nodules.To further investigate the significance of chaperonins in R. sp. BR816, we screened the overall genome of R. sp. BR816 for the presence of groEL homologous sequences.

The role of vesicular arbuscular mycorrhizal (VAM) fungi in fine-root biomass dynamics, in fine-root litter degradation, and in uptake of nutrients from root litter was studied in Leucaena leucocephala, using Zea mays as a test plant. A total fine-root biomass of42.47 to 88.13 dw m-2 was produced in a young stand of Leucaena leucocephala, of which up to 65% was endomycorrhizal. The mycorrhizal fine roots worked as an effective biofertilizer, contributing to a several-fold increase in the growth of Zea mays. Root litter with VAM inoculation had no additional effect; mycorrhizal root litter may also serve as an inoculum for VAM colonisation of maize roots.

Seedlings of three leguminous trees (Paraserianthes falcataria L. Neilson, Acacia mangium Willd. and Leucaena leucocephala Lam. de Wit) were grown in nutrient solution with various concentrations of aluminium (Al) under sterile conditions and the organic acids excreted from their roots analyzed. In the presence of 5 mM Al, root growth in P. falcataria, A. mangium and L. leucocephala were inhibited by 41, 51 and 65%, respectively. The presence of 5 mM Al induced an excretion of citrate in all three species. P. falcataria excreted eight times more citrate than did L. leucocephala. Enhanced excretion of citrate in P. falcataria and A. mangium was unaffected by Al concentrations ranging from 2.5 to 10 mM, while enhanced excretion of citrate in L. leucocephala was suppressed by Al concentrations over 2.5 mM. Phosphorus (P) deprivation did not stimulate excretion of citrate in any of the species. In P. falcataria and A. mangium, citrate contents in the shoots and roots increased with increasing Al concentration in the nutrient solution. Aluminium-enhanced excretion of citrate could be associated with Al tolerance in P. falcataria and A. mangium.

Five fast growing tree species: Acacia mangium, Cassia nodosa, Gliricidia sepium, Gmelina arborea and Leucaena leucocephala were converted to charcoal by pyrolytic process. Charcoal briquettes were prepared from charcoal fines and carbonized wood twigs. The charcoal yield and the combustion related properties of the fuelwood and charcoal, viz: moisture content, density, percentage fixed carbon, volatile matter and gross heat of combustion were determined.

In 8-week-old, hydroponically grown Leucaena leucephala root uptake and accumulation of N and P were increased by external supply of these elements in the absence of Al. N and P relative transport from root to shoot were inversely related to shoot N and P concentration. An external Al concentration of 1 mM severely hampered root growth, and reduced transport of P from root to shoot, but enhanced root P concentration, possibly a result of precipitation of Al-P complex on root cell surfaces.