Agronomic evaluation of Leucaena. Part 1. Adaptation to environmental challenges in multi-environment trials

A multi-environment trial was conducted to evaluate the performance of high yielding accessions from most taxa of Leucaena, for broad and specific adaptation to growth-limiting environments, and to develop an understanding of environmental parameters limiting growth of this important multipurpose tropical tree-legume genus. Eighteen sites were selected to include environments known to constrain the growth of L. leucocephala. Accessions were planted in replicated line plots, with 10 trees/plot, spaced 50 cm apart, and with rows spaced 3 m apart. Environmental parameters measured were maximum and minimum temperatures, rainfall and psyllid pressure. Soil fertility and acidity indices were derived from soil analyses. A KX2 F1 hybrid accession proved broadly adapted with high yield rankings in all environments, and with yield advantage greatest at low temperature and high psyllid pressure sites. Specific adaptation to low temperature environments was identified in L. trichandra OFI53/88, and to a lesser extent in L. pallida CQ3439. No accessions were specifically adapted to acid-infertile soils. Highest dry matter production was achieved in fertile, hot, humid, low psyllid environments. Very low growth rates were achieved in acid-infertile and low temperature environments. Yield was strongly reduced by mean monthly minimum temperatures of 22 °C, mean monthly maximum temperatures of 29 °C, psyllid pressure of >2.5 (1–9 scale of increasing pressure based on damage to young leaves), acidity index of 6 (1–7 scale of decreasing acidity based on soil and Al saturation) and fertility index of 9 (1–12 scale of increasing fertility based on critical soil nutrient levels). This revised version was published online in June 2006 with corrections to the Cover Date.     

Wood and biomass production of Leucaena in subtropical Australia

Although only Leucaena leucocephala is widely used, most members of the Leucaena genus have potential as multipurpose species for tropical agroforestry systems. To investigate the wood and biomass production potential of the Leucaena genus, 116 accessions covering the 22 species were evaluated over a two-year period at Brisbane, southeast Queensland, Australia. Trees were planted into replicated line plots 5 m long, with rows spaced 3 m apart. Trees were initially planted at 0.5 m spacings within the plots, but were thinned to 1 m spacings prior to the evaluation period. The hybrid accessions, KX2 (L. pallida × L. leucocephala) and KX3 (L. diversifolia × L. leucocephala), were the most productive, yielding over 50 kg dry matter (DM)/tree. L. trichandra OFI53/88 and L. diversifolia CPI33820 were the most productive non-hybrid accessions producing total yields of 41 and 37 kg DM/tree, respectively. Cultivar Tarramba (26 kg DM/tree) was the most productive of the 26 L. leucocephala accessions assessed in the trial but all these accessions suffered from psyllid (Heteropsylla cubana) attack at this site. A series of non-destructive growth measurements was recorded every three months over the two-year evaluation period. Root collar diameter (RCD), stem number and plant height were found to be the most useful of the measurements for non-destructive assessment of accession agronomic characteristics. A relationship between yield and a growth index (calculated as RCD² × Height/1000), was derived from data from all accessions and could be used as a reliable predictor of yield (r ² = 0.94). The widespread use of the F1 hybrid leucaenas is currently limited by a lack of seed. Technologies to economically produce F1 hybrid seed on a commercial scale are required before the potential of these accessions in agroforestry systems can be fully realized. This revised version was published online in June 2006 with corrections to the Cover Date.     

Psyllid resistance in Leucaena. Part 1. Genetic resistance in subtropical Australia and humid-tropical Philippines

One hundred and sixteen accessions of Leucaena were assessed for resistance to the leucaena psyllid that has devastated stands of L. leucocephala pan-tropically since the mid-1980s. Damage to young leaf was assessed using a ratings scale, developed at the University of Hawaii, in replicated field trials at Brisbane, Australia and Los Baños, Philippines. The study identified a continuum of resistance among the accessions, from highly resistant to highly susceptible. Resistance levels were consistent between the two sites with few exceptions. L. collinsii subsp. collinsii, L. confertiflora, L. esculenta, L. pueblana, L. retusa, L. greggii and L. matudae were highly resistant at both sites, while L. leucocephala, L. lempirana, L. involucrata and L. multicapitula were highly susceptible at both sites. Other species were intermediate and were allocated to either resistant or susceptible categories. There was considerable variation in psyllid resistance within some species especially, L. trichandra, L. diversifolia and L. collinsii. Regression analysis was used to determine the influence of environmental variables on psyllid populations. Psyllid population outbreaks were restricted to a temperature range of 10?°C minimum temperature and 33?°C maximum temperature, but additional, unidentified factors influenced populations within this range. Leaf chemical characteristics were examined for their potential to confer psyllid resistance, but none were strongly correlated with accession damage ratings.     

Forage dry matter yields and psyllid resistance of thirty-one leucaena selections in Hawaii

Forage yields ofL. leucocephala (Lam). de Wit have been reduced as the result of psyllid damage sinceHeteropsylla cubana Crawford invaded the Hawaiian Islands in 1984. The forage productivity and psyllid resistance of 31Leucaena species and interspecific hybrids were assessed from 5 harvests in Hawaii during 1991 and 1992. The trial consisted of an augmented randomized complete block with 22Leucaena selections in all 4 replicates, 2 selections in 3 replicates and 7 selections in 1 or 2 replicates.Forage (leaves and stems < 6 mm diam.) dry matter (DM) biomass yield over a 13-month period ranged from 1.4 to 34 Mg ha^–1 from total DM ranging from 1.9 to 63.7 Mg ha^–1. Percent forage fractions ranged from 49 to 78% (forage DM/total DM). The 10 selections in this trial of eitherL. pallida Britton & Rose, and its hybrids withL. leucocephala consistently produced both the highest forage and total DM yields averaging 22 and 40 Mg ha^–1, respectively. This represented a three-fold increase in forage production when compared toL. leucocephala K636 (a standard around the world).The excellent performance of theL. pallida lines was attributed to high psyllid resistance and seedling vigor. AllL. pallida selections with the exception of K953 exhibited good psyllid resistance.Leucaena diversifolia Benth. K749,L. pallida K376, andL. esculenta (Moc. & Sesse) Benth. K950 had the highest psyllid resistance (p<0.05). Psyllid damage was negatively correlated to forage DM yield at both harvest 2 and 5 (r=–0.55,p<0.01,n=94). Forage DM was positively correlated to seedling vigor for the first harvest (r=0.83,p<0.001,n=74) and combined harvests (r=0.88,p<0.001,n=74).     

Agronomic evaluation of Leucaena. Part 2. Productivity of the genus for forage production in subtropical Australia and humid-tropical Philippines

Leucaena leucocephala is an important agroforestry species pan-tropically, but relatively little is known of the forage production potential of other species in the genus. The agronomic potential of 116 accessions, represent ing the 28 species and subspecies of the Leucaena genus and several artificial hybrid accessions, was evaluated at Los Baños, Philippines and Brisbane, Australia over a 2.5–year period. Accessions were planted into replicated line plots, with 10 trees/plot spaced 50 cm apart, and with rows spaced 3 m apart. The L. pallida × L. leuco cephala KX2 F ₁ hybrid accessions were highest yielding at both sites, producing dry matter (DM) yields of over 900 g/m row/month at Los Baños and approximately 320 g/m row/month at Brisbane. In the near-optimal growth conditions at Los Baños, L. leucocephala accessions were highly productive, with the best accessions producing total yields of over 500 g/m row/month. The superiority of KX2 hybrids was most pronounced at Brisbane, where high psyllid pressure during summer, and low temperatures during winter severely constrained growth of L. leu cocephala accessions. In the Brisbane environment, psyllid resistant accessions of L. pallida , L. trichandra and L. diversifolia were more productive than L. leucocephala accessions. Leucaena greggii , L. retusa , L. cuspidata , L. confertiflora , L. pulverulenta , L. pueblana and L. involucrata were of inherently low productivity in both the Brisbane and Los Baños environments. Mortality over the experimental period was very low for most species, particularly for L. leucocephala and KX2 accessions. The KX2 F1 hybrid accessions have considerable agro nomic potential as alternatives to L. leucocephala for use in tropical agroforestry.     

Intercropping field crops between rows of Leucaena leucocephala under rainfed conditions in northern India

A field study was conducted for six years (1981–1986) on sandy loam soil on intercropping hedgerows of Leucaena leucocephala (Lam) de Wit. with three field crops viz. maize (Zea mays L), black gram (Vigna mungo L) and cluster bean (Cyamopsis tetragonoloba L Taub.). In treatments 1 and 2 Leucaena hedges were planted as pure crops at close (25 cm × 75 cm) and wide (25 cm × 375 cm) spacings. In treatments 3, 4 and 5 the three field crops were intercropped between the hedgerows of Leucaena at the wide spacing, and in treatments 6, 7 and 8 the field crops were raised as pure crops. Leucaena was topped to 75 cm each time it attained a height of 175 cm. The pure crop of Leucaena at close spacing produced an average, over the six years, of 34 t ha⁻¹a⁻¹ of green fodder and 9.4 t ha⁻¹a⁻¹ of air dry fuelwood. The Leucaena at wide spacing produced 18.9 t ha⁻¹a⁻¹ of green fodder and 6.3 t ha⁻¹a⁻¹ of fuelwood. Intercropping with field crops decreased the yield of green fodder and fuelwood. The yield of all the field crops was less when raised as intercrops than as pure crops. Mean maximum net returns were obtained from intercrops of Leucaena and cluster bean (Rs 3540 ha⁻¹a⁻¹) which were significantly higher than the returns from pure crop of Leucaena at wide spacing but similar to the returns from pure crops of cluster bean. Leucaena with maize (Rs 3273 ha⁻¹a⁻¹) and black gram (Rs 3125 ha⁻¹a⁻¹) gave significantly higher net returns over pure crops of Leucaena at wide spacing, maize and black gram. ICRISAT = International Crops Research Institute for the Semi-Arid Tropics- Hyderabad, India. CIAT = Centro International de Agricultura Tropical - Cali - Columbia     

The potential of alley cropping im improvement of cultivation systems in the high rainfall areas of Zambia II. Maize production

Theee trials to evaluat the potential of alley cropping in maize production on the low fertility, acidic soils in Northern Zambia are described. Leucaena leucocephala, Gliricidia sepium, Sesbania sesban, Albizia falcataria, Fleminga congesta, and Cassia spectabilis, were grown in alley crops with hybrid maize and soybean. All trials received recommended rates of P and K fertiliser; N fertiliser was applied at three rates as a subplot treatment. One trial received lime before establishment.Only in the limed trial was there a significant improvement in maize yields through alley cropping; when no N fertiliser was applied, incorporation of Leucaena leucocephala prunings resulted in an increase of up to 95% in yields, with a smaller improvement being produced by Flemingia congesta. There was a significant correlation between the quantity of prunings biomass applied and the proportional increase in maize yields over the control treatment. It is suggested that the lack of effect of most of the tree species on crop yields was due to low biomass production.An economic analysis showed that alley cropping with limed Leucaena was only profitable when fertiliser costs were high in relation to maize prices. However, lime is both expensive and difficult to obtain and transport for most small scale farmers in the region, and is therefore not a practical recommendation. It is suggested that future alley cropping research should focus on screening a wider range of tree species, including other species of Leucaena, for acid tolerance and higher biomass production.     

Canopy management possibilities for arboreal Leucaena in mixed sorghum and livestock small farm production systems in semi-arid India

A major problem for small farmers in the semi-arid tropics is the chronic shortage of fodder for draft animals. Leucaena leucocephala has improved productivity in many places in India and in various cropping systems, usually as either a pure crop or in a hedgerow alley-cropping configuration. Mixed cropping with arboreal forms is seldom seen. For off-season fodder production, hedgerows have the disadvantage of being open to unmanaged browsing when unfenced (as is usual). Arboreal forms are generally far less vulnerable. In this paper, the components of production of sorghum and arboreal Leucaena are measured under different intensities of canopy lopping. The most productive management system of those examined was pollarding of the Leucaena at the time of under-sowing with sorghum. In a year with less than 50% of average seasonal rainfall, this system gave a yield of 4.6 tonnes/ha/yr fresh wt fodder and 3.8 tonnes/ha/yr dry wt. of fuel harvests, while increasing the standing crop of wood by 1.8 t/ha/yr and retaining a yield of sorghum grain equivalent to 46% of pure sorghum cropping; the LER of this system was 1.35. Cash values of the alternative management systems were estimated, including the discounted Net Present Value of the standing crop of timber. Maximum value was attained with unlopped pure crop Leucaena followed by pollarded Leucaena with sorghum; pure crop sorghum achieved a lower value. These results demonstrate both the high productivity of Leucaena/sorghum based systems, and the stability of production even in poor rainfall conditions. Pollarding transferred the high future value of Leucaena timber to the present value of sorghum grain and fuelwood.     

Vegetative Propagation of Leucaena Hybrids by Cuttings

Many interspecific hybrids have been produced among Leucaena species, some with great potential for high-value wood and forage production. Superior hybrids are often highly sterile, and vegetative propagation would be essential for their exploitation. Four experiments were conducted to investigate factors affecting the rooting of cuttings of Leucaena hybrids. Nine hybrids were studied that represented different ploidy levels (2x, 3x, and 4x), different levels of seedlessness, different ages (5–16 years) and varying leaflet sizes. Rooting ability basically depended on genotype, with only a few hybrids failing to root. Cuttings required leaflets to root, and half or more of a leaf led to higher frequencies of better roots. One-node cuttings had the same rooting ability as two-node cuttings. Rooting ability decreased dramatically in the cooler, low-light winter seasons of lowland Hawaii. Etiolation treatments increased rooting ability significantly for two difficult-to-root hybrids.     

Effect of alley cropping with Leucaena leucocephala and fertilizer application on yield of vegetable crops

Field experiments were conducted to investigate the effect of alley cropping vegetable crops with Leucaena leucocephala (Lam.) de Wit for two seasons on a sandy loam Oxic paleustalf in southwestern Nigeria. Four vegetable crops (Amaranthus cruentus L.; Celosia argentea L.; Okra, Hibiscus esculentus L.; and tomato, Lycopersicon esculentum Mill.) were grown in control plots and in 4-m wide alleys between established Leucaena hedgerows without and with fertilizer (30 N-13 P-24 K kg ha^–1). Leucaena prunings yielded large dry biomass and nutrients during both seasons. Yield of four vegetable crops responded more to fertilizer in control than in alley cropped treatments. Better yield of vegetables in alley cropped plots was in part due to following effect of the Leucaena hedgerows. Fertilizer application increased mean yields of Amaranthus, Celosia, okra and tomato by 325, 164, 47 and 94% in control plots and by 36, 26, 4 and 20% in alley cropped plots, respectively. For both seasons, yields were not significantly different between alley cropped with and without fertilizer and the control with fertilizer treatments. Yield was least in control without fertilizer. Alley cropping with Leucaena can reduce fertilizer requirement for vegetable production. Cost and return analysis using 1988 prices indicated that alley cropping with vegetable crops can be profitable.c/o Miss Maureen Larkin, L. W. Lambourn & Company, 26 Dingwall Road, Croydon CR9 3EE, England     

Alley cropping with Leucaena leucocephala (Lam.) De Wit and Acioa barteri (Hook.f.) Engl.

The effect of alley cropping with seven combinations of Acioa and Leucaena hedgerows and a control (no hedgerow) treatment on sequentially cropped maize and cowpea was studied in 1985 and 1986. The trial was carried out on an Alfisol in the humid zone of southwestern Nigeria. Hedgerows were established in 1983, using 4 m inter-hedgerow spacing and pruned to 25 cm height during cropping. Highest dry matter, wood, and nutrient yields of prunings of Acioa and Leucaena hedgerows were obtained with sole cropping. Growing Leucaena and Acioa in the same hedgerow suppressed dry matter production and nutrient yield of Acioa more than of Leucaena owing to the latter's faster growth. Total pruning dry matter yield was reduced as the proportion of Acioa increased in the combination. Leucaena prunings had higher nutrient yield than Acioa. Under 22-month old uncut hedgerows, weed biomass declined in the presence of Leucaena, either alone or in combination with Acioa. Weed weight under sole Leucaena hedgerows was about a third of that in the control plot. There was no significant effect of alley cropping on weed biomass, although alley cropping with Acioa and Leucaena hedgerows resulted in the dominance of broadleaf weeds while the control had a mixture of broadleaves and grasses. Alley cropping with various combinations of Acioa and Leucaena hedgerows increased maize and cowpea yields compared to control. Nitrogen application in both years increased maize grain yield. Mean yield increase due to N application in both years was highest in the control (47.2%) followed by the sole Acioa hedgerow (25.2%) and less in hedgerows with Leucaena. The results of observations over two years do not show any advantage for the tested Leucaena and Acioa combinations on maize and cowpea crops as compared to the sole hedgerows. B.T. Kang (IITA), c/o Miss Maureen Larkin     

Introduced <Emphasis Type="Italic">Eucalyptus</Emphasis> psyllids in Brazil

In the last 10 years, four species of psyllid were detected in Brazil on eucalypts: Ctenarytaina spatulata in 1994, Blastopsylla occidentalis in 1997, Ctenarytaina eucalypti in 1998 and Glycaspis brimblecombei in 2003. The latter two are serious pests in several countries. In Brazil, G. brimblecombei caused significant damage to the eucalypt plantations in the first years of its introduction. Now this pest is under control due to the programmes of integrated pest management, where the parasitoid is the principal control agent. The four eucalypt psyllid species introduced into Brazil are presented with information on distribution, hosts, biology and control.     

Productivity of annual cropping and agroforestry systems on a shallow Alfisol in semi-arid India

An experiment was conducted at ICRISAT Center, Patancheru, India from June 1984 to April 1988 on a shallow Alfisol to determine whether the productivity of annual crop systems can be improved by adding perennial species such as Leucaena leucocephala managed as hedgerows. Except in the first year, crop yields were suppressed by Leucaena due to competition for moisture. The severity of competition was high in years of low rainfall and on long-duration crops such as castor and pigeonpea. Based on total biomass, sole Leucaena was most productive; even on the basis of land productivity requiring both Leucaena fodder and annual crops, alley cropping had little or no advantage over block planting of both components. Application of hedge prunings as green manure or mulch on top of 60 kg N and 30 kg P ₂ O ₅ha⁻¹ to annual crops did not show any benefit during the experimental period, characterized by below average rainfall. Indications are that (i) alley cropping was beneficial in terms of soil and water conservation with less runoff and soil loss with 3 m alleys than with 5.4 m alleys, and (ii) root pruning or deep ploughing might be effective in reducing moisture competition.     

Variation of leaf characteristics in Populus tomentosa Carr.

An investigation was conducted to determine the extent of variations among nine provenances of Populus tomentosa Carr. in terms of leaf characteristics. A total of 263 accessions were studied under field conditions in the National Gene Bank of P. tomentosa in 2003. All of the accessions were characterized by 17 indices from 1 to 2-dimension constructions. Variance analysis of all characteristics showed that there were significant differences among the nine provenances and among individuals within each provenance. This study reveals that the evaluated germplasm appears to have a wide genetic base and high potential for further genetic improvements and it also indicates that abundant gene resources of P. tomentosa have been collected and preserved in the National Gene Bank. [Supported by the “Tenth Five-year Plan” National Key Project in Science and Technology (Grant No. 2002BA515B0303) and the National “863” Project (Grant No. 2002AA241071)]     

The effect of young Leucaena leucocephala (Lam) De Wit hedges on the growth and yield of maize,sweet potato and cowpea in an agroforestry system in Sierra Leone

An investigation was undertaken at Senehun — Kamajei, a high rainfall region in Sierra Leone, to assess the effects of Leucaena leucocephala, on the growth and productivity of maize, cowpea and sweet potato. The experiment was laid out in a completely randomised design with four replicates of each treatment. The treatments and controls were: (i) pure crops of maize, cowpea, sweet potato, Leucaena clean weeded and unweeded and (ii) intercrops of Leucaena with the food crops, both (iii) with and without applied fertilizers after the first year.The growth of Leucaena was slow but nevertheless tended to reduce grain yields of maize, and tuber and vine yields of sweet potato in the rows in the immediate vicinity of the trees, especially in the nitrogen-treated plots. The maize, in particular, caused an improvement in the early height growth of the trees.     

The potential of alley cropping in improvement of cultivation systems in the high rainfall areas of Zambia. III. Effects on soil chemical and physical properties

A detailed study of the soil chemical and physical properties in seven-year-old alley cropping trial containingLeucaena leucocephala andFlemingia congesta in Northern Zambia is described. There was a strong correlation between the maize yield and the total amount of nitrogen applied, both from prunings and fertiliser, suggesting that a major reason for the observed benefit from alley cropping, particularly withLeucaena, was due to an improvement in nitrogen supply.Leucaena produced significantly more biomass, and its leaves had higher concentrations of nitrogen, phosphorous and potassium and lower C/N and C/P ratios than did those ofFlemingia. There was also evidence that the trees had a beneficial effect on other soil chemical properties; under the hedgerows, particularly those ofLeucaena, there were higher levels of organic carbon, Mg, K and ECEC, and pH values were also highest.It is suggested that higher levels of organic carbon in the alley crop treatments were responsible for the improvements observed in soil physical properties. Lower bulk density, lower penetration resistance, and a higher infiltration rate and pore volume fraction were measured in the alley crops, although there was no significant change in the soil water release parameters.A deteriorating effect of constant applications of nitrogen fertiliser on soil fertility was observed; as the level of urea application increased, there were significant decreases in Mg, K and pH, increases in Al and soil acidity, and higher penetrometer resistance. These results highlight the urgent need for further research on biological methods of maintaining soil fertility.     

A study of the potential of hedgerow intercropping in semi-arid India using a two-way systematic design

The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study.Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea.The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (>4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed.     

Agroforestry systems and soil surface management of a tropical alfisol:

Field runoff plots, 70 x 10 m each, were established on a tropical Alifisol in southwestern Nigeria to monitor water runoff, soil erosion and nutrient loss in water runoff. The non-agroforestry control treatment (A) was established at two levels: plow-till and no-till systems of seedbed preparation. There were two agroforestry systems based on contour hedgerows of (B) Leucaena leucocephala and (C) Gliricidia sepium established at 4-m and 2-m spacings. Field plots were established in 1982 and hydrological measurements were made for uniform maize-cowpea rotation for 12 consecutive growing seasons from 1982 through 1987. Once established hedgerows of Leucaena at 2-m spacing were extremely effective in reducing water runoff and controlling erosion. Runoff, erosion and nutrient losses were generally more from maize grown in the first season than from cowpea grown in the second. Mean seasonal erosion from maize was 4.3, 0.10, 0.57, 0.10, 0.64 and 0.60 t/ha for plow-till, no-till, Leucaena-4m, Leucaena-2m, Gliricidia-2m treatments, respectively. Mean runoff in the first season from treatments listed in the order above was 17.0, 1.3, 4.9, 3.3, 4.3, and 2.4 percent of the rainfall received. There were high losses of Ca and K in water runoff from the plow-till treatment. In contrast to runoff and erosion, losses of bases in water runoff from agroforestry treatments were relatively high, high concentration of bases in runoff was probably due to nutrient recycling by the deep-rooted perennials.     

A tree/crop interface design and its use for evaluating the potential of hedgerow intercropping

The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast.Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years.Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential.The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed.     

Performance of Zebu Steers Grazing on Western Tanzania Native Forages Supplemented with <Emphasis Type="Italic">Leucaena Leucocephala</Emphasis> Leaf Meal

Information is lacking on the potential of leguminous fodder trees such as Leucaena leucocephala as a feed resource to supplement the native forages in traditional grazing management systems in the tropics. Two studies were conducted (1) to assess traditional fodder banks’ forage nutritive potential on animal production, and (2) to investigate the effect of Leucaena leucocephala leaf meal (LLM) supplementation on growth of steers grazing standing hay basal forages in the dry season. The traditional forages had low nutritive values indicated by low mean crude protein (CP) of 23 g kg⁻¹ dry matter (DM), and high fibre contents of 717, 546 and 153 g kg⁻¹ DM for neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL), respectively. The forages were poorly degraded in sacco and had low metabolisable energy (ME) (4.2–4.6 MJ kg⁻¹ DM). Mean washing losses A, slowly degradable DM fraction, B, potential degradability, (A+B) and mean 48 h DM degradability (DMD) of grazing land forages were 70, 471, 541 and 326 g kg⁻¹ DM, respectively. In the supplementation study, 16 growing steers (160.8±0.24 kg) were randomly allocated into four groups, in a completely randomized design. Four LLM treatment diets (T1, T2, T3 and T4), with four levels: 0, 0.4, 0.6 and 0.8 kg DM for control, low, medium and high LLM levels, respectively, were randomly allocated to the animals in the four groups for 70 days (d). LLM supplementation (p<0.05) improved mean weight gain from −0.30 to 0.26 kg steer⁻¹ d⁻¹, for T1 and T4, respectively. Steers on T4 gained (p<0.05) more weight compared to the animals in T1 and T2, though there was no (p>0.05) difference in weight gains between animals on T3 and T4 (0.14 vs. 0.26 kg steer⁻¹ d⁻¹, respectively). Standing hay basal forages alone could not sustain animal productivity during dry seasons unless corrected for protein. Higher levels of LLM supplementation prevented weight losses and improved the performance of grazing steers, a management practice thought appropriate to low income pastoralists in semiarid western Tanzania.