Combining napier grass with leguminous shrubs in contour hedgerows controls soil erosion without competing with crops

We established hedges/barriers of calliandra (Calliandra calothyrsus Meissner), leucaena (Leucaena trichandra (Zucc.) Urban)) and napier grass (Pennisetum purpureum Schumach) and combination hedges of either calliandra or leucaena with napier grass on slopes exceeding 5% to study the effect of vegetative barriers on productivity of arable steep-lands in central Kenya. Hedges/barriers were pruned regularly and biomass incorporated into the plots. Hedge plots were monitored for soil fertility, soil losses and maize crop yield changes. Inorganic-N concentration in the tree hedge plots was higher than in the control and napier barrier plots after 20 months. Napier grass barriers were the most effective in reducing erosion losses across the two seasons. The effectiveness of napier grass to significantly reduce soil erosion was detectable in one year old napier barriers. Soil loss from all the other one year old vegetative treatments was similar to soil loss from the control. Seventeen month old combination hedge plots recorded lower soil losses than tree hedges of the same age (P = 0.012). Maize crop yields throughout the trial period were high and similar for leguminous and combination hedge plots, but lower in the napier grass and control plots. Overall, we observed that the combination hedges seemed to provide a win-win scenario of reduction in soil erosion combined with improvement of maize crop yields and soil fertility enhancement. We conclude that vegetative hedges have a potential for improving soil productivity in arable steep-lands of the central highlands of Kenya, and that in adoption of vegetative hedges for this purpose there are trade-offs between soil conservation, soil fertility and maize crop yields to be considered. Throughout the text, tree hedges and leguminous hedges are used interchangeably to imply calliandra and leucaena hedges while use of barrier/s to refer to a treatment is restricted to monospecific grass strips     

Forage production in natural and afforested grasslands of the Pampas: ecological complementarity and management opportunities

In managed rangelands periods of low primary productivity determine troughs of forage availability, constraining animal production year-round. Although alternative tools to increase forage availability during critical seasons exists, most of them are unaffordable and short-lived in marginal areas. We explore the potential benefits of deciduous tree plantations favoring winter forage productivity by comparing aboveground net primary productivity (ANPP) patterns in herbaceous understory to tree plantations and natural grasslands in the Pampas (Argentina). These temperate subhumid grasslands are characterized by the coexistence of winter species, mainly C3 grasses of the native genera Stipa, Piptochaetium, and Bromus and the exotic genera Lolium and Festuca) and summer species (mainly C4 grasses of the native genera Paspalum, Bothriochloa, and Stenotaphrum) that replace each other throughout the seasons, with domination of the latter. We hypothesize that the natural decoupling of growing seasons between winter deciduous trees and winter grasses could provide the basis for the sustainable promotion of winter forage. We measured ANPP on two 23-year-old Populus deltoides plantations and their understory and compared them with adjacent open grasslands. Afforested stands had 55–75% higher annual ANPP than their non-afforested neighbors, with trees contributing ~70% to total ANPP. Herbaceous canopies beneath plantations achieved about half of the ANPP observed in non-afforested situations with a contrasting seasonal distribution associated with shifts from C4 to C3 grass dominance. Winter ANPP, the most critical source of forage in these grazing systems, was similar or higher in the herbaceous understory of tree plantations to that on their non-afforested counterparts, suggesting that mixed systems involving deciduous trees and understory pastures are a valid and viable option in the region.     

Cutting management of alley cropped leucaena/gliricidia-Guinea grass mixtures for forage production in southwestern Nigeria

A study was conducted at Fasola (7°45 N and 3°5 E) in southwest Nigeria to determine the best tree cutting scheme for forage production and the effects of hedge configurations on tree, grass and total forage productivity of 6–8-year-old leucaena (Leucaena leucocephala Lam. de Wit) and gliricidia (Gliricidia sepium Walp.)-Guinea grass (Panicum maximum Jacq. cv. Ntchisi) mixture. After a uniform cut at the end of January 1990 (mid-dry season), the trees were cut according to the following cutting regimes: one cut after a 12-month regrowth (12M); two cuts after three- and nine-month regrowth (3–9M); two cuts every six months (6-6M); two cuts after nine- and three-month regrowth (9-3M); three cuts, two cuts every three months and the third cut after a six-month regrowth (3-3-6M), and four cuts every three months (3-3-3-3M). Grass was cut every six weeks between April and October followed by a cut in January. The hedge configuration was either one or three hedgerows of mixed stands of leucaena and gliricidia. There were twice as many trees and one-third less grass in the triple than in the single hedgerow hedge configuration.The 3-3-3-3M, 9-3M and 3-3-6M cutting regimes produced the highest total forage (tree foliage + grass) dry matter yields (DM) of 6.54, 5.80 and 5.77 t DM ha^–1 annum^–1, respectively. The magnitude of the difference between the tree forage yields of the triple and single hedgerow plots (16%) did not reflect the theoretical difference in the number of trees (33%) in the two arrangements.     

Modelling competition of paired columns of Eucalyptus on interplanted grass

Adequate evaluation of competition interfaces of tree growth on intercrops is an important consideration in the assessment of agroforestry systems. Spatial methods wherein positional effect of an observation with respect to trees or columns of trees can be accounted for were examined. Yield ofbhabbar grass (Eulaliopsis binata Ritz) planted under paired and staggered columns of Eucalyptus (Eucalyptus tereticornis Smith) was analysed for four years. Grass production at 7 positions recorded across staggered and paired tree columns was significantly different. Spatial correlations among contiguous observations across paired tree columns were significant. Cyclicity corresponding to seven columns of grass of 3.5 m distance between paired tree columns explained variation in grass production significantly during the first observation year. Additional competition interfaces at 1.75 m and 1.17 m appeared in the subsequent years. These competition interfaces were attributed to pairing of trees and staggering. Error distributions of fitting of cyclic patterns were more acceptable as compared to ANOVA. Possibilities of the use of this methodology in many other agroforestry situations are discussed.     

Pasture production in a silvopastoral system in relation with microclimate variables in the atlantic coast of Spain

Grasses and legumes of high productivity and nutritional quality are a good alternative as pasture supplements in rangelands of low quality forage. Orchardgrass (Dactylis glomerata L. cv. `Artabro') and white clover (Trifolium repens L. cv. `Huia') are known as shade tolerant and low flammability species that have been successfully used in agroforestry systems in Galicia, both diminishing fire hazard compared with natural shrublands. In this study, annual and seasonal production of a grass mixture of both species was quantified during 3 years in a pinewood under different tree canopy covers. Regardless of cover, pasture production increased in summer, and decreased from fall to spring. We obtained a significant correlation between annual pasture production and light transmission through the tree canopy (R² = 0.96, P<0.05). Light transmittance through a maritime pine canopy (Pinus pinaster Ait.) was higher than through a Scots pine canopy (P. sylvestris L.), corresponding to 36–57% and 16–21% of full sunlight respectively. The highest herbage production was obtained in no tree stands and the lowest under a P. sylvestris canopy. Fluctuations inlight transmission, temperature and PAR (Photosynthetically Active Radiation) under tree canopy were less apparent compared with no tree stands. Variation in seasonal production was more pronounced in stands without trees, and appeared more uniform when percentage of light intercepted by tree canopy increased.This revised version was published online in November 2005 with corrections to the Cover Date.     

Forage production and nitrogen nutrition in three grasses under coconut tree shades in the humid-tropics

Reduction in forage production (FP) under trees in the humid tropics is well known, but information on how different levels of nitrogen (N) fertilizer influence FP under trees is meager. The present study reports effects of four N fertilizer levels (0, 60, 80 and 120 kg ha⁻¹ N) on net soil N mineralization rate (NMR) and soil moisture (SM), FP, shoot biomass/root biomass ratio (SB/RB), N concentration in SB, N uptake and nitrogen use efficiency (NUE) of three grasses [guinea (Panicum maximum Jacq.), para (Brachiaria mutica (Forssk) Stapf) and hybrid-napier (Pennisetum purpureum Schumach.)] under three canopy positions [under canopy (UC, representing high shade), between canopy (BC, representing low shade) and open] of coconut trees (Cocos nucifera L.) in a coconut based silvopastoral system in the humid tropical climate of South Andaman Island of India. The study was performed for two annual cycles (2005–2006 and 2006–2007). The hypotheses tested were: (1) FP would decline under tree shades, both in N fertilized as well as no N fertilized conditions, when SM was not growth limiting in the open. However, amount of decline in the FP would depend on grass species and intensity of shades i.e., higher was the shade greater would be the decline; (2) N fertilizer would increase FP under tree shades, but the increase depended on grass species, intensity of shades and amount of N applied. Amount of N applied, however, would not annul the shades effects when SM was not growth limiting in the open. The study revealed that the tree reduced light 59% under UC and 32% under BC positions, but the N fertilizer levels increased NMR by 11–51% under UC and 3–44% under BC positions compared to the open. SM did not differ across the canopy positions. Under all situations, FP of all grasses declined under UC (47–78%) and BC (18–32%) positions compared to the open; the decline was greater in Hybrid-napier than Guinea and Para grasses. Forage production of all grasses increased with N fertilizer increments under all canopy positions reaching 32 t ha⁻¹ dry matters for hybrid-napier at 120 kg ha⁻¹ N in the open. Both guinea and para grasses outyielded hybrid-napier grass under UC but not under BC or in the open. N concentration in the forage (SB) also increased as N fertilizer level increased. These observations support our hypotheses and suggest that forage production under coconut palms can be increased by the application of N fertilizer with both guinea and para grasses being more productive than hybrid-napier grass under the high shade. Where light conditions are better, hybrid-napier would produce more forage than the other species.     

Incorporating indigenous knowledge of fodder trees into small-scale silvopastoral systems in Jamaica

A study was conducted to identify and explore indigenous knowledge relating to fodder trees and silvopastoral management systems of small-scale farmers in seasonally dry areas of Jamaica. The objectives of the study were to: 1) explore farmers indigenous knowledge relating to fodder trees and silvopastoral management systems in a subtropical dry climate; 2) examine pastoral land-use systems and technologies in current use; and 3) seek to integrate this information into silvopastoral tree fodder systems. Data were gathered via observation and semistructured interviewing. A snowball sampling strategy was used to purposively select all small-scale farmers who had cattle in the Green Park valley for interview.Of forty farmers interviewed, 37 males (92.5%) and 3 females (7.5%) were primary caretakers of cattle. Twenty-seven of 40 farmers (68%) raised cattle to generate income. During extended droughts farmers are forced to look for alternatives to desiccated, overgrazed pasture grasses, including: 1) local travel to harvest sugar cane tops and to cut Guinea grass (Panicum maximum); 2) purchase of bag feed; and 3) harvest and use of tree fodder. Preferred fodder trees were identified as Bacedar (Guazama ulmifolia), Guango (Albizia saman), Breadnut (Brosimum alicastrum) and Quickstick (Gliricidia sepium).Recommended silvopastoral management systems include fodder hedgerows, three strata forage systems, and living fences. In addition, production of indigenous fodder tree species, introducing improved tree fodder species, and planting improved pasture grasses concurrent with cash trees is suggested.     

Carbon storage and nitrogen cycling in silvopastoral systems on a sodic in northwestern India

Tree-based land-use systems could sequester carbon in soil and vegetation and improve nutrient cycling within the systems. The present investigation was aimed at analyzing the role of tree and grass species on biomass productivity, carbon sequestration and nitrogen cycling in silvopastoral systems in a highly sodic soil. The silvopastoral systems (located at Saraswati Reserved Forest, Kurukshetra, 29°4prime; to 30°15prime; N and 75°15prime; to 77°16prime; E) consisted of about six-year-old-tree species of Acacia nilotica, Dalbergia sissoo and Prosopis juliflora in the mainplots of a split-plot experiment with two species of grasses, Desmostachya bipinnata and Sporobolus marginatus, in the subplots. The total carbon storage in the trees + grass systems was 1.18 to 18.55 Mg C ha⁻¹ and carbon input in net primary production varied between 0.98 to 6.50 Mg C ha⁻¹ yr⁻¹. Carbon flux in net primary productivity increased significantly due to integration of Prosopis and Dalbergia with grasses. Compared to 'grass-only' systems, soil organic matter, biological productivity and carbon storage were greater in the silvopastoral systems. Of the total nitrogen uptake by the plants, 4 to 21 per cent was retained in the perennial tree components. Nitrogen cycling in the soil-plant system was found to be efficient. Thus, It is suggested that the silvopastoral systems, integrating trees and grasses hold promise as a strategy for improving highly sodic soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Herbage response to spacing of loblolly pine trees in a minimal management silvopasture in southeastern USA

Loblolly pine (Pinus taeda L.) silvopastures often are established and maintained on sites of poor soil fertility and minimal fertilizer input. Our objective was to determine whether row spacing affected yield, quality, and botanical composition of minimally managed herbage in loblolly pine early in the tree rotation. Plots were randomly located equidistant from bordering tree rows in each of eight alley width treatments that were 2.4, 3.6, 4.9, 7.3, 9.7, 12.2, 14.6 m wide, and no trees. Row spacing affected the yield, quality, and botanical composition of pasture five to six years in the rotation especially at densities exceeding 840 trees ha^–1. Botanical composition shifted from predominantly cool-season to warm-season grasses between annual first- and second-harvests, respectively, which caused seasonal differences in several yield and quality traits. Tall fescue (Festuca arundinacea Schreb.) production appeared to be unsustainable under minimal management. Herbage yield generally increased, but quality and minerals (crude protein, IVDMD, Ca, and P) tended to decrease with spacing. The 4.9 m row spacing was minimally acceptable for herbage yield and quality. System design should seek to balance tree-crop yield and quality within the context of management constraints and site productivity.This revised version was published online in November 2005 with corrections to the Cover Date.     

Pasture production under different tree species and densities in an Atlantic silvopastoral system

We studied the effect of six tree species planted at six different densities on pasture production seven years after establishment. Annual and seasonal pasture production was studied every six months, over three years. Pasture production was lower under conifer trees (Pseudotsuga menziesii (Mirb.) Franco, Pinus pinaster Aiton, Pinus radiata D. Don) than under broadleaved trees (Betula alba L., Quercus rubra L. and Castanea sativa Mill.). Annual pasture production under Pseudotsuga menziesii and Pinus pinaster decreased progressively starting from 952 trees ha⁻¹, while decline in herbage production under Pinus radiata began to occur at 427 trees ha⁻¹. Tree density effect on pasture production was detected at 2,000 trees ha⁻¹ for all of the deciduous species studied. This effect on pasture production was more important in the first six months of the year (June sampling), while from June to December herbage production was less affected by tree density. The tree effect became more noticeable over time, with the last sampling showing the inverse relationship between tree density and herbage production most clearly. Seven years after tree establishment, pasture production was quite consistent under tree densities between 190 trees ha⁻¹ and 556 trees ha⁻¹ and declined remarkably from 556 trees ha⁻¹ to 2,500 trees ha⁻¹. The study also indicated that by the sixth growing season, annual pasture production under different tree species is inversely correlated with tree leaf area index.     

Napier grass strips and livestock: a bioeconomic analysis

Napier grass strips are gaining some acceptance in Southeast Asia as a vegetative means of soil erosion control, due to the relative ease of establishment and management. In addition, the napier grass strips aid productivity of agroforestry systems by providing mulch or by being fed to livestock. In this paper, a bioeconomic comparison of different ways of utilising the napier grass cuttings is undertaken. The three uses examined for the cuttings were: as mulch in the alley areas, sold as fodder, and fed to animals with manure applied back to the system. The analysis linked the soils-oriented SCUAF model with economic and animal component models. SCUAF was parameterized using field data based on farmer interviews and field visits. Farmer interviews and field visits were conducted at Claveria, Misamis Oriental to gather additional data regarding costs and returns associated with animal production, and also to obtain the farm gate price of napier. Predicted biophysical results produced by the SCUAF model showed that application of napier grass cuttings, back into the system, directly as mulch or indirectly as animal manure resulted in higher maize and napier yields, lower soil erosion rates, and less of a reduction in soil mineral nitrogen and soil labile carbon levels. The comparison was made with the case where napier was sold off-farm as fodder. Cost-benefit analysis showed that higher economic returns were gained when napier grass cuttings were fed to animals, rather than applied directly as mulch. This economic benefit was attributed to the draught and transport services rendered by the animal and to a change in the value of the animals. This analysis highlights the value of utilizing animals within a napier grass strip system for control of erosion.This revised version was published online in November 2005 with corrections to the Cover Date.     

Limits to recruitment of tall fescue plants in poplar silvopastoral systems of the Pampas,Argentina

Forage production in silvopastoral systems of the Flooding Pampa is based on cool season grasses with a relatively asynchronous phenology regarding their accompanying deciduous trees. However, the productivity of cool season grasses in these systems is usually low. The hypothesis of this work is that the low productivity of cool season grasses is caused by tree litter constraining plant recruitment. Emergence and establishment (reproductive propagation), and tillering (vegetative propagation) patterns of tall fescue, a cool season grass in the region, were studied in two pairs of adjacent non-afforested and afforested poplar stands (tree age 26–28 years, tree density 453–797 plants ha⁻¹). Observational and manipulative (i.e. addition of seeds, leaf litter removal) experiments indicated that the recruitment of tall fescue plants is strongly limited by the fall of poplar leaves over emerged seedlings, during autumn. Results suggest that any management practice capable of removing poplar litter, either through grazing or machinery, could neutralize this limitation enhancing the herbaceous primary production of the system.     

Comparative performance of four multi-purpose trees associated with four grass species in the humid regions of Southern India

The results of a field trial conducted at the Livestock Research Station, Thiruvazhamkunnu, Kerala to study the compatibility of different components in a silvo-pastoral system revealed that growth and yield of fodder species were significantly influenced by the tree components only after tree canopy formation. The fodder species such as Pennisetum purpureum Schum., Panicum maximum Jacq., Brachiaria ruziziensis Griseb. and Euchlaena mexicana Schrad. grown in association with Casuarina equisetifolia J. R. & G. Forst. and Ailanthus malabarica DC recorded comparatively higher forage yield even after canopy formation. However, forage crops grown in combination with Acacia auriculiformis A. Cunn. ex Benth. and Leucaena leucocephala (Lam.) de Wit. registered relatively lower values for growth and yield. Increased light infiltration into the understorey due to the cladophyllous canopy can be attributed as reason for the higher fodder productivity under Casuarina. Due to the combination of crown size and shape, tree height and spacing the amount of light intercepted by Ailanthus also was very low. Among the four multi-purpose trees used, Acacia recorded the maximum growth rate followed by Casuarina, Ailanthus and Leucaena. Forage productivity of the four species was in the order: Pennisetum purpureum > Panicum maximum > Brachiaria ruziziensis > Euchlaena mexicana. Casuarina with Pennisetum/ Panicm were found to be optimal tree — forage combinations for silvo-pastoral systems.     

Tree planting pattern effects on forage production in a Douglas-fir agroforest

Resource sharing among agroforestry system components, as expressed by spatial patterns along interfaces between components, is a crucial factor in both understanding present systems and in designing new agroforestry applications. A study of the spatial pattern of forage production surrounding 9–10 year old Douglas-fir trees in a agrosilvopastoral plantation near Corvallis, Oregon, was conducted during 1988 and 1989. Transects of plots were clipped both between trees (tree/tree) and between trees and open pastures (tree/pasture). Best-fit regression models relating forage production to distance from trees (tree/tree R ² = 0.87; and tree/pasture R ² = 0.89) were combined into a single prediction model. Observed forage production increased rapidly with increasing distance from trees during the initial 4 m. Trees had little effect on forage production beyond 4.5 m (approximately 2 canopy diameters) from the nearest tree. Predictions of different combinations of tree density and planting pattern indicated a strong interaction between density and pattern with highly aggregated plantations better able to maintain forage production at high tree densities.     

Nutritional evaluation of “Braquiarão” grass in association with “Aroeira” trees in a silvopastoral system

This study aimed at evaluating the influence of a silvopastoral system (SPS) composed of “Aroeira” trees (Myracrodruon urundeuva) on the nutritional value of Brachiaria brizantha cv. Marandu forage grass over the rainy season. The experiment was conducted in the SPS located in the “Cerrado” biome in Lagoa Santa County, Minas Gerais state, Brazil, in the agricultural year of 2004–2005. It was evaluated the influence of “Aroeira”, whose density in the area was 140 trees/ha, on the following parameters of the B. brizantha cv. Marandu forage grass: forage mass harvest above stubble height, morphogenic attributes, bromatological composition and nutritional value. The effects of “Aroeira” trees on the micro-climatic conditions were also evaluated. The experiment adopted a randomized block design with five blocks (cutting seasons), two treatments (a shaded pasture—B. brizantha cv. Marandu shaded by M. urundeuva—and a pasture in full sun—B. brizantha cv. Marandu in full sun), and three replicates. The tree component, composed of the tree species M. urundeuva in the experimental density adopted, increased dry matter and crude protein of the forage mass harvest above stubble height, without affecting the concentration of neutral detergent fibre or acid detergent fibre, thus causing dry matter and organic matter in vitro degradability as well as effective degradability of the forage grass to remain the same as those obtained in full sun. Therefore, the results of this study show the possibility of using trees and grass to increase both animal production and environmental services.     

Root competition for phosphorus between coconut, multipurpose trees and Kacholam (Kaempferia galanga L.) in Kerala, India

The magnitude of root competition 17 year-old coconut palms suffer from three year-old inter-planted multipurpose trees, Vateria indica L., Ailanthus triphysa (Dennst.) Alston. or Grevillea robusta A. Cunn. and kacholam (Kaempferia galanga L.), a herbaceous medicinal plant, was evaluated based on the extent of absorption of applied ³²P by the palms in sole and mixed crop situations. The multipurpose tree (MPT) species were grown under two planting geometries (single row and double row). The hypothesis that, when grown together, widespread root proliferation of coconut and multipurpose trees occurs in the well-fertilised kacholam beds was tested by root excavation. Interplanted MPTs substantially altered absorption of ³²P by coconut. Both Ailanthus and Vateria exerted a modest depressing effect, while Grevillea enhanced ³²P uptake by coconut. Single rows of MPTs also favoured ³²P recovery by coconut, presumably because of the increased root densities in the subsoil. Ailanthus, Vateria and Grevillea absorbed substantial ³²P. Overall, high ³²P absorption in the coconut-Grevillea plots indicates complementary root-level interactions between these species. ³²P absorption by MPTs was generally higher closer to the trees owing to the greater root concentration of the MPTs, which in turn suggests possible root interference between MPTs and coconut. Hence selection of tree species with low root competitiveness and/or trees with complementary root interaction is of strategic importance in agroforestry. Kacholam showed substantial ³²P content in its foliage. This ³²P appears to have been translocated by coconut into the kacholam beds where new coconut roots were abundant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationship between tree canopy height and the production of pasture species in a silvopastoral system based on alder trees

Silvopastoral systems in New Zealand that incorporate trees planted to control soil erosion on hills largely rely on the productivity of the pastoral system for financial returns. The effect on pasture productivity of increasing the tree canopy height by pruning Italian gray alder (Alnus cordata) was investigated by measuring the response of light, soil moisture, soil temperature, pasture production of major pasture species, and grazing behaviour of sheep. A split-plot design with four replicates was used. The main plot treatments were three levels of shade (81, 23, and 12% of available photosynthetic photon flux (PPF)), created by pruning 11 year old alder grown at the same density. The sub-plot treatments were four pasture mixes: perennial ryegrass (Lolium perenne), Yorkshire fog (Holcus lanatus), and cocksfoot (Dactylis glomerata), each sown with white clover (Trifolium repens), and cocksfoot sown with lotus (Lotus pedunculatus). Soil temperature was highest under light shade. Total herbage yield at 50 mm stubble height from October to May under heavy and medium shade was 60 and 80%, respectively, of the total herbage harvested under light shade. Cocksfoot had the greatest herbage yield, either with lotus or white clover. The tillering of perennial ryegrass was suppressed by shade more than for the other grass species making ryegrass unsuitable for use in this silvopastoral system. More sheep grazed in the light shade than in the heavy shade, but there was no difference in sheep preference for cocksfoot or Yorkshire fog. Lotus was grazed more frequently than white clover. Pruning of alder to increase canopy height has the potential to improve the productivity of the understorey pasture and its acceptability to sheep.     

Growth characteristics and allometry of <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> as a silvopastoral system component

Demand for goat (Capra hircus) meat in the southeastern USA is steadily increasing as a result of preferences exhibited by ethnic communities. Feeding systems that include fodder trees can be developed to take advantage of the natural preference of goats for browse. Data were collected for 2 years on a 5-year old stand of Robinia pseudoacacia L. to evaluate growth characteristics for goat browse and to develop allometric relationships in a randomized complete block design (intra-row spacing 0.5 or 1 m and coppice height 0.25 or 0.50 m) replicated six times. Allometric equations were derived from destructive harvests of 68 trees. Main branch size was not affected by intra-row spacing when trees were coppiced at 0.25 m; however, when coppiced at 0.5 m, trees spaced at 1 m had more and larger branches (P < 0.05) than trees spaced at 0.5 m. Intra-row spacing did not influence tree herbage biomass when trees were spaced at 0.5 m whereas trees coppiced at 0.25 m and spaced at 1 m produced less woody and herbaceous biomass than trees spaced at 0.5 m (P < 0.05). A strong relationship (P < 0.0001) was found between tree herbage biomass and the number of main branches greater than 0.01 m (r ² = 0.80). The results, based on growth characteristics and tree herbage biomass production, suggest that Robinia pseudoacacia L. would be an excellent candidate as a silvopastoral component in the southeastern USA.     

Acacia cyanophylla for forage and fuelwood in North Africa

Forage and wood yield of Acacia cyanophylla, also known as Acacia saligna, was studied in a 300–400 mm precipitation zone in Tunisia. Yields were measured during and after drought. This short (2–8 m) evergreen leguminous tree is used as a forage drought reserve in frost free regions where mean annual precipitation exceeds 250 mm. The standing crop of leafy forage builds up year after year for at least four years or until the tree is cut. It rapidly regrows after cutting from coppice shoots. The leaves provide high protein forage for sheep and goats during the long dry summer season typical of the Mediterranean climate as well as emergency forage during drought. The tree is used to stabilize moving sand dunes, and as a windbreak to protect cropland. It also provides fuelwood and increasaes soil nitrogen by fixation. The need for supplemental irrigation during establishment is a major constraint. Research in the 350 mm precipitation zone of Tunisia found 3.2 year old trees to yield over 1400 kg of forage standing crop per hectare after a severe drought. Trees harvested at 2.5 years of age in May, during the worst drought in over 30 years, yielded a standing forage crop of 724 kg per hectare. Forage regrowth 8 months after cutting and 4 months after rains returned was 700 kg/ha. The forage standing crop for trees harvested only once during the 3.2 year period was double the amount of forage regrowth from trees harvested the previous year, but mean annual forage yield similar. This demonstrates that it is possible for forage to be conserved as a living forage reserve for later use during drought. Total wood yield was only 1621 kg/ha for trees cut twice compared to 3683 kg/ha for trees cut only once. Annual cutting will substantially reduce the amount of forage available during drought and reduce the production of fuelwood. It may also reduce the vigor, productivity and life of the tree. Acacia cyanophylla alley cropped on cereal farmland can protect the soil from erosion, protect the associated crop from wind damage, fix nitrogen, provide fuelwood and provide a reserve of high quality forage for use during drought. This work was supported by the Government of Tunisia and the U.S.A.I.D. Tunisia Range Development and Management Project (664-0312.8).     

Water harvesting in a ‘runoff-catchment’ agroforestry system in the dry lands of Ethiopia

A major production constraint in arid and semiarid areas of Ethiopia is a lack of water for crop growth. Run off water can be harvested by channeling it into micro- catchments (MC) where it slowly infiltrates into the soil. The increased moisture provides more plant growth in these dry lands. An experiment using MC was conducted in eastern Ethiopia to study the growth of four multipurpose tree species intercropped with grass. Trees and grass were grown in 25 m² and 100 m² MC. Plant height, root collar diameter, and mortality rate of trees were determined 12 months after planting. Dry matter yield of grasses and trees were measured and nutrient analysis of plant tissues was determined. In a separate experiment the biomass of trees was determined after 2.5 years of continuous growth without grass competition. Soil moisture, organic matter, texture and bulk density of the soils were also determined. Mean tree height was 10% greater in the 100 m² than in the 25 m² MC. Root collar diameter and survival rate showed similar increase with 13% and 7.8% respectively. Acacia saligna and Leucaena leucocephala showed better growth in both plot sizes than the indigenous Acacia seyal and Acacia tortilis. The dry matter yield of grass (Panicum maximum) was over 12 tons/ha and 8 tons/ha in the 100 m2 and 25 m2 plots respectively. Soil moisture content was greater in MC than in control plots with no water harvesting structures with 31% and 24% during the wet and dry seasons respectively. The use of water harvesting can improve fodder production and carrying capacity of the dry lands of Ethiopia.