The performance of the leaf mulches ofLeucaena leucocephala,Flemingia macrophylla andGliricidia sepium in weed control

The performance of the leaf mulches ofLeucaena leucocephala, Gliricidia sepium andFlemingia macrophylla in weed control has been tested in two trials. The length of the period during which a mulch layer yields significantly less weedbiomass compared to the control plots is called the ‘effective life-span’ of the mulch. Of the three mulch materials only that ofF. macrophylla shows promise in retarding weed development. In the second trialF. macrophylla leaf mulch was applied at rates of 3, 6 and 9 tons dry matter per ha. The effective lifespan of a mulch layer of 3 tons is between 12 and 13 weeks. The treatments 6 and 9 tons have effective life-spans of over 14 weeks. For moderate quantities (up to 5 tons of dry leaf mulch per ha) the effective life-span is estimated at about a 100 days. The value of mulching in weed control is limited to the control of weed species that multiply by seed. Regrowth originating from roots or stumps from former vegetation is unlikely to be checked by a mulch layer. The subject of this paper is part of a broader study, presently conducted in Southern Ivory Coast, on the production, agronomical value and use in alley-cropping systems of the species mentioned in the title of the paper. A final report is scheduled for publication in 1988.     

Litterfall,litter decomposition and the use of mulch of four indigenous tree species in the Atlantic lowlands of Costa Rica

Litterfall, forest-floor litter biomass and nutrients, short-term litter decomposition and the effects of leaf mulches on initial growth of maize were studied for four indigenous tree species with agroforestry potential:Stryphnodendron microstachyum Poepp. et Endl.(S. excelsum), Vochysia ferruginea Mart,Vochysia guatemalensis Donn. Sm. (V. hondurensis) andHyeronima alchorneoides (O), growing in a young experimental plantation in the Atlantic humid lowlands of Costa Rica. Total annual leaf litterfall was higher inV. ferruginea plots, followed byS. microstachyum, V. guatemalensis andH. alchorneoides; all with values comparable to those reported for other tree species grown in agroforestry combinations in humid tropical regions. Forest-floor litter accumulation was highest underV. ferruginea andV. guatemalensis. Both litterfall and forest-floor litter material had similar patterns in nutrient concentrations: N was higher inS. microstachyum, Ca was higher inV. guatemalensis, K was higher inH. alchorneoides; Mg was higher inV. guatemalensis andH. alchorneoides; H. alchorneoides andV. guatemalensis had the highest P.V. ferruginea litter decomposed more slowly, whileS. microstachyum apparently decomposed faster than the other species. The twoVochysia species showed increases in N and P concentration in decomposing litter after seven weeks in the field,H. alchorneoides showed an increase in litter N and a decrease in litter P, andS. microstachyum showed a net decrease in both N and P over the same time period. The patterns found in the litter bag study were confirmed by results obtained in a tethered-leaves experiment.S. microstachyum andV. ferruginea litters lost more weight when mixed in a 11 proportion than either of them alone. Maize seedlings growing in plots mulched withS. microstachyum andH. alchorneoides leaves showed greatest initial growth, confirming patterns found in decomposition and nutrient release studies. The results show that these species could be used in agroforestry combinations with different advantages according to the specific objectives desired, whether these are soil protection, nutrient recycling, or enhancement of the growth of associated crops.     

The performance of selected leaf mulches in temperature reduction and moisture conservation in the upper soil stratum

This paper reports on the effect of the leaf mulches of Leucaena leucocephala, Gliricidia sepium and Flemingia macrophylla on moisture content and temperature in the first 5 cm of the soil. The mulches were applied at a standard quantity of 5,000 kg ha^–1 DM.In order to characterise a mulch material two parameters are distinguished; the initial impact (I _i ) and the effective lifetime (T _e ) of a mulch material. I is expressed in terms of percentage surplus moisture or degrees Celsius average temperature reduction. T quantifies the duration of the effect. Of the three mulch materials that of Flemingia macrophylla performs best in terms of moisture retention and lowering soil temperatures as well as in terms of longevity of the effect. Leucaena leucocephala mulch shows the smallest impact, over the shortest period.     

The performance of the leaf mulches ofLeucaena leucocephala,Flemingia macrophylla andGliricidia sepium in weed control

The performance of the leaf mulches ofLeucaena leucocephala, Gliricidia sepium andFlemingia macrophylla in weed control has been tested in two trials. The length of the period during which a mulch layer yields significantly less weedbiomass compared to the control plots is called the effective life-span of the mulch.Of the three mulch materials only that ofF. macrophylla shows promise in retarding weed development.In the second trialF. macrophylla leaf mulch was applied at rates of 3, 6 and 9 tons dry matter per ha. The effective lifespan of a mulch layer of 3 tons is between 12 and 13 weeks. The treatments 6 and 9 tons have effective life-spans of over 14 weeks.For moderate quantities (up to 5 tons of dry leaf mulch per ha) the effective life-span is estimated at about a 100 days.The value of mulching in weed control is limited to the control of weed species that multiply by seed. Regrowth originating from roots or stumps from former vegetation is unlikely to be checked by a mulch layer.The subject of this paper is part of a broader study, presently conducted in Southern Ivory Coast, on the production, agronomical value and use in alley-cropping systems of the species mentioned in the title of the paper. A final report is scheduled for publication in 1988.     

Selective control of weeds in an arable crop by mulches from some multipurpose trees in Southwestern Nigeria

The use of agroforestry systems in which pruning from trees is used to mulch the companion crops is an important area of research in the tropics. However, previous studies mostly evaluated the contribution of mulch to soil improvement and rarely examined the effect of mulch on weeds. Field experiments were conducted during the 1995 and 1996 growing seasons to investigate the effects of mulch from three woody fallow species on weed composition, biomass and maize grain yield. Treatments consisted of mulch from Leucaena leucocephala, Gliricidia sepium, and Senna siamea applied at rates of five and three tons dry matter ha^–1 at planting and three weeks after planting (WAP), respectively, an unmulched treatment that received 90 kg N ha^–1 of inorganic fertiliser, and an unmulched control plot that received no fertiliser. In both years and sampling dates, plots mulched with G. sepium and S. siamea had significantly lower weed density and biomass than the control plot in each of the sampling times and year of study. There was no significant difference in either weed density or biomass between the plot mulched with L. leucocephala and the unmulched plots. Mulches from G. sepium and S. siamea reduced weed density and weed biomass, while L. leucocephala was less effective in reducing weed biomass and weed density. Weed reduction by the mulches was in the order G. sepium S. siamea > L. leucocephala. Sedges were the dominant species in all the treatments except in G. sepium plots, where Talinum triangulare and other broadleaved species were dominant.This revised version was published online in November 2005 with corrections to the Cover Date.     

Water use efficiency and uptake patterns in a runoff agroforestry system in an arid environment

Water is the most limiting factor for plant production in arid to semiarid regions. In order to overcome this limitation surface runoff water can be used to supplement seasonal rainfall. During 1996 we conducted a runoff irrigated agroforestry field trial in the Turkana district of Northern Kenya. The effects of two different Acacia saligna (Labill.) H. Wendl. tree planting densities (2500 and 833 trees per ha), tree pruning (no pruning vs. pruning) and annual intercrops (no intercrop vs. intercrop: Sorghum bicolor (L.) Moench during the first season and Vigna unguiculata (L.) Walp. during the second season) on water use were investigated. The annual crops were also grown as monocrops. Water consumption ranged from 585 to 840 mm during the first season (only treatments including trees). During the second season, which was shorter and the plants relied solely on stored water in the soil profile, water consumption was less than half of that during the first season. Highest water consumptions were found for non-pruned trees at high density and the lowest were found for the annual crops grown as monocrops. Tree pruning decreased water uptake compared to non-pruned trees but soil moisture depletion pattern showed complementarity in water uptake between pruned trees and annual intercrops. The highest values of water use efficiency for an individual treatment were achieved when the pruned trees at high density were intercropped with sorghum (1.59 kg m^–3) and cowpea (1.21 kg m^–3). Intercropping and high tree density increased water use efficiency in our runoff agroforestry trial. We ascribe the observed improvement in water use efficiency to the reduction of unproductive water loss from the bare soil.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effect of the application of the leaf mulch of Gliricidia sepium on early development,leaf nutrient contents and tuber yields of water yam (Dioscorea alata)

This paper describes the effects of the leaf mulch of Gliricidia sepium on the development and yield of Water Yam, Dioscorea alata. Using leaf mulch, the time taken for the yam setts to sprout can be shortened by approximately 20 percent.Organic mulches contain considerable quantities of plant nutrients. Increasing amounts of mulch improved the leaf nutrient contents of the yam crop and resulted in significantly higher tuber yields. Over a tuber yield range up to c. 15 tons ha^–1 each additional ton DM Gliricidia sepium mulch applied resulted in a yield increment of about 2 ton yam tubers. A nutrient supply — nutrient extraction balance is discussed, comparing mulch applied and yam tubers harvested.Mulching as agricultural technique is a useful and affordable tool in adapting low external input cropping systems to local economic and environmental conditions.     

Effects of mulching materials on nitrogen mineralization,nitrogen availability and poplar growth on degraded agricultural soil

Nitrogen (N) is usually the most limiting nutrient in degraded agricultural soils and affects the growth and ecological function of poplar (Populus spp.) plantations. We hypothesized that application of organic mulch would improve soil nitrogen availability and increase tree growth, while the quality of mulching materials would alter the supply of essential nutrients. In this study, poplar plantations were established in 2004 and two experiments were established in the field. The fresh above-ground biomass of cogongrass (Imperata cylindrica (L.) P. Beauv.), oak (Quercus fabri Hance), Chinese coriaria (Coriaria nepalensis Wallich) and brackenfern (Pteridium aquilinum (L.) Kuhn. var. latiusculum (Desv.) Underw. ex Heller) in the current year was selected as mulching materials, and mulches were annually applied at the rate of 5.0 kg/m² in the N mineralization experiment and 20,000 kg/ha in growth and nutrient availability experiment. Additions of fresh biomass significantly improved annual net N-mineralization estimates and the mulching treatments increased the cumulative N mineralized over the incubation period by 22–30%. However, a significant difference in the cumulative N mineralized was not observed among the mulched treatments, even if the cumulative N mineralized in the treatment mulched with oak (QF) was 5.9, 3.3 and 2.2% greater than that of treatments with brackenfern (PA), Chinese coriaria (CN) and cogongrass (IC), respectively. Application of fresh biomass mulch markedly affected soil available N contents and growth performance of poplar plantations. The mulching treatments with QF, IC, PA and CN increased annual means of available N concentration by 39.0, 29.0, 29.6 and 39.7% respectively. At the end of the fifth growing season, the average height of poplar plantations in treatments mulched with QF, IC, PA and CN was 46.8, 14.9, 42.6 and 57.4% greater than that in Check (CK-no mulch), while mean DBH increased by 35.4, 12.5, 33.3 and 52.1%, respectively. Overall, the productivity was enhanced in mulched plots at the end of the third growing season. Compared with CK, the treatments mulched with QF, IC, PA and CN increased total biomass by 97.4, 96.4, 63.1 and 81.6%, respectively. Based on the results of this study, annual application of 20,000 kg/ha fresh woody biomass would be recommended for soil improvement in young poplar plantations growing on a degraded agricultural soil.     

Decomposition of Erythrina poeppigiana leaves in 3-, 9-, and 18-year-old alleycropping systems in Costa Rica

Timing the application of organic residues and therefore the release of nutrients during decomposition may be critical to the growing crop in tropical alleycropping agroforestry systems. Field experiments were carried out in Turrialba, Costa Rica, to determine differences in Erythrina poeppigiana (Walp.) O.F. Cook leaf decomposition in 3, 9 and 18-year alleycropped agroforestry systems. Treatments consisted of mulch-only, and mulch plus Arachis pintoi Krapov. and W. Gregory var. CIAT 18347 in 3 and 9-year old alleycrops under no-till cultivation. The 18-year old site consisted of treatments with mulch-only and mulch plus chicken manure under disk plow cultivation. Litterbags, filled with E. poeppigiana leaves from 3, 9 and 18-year old trees, were placed on the soil surface and collected over a period of 84 days. Results showed no significant differences in the amount of plant residues remaining after 84 days in the 3-, 9-, and 18-year-old systems, or between the manure and mulch-only treatments. Comparing mulch-only treatments, leaves in the 18-year old system decomposed most rapidly which may be due to disk-plow cultivation practices where litterbags were in direct contact with the soil as opposed to the no-till system in the younger alleycrops.     

Above-ground biomass of seedling and semi-mature Sesbania sesban,a multi-purpose tree species,estimated using allometric regressions

Above-ground biomass production in seedling and semi-mature individual plants of Sesbania sesban varieties were compared to non-destructive measurements of stem allometrics. The results indicate that measurements of stem characteristics (diameter and total height) are suitable for estimating biomass of S. sesban varieties and therefore useful in the selection of particular varieties for inclusion in short-rotation agroforestry systems in arid- and semi-arid regions. Less labour-intensive methods for accurately assessing the productivity of agroforestry species, such as the use of allometric regressions, could significantly increase the number of individual plants that could be screened in any particular trial. A multiple polynomial regression accurately estimated above-ground biomass in all plants ranging in age from six weeks to eighteen months (r ²=0.99;p<0.001).     

Soil and plant N-budget 1 year after planting of a slash-and-mulch agroforestry system in the eastern Amazon of Brazil

Nutrient losses during slash-and-burn clearing in tropical forests, coupled with demand by food crops, can deplete nutrients and result in crop abandonment after 1–2 years. Slash-and-mulch technology prevents nutrient losses from burning, while mulch decomposition may serve as a nutrient source. This research investigates the release of nutrients from the mulch and potential uptake of released N by plant biomass after a multi-species agroforestry system was planted in June 2005, following the clearing of a 1 ha of 7-year-old forest with a mulching tractor in Igarapé Açu, Brazil. The study evaluated soil conditions, mulch decomposition, and nutrient concentrations of Manihot esculenta and native vegetation under treatments of P+K fertilization in combination with four native tree species and N-fixing Inga edulis, or with three native tree species without I. edulis. Mulch layer N, Ca and Mg content decreased in response to fertilization, while mulch layer P and K content increased. Nutrient content increased in M. esculenta stems and tubers with fertilization and in the presence of I. edulis, and in competing vegetation with fertilization. Estimated tree N content increased 311 % with fertilization, but by 154 % in the presence of I. edulis. Fertilization with P+K, as well as the presence of I. edulis, increased N stocks in total biomass.     

黑木相思与尾叶桉苗期氮素传递的研究

以尾叶桉、黑木相思苗木混栽为研究对象,采用¹⁵N土壤和叶片标记法,在温室盆栽下研究2种植物间在根系完全隔离、部分隔离及无隔离处理下的生长变化及N素传递。结果表明:黑木相思的苗高、地径及生物量等生长指标随着根系隔离的减少而逐渐降低;相反,尾叶桉在根系无隔离处理下,其生长指标都要显著高于根系完全隔离处理,结果表明尾叶桉具有强大的养分吸收能力,混栽条件下会抑制黑木相思的生长。在¹⁵N土壤或叶片标记下,尾叶桉在根系部分隔离、无隔离下的总¹⁵N含量显著高于完全隔离处理(5.0和59.6倍);在土壤标记下,根系无隔离处理的黑木相思总¹⁵N含量显著低于完全隔离、部分隔离处理,而在叶片标记下的完全隔离黑木相思,其总¹⁵N含量显著低于其余2种处理。无论土壤或是叶片标记,黑木相思都能将N素传递至相邻尾叶桉,其N素传递率、传递量随着根系隔离的减少而提高。研究结果表明尾叶桉、黑木相思间能通过土壤渗透等方式传递N素,为桉树、相思的混交模式提供可靠的理论依据。     

Decomposition of woody legume nodules in two tree/grass associations under contrasting environmental conditions

Turnover of nitrogen-rich root nodules follows the pruning of legume trees, forming a potentially important yet little studied way of N release to the soil. The effects of soil moisture, herbivory by soil mesofauna and microbial decomposition on the disappearance rate of woody legume nodules was studied in two tree/grass forage production associations. Litter bags containing nodules of Erythrina variegata L. (Papilionoideae: Phaseoleae) were incubated for four weeks in grass-covered alleys between Gliricidia sepium (Jacq.) Walp. (Papilionoideae: Robinieae) hedgerows, established on a deep alluvial Oxisol under a humid tropical climate and on a shallow Vertisol under a subhumid tropical climate in Guadeloupe, French Antilles. Soil moisture was regulated by irrigating or covering small plots from natural rainfall. Fine nylon mesh bags were used to study the rate of microbial decomposition, and open-ended perforated cylinders were used to estimate nodule herbivory. The chemical traits, especially the lignin: nitrogen ratio, of E. variegata and G. sepium nodules were similar (lignin: N 1.70 and 1.55, respectively), and suggest that the results are probably also applicable to the G. sepium nodules in the associations. Both soil moisture and decomposing agent (microbes or mesofauna) had a significant effect on the nodule disappearance rate, but soil type did not have any apparent effect. The nodule half-life varied from three to seven days under different treatments. The N release rate from the nodules was high, with N half-life varying from three to five days. Herbivory accounted for ca. 10% of total mass and N loss from nodules during the four-week field incubation period, but its importance increased towards the end of the incubation, especially in Vertisol, after the most easily decomposable part of the nodules had decayed. After pruning, the nodule N is released to soil more rapidly than from mulch. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth and yield of coffee plants in agroforestry and monoculture systems in Minas Gerais, Brazil

This research compared coffee plants (Coffea arabica L.) grown in an agroforestry and monoculture systems. Data were collected during two years, on vegetative growth, reproductive development, nutritional status and yield of coffee, besides monitoring air temperature and the tree growth. All trees in agroforestry system increased in growth, resulting in a reduction in the magnitude of the diurnal temperature variation and also maximum temperature. Coffee plants in agroforestry system had less branch growth and leaf production, more persistent and larger leaves, and presented earlier flowering, with a smaller number of productive nodes and flower buds, leading to smaller berry yield than plants in monoculture system. In both systems, the coffee plants showed adequate leaf nutrient levels, except for P and K. The yield of 2443 kg ha^-1 of coffee from the monoculture was greater than 515 kg ha^-1 of coffee from the agroforestry system.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Effects of mulching withAzadirachta indica andAlbizia lebbeck leaves on the yield of sorghum under semi-aird conditions in Burkina Faso

From 1988 to 1990, leaves fromAzadirachta indica andAlbizia lebbeck were used as mulch on sorghum (Sorghum bicolor) in semi-arid Burkina Faso. Five different application modes, each representing a different combination of application timing and mulch composition, were evaluated. In one of the modes leaves were combined with sorghum straw. Leaf quantities applied corresponded to dosages of 25, 50 and 75 kg N ha^–1 in all five modes.Dosage had a significant influence on yield all three years. The mulching effect increased progressively over the years and was more pronounced the higher the dosage. Mean grain yields obtained with the highest dosage, relative to an unmulched control, were 203%, 364% and 422%, for the three years, respectively. Application timing had a significant influence on yields in 1988 and 1989, but the response was not consistent. Differences in response were attributed to variation in the rainfall distribution. Mulch composition did not have a significant influence on yield during any of the three years. Of the five modes evaluated, the ones producing the highest yields over the three-year period of study were azadirachta leaves applied (i) at sowing and (ii) 4–6 weeks after sowing. Yields decreased on both the treated and untreated plots between 1988 and 1989. On the treated plots, yield generally increased again in 1990. This increase was attributed to a residual effect of the mulch. The residual effect probably only explained part of the large difference in yield between treated and untreated plots. It is therefore suggested that most of the nutrients released from the mulch were used by the plants during the same season, which increased production. Furthermore, the mulch layer could have reduced evaporation and thus increased the retention of soil water.

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Résumé De 1988 à 1990, des feuilles d'Azadirachta indica et d'Albizia lebbeck ont été utilisées comme mulch sur une culture de sorgho blanc (Sorghum bicolor) au Burkina Faso, en climat semi-aride. Cinq modes d'application ont été évalués, chacun répresentant une compinaison différente en temps d'application et composition de mulch. Dans un des modes, les feuilles ont été combinées avec des tiges de sorgho. Les quantités de feuilles utilisées ont été équivalentes aux dosages de 25, 50 et 75 kg N ha^–1 et ceci dans tous les cinq modes.Le dosage a eu une influence significative sur la récolte pendant toutes les trois années. Leffet a augmenté progressivement d'année en année et a été plus prononcé pour le dosage le plus élevé. Les moyennes de rendement de graines par rapport au témoin sans mulch, obtenues avec la dose de 75 kg N ha^–1, ont été 203% pour la première année, 364% pour la seconde et 422% pour la troisième. Le temps d'application a eu une influence significative en 1988 et 1989, mais les résultats ont varié entre les années. Les différents résultats ont été attribués à la variation en distribution de la pluie. La composition de mulch n'a pas eu d'influence significative sur aucune des trois années. Parmi les cinq modes évalués, les deux qui ont assurés les récoltes les plus élevées sur la période entière de trois ans, étaient les feuilles d'azadirachta appliquées (i) au semis et (ii) 4–6 semaines après le semis. Les rendements ont baissés entre 1988 et 1989, tant sur les parcelles traitées que sur les parcelles non-traitées. Sur les parcelles traitées, les rendements ont de nouveau augmentés en 1990. Cette augmentation a été attribuée a un effet résiduel du mulch. Cet effet résiduel probablement n'explique qu'une partie de la grande différence en rendement entre les parcelles traitées et non-traitées. Il paraît donc que la plupart des élements nutritifs libérés par le mulch ont été utilisés par les plantes au cours de la même saison, et qu'ils ont ainsi augmenté la production. De plus, la couche de mulch a probablement réduit l'évaporation, résultant en une augmentation de la rétention d'eau dans le sol.

     

Multipurpose tree prunings as a source of nitrogen to maize under semiarid conditions in Zimbabwe

When multipurpose-tree (MPT) prunings are used as a source of nitrogen to annual corps in agroforestry systems, it is important that high levels of N recovery are attained. In order to test the effect of pruning quality and method of pruning application on N-recovery rates, a field experiment was conducted using prunings of five MPT species and two methods of application (surface versus incorporation). There was an interaction of pruning quality and method of pruning application on N recovery and maize grain yield. For most MPT species used, incorporated prunings gave high nitrogen recovery compared to surface applied prunings. In order to achieve synchrony between N supply from prunings and N demand by a maize crop, relatively large amounts of N should be released into the soil before peak N demand by the maize crop. This could be achieved by incorporating adequate quantities of high quality prunings such as those ofCajanus cajan andLeucaena leucocephala. Florida Agricultural Experiment Station Journal Series Number R-05489.     

Decomposition and nutrient release from leaves,twigs and roots of three alley-cropped tree legumes in central Togo

The decomposition of leaves, twigs and roots of two diameter classes (<1.5 mm, 1.5–5 mm) were examined in an alley cropping experiment withGliricidia sepium, Calliandra calothyrsus andSenna sianea in the subhumid savanna of Central Togo using the litterbag technique. The effect of the application of leaves and twigs as mulch or green manure was examined. Gliricidia showed the most rapid mass loss. For all species, leaves decomposed faster than roots. Twigs had the lowest decomposition rate except forCalliandra. The two diameter classes of roots decomposed differently in the three species:Gliricidia fine roots decomposed faster than its coarser root fraction, the coarse roots ofSenna decomposed faster than the fine roots.Termites influenced the mass loss of twigs and roots to varying extents for the different species. In the case of twigs this was markedly influenced by the mode of application: green manure showed more termite frass than mulch.Nutrient release resembled the mass loss patterns of the prunings except for K, which was leached independently from mass loss. The release of the different nutrients was in the order CaGliricidia andSenna seemed to be best for mulch and green manure production at our site.     

Alchornea cordifolia,a promising indigenous browse species adapted to acid soils in southeastern Nigeria for integrated crop-livestock agroforestry production systems

Dry matter (DM) production, crude protein, phosphorus fibre contents and goat preference for eight indigenous browse species,Alchornea cordifolia, Diallum guineense, Ficus capensis, Baphia nitida, Manniophytum fulvum, Homalium aylmeri, Glyphaea brevis andRauwolfia vomitoria, and for two exotics,Leucaena leucocephala andGliricidia sepium, in cultivated plots were compared on acid soil in southeastern Nigeria. Total DM production was higher (P<0.05) forAlchornea cordifolia than for the other browse species.Glyphaea brevis andL. leucocephala were the most preferred species, whileA. cordifolia, G. sepium andR. vomitoria were the least. Mean crude protein content of browse species in this study was higher, whileP and neutral detergent fibre were lower than reported for other browse species in Nigeria. It is argued that the ultimate goal of a crop-livestock agroforestry system such as alley farming, could be better achieved through the complementary use of browse species.     

Nitrogen-Fixing Trees in Small-Scale Agriculture of Mountainous Southeast Guatemala

Abstract

Intensive, subsistence agriculture on hillsides of southeast Guatemala has caused extensive soil degradation. This retrospective study evaluated the success of an agroforestry treatment in improving the sustainability of mountainous agricultural systems in terms of soil nutrient status and erosion control. Three years after maize (Zea mays) and pasture fields were alley-cropped with N-fixing Gliricidia sepium trees, soil nutrient levels were examined and compared to nonalley-cropped controls. Agroforestry treatment showed significantly higher soil organic matter (SOM) over paired plots with no alley-cropping (mean 4.3% vs. 3.2% C, p < 0.05). Mean total N was also higher, with 0.12% in the nonagro-forestry control plots compared to 0.16% underthe agroforestry treatment (p <0.05). Some improvement in soil water-holding capacity(WHC) was also observed in the agroforestry systems. Differences in soil levels of available P, ranging from 8.0 to 64.4 μg/g, were not significant and correlated more with site than with agroforestry treatment versus control. Specific soil and site properties such as texture and slope as well as land use and ground cover management largely influenced improvements in soil nutrient status under the agroforestry treatment at each site. Despite increases in soil nutrients, maize plant productivity showed no response to the agroforestry treatment in terms of leaf chlorophyll index or maize plant height. Three years after the initiation of agroforestry, soil erosion rates showed no difference from paired controls; rates were correlated with ground cover and soil characteristics such as texture and surface rockiness rather than with agroforestry treatment. While soil nutrient status had not reached levels optimum for maize growth after three years, the positive trajectory of change in soil nutrients suggests the potential for using agroforestry systems in mountainous regions of Guatemala to increase the sustainability of agricultural production.