Agroforestry Species Research Articles

Casuarina junghuhniana (Casuarinaceae) in India

Casuarina junghuhniana Miq., introduced into India in 1996, is gaining importance as an agroforestry species, with potential use in pulp and paper industry. Tree improvement of the species and attempts at clonal forestry are in progress. A hybrid of Casuarina equisetifolia L. and C. junghuhniana, introduced in 1951 from Thailand, is also planted in India, with the wrong identity as Casuarina junghuhniana. The present paper reviews the silviculture and tree improvement of the species, especially the attempts at introduction to various parts of the world by CSIRO, Australia, with special reference to India. The paper also attempts to resolve the confusion between the hybrid and the pure species, among the planting agencies in India.

Social network effects on the adoption of agroforestry species: Preliminary results of a study on differences on adoption patterns in Southern Ecuador

A case study in South Ecuador serves as an example to understand the dynamics of adoption of agroforestry species. Qualitative research shows that there are potential differences in adoption between two ethnic groups. The adoption rate of Saraguro communal leaders may be an indicator of lower contagion than Mestizo-colonos. Thus, we propose a heterogeneous diffusion model that addresses network exposure effects and a generalized blockmodel for relational data analysis. We hypothesize that Mestizo-colonos have higher adoption rate than Saraguros. The Saraguro indigenous group may have lower access to the information necessary for the adoption of the innovation than Mestizo-Colonos.

Provenance and family variation in growth performance of Eucalyptus tereticornis (Sm.) in a provenance cum progeny trial in Midnapore, India

Eucalyptus tereticornis Sm. is an important species for agroforestry and commercial plantations in India. Results of a combined provenance–progeny trial of E. tereticornis laid out in 2002 at Midnapore (West Bengal) located in eastern tropical region of India are reported and discussed. Twelve provenances representing 70 families from Australia and Papua New Guinea were evaluated up to the age of 3 years. As a local seed source open-pollinated seed collected from a land race, i.e., Mysore gum (commonly known as Eucalyptus hybrid) was used to serve as check material (control). Significant variation in plant height, clean stem height, girth at breast height (GBH) and field survival was observed due to provenances, as well as families within provenances. This offers an ample scope to a breeder for increasing the growth and productivity in E. tereticornis through selection of provenances and families having potential for higher productivity. Heritability (narrow sense) values were appreciable for growth traits. Within provenance individual tree heritability estimates for height, clean stem length, GBH and number of branches at age 3 years were 0.318, 0.215, 0.269 and 0.231, respectively (assuming a coefficient of relationship of 0.4 for open-pollinated families of E. tereticornis). Provenance of Walsh River, Queensland Australia performed best for plant height, clean stem height, GBH, number of branches and field survival. Apart from this, the provenance from Oro bay to Emo, Papua New Guinea and Burdekin river, Queensland also showed good performance. Provenance from Yurammie, SF from New South Wales performed poorest for growth and survival. Correlations on growth traits were high and statistically significant, indicating that substantial gains could be achieved through indirect selection for one trait based on the direct selection for another. Age–age genetic correlations between age 1 and 3 years for the growth traits were highly significant and positive. Geographic clinal variation pattern was observed as latitude was negatively correlated with height and GBH ( P < 0.05); longitude with number of branches (negative, P < 0.05). Fair differences were observed between phenotypic and genotypic coefficient of variability.

Diversity and Economic Importance of Agroforestry species in Dhanore region of Rajouri district, Jammu &amp; Kashmir

Agroforestry system constitutes one of the major sources of livelihood and is an integral part of the economy of the inhabitants of Indian Himalayan Region (IHR). Ironically, very few studies are available on the agroforestry system of the IHR. A study focussing on diversity, nativity, endemism and economic importance of the trees and shrubs constituting the agroforestry system of the Dhanore region of district Rajouri of J&amp;K State was carried out with a view to compile basic data for further studies. A total of 44 species, 30 trees and 14 shrubs, have been listed. The utilization pattern of these species has revealed that all these are used as fuel; 30 species are also used as fodder for cattle; 22 as edibles; 20 as curatives for various ailments and a few species for other purposes. Twenty nine species have multipurpose utility. Strategies and action plan for conservation management of these species have been suggested.

Agroforestry Systems and Podocarpus National Park, Ecuador: Current Status and Recommendations for Future Work

The goal of enhancing human well-being and dignity for the communities surrounding Podocarpus National Park (PNP) is inexorably connected to the goal of protecting ecosystem health and integrity in the southern Andes. While these goals are often viewed as conflicting, one area where they clearly overlap is in agroforestry practices. Agroforestry has the potential to improve food security and economic production while also enhancing forest cover, soil conservation, watershed protection, and habitat quality. A variety of traditional, indigenous, and modern agroforestry practices are available as a foundation for effective sustainability and conservation efforts around PNP. However, the trend of land-use extensification—with large areas dedicated to marginal production of beef and dairy cattle, as well as corn and coffee—continues to lead to new deforestation. Reversing the trend of extensification will require improved technical and resource capacity for agroforestry and reforestation in the region, which can be achieved by strengthening relationships between farmers, farmer organizations, educational and research institutions, and conservation interests. Specific recommendations address agricultural extension/outreach (partnership building), nursery practices, agroforestry species and strategies, and forest regeneration following land abandonment.

Phenology and fruit production of Piliostigma reticulatum (DC), Hochst., an agroforestry forage species in the Sahel

In central Burkina Faso, Piliostigma reticulatum is a more and more adopted agroforestry species by farmers but is increasingly over exploited because of the use of its pods as forage. Therefore, understanding its phenology and fructification becomes urgent for a better management of existing parks. The flowering and fructification stages of two populations (41 trees of 10 years old obtained from stumps and 35 planted trees aged 4 years) were monitored every two days on the same fallow during three consecutive years. Physical parameters of each tree were measured and the pods harvested at maturity, counted, dried and weighted. The fruit production of P. reticulatum happens once a year during the rainy season. Old trees’ flowering as well as their fruit formation started earlier than for younger ones. These stages (flowering and fruit formation) started in July but August is the most determining month because of the regular and sufficient rainfall during this period. Sixty percent of trees aged 10 to 12 years reached 100 % flowering stage while only about 12 % of 4 to 6 years old trees reached this stage. Fifty-six percent of plants aged 10 to 12 years reached 100 % fruit formation stage whereas only 12 % of trees aged 4 to 6 years could reach this stage. The old populations produced more pods than less aged ones (8 kg against 1 kg). Pod production was determined by the magnitude of the tree’s crown, which was strongly correlated with the pod weight (R2= 0.77) and their number (R2= 0.75).

Factors Affecting Agroforestry Sustainability in Bee Endemic Parts of South Eastern Nigeria.

This paper attempts, in an exploratory manner, to identify the various ways in which bad beekeeping and honey hunting practices result in the loss of important multi-purpose agro-forestry tree species in bee endemic parts of South Eastern Nigeria. Both qualitative and quantitative approaches (Participatory Rural Appraisal (PRA), Community Fora, Focus Group Discussions, Key Informant Interviews and Semi-structured interview schedules) were used in an interactive manner to collect data for this study from five randomly selected communities in Nsukka, Igbo-Etiti, Uzo-Uwani, Igbo-Eze South and Udenu Local Government Areas of Enugu State. Results show that beekeeping/honey hunting in the area are traditionally gender-specific occupations, involving only male members of the households, while female members play active role in the processing, preservation and marketing of products. Majority (69.6%) of the beekeepers/honey hunters were within the age range of 31 Ð 50 years and most (75.2%) of them had less than secondary school education. Findings reveal that outright felling of some trees in order to permit the extraction of honey, cutting tree trunks open and/or cutting down tree branches and setting surrounding bush on fire are among the major factors impacting negatively on the agroforestry of the area. However, species of trees particularly at risk include Irvingia gabonensis, young Chlorophera excelsa, Raphia spp., Elaeis guineensis, Brachystegia eurycome, Dialium guineense, Erythrophleum guineese and Strychnos spinosa. Recommendations are proffered towards improving harvesting practices for hive and other non-timber forest products in order to avert the erosion of natural resource-base of the fragile farming ecosystem of the area. Keywords : agroforestry, beekeeping, honey hunting, environmental sustainability. Discovery and Innovation Vol. 19 (1) 2007: pp. 23-32

Decomposition and phosphorus release of agroforestry shrub residues and the effect on maize yield in acidic soils of Rubona, southern Rwanda

Phosphorus release from decomposing leaf biomass of Calliandracalothyrsus Meissner, Tithonia diversifolia Hensley A.Gray and Tephrosia vogelii Hook.f. agroforestry species applied alone or combined with triple super phosphate (TSP) was studied at World Agroforestry Centre (ICRAF) laboratory for 56 days using an incubation method. The effects of above treatments on maize yield were evaluated in the field at Rubona, southern province of Rwanda between the years 2001 and 2004. The net cumulative phosphorus (P) mineralised ranged from 16.2 to 212.2 mg P kg−1. The net P mineralisation rates from green manure, TSP applied alone or combined with green manure decreased in the order green manure > green manure + TSP > TSP > lime > control. The best plant residues quality for predicting P mineralisation is total P, C, and C:P & C:N ratios. Relative to the control, leaf biomass combined with TSP resulted in six times higher maize grain yield at the end of the experiment i.e., from 0.9 to 7.1 t ha−1. In the fourth season, application of Tithonia diversifolia Hensley A.Gray green manure combined with TSP at 50 kg P ha−1 resulted in higher maize yield (25% increase) than TSP and Tithonia diversifolia Hensley A.Gray (9% increase) applied alone at the similar rate. Therefore, application of plant residues and TSP alone might not be sufficient to meet maize plant P requirements and to achieve the yield potential of maize in the Rubona soils unless supplemented with mineral fertilisers.

When Are Native Species Inappropriate for Conservation Plantings?

Summary No species, native or nonindigenous, should be used in planting programs without considering its invasive potential (i.e., by risk assessment). Increased dispersal from tree plant-ing can be the catalyst in converting grassland to woodland when accompanied by change in ecosystem keystone pro-cesses. Consequently, tree planting in North American prai-rie represents a contradiction to conservation of imperiled prairie ecosystems. Indeed, woody plant invasions resulting from introduction of species for aesthetics, conservation, and agroforestry is a global problem. 16,17 If conservation of native species and native grasslands is considered an impor-tant goal in conservation, then programs and activities that facilitate the spread of invasive species, both native and nonindigenous, should be curtailed.

Gas exchange responses of Eucalyptus, C. africana and G. robusta to varying soil moisture content in semi-arid (Thika) Kenya

A dramatic decline in forest cover in eastern Africa along with a growing population means that timber and poles for building and fuelwood are in short supply. To overcome this shortage, the region is increasingly turning to eucalyptus. But eucalyptus raises environmental concerns of its own. Fears that it will deplete water supply, affect wildlife and reduce associated crop yields have caused many countries in the region to discourage farmers from planting this exotic. This paper is part of a series of investigations on the growth and water use efficiency of faster growing eucalyptus hybrids, which was introduced from South Africa to Kenya. The hypothesis is that the new hybrids are more efficient in using water and more suitable for the semi-arid tropics than existing eucalyptus and two popular agroforestry species. Gas exchange characteristics of juvenile Eucalyptus grandis (W. Hill ex Maiden), two eucalyptus hybrids (E. grandis × Eucalyptus camaldulensis Dehnh.), Grevillea robusta (A. Cunn) and Cordia africana (Lam) was studied under field and pot conditions using an infrared gas analyzer was used to measure photosynthetic active radiation (PAR), net photosynthetic rate (A), stomatal conductance (gs) and transpiration rate (E) at CO2 concentrations of 360 μmol mol−1 and ambient humidity and temperature. A, E and gs varied between species, being highest in eucalyptus hybrid GC 15 (24.6 μmol m−2 s−1) compared to eucalyptus hybrid GC 584 (21.0 μmol m−2 s−1), E. grandis (19.2 μmol m−2 s−1), C. africana (17.7 μmol m−2 s−1) and G. robusta (11.1 μmol m−2 s−1). C. africana exhibited high E values (7.0 mmol m−2 s−1) at optimal soil moisture contents than G. robusta (3.9 mmol m−2 s−1) and eucalyptus (5.3 mmol m−2 s−1) in field experiment and G. robusta (3.2 mmol m−2 s−1) and eucalyptus (4.2 mmol m−2 s−1) in pot-grown trees. At very low soil moisture content, extremely small gs values were recorded in GC 15 and E. grandis (8 mmol m−2 s−1) and G. robusta (14 mmol m−2 s−1) compared to GC 584 (46.9 mmol m−2 s−1) and C. africana (90.0 mmol m−2 s−1) indicating strong stomatal control by the species. Instantaneous water use efficiency ranged between 3 and 5 μmol mmol−1 and generally decreased with decline in soil moisture in pot-grown trees but increased with declining soil moisture in field-grown trees.

Influence of varying light regimes on photosynthesis and related variables on tree seedlings of Warburgia ugandensis Sprague and Polyscias fulva (Hiern) harms

The physiology of seedlings of Warburgia ugandensis and Polyscias fulva were studied at varying light levels. Photosynthesis was significantly higher in P. fulva(1.4 mmols CO2 m-2 s-1) than in W. ugandensis (0.3 mmols CO2 m-2s-1) when grown in full sunlight. However, photosynthesis was not significantly (P > 0.05) different under moderate and dense shades (PPFD about 600 mmols m-2s-1 and 350 mmols m-2s-1 respectively) for both species (and ranged between 0.4 and 0.5 mmols CO2 m-2s-1). Generally, P. fulva seedlings had significantly (P < 0.05) greater reductions (from 1.0 to 0.4 mmols CO2 m-2s-1) in photosynthetic rates in response to increasing shade than did W. ugandensis (0.6 to 0.4 mmols CO2 m-2s-1). However, W. ugandensis attained significantly (P < 0.05) higher photosynthetic rates under shade conditions (0.6 mmols CO2 m-2s-1) than full sunlight conditions (0.3 mmols CO2 m-2s-1). Leaf temperatures were highest (30°C) in full sunlight and lowest (27°C) in dense shade for both species. Generally, stomatal conductance, transpiration and water use efficiency showed significantly (P < 0.05) higher values for shade grown W. ugandensis and full sunlight grown P. fulva. Water use efficiency for P. fulva (2.3 mmols CO2 mmol-1 H2O) was significantly (P < 0.05) higher that for W. ugandensis (1.5 mmols CO2 mmol-1 H2O) in full sunlight than. It was concluded that P. fulva was also less adapted to growth at low light intensity while W. ugandensis was better adapted to growth at low light levels because of its significantly greater ability to maintain higher rates of photosynthesis in low light intensity. Therefore in East Africa P fulva can be a better agroforestry species than W. ugandensis. Key words: Net carbon exchange, forest tree seedlings, shade, Warburgia ugandensis, Polyscias fulva

Variability in seed- and seedling-related traits of Millettia ferruginea, a potential agroforestry species

Millettia ferruginea (Hochst.) Baker is a potential agroforestry species endemic to Ethiopia. No documented information exists about genetic variation in this species, thus baseline information is needed to initiate improvement program. Here, we quantified variations in seed size, germination and seedling growth at nursery stage based on seeds collected from six sites across the natural range of distribution of the species in Ethiopia. All seed- and seedling-related traits exhibited highly significant differences among seed sources (P < 0.01), and the magnitude of genetic variation was substantially higher (77–99%) than the environmental variation. The genetic advance as percent of the mean was higher for germination capacity (69.4%) and seed weight (31.7%) than for other traits, suggesting that the population means for these traits may be changed considerably by selecting the superior 5% of the genotypes. There were strong phenotypic (rp = 0.81) and genotypic (rg = 0.89) correlations between seed width and seed weight, so also between seedling height and root collar diameter (rp = 0.95 and rg = 1.00). In conclusion, the results reveal the existence of substantial genetic variation, which can be utilized to initiate tree improvement program of the species and for gene conservation in seed banks.

Australian acacias as multi-purpose agro-forestry species for semi arid regions of Africa

Australian acacias as multi-purpose agro-forestry species for semi arid regions of Africa

Allelopathic potential of Tetrapleura tetraptera leaf extracts on early seedling growth of five agricultural crops

Interference of allelochemicals present in some multipurpose trees on growth and development of adjoining crops necessitate the evaluation of the compatibility of the tree with various crops before integration into an agroforestry system. The allelopathic potential of Tetrapleura tetraptera (Schum and Thonn.)Taub, a multipurpose tree, considered as a potential agroforestry species, was examined using aqueous leaf extracts at different concentrations in laboratory bioassays. The extractions were done for 24 h and 48 h durations. The extracts stimulated production of lateral roots in Lycopersicon esculentum Mill. but inhibited it in Abelmoschus esculentum L. The 24 h extract significantly reduced shoot length at 25% concentration and above in Amaranthus spinosus L. while the 48 h extract significantly stimulated it at the same concentrations in L. esculentum and A. esculentum. However, both shoot and root lengths of Capsicum annum L. were significantly inhibited at all extract concentrations up to 79 and 73% respectively. Significant inhibition of root length at almost all concentrations in all the bioassay species showed that root length is a more sensitive indicator of phytotoxic activity. The degree of inhibition increased with increasing concentration of the 24 h extract.

Potential Nitrification and Nitrogen Mineral of Soil in Coffee Agroforestry System with Various Shading Trees

The role of shading trees in coffee farms has been well understood to establish suitable condition for the growth of coffee trees, on the other hand their role in nitrogen cycle in coffee farming is not yet well understood. The objectives of this study are to investigate the influence of various legume shading trees on the concentration of soil mineral N (N-NH4 + and N-NO3-), potential nitrification and to study the controlling factors of nitrification under field conditions. This field explorative research was carried out in Sumberjaya, West Lampung. Twelve observation plots covered four land use systems (LUS), i.e. 1) Coffee agroforestry with Gliricidiasepium as shade trees; 2) Coffee agroforestry with Gliricidiaas shade trees and Arachis pintoias cover crops; 3)Coffee agroforestry with Paraserianthes falcataria as shade trees; and 4) Mixed/multistrata coffee agroforestry with Gliricidiaand other fruit crops as shade trees. Measurements of soil mineral-N concentration were carried out every three weeks for three months. Results showed that shade tree species in coffee agroforestry significantly affected concentrations of soil NH4 +, NO3- and potential nitrification. Mixed coffee agroforestry had the highest NH4+/N-mineral ratio (7.16%) and the lowest potential nitrification (0.13 mg NO2-kg-1 hour -1 ) compared to other coffee agroforestry systems using single species of leguminous shade trees. Ratio of NH4 + /N-mineral increased 0.8—21% while potential nitrification decreased 55—79% in mixed coffee agroforestry compared to coffee agroforestry with Gliricidia or P. falcatariaas shade trees. Coffee agroforestry with P. falcatariaas shade trees had potential nitrification 53% lower and ratio of NH4 + /N-mineral concentration 20% higher than that with Gliricidia. Coffee agroforestry with P. falcataria as shade trees also had organic C content 17% higher, total N 40% higher, available P 112% higher than that with Gliricidia. The presence of A. pintoiin coffee agroforestry with Gliricidiareduced 56% potential nitrification but increased 19.3% of NH4+/N-mineral concentration. The low soil potential nitrification in the mixed coffee agroforestry had close relationship with the high content of soil organic matter. Key words : Nitrogen-mineral, nitrification, shading trees, agroforestry, Coffea canephora, nitrate, organic matter, intercropping,Gliricidia sepium, Arachis pintoi, Paraserianthes falcataria.

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.

A light-intensity controlled, mist system with water and power backup for rooting cuttings of agroforestry species

Rooting of cuttings is an important part of many components of agroforestry and horticultural research. A technique for rooting cuttings in which the frequency between misting is controlled by environmental sensors is reported here. In developing countries variability in water pressure (or lack thereof) and voltage levels for mist systems often greatly comprises research involved with rooting of cuttings. These problems were overcome with an electrical system comprised of a permanently charged truck battery with a DC mist controller and a high pressure pump. An 800 l ground level storage tank with float valve provided a water reservoir. This system was capable of operating a 2.2 m by 2.2 m, high-pressure, mist bench for about 8 h completely independent of water and electricity. As an added advantage, the mist frequency was proportional to light intensity (and air temperature), thus avoiding over watering.

Growing eucalypt plantation sawlogs on the Gippsland Plains in southern Victoria: A case study

Summary This case study is based on the growth of a 10-y-old plantation at Bairnsdale in Victoria's East Gippsland. The site is owned by the local water management authority. East Gippsland Water, and contains both a dryland blue gum (Eucalyptus globulus) plantation and an irrigated agroforestry trial using municipal wastewater. The irrigated agroforestry trial consists of three eucalypt species watered by two different sprinkler systems. The set-up costs and the relatively poor recorded growth suggest that this is a very expensive way to grow sawlogs. Observations and growth measurements indicate that spotted gum (Corymbia maculata) is a far better agroforestry species than either Sydney blue gum (E. saligna) or southern mahogany (E. botryoides.) From an agricultural viewpoint, this agroforestry trial has provided good shelter and feed for a successful beef cattle venture. Without data to quantify its effect on agricultural productivity, it is difficult to evaluate the trial's overall success. The dryland blue gum plantation has recorded moderate to poor growth. This result, however, must be viewed in the context of the area receiving 17% less than the long-term average annual rainfall since the plantation was established in 1996. Any continuation of this trend, as forecast by CSIRO predictions of global warming, has potential to further reduce the long-term suitability of what was already a marginal site for this species. The results suggest that it may be wise to limit future blue gum sawlog plantations in this area to sites with long-term rainfall averages of at least 800 mm y−1, and to plant more drought-tolerant species such as sugar gum (E. cladocalyx) or spotted gum in the 600–800 mm rainfall zone.

Decomposition and nutrient release from pruning residues of two indigenous agroforestry species during the wet and dry seasons

The decomposition of leaves from Cordia africana Lam. and Albizia gummifera G. F.Gmel was investigated during the wet and dry seasons at Wondo Genet (Ethiopia). Litterbags of leaves were buried in soils under farmland and shaded-coffee agroforestry systems. Residual matter was recovered after 4, 8, 12, and 16 weeks and analysed for nitrogen (N), phosphorus (P), potassium (K), cellulose, lignin, soluble polyphenol and condensed tannin content. Mass-loss and release of N, polyphenols and condensed tannins were greater from Albizia leaves than from Cordia leaves, suggesting that a high polyphenol content does not necessarily retard decomposition. The rates of mass loss and release of the majority of leaf constituents were considerably faster during the wet season than during the dry season. Lignin decomposition, however, proceeded more rapidly during the dry season, and no significant seasonal differences were observed for polyphenol decomposition. The decomposition kinetics of most leaf components during the wet season were best described by a single-exponential model, but a quadratic model provided the best fit during the dry season. Initial leaf chemistry and season were important decomposition factors, while land-use effects were negligible. However, land-use effects showed distinct seasonal differences, with leaf litter decomposing more rapidly in soil under shaded-coffee than under farmland management, especially during the wet season. This study also demonstrated that polyphenol content does not show the predictive effects it has been attributed to have and that other constituents, such as condensed tannins, would be better suited for this purpose.

Effect of organic inputs from agroforestry species and urea on crop yield and soil properties at Wondo Genet, Ethiopia

The effect of combined inputs of green manure (GM) and urea on maize (Zea mays L.) productivity and soil characteristics was studied in an on-farm trial at Wondo Genet, southern Ethiopia. The GM species used were the legumes Albizia gummifera G.F. Gmel and Milletia ferruginea (Hochst.) Baker and the non-legumes Cordia africana Lam and Croton macrostachyus Del. The GM and urea were applied separately or combined in different proportions to give equal rates of 100 kg N ha−1, while varying amounts of P and K were supplied by the GM. The experiment was carried out for two consecutive cropping seasons, but treatments were applied only during the first season. Yield increased by 10–84% in the combined treatments compared to the control, with the increase being significant in those treatments containing GM from Cordia and Croton, which had higher P and K but lower N and total polyphenol contents than those from Albizia and Milletia. Increasing the proportion of GM from the non-legumes tended to increase yield, but the opposite was true when the proportion of GM from the legumes was increased. This suggests that N interacted negatively with polyphenols, and/or the P and K supply from GM was more important than that of N. However, treatment effects on soil properties were not pronounced. It was concluded that a ȁ8modestȁ9 input of ≤3.0 Mg ha−1 GM from Cordia/Croton might effect a reasonable yield but that the additional use of inorganic fertilisers is necessary for the GM to have a substantially increased effect. In addition, when organic materials having both high N and high total polyphenol contents (e.g. Albizia and Milletia) are used, they should constitute the smaller proportion of the GM/fertiliser mixture.