A cost-benefit analysis of hedgerow intercropping in the Philippine uplands using the SCUAF model

Soil erosion in the Philippine uplands is severe. Hedgerow intercropping is widely advocated as an effective means of controlling soil erosion from annual cropping systems in the uplands. However, few farmers adopt hedgerow intercropping even in areas where it has been vigorously promoted. This may be because farmers find hedgerow intercropping to be uneconomic compared to traditional methods of farming. This paper reports a cost-benefit analysis comparing the economic returns from traditional maize farming with those from hedgerow intercropping in an upland community with no past adoption of hedgerows. A simple erosion/productivity model, Soil Changes Under Agroforestry (SCUAF), is used to predict maize yields over 25 years. Economic data were collected through key informant surveys with experienced maize farmers in an upland community. Traditional methods of open-field farming of maize are economically attractive to farmers in the Philippine uplands. In the short term, establishment costs are a major disincentive to the adoption of hedgerow intercropping. In the long term, higher economic returns from hedgerow intercropping compared to open-field farming are realised, but these lie beyond farmers limited planning horizons.     

Trees,grasses, and weeds: species choices in farmed-developed contour hedgerows

Innovations intended to conserve soils and improve soil nutrient cycling have not been widely adopted because of technical problems and lack of fit with farmers' cricumstances. Research in Claveria, the Philippines, facilitated and monitored farmers' adaptation of contour hedgerows to fit their particular needs. Farmers tested different establishment methods and many hedgerow species. They initially planted a combination ofGliricidia sepium (a legume tree) andPennisetum purpureum. (grass). Later adoptors chose fodder grasses (especiallySetaria spp.) or naturally occuring vegetation in their hedgerows-either solely or in combination with other species, including weeds such asRottboellia cochinchinensis identified as crop problems. Upland rice and maize farmers who adopted contour hedgerows from 1987 through 1991 were interviewed in 1992. Although hedgerow-crop competition, grazing by neighbors' cattle, and added labor were problems, farmers viewed hedgerows as a way to reduce soil erosion and provide fodder. Farmers planting mulberry were disappointed after a silkworm project folded. Farmers now face the problem of soil nutrient depletion, leading to fallowing of fields with hedgerows and shifting to other parcels. A farmer decision tree model of the minimum necessary criteria for sustainable adoption of contour hedgerows is hypothesized.     

Improving adoptability of farm forestry in the Philippine uplands: a linear programming model

In the Philippines, smallholder farmers have become major timber producers. But the systems of timber production practiced have several limitations. In intercropping systems, the practice of severe branch and/or root pruning reduces tree-crop competition and increases annual crop yields, but is detrimental to tree growth and incompatible with commercial timber production. In even-aged woodlots, lack of regular income and poor tree growth, resulting from farmers’ reluctance to thin their plantations, are major constraints to adoption and profitable tree farming. In the municipality of Claveria, Misamis Oriental, the recent practice of planting trees on widely spaced (6–8 m) contour grass strips established for soil conservation suggests ways to improve the adoptability (i.e., profitability, feasibility and acceptability) of timber-based agroforestry systems. Assuming that financial benefits are the main objective of timber tree farmers, we develop a simple linear programming (LP) model for the optimal allocation of land to monocropping and tree intercropping that maximizes the net present value of an infinite number of rotations and satisfies farmers’ resource constraints and regular income requirements. The application of the LP model to an average farmer in Claveria showed that cumulative additions of widely spaced tree hedgerows provides higher returns to land, and reduce the risk of agroforestry adoption by spreading over the years labour and capital investment costs and the economic benefits accruing to farmers from trees. Therefore, incremental planting of widely spaced tree hedgerows can make farm forestry more adoptable and thus benefit a larger number of resource-constrained farmers in their evolution towards more diverse and productive agroforestry systems.     

Enhancing the food security of upland farming households through agroforestry in Claveria,Misamis Oriental,Philippines

The impact of agroforestry on food security of upland farmers is least recognized and appreciated given that the linkage between them is quite complex and not well understood. The crucial role of agroforestry in enhancing food supply and augmenting family income is commonly ignored. This study aimed to get a deeper understanding of the role of agroforestry in ensuring food security of farming households in the Philippine uplands. A combination of participatory approaches including participatory rural appraisal, household survey, focused group discussions, field experiments and simulation modeling were used for the study conducted in Claveria, Northern Mindanao, Philippines. The first major finding was that the prime responsibility for ensuring adequacy of food production and supply for the farming households rested on the husband and wife. The second major finding based on the simulation results was that agroforestry increased and stabilized corn yields under hedgerow system. Moreover, fruits from perennial crops and trees served as secondary food crops especially during lean months of food supply. The last major finding was that the adoption of agroforestry significantly increased the level of benefits by around 42–137%, compared with the low income from continuous annual monocropping. The key to making upland farm households food secure is to increase the productivity of their farms and home gardens. A good start is to promote the agroforestry system in upland areas, and it is thereby recommended that both national and local government units mainstream their policies and efforts toward promotion of agroforestry adoption in the Philippine uplands.     

Financial evaluation of smallholder timber-based agroforestry systems in Claveria, Northern Mindanao, the Philippines

In the Philippines, timber production on small farms has become profitable as a result of reduced supplies due to extensive deforestation and increasing demand. In the early 1990s, when the price of timber was high, farmers were promised huge returns from tree farming. However, widespread planting of few species has led to oversupply and a sharp decline in the price of farm-grown timber. Moreover, low intercrop yields as a result of competition from fast-growing trees and low timber yields due to poor tree management, further reduce net economic returns. In spite of this, interest in tree farming remains high. This paper examines the private profitability of two tree-maize systems, namely trees in blocks and trees in hedgerows, compared with the alternative of maize monocropping. The analysis reveals that maize monocropping provides higher returns to land at the current timber price, but considerably lower returns to labour, than the maize-tree systems tested. This suggests that tree farming is a more attractive option for labour and capital-constrained households or those with off-farm opportunities that compete for their labour. These farmers may raise productivity and income by planting trees on the excess land that cannot be devoted to annual crops. The analysis also indicates that wide-spaced tree hedgerows are superior to tree blocks, due to lower establishment and management costs, longer periods of viable intercropping and more rapid tree growth.     

Impact of contour hedgerows on upland maize yields in the Philippines

An agricultural production function is used to examine the yield impacts of contour hedgerows constructed using double rows of the N₂-fixing species Desmodium rensonii and Flemengia macrophylla. The analysis uses data from a sample of upland Philippine maize farms and controls for input use and plot characteristics. Results support a hypothesis that the long-run impact of hedgerows on maize yields is positive. However, results suggest that in the short run, hedgerows not only reduce area available for cultivation on a plot, but also reduce the performance of corn in the remaining alleys. For newly established hedgerows an increase in hedgerow area is associated with a reduction in maize yield. The time required for hedgerows to compensate for the area they occupy is found to be approximately eight years. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effects of alley cropping withLeucaena leucocephala and of different management practices on the productivity of maize and soil chemical properties in lowland coastal Kenya

The effects of leucaena hedgerows, mulching with leucaena foliage (0,50 and 100% of harvested foliage), cowpea intercropping and adition of dairy cattle slurry (55 t ha^–1 per maize crop) on the yield of maize from a sandy soil were assessed. The four-year results from five maize crops are reported.Except in the first year, yields of maize grain and stover were significantly reduced by 30% in the presence of leucaena hedgerows. Use of leucaena mulch eliminated this effect; application of all the harvested leucaena mulch (100%) increased the total maize grain yield of the five crops by 44% over sole maize. Hedgerow and mulching management required an additional 36 mandays labour ha^–1 which was more than compensated by the increased maize yields. Furthermore leucaena hedgerows substantially depressed the growth of weeds between cropping seasons.Intercropping with cowpea significantly depressed yields of maize grain and stover when both crops were sown together, but not in later seasons when cowpea was sown four weeks after the maize. Application of slurry increased the total yields of maize grain and stover by 35 and 37%, respectively. The grain yield of maize in leucaena hedgerow treatments fertilized with slurry did not respond to application of more than 50% of leucaena foliage, which suggested that half of the foliage could be spared for feeding to livestock. The cumulative yield of maize grain from the highest yielding organic system was 85% of the yield from the fertilizer treatment.The study, which is continuing, demonstrates that large increases in agricultural productivity are possible through the intercropping of maize with woody forage and grain legumes and the integration of dairy cattle production into the system. It thus shows the importance of exploiting crop/livestock interactions.     

Food-crop-based production systems as sustainable alternatives for Imperata grasslands?

Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to labour tend to decrease in successive years as weed pressure intensifies and soil quality declines.Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades.On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize labour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses.The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.     

Agroforestry in the management of sloping lands in Asia and the Pacific

Steeply sloping lands are widespread in the tropics. An estimated 500 million people practice subsistence agriculture in these marginal areas. Continued population growth has led to the intensified cultivation of large areas of the sloping lands, exacerbating the problem of soil erosion. Although research shows that alley cropping and other contour agroforestry systems can stabilize the sloping lands, these systems have not been widely adopted by farmers. The Framework for Evaluating Sustainable Land Management (FESLM) has been tested in sloping land areas in the Philippines. Sustainable land management must be productive, stable, viable, and acceptable to farmers, while protecting soil and water resources. Farms on which contour hedgerow intercropping has been adopted meet the multifaceted requirements of FESLM, whereas the farmers' current practice does not. Appropriate land management measures for particular locations depend on a complex suite of social, economic, and biophysical factors, and need to be developed in participation with farmers. The role of agroforestry in sustainable management of sloping lands is the subject of networks coordinated by the International Board for Soil Research and Management (IBSRAM) in seven countries in Asia (ASIALAND) and four countries in the Pacific (PACIFICLAND). We review selected outcomes from a wealth of network data. From these results the following conclusions about the sustainability of various agroforestry systems for sloping lands can be drawn: • In the Pacific, soil loss from sloping lands due to water erosion under farmers' current practices is episodic, unpredictable, and possibly not severe; • Agroforestry systems that utilize legume shrubs, fruit trees, coffee (Coffea spp.) or rubber (Hevea brasiliensis) provide useful economic returns, but are not an essential component in terms of soil protection because grass or pineapple (Ananas comosus) planted on the contour are equally effective in reducing erosion; • Agricultural intensification will lead to nutrient mining, reduction of aboveground biomass, declining yields, and less soil protection unless external sources of nutrients are used; • nitrogen can be effectively supplied using legumes; • Cash derived from hedgerow trees and/or shrubs may providean incentive for their adoption by farmers, as well as funds to purchase external inputs such as fertilizers; • Labor may be a major constraint to the adoption of complex agroforestry systems. We also discuss the information management systems required to effectively manage and utilize the extensive sets of experimental and indigenous data being accumulated. We believe such information systems can facilitate technology transfer across and between regions, and improve the efficiency of research into agroforestry and other land-management approaches. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen fixation capacity in the component species of contour hedgerows: how important?

The choice of an appropriate hedgerow species is one of the most critical decisions in exploiting the value of a contour hedgerow system. The implications of hedgerow species with nitrogen (N)-fixation capacity on hedgerow-crop competition and crop productivity have been widely debated. We examined the agronomic significance of N-fixation by comparing the performance of species representing three classes of hedgerow vegetation: A nitrogen-fixing tree legumeGliricidia sepium), a non-nitrogen fixing tree (Senna spectabilis syn.Cassia spectabilis), and a forage grass (Pennisetum purpureum). The 4-year study investigated the hedgerow biomass and nutrient yields, and their relative effects on the performance of two annual crops commonly grown in alley farming systems, with emphasis on hedgerow-crop interference. The work was done on an Ultic Haplorthox (pH 4.8, organic C 1.9%, total N 0.18%).Senna produced 46% more pruning biomass on an annual basis than didGliricidia; N supplied to the alley crops was similar toGliricidia in the first year of observation, but 20–30% higher in the succeeding years. Upland rice and maize grain yields and total dry matter were unaffected by tree species, but the nitrogen-fixing tree exerted less competitive effects on the annual crops growing in adjacent rows. Grass hedgerows reduced maize yields 86% by the second year, indicating an unsustainable drawdown of nutrients and water. We conclude that hedgerow systems composed of a nitrogen-fixing tree did not exert significant advantages compared to a non-fixing tree species, and that factors other than N-fixation were more important determinants for the choice of hedgerow species.     

Grain crop response to contour hedgerow systems on sloping Oxisols

Farming systems that minimize the rate of soil degradation and optimize food crop yields are needed to sustain soil productivity on sloping, acid, infertile soils in the humid tropics. Research was conducted on two Oxisols with slopes ranging from 22 to 30% to evaluate the performance of several contour hedgerow systems, with and without the addition of 60 kg N ha−1 per crop, on rice (Oryza sativa) and maize (Zea mays L.) production. Contour hedgerows were double rows of the tree legume Gliricidia sepium (G); Gliricidia and the native grass Paspalum conjugatum (GPas); Gliricidia and an exotic fodder grass Penisetum purpureum (GPen); double rows of Penisetum (Pen); and a conventional open field (C) farming system without hedgerows. Gliricidia prunings and all crop residues were applied to the soil surface in the alleys, but Penisetum was harvested. Food crop yields in all hedgerow treatments tended to be less than the Control for the first two years, presumably due to the displacement of land planted to the food crop. In the third and the fourth years, the rice and maize yields of Treatments G and GPas exceeded the Control, most consistently when N was not applied. Penisetum reduced food crop yields regardless of N application presumably due to nutrient removal in the fodder. The results indicate that Gliricidia in a contour hedgerow increases food crop yield on strongly acid Oxisols by recycling nutrients and partially supplementing the N demand by the food crops. This revised version was published online in June 2006 with corrections to the Cover Date.     

Potential contribution of Leucaena hedgerows intercropped with maize to the production of organic nitrogen and fuelwood in the lowland tropics

Available information is applied to formulate quantitative hypotheses on the impact of intercropping Leucaena hedgerows with maize upon the physical productivity of grain and fuelwood. Data would indicate that productivity of organic nitrogen (N) by Leucaena hedgerows cut approximately every 8 weeks at a height of 15–30 cm and planted at a distance between rows wider than 150 cm is 45 g m^?1 yr^?1. When soil-N availability is the limiting factor, utilization of Leucaena-N by the maize crop appears to be negatively related to baseline maize production. The grain: Leucaena-N ratio declines from 20:1, when maize productivity is in the order of 500 kg ha^?1, to 3:1, when the 4000 kg level is achieved. Hedgerow N productivity, N utilization by the maize crop, and proportion of land planted to maize were used to derive yield estimates per area of intercropped land under different intercropping arrangement. It seems that the impact of hedge intercropping on maize productivity, although substantial, would be limited to systems where existing production levels of maize are lower than 1500 kg ha^?1. As expected, production per hectare decreases as spacing between Leucaena hedgerows increases. For a 1000 kg ha^?1 baseline, hypothetical increments expressed as percentage of baseline production range from 112% to 28% for between-hedgerow spacings of 1.5 and 6 m respectively. Information analyzed would indicate apotential for Leucaena hedgerow intercropping to increase maize productivity. Research required to substantiate the formulated hypotheses is discussed.     

Insect pests and beneficial arthropods population under different hedgerow intercropping systems in semiarid Kenya

Exploiting the principles of biological control of crop pests is an important management strategy for the resource-poor smallholder farmers of the tropics. The effects of nine hedgerow species on the abundance of major insect pests of beans and maize, and predatory/parasitic-arthropods were monitored over two cropping seasons and the intervening dry period. The tree/shrub species evaluated were Gliricidia sepium, Grevillea robusta, Senna siamea, Senna spectabilis, Flemingea congesta, Croton megalocarpus, Morus alba, Calliandra calothyrsus and Lantana camara. Arthropod abundance was monitored through counts of infested plants and using yellow pan and pitfall traps. Beanfly (Ophiomyia spp.) infestation was significantly higher in the presence of hedgerows (35%) than in their absence (25%). Hedgerows did not influence aphid (Aphis fabae) infestation of beans. In contrast, maize associated with hedgerows experienced significantly lower stalk borer (Busseola fusca and Chilo spp.) and aphid (Rhophalosiphum maidis) infestations than pure maize, the margin of difference being 13% and 11% respectively for the two pests. Ladybird beetles closely followed their prey, aphids, with significantly higher catches in sole cropped-plots than in hedgerow-plots and away from hedgerows. Activity of wasps was significantly greater close to hedgerows than away from them. Spider catches during maize season were 77% greater in the presence of hedgerows than in their absence, but catches during other seasons were similar between the two cropping systems. Differences among hedgerow species were not significant for most of the arthropods monitored, except that beanfly infestation was greater with Gliricidia hedgerows. The study indicates that the effect of hedgerows on pest infestations of crops and their role as refugia for predators cannot be generalized but depends on the specific arthropods.This revised version was published online in November 2005 with corrections to the Cover Date.     

Productivity of alley farming with leucaena (Leucaena leucocephala Lam. de Wit) and Napier grass (Pennisetum purpureum K. Schum) in coastal lowland Kenya

Inadequate supply of fodder is a serious constraint to the potentially-promising small-holder-dairy production system in coastal Kenya. Alley farming could be an approach to addressing this problem. A study of forage production based on Napier grass and leucaena in an alley cropping system was conducted on an infertile sandy soil in lowland coastal Kenya. The effects of leucaena hedgerows,Clitoria ternatea (L.) intercropping, addition of slurry (110 t ha^–1 yr^–1) and two harvesting managements (severe and lenient) on the yield of Napier grass fodder, were assessed. The study was initiated in 1989 and three years results are reported.Napier grass fodder yields did not decline in the presence of leucaena heggerows in most harvests. Generally, the Napier rows adjacent to the hedgerows gave greater yields than in either the centre or sole Napier rows. Interplanting clitoria between Napier rows had a beneficial effect on Napier yields in the later harvests. Compared with sole Napier, the hedgerow treatment receiving slurry increased yield ha^–1 of Napier by 50%, of total forage by 80%, and of nitrogen (measured over two harvests) by 200%.During the first two years of cropping most treatments did not affect the OM and nitrogen content of the soil but by the end of the third cropping year, slurry application increased soil OM by 21% and slurry and clitoria treatments each increased soil nitrogen by 33%.The study demonstrated the increases in the supply and quality of forages for dairy cattle that can be achieved by planting complementary forages, legume and grass species in an intercropping system like alley farming and the benefits to soil composition by the return of slurry.     

Effects of contour hedgerows on water and soil conservation,crop productivity and nutrient budget for slope farmland in the Three Gorges Region (TGR) of China

Soil erosion has long been recognized as a major environmental problem in the Three Gorges Region (TGR) where slope farming is commonly practiced but the local topography is hilly. In consideration of the poor socioeconomic position of local farmers, low cost hedgerows had been introduced as a soil conservation measure to the TGR in the late 1980s. A collaborative research programme was initiated by the Chinese University of Hong Kong, the Chinese Academy of Science, the Huazhong Agricultural University, and the Bureau of Soil and Water Conservation of Zigui County to study the potential of adopting hedgerows in the TGR. Six experimental plots (10 m × 2 m, gradient = 25°) were constructed at Zigui County, Hubei Province to study effects of hedgerows on erosion, nutrient loss and crop productivity. Results indicated that there were significant relationships between rainfall and runoff, and rainfall and soil loss, respectively. Conventional slope farming could not be considered a sustainable agricultural practice because it resulted in severe erosion and low crop yield. Hedgerows per se seemed not to be effective in reducing soil loss and boosting crop productivity, but performances could be greatly improved when they combined with the use of fertilizers. Current farming and fertilization practices, however, generally did not meet N demands of crops. Results and findings of this paper will contribute towards a technical reference for the promotion and adoption of hedgerows in the TGR.     

Contour hedgerow intercropping in the mountains of China: a review

Hedgerow intercropping systems were introduced in China in early 1990s. Achievements in research and extension of contour hedgerow intercropping in China during the past 15 years are reviewed here. Results reported in over 70 published papers have shown that hedgerow intercropping contributes to soil and water conservation, soil fertility amelioration, land productivity improvement, bio-terrace formation, and gives more options for income generation based on local resources in mountain areas. Research and demonstration works on contour hedgerow systems have achieved success by integrating local resources and needs into the system, especially in the dry valleys of the upper reaches of the Yangtze River, and the Three Gorges region. Contour hedgerow intercropping has attracted the attention of researchers, policy-makers, and farmers, and has been taken as an alternative to implementation of the Grain for Green policy, and ecological reconstruction and restoration today. To date, hedgerow intercropping has been demonstrated and applied practically on sloping land in more than six provinces of China, particularly Sichuan, Guizhou, Shanxi, Shaanxi, as well as in the Three Gorges region of Chongqing and Hubei Province. The intercropping system has also been practiced as an optimized technology for conserving farming on sloping lands, improving cash income, and reducing agricultural risks in depressed mountainous regions in southwest and northern China over recent years. Some misunderstandings and problems in studies and extension of the system in China are summarized and clarified, and some recommendations for further research and expansion of the system are also presented in this paper.     

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

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

What do farmers think? Farmer evaluations of hedgerow intercropping under semi-arid conditions

Results from farmer evaluations of exploratory on-farm trials with hedgerow inter-cropping in a semi-arid region of Kenya (the Yatta Plateau of Machakos District) are presented. Hedgerows ofCassia siamea, Gliricidia sepium andLeucaena leucocephala, which were managed by eight farmers to enhance soil fertility, were established in the mid-1980s. Although trial farmers appear convinced of the ability of the technology to increase crop yields, reduce erosion and provide firewood, most did not feel that the short-term risks (i.e. reduction in crop productivity) and the extra labour required were worth the long-term benefits. Hence, few of the eight farmers were willing to extend their hedges. The discussion suggests that in the risky production environment of the Yatta Plateau, where crop yields fluctuate constantly with the amount of rainfall, soil fertility is not of urgent concern to farmers. A participatory case study approach, which emphasizes farmers' opinions, preferences and ideas elicited through regular farmer evaluation exercises, as distinct from on-farm technology testing for validation, is recommended for on-farm research on new and complex agroforestry technologies. This approach permits between understanding of some of the complex socio-economic factors affecting the adoption of hedgerow intercropping and is the most cost-effective way to gather in-depth and contextual information on farmer decision-making and management of externally introduced agroforestry technologies.     

Agroforestry for soil and water conservation in the western Himalayan Valley Region of India 1. Runoff, soil and nutrient losses

Erosion losses were investigated in a field experiment, from 90 × 15 m erosion plots at 4% slope in the western Himalayan valley region of India. The plots were planted with Leucaena leucocephala and Eucalyptus hybrid, either as block plantation or in alley farming with maize (Zea mays), Chrysopogon fulvus grass or turmeric (Curcuma longa). The treatments also included contour planting of sole maize, sole Chrysopogon fulvus grass and a clean weeded cultivated fallow. During the nine year study period, the average annual monsoon rainfall was about 1000 mm and it caused 347 mm runoff and 39 Mg ha^-1 soil loss per year from fallow plots. The runoff and soil loss were reduced by 27% and 45% by contour cultivation of maize. Contour tree-rows or leucaena hedges reduced the runoff and soil loss by 40% and 48%, respectively, over the maize plot, reducing soil loss to about 12.5 Mg ha^-1. This reduction in erosion was primarily due to the barrier effect of tree or hedgerows and micro-terraces formed through sediment deposition along the contour barriers. Such vegetative measures, that are productive while being protective, offer viable alternative for erosion control in areas with gentile slopes of the valley region. High density block plantations of eucalyptus and leucaena almost completely controlled erosional losses and can be recommended for steeper slopes that are vulnerable to heavy erosion. This revised version was published online in June 2006 with corrections to the Cover Date.     

Conservation farming practices for small reservoir watersheds: a case study from Sri Lanka

Traditional agricultural villages in the dry zone of Sri Lanka are minor watersheds where small earth bank reservoirs provide water for irrigation and domestic purposes. The farmers practise rainfed farming on a shifting basis called chena in the reservoir catchments, which are being degraded due to soil erosion. The consequent sedimentation in reservoirs has reduced the extent of irrigation, and the total farming system has lost its ecological balance and economic sustenance. The present study aimed at identifying suitable farming methods for reservoir catchments in order to prevent further deterioration.The investigation was carried out on plot basis to assess soil loss and runoff from forest, scrub and cultivated lands as well as from four other types of farming lands namely plough-farming, bund-farming and two conservation farming practices: strip mulch and graded hedgerow farming. In graded hedgerow farming hedgerow trees are planted across the slope with a mild gradient of 0.4–0.5%. The study was carried out in a reservoir watershed at Maha Illuppallama, Sri Lanka during 1989/90 major rainy season.Results indicated that the two conservation farming practices generate 33–34% annual runoff while replenishing soil moisture of the watershed. Soil loss data showed that the conservation farming practices provide more than 80% protection against soil erosion while bunding can provide only 40% protection compared to existing shifting cultivation practices.