Alley cropping was introduced in the humid forest zone of Cameroon to increase soil fertility in 1987, but until 1992 the adoption rate had remained low. To better understand the reasons behind this, three types of on farm trials were established from fully researcher controlled to fully farmer controlled. During the evaluation of the technology with farmers a number of modifications were registered (1) Pruning height and frequency: Because of the difficulties to consistently cut back at 30 cm, farmers decided to slash at ground level as they normally do while slashing the natural fallow vegetation. This equally allowed for more flexibility in time of pruning. (2) Cropping intensity and pattern: Initially, alleys were cropped each year. This however had several shortcomings. Having observed the positive impact of incidental fallow period in a farmer’s field, it was decided to introduce a fallow phase of at least one year. During the fallow period the plot can be used for fodder production, bee farming and production of stakes. (3) Residue management: Fire went incidentally in a farmer’s tree plot after slashing, and the trees were not affected. This gave farmers an alternative way to manage the residue, by controlling the fire, before bringing in other crops such as groundnut and cassava. (4) Agroforestry species: Because Leucaena leucocephala, in spite of it soil fertility restoration potential, rapidly became a noxious weed, farmers have asked for a less invasive species. Calliandra calothyrsus was introduced for this purpose and became a good bee forage. With these modifications, the original alley cropping system has evolved into a rotational tree fallow with higher adoption potential. From about 15 farmers who were testing the technology in 1992, the number increased to 52 in 1996, 120 in 1997 and 236 in 1998.
Tag: alley cropping
Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths
Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched 15N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (two-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44–58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha–1 and Peltophorum an estimated 42 kg N ha–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments.
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 ha1 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
A landscape / lifescape approach to sustainability in the tropics: the experience of the SANREM CRSP at three sites
The Sustainable Agriculture and Natural Resource Management Collaborative Research Support Program (SANREM CRSP), funded by U.S. AID, aims to develop principles and methodologies for achievement of sustainable ecosystem management at the watershed and landscape scale. In contrast to much of the earlier literature in environmental, agricultural, and ecological science which portrays humans as the despoilers of ecosystems, the SANREM approach acknowledges the role of people as integral actors who must be directly engaged in sustainable development if it is to be successful. The SANREM approach, therefore, uses an interdisciplinary, farmer-participatory research, training and information exchange strategy to bridge between scientific knowledge and local expertise in the resolution of problems. A landscape ecology approach is used to describe and understand the complex internal, external, and interactive processes within and between the individual ecosystems of a toposequence transecting two or more agroecological zones. Coupled with the landscape notion is that of “lifescape”, or the human dimension, which includes economic, cultural and social aspects in interaction with the physical and biological dimensions of ecosystems. Interventions appropriate to the local farm community members are designed and evaluated in concert with the ultimate users who are involved in all steps of the research process. The approach includes emphasis on collaboration between biological and social scientists and development practitioners in the U.S. and host countries. It also strives for interinstitutional collaboration that involves private and public institutions from each country as well as the U.S. The SANREM project is considered one of the first of its kind, a pioneering effort to solve complex natural resource and sustainable agriculture problems involving a wide range of stakeholders who may have conflicting interests among themselves. These stakeholders include local communities, international research and development organizations, U.S. universities, host country universities and government agencies, local government and nongovernment organizations (NGOs). Also, there is a need to address experimentally a hierarchical range of spatial and temporal scales across a landscape. In attempting to meet these challenges, we have many successes, many failures and many lessons learned. This chapter outlines the experiences of SANREM at the core sites in the Philippines, Burkina Faso, and Ecuador, and presents critical lessons learned in implementing a large landscape-scale research and education program
Dynamics of soil physical properties under alternative systems to slash-and-burn
A change from slash-and-burn to continuously cropped agricultural systems is occurring in heavily populated areas in the humid tropics. Well managed alternative systems to slash-and-burn can reduce soil structure deterioration, maintain soil fertility, and promote long-term productivity. The objectives of this paper are to describe the dynamics of soil physical properties under slash-and-burn and some alternative systems. Different land-clearing methods and post land-clearing management systems were evaluated on Typic Paleudults at Yurimaguas, Peru, for their effects on soil physical properties such as: bulk density, soil water characteristic, infiltration rate, aggregate stability, and penetrometer cone resistance. Mechanical clearing reduced the infiltration rate from 420 mm h1 before clearing to 35 mm h1 for the straight blade and 95 mm h1 for the shear-blade bulldozing. Straight-blade clearing damaged soil structure the most as indicated by a decrease in the percentage of larger soil aggregates. The practice of planting on raised beds prevented foot compaction of soil near the plants; bulk density was 1.14 and 1.29 Mg ha1 for bedded and flat planted soil, respectively. Of the various agroforestry systems evaluated (multistrata, peach palm production, shifting agriculture low input and high input continuous cropping) bulk density was lower after 4 years for the systems with trees or cover crops. Mean annual soil loss for alley cropping on sloping soils was 0.2 Mg ha1 year1 compared with 53 Mg ha1 year1 for two annual crops per year. The infiltration rate after 5 years of intensive grazing on five associations of legumes with grasses was reduced from 127 to 41 mm h1. Overgrazing caused severe soil compaction and reduced earthworm biomass. Research indicates that the greatest change in soil physical properties occurs during mechanical land clearing. Agroforestry systems improved soil physical properties when cover crops and trees were included in the system.
Soil and water conservation by contour hedging in the humid tropics of Peru
A study was conducted for over 6 years (October 1987–December 1993) in the humid tropics of Peru at Yurimaguas (annual rainfall 2200 mm) on a sloping (15–20%) Typic Paleudult to evaluate the soil and water conservation potential of contour hedgerows of Inga edulis (locally known as guaba). The experiment involved two treatments: (a) sole crops of rice and cowpea in annual rotation and (b) intercropping of annual crops between inga contour hedgerows 4 m apart, replicated three times in a randomised block design. Non-replicated plots of bare-fallow and secondary forest were also monitored for soil loss and runoff. Contour hedgerow intercropping conserved, on average annually, 287 mm water and 73 t ha1 soil, which represented 83% and 93% respectively of the amounts that were lost from sole cropping; it maintained soil nutrients at a much higher level and improved soil physical conditions compared with sole cropping of annuals. The significant soil and water conservation achieved by hedgerows, however, did not translate into a striking crop yield increase during the 5 year monitoring period; only the yields of three out of 15 crops in the last 2 years were significantly higher in hedgerow intercropping than in sole cropping. The lack of response was partly due to the fact that 22% of the land area was lost to the hedgerows and partly that a longer time span may be required to realise the benefits of soil conservation. However, contour hedgerow intercropping is recommended for moderate sloping lands of the humid tropics in Peru, considering the long-term conservation of land resource and the potential for continuous cropping with minimal inputs.
Assessing the adoption potential of hedgerow intercropping for improving soil fertility, western Kenya
The biophysical and socioeconomic performance of hedgerow intercropping for soil fertility improvement was assessed in a farmer-participatory trial in western Kenya over 3 years. Farmers successfully established dense hedgerows but planting and pruning considerably increased labour use during the busiest period of the year. Women did not generally prune the hedges. The yields of hedgerow prunings of Leucaena leucocephala and Calliandra calothyrsus (1–4 t ha1 year1, n = 24) were low compared to potentials in the region (4–8 t ha1). The hedgerows had no effect on grain yield over five seasons. But they reduced slopes from 7.2 to 4.5% within alleys (P < 0.01) and thus were likely to have decreased soil erosion. The average extra maize yield required each year, beginning in the second year, to cover the added cost of hedgerow intercropping was 10.5% (SD = 5.5%) when based on returns to land, and 17.5% (SD = 6.5) based on returns to labour. Although about half the farmers claimed that hedges improved crop yields, after 3 years of experimentation, only about a fifth planted additional hedges and only14% did so to improve soil fertility. It thus appears that the potential for its adoption as a soil fertility practice in this area is low. Hedgerow intercropping appears to have greater adoption potential if its aim is to provide feed for an intensive dairy operation or for curbing soil erosion. Control plots were of little use as farmers were more interested in contrasting test-plot yields with past yields than comparing the test and control plots. Different types of trials may be required to obtain reliable biophysical data on yield response and socioeconomic data on farmer assessment of complex agroforestry technologies.
Biophysical interactions in the alley cropping system in Saskatchewan
Crop production in alley cropping systems and in other mixed-species systems is dependent on the net effects of facilitative and competitive interactions on availability of growth resources (moisture, nutrients, and light) to the crop and trees components of the system. Controlling these interactions can benefit producers through the increased system productivity associated with optimized yields crops and trees. Previous research in the Canadian Prairies has focused on biophysical interactions in shelterbelts. These studies have demonstrated that trees in the shelterbelt system ameliorate soil moisture and temperature by reducing wind speed and trapping snow; this in turn reduces evaporative and heat stress leading to increased yields of intercrops (Marchand and Masse, 2008; Kort et al. 2009). Unlike Eastern Canada and United States (US), there is inadequate information on the on tree-crop interactions under alley cropping systems in the Canadian Prairies. Studies in these areas indicate that nutrient recycling by trees through nitrogen (N)-fixation and litter and root turnover can enhance soil nutrients, especially N thereby reducing fertilizer inputs in the alleyways (Thevathasan and Gordon, 2004). Because of the reduced N inputs and highly efficient capture of nitrate leaching to sub-soils by tree roots, alley cropping systems also hold high promise to reduce N 2 O emissions and groundwater contamination (Doughterty et al. 2009). When plant growth is not limited by water and nutrients, plant biomass production is directly related to the radiant energy up to species-specific saturation points. In the absence of these growth-limiting factors, shading acts as facilitative rather than a competitive effect in agroforestry systems (Jose et al. 2004). Positive ecological interactions discussed here have been demonstrated to increase productivity of food, forage and bioenergy crops in alley cropping systems in Eastern Canada and US, but this has not been done in the Canadian prairies. Thus, it is necessary to assess biophysical interactions in the alley cropping system in this region because impacts of these interactions on plant growth and yield usually depends on many factors including site specific and climatic conditions, age and type of tree species.
Soil property changes in contour hedgerow systems on sloping land in the Philippines
The impact of contour hedgerow systems on soil sustainability under acidic conditions has been widely criticized. A study was undertaken to determine the effects of management and hedgerow species on soil properties. Cassia spectabilis (a non-N-fixing tree legume), Gliricidia sepium (an N-fixing tree legume), Pennisetum purpureum (a forage grass), and Stylosanthes guyanensis (a forage legume) contour barriers were compared with an open field (non-hedgerow treatment) over 1 cowpea and 2 rice seasons. Three types of management viz.: prunings applied + N0P0K0, prunings applied + N50P20K20 and prunings removed + N50P20K20 were used as subplot treatments. The soils were strongly acidic (pH 4.5) and classified as clay Orthoxic Palehumult. Cassia performed better than the other species in terms of pruning biomass, N and P contributions over a period of 20 months. There was a combined positive effect of pruning biomass and fertilizers on rice and cowpea yields in Pennisetum and Gliricidia systems, while a tendency towards a positive effect of pruning biomass on rice was found in the Cassia system. The pruning biomass and/or fertilizer application did not significantly influence the top soil organic C, N and available P in the hedgerow systems. Soil bulk density was significantly reduced by the application of Cassia prunings after 12 months. Organic C, N and P dynamics indicated that in situ pruning biomass was not sufficient to maintain their level in the soil. But the cassia systems with prunings applied + N50P20K20 experienced the lowest degradation in soil organic C (2.1 t ha1) followed by the Gliricidia systems (4.1 t ha1). The overall results imply that the application of pruning and inorganic fertilizer is imperative to conserve soil resources, and non- N-fixing tree species can exert a significant advantage in biomass and thereby in soil N-recycling under acidic soil.
Why tree-crop interactions in agroforestry appear at odds with tree-grass interactions in tropical savannahs
This paper describes recent research findings on resource sharing between trees and crops in the semiarid tropics and attempts to reconcile this information with current knowledge of the interactions between savannah trees and understorey vegetation by examining agroforestry systems from the perspective of succession. In general, productivity of natural vegetation under savannah trees increases as rainfall decreases, while the opposite occurs in agroforestry. One explanation is that in the savannah, the beneficial effects of microclimatic improvements (e.g. lower temperatures and evaporation losses) are greater in more xeric environments. Mature savannah trees have a high proportion of woody above-ground structure compared to foliage, so that the amount of water ‘saved’ (largely by reduction in soil evaporation) is greater than water ‘lost’ through transpiration by trees. By contrast, in agroforestry practices such as alley cropping where tree density is high, any beneficial effects of the trees on microclimate are negated by reductions in soil moisture due to increasing interception losses and tree transpiration. While investment in woody structure can improve the water economy beneath agroforestry trees, it inevitably reduces the growth rate of the trees and thus increases the time required for improved understorey productivity. Therefore, agroforesters prefer trees with more direct and immediate benefits to farmers. The greatest opportunity for simultaneous agroforestry practices is therefore to fill niches within the landscape where resources are currently under-utilised by crops. In this way, agroforestry can mimic the large scale patch dynamics and successional progression of a natural ecosystem.