Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) or poro (Erythrina poeppigiana) in Costa Rica

Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r² 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r² = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha^–1.a^–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha^–1.a^–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha^–1.a^–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m³.ha^–1.a^–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha^–1.a^–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha^–1.a^–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha^–1 in the E. poeppigiana plots and from 168–184 t.ha^–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients

Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica. For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered. The implications of the models are discussed in detail. Aspects of net primary production in the systems studied are considered. N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana. For part I see Vol. 4, No. 3, 1986 For part II see this issue Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients

Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica.For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered.The implications of the models are discussed in detail.Aspects of net primary production in the systems studied are considered.N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana.For part I see Vol. 4, No. 3, 1986 For part II see this issueAgroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha^–1.a^–1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity.Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha^–1.a^–1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha^–1.a^–1.Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha^–1.a^–1 and underC. alliodora 7.07 t.ha^–1.a^–1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles.The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha^–1.a^–1): For part I see Vol. 4, No. 3, 1986.Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha⁻¹.a⁻¹ cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity. Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha⁻¹.a⁻¹): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha⁻¹.a⁻¹. Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha⁻¹.a⁻¹ and underC. alliodora 7.07 t.ha⁻¹.a⁻¹. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles. The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha⁻¹.a⁻¹): For part I see Vol. 4, No. 3, 1986. Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and cacao with poro (Erythrina poeppigiana) in Costa Rica

The hydrological balances for the agroforestry systems of Theobroma cacao with Cordia alliodora or Erythrina poeppigiana were calculated using measurements taken over four years (1983–1987) of the following parameters: climatic (precipitation, evaporation); edaphological (texture, soil moisture tension, hydraulic conductivity, variations in soil moisture content). Water fluxes (interception, simulation of transpiration and percolation) were estimated from one year of measurements (1986–1987). Weekly samples of percolated water were taken from March 1986 – March 1987 using lysimetric capsules at 100 cm soil depth. N, P, K, Ca and Mg concentrations were determined to calculate the annual leaching losses. Nutrient concentration values were extrapolated for the whole 4 years observation period, in order to calculate leaching losses for the whole study period. Precipitation samples were also taken to determine the corresponding annual nutrient inputs.     

Survival, growth, timber productivity and site index of Cordia alliodora in forestry and agroforestry systems

Matching tree species to appropriate site conditions and stand management is crucial for sound agroforestry production. In this study, survival, growth and site index for laurel (Cordia alliodora (Ruiz and Pavón) Oken.) were measured between 1987–1999 in two forestry (line plantings and pure plantations) and four agroforestry systems (taungya and three laurel – cacao (Theobroma cacao L.) systems) in the lowland humid tropics of Costa Rica and Panama. Mortality ranged between 2 and 52% at age nine years. Poor drainage, flooding and high water tables resulted in low laurel survival on some sites. At age 5, laurel site index was 21 m in cacao – plantain (Musa AAB) – laurel associations (CLP), but only 15 m in line plantings. Diameter at breast height at that age was 28.5 cm in CLP and only 15.6 cm in pure plantations. Laurel growth and site index were high when planted in association with intensively managed crops (e.g., cacao, plantain or taungya sequences).     

Fine root and nodule dynamics of Erythrina poeppigiana in an alley cropping system in Costa Rica

Fine root and nodule production and turnover in pruned 2- and 8-yr-old Erythrina poeppigiana (Walp.) O.F. Cook trees were estimated under humid tropical conditions by applying the compartment flow model (CFM) to fine root and nodule biomass and necromass measured in sequentially taken core samples. Shoot pruning intensities compared were complete pruning (i.e., complete removal of shoots) and partial pruning (i.e., retention of one branch on the pruned stump). The CFM provided reasonable estimates of nodule dynamics but did not apply to fine root data. Over a five-month observation period, nodule production in completely and partially pruned 2-yr-old trees was 58.2 and 115 g tree^–1, respectively, and the corresponding values in 8-yr-old trees were 26.8 and 26.4 g tree^–1. Senescent nodules and fine roots pass to soil organic matter via decomposition. Partially and completely pruned 2-yr-old trees added 95.4 and 50.4 g tree^–1 decomposed nodules to soil, respectively. The respective value for 8-yr-old trees were 26.7 and 36.5g tree^–1. Nodule and fine root turnover was compensated for by new production at 10–14 weeks after pruning. The retention of a branch on the pruned E. poeppigiana tree stump allows better fine root and nodule survival, and enhances tree biomass production.This revised version was published online in November 2005 with corrections to the Cover Date.     

Litter production and nutrient cycling in coffee (Coffea arabica) or cacao (Theobroma cacao) plantations with shade trees

The relative importance of N fixation, organic material inputs and nutrient inputs in litterfall, as justifications for including shade trees in plantations of coffee or cacao, is discussed. According to existing data, N fixation by leguminous shade trees does not exceed 60 kg.N/ha/a. However, these trees contribute 5,000–10,000 kg. organic material/ha/a.Comparisons are made between the leguminous shade tree Erythrina poeppigiana and the non-leguminous timber tree Cordia alliodora. The former, when pruned 2 or 3 times/a., can return to the litter layer the same amount of nutrients that are applied to coffee plantations via inorganic fertilizers, even at the highest recommended rates for Costa Rica of 270 kg.N, 60 kg.P, 150 kg.K/ha/a. The annual nutrient return in this litterfall represents 90–100 percent of the nutrient store in above-ground biomass of E. poeppigiana, and hence the consequences of competition with the crop should not be a serious limitation. In the case of C. alliodora, which is not pruned, nutrient storage in the tree stems, especially of K, is a potential limiting factor to both crop and tree productivity.It is concluded that, in fertilized plantations of cacao and coffee, litter productivity is a more important shade tree characteristic than N fixation.An early version of this review was presented at the CATIE-IUFRO meeting Los Arboles de Uso Multiple en Sistemas Agroforestales, June 1985, Turrialba, Costa Rica.     

Research methods for multistrata agroforestry systems with coffee and cacao: recommendations from two decades of research at CATIE

This paper reviews the research themes and methodologies used by CATIE in agroforestry research with shade trees over coffee (Coffea arabica) and cacao (Theobroma cacao) during the past 20 years. Initially research focused on characterization and production studies (of crop and timber including border areas) of traditional systems using temporary and permanent sample plots on private farms. The assessment area of traditional shade-coffee (or cacao) systems should be the whole plot, including the border areas, and not some subjectively selected central area which supposedly represents unit area productivity. Uncontrolled crop, tree, and management heterogeneity limited extrapolation of early on-farm research results to other farmers' fields. Replicated case studies of best bet technologies (traditional or experimental) on different farms are often preferable to the use of formal experimental designs. On-station research included the use of systematic spacing designs to test extreme shade tree density treatments of coffee. Most nutrient cycling studies were also carried out on-station, using service and timber shade species over coffee and cacao to evaluate the ability of these agroforestry systems to maintain nutrient reserves and diversify production. Plot size (even 36 × 36 m) was limiting for long term research because of inter-plot interference, both below- and above ground, when using fast growing, tall timber trees as shade. These experiences suggest a minimum plot size of 2,500 m². Individual tree designs and tree-crop interface studies (e.g. regression analysis of data taken along transects) are promising experimental/sampling approaches that need further development. The principal research thrusts proposed for the next five years are bio-physical process research on coffee responses to shade and competition with trees (growth, carbon allocation, phenology, disease-pest tolerance, yields and coffee quality effects) and socioeconomic analyses of both traditional and new or improved shade – coffee combinations vs. monocultures. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Timber harvest,damage to crop plants and yield reduction in two Costa Rican coffee plantations with Cordia alliodora shade trees

Both model and field estimations were made of the damage inflicted to coffee plants due to the harvest of timber shade trees (Cordia alliodora) in coffee plantations. Economic analyses were made for different coffee planting densities, yields, and both coffee and timber prices.Damage due to tree felling and log skidding should not be a major limitation to the use of timber shade trees in coffee plantations. The timber price that would balance all discounted losses and benefits to zero, for scenarios with and without trees ranged between 8–20 US $/m³ (current overbark log volume at the saw mill yard is US$ 66/m³). There will be lower margins for coffee damage in high yielding plantations, specially in years of good coffee prices. Nevertheless, the use of timber shade trees is recommended even in these scenarios.     

Smallholder Cacao (Theobroma cacao Linn.) cultivation in agroforestry systems of West and Central Africa: challenges and opportunities

The cultural features, management practice, environmental sustainability, and economic profitability of smallholder cacao (Theobroma cacao)production in West and Central Africa are reviewed. The aim is tohighlight factors affecting the cacao production and marketing sectorand to propose appropriate strategies to ensure sustainable and profitable cacao production in the region. The cacao cultivation system causes minimum damage to soil resources. In terms of carbon sequestration and below- and above-ground bio-diversity, the cacao agroforest is superior to the alternative food crop production land use. The food crop production system is based on the practice of slash-and-burn farming, which, due to population pressure and reduced fallow cycle, is no longer sustainable. Economic profitability analysis of this system in Cameroon showed that, at current prices, even with no value assigned to the tree species, the sector could still be profitable. Based on the current review and our knowledge of West and Central Africa, there is an urgent need to: (a) rationalize and optimize arrangement of the various components in cacao agroforest, (b) domesticate high value and shade tolerant indigenous species such as Gnetum africanum and integrate into the system in order to enhance the system's diversity and profitability, (c) develop shade-tolerant and disease-resistant cacao varieties, (d) integrate small-stock production into the system, and (e) develop an enabling policy environment addressing cacao marketing, plant protection, land tenure and transformation of non-cacao primary products from the cacao agroforests. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temporal changes in soil carbon and nitrogen in west African multistrata agroforestry systems: a chronosequence of pools and fluxes

The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry, a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon (C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha⁻¹; 15 years: 17.6 Mg C ha⁻¹; 25 years: 18.2 Mg C ha⁻¹) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha⁻¹ but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration rates were 3 Mg C ha⁻¹ y⁻¹, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system.     

Modelling of planted legume fallows in Western Kenya using WaNuLCAS. (I) Model calibration and validation

Poor soil fertility is the biggest obstacle to agricultural productivity in Sub-Saharan Africa. Improved fallows can help to raise agricultural productivity in these systems of low financial capital, however, experimental testing of their potential application domain and design is costly and time consuming. Models can evaluate alternative systems relatively quickly and at relatively low cost, but must first be validated to assess satisfactory simulation of the target systems. Specific climatic, edaphic, crop and fallow growth data was used from five sites in Western Kenya to calibrate and validate simulations of maize and improved fallow growth using the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model. The model predicted continuous maize yields across the sites with an R ² of 0.72, an EF (model efficiency) of 0.66 and a CD (coefficient of determination) of 2.73, although the default pedotransfer functions (PTF) for volumetric soil water content used in the model had to be substituted for a tropical soils specific PTF before this was achieved. Predicted maize yield was consistently related to fallow biomass (i.e. higher fallow biomass correlated with higher subsequent maize yields) at two sites and the model predicted maize yields following fallow growth from this subset of the data with an R ² of 0.42. This relationship of fallow biomass to subsequent maize yield was not observed across the whole data set due to incomplete fallow litterfall data, factors not included in the model and associated poor model prediction of recycled tree biomass. After site and tree calibration, the model can thus be applied to assess fallow management strategies for sites limited by water and nitrogen.     

The role of agroforestry in the farming systems in Rwanda with special reference to the Bugesera-Gisaka-Migongo (BGM) region

The Rwandan farmers, faced with a perpetual land shortage, have evolved certain intensive systems of organic agriculture. These systems, particularly the homestead (compound) farming, involve the combination of food, fodder and tree crops. to a certain extent these systems can satisfy the multiple needs of the subsistence farmers living under several risks and constraints. However, they cannot cope with the expanding food demand of the rapidly increasing population. Some multipurpose, low-input technologies and agroforestry approaches have been designed to improve the productivity of these traditional systems; these include inter/mixed cropping systems and rotations, alley cropping with leguminous trees and shrubs, use of planted fallow, planting tree legumes on anti-erosive lines, mixed farming,community forestry and woodlots, and tree planting on farm/field boundaries. The essential aspects of these technologies are briefly discussed.ISAR-IITA FSR PROJECT, B.P. 629, Kigali RwandaISAR-Swiss Intercooperation, c/o Forestry Department, B.P. 617, Butare, Rwanda