Climate change impact
Soil nutrient depletion has been one of the leading reasons for the environmental damage caused by the expansion of cocoa plantations into virgin forest lands. These forests provide the cocoa plant with very fertile soil, low weed pressure and a favorable microclimate. CSC is focused on increasing the organic matter content of the soil and improving its water holding capacity thereby increasing the resiliency of the farm to droughts and strong winds. Improving soil structure, nutrient content, and water capacity increases adaptation to environmental risks. Adequate soils facilitate replanting of cocoa and reduce farmers motivation to abandon their cocoa farm and encroach on forest land.
Description of practices
Soil management starts at establishment, conversion of forested land should occur through slash and mulch techniques instead of slash and burn. Mulching, has been found to be beneficial for young cocoa trees, increasing root and shoot size (Carr and Lockwood, 2011). Mulch species should be grown alongside cocoa to reduce the costs of this practice (Carr and Lockwood, 2011). Furthermore, systematic weeding and cutting of cover crops reduces nutrient competition (Akrofi-Atitianti, et al. 2018). The remains of pruning and husks of cocoa can be transformed into compost tea which improves soil nutrient content and facilitates the distribution of nutrients across the farm. Soil nutrient analyses improve inputs selection and management methods. When using fertilizer, yields may not increase if the level of shading is too high or if the plantation is poorly maintained (Schroth, et al. 2016). Shade trees increase soil water retention, by decreasing soil temperatures and evapotranspiration (Schroth, et al. 2016), and prevent nutrient leaching caused by prolonged and intensive rainfall. Drainage systems and protective layers of ground cover reduce soil erosion during floods and heavy rainfall (Dohmen, et al. 2017).
State of the art
Converted tropical forests, sloping, young, and full-sun farms are very susceptible to getting washed out of nutrients (Hartemink, 2005). Full-sun cocoa production systems rely heavily on chemical fertilizers to raise yields. Furthermore, carbon breakdown caused by land clearing is assumed to be the leading cause of soil organic matter loss, erosion, acidification, and mineralization (Tondoh, et al. 2015). The quality of the soil in tropical ecosystems is strongly linked to the plant residue inputs and litter residence times which protect soil and provide food for soil organisms (Tondoh et al 2015). Shade trees protect the soil in cases of extreme rainfall, by reducing raindrop impact on soil and runoff when their litter is left on the plot. However, the results of a field trial in Bolivia showed no difference in field moistures between different production systems (Alfaro, et al. 2015). The water-holding capacity of the soil depends on its composition. In particular, the organic-matter content of the soil will determine this capacity (Smith, 1964).
Practices that improve soil adequacy for replanting and increase yields have a distinct potential in mitigation (less deforestation) and productivity (higher yields). Medina and Laliberte (2017) note that there is still significant uncertainty in terms of adequate levels of mineral nutrients for better cocoa production. The relationship between available potassium levels and drought tolerance in cacao is promising but requires further study. More research is required into which species are most adequate for use in mulching in different regions and into the nutrient competition of companion tree species. The availability of nutrient-specific fertilizers could reduce costs for farmers and improve yield outcomes in the future.
Importance in terms of CSA
Productivity: Soil fertility declines are a leading factor of decreasing cocoa yields in mature cocoa farms (Vaast and Somarriba, 2014). The employment of chemical fertilizer is often not an option for cocoa smallholders, either because of lack of access or its high cost. Mulching, compost teas, and other soil management practices may help increase cocoa farm productivity.
Adaptation: Extreme climatic events and less favourable weather are expected to lead to soil erosion, loss of soil fertility, and water competition. Increasing soil organic content and the water holding capacity is the main objective of CSC adaptation with respect to the characteristics of cocoa farm soils.
Mitigation: By maintaining and improving the characteristics of the soil for cocoa production across its life-cycle the costs of replanting on the same plot are reduced. If successful replanting can be performed, encroachment into native forestland will be less likely and the carbon liberation of land transformation avoided. Some operations, like organic mulching, can also mitigate greenhouse gasses by generating carbon sinks.
Complexity and link to other practices
The effect of land conversion on nutrient composition and the properties of the soil is unclear and may be dependent on localized factors and the original characteristics of the land (for a list of contradicting studies see Dawoe, et al. 2014). Moreover, the quantification of nutrient loss and gain through litter is difficult, there are widely differing estimates. With increasing fertilizer costs (Jezeer, et al 2017) the CSC practices of agroforestry, pruning, and mulching can be cost-efficient alternatives for increasing soil organic matter. Agroforestry systems have superior water retention and water quality than monoculture systems (Jacobi, et al. 2014). Shade trees also reduce soil erosion caused by raindrop impact and create root channels to minimize the negative effects of heavy rainfall. Lastly, cocoa husks left on plantation to decompose increase the number of natural enemies and pollinators (Forbes, et al. 2017).
–Tondoh, J.E., Kouamé, F.N.G., Guéi, A.M., Sey, B., Koné, A.W. and Gnessougou, N., 2015. Ecological changes induced by full-sun cocoa farming in Côte d’Ivoire. Global Ecology and Conservation, 3, pp.575-595.
Case study 1: Bolivia
Microbial biomass and cellulose activity in soils under five different cocoa production systems in Alto Beni, Bolivia – Alfaro-Flores and Morales-Belpaire 2015
As the major crop in the region, cocoa defines agriculture and livelihood for many smallholders in Alto Beni, Bolivia. Detailed measurements of soil characteristics and inputs in different production systems were taken by the authors of this study for 3 years. The aim was to fill a gap in the literature on cocoa by relating microbial biomass to different production systems and input applications. The landscape where this experiment took place was fallow (secondary forest) land and slightly sloping.
Relation to CSA
This article presents research on multiple CSA related practices. It compares different land preparation techniques (slash and mulch vs. slash and burn), production systems (agroforestry vs. monoculture), and input uses (organic vs. conventional). CSC recommends slash and mulch over burning because of the GHG emissions from burning and the positive impact of mulch on cocoa plots. Soil water content and microbial biomass carbon were similar in agroforestry and monoculture plots. Microbial biomass nitrogen was lower in monoculture and highest in organic agroforestry systems even though these effects were not statistically significant. Cellulase activity was also not significantly affected by the production system, but it was higher in organic and successional agroforestry systems. Mulching did not have any significant differences to burning in terms of microbial biomass. The authors note that this is a special case of burning as it is prescribed and controlled and not a wildfire. Other studies on slash and burn show significant reductions in microbial biomass which takes 5 to 10 years to recover. Microbial community efficiency was highest in conventional agroforestry and lowest in organic monoculture. Plant diversity is more important in terms of microbial biomass than the choice of organic or conventional management.
Case study 2: Brazil
Climate friendliness of cocoa agroforests is compatible with productivity increase. – Schroth, et al. 2016
This study looks at shaded cocoa production in southern Bahia, the main cocoa region of Brazil. The authors analyze whether climate-friendly practices are compatible with increased yields. Effects on climate are measured in terms of carbon stocks and the carbon footprint of agrochemical inputs and fuel used. Data were collected in 26 farms through interviews and inventories. The foundation for this study is an earlier publication (Schroth, et al. 2016) in which cocoa stocks of intensified production systems only had half of the carbon stocks of traditional systems. Therefore, the question arose on whether climate friendliness could be enhanced while increasing yields.
Relation to CSA
The authors study whether productivity and mitigation objectives are compatible by drawing on a diverse sample of farms (shade levels ranged from 20 to 90%). Findings of this study suggest that yields in Bahia could be doubled while maintaining a low-input carbon footprint. Positive effects were found in the use of mineral fertilizer in farms that were subject to good maintenance practices and adequate shade. The authors suggest that special incentives should be available for farmers whose carbon stocks are high (for example companies attempting to lower the carbon footprint of their product may be willing to pay more for cocoa from high carbon stock plots). Intensification through mineral soil fertilization can be combined with increasing carbon stocks in plots were current carbon stocks are low to achieve both productivity and mitigation objectives.