Climate change impact
Rainfall is expected to become more erratic and extreme events like droughts and floods are likely to become more common in the future. Parts of West Africa are becoming dryer over time (Medina and Laliberte, 2017), and cocoa seedlings are particularly vulnerable to extended drought periods (Carr and Lockwood, 2011). Moreover, many regions in Central and South America are already experiencing flooding and the incidence of floods in West Africa is also expected to increase. Farms affected by floods are more vulnerable to pests and diseases. A climate resilient water management approach is required to maintain plantations in the establishment phase and along maturity.
Description of practices
Water harvesting (rainfall water collection in large tanks for use during extended dry periods) and irrigation are useful to reduce water stress. Low-cost irrigation systems using bamboo or plastic bottles increase the accessibility of this practice. Polymers and biopolymers can be used on the farm for increased soil water retention. (Maghchiche, et al. 2009). Drip irrigation refers to controlled irrigation where water is input at low rates through a network of plastic pipes increasing water use efficiency (FAO, n.d.).
When close to a water body, buffer zones should be prepared to avoid flooding (WCF, 2017). Cocoa varieties well adapted to floods have been used in Brazil and the Amazon floodplain and could be promising for other flood-prone regions. Cover crops, some tree species, and contour planting have also been reported to decrease the effects of extreme weather including droughts and flooding. Additional options include the installment of drainage systems (e.g. trenches to reduce the effects of soil erosion caused by flooding (WCF, 2017).
State of the art
Research on water management and cocoa is very limited (Medina and Laliberte, 2017). Early studies on the relationship between irrigation and yield were inconclusive. Studies in Malawi and Malaysia showed significant yield increases in more frequently irrigated plots, though with large variability (Carr and Lockwood, 2011). In Côte d’Ivoire, drip irrigation was found to increase yields using 50% less water than sprinklers. Research shows that the frequency of irrigation is relatively more important than the amount of water used (Ayegboyin and Akinrinde, 2016). Furthermore, there have been reports of successful implementation of low-cost drip irrigation systems using bamboo in Sulawesi, Indonesia (Lumban Gaol, 2016).
Controlled trickle irrigation of crops through. Water is input at low rates through a network of plastic pipes (FAO).
Water use efficiency + Avoid production losses caused by drought + Improve seedling health + Potential yield increases + Better crop health and development + Potential combination with nutrient interventions (Fertigation)
Low cost alternatives:
Drip irrigation using bamboo
Drip irrigation using plastic bottles
Input of water without taking into account distribution, quantity and method considerations.
Possible increase in fungal disease incidence + Increased soil erosion and loss of fertility (OECD, 2017)
Direct manual or mechanical spraying of crops with water.
Prevent wilting + Protection of seedlings from drought
Flooding (Coder, 1994) (WCF, 2017)
Tree damage caused by:
– Soil saturation and tree changes
-Physical damage of water
-Emergence of chronic problems, tree reactivity changes and changing environment
Determinants of flooding damage:
-Tree, site and flood
-Season, water oxigen content and temperature
-Stagnant water is worse than flowing water
Cocoa tree age:
-Seedling mortality increases
-Very young and very old trees are the most vulnerable
Pests and diseases:
-Humidity will increase presence of fungi
-Flood caused tree stress increases vulnerability to pests and diseases
-Pest management may be required for as much as 5 years after the flood
Management for prevention:
-Buffer zones (riparian buffer zones
– Potassium fertilization
-Removal of diseased trees
-No green-wood pruning
Limited capital is one of the main barriers to adoption of drip irrigation, a problem that will be made worse by decreasing yields from more erratic rainfall (Abdulai, et al. 2011). Accessibility problems are persistent, and many farmers consider irrigation systems a luxury (Carr and Lockwood, 2011). As part of climate adaptation plans in West Africa, irrigation infrastructures should be built, they will be valuable in periods of reduced rainfall (Ofori, et al. 2014).
Importance in terms of CSA
Productivity: The climate change effects on water could be considered the most crucial factor in crop productivity loss and food security (Okoffo, et al. 2016). Rainfall variability reduces the planning capacity of farmers (Hutchins, et al. 2015). CSC promotes the adoption of management that makes yields less reliant on rainfall.
Adaptation: The effect of climate change on water availability is twofold: lower and more erratic patterns of rainfall, and increased evapotranspiration as a consequence of increasing temperatures (Schroth, et al. 2016). Water management practices will aid in sustaining yields as rainfall variability increases. In regions where extended and regular droughts are expected to occur, irrigation could be a possible solution, however, its costs may make shifting cultivation or other income sources more profitable (Abdulai, et al. 2017).
Mitigation: Irrigation positively affects the growth of shade trees and cocoa thereby increasing their capacity as carbon sinks. GHG emission increases are assumed to be small for drip irrigation using bamboo or recycled plastic bottles. For machinery intensive systems of irrigation, emission increases should be taken into account.
Complexity and link to other practices
As rainfall becomes more erratic farming management decisions will be better informed by weather forecasts instead of calendars. The literature on increasing resilience to drought has largely been focused on the development of drought-tolerant cocoa varieties (Medina and Laliberte, 2017). Higher temperatures lead to higher rates of evapotranspiration which could be countered by greater shade cover or the planting of cover crops and mulching. Species that increase soil structure (to reduce nutrient leaching due to heavy rainfall or flooding) and/or increase the water retention capacity of the soil should be planted. For agroforests, species with roots at a different depth than cocoa should be selected to reduce water competition (Abdulai, et al. 2017). Water management affects the rate of canopy expansion and, in turn, pruning costs (Carr and Lockwood, 2011). Moreover, incorrect (indiscriminate) irrigation and floods may increase the risk of production losses due to pests and diseases.
Case study 1: Nigeria
Effect of water deficit imposed during the early developmental phase on photosynthesis of Cocoa (Theobroma cacao L.) – Ayegboyin, K. O. and Akinrinde, E. A., 2016
Cocoa trees are especially vulnerable to water stress during early development. Four cocoa genotypes (F3 Amazon, T1, T7, and Amelonado) were tested in Nigeria under four different irrigation regimes (daily and every 3, 5, and 7 days) to study the effects of water stress during this critical period. Researchers collected data on the physiological effects on cocoa of the different interventions. The physiological characteristics of cocoa are directly related to their sensitivity to water stress. Data was recorded in 4-week intervals until the 28th week after sowing.
Relation to CSA
Cocoa seedlings experience increased mortality under drought conditions, but water stress continues to be a critical factor for cocoa in its developmental phase. Irrigation systems are sometimes used to increase resilience and limit the yield-reducing physiological changes induced by water stress. Stomatal closure and dehydration of the photosynthetic apparatus are some of the changes that can be expected during prolonged dry periods and droughts leading to lower growth of the cocoa tree. Different genotypes, however, responded differently to water stress situations. The worst response came from the Amelonado variety, which is commonly used in West Africa. In fact, most Amelonado species in the 7-day interval group had died by the last day of data collection. In terms of watering regimes, daily watering did not translate into greater growth although a linear relationship was identified between water quantity and most morphological variables. Furthermore, leaf growth decreases before photosynthesis and stomatal conductance decrease thereby acting as an early indicator of water stress. Correct irrigation practices along with planting variety increase productivity and adaptation.