THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF COCOA (THEOBROMA CACAOL.): A REVIEW

Abstract

The results of research into the water relations of cocoa are reviewed in the context of drought mitigation and irrigation need. Background information on the centres of production of the cocoa tree, and the role of water in crop development and growth processes, is followed by reviews of the effects of water stress on stomatal conductance, leaf water status and gas exchange, together with drought tolerance, crop water use and water productivity. Leaf and shoot growth occur in a series of flushes, which are synchronized by the start of the rains following a dry season (or an increase in temperature), alternating with periods of 'dormancy'. Flowering is inhibited by water stress but synchronous flowering occurs soon after the dry season ends. Roots too grow in a rhythmic pattern similar to that of leaf flushes. Roots can reach depths of 1.5-2.0 m, but with a mass of roots in the top 0.2-0.4 m, and spread laterally >5 m from the stem. Stomata open in low light intensities and remain fully open in full sunlight in well-watered plants. Partial stomatal closure begins at a leaf water potential of about −1.5 MPa. Stomatal conductance is sensitive to dry air, declining as the saturation deficit increases from about 1.0 up to 3.5 kPa. Net photosynthesis and transpiration both consequently decline over a similar range of values. Little has been published on the actual water use of cocoa in the field. Measured ETc values equate to <2 mm d −1 only, whereas computed ETc rates of 3-6 mm d −1 in the rains and <2 mm d −1 in the dry season have also been reported. Despite its sensitivity to water stress, there is too a paucity of reliable, field-based published data of practical value on the yield responses of cocoa to drought or to irrigation. With the threat of climate change leading to less, or more erratic, rainfall in the tropics, uncertainty in yield forecasting as a result of water stress will increase. Social, technical and economic issues influencing the research agenda are discussed.

Predicting the future climatic suitability for cocoa farming of the world’s leading producer countries, Ghana and Côte d’Ivoire

“…The reason why cocoa is not usually grown in the savanna is mostly because it is drier, not because it is hotter than the rainforest zone; the rainforest zone of Malaysia, which is about 2°C hotter than that of West Africa, is very suitable for growing cocoa (Wood and Lass, 2001). Similarly, the expected temperature increase of the next several decades, with little change in rainfall, will presumably affect cocoa not so much directly via heat stress as indirectly via the increase in ETP and thus decrease in water availability to the crop (Anim- Kwapong and Frimpong, 2005;Carr and Lockwood 2011). In this sense cocoa is different, for example, from Arabica coffee where there is a direct temperature effect because coffee quality, and thus its price, is highly sensitive to ambient temperature (Läderach et al, 2010).…”

“…Among the priority measures to reduce the vulnerability of the West African cocoa sector to climate change is the initiation of breeding programs for greater drought resistance (Carr and Lockwood, 2011). For being effective, these need to be combined with programs to put selected germplasm in the hands of the cocoa farmers, who still commonly use local seeds for planting.…”

“…Cocoa is an understory rainforest tree and is known to be sensitive to drought, though quantitative information on crop water relations from mature field-grown plants are scarce (Carr and Lockwood, 2011). Until recently, climatic forecasts for the West African rainforest belt have been highly uncertain.…”

Analysis of Agroecology and The Requirement of Supplemental Irrigation on Cacao Plants in Lampung

“…Tanaman kakao dikategorikan sebagai tanaman yang sensitif terhadap kekeringan (Carr & Lockwood, 2011). Kondisi defisit air akan lebih berpengaruh negatif terhadap hasil biji daripada pertumbuhan kakao (Moser et al, 2010).…”

A Microeconometric Analysis of Climate Change Drivers for Coffee Crops Transition to Cacao in Mesoamerican Countries

“…Cocoa tree is a sylvatic plant which is known to be sensitive to drought, though quantitative information about the hydric relationship of cultivated plants is scarce [11]. Cocoa has played a fundamental role in wood conservation and biodiversity both in a positive and in a negative way.…”