Foreword

Water scarcity is one of the most pressing issues facing humanity. Globally, 70% of all water withdrawn from rivers and groundwater is consumed by agriculture and yet, surprisingly, water for producing food hardly gets onto the international development agenda except when there is drought and famine such as in the Horn of Africa in 2011. Despite the media attention there still seems to be little appreciation of water's critical role in producing food and fibre at a time when about 20% of the world's rivers run dry before reaching the sea, and more than 1.4 billion people live in water-stressed river basins – a situation that is set to worsen. By 2050 the world needs to produce as much as 70% more food on less land, using less water, energy, fertiliser and pesticides while at the same time bringing down sharply the level of greenhouse gas emissions. Climate change is yet another dark cloud on the horizon.

This is a daunting challenge but history tells us that we should be optimistic. Irrigated farming was, for example, one of the agricultural and engineering success stories of the twentieth century, witness the Asian ‘green revolution’ in the 1960s and 70s. Food production has more than doubled over the past 50 years in response to a doubling of the world's population and agricultural productivity has risen steadily over the past 40 years. Our understanding of the importance of water ecosystem services has also grown and so too has our appreciation of the need for sustainability and for a balance between the ever-conflicting water demands of people, industry, food and the environment.

A diverse range of crops has been covered in the preceding chapters, embracing a wide range of products, all united by the common collective title of plantation crops. An attempt is now made to synthesise the findings reported for each crop, despite the difficulties in making direct comparisons, to review the reporting of research findings, and finally to draw some collective conclusions in order to identify a way forward.

Crop comparisons

Summaries of the main findings from the review process are presented for ease of comparison in Tables 11.1 (origins and centres of production), 11.2 (stages of crop development), 11.3 (plant water relations) and 11.4 (water productivity) for each crop.

Origins and centres of production

In nearly all cases the centres of production of a crop are well away from its centre of origin or diversity (Table 11.1). Tea and coconuts are perhaps exceptional in that they are examples of crops that are still grown in quantity in areas close to their origin, although both, like others, continue to spread around the world. Most plantation crops have until relatively recently been associated with large estates but, in nearly all the examples described here, smallholders now dominate in global terms, the exceptions probably being tea and sugar cane. But that generalisation does not hold for individual countries, where the balance between the two main production systems is one of continuing change. In terms of the total harvested area of each crop, sugar cane is the largest (22.7 million ha) followed by oil palm (14.7 million ha). The smallest in area is sisal (0.4 million ha), a crop in decline, followed by tea (3 million ha, but expanding). The world total for all nine crops covered here is about 84 million ha, but the reliability of some of these area estimates is open to question. To put these figures into context there are, for example, about 225 million ha of wheat, 161 million ha of rice and 159 million ha of maize (grain) (FAO, 2011b).

Introduction

There are two principal types of coffee grown commercially: Coffea arabica L., commonly known as ‘arabica’ coffee, and Coffea canephora Pierre ex Froehner, commonly known as ‘robusta’ coffee. A third (Coffea liberca Bull ex Hiern) is grown only on a very small scale. The useful product is the bean, a relatively heavy seed that ripens within a sweet red fruit. The seeds, rich in caffeine, form the basis of a beverage widely traded and consumed throughout the world.

Many of the physiological characters of coffee can best be understood by recalling the conditions under which these species evolved, particularly the responses to water. The centre of origin of C. arabica is considered to be the cool, shady environment in the understorey of forests in the Ethiopian highlands. At these latitudes (6–9° N) and altitudes (1600–2000 m) the mean average air temperature is in the range 15–20 °C, the annual rainfall is 1600–2000 mm and there is a single dry season lasting three to four months. Only relatively recently has arabica coffee been grown in open sunny situations (Figure 5.1), including regions closer to the equator where there are two annual dry seasons (Cannell, 1985). According to Van der Vossen (2001, 2005), virtually all current cultivars of C. arabica are descendants of early introductions of coffee from Ethiopia to Arabia (Yemen), where they were subjected to a relatively dry ecosystem without shade for a thousand or more years, before being introduced into Asia and South America around AD 1700 and two centuries later into East Africa.

Introduction

The centre of origin of the wild banana Musa species, a giant perennial herb, is believed to be in South-east Asia, where it opportunistically exploits breaks in the rainforest such as river margins (Simmonds, 1962). Wild bananas are jungle weeds, pioneers in the succession to rainforest, and intolerant of shade (Price, 1995). From here, the banana is believed to have spread outwards into the Pacific and then westwards, reaching sub-Saharan Africa about two thousand years ago. The banana became a staple crop in upland East/Central Africa, which is still the greatest centre of cultivation. In the sixteenth century, early European travellers may have taken the banana from West Africa across the Atlantic Ocean to the Americas where it was quickly adopted (Simmonds, 1995).

Bananas can now be found throughout the tropics and subtropics. They are mostly grown between latitudes 30° N and 30° S of the equator, at altitudes up to about 1500 m, except in central and eastern Africa where some clones are grown up to 2000 m (Stover and Simmonds, 1987). In the tropics, they are grown for subsistence and as a cash crop, and play a very important role in diets and in local domestic economies (Figure 2.1). The fruit can be eaten either fresh or after cooking, used for brewing, sold in local markets or exported. The leaves and leaf sheaths are variously used as animal feed, to wrap food for steaming, for thatching, for making mats and ropes, and in handicrafts. In these diverse ways bananas support the livelihoods of millions of people (Fleuret and Fleuret, 1985; van Asten et al., 2011).

Introduction

The sisal plant (Agave sisalana Perrine) is a source of coarse leaf fibres. These are used by industry in the manufacture of twines and ropes, carpet-backing, bags and matting (Figure 8.1). The principal areas of production are Brazil, where it is predominantly a smallholder crop, and East Africa, where it is a large-scale plantation crop (Figure 8.2). The importance of the crop, which is adapted to dry areas, has declined since the mid 1960s due mainly to competition from synthetics made from oil-based polypropylenes. As a result, little has changed in production methods in the last 50 years, and resources for research have been limited (Shamte, 2001).

Sisal belongs to a botanically complex group of American plants, the Agavaceae. It differs from many other plantation crops (except pineapple) in that it has a photosynthetic adaptation (crassulacean acid metabolism, CAM) that facilitates the uptake of carbon dioxide at night. This dramatically improves its water-use efficiency when it is grown under dry conditions.

Introduction

The centre of diversity of the cocoa tree (Theobroma cacao L.) is believed to be within the rainforests of lowland northern South America where the greatest range of variation in natural populations exists (Cheesman, 1944; Simmonds, 1998). The plant is grown for its fruits known as cocoa pods (botanically indehiscent drupes). The pods contain seeds, which are fermented with the mucilage surrounding them and then dried to give fermented dried cocoa, the raw material used in the food industry for the production of chocolate and powder (for drinking, baking and ice cream manufacture). A small proportion is also sold as cocoa butter, which is used in the pharmaceutical and cosmetic industries (Wood, 1985a).

In its natural habitat cocoa is a small tree in the lower storey of the evergreen rainforest. Cocoa has been cultivated since ancient times (at least 2000 years) in Central America, from Mexico to southern Costa Rica. After the arrival of the Spaniards in the sixteenth century, cocoa spread rapidly in the New World. It was introduced into South-east Asia in the seventeenth century and to West Africa in the nineteenth century. By 2008, the total planted area of cocoa in the world was estimated to be about 8.6 million ha, of which 67% is in West Africa and only 17% in the Americas and the Caribbean. It is nearly all grown within 20° N and 20° S of the equator (World Cocoa Foundation, 2010). The largest individual producer is Côte d'Ivoire (1.22 million tonnes; 2.3 million ha in 2008), followed by Ghana (662 000 t; 1.75 million ha), Indonesia (490 000 t; 990 000 ha), Nigeria (250 000 t; 1.15 million ha), Cameroon (227 000 t; 500 000 ha) and Brazil (157 000 t; 641 000 ha) (areas harvested from FAO, 2010a: production from ICCO, 2010). West Africa now produces 69% of the world's annual total of 3.6 million tonnes of cocoa. The market value of the cocoa crop is US$5.1 billion (World Cocoa Foundation, 2010).