The impacts of climate change on agriculture may add significantly to the development challenges of ensuring food security and reducing poverty. We show the possible impacts on maize production in Africa and Latin America to 2055, using high-resolution methods to generate characteristic daily weather data for driving a detailed simulation model of the maize crop. Although the results indicate an overall reduction of only 10% in maize production to 2055, equivalent to losses of $2 billion per year, the aggregate results hide enormous variability: areas can be identified where maize yields may change substantially. Climate change urgently needs to be assessed at the level of the household, so that poor and vulnerable people dependent on agriculture can be appropriately targetedin research andd evelopment activities whose object is poverty alleviation. r 2003 Elsevier Science Ltd. All rights reserved.

The potential impacts of climate change on maize production in Africa and Latin America in 2055

J.J. Stoorvogel, E.M.A. Smaling, 1990. Assessment of soil nutrient depletion in Sub-Saharan Africa: 1983-2000. Wageningen (The Netherlands), The Winand Staring Centre. Report 28, 4 VolL111es; Vollllle 1. 134 p.; 41 figs.; 96 tables.; 138 ref. On request of FAO a methodology.was developed to assess the state of soil nutrient depletion under agriculture in Sub-Saharan Africa for 1983 and the year 2000. The nutrient balance is described with five input and five output factors, which result in a nutrient loss rate. Production figures and data on fertil izer cona~tion for 1983 and projectiona for the year 2000 were provided by FAO. Date on nutrient balances es well as additional country information were collected from the l iterature. Nutrient depletion rates for Sub-Saharan Africa are approximately 20 kg N, 10 kg P:JJ5 and 20 kg KIJ per ha on everage up to a maxinun of 40 kg N, 20 kg PIJ5 and 40 kg KIJ per ha in Eest Africa.

Assessment of soil nutrient depletion in sub-Saharan Africa: 1983-2000.

Cassava or manioc (Manihot esculenta Crantz), a perennial shrub of the New World, currently is the sixth world food crop for more than 500 million people in tropical and sub-tropical Africa, Asia and Latin America. It is cultivated mainly by resource-limited small farmers for its starchy roots, which are used as human food either fresh when low in cyanogens or in many processed forms and products, mostly starch, flour, and for animal feed. Because of its inherent tolerance to stressful environments, where other food crops would fail, it is often considered a food-security source against famine, requiring minimal care. Under optimal environmental conditions, it compares favorably in production of energy with most other major staple food crops due to its high yield potential. Recent research at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia has demonstrated the ability of cassava to assimilate carbon at very high rates under high levels of humidity, temperature and solar radiation, which correlates with productivity across all environments whether dry or humid. When grown on very poor soils under prolonged drought for more than 6 months, the crop reduce both its leaf canopy and transpiration water loss, but its attached leaves remain photosynthetically active, though at greatly reduced rates. The main physiological mechanism underlying such a remarkable tolerance to drought was rapid stomatal closure under both atmospheric and edaphic water stress, protecting the leaf against dehydration while the plant depletes available soil water slowly during long dry periods. This drought tolerance mechanism leads to high crop water use efficiency values. Although the cassava fine root system is sparse, compared to other crops, it can penetrate below 2 m soil, thus enabling the crop to exploit deep water if available. Leaves of cassava and wild Manihot possess elevated activities of the C4 enzyme PEP carboxylase but lack the leaf Kranz anatomy typical of C4 species, pointing to the need for further research on cultivated and wild Manihot to further improve its photosynthetic potential and yield, particularly under stressful environments. Moreover, a wide range in values of Km (CO2) for the C3 photosynthetic enzyme Rubisco was found among cassava cultivars indicating the possibility of selection for higher affinity to CO2, and consequently higher leaf photosynthesis. Several plant traits that may be of value in crop breeding and improvement have been identified, such as an extensive fine root system, long leaf life, strong root sink and high leaf photosynthesis. Selection of parental materials for tolerance to drought and infertile soils under representative field conditions have resulted in developing improved cultivars that have high yields in favorable environments while producing reasonable and stable yields under stress.

Cassava biology and physiology

Publisher Summary This chapter reviews the characteristics identified for improved drought resistance in two frameworks outlined in Turner (2000) and evaluate the potential of these characteristics to improve breeding efficiency. The first framework, the “Drought-Resistance Framework,” identifies the specific physiological and biochemical characteristics that lead to improved yields in drought-prone environments through drought escape, dehydration postponement, and dehydration tolerance. The second framework “Yield Component Framework” considers yield variation in terms of characteristics affecting water use, water use efficiency, and harvest index. Both frameworks are required if progress is to be made in breeding for drought-prone areas using physiological approaches. In recent years, the development of molecular approaches or methods to identify physiological and biochemical traits in breeding populations potentially has major implications for breeding crops targeted for drought-prone environments, and progress in this area of research is reviewed. However, the focus of this chapter is grain legumes, but it is necessary to draw on studies with cereals and other species to enable critical evaluation of traits and strategies.

Adaptation of grain legumes (pulses) to water-limited environments

Common beans (Phaseolus vulgaris L.) originated in the New World and are the grain legume of greatest production for direct human consumption. Common bean production is subject to frequent droughts in highland Mexico, in the Pacific coast of Central America, in northeast Brazil, and in eastern and southern Africa from Ethiopia to South Africa. This article reviews efforts to improve common bean for drought tolerance, referring to genetic diversity for drought response, the physiology of drought tolerance mechanisms, and breeding strategies. Different races of common bean respond differently to drought, with race Durango of highland Mexico being a major source of genes. Sister species of P. vulgaris likewise have unique traits, especially P. acutifolius which is well adapted to dryland conditions. Diverse sources of tolerance may have different mechanisms of plant response, implying the need for different methods of phenotyping to recognize the relevant traits. Practical considerations of field management are discussed including: trial planning; water management; and field preparation.

N. M. Fisher

Papers

The Physiology of tropical field crops

Fisiologi tanaman budidaya tropik

FISIOLOGI Tanaman Budidaya Tropik / editor; Peter R Goldsworthy; N.M. Fisher