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Origin and history
Potatoes (Solanum tuberosum) originated in South America. Its native home is often claimed to be the Andean region of Peru and Bolivia, where the Incas cultivated the plant mainly for food. In these regions, the potato’s close botanical relatives still flourish and make the gene pool abundant for improvement (Brown, 1993; Rolot & Seutin, 1999). Potatoes are highly diversified by their nature and, at early human settlement in the highlands of Bolivia; men started to select suitable cultivars for food. Potatoes are believed to have been introduced to Europe by the Spanish conquest in the 16th century and remained a botanical curiosity until it was popularised by Antoine-Augustine from 1780 onwards Smith, 1968 (Rolot & Seutin, 1999). It was taken to the United States in 1719 by Scottish-Irish settlers and, during the 19th century, thousands of varieties originated by plant breeders, among which only small numbers were accepted for large-scale production (Smith, 1968). Potatoes were introduced to Africa as recently as the end of the 19th century. The improved species of South American clones that were co-ordinated by the Centro Internacional de la Papa (CIP) in Peru have helped to introduce a wide range of adaptability worldwide. A fresh potato contains about 80% water (SFC, 1992). The solids or dry matter are highly correlated with texture. Mealy textures are usually associated with high solids, while waxy textures are usually associated with low solids. Although individual tastes may vary greatly, varieties with high mealy texture are usually considered best for baking or french-frying. On the other hand, varieties that are of waxy texture are more often used for boiling or in salad. Potatoes are a rich source of carbohydrates and contain valuable amounts of protein, minerals and vitamins. The nutrient level varies not only by variety, but also according to the maturity of the crop and storage time (SFC, 1992).
Climatic requirements
The wild species of potatoes with some food value survive on the snow line as high as about 4 800 m and are more resistant to frost than the modern varieties (Smith, 1968). Potatoes grow in a wide range of climatic conditions and altitudes. In tropical Africa, it does well between 1 800 and 2 300 m as the climate is tempered by altitude, or at lower altitudes during the cool seasons (Smith, 1968; Brown, 1993; Rolot & Seutin, 1999). Potato vine growth is enhanced by day temperatures of more than 27oC as well as by night temperatures higher than 23 oC. Vine growth is further enhanced by long days, while short days stimulate the production of tubers. Low night temperatures of about 16oC are ideal for tuberisation, up to as high as 29oC of day temperatures, above which tuber formation could be inhibited (Struik et al., 1997). The ideal environment that stimulates flowering usually promotes the development of tubers. Yields are usually lower in eastern tropical Africa than in temperate zones. It could be attributed to the detrimental effect of short day length and high air and soil temperature (Smith, 1968; Bradley et al., 2005). Besides the night-time temperature, photoperiod plays an important role in tuberisation, which is triggered when the daylight falls below a certain critical threshold. Under short day-length conditions, tubers are initiated much earlier than under long-day conditions, making tuberisation more abrupt and leading to maturity much faster. Despite this, the origin and early cultivation of potatoes began in the Andes where the days are short throughout the year and where potatoes are especially adapted to short-day conditions. Smith (1968) suggests that short days hasten maturity, reduce growth of tops and increase the efficiency of tuber formation. However, it is more convenient and faster to develop European long-day cultivars under short-day conditions, especially for the production of commercial planting materials.
When long-day material is put under short-day conditions, it will undergo some physiological changes, namely stem elongation will terminate earlier, tubers initiate earlier and plants die earlier than under long-day conditions. In addition, the mass of leaves and stems, as well as the number of leaves per stem would be lower, while leaflets are larger (Brown, 1993; Struik et al., 1997). The ratio of leaf-stem mass is higher under short-day than under long-day conditions. Tuber mass is comparably higher in the early development stage under short-day conditions. However, when cultivars with a long maturity period are grown under long-day conditions, it attains a higher final production despite its later tuber initiation. Overall, the critical day length is severely influenced by temperature and light intensity and it decreases with an increase in temperature or a decrease in light intensity (Smith, 1968).
At low light intensity, tuber mass is higher at an average temperature of about 12oC. Optimum tuber mass occurs with higher light intensity and temperatures higher than about 18oC. However, tuber growth is most favoured by high day temperatures (18- 24oC) and low night temperatures of about 17oC. The number of tubers decreases with increasing night temperatures. A high night temperature favours more growth above the ground than underground, during which plants develop many new leaves, many branches, and flowers. Under such conditions, stolons emerge above the soil, form new stems and leaves and result in a low tuber yield with a small number of tubers. At low temperatures, however, more growth occurs underground than above ground, where plants form a small number of leaves, few or no branches, no flowers, no stolons above ground, but a large number of tubers resulting in a high tuber yield.
Soil and water requirements
Selection of the right soil type is very important for potato crop production. Potatoes are shallow-rooted and sensitive to water stress. Hence, well-drained light-texture soils, such as sandy loams or loamy sands are generally suitable for the production of a high yield of good quality potatoes. Such soils can store large amounts of water and nutrients, even though any soil can become unproductive under poor management. Soils with good structure are loose and friable and the surface of these soils does not form a crust so that they remain open for air and water for further circulation in the crop root zone (Smith, 1968; Brown, 1993).
Potatoes should preferably not be planted in heavy soils. Under water logging conditions, the chemical reaction necessary for maintaining a proper environment for potato roots cannot take place and, when air is excluded, plant materials cannot decompose properly and the potato root cannot grow vigorously. When heavy soils are used, artificial drainage facilities need to be provided and an incorporation of organic matter also makes a big improvement. Studies conducted by Brown (1993) and Struik et al. (1997) confirm that potato yields increase as organic matter and bulk density on Caribu soils increase. Organic matter is important for most crops in general and for potatoes in particular. The ideal potato soil contains up to 3% organic matter, which helps in maintaining its granular structure (Smith, 1968). Organic matter is best maintained under well-mixed crop rotations. Potatoes are usually grown in rotation with other crops to maintain desirable soil structure, fertility status, build-up organic matter, reduce crop loss from insect and disease, and to increase yields (Smith, 1968). Many potato growers follow a crop rotation of not more than two years of potatoes, one year of small grain and one year of grasses. Soils under such rotation would have a good granular structure, high water-holding capacity, adequate aeration, and abundant available plant nutrients. Organic matter usually facilitates ploughing and cultivation, enables potato plants to penetrate the soil readily, retains soil water, provides food for the growth of desirable micro-organisms, and supplies plant nutrients to the crop (Smith, 1968; Brown, 1993). Potato tubers develop and maintain their normal shape better in soils with adequate organic matter. In conditions where continuous potato growing is desired, a breaking cover-crop should at least be seeded just after harvest (Smith, 1968; Brown, 1993).
CHAPTER 1 GENERAL INTRODUCTION
CHAPTER 2 LITERATURE REVIEW
2.1 Community-based irrigation water management: The need for social structure
2.2 Water management and irrigation scheduling
2.3 Cultivation of some economical crops under traditional irrigation
CHAPTER 3 MONITORING AND EVALUATION OF COMMUNITY-BASED IRRIGATION WATER MANAGEMENT AT THE GODINO SCHEME OF ETHIOPIA
3.1 Introduction
3.2 Materials and methods
3.3 Results and discussion
3.4 Conclusions
CHAPTER 4 COMPARISON BETWEEN TRADITIONAL AND SCIENTIFIC IRRIGATION SCHEDULING PRACTICES FOR FURROW IRRIGATED POTATOES IN ETHIOPIA
4.1 Introduction
4.2 Materials and methods
4.3 Results and discussion
4.4 Conclusions
CHAPTER 5 EVALUATION OF GROWTH PERFORMANCE AND DRY MATTER PARTITIONING OF FOUR POTATO CULTIVARS
5.1 Introduction
5.2 Materials and methods
5.3 Results and discussion
5.4 Conclusions
CHAPTER 6 EVALUATION OF TUBER-PROCESSING QUALITY OF FOUR POTATO CULTIVARS
6.1 Introduction
6.2 Materials and methods
6.3 Results and discussion
6.4 Conclusions
CHAPTER 7 GROWTH AND YIELD RESPONSE OF ONIONS (ALLIUM CEPA L.) TO WATER STRESS IN DIFFERENT GROWTH STAGES
7.1 Introduction
7.2 Materials and methods
7.3 Results and discussion
7.4 Conclusions
CHAPTER 8 CALIBRATION AND VALIDATION OF THE SOIL WATER BALANCE MODEL FOR POTATO CULTIVARS, IRRIGATION REGIME AND ONION WATER STRESSED AT DIFFERENT GROWTH STAGES
8.1 Introduction
8.2 Model description
8.3 Materials and methods
8.4 Results and discussion
8.5 Conclusions
CHAPTER 9 PREDICTING CROP WATER REQUIREMENTS FOR POTATOES AND ONIONS GROWN AT DIFFERENT AGRO-ECOLOGICAL ZONES OF ETHIOPIA USING THE SOIL WATER BALANCE MODEL
9.1 Introduction
9.2 Materials and methods
9.3 Results and discussion
9.4 Conclusions
CHAPTER GENERAL CONCLUSION AND RECOMMENDATIONS 10.1 General conclusion
10.2 Recommendations
REFERENCE
