Contents & Foreword, Characterizing And ... - IRRI books

The completeness of characterization and classificationIncompleteness in characterization was another weakness of many early attempts tocharacterize and classify rice-growing environments. Several environmental factorsmay be static, but several other parameters are very dynamic in nature. For example,although environmental parameters such as altitude, longitude, latitude, soil texture,landform and slope, and even soil pH are more or less static, parameters such asgroundwater table, depth of flooded water layer, temperature, solar radiation, andothers are very dynamic in nature. An incomplete characterization may lead to imperfectclassification. For example, theoretically, rainfed rice production is not feasiblein areas where rainfall is less than 800 mm. Rainfed rice production has been successful,however, in many inland valleys in the Sudan Savanna Zone in West Africa,where annual precipitation ranges from 550 to 900 mm (Windmeijer and Andriesse1993). The water supply in rice production in this area comes not only from rainfallbut also from the groundwater table, runoff, and seepage from surrounding areas.The concept of minimum data set (MDS) has been proposed for characterizingthe ecological conditions of crop production. This concept has been used in manyprojects, such as the project on the International Benchmark Sites Network forAgrotechnology Transfer (Uehara and Tsuji 1991). The MDS is supposed to providebasic environmental factors that have potential effects on plant growth, health, anddevelopment. The MDS, however, may be too simple for some studies. For example,results of experiments to evaluate rice germplasm for salinity tolerance may be misleadingif soil alkalinity was not included in the environmental characterization of theexperimental sites. Soil salinity is usually associated with soil alkalinity and bothhave negative effects on the growth and development of rice plants. Similarly, Penningde Vries et al (1989) considered that the minimum data sets used in many experimentsto evaluate drought tolerance of rice varieties are not adequate for simulationmodeling. They opined that, to evaluate the level of drought stress in a given environment,parameters such as rainfall, humidity, light, temperature, and soil characteristicsin the root zone are needed. Andriesse and Fresco (1991) noted the weakness ofthe broad agroecological classification of rice environments when they reviewed theresults characterizing rice-growing environments in West Africa.The objectiveness of characterization and classificationThe sources of information used to characterize and classify rice production environmentsare another factor. Most activities to characterize and classify rice productionenvironments in the past were carried out mainly by researchers and scientists orpeople responsible for rice development. The characterization and classification maytherefore be subjective, which consequently renders them less useful. Several technologiesand infrastructures supporting rice production developed based on the characterizationand classification of rice production environments in the past have provento be unsuitable or unsustainable when they are viewed environmentally and socioeconomically.Many farmers in several countries still plant many traditional rice varietiesregardless of the availability of improved rice varieties and extension efforts.Similarly, many large irrigated rice schemes built in Africa during the 1970s and48 Van Nguu Nguyen