Methods of Soil, Plant, and Water Analysis: A manual for the West Asia and North Africa region
Soil is a non-renewable resource upon which mankind depends for survival. Historically, the rise of great civilizations has been linked to the quality of soil and the availability of water. Equally, the demise of such civilizations is often attributed to mismanagement of soil and land in its broadest sense. Crop productivity and soil fertility are thus synonymous. In today’s overcrowded world, the challenge to feed and clothe the burgeoning populations of developing countries is a daunting task. Yields have to be increased from existing land areas; adding fertility to the soil to satisfy the demands of higher-yielding crops is essential. Soils vary greatly in their capacity to grow crops without fertilizer; even the richest soils experience declining yields without man’s intervention. In essence, soil is not always a perfect medium for growing plants; it is, however, the only one that is available. Soils vary greatly throughout the world; they have inherent weakness, primarily deficiencies in nutrients that are essential to growing crops. Even when adequately supplied in the early stages of land cultivation, the nutrient-supplying capacity invariably diminishes with time. Most soils are deficient in nitrogen (N); it is transient in nature, and plants need a lot of it. In many cases, phosphorus (P) is just as critical; soil chemical reactions reduce the effectiveness of P fertilizers. The soils of the West Asia and North Africa (WANA) region are generally well supplied with potassium (K), and usually don’t need fertilization, especially for low-yielding rainfed crops. In recent years, there is a growing realization has grown that other elements, e.g., micronutrients, are deficient in some areas of the region. As no essential element can substitute for another, it is critically important to identify where and when such deficiencies occur. That’s where the role of soil and plant analysis comes in. Techniques have been developed to evaluate soil fertility constraints based on soil chemical extraction and analysis of the plants that grow on such soils. Both are complementary and, when calibrated with field crop responses to fertilizer, provide a rational basis to identify what elements are missing, and how much fertilizer, whether organic or inorganic, to apply. Therefore, soil and plant analysis laboratories have a vital role in agricultural development of the WANA region. However, the process does not end there. To be meaningful and valid, tests have to be appropriate for the purpose intended and reliable and repeatable. The idea for this soil, plant and water analysis manual grew out of the Soil Test Calibration Program within the region’s national agricultural programs that laid the basis for sound fertilizer recommendations. Thus, it was appropriate that ICARDA should address this fundamental issue. If soil and plant tests are not reliable, the process of sampling and analysis is meaningless and undermines the validity of any agronomic trials. This manual is a cornerstone in ICARDA’s soil and water-related research program as well as its training program and is a vital link with agricultural scientists of the ICARDA’s mandate region.