Are Mineral Fertilizers Panacea for Increase in Crop Yield? Review

Abstract

Fertilizers are important in increasing crop yield and many of the increases in world food production are attributed to the judicious application of mineral fertilizers. Among the 18 essential elements, nitrogen, phosphorus and potassium are the major ones and the first two are imported to and used in Ethiopia. Nitrogen is the most limiting nutrient in plant growth. It is a constituent of chlorophyll, plant proteins, and nucleic acids. Phosphorus is essential component of Adenosine triphosphate, deoxyribonucleic acid and ribonucleic acid, whereas potassium is useful in activation of enzymes, photosynthesis, starch synthesis, nitrate reduction and sugar degradation as well as helping plants withstand stresses like drought, winter hardiness, tolerance to diseases, insect pests and frost damage. The other macro and micro nutrients are also important in the various physiological processes of plants. Mineral fertilizers have been responsible for an important share of worldwide improvement in agricultural productivity and fertilizers account for more than half of the increase in yield worldwide. The yield increase recorded in Ethiopia has been attributed mainly to the use of mineral fertilizers together with improved seeds. It is, however, important to note that fertilizers will be effective if other conditions are fulfilled. These factors include soil factors (soil reaction, clay mineralogy and clay content, moisture regime of the soil, impermeable soil layer, soil texture and bulk density and availability of other nutrients in the soil, availability of moisture;climatic factors (temperature, light intensity and length of the day); crop factors (crop adaptability to local conditions, fertilizer requirement, resistance to disease, pests, drought and other stress factors); fertilizer characteristics and management practices (erosion control, land preparation, planting date and practice, weed, and pest and disease management). Crop yield, therefore, can be improved not by application of mineral fertilizers alone but by the combination of genotype (G), optimum environmental condition (E), appropriate management practices (M) and yield = G x E x M.