Types of fertilizers

Plants build their bodies with “blocks” — chemical substances collected from the environment, like carbon from the air, and water and minerals from the soil. The sun provides crops with the energy to drive the long chain of transformations to produce carbohydrates, proteins, fats, and fibre, all valuable constituents of yield and ultimately food for humans and animals. For healthy growth plants require about 17 nutrients. Inorganic substances, containing nutrients demanded by crops are called fertilizers.

Most of the agricultural land in Africa is not considered highly suitable for cropping, because extremely low soil fertility levels limit farmers’ yields. Furthermore, low-input farming fails to replenish nutrient reserves mined by crops. To avoid further soil degradation and inevitable drop in yield levels, growers should use fertilizers. Unlike the organic component of the soil, inorganic fertilizers applied on top of the ground or incorporated into the upper soil layer deliver vital nutrients directly to the roots in immediately available for plant uptake and assimilation form. Simply put, fertilizer is the food for the crop. By applying it one significantly simplifies the long chain of complicated processes from root exploration to nutrient extraction and absorbing, and immediately gets a vivid positive respond.

For healthy growth plants require about 17 nutrients. Among them, nitrogen is known to be the most limiting followed by potassium and phosphorus. These three nutrients are called primary, as they are demanded in large quantities compared to other elements. Nitrogen is the main constituent of proteins. Its supply determines the plant’s growth, vigour, and yield. Nitrogen is highly mobile in soil, which makes it prone to volatilisation and leaching. Nitrogen is also acquired by microorganisms. However, one should not just confine oneself to nitrogen fertilizer. In reality, the efficiency of each applied kilogram of nitrogen fertilizer is directly related to sufficient availability of other nutrients. Phosphorus is vital for adequate root development. Its availability directly influences the ripening of seed and fruit. Further, the role of potassium is very often underestimated in crop nutrition. The effect of the application of potassium-containing fertilizers might be masked by the response from nitrogen, especially during the initial stages of growth. Vigorous growth and intensification of green colouration of leaves are the consequences of using nitrogenous fertiliser alone, but also in combination with potassium. Nevertheless, the role of potassium in crop production is difficult to overestimate. Potassium is a key element to water balance in plants, which drives their vigour. The timely supply of potassium to crop tissue provides a synergetic (mutually beneficial) effect on nitrogen, increasing its assimilation. Potassium is associated with root growth, transport of nutrient compounds between different plant organs, crop quality and crop resistance to lodging, disease and drought. A balanced crop nutrition approach is crucial to provide the right ratio of nutrients throughout the growing season, according to crop requirements and soil conditions. The correctly designed fertilizer programme should be based on the results of soil analysis and yield target (nutrient removal). It should therefore consist of basal application and in-season top-dressing.