According to research done by Kumar

According to research done by Kumar, 2013, nitrogen is absorbed by the plant roots in two forms, nitrate form (NO3) and ammonical form (NH4). Most crop plants prefer nitrogen in nitrate form while paddy and few other higher plants prefer nitrogen in ammonical form. Ammonical form of nitrogen is easily converted into nitrate form. However, urea, contains nitrogen in amide form but this form of nitrogen is rapidly converted by soil micro-organisms into ammonical form and then into nitrate form (Vinod Kumar, 2013). Based on the forms of nitrogen they have, nitrogenous fertilizers are classified into following:
Nitrate fertilizers: most common is sodium nitrate or calcium nitrate. Nitrates group of fertilizers are soluble in water and hygroscopic (absorbs moisture from the atmosphere to become sticky). It is alkaline in nature and the constant use of sodium nitrate, creates deflocculation of clay particles and poor drainage. Nitrate is not absorbed by the soil and is liable to fast leaching hence, applied in small doses and repeated at intervals on standing crops (Inadarjit, 2017).
Ammonium fertilizer: ammonium sulphate is the most common. They are acidic and have higher levels of nitrogen than nitrate fertilizers but are less readily available to plants. The ammonical nitrogen has to nitrify in the soil and converted into nitrate before it can be taken up by plants. During fixation, ammonia releases an equivalent quantity of calcium from the soil and the application of ammonium (eg ammonium sulphate) reduces the quantity of reserve calcium in the soil. Repeated and heavy doses of ammonium sulphate without adequate supplies of lime in the soil will lead to acidity. Mainly are used in basal application on standing crops (Inadarjit, 2017).
Nitrate and Ammonium fertilizer: are soluble in water and slightly hygroscopic (eg calcium ammonium nitrate). Both nitrate and ammonium are present and readily available to plants; the availability of ammonium reduces leaching loss. These are generally acidic excluding calcium ammonium which is neutral and used on standing crops and basal application.
Amide fertilizers-are water-soluble and hygroscopic. They are converted to ammonium carbonate and then to nitrates due to action of micro-organisms. The conversion of amides into ammonical and nitrate form takes about 6-7 days. Leaching loss is very low because once amides is converted to ammonical form, it is absorbed by soil colloids and slowly released and nitrified to nitrates. Includes:
Urea- slightly acidic and its application to soil creates a small loss of calcium from the soil. It is desirable that urea be mixed with ashes/ small quantity of soil to facilitate an even distribution to avoid plant damage. It can be used in the liquid form as foliar application.
Calcium cynamide- is non-leachable, synthetic organic fertilizer where its alkalinity is three times as high as that of sodium nitrate, and is advisable for the use on acid soils. Certain intermediary components formed during its decomposition injure tender germinating seedlings (Inadarjit, 2017).
Nitrogen consumption:
Africa accounted for 3 percent of world fertilizer consumption in 2013 with 3.1 percent. Egypt and Morocco having the major share of nitrogen consumption in North Africa. Sub-Saharan Africa accounts for 1.5 percent. Meanwhile, total fertilizer nutrient consumption in the Americas was 24.2 percent, of which North America accounts for 12.9 percent while Latin America and the Caribbean accounting for 11.3 percent. Brazil, Argentina, Mexico and Colombia though, are the major users of fertilizer in the South American region. The share of the Americas in world consumption of nitrogen is 19.7 percent (FAO, 2017).