Keywords: Urea, Nitrogen fertilisation, Ammonia volatilization, Crop responses to urea, Urease inhibitors, Urea compared with ammonium nitrate.

Synopsis:
The use of urea as a nitrogenous fertilizer has increased very rapidly during the past decade and the characteristics of the behaviour of the compound in soil have been defined by many detailed studies. Rapid enzymatic hydrolysis may lead to the formation of free ammonia and in practice the severity of the problems which arise depends on a number of interacting factors. These include the rate and method of application, the nature of the soil and temperature and rainfall patterns. The problems may largely be overcome by working urea into the soil but this is often impracticable and in consequence the risk of variability of fertilizer effectiveness must often be accepted. On the other hand, urea tends to acidify soils less than equivalent dressings of ammonium sulfate and in many situations this is potentially of great importance. Attempts have been made to overcome the problem of variable efficiency, but the addition of acidic compounds or of urease inhibitors as yet has only been partially successful while the use of fertilizer coatings modifies the whole pattern of nitrogen availability.

T E Tomlinson, MA, DPhil., Imperial Chemical Industries Ltd, Jealott's Hill research Station, Bracknell, Berkshire, UK.

76 Pages, 20 Figures, 507 References.