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Abstract
INTRODUCTION
The food gap, caused by the ever growing population will ever exist and widen unless efforts are made to over come it. Therefore, the calcareous soils are new toward to insure the vertical development to increase the crops production per unit area.
In Egypt, the newly reclaimed lands are a wide area; the calcareous soils represent about 12 million feddan, at Nubaria region its represent about 290.000 feddan. The Egyptian government worked to increase reclaimed desert lands areas to insure the horizontal development to decrease the food gab. Wheat (Triticum aestivum L.) is the most contributing crop to this food gap because the local production is not sufficient to supply the annual demand of local requirements. Wheat is the most important and widely adapted food cereal in Egypt. However, Egypt supplies only 40 % of its annual domestic demand for wheat. Therefore, it is necessary to increase wheat production in Egypt by raising the wheat grain yield.
Calcareous soil is poor in its fertility. Therefore, low content of nitrogen and phosphorus elements is main cause of their low productivity.
Inorganic nitrogen is essential plant nutrient in most cropping systems if maximum yields are to be realized. Nitrogen fertilizers may be applied any time from just before planting up to the time the plant is well established. They are biologically transformed into nitrate within a period of few days.
Urea is the major nitrogen fertilizer used for crop production in tropical and subtropical countries. It is high nitrogen content (46% N in fertilizer grade material), which less than the other nitrogen fertilizers (ammonium sulphate and ammonium nitrate) in transport, spreading and costs per N unit. It is very soluble and so suitable for applying in solution either to the soil or as a foliar spray, and the solution is not corrosive. Urea can be mixed with some other fertilizers to make compound fertilizer.
Urea application to the calcareous soil as a nitrogen fertilizer has some problems:
1- Surface application, is susceptibility to loss through various pathways resulting in low use efficiency, NH3 volatilization is the major nitrogen loss mechanism when urea is broadcast applied in flooded paddies and upland soils.
2- Following broadcast on the surface on moist soils urea under goes hydrolysis aided by the urease enzyme and creates alkaline micro sites.
3- An alkaline pH caused with a high concentration of ammonium ions (NH4) is the driving force for NH3 volatilization.
However, several attempts have been made to develop various means of controlling ammonia evolution from urea. These approaches include using soil amendments such as F.M. and sulphur.