1. Beaton JD (1978) Urea: its popularity grows as a dry source of nitrogen. Crop Soils 30:11?14
2. Phosphorus in agriculture, Bulletin Doc No 53;GW Cooke,1969
3. Douglas LA, Bremner JM (1970) Extraction and colorimetric determination of urea in soils. Soil Sci Soc Am Proc 34:859?862
4. Engelstad OP, Hauck RD (1974) Urea: will it become the most popular nitrogen carrier? Crop Soils 26:11?14
5. Gasser JKR (1964) Urea as a fertilizer. Soils Fert 27:175?180