Urea, also known as urea, carbamide, suitable for all crops and all soils, can be used as base fertilizer and topdressing, dry paddy fields can be applied. Due to the conversion of urea in the soil can accumulate a large number of ammonium ions, resulting in a pH increase of 2-3 units, coupled with urea itself contains a certain amount of biuret, its concentration at 500ppm, it will work on crop roots and buds, so urea should not be used as seed fertilizer.