Urea: Urea is a high concentration of nitrogen, is a neutral fertilizer available, can also be used to produce a variety of complex fertilizers. In the soil without leaving any harmful substances, long-term application no adverse effects. Livestock can be used as feed for ruminants. But in the granulation temperature is too high will produce a small amount of biuret, also known biuret, crop inhibition. China provides fertilizer urea biuret content should be less than 0.5%. When biuret content of more than 1%, can not do kind of fertilizer, Miaofei and fertilizer, urea content of other application period should not be too much or too concentrated. Urea is an organic nitrogen fertilizer, through soil urease, hydrolysis into ammonium carbonate or bicarbonate after, in order to be absorbed by the crop. Therefore, urea should be administered 4 to 8 days before the crops need fertilizer period. Urea apply for basal and top dressing, sometimes used as a kind of fat. Before the conversion of urea molecular state, can not be adsorbed soil, should prevent water loss with; ammonia formed after the conversion is also volatile, so deep placement of urea also overburden