Plants need three macro-nutrients for their growth. These are nitrogen, phosphorus and potassium. Urea is a source for nitrogen.
Organic alternatives of urea include compost which is derived by microbial decomposition of organic waste. Organic alternatives to urea are superior to urea in many ways. They improve the ability of the soil to hold water, improve its texture, do not cause plant damage due to excessive nitrogen availability, etc. The nitrogen availability in the soil can also be increased using nitrogen fixation by growing alternate crops of legumes that have nodules in their roots which can take nitrogen from the air and convert it to a form that can be used by plants. The symbiotic relation enriches the soil and eliminates the requirement for a nitrogen fertilizer.
But these methods are not possible to use if there is intensive farming of non-leguminous crops and sufficient amounts of organic manure is often difficult to obtain.
The benefits of urea which outweigh the benefits of organic fertilizers are that it can be transported easily as urea has one of the highest concentrations of nitrogen. Urea releases ammonia which is acted upon by microbes in the soils and converted to ammonium compounds that can be absorbed by plants. Urea can be easily spread out over the entire field and if this is done at the right time and the right quantity is used, the utilization of the nitrogen in the urea is high.