Urea is known to make fields barren. Urea destroys the humus in the soil and makes the soil compact. It also interferes with the beneficial microbes in the soil, and destroys their colonies, thus destroying not only the composition of the soil but also the texture of the soil.
In the short run, urea does increase crop yield, however in the long run, as the years roll on, the crop demands an increasing quantity of urea to sustain this yield. Finally, urea destroys the soil ecosystem and makes the land unviable.
On a paddy field in front of our house, I sat and watched this farmer spread urea on his crop, wondering how long will this greenery last.