Just punch and cover it. Maybe dilute and. spray.
It is simple. If using a 20 litre knapsack sprayer, put urea granules on the filter then pour water to dissolve as it enters the knapsack. Similar procedure as you do for foliar feeds, pesticides, herbicides, etc.
How is the measurements for 16 litres of knapsack?
Two (2) glasses or one and half tea cup is okay. But apply at an early stage to broad leaves. You can also mix with selective herbicide to clear weeds faster, eg. on beans, potatoes, etc. Very effective as booster.
However, I have heard from few farmers who recommend not to try it. They say urea will burn your plant. Search for foiler urea instead, they recommended.
So, on which types of crop and the stage before spray?
Just the broad leaves and at early stage.
I do large scale farming in beans, potatoes and i have been diluting plus spraying urea at an early stage for many years with positive results. It acts as a booster to fast growth if you apply right measure only once. You also protect your soil by applying as foliar.
Or forget spraying. Dig apply and cover