Does mixing urea into irrigation water work, and how do I do it safely?

Applying urea with irrigation water can work because urea dissolves easily and the water carries the nitrogen into the soil, which reduces the loss you get from spreading on dry surface. But it needs care to be even. The main risk is that the nitrogen concentrates near the inlet end of the field and runs short at the far end, giving patchy growth. To do it well: meter the urea steadily into the water flow rather than dumping it all at the inlet, ensure even water distribution across the field, and avoid letting heavily fertilised water run off the field, which both wastes nitrogen and pollutes. On a proper drip or sprinkler system this is far more controllable than on open flood. Split the nitrogen across the season rather than one big slug. For uniformity, level fields and controlled flow help a lot. Follow your KVK advice for your crop, keep the total nitrogen within your Soil Health Card or soil test recommendation, and do not over-apply.