How much rain for nitrogen fertilizer incorporation in soil?

[eclipseman]

I keep hearing that it is bad to fertilize until you have a rain or else you may lose the nitrogen portion to the air, especially if that is what you are targeting for something like brassica. I plan on spreading straight urea soon for my brassicas since it is now 4 weeks after they have germinated but wanted to know what are the consequences of spreading the urea before a rain and it does not rain enough? How much rain do you need to incorporate the fertilizer into the soil? I heard the worst thing for nitrogen loss is UV degradation from the sun. If this is true, doesn't that mean that the brassica canopy will help protect somewhat against that now since the brassicas basically cover all of the soil (at least in my plot they are)? The reason im asking is there is only a 60% chance of rain tomorrow and the forecast for the next 2 weeks is not sounding that great for rain so im thinking the hell with it I'm just going to flip the coin and fertilize now and hope it rains tomorrow. Thanks!

 

[bueller]

It's always a roll of the dice. Too much rain is no good either. The nitrogen will leach right through the soil especially in sand like I have. I delayed applying mine last weekend because heavy rain was in the forecast. Well the weather man was correct and we got over 7" of rain. Glad I held off. This past weekend I applied it with more rain in the forecast. We've gotten about 1" since I spread it on Friday, just perfect. Forecast has potential for heavy rain tomorrow, hopefully it misses.

As for your question, I'd say if you get between a 1/2" and 1 1/2" in the 5 days after top dressing nitrogen you are getting a good return on your bet. Any more or less and the results start dropping off, although from what I have read the drop-off is slow and you should still see a good response to your application.

 

[Don'tWorryIHuggedItFirst]

Publications I've seen say you want somewhere between .25 and .5 to dissolve the urea.