how much nitrogen volatilizes over the winter?

Next year, once coffee shops are open again (if they are!) I'm going to really try to collect a lot of coffee grounds for nitrogen. The thing is, I don't have a lot of time to collect them in the spring, and that's when everyone else wants them. I was thinking that I'd collect them in the late Fall and early Winter, and spread them on the garden beds under a layer of mulch. With our high desert climate, I don't have to worry about any nitrogen leaching away. How much do you suppose I'd loose by volatilization by the time spring came around? These are dug semi-intensive beds for annual vegetables, so in the spring I'd dig the decayed mulch (leaves and chopped up plants, nothing woody) and coffee grounds in.