@alan so it’s not too late for me to apply either with granules or dissolving it in water first? I have fruit already and some of it still has shucks split but still attached
I also don’t think that leaching was mentioned here. Early in the season, large applications of nitrogen are more likely to leach past the root zone due to an inability of the plants to uptake the nitrogen before it is washed out. This all depends on growth rate, rain, soil type, nitrogen form, etc.
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I don’t know if I can add much to the discussion here, some good points.
We’ve used foliar applications of low biuret urea, and soil applications. We’ve also used DAP (broadcast) if P and N are both needed. I prefer to wait till fruit set before applying any N. Peach trees here will become too vigorous if the crop is lost due to spring freezes. Fertilizing mature peach trees with no crop simply results in a lot of extra pruning.
We use N on young peach trees because we want to size them fast. I like to have a 3" trunk after 3 seasons (ideally) so we tend to push the N pretty hard at the orchard on young trees. In my backyard, it’s a more laissez-faire approach. The young peach trees don’t get much, if any, N. They size when they size.
As in the article Kris linked, we look at shoot growth to gauge the amount of N to apply to mature peach trees. We like to see about 2’ (as an average) of shoot extension per season. I’ve noticed some varieties are more apt to suffer low vigor as they get older (especially Earlystar) and tend to want to put out mostly short shoots, if not adequately fertilized with supplemental N.
As Tippy mentioned coated urea (urease inhibitor) or mixing with water reduces volatilization substantially. In terms of volatilization losses of uncoated broacast urea, it depends on so many factors, I think it’s hard to put a number on it.
I have noticed when we have broadcast it, under the worst conditions (i.e. warm, windy, with the soil moist) the uncoated white granules seem to completely evaporate. I really wonder if much gets into the soil under these circumstances.
For uncoated urea we prefer to broadcast right before a rain. 1/2" rain is ideal for our conditions. Too little rain, and volatilization is a problem. Too much rain, and N washes away as run-off. It would be nice if we could irrigate after application (or fertigate with drip) but we aren’t set up to do that.
Coated urea is more expensive, but I plan to start using it. It’s a pain to try to time urea applications with immediate rainfall.
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One important factor, apparently, is when spreading urea on mulch there is likely to be high volatilization if it isn’t immediately and thoroughly watered in. I’ve read this in credible sources but it never came with an explanation. Maybe someone can help me on that.
See here, page 4, under “Soil Organic Matter and Residue” short explanation