Urea can be used to make bombs but should still be available from farm suppliers. You can pay a little more for it in the form of lawn fertilizer that typicially have about 25%N and 2 or 3% P and K.

Why do you think your trees aren't getting enough N? Why not have a farmer friend evaluate your orchard because your mulch should definitely be adequate. I can grow great corn with nothing but grass clippings. I would consider them too hot as a regular fruit tree fertilizer. It sounds like you're just going for a magic bullet that's not too much trouble.

For fruit trees, N need only be applied once- right as they start to grow. I'd put it down when the buds begin to swell. A mid-summer application might give you a little more growth, especially for the cherries, but most orchardists of free standing trees do a single ground application.

Ammonium sulfate is possibly the cheapest N fertilizer around here. Rarely found (though not never) at a Lowes but can be obtained at a farm supply store. Calcium nitrate is available too. And sodium nitrate. And sometimes ammonium nitrate with enough other N fertilizer mixed in to make it not suitable for explosives. Urea is outlawed in this state for unrestricted sale, same as ammonium nitrate, though urea poses far less of a risk.

Soils vary tremendously in their nitrogen fertility and in their ability to hold unto nitrate nitrogen when it forms from breakdown of organics. I did research on one soil in Texas where it was nearly impossible to leach out nitrates. If we over fertilized the only way to remove the excess was by cropping it out. That took one year minimum and sometimes 3-4 years. I learned to be very careful about how much nitrogen I applied to fruits or field crops. The soil I'm on now even though it's clay loam texture I can leach out the nitrogen with one heavy watering. This current soil has a saturated flow rate of one inch per hour. Unless I apply nitrogen regularly the grass and trees show nitrogen deficiency on a regular basis. Growth slows and the leaves become smaller and light green or yellow.

On a very sandy soil, which the original poster stated he has, nitrogen fertility could limit fruit tree growth rather sharply. I've gone to the controlled release fertilizer on potted trees. This is a complete fertilizer which I think helps with such a small soil volume. For a large acreage controlled release is expensive. I think the OP has the right idea, chemical this year and manure next. If nitrogen doesn't help growth next year he'll only be out a few dollars.

Foliar leaf analysis in summer will tell the story but that costs money too.

N. is usually cheaper the least processed. Farmers often use anhydrous ammonia even though it's highly flammable and dangerous, but it's the form it's in when they pull it out of the atmosphere. The next least processed form is urea. The only reason I can think why Lowes would carry ammonium sulphate is for use in the alkaline west. It's also good for fertilizing in anaerobic conditions, like when you're growing rice. Maybe there are deals on it in some parts of the country where it's a bi-product of air pollution control.

Fruitnut, oldryder also stated that he mulches annually quite heavily with grass clippings, manure and leaves and has for 5 years. I know of no normal soil situation that would stop that soil from having adequate N for fruit trees after 5 years of this management. There should be a nice 5" layer of pure humus and a steady slow release of ample N by now, unless oldryder has a different definition of a heavy mulching than the rest of us.

oops, I thought oldryder was dirtslinger who had posted a similar question earlier- scratch my last comment and most of my first.

Everyone, thx for input. With info provided and 3 months to work it out I'll be ready this spring.

I ordered another 20 trees today so I'll be able to compare growth on 2011 trees to the 2009 and 2010 trees that weren't fertilized. I'm hoping for an obvious difference and I'll have learned something

hrvestman, thx for clarification. I was confused for a while there.

Just to let you know that "Urea" does not make bombs. It is "ammonium nitrate" that does. Up here in Ontario there are restrictions against it...only Urea is allowed for sale to the public.

I find that if nitrogen is over applied in sandy soil there is less harm done to a plant as apposed to a heavier clay soil, where the clay holds onto the nutrient longer. The Clay soil can hold on to nirtrogen and fertiizer better than sandy soils. I have burned more trees with nitrogen application in heavier clay soils as opposed to sandier soils, where it flushes out more easily.

Urea can be made into an explosive (but so can your cotton shirt) while ammonium nitrate already is an explosive.

I guess that ammonium sulfate is available readily in the acid-soil southeast for acid-loving plants, such as azaleas. Even our most common yard grass (centipede) prefers marginally acidic conditions I'm told and is not limed like for most grasses. Ammonium sulfate also may simply be the cheapest high-N granular fertilizer that is not bothered with restrictions.

Ok, my bad. Yeah Ammonium Sulfate is the easiest to get.
Got to a farm outlet store and get the granular type. not crystal grade.

I know what you mean with fertilizing, I have 100 mature olive trees and 900 3 year old trees and I fetilize by hand no machines....

In and of itself, ammonium nitrate is not an explosive though it can self ignite @ 300 deg. C. read the MSDS below. I don't understand why so many confuse urea with amm. nit. when it comes to explosives.

It is sad that I can't get amm. nit. to use as a Spring fertilizer when the soil is still very cold, too cold to rapidly convert all the other dry N fertilizers to NO3 which the veggies and trees will readily take up. Yes, there are the liquid URANs which are great for fertigation.

I don't find the vegetables will grow in that cold soil anyway. That's why I size up most things in the cold frame (actually an unheated greenhouse). No sense putting out stuff before the soil warms.

Commercial fruit growers have always used urea primarily as both their soil and foliar N source to my knowledge. When the soil is too wet and cool it will still turn over to ammonium and be held by the soil until the trees can pick it up according to Cornell. Or at least according to my remembrance of Cornell recommendations.

Half or more off topic, planting the early cole crops, onion, spinach and lettuce must be done early here when the soil is still pretty cold. The good news is the ground is warm enough for the TP roots to get going prior to the warmer weather and top growth speeding up, transplant survival rate and cropping in general before the heat sets in works very well this way. I could use plastic mulched raised beds (ala the commercial method), low tunnels, floating row covers and high tunnels but the budget and my body would take them too well so, it's plant TPs early and cover when needed for killing frosts.

Yep H-man, that cold wet soil and urea issue makes me pine for the days of strolling into the elevator and picking up a 25# bag of amm. nit. for $12.00. Oops, just dated myself!

Elliot Coleman talks about the main nutritional difficulty in organic gardening being that the soil must warm up to allow the plants to get P. In a book I have on my shelf that he wrote he doesn't suggest that N is a major issue in terms of cool weather growing.

I don't actually have much first hand experience experimenting with different store bought fertilizer on my vegetables, however- I get early greens going with my magic urine which is still a real bargain and loaded with all the quick release NPK my vegies need to get out of the gate.

No, in and of itself, ammonium nitrate IS an explosive. Some of the biggest accidental explosions in history have been of ammonium nitrate without boosting (or fuel) additives.

One of many examples:
http://www.local1259iaff.org/disaster.html

Earlier in that century there was a far bigger explosion in Germany, heard in England I believe (some idiots tried to break up a gigantic stockpile of hard ammonium nitrate for shipping, using dynamite!). US Army road cratering charges are (or were) small drums of cast ammonium nitrate.

Mining and terrorist uses usually do have additives (although they differ).

Hi H-man: ditto on the cold soil P issue. It has been my experience that when starting veggie TPs in the ground early, particularly onions, lettuce and cole crops that the top growth is significantly reduced using pre-plant, incorporated urea. It appears that even after the root systems have become established in cold soil, the urea has not yet converted to NO3. The main objective in cropping with TPs and planting early is to get the plant frame big as early as possible before day length and heat start to have the anticipated effects of causing the crop(s) to go from vegetative growth to reproductive. Of course, a lack of plant available N will have serious consequences for top growth including less of it and early onset of the conversion to reproductive growth.

With onions and other veg. crops, getting lots of crown/leaves/photosynthesis factories developed prior to the plants transition to it's reproductive phase is paramount to developing the structures we want, I.E. big broccoli crowns and onion bulbs. Poor leaf production = poor yield.

Having the available N (NO3)present in cold soil is easily achieved with amm. nit. (prilled) and it's liquid forms (URANs). As you know, Urea has to get converted in cold soils to NO3 after it's application and this takes time. In my cropping system, that time lag leads to yield reductions in cole crops and onions and to a lesser extent in spinach and lettuce. The longer our Springs stay cool, the better the yields; quite often, our Springs go from excellent growing conditions for the cool season stuff to heat, if the crowns aren't adequately developed by then, yield suffers. Needless to say, I push for early season top growth and NO3 ferts. work well for that whereas urea does not. Yep, I fertigate early with a measly 25lb/A N from 28-0-0 (URAN) and also incorporate urea for the later season N source at planting with the ability to use more URAN later if we get (the rare) leaching rains.

Michael, OK, we've officialIy hijacked the thread but I figure the original question's been answered anyway.

I push up soil temps by growing on raised beds under black plastic that I cover with hay when temps are warm enough but this is only about getting enough vegetables for home use.

If urea takes longer to convert to ammonium in cool soil why not spread it earlier? I thought most plants can absorb ammonium without much difficulty- some can even use urea as I recall.

I'm looking at one of my text books right now written for an education in agricultural production and I can't find any list of crop preferences for specific N forms. I remember reading about certain species preferring ammonium but not about others responding only to nitrate. Maybe you can enlighten me here.

Sure would be a disadvantage to only be able to absorb nitrate in the great competition for this most limiting nutrient.

Yer right H-man, hijacked it was. I thought maybe someone might be able to extract something useful to the OP from our hijacking but it's probably time to hand the reins back over.

We did a lot of research on veggies in FL on methods to increase earliness for the commercial growers and as you mention, there are definitely ways to do so.

It certainly is possible to Fall apply urea, many major grain farmers apply anhydrous in the Fall. I have never looked into it but, I presume the N from Fall applied urea and anhydrous has not fully converted to leachable NO3 to soon in the Spring or substantial amounts could be lost to Spring rains. Most likely, the Fall applied stuff pretty much sits there until soil temps and moisture allow it to begin converting.

I believe sweetcorn is one species that utilizes ammonium more efficiently than the average vegetable, past that, I just don't remember. Do fruit trees preferentially take up a particular form of N?

In veggie growing I can manage N inputs easily as far as quantity and timing through drip irrigation, doing so allows a grower to get by with significantly less N when managed properly. As my good friend Dr. George Hochmuth likes to say, "It is the water, folks, it is the water..........
If we teach them how to manage irrigation,
then they will be able to manage fertilizer."

To the best of my fallible recollection, veggies take up the large majority of their N in the NO3 form.

Hot dog, the wife has informed me that it's raspberry + peach juice for breakfast tomorrow, I was getting tired of the raspberry pear.

Happy trails.