When they are talking about nitrogen here, they are talking about total nitrogen, and you have to factor by the total percent in the formula that you are applying to get total pounds. For example, 34% x AN weight = total nitrogen weight of AN. 100 pounds of AN is 34 pounds of nitrogen. 100 pounds of urea is 46 pounds of N, and 100 pounds of AS is 21 pounds of N. See? Typically fertilizers are rated for use in pounds per acre. So are pesticides and herbicides. It can be a pain to figure out smaller amounts on smaller plots. We had to figure out what rate to apply and how many spreader cans to fill on our spreader that we had mounted on the back of our Polaris ATV that we used to fertilize the pastures with. We had about 25 acres in pasture there. Its a guessing game at best. What they are recommending and when makes sence; apply high nitrogen fertilizers during the shoulder months when you are going to get your highest rate of growth in grasses. That was the way it was on our pastures that we had our sheep on in central west Oregon. Here grasses grow in the spring, and they die off when the rains end in summer, and they resume growth again in the fall when the rains return. 2nd growth cutting was the hay that we always wanted; it was the best and the sheep prefered eating it. What they are talking about regarding application of urea in dry conditions is what I was saying before; warm dry conditions after application will favor the ammonia vaporizing into the air from the soil, and being 'lost'. Some online sources claim that up to 50% of the nitrogen in urea can be lost to volitization if conditions are not right. Seemingly urea is being used a lot more now that AN is being phased out for 'national secutity' reasons. Ammonium sulphate is being used more, but even if half the nitorgen is lost in urea, it would be about the same as using ammonium sulphate. There are some new types of urea with volitization inhibitors coming on the market now as well.
As for the difference between Urea, AS, UN, UAN, or several other high N fertilizers out there, as my earlier post pointed out, they all start out with or turn into ammonia at some point, and they all break down in the nitrification process to nitrites and then into nitrates in the end. The urea is more volitile than the others when used on soils and then the weather turns dry, and/or when used on soils with a pH higher than 7.5, which your soil is. The higher pH volitizes the urea into an aresol form of ammonia which is lost to the air. However, urea is a lot more potent than any other form of high N fertilizer, and thus it is not really an issue from my experience. We usually used urea and we had high pH soils. I used about the same amount of AN as Urea for the same area, and more AS than either of those. The prices and availability varied from year to year (usually going up in price), and we bought it by the 100 pound lot at the local farm co-op. You have to factor for the total nitrogen, and compare the cost and potential losses of N using urea to volitility when calculating what is the cheapest/best source of nitrogen. Welcome to the head scratching part of pasture management.
As to how this applies to bamboo? Well, a lot of big boo growers apply urea here in the late winter just the same as you would apply it to pastures. I am not sure about the rate though. Bamboos are grasses... giant Moso pastures? As for being an expert, I do not really know jack about anything. I am really a convict in jail in San Quentin, logged onto the computers at the library for good behavior. That guy that went to the PNW bamboo conference this weekend in Springfield, OR was an imposter that looks just like me
I get my info about bamboo from my cellmate, who talks about it in his sleep all the time. The other stuff I just make up after hitting the bottle of Jack Daniels, er, that is what we call "Koolaide" here in the big house. I trade all my cigarettes for it.
Note: I updated the above to add figuring out total N examples of AS, AN and urea.
Happy trails...
