Let's see. First let's put fert in 4 basic groups 1,synthetic inorganics 2,natural organics, 3,synthetic organics and 4, coated products. Now lets look at the most complex group #3 the synthetic organics and split it into 2 groups, water-soluble & water-insoluble. We use 2 types of water soluable synthetic organic nitrogen carriers, urea and calcium cyanamide. The water insoluble synthetic organic nitrogen group is primarily composed of ureaformaldehydes(UF) and methylene ureas(MU). These two carriers are react products of urea, and its availability to the plant is measured by 3 distinct fractions based on solubility. One fraction is known as cold water soluble nitrogen (CWSN) and is immediately available to the plant. The CWSN includes unreacted urea plus some methylene ureas of low molecular weight. The second faction, cold water-insoluble nitrogen(CWIN) is less soluble than CWSN, but can still be available to the plant throughout the typical growing season. This fraction is composed of larger or heavier(molecular weight) methylene ureas that have to be microbially hydrolyzed to smaller units before they can be used by the plant. The third component of these nitrogen carriers is labeled hotwater-insoluble nitrogen(HWIN). This fraction may take years to break down into plant usable form. These carriers have similar characteristics to the natural organics including, intermediate release rate, low foliar burn potential, long residual response & high cost per unite of N. In this category N release is dependent on the activity of soil nicroorganisms, soil temps., PH, and nutrient level. Below 50d N release can be quite slow. It is important to understand the amount of CWIN in the water-insoluble groups is using them for a early spring application. And then there is IBDU. At least that is what Tom Voigt at the U of Ill had to say bout it last year. Sorry--did I try to answer the question after the answer was given?