Nearly all N fertilizers are completely water soluble. Because of their high water solubility, granule size and band placement are generally not important. Both forms can be taken up and utilized by plants. However, crops such as tobacco, potatoes and tomatoes prefer nitrate as their source of N. Because nitrate is much more mobile than ammonium, ammonium forms of N are recommended when the application is made prior to the time of greatest need. This practice minimizes potential loss by leaching.
Most phosphate fertilizers are highly water soluble.
Phosphate water solubility is very important for early plant growth. During cool and wet conditions when plant growth is slow and the root system is shallow, band placement of P fertilizers becomes extremely important. Consequently, water solubility is of little importance where P fertilizers are broadcast. Phosphorus availability in the band is generally improved by the addition of N to the P starter and by increasing the granule size. Large granules contact less soil per unit of P than small granules.