If you select the wrong one, or apply it at the wrong time, your plants will starve. The amount of nitrogen available to your plants depends on the type of organic fertilizer you select and on the environmental conditions. Organic fertilizers decompose at different rates and therefore release nitrogen at different rates.

2.5% of the nitrogen is available to plants right away, but what about the other 2.5%? What happens to it? Organic compounds continue to decompose and eventually the nitrogen will become ammonium or nitrate and be plant available. Let’s continue with the fish fertilizer example. Knowing the PAN value is important so that you add the right amount of nitrogen. You think you added 5% nitrogen, but if half of this is organic nitrogen then you only added 2.5% plant available nitrogen (the PAN is 2.5%). Why is this important? Lets say you add some fish fertilizer to plants and the NPK is 5-1-1. These contain nitrogen, but plants can’t absorb them through roots. Non-available nitrogen is also called “organic nitrogen” since the nitrogen is tied up in large molecules like proteins. Scientists use the term “PAN” to describe the amount of Plant Available Nitrogen, which consist mostly of ammonium and nitrate. Gardeners deal with two groups of nitrogen compounds those available to plants and those that are not available to plants. The nutrient that is most often missing is nitrogen, so I will use nitrogen as the main example in this post, but most of the contents also apply to the other nutrients.

We don’t feed plants! We replace missing nutrients in soil.

Chemical garden book