The N-delivery capacity is the amount of nitrogen from organic matter that can be made available over a longer period of time.
The ratio of carbon (C) to nitrogen in the soil provides information on how easily nitrogen can be released.
If the C/N ratio is low, then there is a lot of nitrogen in the organic matter and decomposition and mineralisation of organic matter is high. If there is a lot of C in organic matter, the C/N is high (= low mineralisation).
A high C/N does not necessarily mean something is wrong. The optimal C/N ratio is, in part, dependent on your intentions. For example, a high C/N implies little decomposition of organic matter, and the organic matter that remains present is good is for workability, anti-slemp, CEC binding, and water balance, etc.