How are nitrates leached from the soil?

Nitrogen and carbon bind together in decomposition. This is how compost is made. Nitrate leaching occurs when rain falls on soils whose available nitrogen exceeds soil carbon. This means that there is nothing for the nitrogen atoms to bind to in the soil, and so they are lost to the subsoil as water drains through. One solution to excessive nitrogen is to add highly carbonaceous materials such as wood chips to the problem area.