One indicator for leaching is the Exchange frequency of the soil solution (EF), calculated as ratio of a transport and a storage term (Müller, 2004).
EF (% y-1) = (SeepRate*100)/WHC(rz)
SeepRate = groundwater recharge in mm y-1
WHC = water holding capacity
A low EF is equivalent to a long residence time of water in the root zone and therefore to a low risk of leaching. According to Buczko et al. (2010), it is often used in Germany.