In the effluent block, the slow release of effluent leads to higher predicted soil available N (see Block Details Reports - Change in nitrogen pools) and hence N leaching. Background N losses incorporates the losses from effluent, fertiliser and soil available N. The cumulative amount of N available from effluent is shown on the ‘Changes in N pool’ graph.
When there is no differentiation between nitrogen fertiliser application on effluent and non-effluent blocks, the total N pool is higher therefore N leached from root zone is higher.