Because of the reduction in soil available for input the amount of nitrogen in the system also decreased over time. When this happened there was less nitrogen to expel. The input decreased rapidly to 4.5 after 6 years. These values indicate that nitrogen in the system constantly decreased. In order to model these increased losses and reduced availablilities, a model which relates the losses to another variable.
Rainfall causes the most loss.
Putting rainfall in by month and precipitation level will give a more accurate view of the system. Sliders could be inserted to easily manipulate the values.