For each type of fertiliser N, a maximum VOL rate (VMAX) is defined in the model. VMAX varies exponentially with soil pH between pH 5.5 and 8.5 [29]. The VOL factor V is given by the relationship: V = V MAX ÷ 500 × ex p[0.6×(pH−5.5)] − 1 (12) Gx = V × XNH4...