Addition of N, P, or S in fertilizer are added as monthly amounts in g/m2. The management schedule event FERT specifies the fertilization option, which specifies the monthly amount. The amount flows directly into the soil mineral pools for that element, and is then available for microbial and plant uptake and leaching, and for N, volatization.
Fertilizer addition can be either fixed amounts
(FERAMT(*), fert.100)
or calculated automatically
(AUFERT ≠ 0.0, fert.100)
according to the crop requirements. The automatic option can be set to maintain crop growth
at a particular fraction of potential production with the minimum nutrient concentration
(0.0 < AUFERT ≤ 1.0)
or to maintain maximum production with plant nutrient
concentrations at a nominated level between the minimum and maximum for that
growth stage (1.0 < AUFERT ≤ 2.0).
The total N,P, and S amounts in fertilizer that are add to the soil pools are accumulated monthly in EFERT(*), and annually in FERTOT(*).
Nitrogen made available from symbiotic fixation (legumes) is decribed in Nutrient Availability Effect upon Production.
Fertilization can also occur by adding organic matter to the surface of the soil. The management schedule event OMAD specifies this option, and the option parameters specify the C, N, P, S amounts to be added. See Organic Matter Addition Parameters.