FERTNITRO

[Chr]

All,

I have a question regarding N fertilizer application in CLM5. I am running a regional case, and I wanted to adjust CONST_FERTNITRO to field data, and make sure that I apply the correct amounts of N.
I noticed that the input variable CONST_FERTNITRO does not match up with the output variable FERTNITRO (both g/m2/yr), or the output variable NFERTILIZATION (extrapolated from sec to year). The median values decrease in the order CONST_FERTNITRO > FERTNITRO > NFERTILIZATION.

Does this mean that not all fertilizer was applied as specified in CONST_FERTNITRO?
Could you explain how this three variables are connected, what their meaning is, and how to use it? I wasnt able to find information on it somewhere else.

Thanks for your help.

 

[oleson]

There is some information about fertilization here:

2.26. Crops and Irrigation — ctsm CTSM master documentation

CONST_FERTNITRO_CFT should be applied in a non-transient case.

In transient simulations, annual fertilizer application is specified on the land use time series file by the field FERTNITRO_CFT.

In addition to the industrial fertilizer, background manure fertilizer is specified on the CLM parameter file by the field ‘manunitro’. Total fertilizer applied would be the total of industrial and background manure fertilizer.

Looking at the code, it seems like FERTNITRO should be the same as CONST_FERTNITRO_CFT or FERTNITRO_CFT depending on if transient or not. And NFERTILIZATION should be the sum of industrial and background manure fertlization.