ICN_DIST - Initial Soil N distribution function

Given a total inorganic N amount for the soil profile, this function distributes the N over the soil layers assuming a constant concentration of NO3 (90%) and NH4 (10%).

Inputs:

• ICIN = Total soil N over the profile (kg[N]/ha)

Implicit inputs (i.e., available in the data)

• SLLB = array of depths to bottom of soil layers
• SLBDM = bulk density by soil layer (g/cm3)

Outputs:

• ICN_TOT = initial inorganic N by layer (kg[N]/ha)
• ICNO3 = initial nitrate concentration by layer (ppm)
• ICNH4 = initial ammonium concentration by layer (ppm)

Procedure:

1. Calculate soil layer thicknesses

   thick(j) = SLLB(j) - SLLB(j-1), except for first layer thick(1) = SLLB(1)
   

2. Calculate total inorganic N amount per soil layer (kg/ha)

   ICN_TOT = SLBDM * thick * ICIN /  ∑(SLBDM * thick)
   

3. Calculate total soil N concentration

   Nppm = ICIN * 10. / ∑(SLBDM * thick)
   

4. Calculate ammonium and nitrate concentrations (all layers have same concentration)

   ICNH4 = 0.1 * Nppm
   ICNO3 = 0.9 * Nppm
   

Example:

FILL, ICIN, ICN_DIST(), 25

ICIN = 25 kg[N]/ha

Nppm = 25 / 225.75 * 10.0 = 1.11 ppm

SLLB (cm)	thick (cm)	SLBDM (g/cm3)	SLBDM * thick (g/cm2)	ICN_TOT (kg/ha)	ICNH4 (ppm)	ICNO3 (ppm)
15	15	1.15	17.25	1.91	0.11	1.00
60	30	1.21	36.3	4.02	0.11	1.00
30	15	1.16	17.4	1.93	0.11	1.00
30	15	1.16	17.4	1.93	0.11	1.00
90	30	1.23	36.9	4.09	0.11	1.00
120	30	1.31	39.3	4.35	0.11	1.00
150	30	1.31	39.3	4.35	0.11	1.00
180	30	1.31	39.3	4.35	0.11	1.00
		225.8	25.0

Notes:

If this is a REPLACE operation, then all existing values will be overwritten using the input provided.

If this is a FILL operation, and values for ICNO3 and ICNH4 or ICIN or ICN_TOT already exist, then this function should be modified.

FILL functions

If the database contains:

• ICIN
  • Use the existing ICIN and calculate other values in the same way
• ICNO3 and ICNH4 arrays
  • ICN_TOT = (ICNH4 + ICNO3) * SLBDM * thick / 10.
  • ICIN = sum(ICN_TOT)
• ICN_TOT array
  • ICIN = sum(ICN_TOT)
  • ICNH4 & ICNO3 computed as with original function

More Samples:

The following DOME spreadsheet is using this function. Machakos Overlay DOME

Dome functions page

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