SWAT calibration for nitrogen - nitrate

[Pradeep]

Hi All!



I was wondering if somebody could help me out in calibrating my model
for nitrogen - nitrate. I tried everything, but nothing works. I
really don’t know where I am committing the mistake. Somehow I am not
able to reduce the amount of NO3 leached, and therefore, getting very
low amount of NO3 in surface runoff. I have changed NPERCO value to
maximum (i.e., 1), but still NO3 is very low in surface runoff. I have
used following values for various nitrogen variable in the model.



RCN: 1.0

CMN: 0.0015

CDN: 0.0

SDNCO: 1.0

NPERCO: 1.0

N_UPDIS: 5.0

ERORGN: 0

SOL_ORGN: 100 for all soil types

SOL_NO3: 0.0 for all soil types





Here is the model output summary for nutrients which clearly indicate
low NO3 in surface runoff and high leached NO3:



NUTRIENTS

ORGANIC N = 0.276 (KG/HA)

ORGANIC P = 0.054 (KG/HA)

NO3 YIELD (SQ) = 1.778 (KG/HA)

NO3 YIELD (SSQ) = 0.071 (KG/HA)

SOL P YIELD = 0.360 (KG/HA)

NO3 LEACHED = 28.076 (KG/HA)

P LEACHED = 2.500 (KG/HA)

N UPTAKE = 125.735 (KG/HA)

P UPTAKE = 18.093 (KG/HA)

NO3 YIELD (GWQ) = 7.877 (KG/HA)

ACTIVE TO SOLUTION P FLOW = 19.753 (KG/HA)

ACTIVE TO STABLE P FLOW = 15.548 (KG/HA)

N FERTILIZER APPLIED = 175.626 (KG/HA)

P FERTILIZER APPLIED = 41.934 (KG/HA)

N FIXATION = 36.335 (KG/HA)

DENITRIFICATION = 0.000 (KG/HA)

HUMUS MIN ON ACTIVE ORG N = 26.618 (KG/HA)

ACTIVE TO STABLE ORG N = 15.856 (KG/HA)

HUMUS MIN ON ACTIVE ORG P = 8.187 (KG/HA)

MIN FROM FRESH ORG N = 85.695 (KG/HA)

MIN FROM FRESH ORG P = 19.992 (KG/HA)

NO3 IN RAINFALL = 1.895 (KG/HA)

INITIAL NO3 IN SOIL = 54.125 (KG/HA)

FINAL NO3 IN SOIL = 52.238 (KG/HA)

INITIAL ORG N IN SOIL = 1750.469 (KG/HA)

FINAL ORG N IN SOIL = 2583.207 (KG/HA)

INITIAL MIN P IN SOIL = 331.169 (KG/HA)

FINAL MIN P IN SOIL = 1265.305 (KG/HA)

INITIAL ORG P IN SOIL = 214.432 (KG/HA)

FINAL ORG P IN SOIL = 455.040 (KG/HA)

NO3 IN FERT = 1.591 (KG/HA)

AMMONIA IN FERT = 114.828 (KG/HA)

ORG N IN FERT = 59.207 (KG/HA)

MINERAL P IN FERT = 21.096 (KG/HA)

ORG P IN FERT = 20.838 (KG/HA)

N REMOVED IN YIELD = 65.931 (KG/HA)

P REMOVED IN YIELD = 7.634 (KG/HA)

AMMONIA VOLATILIZATION = 0.910 (KG/HA)

AMMONIA NITRIFICATION = 23.189 (KG/HA)

NO3 EVAP-LAYER 2 TO 1 = 12.084





Any help is greatly appreciated.

Pradeep

[Naresh Pai]

From the output it appears that there is no denitrification being simulated which explains the high nitrate volume. Try to reduce SDNCO to about 0.6 - 0.7 and see if it helps.

Naresh Pai

[Pradeep]

Hi!

Thanks Naresh!

As suggested, I changed the value of SDNCO to 0.6 and CDN to 1.4, but
it did not work. Still denitification amount is 0.0, and these changes
have no impact on NO3 yield in surface runoff.

Pradeep