N an P export values in NDR

Hi there,
I just ran the NDR model and believe I have some low results: 0.5kg/ha/yr export N and 1.0 kg/ha/yr export P. I was wondering if there is a general range that I can use to place some context around these results? My LULC comprises an area with forest, agriculture, developed land, shrub land, wetlands, and more- it’s quite diverse.

Furthermore, I have two additional questions.

For annual precipitation, is there a unit requirement? Mine is from a U.S. database and is in inches I believe. I am just wondering if this would impact the results.

Lastly, I used values from the nutrient database excel sheet provided via the link in the user guide, do these values need to have the loads corrected for? For agriculture I used actual nutrient application (fertilizer) rates for my region but for all other LULC categories I used an average of values from the excel sheet for my koppen climate, and am not sure if I need to apply the correction or not. Any feedback is appreciated! Thank you.

Kind regards,

Hi @michelle.vanhilten -

When you report values of 0.5 and 1.0kg/ha/year, what exactly do they represent? Max export value? Mean over the watershed? Something else? The model itself outputs values of kg/pixel, and it would be expected that small pixels would have small export values.

For precipitation units, I’d say that there is no requirement, since the model normalizes the raster before doing calculations with it. I should add that to the User Guide.

It’s been a while since I’ve looked at the values in the nutrient spreadsheet, and am chagrined to see that we do not provide units, nor an explicit note on whether they are loading or export values. At least several of the cited literature sources provide export values, which, according to the User Guide, would indicate that they do need to be adjusted by the efficiency of that land cover type. I’m trying to come up with a definitive answer to this, will let you know (it might take a while, given our geographies and vacations) and will get our documentation updated. Meanwhile, I would consult with whichever source(s) you used, verify whether they are export or loading values, and adjust (or not) accordingly.

~ Stacie