You can see similar discussions (with suggested references) about your question in the links below:

https://www.researchgate.net/post/What_is_the_relationship_between_chlorophyll_meter_readings_and_total_nitrogen_content

https://www.researchgate.net/post/What_is_the_relationship_between_leaf_nitrogen_and_total_chlorophyll/1

https://www.researchgate.net/post/Relationship_between_chlorophyll_content_of_plants_plant_growth_and_nutrient_status_of_plants/1

the question is specific to a species, but you should calibrate chl with nitrogen content values. Please note that yield response flattens at optimal N supply as in Blackman roof ceiling theory. Abosrbed nitrogen can also be measured by quadrant method, taking the difference between N content in the soil during plant growth. Basic infos in http://www.ncbi.nlm.nih.gov/pmc/articles/PMC439849/ for chl and N and https://www.researchgate.net/publication/47817797_Nitrogen_Responses_and_Nitrogen_Management_in_Potato for quadrants

Article Nitrogen Responses and Nitrogen Management in Potato

Maybe the following publication which showed relationship between chlorophyll content and nitrogen applications can help

As said well by others it is necessary to relate the measured chlorophyll  content  to the measured N in the leaf, and then relate that to the N supply.  But there is much information in the literature , see my earlier comments please.

There are many ways to group plants or even leaves according to their water, Starch, fat, fibers or pigment content etc . e.g. what is green and you can eat raw as salad, or boiled or you store it even dry like tea. In a similar way plants can be grouped empirically according to a DW/FW ratio and per meter square growing area and time. e.g. a way to group the "energy plants".

In Science you are allowed to do every thing you want (within your responsibility), however you have to say what you did and how you did it. The DW/FW ratio drives into the center of interest. Your question has high actuality.

Reto