Yes , there is strong possibility , it is nothing but dilution effect of dry matter accumulation with time on the concentration of nitrogen as sink-to-source relationship...

Fast growing corn has high nutrient requirements. especially nitrogen. The negative relationship can reflect a dillution effect. Although you supplied solution 3 times a week, the tissue concentration largely will depend on the volumen of solution supplied and the plant density in your system

The above is all true.  The limitation of major nutrients presumably relates to the volume of Long Ashton solution/plant each week.  During the fastest growth period (not the period of fastest relative growth rate) you could compare the nutrient supplied and those taken up . 

Off course , nitrogen partitioning vis-a-vis crop phenology will reveal these facts  more precisely. i agree with you Paul,, good point. 

Yes you must estimate nutrient uptake with the same nutrient supply  during the fastest growth period to have get the right  ammagination for this case .

Hi Ebony,

Yes, all of above comments are correct.

In mature corn plants, 1 -3% N concentration (on dry matter basis) is normal.  If you had analyzed the time course of N concentration as the corn plant develops, you would have seen 4-5% N concentration (on dry matter basis) at the ‘six leaf’ stage of corn up to ‘silking’ stage.   After silking stage of plant growth, N concentration (on dry matter basis) declines due to rapid dry matter accumulation relative to N uptake.  However, total N content (g N/plant) still increases.   There are few useful figures showing the trends in N, P, and K accumulation and dry matter accumulation of the corn plant, as it develops can be found in the page 19-20 in following publication.

http://publications.iowa.gov/18027/1/How%20a%20corn%20plant%20develops001.pdf

(How a corn plant develops) Iowa State University publications.

Thank you all for your insight.  To clarify, these plants were at the V6 (six-leaf) growth stage when their nutrients were measured, and plants I have reared in field soils tend to have 4-5% N at this growth stage, consistent with what Susantha reports.  I will look into the growth-nutrient relations that you all have suggested.  Any references you could point me toward, especially for corn plant development (like the Iowa State publication -- thank you Susantha!) -- would be extremely helpful.

All the answers given above are true and interesting. But to add may be repeated, as for the question, it depends on the availability of N. When N is limited, N% and dry matter are negatively correlated. I think it is also interesting to see the N-acquisition and N storage as well  at a given N status. For more, it may help, refer the study on Arabidopsis  thaliana by Chardon et al., 2010 (Journal of Experimental Botany ,  61(9): 2293-2302 

Let me put up  an interesting fact. If we chase down the concentration of nitrogen across different growth stages on a soil previously well fertilized , do you feel , the nitrogen concentration curve will depend upon  plant asimilable nitrogen content  in soil ..?

Yes I do. For instance, when we see the transport system of nitrate in many plants, it has a long distance to be assimilated compared to ammonium. But in some crops like rice in paddy soils, the rate of uptake for both N forms is comparable, as I learned from some literatures.

Have you measured RGR, NAR and LAR in control and treated plants?

Whether the plants grown in height (taller ) were healthy or stronger?

 The answers to these Q may throw some light.

We surely need nitrogen partitioning vis-a-vis critical growth stages to arrive at concrete conclusions ...