Three clones of Populus deltoides were planted on a degraded alluvium from the river Ganges at Lucknow, India (80 degrees 53＇E, 26 degrees 42＇N). These were studied for biomass production, energy conservation and nitrogen (N) cycling efficiency at 6-7 years of growth stage. The clones did not differ from each other in energy and carbon (C) concentration. however, N concentration decreased significantly in the order G3 > D121 > G48. The average N concentration of the aerial plant components increased about 21% from lower to upper portions of the trees. Energy values in the root were less than the shoot. The C concentration was greater in woody components in comparison to leaf tissues, whereas the inverse pattern was recorded for N concentration. Energy, C and N contents in the standing crop were greatest in clone G3 followed by G48 and D121 clones. Though the fluxes of energy, C and N were greatest for clone G3 at community levels (tree and grass), at tree populations G48 was found to be more efficient in energy flow as well as C and N cycling. Trees having high N concentration in their foliage (G3) had greater N resorption prior to senescence. Clone G48 was found to be superior to others in N use efficiency based on wood or net production per unit of net N uptake. Integration of N uptake with energy fixation and C intake through a mathematical model estimated about 20 kg ha(-1) year(-1) of N demand for the sustained production of P. deltoides under the present set of conditions.