An attempt is made to investigate the carrier contribution to the elastic constants in nonlinear optical and optoelectronic compounds in the presence of crossed electric and quantizing magnetic fields on the basis of a new dispersion relation within the frame work of k·p formalism. It is found, taking n-CdGaAs2 as an example, that the said contribution increases with increasing electron concentration and oscillates with inverse quantizing magnetic field. In addition the contribution also increases with decreasing alloy composition for n-Hg1-xCdxTe and InxGa1-xAsyP1-y lattice matched to InP which is totally band structure dependent. The electric field decreases the numerical magnitudes in all the cases. The corresponding results for the proposed dispersion law, three band Kane model, two band model and that of well-known wide band model under magnetic quantization have been obtained as special cases of our generalized formulations. We have also suggested an experimental method of determining the carrier contribution to the elastic constants in nonlinear optical and optoelectronic materials having arbitrary dispersion laws.