  We present the results of a time-dependent Dalitz plot analysis of B0 -> pi+
pi- pi0 decays based on a 414fb^-1 data sample that contains 449MBB pairs
collected on the Upsilon(4S) resonance with the Belle detector at the KEKB
asymmetric energy e+e- collider. The direct CP violating parameters of B0 ->
rho+-pi-+ decay mode are measured to be A_rhopi^+- = +0.22 +- 0.08(stat.) +-
0.05(syst.) and A_rhopi^-+ = +0.08 +- 0.17(stat.) +- 0.12(syst.). We also
measure the CP violating parameters of the decay mode B0 -> rho0pi0 as
A_rho0pi0 = -0.45 +- 0.35(stat.) +- 0.32(syst.) and S_rho0pi0 = +0.15 +-
0.57(stat.) +- 0.43(syst.). Combining our analysis with information on charged
B decay modes, we perform a full Dalitz and isospin analysis and obtain a
constraint on the CKM angle phi_2, phi_2 = (83^+12_-23)^\circ. A large
CKM-disfavored region (phi_2<8^\circ and 129^\circ <phi_2) also remains at
68.3% confidence level.
