The recently proposed turbo-binning scheme is shown to be both efficient and optimal for uniform source Slepian-Wolf coding problem (Z. Tu et al., 2003). This paper studies the case when sources are i.i.d. but nonuniformly distributed. It is firstly shown that any algebraic binning scheme based on linear codes is optimal for nonuniform sources only asymptotically. Next two modifications are proposed to improve the performance of the turbo-binning scheme for nonuniform sources. The first is to carefully design the constituent encoder structures to maximally match the turbo code to the nonuniform source distribution, and the second is to use variable-length syndrome sequences to index the bins. Simulations show that the combination of both strategies can lead to an improvement of as much as 0.22 bit/symbol in overall compression rate for highly nonuniform sources.