I use the OECD's Total Support Estimates (TSE), which I think is a proper measure of total agricultural subsidies (but correct me if I'm wrong).
China's TSE is by far the largest at \$239B in 2017 and even its per-capita TSE (PPP*) is higher than the US's.
Here are some explanations I have come across for why agriculture is heavily subsidized in the rich democracies:
- Rural voters wield disproportionate power.
- The costs (of the subsidies) are diffuse and so no single voter has much incentive to organize/lobby against the subsidies.
- Voter inattention: The voters who pay for the subsidies are simply unaware that they are doing so.
However, China is not a democracy and so it would seem that the above explanations do not apply. So what explains China's large agricultural subsidies?
*I think (but am not sure) the TSEs given by the OECD have not been corrected for PPP. And so, I have taken the liberty of converting them.