I believe "flat" rather than "rich" is more of the limitation. Machines cost almost nothing in China, but the access or field topography very often makes them untenable.
Are you talking about the machines that can mechanize the planting of rice seedlings? I find it hard to believe that poor farmers in China can afford these machines, unless this state is providing for free, or with zero interest loans and very long repayment periods.
Also, most rice farming in China isn't done on difficult topography. I call that stereotype the "National Geographic" effect. If you look where most rice farming is done, it isn't very steep or mountainous. See more here: https://www.statista.com/statistics/242360/production-of-ric...
China makes almost all of the world's EVs, the world's motors and the world's wheels. Putting together any kind of agricultural vehicle is cheaper in China than elsewhere. That's just how it is. How do I know this? I just returned from seven years making robots in China. I will stop short of looking them up and pricing them, but feel free to do so.
AFAIK the Agricultural Bank of China is the largest bank in the world by some measures. It almost certainly has the most branches, and these are overwhelmingly located in agricultural towns and villages. Recall also, in communism sharing equipment is normal. People don't all need to buy their own. Chinese villagers like villagers elsewhere help one another.
Yes, flat areas exist. But they are not the test area, Yunnan. And if you were to look at the historical spread of rice farming (a subject of considerable academic debate) you would notice that all academic suggestions of the earliest invention of rice agriculture itself, with very few exceptions, appear to disperse through or via the test area, because it is the natural headwaters of rivers feeding the majority of mainland East, Southeast and (very close by) South Asia, including the Yangtse, the Pearl River, the Red River, the Mekong, the Salween, the Irrawaddy, and the Brahmaputra. Given we know that in ancient times river valleys formed natural communications paths this give us a fair case for the general dispersion of rice farming technology specifically through steep terrain areas and specifically through the test area.
