The headline on this piece, "50,000,000 Acres..." seems to be unsupported. It's carried over from the post to which it refers, but nowhere do I see any supporting figures which add up to 50 mill. 6 or 7 million seems more like it.
I'm skeptical these acquisitions will be terrible. It's not clear how they're going to be farmed. My prejudices say a big farm of 1,000,000 acres is not the way to go. I'd guess the Chinese aren't going to sell off 500 acre farms to Chinese farmers, although China has some recent experience with the problems of communally owned land operated as one enterprise. Assuming the countries can figure out how to manage the enterprises and the land effectively, things could work out. There would be an investment in infrastructure, which many places in Africa lack, and in equipment, fertilizer, and pesticides which African agriculture needs.
Of course the greens would argue organic agriculture in Africa has proven its ability to out-produce the methods currently used in African agriculture. The investments by the countries mean a different model of agriculture (I assume, but maybe the Koreans and Chinese are going for the organic model ;-). We'll see what works.