Johannesburg - Foreign farms are spreading across Africa to grow food and biofuels for global markets, bringing much-needed investments but also new troubles for a continent struggling to feed itself.
China, Malaysia, Singapore and Bangladesh are just some of the countries spending billions of dollars in what critics have dubbed a new "scramble for Africa", a reference to Europe's 19th century colonisation drive.
But Africa holds an estimated 60% of the world's uncultivated, arable land, making the continent a critical component to international efforts to feed the planet's growing population.
How to achieve global food security is one of the most contentious issues at the upcoming Rio Summit on the environment, where activists are expected to sound the alarm over "land grabs" in Africa.
Many of the deals are with private companies, from Asian states seeking to feed large, growing populations to Europeans looking to produce biofuels, and their arrival on the continent has sometimes provoked angry backlashes.
Bangladesh's government explicitly encourages such schemes as a way to feed its 150 million people, as its own farmland falls to urban and industrial growth.
Bangladeshi companies have deals to grow rice in Uganda and Tanzania, but across the continent in Gambia, the government rejected a deal following an uproar over a foreign farm project in neighbouring Senegal.
Last year two people died in protests in Senegal over a 20 000ha biofuel scheme. The government in Dakar put the scheme on ice.
The most dramatic case so far has been South Korean conglomerate Daewoo's $6bn plan to grow corn and palm oil in Madagascar, on an area the size of Belgium.
Public outrage at the deal was one of the sparks to protests that toppled then-president Marc Ravalomanana in 2009. The deal was scrapped after the coup, which tipped the island into an ongoing crisis.
Conflicts with local residents, often caused by shady contracts, are one of the biggest problems caused by the large-scale deals. Some communities are resettled, others complain about competition for water.
"Recent land acquisitions in Cameroon all look shocking, due to their scale, their low cost [as little as 50 US cents a hectare a year], their length [of up to 99 years], and their secrecy," said Samuel Nguiffo, of the Centre for Environment and Development.
In Liberia, such deals could cover up to half of the nation's arable land, squeezing the land left for riverside communities to grow food, according to Columbia University's Centre for International Conflict Resolution.
Riots erupted over a 2009 deal with Malaysia's Sime Darby to plant rubber and palm oil plantations, forcing President Ellen Johnson Sirleaf in December to admit to "mistakes" in the $3bn contract.
"I don't know where I am going to make farm this year. The land my great parents left with me has been taken from me and given to Sime Darby," said local farmer Fred Dassen, 61, on a recent radio report.
Activists argue that policymaking is tilted toward agro-industry, while Africa should support its own small farmers with better seeds or extension services.
African farm productivity is low, about one-quarter the global average, according to the UN Food and Agriculture Organisation. Just 8.5% of arable land is cultivated, and only 5.4% irrigated.
Governments argue that big foreign investment can change that as companies improve infrastructure and train new farmers. New crops can also bring new industry: Liberia hopes its oil plantations will lead to a soap factory.
Gabon has attracted $4.5bn in investments in rubber and palm oil by Singapore's agro-food giant Olam.
The government says the company's new rubber plantation and factory would create 6 000 direct jobs and 5 000 subsidiary jobs. The company will also build thousands of homes as well as schools and a health clinic.
Marc Ona, founder of the Brainforest pressure group, said the concern is more about the lack of oversight of the deals and the impact on the environment and society.
"Faced with the challenge of food security, the choice is often geared toward agro-industry, with decisions made in illegal circumstances, without judicial oversight," he said.