But no matter how much we maximize crop yield per acre, the limiting factor for food production is land.

但是不管我们如何最大化粮食亩产量，最大的制约因素还是土地。

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They say the fall in crop production is causing food prices to rise.

他们指出，粮食产量下降正导致价格上涨。

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Economists blamed the crisis on different causes, including high energy costs, bad weather and the use of food-crop lands for biofuel production.

VOA: special.2010.03.23

The method might be the key to the widescale production of fuel from algae, which is thought to be the better option over making it from land-based crops such as soya and corn, since the yields are much greater and there is no competition with food-crop production, and provide a real alternative to a globalized world that is utterly dependent on supplies of imported crude oil.

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"There are implications to dedicating more and more crop land to fuel production rather than food production, " said Tyson Clocum of the consumer watchdog group Public Citizen.

CNN: Farmer turns to fruit tree to power tractors

The report does not give an answer but some economists have made the attempt, variously citing demand from China and other developing nations, the diversion of crop use from food to fuel oil, and production constraints.

ECONOMIST: Investors may not have caused commodity price rises