Reuters - DEFRA, Other Agencies & Universities Probing Apparent Global Crop Plateau
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Beginning in the 1980s, however, that has become more difficult. Around that time, rice yields in the Republic of Korea stopped increasing, and in the United States, some of the best maize farmers were increasingly hitting a wall.
Every year, farmers from all over the United States enter state and national farming contests to see who has the highest yield. The winner gets free seeds and tractors, and is paid to tour the country and give talks about how he or she did it. "Thousands of farmers are motivated to win that contest, Cassman said.
Yet, by the late 1990s, Cassman noticed the winning yields in those competitions had not changed significantly for several years. He gathered that if the most motivated farmers in the country failed to increase their yields, it was likely because they could not. He hypothesised they had hit the crops yield potential, or the highest yield attainable using the best seeds and optimal levels of nutrients and water.
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A report produced for the UKs Department of Environment, Food and Rural
Affairs (DEFRA) in 2012 investigated apparent yield plateaus for wheat and oilseed rape (used to produce vegetable oil) and found a variety of factors at play, including individual farming practices and regulatory constraints on fertilisers. Its not a black and white picture, said Simon Kightley of the UK-based National Institute for Agricultural Botany and an author of the report. Still, most people have a hunch what the major forces are holding back growth of yields. Kightley said he thinks on-the-farm practices, like how much or how little farmers plow, play a significant role in why yields are plateauing.
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http://www.trust.org/item/20131119230754-aynqh/?source=hptop