USDA says a study it has completed supports its priority on responding to climate change. The study compared tillage practices under high CO2 levels. The results show that elevated CO2 causes soybean and sorghum plants to increase photosynthesis while reducing transpiration - the amount of water the plants release. This resulted in increased water use efficiency, whether the crops were grown with no-till or conventional tillage.
Scientists with the Agricultural Research Service compared soybean and sorghum rotations with both conventional tillage and no-till. The scientists also compared current ambient CO2 levels, about 370 parts per million, with levels of 720 ppm expected within this century. With the higher level of CO2, regardless of tillage method, soybean photosynthesis increased by about 50%, while sorghum photosynthesis rose by only 15%. This was expected because crops like soybean are known to respond better to high CO2 levels than crops like sorghum and corn. No-till didn't make a difference as far as crops responding to high CO2.
Water use efficiency response to high CO2 was much greater for soybeans than for sorghum over the six-year study. Sorghum's increased water use efficiency was mainly due to less water transpired or lost through the leaf pores.
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