WEST LAFAYETTE, Ind. --Spurred by predictions that we may have only 90 years of high-quality rock phosphate fertilizer left, Purdue University researchers have taken a step toward helping plants get the nutrient out of soil.
They were the first to isolate genes that help plant roots take up phosphate, a common form of phosphorus. Their work was reported in the Proceedings of the National Academy of Science.
"Lack of phosphorus fertilizer is going to be a serious problem in the future in certain parts of the United States and especially in the tropics, unless we find another source of phosphorus in the world or unless we create plants that are more efficient phosphorus users," says K.G. Raghothama (RAG-oh-TOM-uh), Purdue assistant professor of horticulture.
Based on currently known reserves, rock phosphate mines will be depleted by 2090, according to calculations by a Canadian researcher in 1996.
Among the big three nutrients -- nitrogen, phosphorus and potassium -- phosphorus is the hardest for plants to get out of soil. The degree of phosphorus availability varies from place to place, but many soils jealously guard their phosphorus supplies.
The very acid soils of the tropics contain many molecules of iron and aluminum, which latch onto and tie up nearly all available phosphorus.
"We also have problems in the Southeastern United States and on calcareous soils in the Great Plains of the American West," says Purdue agronomist Dave Mengel. "In alkaline soils of the West, calcium reacts with the phosphorus and essentially fixes it."
Midwestern soils hold the mineral less tightly, but generally still require annual applications of phosphorus to keep crops healthy, Mengel says. Even in the Midwest, soil phosphorus is the least available of the big three nutrients.
When soil phosphorus is sparse and plants can't get what they need, they make some
internal changes to bring in more of the mineral, according to Raghothama. Some pla
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