The big three nutrients needed for crop production are nitrogen, phosphorus and potassium. Of the three, phosphorus is the hardest for plants to get out of the soil.
“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,” said K.G. Raghothama, assistant professor of horticulture at Purdue University in West Lafayette, Ind.
Purdue researchers are said to be the first to isolate genes that help roots take up phosphate, a common form of phosphorus. Their work has been reported in the Proceedings of the National Academy of Science.
The research toward helping plants get the nutrient out of the soil has been spurred by predictions that we might have only 90 years of high-quality rock phosphate fertilizer. The concern stems from calculations by a Canadian researcher that, based on known reserves, rock phosphate mines will be depleted by 2090.
Researchers note that the very acid soils of the tropics contain many molecules of iron and aluminum that 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,” said Purdue agronomist Dave Mengel. “In alkaline soils of the West, calcium reacts with phosphorus and essentially fixes it.”
Midwestern soils hold the mineral less tightly, Mengel said, but generally still require annual applications of phosphorus to keep crops healthy. Even in the Midwest, soil phosphorus is the least available of the big three nutrients.
Raghothama explained that 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. Some plants develop more roots. Some produce and release organic acids and enzymes that can pry the nutrient away from the attraction of the soil clay and organic matter.
In some plants, phosphorus starvation flips a genetic switch that changes certain molecules in roots and makes plants better at acquiring phosphate.
In collaboration with Jose Pardo from the Instituto de Recursos Naturales y Agrobiologia in Spain, Raghothama decided to concentrate on plants’ genetic and molecular responses to phosphorus deficiency. Perhaps, he thought, he could find out what mechanism makes plants better at phosphorus uptake, then track down the genes that turn on the mechanism.
He predicted that once they understand it, researchers might enhance a plant’s natural ability to compete for the few phosphorus molecules found free in the soil.
