Urbana Laboratories, St. Joseph, MO, sold enough of the patented strain in 1995 to treat 227,000 acres, and sold one-third more in 1996. Some 10 to 12 million acres of soybeans are inoculated each year. The new inoculant, a product of conventional bacterial genetics by ARS scientists, resulted in plants that develop 25 percent more root nodules. Inside these nodules, bacteria live and convert nitrogen from the air into a form the plants can use. As a result, bacteria living in nodules on the roots are still able to fix nitrogen.
Nodules have to maintain just the right amount of oxygen.
Too much or too little harms the bacteria's ability to supply nitrogen from the air to the plant. No one is sure how nodules regulate their oxygen supply, but ARS researchers used microelectrodes to discover that electrical changes are linked to changes in oxygen supply in soybean, alfalfa, clover and birdsfoot trefoil nodules under oxygen stress. This discovery could eventually lead to improvements in stress tolerance of root nodules, allowing them to continue supplying the crop with nitrogen even under moderate drought or after cattle grazing. The electrical response to stress was discovered after excess oxygen was pumped around the nodules. To the researchers' surprise, the negative electrical charge on the inside walls of the nodules' cells dropped.