A soil scientist with the USDA Agricultural Research Service has stunned plant scientists with a finding that seeds do not need to be in direct contact with soil to obtain liquid water needed for germination.
Stewart B. Wuest of the Columbia Plateau Conservation Research Center in Pendleton, OR, showed from his research, that wheat seeds use water vapor in the soil for germination.
With a relative humidity of close to 99 percent in soil, seeds don't need to be tightly compacted in the soil to grow. In fact, seeds that were separated from the soil by crop residue still germinated, because the vapor was able to reach them.
Wuest found that, thanks to water vapor, seeds separated from soil by a layer of fiberglass cloth germinated just as well as those touching the soil. He was even able to germinate seeds suspended in air above water, using just the vapor rising from it.
An ARS report says water vapor is all around us, measured as humidity. That's what makes a dry cracker left out in a room with high humidity turn soggy from adsorption of water from the air. Similarly, seeds are able to adsorb their needed water from vapor in the soil. In fact, liquid water is not nearly as important as previously thought and may only account for 15 percent of water taken up by germinating seeds.
In light of this discovery, approaches to water adsorption models and measurements techniques may need to be changed. The design of some seeding equipment may also change, since actual seed-soil contact is not as important as earlier believed. Emphasis is likely to shift to tactics for retaining water vapor near the seed, according to the ARS study.