Liquid Water--Spurs Seeds' Sprouting
By David Elstein
January 7, 2003
A new finding by
Agricultural Research Service soil
scientist Stewart B. Wuest has stunned many plant scientists. Until recently,
it was generally believed that seeds must be in direct contact with soil to
obtain liquid water needed for germination. Then Wuest discovered the
importance of water vapor.
From his research on wheat seeds at ARS'
Conservation Research Center in Pendleton, Ore., as well as from studying
previously published data, Wuest concluded that water vapor in the soil is
actually what makes seeds germinate. With a relative humidity of close to 99
percent in soil, the seeds didn'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 also 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.
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 absorption of
water from the air. Similarly, seeds are able to absorb 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
In light of this discovery, approaches to water absorption models and
measurement 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.
Findings from Wuest's research were published in a recent issue of the Soil Science Society of America
ARS is the U.S. Department of
Agriculture's chief scientific research agency.