The Rural Voice, 1998-11, Page 23NATURE'S PARTNERSHIP
University of Guelph researchers see if trees and
crops can combine to increase farm profits
Story a,:d photos by Keith Rouiston
Recent research, and the use of
yield monitors on combines,
is confirming what some
farmers have suspected for years: that
crop yields. in areas protected by trees
arc larger than in open, wind-swept,
fields.
With high prices for hardwood
timber, recently, woodlot owners
have come to realize'there is a
potential to make as much money per
acre, per year from their woodlot as
there is from their cropping acreage.
Given these facts, what about
growing trees and crops together?
Will there be a benefit to both? On a
high, windswept hill on the
University of Guelph's Guelph Turf
Grass Institute, university researchers
have been exploring the idea since
1988 and this October, welcomed
visitors to an Agroforestry field tour
to learn some of the results. The
challenge, researchers said on the
tour, is to make best use of the
benefits of having trees beside crops
(creating a micro -climate, improving
soil organic matter, nitrate levels and
earthworm populations) and
minimize the adverse effects of
shading on crops.
The challenge to the research team
was daunting when they took over a
30 ha parcel of degraded farmland
east of Guelph and planted it with
rows of spruce, pine, walnut, ash,
sugar and silver maple, black locust,
red oak and hybrid poplar. The rows
were in two different spacings of 12
and 15 meters apart and the trees
were spaced 5 and 6.25 meters apart
within the rows. Between the rows a
rotation of soybeans, corn and winter
wheat were grown. In the intervening
years the researchers have been
trying to understand the interaction
between the trees and the crops.
Researchers have found that the
economics of the experiment can be
positive for depending on the tree
species used. For instance, selecting a
variety of trees with small compact
crowns will reduce the amount of
crop -shading.
Dr. Haresh V. Thevathasan found
that the trees deposited leaves on the
soil in the fall which dccay creating
30 per cent more organic material in
the soil than in monoculture -field
crop fields over an eight to 10 year
period. The greater portion of organic
material helps trap 40-50 per cent of
nitrates in the field rather than have
them leach into the ground water
supply or run off to streams. This in
turn can help fertilize crops.
Researchers also found they could
lower crop input costs because less
nitrogen was needed for the crops
grown between the trees.
Where does the saving come
from? In some cases, out of thin air.
Andrew Gordon speak to lour
participants in front of the Guelph
agroforestry plot.
Researcher Ping Zhang, working
with Andrew Gordon, analyzed
rainfall filtering through the leaves of
the trees to the crop below or running
down the stems (tree trunks) and
compared it to rainfall collected away
from the trees. They found that the
nutrient levels in the water in
thrqughfall or stemflow were up to
five times higher than in the
precipitation captured away from the
trees.
Crops
are also helped by the
ability of trees to act like a
pump, reaching deep into the
soil for nutrients that field crops can't
get, then bringing them up to the
surface to be dripped onto the field
through rainfall or deposited in
leaves.
The increase in nitrogen available
for the crops enhanced the nutrient
value of the crops grown. The
nutrient level of wheat, as well as the
amount of straw and roots (biomass),
increased closer to the trees (of the
five species of trees tested ash
seemed to have the greatest increase
on the biomass of wheat). The above-
ground biomass for wheat, grain
yield and average number of tillers
per row increased nearer the tree
rows compared to the centre of the
NOVEMBER 1998 19