Agriculture Reference
In-Depth Information
Cultivation in the form of tillage was limited to horse-drawn implements and
hand weeding. Trees were often planted in square grids with a tree at each
corner of the square, allowing cultivation in all directions. Given reasonable
care, soil compaction was minimal and biodiversity within the orchard high.
Advent of the Tractor and Herbicides
With the introduction of these two factors, the situation changed. As re-
cently as the early 1980s, many commercial orchards were kept bare of all
vegetation except trees by using a combination of mechanical cultivation
and herbicides. While the scorched earth approach to orchard floors elim-
inated weed competition, serious problems began developing. In many orch-
ards, soil compaction and erosion became severe. With the compaction and
loss of soil structure, water infiltration decreased and root damage from dis-
eases and physiological disorders became common. Root damage from im-
proper mechanical cultivation was sometimes serious. Erosion became even
more severe, and concentrations of soil organic matter decreased, as did pop-
ulations of micro- and macroorganisms.
By the mid-1980s, much research on the use of alley crops was under way.
The focus was initially on reducing soil compaction and erosion. With the
introduction of size-controlling rootstocks for apples and pears, tree dens-
ity began increasing — we went from about 100 trees per acre or fewer to
around 200 or more trees per acre planted relatively closely together in rows
separated by distinct alleys. The use of permanent alley crops, narrower al-
leys, and more closely spaced trees altered mechanical soil cultivation prac-
tices.
Most of the alley crops originally tested were monocultures or blends of
sod-forming grasses. Tree rows were kept weed-free with preemergence and
contact herbicides. Erosion and soil compaction were reduced, but some of
the early results showed disappointing fruit yields and rates of tree growth.
Some turf crops appeared to reduce tree growth rates, not only due to com-
petition for water and nutrients, but also due to alleopathic effects of the
grasses on the trees. Rodent problems also increased as alley crops were re-
