Agriculture Reference
In-Depth Information
Effects of herbicide use
Apple and pear orchard surfaces have, in different historical periods, been
cultivated, had a surface cover of mown grass with small areas kept clear
around the tree trunks, or had different proportions of the surface kept free
from grass by the use of herbicides. With the development of high-density
dwarf fruit tree systems in which the fruit trees were very closely spaced within
the row (e.g. with
m apart) the
herbicide-strip system, in which a central alleyway was grassed to provide a
working surface for tractors and the soil under the trees was kept clear of grass
using herbicides, came into use. With multirow or bed systems the trees were
in double or triple rows, or multirow beds, with just
-
m between trees in the row and rows
-
m or less between
the trees within the beds, this soil being kept clear of grass between the trees,
and narrow grass alleyways kept between beds. Alternatively, irrespective of
tree spacing and arrangement the entire surface of the soil was treated with
herbicides in an overall-herbicide system.
The effects on nutrient consumption of changes between these systems are
very large. In the Netherlands, overall grassed orchards were given about
-
.
kg K per hectare. After the change to herbicide
strip culture annual dressings were reduced to around
kg N,
kg P and
kg N,
kg P and
kg K per hectare without adverse effects on tree nutrient status (Delver,
a). Clearly, under the 'grassed-down' system the major nutrient use was by
the grass. A grass sward is very efficient at withdrawing nutrients from the soil
and grass competition for both water and nutrients needs to be compensated
for. A further complication is that in the herbicide strip system grass cuttings
may be deposited on the herbicide strip, so effecting a transfer of nutrients
from the alleyway to the under-tree area. The soil in the herbicided strips has
pH levels about
unit lower, much higher available P and somewhat higher
available K than that in the grassed alleys in the upper
cm (Atkinson and
White,
).
Trees growing under overall-herbicide conditions have larger root systems
than those in the herbicide-strip system which, in turn, have larger root systems
than those grown in grass (Atkinson and White,
). Under both systems of
herbicide management the tree roots are much more frequent in the surface
layer of soil than in grassed-down orchards (Figure
). In overall-herbicide
treated orchards apple tree roots are much more evenly distributed throughout
the row and alley than in grassed or herbicide-strip orchards (Atkinson and
White,
.
). Uptake of N into apple leaves is much less in grassed orchards
than where herbicides are used. In the herbicide-strip orchards N uptake is
much greater from the strip than from the alley. In overall-herbicide orchards
there is less effect of proximity of placement to the trunk. Uptake of P
is much lower in overall-herbicide treated orchards. This effect, which was
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