Agriculture Reference
In-Depth Information
MUSTARD COVER CROP FOR FUJI APPLES
Using cover crops to suppress the growth of invasive weeds can help reduce the need for herbicides in an agroecosystem.
To be useful, however, a cover crop must exclude other weeds without inhibiting the growth of the crop plant. Wild
mustard ( Brassica kaber ) appears to be a cover crop that meets these requirements well, when planted in fruit orchards
(Figure 15.4).
In a study of the conversion from conventional to organic management of young Fuji semidwarf apple trees,
James Paulus, a graduate student researcher at the University of California, Santa Cruz, demonstrated the potential
use of mustard as a cover crop species (Paulus, 1994). He grew several different types of cover crops between the
trees in different plots and examined their effectiveness at weed control. The cover crop treatments were compared
to conventional management with herbicides and to an organic conversion plot using plastic tarp for weed control.
Mustard was the only cover crop tested that controlled weeds as effectively as conventional herbicides or plastic
tarp. Forty-five days after mustard emerged, it had displaced nearly all of the other weed plants in the plot and
accounted for 99% of the total weed biomass present. Other covercrops only achieved partial dominance, accounting
for no more than 42% of the total weed biomass in their respective plots.
It appears that mustard achieves this level of dominance through allelopathic inhibition of other weeds. Many members
of the genus Brassica, including mustard, have been observed to inhibit weed growth in the field, and research has shown
they contain potentially allelopathic chemicals called glucosinolates, which inhibit seed germination in the laboratory
(Gliessman, 1987). Seeds of monocot grasses — often a problem as weeds — are the most strongly inhibited.
Paulus found that the mustard not only inhibited weeds effectively, but actually helped increase apple production.
Trees in the plots with a mustard cover crop produced more than three times as many apples per tree than trees in
the conventional plots. Moreover, the trees grown with mustard increased in girth more rapidly, showing diameters
as much as 50% larger than trees in the conventional plots after 2 years.
At least part of the yield advantage in the mustard-cover cropped plots was due to improved nutrient cycling.
Analysis showed that the weed cover took up significant amounts of nitrogen during the winter, lowering its concen-
trations in the soil. When the winter rains came, nitrogen in the bare soil treatments was leached out and lost from the
system, whereas the nitrogen in the covercrop treatments was immobilized in the weed biomass. When the cover crop
was cut down in the spring, the nitrogen was made available to the trees to use for spring and summer growth.
FIGURE 15.4 Wild mustard cover crop in an apple orchard. Wild mustard ( Brassica kaber ) adds an array of species interactions
to an apple agroecosystem by attracting beneficial insects to its flowers and allelopathically inhibiting other weedy plants.
 
Search WWH ::




Custom Search