C. Lemieux et C. Delisle, USING COVER CROPS TO ESTABLISH WHITE AND BLACK SPRUCE ON ABANDONED AGRICULTURAL LANDS, Phytoprotection, 79(1), 1998, pp. 21-33
Vegetation control is a critical factor in reforestation. On abandoned
agricultural lands, an alternative to herbicide application is the us
e of cover crops to compete with the weeds a nd to improve survival an
d growth rates of transplanted species. A factorial experiment was car
ried out on four sites to test this hypothesis. The experiment include
d three factors. The first factor consisted of lime versus no lime app
lication. The second factor included four cover crop combinations and
a control. Cover crop combinations were winter barley (Hordeum vulgare
) underseeded with either birdsfoot trefoil (Lotus corniculatus), Kent
ucky bluegrass (Poa pratensis), ladino clover ( Trifolium repens), or
a mixture of Kentucky bluegrass and ladino clover. The third factor co
nsisted in planting either white (Picea glauca) or black (Picea marian
a) spruce seedlings. Winter barley did not establish as rapidly and vi
gorously as expected. Nevertheless, the cereal reduced weed population
s in the establishment year. For broadleaf weeds, this reduction was n
ot large enough to allow a carryover during subsequent years. In contr
ast, subsequent increase of the grassy weed populations was slowed dow
n in the presence of cover cro ps. The establish ment of the other cov
er crops was poor and highly variable from site to site. It is not cle
ar whether this relative failure was due to growing conditions, poor e
stablishment of the cereal cover crop, or to other factors. Liming and
cover crops had little effect on spruce growth but black spruce seedl
ings grew taller than white spruce seedlings at two out of four sites,
and basal diameter of white spruce reached larger values than did bla
ck spruce. For white spruce, this might constitute an advantage in old
fields where seedlings are prone to lodging under weed pressure. Fina
lly, it was noted that seedling survival was exceptionally high in all
treatments.