S. Bittman et al., LONG-TERM EFFECTS OF FERTILIZER ON YIELD AND SPECIES COMPOSITION OF CONTRASTING PASTURE SWARDS IN THE ASPEN PARKLAND OF THE NORTHERN GREAT-PLAINS, Canadian Journal of Plant Science, 77(4), 1997, pp. 607-614
Little is known about the effects of long-term application of fertiliz
er on the complex pasture swards of the Aspen Parkland region of weste
rn Canada. Experiments were conducted, lasting from 1980 to 1992, on f
ive contrasting swards representative of permanent pastures in northea
st Saskatchewan to determine the long-term effects of N, P, K and S fe
rtilizer on herbage yield and species composition. The experimental sw
ards consisted primarily of smooth bromegrass (Bromus inermis Leyss.),
Kentucky bluegrass (Pea pratensis L), and creeping red fescue (Festuc
a rubra L.), in varying amounts. Seven fertilizer treatments were appl
ied at each site from 1980 to 1991 (shown as N-P-K-S in kg ha(-1)): 0-
0-0-0, 45-0-0-0, 45-20-0-0, 90-0-0-0, 90-20-0-0, 90-20-50-20, 180-20-0
-0. Another treatment (90-20-0-20) was added in 1984. An area within e
ach plot was protected from grazing with wire exclosures and harvested
in July and September. Harvested samples were classified according to
coarse-leafed grasses (mostly smooth bromegrass), fine-leafed grasses
(mostly Kentucky bluegrass and creeping red fescue), legumes and weed
s before drying and weighing. Ground cover composition of all plots wa
s measured by a modified line transect technique in 1980, 1987 and 199
2. All swards, regardless of species composition, responded positively
to fertilizer. The yield increase obtained from applying 45 or 90 kg
N ha(-1) (0.8 and 0.7 t ha(-1), respectively) was more than doubled by
adding 20 kg P ha(-1) with the N. Nitrogen applied alone did not affe
ct the proportion of bromegrass but increased the proportion of fine g
rasses in the herbage; adding N and P increased the proportion of coar
se grass and at the expense of fine grasses. With respect to sward com
position: N decreased the proportion of bromegrass and increased the p
roportion of bluegrass and fescue whereas adding N and P had the oppos
ite effect. Application of S increased yield 0.9 to 1.8 t ha(-1) and g
reatly increased the proportion of bromegrass in the sward and the har
vested herbage of the three sites with low levels of soil S. The resid
ual effect of the N and P treatments on yield was small but the effect
on species composition of the herbage was substantial; S produced a r
esidual effect on yield in 1992 and a large residual effect on species
composition. The results indicate the need for balanced nutrient appl
ication to enhance yield and maintain or improve sward species composi
tion of pastures in the Aspen Parkland. Fertilizer can be used to impr
ove yield on a wide range of sward types.