The benefits and environmental impacts of using fertilizers rather tha
n legumes to promote more sustainable agricultural production systems
are in question. The objective of this study was to demonstrate the lo
ng-term consequences of withholding fertilizer N and P on wheat (Triti
cum aestivum L.) yields, and to determine if inclusion of legume-green
manures (GM), or hay crops in rotations can maintain wheat yields. A
34-yr crop rotation experiment being conducted at Indian Head, Saskatc
hewan, on a Udic Haploboroll with heavy clay texture, was used to asse
ss the influence of fertilizer (N and P), sweet-clover (Melilotus offi
cinalis L.) GM, and alfalfa-bromegrass (Medicago sativa L. - Bromus in
ermis Leyss.) hay on yield trends of hard red spring wheat grown on wh
eat stubble in rotations of varying cropping intensity. When no fertil
izer was applied, yields of wheat grown on wheat stubble trended stead
ily downward for fallow-wheat-wheat (F-W-W),(decline of 0.41 bu/acre/y
r) due to increased soil erosion and declining fertility; yield trends
declined less sharply (0.16 bu/acre/yr) for unfertilized continuous w
heat, because of less soil erosion. Inclusion of GM in an unfertilized
GM-W-W rotation increased the yields of wheat grown on stubble, but t
he yield trends were still negative (decline of 0.39 bu/acre/yr), prob
ably because legumes do not provide any P to the system. Even though t
he unfertilized F-W-W-hay (H)-H-H system had low available P, it maint
ained stubble wheat yields at a generally constant level (decline of 0
.08 bu/acre/yr) due to low soil erosion and because the hay-containing
system markedly increased N-supplying power of the soil. The addition
of N and P fertilizer at rates based on soil tests resulted in a posi
tive divergence in yield trends of wheat grown on stubble in F-W-W and
continuous wheat systems as both available N and P were maintained at
a high level. Legumes probably will require added P if they are to su
stain crop production in a manner similar to that provided by responsi
ble use of fertilizers.