Mj. Jones et M. Singh, Long-term yield patterns in barley-based cropping systems in Northern Syria. 1. Comparison of rotations, J AGR SCI, 135, 2000, pp. 223-236
Trials, reflecting the feed needs in dry Mediterranean environments of smal
l-ruminant production systems based on barley, were established at two site
s in Syria in 1982. They compared various 2-course rotations of barley with
feed legumes, fallow or more barley. This paper summarizes a 14-year seque
nce of results from an incomplete factorial combination of four rotations (
B-V, B-L, B-F? B-B) of barley with vetch (Vicia sativa), lathyrus (Lathyrus
sativus), fallow, and barley, with two fertilizer regimes, zero control an
d biennial NP applied to the barley phase, in terms of long-term mean yield
s, production stability and yield trends over time.
On a 2-year rotational basis, most barley was produced by barley-only rotat
ions, and differences between B-F and B-B were small; but, in terms of tota
l biomass production? feed legume rotations (B-V and B-L) outyielded barley
-only rotations by 29 % at one site and 19 % at the other. Responses to bie
nnial fertilization were large but did not interact significantly with rota
tion treatment. The crude protein status (% N) of barley grain and straw wa
s strongly determined by seasonal rainfall, but that of the grain could be
enhanced, irrespective of rainfall, by a preceding feed-legume crop; and, a
ltogether, the total mean crop nitrogen output of legume-based rotations ex
ceeded that of barley-only rotations by 80% and 64% at the two sites. The i
nclusion of legumes thus enhances both quantity and quality of feed product
ion.
Annual yield fluctuations, attributable mainly to rainfall difference, were
greater at the drier site. No consistent effect from fertilizer was observ
ed. but at the wetter site rotation differences were appreciable, with B-F
rotation giving the most stable yields. A number of time trends in yield va
lues were tentatively identified. On a relative basis, some widening over t
ime of the gap between fertilized and unfertilized treatments was observed
in feed-legume yields at both sites and barley yields at the wetter site; o
ver 14 years, yields in unfertilized plots had apparently declined relative
to those receiving biennial NP. But, apart from a probable decline in lath
yrus productivity compared to that of common vetch, changes in relative yie
ld performance between rotations were difficult to detect. Regression model
s developed to describe absolute yield trends indicated a real decline over
time in barley grain yields in continuous barley (B-B) at both sites and i
n unfertilized plots of all four rotations at the wetter site.