Diversifying crop rotations with temporary grasslands - Université de ...

Table 13: Mechanisms causing the impacts of perennial forage crops (PFCs) on weeds.
Hypothetic impacts of three characteristics of PFCs (A, B, C) on seven stages of the weed life cycle (1-7,
corresponding to Fig. 20).
Weed life cycle
stage
(1) Germination
(2) Emergence
(3) Vegetative
growth
(4) Plant survival
A) Absence of soil tillage
Reduce*** (M3)
(lack of stimulation
by light or oxygen,
lack of soil contact,
no seeds digged up?)
or increase 0
(M3) (seeds
not deeply
buried?)
Increase*** (M3)
(reduced plant destruction)
Characteristics of PFCs
100
B) Temporally extended
vegetation cover
Reduce* (M3)
(less light quantity and
modified light quality
under plant canopy?)
Reduce*** (M3, M5)
(competition for light,
water and nutrients)
C) Frequent hay cuttings
Increase 0
(M3)
(temporarily reduced
vegetation cover
-> more light on soil
surface?)
/ or increase 0
Reduce***
(increased
shoot
destruction,
M3, A4, A5)
(temporarily
reduced
competition
for light?,
M3, A5)
(5) Flowering /
(6) Seed production /
(7) Seed survival
Reduce*
(seeds stay on surface: more seed
predation A6-8, higher mortality,
more fatal germinations?)
Reduce**
(better habitat for seed
predators, A8)
Increase*
(reduced seed predation due
to habitat modification or
predator destruction,
A8)
*** high evidence; ** medium evidence; * low evidence; 0
no evidence; / probably no strong impacts; M3
Manuscript 3, A8 Article 8, etc.
C.II.4.3.1 Soil tillage (A)
Soil tillage is known to be one of the most important crop management techniques
determining weed population dynamics and community composition in arable fields (Kegode
et al., 1999; Barberi and Lo Cascio, 2001; Menalled et al., 2001; Davis et al., 2005; Murphy et
al., 2006). In our experiment, the observed differences in weed population dynamics between
(i) annual and perennial crops, (ii) spring and autumn sown perennial crops and (iii) the
different intercrop treatments of the annual crops were probably caused in large parts by
differences in soil tillage (see Table 12 for an overview).
The experimental results give evidence for two major and well-known impacts of soil tillage
on weeds: (1) the mechanical destruction of established weed plants and (2) the stimulation of
new weed emergence. The first mechanism has mainly negative effects on weed population
dynamics (and is therefore widely used in various forms of mechanical weed control).
However, in destroying weed (and crop) plants, soil tillage and other mechanical disturbances
may also create a less competitive environment that may be beneficial for other weeds (see