Agriculture Reference
In-Depth Information
Table 1
Criteria for assessing the probability of weed suppression in organic no-till systems
C:N ratio, carbon to nitrogen ratio (weight to weight basis); minimum weed-free period (MWFP), defined as the
length of time a crop needs to remain free of weeds after planting to prevent yield loss - normally, the MWFP coincides
with the time of canopy closure; fertigation, when water and soluble organic fertiliser are applied in the irrigation
system.
Site factor criterion
Probability of achieing weed suppression
Low
Moderate
High
Mulch quantity
A
- dry wt (g m
-2
)
<400
400-800
>800
- soil coverage (%)
<75
75-95
>95
- depth (cm)
<5
5-10
>10
Mulch quality - C:N ratio
<15
15-25
>25
Perennial weeds (% total weeds)
>20
2-20
<2
MWFP (canopy closure, weeks)
>6
4-6
<4
Monthly in-season rainfall (mm)
>100
40-100
<40
Fertigation method
Overhead
Furrow
Drip
A
J.R. Teasdale, pers. comm., 2004.
When attempting to adopt organic no-till systems, a major challenge is to predict accu-
rately the weed suppression potential of any given situation. Six criteria for assessing the prob-
ability of achieving weed suppression in organic no-till systems are presented in Table 1. Weed
suppression is likely when most or all the six factors are in the medium to high probability cat-
egories (Table 1). When weed predictions reveal a low potential for weed suppression or when
actual field weed excesses occur, growers may decide that remedial weed management tactics
are necessary. Three common scenarios are presented in Table 2, in which predicted (using
Table 1) or actual weed densities warrant remedial intervention to preserve crop yield (Barker
and Bhowmik 2001).
Table 2
Remedial weed management methods recommended when predicted (using Table 1)
and/or when actual weed incidence is high in organic no-till fields
Growth stage of cash crop
when weeding is
considered necessary
Optional weed management methods
Pre-plant (1-4 weeks before
planting cash crop)
Objectie: reert to green manure, non-inersion-till systems
flail mow, if needed, and shallow incorporate cover crops and
weeds
after incorporating residues, use stale-seedbed techniques -
shallow till or flame weed seedlings
apply plastic mulch
after planting, cultivate or flame weed seedlings and apply
organic mulch
•
•
•
•
Early crop establishment
(2-3 weeks after planting)
before weed-crop
competition occurs
Objectie: preent weed-crop competition
shallow cultivate between rows
apply acetic acid, using a shielded sprayer
hand weed in-row areas
after weeding, apply organic mulch
•
•
•
•
Rapid crop growth (3-6
weeks after planting);
weed-crop competition
present
Objectie: minimise crop yield loss and preent production of
weed seeds
shallow cultivate between rows, if possible
apply acetic acid, using a shielded sprayer
rogue out large weeds by hand or use high-residue cultivators
or elevated mowers
•
•
•
