Agriculture Reference
In-Depth Information
1 using vigorous seeds and transplants;
2 planting in high-density multiple rows; and
3 precision placement and timing of fertiliser and water.
Excessively weedy fields (especially those containing perennial weeds) should be cleaned up
before attempting organic no-till systems. Growing successive smother crops and/or employ-
ing stale seedbed techniques for 1-2 years before attempting organic no tillage will often pay
great dividends with future cash crops (Bond and Grundy 2001).
Limitations
Maintaining weeds below yield-limiting levels without using chemical herbicides or cultiva-
tion is extremely difficult. Under ideal conditions, weed suppression and an acceptable balance
between crop yields and production capacity (sustainability) can be maintained or even
enhanced in organic no-till systems. However, in less than ideal conditions, levels of weed
seeds and/or perennating parts (tubers, bulbs, rhizomes, stolons) may be sufficiently high and
cover crop biomass may be sufficiently low that the potential for early season weed growth
warrants use of remedial non-inversion tillage weed implements and techniques to prevent
crop yield loss (Teasdale
et
al
. 2004).
Non-inersion tillage tradeoffs
Inversion tillage (ploughing) normally requires multiple field operations, resulting in exces-
sive soil aeration, decomposition of fresh organic residues and SOM and degradation of soil
structure. Rotational tillage is a trade-off or compromise between the two extremes, perma-
nent no tillage and inversion tillage. Rotational tillage is defined here to mean the strategic
sequencing of no-till and non-inversion tillage practices to achieve a balance between short-
term productivity and long-term production capacity (sustainability) (Jackson
et
al
. 2004).
This rotational-till concept is a type of reduced tillage that calls for avoidance of inversion
tillage in favour of a critical balance between no-till and non-inversion tillage practices. No-
till and non-inversion tillage practices are preferred since they generate only moderate inter-
vention in soil structure. Different types of non-inversion equipment can be used, ranging
from shallow tillage with rototillers, rotary hoes, powered harrows or high-residue cultivators,
to deep subsurface soil loosening with chisel ploughs or subsoiling and spading machines.
Shallow (5-8 cm deep) rototilling is included in non-inversion tillage because the integrity of
the subsoil layers is maintained (El Titi 2003).
When used in organic cropping systems, the objectives of non-inversion tillage are to
accomplish necessary weed management, enhance short-term nutrient availability, incorpo-
rate crop residues and soil amendments, and alleviate soil compaction, with minimum soil
disturbance and degradation of SOM. Ideally, non-inversion tillage is accomplished in one or
two field operations. Shallow non-inversion tillage can kill cover crops and weeds and incor-
porate their residues 5-8 cm deep without excessive disturbance or aeration of the lower soil
layers. Non-inversion in-row subsoiling (chisel ploughing) can alleviate compaction and facil-
itate deep placement of
in
situ
crop residues and soil amendments (vertical zone mulching and
soil building), thus deepening root exploration and increasing water and nutrient availability
(Reetz 2000). Using permanent controlled-traffic raised beds is another aspect of rotational
tillage that can create low bulk density/high tilth soil in designated plant-growing areas (grow
zones) on bed tops (Magdoff and van Es 2000).
