Agriculture Reference
In-Depth Information
systems realise that, although feasible in a limited short-term scenario, permanent organic no-
till systems present unique challenges because fewer weed management options are available
in organic no tillage, compared to chemical no tillage. Thus, using permanent no-till systems
for production of organic crops is considered a long-term, but obtainable goal (Schjønning
et
al
. 2004, Trewavas 2004).
Organic no-till systems present many challenges, including production and management of
high-residue cover crops, establishment of cash crops and weed management. Each challenge is
discussed below with desired objectives, recommendations for success, and limitations.
Production of high-residue coer crops
Objective
To produce uniformly distributed high-residue (≥6 t ha
-1
biomass), grass-legume cover crop
mixtures on permanent controlled-traffic raised beds, keeping the soil continuously covered
using diverse rotations of cash and cover crops.
Recommendations
Proper erection of wide raised beds (1.5-2.0 m wide and 0.15-0.25 m high) will help alleviate
existing compaction, especially if organic-approved soil amendments (compost, manure, lime,
gypsum) are thoroughly mixed deep into the soil profile during bed establishment. If wheel
traffic is restricted to alleyways between beds, the integrity of bed tops can be maintained and
the soil quality improved over time by growing high-residue cover crops, applying soil amend-
ments and rebuilding bed margins as needed. Weed seedbanks can be reduced and soil quality
improved over 3-6 years, if judicious weed seed sanitation and tillage practices are consistently
followed (Bond and Grundy 2001, Teasdale
et
al
. 2004).
Limitations
Keeping the soil permanently covered with dead and/or living residues requires timely and
effective plant establishment and application of growth inputs (water and nutrients). Uniform
dense cover crop stands are achieved most effectively using modern no-till seed drills (Morse
1999). Inexperience with seed drills and their high cost are often serious constraints for organic
farmers, especially small-scale (1-2 ha) growers. Although labour intensive, drilling small
plots with push seeders is a highly effective method of establishing cover crops (R. Morse and
M.W. Schonbeck unpublished data, 2005).
Residue management
Objective
To mechanically kill cover crops, generating either:
1 a thick uniform dead mulch over the entire bed (bed tops, alleyways); or
2 a strip-killed mulch on bed tops and a non-competing living mulch in alleyways between
beds.
Recommendations
Complete killing of cover crops (either the entire bed or just bed tops) is generally essential to
avoid competition with cash crops. Implements used to kill cover crops include f flail mowers,
undercutters, rollers or roller-crimpers (Creamer and Dabney 2002).
Limitations
Incomplete kill and subsequent regrowth of cover crops can be major problems for organic
growers. Unavailability and inexperience with mechanical-kill equipment are major constraints
