Agriculture Reference
In-Depth Information
Conclusions and recommendations
Production and appropriate management of high-residue, grass-legume mixtures are highly
recommended cultural practices for improving productivity and soil quality in all cropping
systems: organic, chemical or integrated. Use of cover crops as green manures is a common
and highly valued practice of many organic growers. Because cover crops are now being used
extensively in chemical no-till systems, many proponents and some practitioners of organic
agriculture believe that organic no tillage is the ideal system to achieve a desirable balance
between short-term productivity (yield) and production capacity (sustainability).
The question is not whether integration of organic cropping systems with no-till practices
is a sound concept, it is how to produce organic no-till cash crops without herbicides. Most
growers and agricultural professionals recognise the potential immediate and emergent (syn-
ergistic long-term) benefits of organic no-till integration; unfortunately, experience has often
been disappointing. Generally, however, good weed suppression and high yields are achieved
in warm long-season climates where organic cash crops are effectively established in high-
residue dead cover crop mulch.
Using site-specific tillage rotations (strategic sequencing of no tillage and non-inversion
tillage) can help growers bridge the gap between the ideal scenario (organic no tillage, i.e. weed
suppression without chemicals or tillage) and weed management problems that frequently
occur in organic no-till fields. Two distinct situations are possible when organic no-till growers
may revert to using non-inversion tillage implements. First, just before or after planting cash
crops, a grower may determine that a remedial weed management tactic needs to be used to
prevent production of weed seeds and preserve the cash crop (Tables 1 and 2). Second, after
harvesting cash crops and before drilling overwintering cover crops, growers may choose to
employ a single or a combination of non-inversion tillage equipment to:
1 kill residual vegetation (cash crops and weeds);
2 incorporate plant residues and applied soil amendments;
3 alleviate subsoil compaction; and
4 prepare an improved seedbed for drilling cover crops.
In the following spring or summer, overwintering cover crops could then be used as a high-
residue mulch for production of organic no-till or reduced-till cash crops.
In summary, organic no-till systems are recommended only where high-residue cover crops
can be grown and managed properly, and when productivity of cash crops is favourably affected
by root and shoot biomass (surface residue mulch) of the cover crops. Research and grower
experience have shown that organic no-till systems are most likely to succeed:
1 in warm, long-season climates, especially Mediterranean-like regions;
2 in well-drained, fertile soils, especially on sloping, erosion-prone land;
3 with late plantings, i.e. when there is not an early-season market demand;
4 when cash crops are established from transplants or large seeds; and
5 when cover crops produce high-residue levels of persistent biomass that can suppress weeds
(Table 1).
Tilling only in-row areas (grow zones) and leaving the alleyways untilled and covered with
sod or cover crops is an alternative 'hybrid' system that can be used in more challenging cir-
cumstances such as compacted soils and cold short-season climates. Depending on the site-
specific situation, in-row tilled areas can be either covered with pre-plant plastic mulch or
post-plant organic mulch, or left uncovered as strip-till or ridge-till (raised-bed) systems (El
Titi 2003).
