Conservation Agriculture

Conservation Agriculture, as defined by the Food and Agriculture Organisation of the United Nations (FAO), is receiving growing acceptance internationally as the optimal crop production system, and includes all farming systems which involve simultaneous adherence to the principles of:

• Continued minimal soil disturbance (including NO soil inversion) – to retain root channels and encourage the build-up of soil biota populations and hence soil structure;
• Permanent organic soil cover (either by living crops or by crop or other plant residues) – to diminish the impact of raindrops and reduce water runoff (and consequently soil loss); and
• Diversification of crop species growing in sequence and/or associations (especially crop rotation) – to increase the diversity of food sources and hence soil biota, especially predators, and break pest and disease cycles.

Note that, although some organic farmers practice Conservation Agriculture, where production systems require the inversion or cultivation of the soil more than is necessary to insert the seed or seedling (for example, in the incorporation of manures), such systems can not be described as Conservation Agriculture systems.

No Till (also called Zero Till or Direct Seeding)

This is a crop production system that involves no seed bed preparation other than the opening (via a slit or punched hole) of the soil for the purpose of placing seed or seedling. No cultivation is performed during the growing season. As with Conservation Agriculture, weed control is accomplished using mulches, allelopathy (the antagonism of some plants or plant residues to other plants), crop rotation or appropriate (preferably narrow spectrum bio-friendly) herbicides.

Minimum Tillage

These are systems that involve minimal soil manipulation for crop production. Also referred to as reduced tillage, Minimum Tillage’s major objectives include:

• to perform the minimum number and severity of operations thought necessary to optimise soil conditions, frequently differentiating between the in- and inter-row areas;
• to minimise the number of trips over the field to avoid soil compaction and structural degradation;
• to conserve moisture;
• to reduce soil erosion; and
• to reduce mechanical energy and labour requirements

Some common Minimum Tillage systems include:

Till and Plant: Tractor-driven equipment prepares narrow strips utilising shallow secondary tillage after the primary tillage and just ahead of the planter.

Strip Tillage: Combination units perform strip or zone tillage just ahead of the planter in untilled soil (usually utilising a chisel plough, with the sole aim of improving porosity and rooting depth in root zone). Specific practices include

• Rip-on-row: A heavy tine at a depth of 300-450mm is drawn in the line of the planned (often also the previous) row ahead of the planter.
• Chisel: Lighter chisel tines are drawn at a depth of 200-300mm as the sole cultivation prior to planting.
• Chisel & disc: Primary tillage is conduced using chisel tines only, followed by a light disc immediately prior to planting.
• Disc-plant: One discing operation before planting is done to loosen the compacted soil surface, to control weeds, and to leave most of the residue on the surface.
• Bed-plant: This method is commonly used for soil moisture management especially in surface irrigated crops where furrows are made at appropriate intervals raising the bed between.

Ridge Till

This is a planting method where crops are planted on the ridge top, in the furrow or along both sides of a ridge. The ridges may be on the contours with graded furrows draining into a grassed water way, or use short cross-ties to create a series of basins to store water in ‘tied-ridges’.

Mulch Till

This is a system that involves cutting the roots of weeds and other plants, leaving the crop residue on the surface or mixed into the top few centimetres of the soil.

To plough or not to plough – old and new paradigms in crop production

Source for above table: After Derpsch 2004.