FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS - helping to build a world without hunger

The main principles of conservation agriculture
Conservation agriculture systems utilize soils for the production of crops with the aim of reducing excessive mixing of the soil and maintaining crop residues on the soil surface in order to minimize damage to the environment.

By doing this CA will:
  • Provide and maintain an optimum environment of the root-zone to maximum possible depth. Roots are able to function effectively and without restrictions to capture high amounts of plant nutrients and water.
  • Ensure that water enters the soil so that (a) plants never, or for the shortest time possible, suffer water stress that will limit the expression of their potential growth; and so that (b) residual water passes down to groundwater and stream flow, not over the surface as runoff.
  • Favour beneficial biological activity in the soil in order to (a) maintain and rebuild soil architecture; (b) compete with potential in-soil pathogens; (c) contribute to soil organic matter and various grades of humus; (d) contribute to capture, retention, chelation and slow release of plant nutrients.
  • Avoid physical or chemical damage to roots that disrupts their effective functioning.
The three principles of conservation agriculture include:

Direct seeding or planting
Direct seeding involves growing crops without mechanical seedbed preparation and with minimal soil disturbance since the harvest of the previous crop. The term direct seeding is understood in CA systems as synonymous with no-till farming, zero tillage, no-tillage, direct drilling, etc. Planting refers to the precise placing of large seeds (maize and beans for example); whereas seeding usually refers to a continuous flow of seed as in the case of small cereals (wheat and barley for example). The equipment penetrates the soil cover, opens a seeding slot and places the seed into that slot. The size of the seed slot and the associated movement of soil are to be kept at the absolute minimum possible. Ideally the seed slot is completely covered by mulch again after seeding and no loose soil should be visible on the surface.

Land preparation for seeding or planting under no-tillage involves slashing or rolling the weeds, previous crop residues or cover crops; or spraying herbicides for weed control, and seeding directly through the mulch. Crop residues are retained either completely or to a suitable amount to guarantee the complete soil cover, and fertilizer and amendments are either broadcast on the soil surface or applied during seeding.
A three-row no-till planter planting through a cover crop flattened by a knife roller. (T. Friedrich).

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Permanent soil cover
A permanent soil cover is important to: protect the soil against the deleterious effects of exposure to rain and sun; to provide the micro and macro organisms in the soil with a constant supply of "food"; and alter the microclimate in the soil for optimal growth and development of soil organisms, including plant roots.
Cover crops need to be managed before planting the main crop. This can be done manually or with animal or tractor power. The important point is that the soil is always kept covered. (FAO).

The effects of soil cover:
  • Improved infiltration and retention of soil moisture resulting in less severe, less prolonged crop water stress and increased availability of plant nutrients.
  • Source of food and habitat for diverse soil life: creation of channels for air and water, biological tillage and substrate for biological activity through the recycling of organic matter and plant nutrients.
  • Increased humus formation.
  • Reduction of impact of rain drops on soil surface resulting in reduced crusting and surface sealing.
  • Consequential reduction of runoff and erosion.
  • Soil regeneration is higher than soil degradation.
  • Mitigation of temperature variations on and in the soil.
  • Better conditions for the development of roots and seedling growth.
Means and practices:
  • Use of appropriate/improved seeds for high yields as well as high residue production and good root development.
  • Integrated management and reduced competition with livestock or other uses e.g. through increased forage and fodder crops in the rotation.
  • Use of various cover crops, especially multi-purpose crops, like nitrogen-fixing, soil-porosity-restoring, pest repellent, etc.
  • Optimization of crop rotations in spatial, timing and economic terms.
  • " Targeted" use of herbicides for controlling cover crop and weed development.
Crop rotation
The rotation of crops is not only necessary to offer a diverse "diet" to the soil micro organisms, but as they root at different soil depths, they are capable of exploring different soil layers for nutrients. Nutrients that have been leached to deeper layers and that are no longer available for the commercial crop, can be "recycled" by the crops in rotation. This way the rotation crops function as biological pumps. Furthermore, a diversity of crops in rotation leads to a diverse soil flora and fauna, as the roots excrete different organic substances that attract different types of bacteria and fungi, which in turn, play an important role in the transformation of these substances into plant available nutrients. Crop rotation also has an important phytosanitary function as it prevents the carry over of crop-specific pests and diseases from one crop to the next via crop residues
An example of crop rotation to maintain soil fertility and break pathogen carry-over

The effects of crop rotation:
  • Higher diversity in plant production and thus in human and livestock nutrition.
  • Reduction and reduced risk of pest and weed infestations.
  • Greater distribution of channels or biopores created by diverse roots (various forms, sizes and depths).
  • Better distribution of water and nutrients through the soil profile.
  • Exploration for nutrients and water of diverse strata of the soil profile by roots of many different plant species resulting in a greater use of the available nutrients and water.
  • Increased nitrogen fixation through certain plant-soil biota symbionts and improved balance of N/P/K from both organic and mineral sources.
  • Increased humus formation.
Means and practices:
  • Design and implementation of crop rotations according to the various objectives: food and fodder production (grain, leaf, stalks); residue production; pest and weed control; nutrient uptake and biological subsurface mixing / cultivation, etc.
  • Use of appropriate / improved seeds for high yields as well as high residue production of above-ground and below-ground parts, given the soil and climate conditions.

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