Conservation agriculture: the three principles and how to start

Ploughing turns the soil, buries weeds and gives a clean seedbed, but it also breaks down soil structure, burns up organic matter and leaves the surface bare. On bare soil, the first heavy summer storm can wash away topsoil that took centuries to form, and much of the rain runs off instead of soaking in. Conservation agriculture is a way of farming that works with the soil instead. It rests on three principles, and it works best when all three are applied together.

Principle 1: Minimum soil disturbance

Disturb only the soil where the seed and fertiliser go. Instead of ploughing and disking the whole field, you plant directly into the undisturbed soil and last season's crop residue.

• Smallholders often start with planting basins: small pits dug by hand in the same place every year, where seed, fertiliser and manure are concentrated.
• Animal-drawn rippers open a narrow slot along the row without turning the soil.
• Hand jab planters place seed through residue with very little disturbance.
• Commercial farms use no-till planters with discs or tines that cut through residue.

Principle 2: Permanent soil cover

Keep the soil covered as much of the year as possible, with crop residue, mulch or a living cover crop. A common target is at least 30 percent of the surface covered after planting, though more is better. Cover protects the soil from raindrop impact and wind, keeps it cooler, slows evaporation and feeds soil organisms.

Where rainfall allows, cover crops can be grown between main crops. Examples used in parts of Africa include oats and vetch in winter where there is enough moisture, and sunn hemp, lablab, velvet bean or cowpea in summer. In dry areas, simply keeping the previous crop's stalks on the field is the realistic goal.

Principle 3: Crop diversity and rotation

Growing the same crop on the same land year after year builds up its pests, diseases and weeds. Rotating cereals with legumes breaks those cycles, and legumes such as soybeans, groundnuts, cowpeas and dry beans can add nitrogen to the soil for the next crop. Intercropping, such as maize with cowpea or pigeon pea, adds diversity within a season.

What to expect

The benefits build over time. Farmers who make the change commonly report better water infiltration, less erosion and less time and fuel spent on land preparation. Crops may cope better with dry spells because more rain soaks in and less evaporates. But the full soil benefits usually take several seasons to appear, and the first year or two can be the hardest.

The common stumbling blocks

Weeds

Without ploughing, weeds must be controlled another way: by hand hoeing (shallow, to avoid disturbing the soil), by mulch that smothers them, by herbicides, or by a combination. Early weeding is critical in the first seasons. If you use herbicides, use products registered for the crop and follow the label, and calibrate your sprayer first. Weed pressure generally falls over time if weeds are not allowed to set seed.

Competition for residue

In mixed crop-livestock systems, crop residue is valuable winter feed, and in communal areas cattle often graze fields freely after harvest. Keeping residue on the field may need agreement with neighbours or the community, fencing, or growing extra fodder elsewhere. Leaving even part of the residue helps.

Equipment and know-how

Planting into residue needs suitable tools. Commercial no-till planters are expensive, so hiring or contracting is an option at first. For smallholders, rippers, jab planters and basins are affordable. Learning from a farmer nearby who already practises conservation agriculture is often the fastest way to avoid mistakes.

A practical way to start

1. Choose one field or plot, not the whole farm. Pick one with reasonable fertility and a manageable weed problem.
2. Correct soil acidity with lime before you stop ploughing, because it is harder to work lime into untilled soil.
3. Keep the residue from this season's crop on that field.
4. Plant next season using basins, a ripper or a no-till planter, with seed and fertiliser placed in the row.
5. Plan weed control before planting and weed early.
6. Plan a rotation with a legume for the following season.
7. Keep records of costs, labour and yield, and compare with a conventionally tilled field for a few seasons.

Key points

• Disturb the soil only where seed and fertiliser go.
• Keep the soil covered with residue, mulch or cover crops.
• Rotate cereals with legumes and other crops.
• Plan for weeds and residue competition, and start small.
• Give it several seasons before judging the results.