In short
Summer fallow, also called clean fallow, leaves a field without a crop for a season and keeps weeds down by tillage or herbicide, so the soil can store water for the next crop.
It pays where rain is short, and it costs a year of production and raises the risk of erosion. Planva keeps crop rotation by season for every field, which is where the decision to fallow starts.
What summer fallow is
Summer fallow is the practice of leaving land idle during the growing season. Farmers use it to manage risk and improve the chance of a good crop the following year. Weeds are controlled during the fallow year by tilling or by spraying herbicides.
In drier areas land traditionally lay fallow every second year. In wetter areas it was cropped continuously or fallowed every third or fourth year. The practice spread on the Canadian prairies after land left fallow in 1885 gave a bigger crop the next year, and it was promoted widely until the 1960s.
Types of fallow
| Type | How weeds are controlled | What the sources report |
|---|---|---|
| Tilled fallow | Repeated tillage | Tillage causes soil moisture losses. Conventional summer fallow tillage is linked to loss of organic matter and topsoil. |
| Chemical fallow | Herbicide in place of tillage | Gave higher fallow wheat yields than tilled fallow in years of high moisture stress. Residue traps snow and lowers wind speed at ground level. |
Some farms skip fallow altogether. In Kazakhstan, traditional fallows are declining as farmers use rainfall to grow oats, sunflower and canola.
The case for fallow: water and weeds
- Water. Fallow raises soil water reserves. Only about 30 percent or less of the rain that falls in the fallow period is conserved, but that can be enough to support a crop in the next year.
- Weeds. A fallow year lets the farmer control weeds by tillage or herbicide without a crop in the way.
- Nutrients. Nutrients are released from soil organic matter, which can reduce the fertiliser the next crop needs.
- Pests and disease. A year without the crop breaks insect and disease cycles.
The costs: erosion, organic matter and lost output
| Cost | What it means |
|---|---|
| Lost production | The fallow year gives no crop, so its costs must be recovered in later years. |
| Erosion | Bare soil is exposed to wind and water erosion, and dust storms are more common in drought years. |
| Organic matter | Scientists estimate that about 30 percent of the soil organic matter of the Canadian prairies has been lost since cultivation began. |
| Salinity | Fallowing raises the water table in sensitive areas and brings salts to the root zone. |
These costs explain the trend. In Saskatchewan the share of cultivated land in summer fallow fell from more than a third in 1976 to about one acre in six in 2001, as conservation tillage, direct seeding and more varied rotations replaced it. In Kazakhstan, land no longer ploughed at all rose from nil in 2000 to 1.4 million hectares by 2008.
When fallow still makes sense
- Rain is short and variable. Where a crop depends on stored water, fallow is a form of insurance.
- Residue is kept. Chemical fallow with surface residue cuts the water and wind losses of tilled fallow.
- The next crop is worth it. A fallow year only pays if the crop after it earns the missing year back.
- A crop can use the rain. If a short crop fits the rainfall, it may replace the fallow, as farmers in Central Asia have begun to do.
How this works in Planva
- Crop rotation. Seasons with crop, variety, sowing and harvest dates, yield and harvest in tonnes.
- Rotation map. A crop filter on the map prints to PDF or JPEG with an area summary.
- What Planva does not do. It records the rotation. It does not tell you whether to fallow a field.
For the crop that comes after fallow, read best preceding crops for winter wheat. To plan a whole rotation, use the crop rotation plan.
Sources
Common questions
It is leaving a field without a crop for a growing season, while controlling weeds by tillage or herbicide, so that the soil stores water for the next crop.
The real Planva interface, shown with test data.
