Description

Crop rotation consists in sequentially producing plant species in a given location by alternating crops every year, every two years or every three years. This diversified production system prevents the build-up of pests and diseases as well as the exhaustion of the soil that usually occur with production of a single crop (or crops of a single family) in successive agricultural cycles. The rotation sequence is planned such that the requirements of one crop complement those of the next in order to maintain the soil nutrient balance. This technique is used, in particular, to sow and harvest green manures to complement the cultivation of commercial or in-house consumption products.

Location

A range of soil types, altitudes and climate conditions is suitable for crop rotation. Nevertheless, the specific characteristics of the site in terms of the nutritional requirements of the crops and the interaction among them when they are alternated must be taken into account. This technique is particularly relevant for poor, eroded or exhausted soil that has lost its fertility because of the use of synthetic fertilizers, the repeated cultivation of the same crop or the increased intensity of climate events. Threats and Impacts Attended: The threats of changing rainfall patterns, drought, frost and intense rainfall may be managed on a single piece of cropland, but at different times in the year, by rotating crops resistant to adverse climate conditions. Crop rotation increases food security and decreases the need for agricultural inputs, in addition to being an efficient way to control pests and diseases.

Implementation Steps

1. Select a plot for recurrent and systematic cultivation.
2. Carry out a study to determine market demand for potential crops.
3. Consider if adapting the selected crops to the climate and soil conditions of the farm will be feasible.
4. Evaluate the availability of economic and technological resources (labour, seeds, machinery).
5. Establish rotations making it possible to take maximum advantage of the farm's resources, and avoid sowing plants of the same family in order to break pest cycles and complement nutritional requirements.
6. Sow plants with different root systems in order to ensure that they efficiently use all the soil layers during the different rotations.

Inputs and Costs

The cost of a rotation system with maize and beans on 1 ha of land, including inputs for fertilization and pest control, is given below. The main expenses are for farm labour and the production of organic fertilizers and ecological pesticides. Three days of training on how to establish beneficial rotations are assumed.

Economic and Ecosystemic Benefits

Crop rotation keeps the soil covered, promotes biological equilibrium, diminishes pest cycles and diseases, incorporates nutrients and conserves energy. For example, Altieri (1999) cites a 1978 study in which maize-based crop rotation that incorporated forage legumes and grains reduced fossil fuel consumption by up to 45% compared with continuous cultivation. He also cites a 1983 study in which the native legume Lupinus mutabilis contributed up to 200 kg of nitrogen per hectare for the following potato crop. The economic benefits are the higher yields and the distribution of losses in the event of disease or climate events (Sauca and Urabayen, 2005; Altieri and Nicholls, 2004). These benefits also stem from reduced pesticide and fertilizer use due to the greater availability of nutrients, the breaking of pests’ life cycles and the intensification of biologic activity in the soil.

Limiting Factors

At the time of rotation, technical and economic variables must be considered, including the amount of time available to seed and harvest the next crop and the demand for products in different periods of the year. Crop calendars are, therefore, very important for implementing rotation. Rotation strategies take into account periods during which the land is left fallow, whereas in conventional agriculture such periods might be considered a failure to fully utilize the land.

Learned Lessons

Proper sequencing is fundamental for the success of crop rotation, because the production of a given crop depends on the nutrients required by its predecessor. For example, experiences in Central America show that continual rotation of maize and velvet beans (Mucuna pruriens) may be maintained for up to 15 years with a reasonable level of productivity (2-4 t/ha) and without any apparent decline in soil quality (Altieri and Nicholls, 2004).

Additional Considerations

Rotation also helps ward off insects, weeds and disease by effectively breaking the lifecycle of pests. Certain crops—for example, garlic and some aromatic plants—act as repellents. Hence, they are rotated with vegetables, to bring about efficacious pest and disease control (Nuñez and Vatovac, 2006; FEDEARROZ, 2011).

Units to Monitor Project Progress

Area under rotation schemes (ha).

Unites to Monitor Measure's Impact

Expenses on agricultural inputs (US$/ha).

References

• Sauca, E. and D. Urabayen (2005). “Rotaciones y Asociaciones de Cultivos”. Navarra: Bio Lur, Biharko Lurraren Elkartea (B.L.E.). Monográficos Ekonekazaritza No. 7. Government of Navarra.
• FEDEARROZ (2011). Boletín informativo de la Federación Nacional de Arroceros, Fondo Nacional de Arroz. FEDEARROZ No. 256 (April).
• Nuñez, R. and A. Vatovac (2006). La Huerta Orgánica. Bolivia: Editorial Fundación Amigos de la Naturaleza, FAN.
• Altieri, M.A. (1999). Agroecología: Bases científicas para una agricultura sustentable. New York: Sustainable Agriculture Networking and Extension (SANE) UNDP.
• Altieri, M.A. and C.I. Nicholls (2004). “An agroecological basis for designing diversified cropping systems in the tropics” in Dimensions in Agroecology. D.R. Clements and A. Shrestha (eds). New Haworth Press, N.Y.