HOME GARDEN TECHNOLOGY LEAFLET 12
In large-scale farming, monocropping or, the growing of only one type of crop, is common because of the ease of planting and harvesting, but there tend to be problems with weeds and pests. Multiple cropping, or growing one crop species more than once on the same field in a year, or growing different types (classes) of crops simultaneously or in sequence on the same piece of land in a year, is a common practice in African agriculture. From this well-established tradition, cultivation methods can be developed for achieving optimum output of home garden produce on a sustainable basis. If the appropriate climatic conditions and sufficient water are available, multiple cropping can provide a year-round supply of fruits and vegetables.
The practice of multiple cropping takes into account the interactions that different crop plants have with one another and with their environment. Apart from being one of the keys to achieving a continuous supply of different foods, this idea can also be a helpful part of disease-control strategies.
INTERCROPPING PRODUCES HEALTHY CROPS
Growing a variety of crops together minimizes pest problems and makes efficient use of soil nutrients. Plants such as garlic, pepper, onion and basil repel some plant pests and can be planted between tomatoes, carrots or any other crop, as long as all plants have sufficient sunlight and space to grow properly.
Crops such as cowpea, groundnut, beans, bambara groundnut and other leguminous crops have roots that are able to make soil nitrogen available to other plants. Therefore, when such legumes are intercropped with other crops, particularly those that require plenty of nitrogen (e.g. young maize plants and sorghum), the non-legume crops benefit greatly. Another beneficial intercropping scenario would be to intercrop groundnut or beans with root crops such as cassava or yam.
When intercropping, it is important to avoid planting crops that belong to the same family in exactly the same place for more than two harvests. This measure prevents the build-up in the soil of the pests and diseases that affect a particular family of crops. Table 2 in Home Garden Technology Leaflet 15, "Intensive vegetable plots", lists some of the same-family crops that should be rotated in a garden (e.g. replanted in the next row). Since they supply nitrogen, it is best to plant legumes first, before planting crops of the other families. Cassava, maize and other food crops can be intercropped with other crops.
Intercropping with trees
Palms, such as the coconut, and trees, such as citrus, can be planted 6 to 10 m apart. The area between them is initially suitable for other crops such as coffee or cocoa, but especially for the regular intercropping of annual crops (e.g. groundnut or maize or vegetables) or the perennial shrub cassava. Other perennials, such as oil-palm which grows mainly in coastal West Africa (also in some parts of East and southern Africa where adequate water resources are available) can be intercropped for the first three to four years (for example, with cowpea or soybean). After this, smaller plants can be planted underneath the taller palms for an additional one to two years or until shade becomes restrictive. In this way, the area between the trees can be used to plant other crops, particularly when the trees are still small. Care should be taken not to intercrop oil-palm with plants that have aggressive root systems (e.g. cassava, except for the first two years), because the oil-palm's roots are superficial and easily damaged.
CONTINUOUS FOOD SUPPLY
Staggering planting times in order to overlap the harvesting times of several different crops provides the household with a continuous supply of a variety of foods all year round. This relay cropping is used when the same crop is sown or planted in small amounts, in a staggered manner over a period of time, to ensure a continuous supply of that particular crop. This approach is used for foods that are eaten regularly but cannot be easily stored, such as leafy vegetables.
Food crop planting sequences
The sequence of crops planted should follow the seasonal changes. The start and end of the rainy season are important in the agricultural and cropping calendars. If a home garden has reliable supplementary watering facilities, food crops can be grown all year round. In the dry season, leafy vegetables and leaf crops can be planted in the shade of trees, and crops such as beans and cassava can be planted in beds that are watered frequently. Figure 1 provides an example of multiple cropping patterns for the humid tropics.
Intercropping with trees
Under arid and semi-arid conditions, the possibility of practising relay and sequential cropping of annual crops is limited by the shortage of water. As a result, the storage and preservation of seasonal home garden produce becomes an important concern. (See Home Garden Technology Leaflet 18, "Processing, preservation and storage", for details.)