Multiple cropping is not a new subject, although it is not popular in the plantation areas. It is the practice of growing two or more crops in the same space during a single growing season. The various patterns of multiple cropping reflect essentially two underlying principles - growing individual crops in sequence- sequential cropping- or growing crops simultaneously.

Crops are grown sequentially one after another so that time is used to obtain more production or crops can be mixed and grown together simultaneously intercropped. With the latter, since the participating crops have different growth requirements, mixtures of crops of similar length to maturity can have higher productivity than a single crop.

However, crops commonly used in mixtures usually differ in maturity, so their growth requirements are further separated in time and competition between them is lower.





Characteristics
There is plantation of two or more crops in the space during a growing cycle. More than one type of crop is usually incorporated on the same piece of land during the growing period.

This type of system requires large tracts of land and also a lot of capital for the smooth running of farming activities, such as purchase of seeds and plants and employment of equipment in the farm. It is also labour intensive.





Criteria for crop selection  
Multiple cropping has proved successful because of the right criteria of selection of crops. Agriculturalists and farmers select component crops for multiple based on criteria below.

Duration of crops: One crop is of long duration and the other is of short duration. When choosing the crops to be grown, the time taken by the different crops to mature should be considered as this will determine the productivity of the crops.

Growth habit: The two component crops grow to different heights with different canopy. The taller crops should not be a dense canopy that cuts out light from those below. The maize plant canopy does allow a reasonable of light for shorter plants like beans and plants.

Root pattern: One crop component should be deep rooted whereas the other is shallow rooted. The roots should not explore the same soil layer that is plants with a shallow root system should be intercropped with plants with a deep-root system - for example, bananas (shallow rooters) and rubber (deep rooter). This is aimed at avoiding competition for nutrients and moisture. At the same time, nutrients from different soil layers are exploited.

Water need: One crop component should require comparatively lesser water than the other. This is to avoid competition of the plants for water.
Nutrient demand: One crop component should require more nutrients and the other lesser nutrients.

Crops belonging to the same family: These should not be planted together as they are attacked by the same pests and diseases - for example tomatoes, egg plants and ntula and maize, sorghum and millet.









Advantages of multiple cropping
Multiple cropping could also help in maintaining soil fertility provided suitable crops, such as legumes, are included in the cropping system. For example, intercropping of a legume crop with others could increase the process of nitrogen fixation that would enhance the nutrient status of the soil.

An important aspect of multiple cropping is the utilization of nutrients more efficiently as the crops growing on the same piece of land simultaneously would have different nutritional requirements.

Diverse food outputs are obtained through multiple cropping, thus providing a chance of choice for using food commodities. Multiple cropping is also important from a marketing point of view. As we are getting more than one crop simultaneously, even if the selling price of one commodity is less in the market, the other will be there to compensate.

Multiple cropping narrows the space available for weeds to grow and hamper their growth through exudation of all elochemicals. Nevertheless, weeds are the hidden enemy of crops imparting irreversible damages to resources. Weed’s suppression through multiple cropping will thus lead to enhanced production.

Soil erosion control in that multiple cropping systems result in efficient use of land resources. Some of these systems provide year-round coverage of crop land, thus reducing erosion and sustaining top soil.

There is also minimisation of pest damage as crops of a particular species are more prone to a particular type of pest infestation. When different types of crops are grown together, chances of pest infestation are reduced as one crop may provide cover to the other against such agents through biological control.
No risk of crop failure - the risk of total crop failure due to uncertain monsoon is reduced if two crops of different nature are grown simultaneously as a mixed crop.
Increases in yield - component crops have an effect on one another. For example, legume crops have a beneficial effect on the main plantation crops as they help in fixing nitrogen in the soil. There is high yield by this method.

Multiple cropping also optimizes production from small plots thus helping farmers cope land shortages since a variety of crops are grown on the same piece of land.  
The integration of many farm enterprises gives farm families several advantages. More crops can be planted in a small space. For example, intercropping and relay cropping can allow a farmer to plant two crops - like a plantation crop and vegetables - in his field at the same time. The production of crops is usually spread over a longer period of the year, allowing for better vegetative cover to protect the soil.





Disadvantages of multiple cropping
Sometimes pests and diseases may get a more favourable environment to flourish, thus damaging and deteriorating crop yields. The presence of crops in the field throughout the year allows crop pests to survive more easily. Some pests can shift from one crop to another. The large number of different crops in the field makes it difficult to weed and spacing to get optimum plant population is not easy.

New technologies such as modern weeding tools and improved varieties may be difficult to be introduced. Also, it is not easy to carryout operations such as spraying. Sometimes it wastes fertilizers that have to be given even to those crops in the mixture, which are less profitable.
Multiple cropping also makes mechanization almost impossible after planting and during harvesting - for example, the use of tractors and combine harvesters, respectively.





Environment
Erosion control and runoff management - growing different types of crops provides a canopy which reduces the impacts of rainfall on the soil and hence, reduction in chances of erosion. Cover for the soil from the other agents of erosion as their leaf falls cover the soil and their roots hold the soils together. Strengthening nutrient cycling mechanism leading to savings in fertilizer use - growing different species varieties of crops help in nutrient cycling and fixation in the soil. These assist in the reduction of other costs and in maintaining the fertility of the soil naturally.

Due to the continuous growing of different crops in the same area, there is maximum uptake of the soil nutrients by the different crops, thus reducing the fertility of the soils.

With the longer growing season required by the cultivation of more crops on the same piece of land, the effects on productivity of environmental changes from one location to another is expected to increase. This is to be expected because variation among locations in terms of water availability, a major determinant of yield. This will lead to more uptake of water by the crops thus depriving the soil of its water.

Annual row multiple cropping leaves the soil bare and exposed to erosion too most of the year, especially when fields are ploughed immediately after harvest thus resulting into soil degradation.





Sustainability issues in monocultures
Monocultures are large areas of land cultivated with a single crop, using methods that imply a high use of inputs such as agro chemicals and machinery. Monoculture crops and plantations have a host of social and environmental problems associated with their cultivation. In many regions, monoculture plantations are large scale and often produce bulk products for the export market, not for local use.

Monocultures include crops (food-based agriculture) and trees (rubber, tea plantations). Crops grown in industrial monocultures are cultivated for both food products (wheat, canola, corn, palm oil, sugar cane), animal feed and oils (soy, corn), and agrofuels (soy, canola, palmoil, jatropha, sugar cane), while forest plantations (eucalyptus, pine and acacia) are largely used for paper pulp, charcoal, timber and increasingly, biomass (with the possibility that they will be used for agrofuels in future).

The social impacts of large-scale monocultures are often disastrous for communities who continue to grow local foods using sustainable practices. Small-scale farmers often cultivate local species which not only contain important minerals for the soils and for human health but also have adapted to the local environment over many years. When small-scale farmers are confronted with industrial large-scale monocultures in their area, they are faced with water and other resources shortages, contamination from pesticide spraying and from GMO crops.

The takeover of land by monocultures also causes rural depopulation, destroying local community life and local economies. Monoculture plantations usually provide only temporary labour, for which workers are often hired from outside the region. Land grabbing and forced evictions of local populations are strongly linked to the expansion of monocultures.

By externalising social and environmental costs, monocultures are economically more profitable and therefore out-compete local producers. Markets become dominated by only a few large companies or multinational corporations that control the production, financing, trade and/or input production.

All large-scale monocultures take a toll on the earth, one reason being that the growers view what were once local and natural plants and animals as weeds or pests. This upsets the local ecological balance, causing outbreaks of illnesses and negative feedback cycles. In the monoculture system, locally and naturally occurring plants and animals are merely seen as pests that have to be destroyed.

(N. Yogaratnam can be contacted at [email protected])